Lahars

ABSTRACT Ignimbrite flow units commonly show reverse grading of large pumice clasts and normal grading of large lithic clasts. Ignimbrites show coarse‐tail grading, in which particles beneath a critical diameter, ranging from 64 to 2 mm, are ungraded. Above this size the larger the clast diameter the more pronounced the segregation. The grading is consistent with the theoretical settling rates of particles in a dispersion with a high particle concentration. Ignimbrite flow units show a reversely graded, fine grained basal layer which is attributed to the action of boundary forces during flow. Ignimbrites are commonly associated with cross‐stratified pyroclastic surge deposits and fine ash fall deposits formed in the same eruption. The fine ash fall deposit is depleted in crystals and is thought to be the deposit of the fine turbulent cloud observed making up the upper parts of nuées ardentes. Pyroclastic flows are postulated to be dense, poorly expanded partly fluidized debris flows. Only its fine grained components can be fluidized by gas. Pyroclastic flows are believed to behave as a dispersion of larger clasts in a medium of fluidized fines, which acts as a lubricant similar to water in mud‐flows. Poor sorting in ignimbrites is attributed to high particle concentrations not turbulence. Many pyroclastic flows may be laminar in their movement with apparent viscosities, deduced from the lateral grading of large lithic clasts, in the range 10 1 −10 3 poise.

@article{doi101111j136530911976tb00045x,
    author = "Sparks, R. S. J.",
    title = "Grain size variations in ignimbrites and implications for the transport of pyroclastic flows",
    year = "1976",
    journal = "Sedimentology",
    abstract = "ABSTRACT Ignimbrite flow units commonly show reverse grading of large pumice clasts and normal grading of large lithic clasts. Ignimbrites show coarse‐tail grading, in which particles beneath a critical diameter, ranging from 64 to 2 mm, are ungraded. Above this size the larger the clast diameter the more pronounced the segregation. The grading is consistent with the theoretical settling rates of particles in a dispersion with a high particle concentration. Ignimbrite flow units show a reversely graded, fine grained basal layer which is attributed to the action of boundary forces during flow. Ignimbrites are commonly associated with cross‐stratified pyroclastic surge deposits and fine ash fall deposits formed in the same eruption. The fine ash fall deposit is depleted in crystals and is thought to be the deposit of the fine turbulent cloud observed making up the upper parts of nuées ardentes. Pyroclastic flows are postulated to be dense, poorly expanded partly fluidized debris flows. Only its fine grained components can be fluidized by gas. Pyroclastic flows are believed to behave as a dispersion of larger clasts in a medium of fluidized fines, which acts as a lubricant similar to water in mud‐flows. Poor sorting in ignimbrites is attributed to high particle concentrations not turbulence. Many pyroclastic flows may be laminar in their movement with apparent viscosities, deduced from the lateral grading of large lithic clasts, in the range 10 1 −10 3 poise.",
    url = "https://doi.org/10.1111/j.1365-3091.1976.tb00045.x",
    doi = "10.1111/j.1365-3091.1976.tb00045.x",
    openalex = "W2122122894",
    references = "doi1010160040195171900382, doi10130674d723b52b2111d78648000102c1865d"
}

@article{fritz1980stumps,
    author = "Fritz, William J.",
    title = "Stumps transported and deposited upright by Mount St. Helens mud flows",
    year = "1980",
    journal = "Geology",
    url = "https://doi.org/10.1130/0091-7613(1980)8<586:stadub>2.0.co;2",
    doi = "10.1130/0091-7613(1980)8<586:stadub>2.0.co;2",
    number = "12",
    pages = "586",
    volume = "8"
}

@misc{fritz1980stumps1,
    author = "Fritz, W. J",
    title = "Stumps transported and deposited upright by Mount St. Helens mud flows",
    year = "1980",
    howpublished = "Geology, v. 8, p. 586-588",
    note = "talkorigins\_source = {true}; raw\_reference = {Fritz, W. J., 1980, Stumps transported and deposited upright by Mount St. Helens mud flows: Geology, v. 8, p. 586-588.}"
}

@article{fritz1981comment,
    author = "Fritz, William J.",
    title = "Comment and Reply on ‘Reinterpretation of the depositional environment of the Yellowstone “fossil forests” ’ and ‘Stumps transported and deposited upright by Mount St. Helens mud flows’",
    year = "1981",
    journal = "Geology",
    url = "https://doi.org/10.1130/0091-7613(1981)9<147:caroro>2.0.co;2",
    doi = "10.1130/0091-7613(1981)9<147:caroro>2.0.co;2",
    number = "4",
    openalex = "W2053741117",
    pages = "147",
    volume = "9"
}

@article{yuretich1981comment,
    author = "Yuretich, R. F.",
    title = "Comment and Reply on ‘Reinterpretation of the depositional environment of the Yellowstone “fossil forests” ’ and ‘Stumps transported and deposited upright by Mount St. Helens mud flows’",
    year = "1981",
    journal = "Geology",
    url = "https://doi.org/10.1130/0091-7613(1981)9<146:caroro>2.0.co;2",
    doi = "10.1130/0091-7613(1981)9<146:caroro>2.0.co;2",
    number = "4",
    openalex = "W2098032594",
    pages = "146",
    volume = "9"
}

@article{doi101038299720a0,
    author = "Harrison, Sylvia and Fritz, William J.",
    title = "Depositional features of March 1982 Mount St Helens sediment flows",
    year = "1982",
    journal = "Nature",
    url = "https://doi.org/10.1038/299720a0",
    doi = "10.1038/299720a0",
    openalex = "W2049818693"
}

ABSTRACT Four principal mechanisms of deposition are effective in the formation of sediment gravity flow deposits. Grains deposited by traction sedimentation and suspension sedimentation respond individually and accumulate directly from bed and suspended loads, respectively. Those deposited by frictional freezing and cohesive freezing interact through either frictional contact or cohesive forces, respectively, and are deposited collectively, usually by plug formation. Sediment deposition from individual sediment flows commonly involves more than one of these mechanisms acting either serially as the flow evolves or simultaneously on different grain populations. Deposition from turbidity currents is treated in terms of three dynamic grain populations: 1) clay- to medium-grained sand-sized particles that can be fully suspended as individual grains by flow turbulence, 2) coarse-grained sand to small-pebble-sized gravel that can be fully suspended in large amounts mainly in highly concentrated turbulent suspensions where grain fall velocity is substantially reduced by hindered settling, and 3) pebble- and cobble-sized clasts having concentrations greater than 10 percent to 15 percent that will be supported largely by dispersive pressure resulting from clast collisions and by buoyant lift provided by the interstitial mixture of water and finer-grained sediment. The effects of hindered settling, dispersive pressure, and matrix buoyant lift are con entration dependent, and grain populations 2 and 3 are likely to be transported in large amounts only within flows having high particle concentrations, probably in excess of 20 percent solids by volume. Low-density turbidity currents, made up largely of grains of population 1, typically show an initial period of traction sedimentation, forming Bouma (Tb) and Tc) divisions, followed by one of mixed traction and suspension sedimentation (Td), and a terminal period of fine-grained suspension sedimentation (Te). The sediment loads of high-density turbidity currents commonly include grains belonging to populations 1, 2, and 3. Consequently, deposition often occurs as a series of discrete sedimentation waves as flows decelerate and individual grain populations can no longer be maintained in transport. Each sedimentation wave tends to show increasing unsteadiness and accelerating sedimentation rate as it evolves, passing from an initial stage of traction sedimentation, to one of mixed frictional freezing and suspension sedimentation within traction carpets, to a final stage of direct suspension sedimentation. Sequences of sedimentary structure divisions representing this succession of depositional stages are here termed the ecoR1-3) sequence, representing population 3 grains, and the S1-3) sequence, representing population 2. Deposition of the high-density suspended load leaves behind a residual low-density turbidity current composed largely of population 1 grains. At their distal ends, high-density turbidity currents deposit mainly by suspension sedimentation, forming thin (S3) divisions. These (S3) divisions are the same as Bouma (Ta) and, if subsequently capped by (Tb-e) deposited by the residual low-density flows, become the basal divisions of normal turbidities. Liquefied flows deposit by direct high-density suspension sedimentation. Grain flows of sand are characterized by frictional freezing and their deposits are limited mainly to angle-of-repose slipface units. Density-modified grain flows, in which larger clasts are partially supported by matrix buoyancy, and traction carpets, in which a dense frictional grain dispersion is driven by an overlying turbulent flow, are important in the buildup of natural deposits on submarine slopes. Cohesive debris flows depost sediment mainly by cohesive freezing, commonly modified by suspension sedimentation of the largest clasts.

@article{doi101306212f7f312b2411d78648000102c1865d,
    author = "Lowe, Donald R.",
    title = "Sediment Gravity Flows: II Depositional Models with Special Reference to the Deposits of High-Density Turbidity Currents",
    year = "1982",
    journal = "Journal of Sedimentary Research",
    abstract = "ABSTRACT Four principal mechanisms of deposition are effective in the formation of sediment gravity flow deposits. Grains deposited by traction sedimentation and suspension sedimentation respond individually and accumulate directly from bed and suspended loads, respectively. Those deposited by frictional freezing and cohesive freezing interact through either frictional contact or cohesive forces, respectively, and are deposited collectively, usually by plug formation. Sediment deposition from individual sediment flows commonly involves more than one of these mechanisms acting either serially as the flow evolves or simultaneously on different grain populations. Deposition from turbidity currents is treated in terms of three dynamic grain populations: 1) clay- to medium-grained sand-sized particles that can be fully suspended as individual grains by flow turbulence, 2) coarse-grained sand to small-pebble-sized gravel that can be fully suspended in large amounts mainly in highly concentrated turbulent suspensions where grain fall velocity is substantially reduced by hindered settling, and 3) pebble- and cobble-sized clasts having concentrations greater than 10 percent to 15 percent that will be supported largely by dispersive pressure resulting from clast collisions and by buoyant lift provided by the interstitial mixture of water and finer-grained sediment. The effects of hindered settling, dispersive pressure, and matrix buoyant lift are con entration dependent, and grain populations 2 and 3 are likely to be transported in large amounts only within flows having high particle concentrations, probably in excess of 20 percent solids by volume. Low-density turbidity currents, made up largely of grains of population 1, typically show an initial period of traction sedimentation, forming Bouma (Tb) and Tc) divisions, followed by one of mixed traction and suspension sedimentation (Td), and a terminal period of fine-grained suspension sedimentation (Te). The sediment loads of high-density turbidity currents commonly include grains belonging to populations 1, 2, and 3. Consequently, deposition often occurs as a series of discrete sedimentation waves as flows decelerate and individual grain populations can no longer be maintained in transport. Each sedimentation wave tends to show increasing unsteadiness and accelerating sedimentation rate as it evolves, passing from an initial stage of traction sedimentation, to one of mixed frictional freezing and suspension sedimentation within traction carpets, to a final stage of direct suspension sedimentation. Sequences of sedimentary structure divisions representing this succession of depositional stages are here termed the ecoR1-3) sequence, representing population 3 grains, and the S1-3) sequence, representing population 2. Deposition of the high-density suspended load leaves behind a residual low-density turbidity current composed largely of population 1 grains. At their distal ends, high-density turbidity currents deposit mainly by suspension sedimentation, forming thin (S3) divisions. These (S3) divisions are the same as Bouma (Ta) and, if subsequently capped by (Tb-e) deposited by the residual low-density flows, become the basal divisions of normal turbidities. Liquefied flows deposit by direct high-density suspension sedimentation. Grain flows of sand are characterized by frictional freezing and their deposits are limited mainly to angle-of-repose slipface units. Density-modified grain flows, in which larger clasts are partially supported by matrix buoyancy, and traction carpets, in which a dense frictional grain dispersion is driven by an overlying turbulent flow, are important in the buildup of natural deposits on submarine slopes. Cohesive debris flows depost sediment mainly by cohesive freezing, commonly modified by suspension sedimentation of the largest clasts.",
    url = "https://doi.org/10.1306/212f7f31-2b24-11d7-8648000102c1865d",
    doi = "10.1306/212f7f31-2b24-11d7-8648000102c1865d",
    openalex = "W2087125749"
}

Distinctive patterns of growth rings in increment cores from old-growth Douglas-fir (Pseudotsuga menziesii) stands identify A.D. 1800 as a more precise date for the eruption of tephra layer T by Mount St. Helens, Washington. Layer T was previously inferred to date to about A.D. 1802. Growth patterns also establish A.D. 1480 as the date of eruption of the earlier layer Wn, previously estimated as dating to about A.D. 1500. The timing of radial tree growth places a small limitation on the seasonal resolution of these new tree-ring dates.

@article{doi1010160033589483900807,
    author = "Yamaguchi, David K.",
    title = "New Tree-Ring Dates for Recent Eruptions of Mount St. Helens",
    year = "1983",
    journal = "Quaternary Research",
    abstract = "Distinctive patterns of growth rings in increment cores from old-growth Douglas-fir (Pseudotsuga menziesii) stands identify A.D. 1800 as a more precise date for the eruption of tephra layer T by Mount St. Helens, Washington. Layer T was previously inferred to date to about A.D. 1802. Growth patterns also establish A.D. 1480 as the date of eruption of the earlier layer Wn, previously estimated as dating to about A.D. 1500. The timing of radial tree growth places a small limitation on the seasonal resolution of these new tree-ring dates.",
    url = "https://doi.org/10.1016/0033-5894(83)90080-7",
    doi = "10.1016/0033-5894(83)90080-7",
    openalex = "W2082536873"
}

An explosive eruption of Mount St. Helens on 19 March 1982 had substantial impact beyond the vent because hot eruption products interacted with a thick snowpack. A blast of hot pumice, dome rocks, and gas dislodged crater-wall snow that avalanched through the crater and down the north flank. Snow in the crater swiftly melted to form a transient lake, from which a destructive flood and lahar swept down the north flank and the North Fork Toutle River.

@article{doi101126science22146181394,
    author = "Waitt, Richard B. and Pierson, Thomas C. and MacLeod, N. S. and Janda, Richard J. and Voight, B. and Holcomb, Robin T.",
    title = "Eruption-Triggered Avalanche, Flood, and Lahar at Mount St. Helens—Effects of Winter Snowpack",
    year = "1983",
    journal = "Science",
    abstract = "An explosive eruption of Mount St. Helens on 19 March 1982 had substantial impact beyond the vent because hot eruption products interacted with a thick snowpack. A blast of hot pumice, dome rocks, and gas dislodged crater-wall snow that avalanched through the crater and down the north flank. Snow in the crater swiftly melted to form a transient lake, from which a destructive flood and lahar swept down the north flank and the North Fork Toutle River.",
    url = "https://doi.org/10.1126/science.221.4618.1394",
    doi = "10.1126/science.221.4618.1394",
    openalex = "W1974964313"
}

Following about two months of intense outward movement and strength deterioration associated with magmatic intrusion, seismicity and gravitational creep, an earthquake on 18 May 1980 marked the collapse of the hot, fluid-rich, north sector of Mount St Helens. Pressure release associated with slide movements resulted in hydrothermal and magmaiic explosions. These explosions produced a lateral blast that partly overran the first slide pulse and devastated a landscape of over 550 km 2. Disruption of the sliding masses resulted in the formation of an enormous avalanche of debris that travelled for about 10 min, as far as 23 km. Average velocity was about 35 m/s, and peak velocity about 70 m/s. An area of 60 km 2 was buried with 2·8 km 3 of hummocky, poorly sorted debris to an average depth of 45 m, and levees to 30 m high were plastered against valley walls and impounded tributaries. One avalanche lobe entered a lake and caused wave run-up to 260 m. Limiting equilibrium analyses and laboratory testing of slide debris suggest that initial failure occurred in a material with c <6 bar, &hi&i;40°, with significant pore fluid pressures and transient shear stresses from a trigger earthquake. Early motion can be characterized by block sliding with an apparent basal friction coefficient of about 0·1. Disintegration of the slide blocks then led to fully developed avalanche flow, to a first approximation involving a Bingham material with strength of about 0·1–1 bar and viscosity 10 5 –10 6 P. The high mobility of the Mount St Helens avalanche, typical for volcanic avalanches, was induced by hot fluids of the depressurized magmatic-hydrothermal system. À la suite d'environ deux mois de poussée intense vers l'extérieur et d'une réduction de résistance due à des intrusions magmatiques accompagnant des événements séismiques et au fluage par gravité, l'affaissement du secteur nord du Mont St Helens, chaud et riche en fluides, fut marqué par un tremblement de terre qui eut lieu le 18 mai 1980. Une chute de pression associée à des mouvements glissants causa des explosions hydrothermales et magmatiques. Ces explosions créèrent un souffle latéral qui dépassa en partie la première pulsation de glissement et dévasta un paysage de plus de 550km 2. La rupture des masses glissantes créa une coulée énorme de débris qui se déplaça pendant environ 10 min jusqu'à une distance de 23 km à une vitesse moyenne d'environ 35 m/s, la vitesse maximale étant d'environ 70 m/s. Un terrain couvrant 60 km 2 fur enseveli sur une profondeur moyenne de 45 m sous 2·8 km 3 de débris accidentés et mal assortis, et des levées jusqu'à une hauteur de 30m furent plaquées contre les côtés des vallées et bloquèrent les affluents. Une branche de l'avalanche pénétra dans un lac, causant des vagues jusqu'à une hauteur de 260 m. Des analyses de l'équilibre limite et des essais de laboratoire des débris de glissement donne l'impression que la rupture initiale a eu lieu dans une matière de c′<6 bar, ø&i;40°, avec des pressions interstitielles considérables et des contraintes transitoires de cisaillement à partir d'un tremblement de terre causateur. Les premiers mouvements peuvent être qualifiés de glissements de blocs avec un coefficient de frottement évident à a la base d'environ 0-1. La désintégration des blocs glissants entraîna alors à une véritable coulée d'une matière du type Bingham ayant en première approximation une résistance de l'ordre de 0·1 — 1 bar et une viscosité de 10 5 —10 6 P. La grande mobilité du Mont St Helens typique des coulées volcaniques fut provoquée par des fluides chauds du système magmatique-hydrothermal décomprimé.

@article{doi101680geot1983333243,
    author = "Voight, B. and Janda, Richard J. and Glicken, Harry and Douglass, P. M.",
    title = "Nature and mechanics of the Mount St Helens rockslide-avalanche of 18 May 1980",
    year = "1983",
    journal = "Géotechnique",
    abstract = "Following about two months of intense outward movement and strength deterioration associated with magmatic intrusion, seismicity and gravitational creep, an earthquake on 18 May 1980 marked the collapse of the hot, fluid-rich, north sector of Mount St Helens. Pressure release associated with slide movements resulted in hydrothermal and magmaiic explosions. These explosions produced a lateral blast that partly overran the first slide pulse and devastated a landscape of over 550 km 2. Disruption of the sliding masses resulted in the formation of an enormous avalanche of debris that travelled for about 10 min, as far as 23 km. Average velocity was about 35 m/s, and peak velocity about 70 m/s. An area of 60 km 2 was buried with 2·8 km 3 of hummocky, poorly sorted debris to an average depth of 45 m, and levees to 30 m high were plastered against valley walls and impounded tributaries. One avalanche lobe entered a lake and caused wave run-up to 260 m. Limiting equilibrium analyses and laboratory testing of slide debris suggest that initial failure occurred in a material with c <6 bar, \&hi\&i;40°, with significant pore fluid pressures and transient shear stresses from a trigger earthquake. Early motion can be characterized by block sliding with an apparent basal friction coefficient of about 0·1. Disintegration of the slide blocks then led to fully developed avalanche flow, to a first approximation involving a Bingham material with strength of about 0·1–1 bar and viscosity 10 5 –10 6 P. The high mobility of the Mount St Helens avalanche, typical for volcanic avalanches, was induced by hot fluids of the depressurized magmatic-hydrothermal system. À la suite d'environ deux mois de poussée intense vers l'extérieur et d'une réduction de résistance due à des intrusions magmatiques accompagnant des événements séismiques et au fluage par gravité, l'affaissement du secteur nord du Mont St Helens, chaud et riche en fluides, fut marqué par un tremblement de terre qui eut lieu le 18 mai 1980. Une chute de pression associée à des mouvements glissants causa des explosions hydrothermales et magmatiques. Ces explosions créèrent un souffle latéral qui dépassa en partie la première pulsation de glissement et dévasta un paysage de plus de 550km 2. La rupture des masses glissantes créa une coulée énorme de débris qui se déplaça pendant environ 10 min jusqu'à une distance de 23 km à une vitesse moyenne d'environ 35 m/s, la vitesse maximale étant d'environ 70 m/s. Un terrain couvrant 60 km 2 fur enseveli sur une profondeur moyenne de 45 m sous 2·8 km 3 de débris accidentés et mal assortis, et des levées jusqu'à une hauteur de 30m furent plaquées contre les côtés des vallées et bloquèrent les affluents. Une branche de l'avalanche pénétra dans un lac, causant des vagues jusqu'à une hauteur de 260 m. Des analyses de l'équilibre limite et des essais de laboratoire des débris de glissement donne l'impression que la rupture initiale a eu lieu dans une matière de c′<6 bar, ø\&i;40°, avec des pressions interstitielles considérables et des contraintes transitoires de cisaillement à partir d'un tremblement de terre causateur. Les premiers mouvements peuvent être qualifiés de glissements de blocs avec un coefficient de frottement évident à a la base d'environ 0-1. La désintégration des blocs glissants entraîna alors à une véritable coulée d'une matière du type Bingham ayant en première approximation une résistance de l'ordre de 0·1 — 1 bar et une viscosité de 10 5 —10 6 P. La grande mobilité du Mont St Helens typique des coulées volcaniques fut provoquée par des fluides chauds du système magmatique-hydrothermal décomprimé.",
    url = "https://doi.org/10.1680/geot.1983.33.3.243",
    doi = "10.1680/geot.1983.33.3.243",
    openalex = "W2073697741"
}

Abstract Conglomerates originating in coastal environments represent mainly beachface, shoreface, fan-deltaic or deltaic mouth bar, and Gilbert-type delta sequences. They show structures, textures and other features created mainly by the varied influence of waves and fluvial output in the shallow marine setting. Transitional, alluvial/marine systems show a broad range of facies characteristics and sequences, and these are discussed in detail. Conglomerates originating in alluvial environments comprise mainly braided stream and mass flow sequences. The former include regular braided river and fan (distributary) channel deposits, and show textures and structures which vary greatly with source and climatic setting. Braided stream sequences commonly show an upward fining motif, due to falling flood stage or to gradual abandonment of alluvial tracts. Mass flow conglomerates originate from a variety of debris flows in subaerial settings, but fluidal gravelly flows (like many ‘sheetfloods’ or ‘streamfloods’) may also be important, and they often become prominent subaqueously (high-density gravelly turbidites). In both instances, the deposits show remarkably varied texture, structure, and fabric. Subaerial flows are often considerably transformed when passing into water. A review of diagnostic features and facies sequences is presented. When interpreting the emplacement mechanics of mass flow conglomerates, particular effort must be made to extract maximum information from the individual bed characteristics. We illustrate with examples that even such basic data as bed thickness and maximum clast size may serve as a valuable source for some genetic inferences.

@article{openalexw1598633756,
    author = "Nemec, Wojciech and Steel, R. J.",
    title = "Alluvial and Coastal Conglomerates: Their Significant Features and Some Comments on Gravelly Mass-Flow Deposits",
    year = "1984",
    abstract = "Abstract Conglomerates originating in coastal environments represent mainly beachface, shoreface, fan-deltaic or deltaic mouth bar, and Gilbert-type delta sequences. They show structures, textures and other features created mainly by the varied influence of waves and fluvial output in the shallow marine setting. Transitional, alluvial/marine systems show a broad range of facies characteristics and sequences, and these are discussed in detail. Conglomerates originating in alluvial environments comprise mainly braided stream and mass flow sequences. The former include regular braided river and fan (distributary) channel deposits, and show textures and structures which vary greatly with source and climatic setting. Braided stream sequences commonly show an upward fining motif, due to falling flood stage or to gradual abandonment of alluvial tracts. Mass flow conglomerates originate from a variety of debris flows in subaerial settings, but fluidal gravelly flows (like many ‘sheetfloods’ or ‘streamfloods’) may also be important, and they often become prominent subaqueously (high-density gravelly turbidites). In both instances, the deposits show remarkably varied texture, structure, and fabric. Subaerial flows are often considerably transformed when passing into water. A review of diagnostic features and facies sequences is presented. When interpreting the emplacement mechanics of mass flow conglomerates, particular effort must be made to extract maximum information from the individual bed characteristics. We illustrate with examples that even such basic data as bed thickness and maximum clast size may serve as a valuable source for some genetic inferences.",
    openalex = "W1598633756"
}

The Mount St. Helens, May 18 pumice is a dacite containing 60% glass by weight and phenocrysts of plagioclase, orthopyroxene, amphibole, titaniferous magnetite, and ilmenite. The glass is uniform in composition, a rhyodacite with 73 wt % SiO 2; the phenocrysts are also uniform in composition except for the plagioclase, which has cores averaging An 57 and rims averaging An 49. Analyses of seven pairs of coexisting Fe‐Ti oxides in a representative sample of the light pumice were recast using various mineral calculation procedures; they yielded temperatures ranging from 920° to 940°C and a ‐log ƒ O 2 of 10.3–10.1. Electron microprobe analyses of 57 glass inclusions trapped in plagioclase phenocrysts in the light pumice showed little deviation from an average rhyodacitic composition (69.90±0.87 wt % SiO 2) when special care was taken to account for Na loss during the analysis. The difference between the average total of these glass inclusion analyses and 100% is 4.6±1 wt %, which is interpreted to be volatiles dissolved in the glass. On an anhydrous basis the average glass inclusion composition is identical to the matrix glass, indicating that neither underwent significant fractionation after melt was trapped by the plagioclase. Experimentally determined phase relations for the representative dacite sample place limits on conditions in the May 18 Mount St. Helens magma chamber, assuming that the dissolved volatiles were 4.6±1 wt % and the temperature was 920°–940°C. Hydrothermal experiments over a range of P, T, and ƒ O 2 indicate that at no pressure is the observed phase assemblage and residual melt chemistry produced when P H 2 O = P Total. Experiments using CO 2 ‐H 2 O fluids to achieve P H 2 's less than P Fluid did reproduce the observed residual melt chemistry and an An 50 plagioclase at a specific set of conditions, i.e., at ƒ O 2 's between the NNO and MNO buffers, at a P Fluid of 220 MPa (2.2 kb), and at a P H 2 = 110 MPa (all at 920°–940°C). Amphibole was not stable under these conditions but possibly would be if the P H 2 / P Fluid ratio was raised to 0.7 or if fluorine were added to the experimental system. It is concluded that just prior to eruption, the upper part of the Mount St. Helens magma chamber was at a pressure of 220±30 MPa corresponding to a depth of 7.2±1 km, P H 2 was 0.5 to 0.7 P Total, and the temperature was 930°±10°C.

@article{doi101029jb090ib04p02929,
    author = "Rutherford, M. J. and Sigurdsson, Haraldur and Carey, Steven and Davis, Andrew",
    title = "The May 18, 1980, eruption of Mount St. Helens: 1. Melt composition and experimental phase equilibria",
    year = "1985",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "The Mount St. Helens, May 18 pumice is a dacite containing 60\% glass by weight and phenocrysts of plagioclase, orthopyroxene, amphibole, titaniferous magnetite, and ilmenite. The glass is uniform in composition, a rhyodacite with 73 wt \% SiO 2; the phenocrysts are also uniform in composition except for the plagioclase, which has cores averaging An 57 and rims averaging An 49. Analyses of seven pairs of coexisting Fe‐Ti oxides in a representative sample of the light pumice were recast using various mineral calculation procedures; they yielded temperatures ranging from 920° to 940°C and a ‐log ƒ O 2 of 10.3–10.1. Electron microprobe analyses of 57 glass inclusions trapped in plagioclase phenocrysts in the light pumice showed little deviation from an average rhyodacitic composition (69.90±0.87 wt \% SiO 2) when special care was taken to account for Na loss during the analysis. The difference between the average total of these glass inclusion analyses and 100\% is 4.6±1 wt \%, which is interpreted to be volatiles dissolved in the glass. On an anhydrous basis the average glass inclusion composition is identical to the matrix glass, indicating that neither underwent significant fractionation after melt was trapped by the plagioclase. Experimentally determined phase relations for the representative dacite sample place limits on conditions in the May 18 Mount St. Helens magma chamber, assuming that the dissolved volatiles were 4.6±1 wt \% and the temperature was 920°–940°C. Hydrothermal experiments over a range of P, T, and ƒ O 2 indicate that at no pressure is the observed phase assemblage and residual melt chemistry produced when P H 2 O = P Total. Experiments using CO 2 ‐H 2 O fluids to achieve P H 2 's less than P Fluid did reproduce the observed residual melt chemistry and an An 50 plagioclase at a specific set of conditions, i.e., at ƒ O 2 's between the NNO and MNO buffers, at a P Fluid of 220 MPa (2.2 kb), and at a P H 2 = 110 MPa (all at 920°–940°C). Amphibole was not stable under these conditions but possibly would be if the P H 2 / P Fluid ratio was raised to 0.7 or if fluorine were added to the experimental system. It is concluded that just prior to eruption, the upper part of the Mount St. Helens magma chamber was at a pressure of 220±30 MPa corresponding to a depth of 7.2±1 km, P H 2 was 0.5 to 0.7 P Total, and the temperature was 930°±10°C.",
    url = "https://doi.org/10.1029/jb090ib04p02929",
    doi = "10.1029/jb090ib04p02929",
    openalex = "W2097386223"
}

Nearly instantaneous melting of snow and ice by the March 19, 1982, eruption of Mount St. Helens released a 4 × 10 6 m 3 flood of water from the crater that was converted to a lahar (volcanic debris flow) through erosion and incorporation of sediment by the time it reached the base of the volcano. Over the next 81 km that it traveled down the Toutle River, the flood wave was progressively diluted through several mechanisms. A transformation from debris flow to hyperconcentrated streamflow began to occur about 27 km downstream from the crater, when the total sediment concentration had decreased to about 78% by weight (57% by volume). The hyperconcentrated lahar‐runout flood wave, transporting immense quantities of sand in suspension, continued to experience progressive downstream dilution. Although turbulence was significantly dampened by the extremely high suspended load, very large standing waves and antidune waves were observed. The hyperconcentrated lahar‐runout flow deposited an unusual, faintly stratified, coarse sand which locally contained small, isolated gravel lenses. Very similar deposits in the Quaternary stratigraphy of Mount St. Helens and other Cascades volcanoes suggest that lahars may be more frequent than previously recognized.

@article{doi101029wr021i010p01511,
    author = "Pierson, Thomas C. and Scott, Kevin M.",
    title = "Downstream Dilution of a Lahar: Transition From Debris Flow to Hyperconcentrated Streamflow",
    year = "1985",
    journal = "Water Resources Research",
    abstract = "Nearly instantaneous melting of snow and ice by the March 19, 1982, eruption of Mount St. Helens released a 4 × 10 6 m 3 flood of water from the crater that was converted to a lahar (volcanic debris flow) through erosion and incorporation of sediment by the time it reached the base of the volcano. Over the next 81 km that it traveled down the Toutle River, the flood wave was progressively diluted through several mechanisms. A transformation from debris flow to hyperconcentrated streamflow began to occur about 27 km downstream from the crater, when the total sediment concentration had decreased to about 78\% by weight (57\% by volume). The hyperconcentrated lahar‐runout flood wave, transporting immense quantities of sand in suspension, continued to experience progressive downstream dilution. Although turbulence was significantly dampened by the extremely high suspended load, very large standing waves and antidune waves were observed. The hyperconcentrated lahar‐runout flow deposited an unusual, faintly stratified, coarse sand which locally contained small, isolated gravel lenses. Very similar deposits in the Quaternary stratigraphy of Mount St. Helens and other Cascades volcanoes suggest that lahars may be more frequent than previously recognized.",
    url = "https://doi.org/10.1029/wr021i010p01511",
    doi = "10.1029/wr021i010p01511",
    openalex = "W1974792361",
    references = "doi1010160040195171900382"
}

@article{fritz1985transported,
    author = "Fritz, William J. and Harrison, Sylvia",
    title = "Transported trees from the 1982 Mount St. Helens sediment flows: Their use as paleocurrent indicators",
    year = "1985",
    journal = "Sedimentary Geology",
    url = "https://doi.org/10.1016/0037-0738(85)90073-9",
    doi = "10.1016/0037-0738(85)90073-9",
    number = "1-2",
    openalex = "W2044545104",
    pages = "49-64",
    volume = "42",
    references = "doi101038299720a0, doi101038scientificamerican0464106, doi101126science22146181394, doi1011300091761319819109oolitt20co2, doi10113000917613198311298efsisl20co2, doi10113000917613198412159yffnef20co2, doi101680geot1983333243, doi102113gseegeoscixx2125, fritz1980reinterpretation, openalexw1419417595, yuretich1981comment"
}

@article{doi101007bf01073510,
    author = "Mullineaux, Donald R.",
    title = "Summary of pre-1980 tephra-fall deposits erupted from Mount St. Helens, Washington State, USA",
    year = "1986",
    journal = "Bulletin of Volcanology",
    url = "https://doi.org/10.1007/bf01073510",
    doi = "10.1007/bf01073510",
    openalex = "W2079065156"
}

@misc{crandell1987deposits,
    author = "Crandell, D.R.",
    title = "Deposits of pre-1980 pyroclastic flows and lahars from Mount St. Helens Volcano, Washington",
    year = "1987",
    booktitle = "Professional Paper",
    url = "https://doi.org/10.3133/pp1444",
    doi = "10.3133/pp1444",
    openalex = "W1498707816",
    references = "doi101007bf01073511, doi10130674d723b52b2111d78648000102c1865d, doi1015159781400876525021, openalexw2167464155, openalexw2623958108"
}

Many timed observations make it possible to subdivide the 9‐hour Plinian eruption of Mount St. Helens on May 18, 1980, into six phases, defined by eruption style. The phases are correlated with stratigraphic subunits of ashfall tephra and pyroclastic flow deposits. The suite of pyroclastic deposits indicates that the eruption became more pumice‐rich and compositionally diverse with time, perhaps owing to concurrent eruption of less evolved, gas‐poor parts of the magma body with the more evolved, gas‐rich parts. The paroxysmal phase I (0832–0900) consisted of landslides, lithic pyroclastic flows of a lateral blast and other explosions, and a weak pre‐Plinian column. Phase I pyroclastic deposits include lithic ash flow deposits intercalated with and overlying the voluminous debris avalanche deposit and basal pumice lapilli tephra that underlies a pisolitic ash layer. The early Plinian phase II (0900–1215) consisted of vertical ejection of tephra with an early pulse of small pyroclastic flows on the upper flanks (1010–1035), a brief period of lithic ash ejection (1035–1100), and a pumice‐rich pulse that accompanied growth in height of the eruption column (1100–1215). Deposits include minor pyroclastic flows on the crater rim and a reversely graded sequence of proximal tephra that include the lower pumice lapilli layer, the lower lithic ash layer, and the middle pumice lapilli layer, all of which consist of evolved white dacitic pumice (63–64% SiO 2). During the early ash flow phase III (1215–1500) the height of the eruption column decreased, vertical ejection of tephra ceased, and pyroclastic flows were fed from intermittent fountains. Phase III deposits consist of a poorly exposed sequence (.≤12 m) of ash flow tuff that consist of many thin flow units (≤2 m each) containing pumiceous white dacite (63–64% SiO 2) and denser, gray silicic andésite (61–62% SiO 2), and fine‐grained ash cloud deposits interbedded with a nongraded middle pumice ash layer. The climactic phase IV (1500–1715) developed in two stages: fountain‐fed pyroclastic flows, followed by a short pulse (1625–1715) of vigorous vertical ejection of tephra. These stages were accompanied by the peak seismic energy release and peak eruption column height, respectively. Climactic deposits consist of a thick (≤35 m) sequence of thick, lapilli‐rich ash flow sheets (4–12 m each) with white and gray pumice, and streaky scoria bands (60% SiO 2) in pumice breccia clasts, and the reversely‐graded, upper pumice lapilli layer that is interbedded with fine‐grained ash cloud deposits. During the late ash flow phase V (1715–1815) eruption intensity waned but included a brief episode of small pyroclastic flows (1745–1815). Phase V deposits consist of small distributary lobes of ash flow tuff containing white and gray pumice, and minor fine‐ash deposits. Phase VI activity (1815 to May 19, 1980) consisted of a low‐energy ash plume, with transient increases in intensity, while seismicity continued at depth. Sustained vertical discharge of phase II prodeced evolved dacitewith high S/Cl ratios. Ash flow activity of phase III is attributed to decreases in gas content, indicated by reduced S/Cl ratios and increased clast density of the less evolved, gray pumice. Climactic events are attributed to vent clearing and exhaustion of the evolved dacite.

@article{doi101029jb092ib10p10237,
    author = "Criswell, C. William",
    title = "Chronology and pyroclastic stratigraphy of the May 18, 1980, Eruption of Mount St. Helens, Washington",
    year = "1987",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "Many timed observations make it possible to subdivide the 9‐hour Plinian eruption of Mount St. Helens on May 18, 1980, into six phases, defined by eruption style. The phases are correlated with stratigraphic subunits of ashfall tephra and pyroclastic flow deposits. The suite of pyroclastic deposits indicates that the eruption became more pumice‐rich and compositionally diverse with time, perhaps owing to concurrent eruption of less evolved, gas‐poor parts of the magma body with the more evolved, gas‐rich parts. The paroxysmal phase I (0832–0900) consisted of landslides, lithic pyroclastic flows of a lateral blast and other explosions, and a weak pre‐Plinian column. Phase I pyroclastic deposits include lithic ash flow deposits intercalated with and overlying the voluminous debris avalanche deposit and basal pumice lapilli tephra that underlies a pisolitic ash layer. The early Plinian phase II (0900–1215) consisted of vertical ejection of tephra with an early pulse of small pyroclastic flows on the upper flanks (1010–1035), a brief period of lithic ash ejection (1035–1100), and a pumice‐rich pulse that accompanied growth in height of the eruption column (1100–1215). Deposits include minor pyroclastic flows on the crater rim and a reversely graded sequence of proximal tephra that include the lower pumice lapilli layer, the lower lithic ash layer, and the middle pumice lapilli layer, all of which consist of evolved white dacitic pumice (63–64\% SiO 2). During the early ash flow phase III (1215–1500) the height of the eruption column decreased, vertical ejection of tephra ceased, and pyroclastic flows were fed from intermittent fountains. Phase III deposits consist of a poorly exposed sequence (.≤12 m) of ash flow tuff that consist of many thin flow units (≤2 m each) containing pumiceous white dacite (63–64\% SiO 2) and denser, gray silicic andésite (61–62\% SiO 2), and fine‐grained ash cloud deposits interbedded with a nongraded middle pumice ash layer. The climactic phase IV (1500–1715) developed in two stages: fountain‐fed pyroclastic flows, followed by a short pulse (1625–1715) of vigorous vertical ejection of tephra. These stages were accompanied by the peak seismic energy release and peak eruption column height, respectively. Climactic deposits consist of a thick (≤35 m) sequence of thick, lapilli‐rich ash flow sheets (4–12 m each) with white and gray pumice, and streaky scoria bands (60\% SiO 2) in pumice breccia clasts, and the reversely‐graded, upper pumice lapilli layer that is interbedded with fine‐grained ash cloud deposits. During the late ash flow phase V (1715–1815) eruption intensity waned but included a brief episode of small pyroclastic flows (1745–1815). Phase V deposits consist of small distributary lobes of ash flow tuff containing white and gray pumice, and minor fine‐ash deposits. Phase VI activity (1815 to May 19, 1980) consisted of a low‐energy ash plume, with transient increases in intensity, while seismicity continued at depth. Sustained vertical discharge of phase II prodeced evolved dacitewith high S/Cl ratios. Ash flow activity of phase III is attributed to decreases in gas content, indicated by reduced S/Cl ratios and increased clast density of the less evolved, gray pumice. Climactic events are attributed to vent clearing and exhaustion of the evolved dacite.",
    url = "https://doi.org/10.1029/jb092ib10p10237",
    doi = "10.1029/jb092ib10p10237",
    openalex = "W1988813554",
    references = "openalexw2623958108"
}

The most frequent and voluminous eruptive products at Mount St. Helens are dacitic in composition, although a wide variety of magma types (basalt to rhyodacite) is represented. To address the petrogenesis of the dacites, we present major and trace element analyses of samples of pumice clasts and dome or flow lavas erupted during the past ∼40,000 years. The dacites have similar (in some cases even lower) contents of many incompatible elements (e.g., Zr, Hf, REE, U, Be, Ta, Nb) compared with those in associated basalts and andesites, whereas Ba, Rb, K, Cs, and Sr are relatively enriched. The unusual depleted nature of the dacites and generally low bulk distribution coefficients (estimated from glass/whole‐rock pairs) for numerous trace elements preclude an origin of these magmas principally by crystal fractionation of associated mafic magmas. A more plausible model for their origin involves melting of metabasaltic crustal rocks that have been enriched in Ba, Rb, Cs, and Sr by either intercalation of sediments with depleted basalt or selective metasomatic enrichment of the source region. Melting at crustal levels presumably is related to intrusion of mantle‐derived basaltic magmas. Compositional diversity among the erupted dacites can be attributed to spatial or temporal heterogeneity of the magma sources or, in some specific cases, to such processes as crystal fractionation, assimilation, and magma mixing.

@article{doi101029jb092ib10p10313,
    author = "Smith, Diane R. and Leeman, William P.",
    title = "Petrogenesis of Mount St. HElens dacitic magmas",
    year = "1987",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "The most frequent and voluminous eruptive products at Mount St. Helens are dacitic in composition, although a wide variety of magma types (basalt to rhyodacite) is represented. To address the petrogenesis of the dacites, we present major and trace element analyses of samples of pumice clasts and dome or flow lavas erupted during the past ∼40,000 years. The dacites have similar (in some cases even lower) contents of many incompatible elements (e.g., Zr, Hf, REE, U, Be, Ta, Nb) compared with those in associated basalts and andesites, whereas Ba, Rb, K, Cs, and Sr are relatively enriched. The unusual depleted nature of the dacites and generally low bulk distribution coefficients (estimated from glass/whole‐rock pairs) for numerous trace elements preclude an origin of these magmas principally by crystal fractionation of associated mafic magmas. A more plausible model for their origin involves melting of metabasaltic crustal rocks that have been enriched in Ba, Rb, Cs, and Sr by either intercalation of sediments with depleted basalt or selective metasomatic enrichment of the source region. Melting at crustal levels presumably is related to intrusion of mantle‐derived basaltic magmas. Compositional diversity among the erupted dacites can be attributed to spatial or temporal heterogeneity of the magma sources or, in some specific cases, to such processes as crystal fractionation, assimilation, and magma mixing.",
    url = "https://doi.org/10.1029/jb092ib10p10313",
    doi = "10.1029/jb092ib10p10313",
    openalex = "W2085480633"
}

In the 6 yr following the 1980 eruption of Mount St. Helens in Washington state, vascular plant invasion of barren substrates in subalpine habitats has been limited despite the proximity of seed sources from resprouted vegetation. From 1983—1985 we counted 1st—yr seedlings and estimated percent cover of adults in grids of permanent plots located across the ecotone between residual vegetation and barren substrate created in 1980. We found that (1) seedling recruitment declined from 1983 to 1985, apparently in response to drought; (2) most seedlings occurred within 3 m of a conspecific adult; and (3) plots with an intermediate vegetation cover (5—72%) contained a significantly higher fraction of seedlings than did unvegetated plots. Thus, dispersal is limited in many species and nurse plants may play a key role in trapping seeds and promoting seedling establishment. We sowed 16 000 viable seeds from 22 subalpine species into 264 plots in barren substrates at two sites on the volcano. The design was a complete factorial, with species, site, and fertilizer as treatments. Survivorship through 1985 varied from 0 to 12%, with Sitanion jubatum, Stipa occidentalis, Polygonum newberryi, Eriogonum pyrolifolium, and Spraguea umbellata attaining the highest values. Survivorship was correlated with seed mass, and was higher at the site where the pre—eruption surface was exposed. Fertilizer increased the size of most seedlings but had only a marginal effect on survivorship. Species with high environmental tolerance generally dispersed short distances, whereas species that dispersed farther generally had low tolerances and apparently require site amelioration prior to establishment. The path of early succession depends upon the spatial position and dispersal abilities of species in the seed pool, and may not reflect environmental gradients.

@article{doi1023071938349,
    author = "Wood, David M. and del Moral, Roger",
    title = "Mechanisms of Early Primary Succession in Subalpine Habitats on Mount St. Helens",
    year = "1987",
    journal = "Ecology",
    abstract = "In the 6 yr following the 1980 eruption of Mount St. Helens in Washington state, vascular plant invasion of barren substrates in subalpine habitats has been limited despite the proximity of seed sources from resprouted vegetation. From 1983—1985 we counted 1st—yr seedlings and estimated percent cover of adults in grids of permanent plots located across the ecotone between residual vegetation and barren substrate created in 1980. We found that (1) seedling recruitment declined from 1983 to 1985, apparently in response to drought; (2) most seedlings occurred within 3 m of a conspecific adult; and (3) plots with an intermediate vegetation cover (5—72\%) contained a significantly higher fraction of seedlings than did unvegetated plots. Thus, dispersal is limited in many species and nurse plants may play a key role in trapping seeds and promoting seedling establishment. We sowed 16 000 viable seeds from 22 subalpine species into 264 plots in barren substrates at two sites on the volcano. The design was a complete factorial, with species, site, and fertilizer as treatments. Survivorship through 1985 varied from 0 to 12\%, with Sitanion jubatum, Stipa occidentalis, Polygonum newberryi, Eriogonum pyrolifolium, and Spraguea umbellata attaining the highest values. Survivorship was correlated with seed mass, and was higher at the site where the pre—eruption surface was exposed. Fertilizer increased the size of most seedlings but had only a marginal effect on survivorship. Species with high environmental tolerance generally dispersed short distances, whereas species that dispersed farther generally had low tolerances and apparently require site amelioration prior to establishment. The path of early succession depends upon the spatial position and dispersal abilities of species in the seed pool, and may not reflect environmental gradients.",
    url = "https://doi.org/10.2307/1938349",
    doi = "10.2307/1938349",
    openalex = "W2052118511"
}

The early part of the Kalama eruptive period may be analogous to the dacitic eruptive activity that began at Mount St. Helens in 1980 with an explosive eruption followed by dome extrusion. If the current eruptive sequence repeats the events of Kalama time, future volcanic activity will include multiple eruptions of dacite in the form of domes, tephra, and pyroclastic flows, and andesite in the form of lava flows, tephra, and pyroclastic flows, and will continue intermittently for at least a century.

@article{doi103133pp1444,
    author = "Crandell, Dwight Raymond",
    title = "Deposits of pre-1980 pyroclastic flows and lahars from Mount St. Helens Volcano, Washington",
    year = "1987",
    journal = "USGS professional paper",
    abstract = "The early part of the Kalama eruptive period may be analogous to the dacitic eruptive activity that began at Mount St. Helens in 1980 with an explosive eruption followed by dome extrusion. If the current eruptive sequence repeats the events of Kalama time, future volcanic activity will include multiple eruptions of dacite in the form of domes, tephra, and pyroclastic flows, and andesite in the form of lava flows, tephra, and pyroclastic flows, and will continue intermittently for at least a century.",
    url = "https://doi.org/10.3133/pp1444",
    doi = "10.3133/pp1444",
    openalex = "W1498707816",
    references = "doi101007bf01073511, doi10130674d723b52b2111d78648000102c1865d, doi1015159781400876525021, openalexw2167464155, openalexw2623958108"
}

Additional experiments have been done with the May 18, 1980, Mount St. Helens dacite and a more mafic, October 1980 sample to resolve questions concerning amphibole stability and dissolved volatiles in the magma chamber prior to the May 18 eruption. The experiments were done at 920°C, at fluid pressures of 220 or 320 MPa, and, in contrast to previous work, at an ƒ O 2 between the NNO and MnO‐Mn 3 O 4 oxygen buffers. Fe‐Ti oxides are present in the melt under these conditions, and amphibole is stable when X H 2 O in the fluid is greater than 0.67. The An content of plagioclase in equilibrium with melt decreases with decreasing X H 2 O in the fluid and, in the amphibole‐bearing experiments, reaches the natural plagioclase rim compositions (An 49) at an X H 2 O of 0.67. Under these H 2 O‐undersaturated conditions the experimentally produced amphibole, low‐Ca pyrpxene, and Ca‐rich pyroxene are compositionally equivalent to phenocrysts in the May 18 white pumice. The melts (glasses) in amphibole‐bearing experiments range from the average plagioclase melt inclusion composition [Rutherford et al., 1985] to slightly less evolved compositions as X H 2 O approaches 1.0. Melt inclusions in natural amphiboles were analyzed, and the compositions were plotted on SiO 2 variation diagrams along with experimental glass analyses. The amphibole melt inclusions define a liquid line of descent for the magina which extends from relatively primitive compositions (68 wt % SiO 2, anhydrous basis) to the more evolved average plagioclase melt inclusion composition (73 wt % SiO 2). The volatile content of the amphibole melt inclusions (difference method) reaches 5.0±0.5 wt %, which compares favorably with the volatile content of the amphibole‐bearing experimental melts produced at X H 2 O = 0.67.

@article{doi101029jb093ib10p11949,
    author = "Rutherford, M. J. and Devine, Joseph D.",
    title = "The May 18, 1980, eruption of Mount St. Helens: 3. Stability and chemistry of amphibole in the magma chamber",
    year = "1988",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "Additional experiments have been done with the May 18, 1980, Mount St. Helens dacite and a more mafic, October 1980 sample to resolve questions concerning amphibole stability and dissolved volatiles in the magma chamber prior to the May 18 eruption. The experiments were done at 920°C, at fluid pressures of 220 or 320 MPa, and, in contrast to previous work, at an ƒ O 2 between the NNO and MnO‐Mn 3 O 4 oxygen buffers. Fe‐Ti oxides are present in the melt under these conditions, and amphibole is stable when X H 2 O in the fluid is greater than 0.67. The An content of plagioclase in equilibrium with melt decreases with decreasing X H 2 O in the fluid and, in the amphibole‐bearing experiments, reaches the natural plagioclase rim compositions (An 49) at an X H 2 O of 0.67. Under these H 2 O‐undersaturated conditions the experimentally produced amphibole, low‐Ca pyrpxene, and Ca‐rich pyroxene are compositionally equivalent to phenocrysts in the May 18 white pumice. The melts (glasses) in amphibole‐bearing experiments range from the average plagioclase melt inclusion composition [Rutherford et al., 1985] to slightly less evolved compositions as X H 2 O approaches 1.0. Melt inclusions in natural amphiboles were analyzed, and the compositions were plotted on SiO 2 variation diagrams along with experimental glass analyses. The amphibole melt inclusions define a liquid line of descent for the magina which extends from relatively primitive compositions (68 wt \% SiO 2, anhydrous basis) to the more evolved average plagioclase melt inclusion composition (73 wt \% SiO 2). The volatile content of the amphibole melt inclusions (difference method) reaches 5.0±0.5 wt \%, which compares favorably with the volatile content of the amphibole‐bearing experimental melts produced at X H 2 O = 0.67.",
    url = "https://doi.org/10.1029/jb093ib10p11949",
    doi = "10.1029/jb093ib10p11949",
    openalex = "W2059811363"
}

At least 1 large lahar extended to Cowlitz R.

@article{doi103133pp1447a,
    author = "Scott, Keith",
    title = "Origins, behavior, and sedimentology of lahars and lahar-runout flows in the Toutle-Cowlitz River system",
    year = "1988",
    journal = "USGS professional paper",
    abstract = "At least 1 large lahar extended to Cowlitz R.",
    url = "https://doi.org/10.3133/pp1447a",
    doi = "10.3133/pp1447a",
    openalex = "W1590567012",
    references = "openalexw2167464155, openalexw2623958108"
}

@article{doi101007bf00301553,
    author = "Waitt, Richard B.",
    title = "Swift snowmelt and floods (lahars) caused by great pyroclastic surge at Mount St Helens volcano, Washington, 18 May 1980",
    year = "1989",
    journal = "Bulletin of Volcanology",
    url = "https://doi.org/10.1007/bf00301553",
    doi = "10.1007/bf00301553",
    openalex = "W2037590821",
    references = "openalexw2623958108"
}

Abstract Stream channel development in response to the eruption of Mount St. Helens on 18 May 1980, resulted in some of the largest sediment yields documented anywhere on earth. Development of new channels on the 2.7 km3 debris-avalanche deposit in the North Fork Toutle River caused net erosion of as much as 1.3 x 105 t km−2 annually. Development of these channels followed a four-stage sequence of channel initiation, channel incision with relatively constant width-to-depth ratio, channel widening accompanied by aggradation, and channel widening accompanied by scour-and-fill with little change in average channel elevation. These channels remain unstable both in width and elevation. Lahars affected channel and valley morphology on all flanks of the volcano. Steep, upstream reaches generally incised and widened during the first year following the eruption and aggraded during the following three years. Gently sloping downstream reaches aggraded and widened during the first year and incised during the following three years. The most rapid adjustments occurred during the first two winters following the eruption. The principal effect of the blast on channels throughout the 550 km2 devastated area was the subsequent rapid delivery of sand- and silt-size sediment eroded from hillslopes. Channels aggraded during early storms of the 1980–1981 winter but incised during later storms the same winter. Subsequent channel enlargement was constrained by logs deposited in channels by the blast and by post-1980 shallow debris slides. Since 1984, instability and sedimentation in laharand blast-affected channels have been within the range of pre-1980 levels.

@article{doi10108002626668909491318,
    author = "Meyer, David F. and Martinson, Holly A.",
    title = "Rates and processes of channel development and recovery following the 1980 eruption of Mount St. Helens, Washington",
    year = "1989",
    journal = "Hydrological Sciences Journal",
    abstract = "Abstract Stream channel development in response to the eruption of Mount St. Helens on 18 May 1980, resulted in some of the largest sediment yields documented anywhere on earth. Development of new channels on the 2.7 km3 debris-avalanche deposit in the North Fork Toutle River caused net erosion of as much as 1.3 x 105 t km−2 annually. Development of these channels followed a four-stage sequence of channel initiation, channel incision with relatively constant width-to-depth ratio, channel widening accompanied by aggradation, and channel widening accompanied by scour-and-fill with little change in average channel elevation. These channels remain unstable both in width and elevation. Lahars affected channel and valley morphology on all flanks of the volcano. Steep, upstream reaches generally incised and widened during the first year following the eruption and aggraded during the following three years. Gently sloping downstream reaches aggraded and widened during the first year and incised during the following three years. The most rapid adjustments occurred during the first two winters following the eruption. The principal effect of the blast on channels throughout the 550 km2 devastated area was the subsequent rapid delivery of sand- and silt-size sediment eroded from hillslopes. Channels aggraded during early storms of the 1980–1981 winter but incised during later storms the same winter. Subsequent channel enlargement was constrained by logs deposited in channels by the blast and by post-1980 shallow debris slides. Since 1984, instability and sedimentation in laharand blast-affected channels have been within the range of pre-1980 levels.",
    url = "https://doi.org/10.1080/02626668909491318",
    doi = "10.1080/02626668909491318",
    openalex = "W2064677586"
}

Abstract Infiltration and erosion characteristics of two tephra deposits from the 1980 eruption of Mount St. Helens, Washington, were evaluated using a rainfall simulator and selected process models. The deposits were a 20 cm thick silty-sandy profile in the Shultz Creek drainage and a 35 cm thick profile containing a 15–20 cm pumice-gravel layer in the Clearwater Creek drainage. At Shultz Creek, infiltration was affected by surface crusting and erosion. Steady-state infiltration rates ranged from 0.21 to 0.51 cm h−1 in September 1980, and from 0.41 to 0.71 cm h−1 in August 1981. Rill erosion countered the effects of crusting by exposing the more permeable tephra and pre-emption surface. Erosion rates in 1980 decreased rapidly with successive rainfall simulations. Erosion rates in 1981 were 65–80% less than those in 1980 and were more stable. At Clearwater Creek, surface crusting was less evident and sheet erosion was dominant. The steady-state infiltration rate in 1981 was 2.92 cm h−1. The surface runoff volume was small but subsurface flow through the pumice gravel was substantial.

@article{doi10108002626668909491338,
    author = "Leavesley, G. H. and Lusby, Gregg C. and Lichty, R.W.",
    title = "Infiltration and erosion characteristics of selected tephra deposits from the 1980 eruption of Mount St. Helens, Washington, USA",
    year = "1989",
    journal = "Hydrological Sciences Journal",
    abstract = "Abstract Infiltration and erosion characteristics of two tephra deposits from the 1980 eruption of Mount St. Helens, Washington, were evaluated using a rainfall simulator and selected process models. The deposits were a 20 cm thick silty-sandy profile in the Shultz Creek drainage and a 35 cm thick profile containing a 15–20 cm pumice-gravel layer in the Clearwater Creek drainage. At Shultz Creek, infiltration was affected by surface crusting and erosion. Steady-state infiltration rates ranged from 0.21 to 0.51 cm h−1 in September 1980, and from 0.41 to 0.71 cm h−1 in August 1981. Rill erosion countered the effects of crusting by exposing the more permeable tephra and pre-emption surface. Erosion rates in 1980 decreased rapidly with successive rainfall simulations. Erosion rates in 1981 were 65–80\% less than those in 1980 and were more stable. At Clearwater Creek, surface crusting was less evident and sheet erosion was dominant. The steady-state infiltration rate in 1981 was 2.92 cm h−1. The surface runoff volume was small but subsurface flow through the pumice gravel was substantial.",
    url = "https://doi.org/10.1080/02626668909491338",
    doi = "10.1080/02626668909491338",
    openalex = "W1979668137"
}

@article{mcewen1989dynamics,
    author = "McEwen, Alfred S. and Malin, Michael C.",
    title = "Dynamics of Mount St. Helens' 1980 pyroclastic flows, rockslide-avalanche, lahars, and blast",
    year = "1989",
    journal = "Journal of Volcanology and Geothermal Research",
    url = "https://doi.org/10.1016/0377-0273(89)90080-2",
    doi = "10.1016/0377-0273(89)90080-2",
    number = "3-4",
    openalex = "W2045898649",
    pages = "205-231",
    volume = "37",
    references = "doi1010029780470172766, doi1010079783642858291, doi1010079783709128343, doi101007bf01301796, doi1010160148906274922050, doi1010160377027384900027, doi101098rspa19540186, doi101098rsta19560020, doi10113000167606197586129cdssgb20co2, doi101306212f7f312b2411d78648000102c1865d"
}

Part 1 Heat and mass transport in magmatic systems: a compaction model for melt transport in the earth's asthenosphere - The basic model, applications, A.C. Fowler hot spots, swells and mantle plumes, P. Olson magma waves and diapiric dynamics, J.A. Whitehead an experimental study of melt migration in an olivine-melt system, G.N. Riles, Jr. and D.L. Kohlstedt solidification and melting along dykes by the laminar flow of basaltic magma, P.M. Bruce and H.E. Huppert on the role of laminar and turbulent flow in buoyancy driven magma fractgures, D.L. Turcotte computer simulations of explosive volcanic eruptions, K.H. Wohletz and G.A. Valentine the in-situ thermal transport properties and the thermal structure of Mount Saint Helens eruptive units. M.P. Ryan et al. Part 2 Transport structure, mechanics and dynamics of magmatic systems: melt extraction from mantle peridotites: hydrofracturing and porous flow, with consequences for oceanic ridge activity, A. Nicolas on the physical nature of the Icelandic magma transport system, M.P. Ryan dynamics of Drafla Caldera North Iceland - 1975-1985, J.A. Ewart et al magma generation in the upper mantle inferred from seismic measurements in peridotite at high pressure and temperature, H. Sato and I.S. Sacks differences in magma storage in different volcanic environments as revealed by seismic tomography - Silicic volcanic centers and subduction-related volcanoes, H.M. Iyer geophysical and observational constraints for ascent rates of dacitic magma at Mount Saint Helens, E.T. Endo et al pressure sources and induced ground deformation associated with explosive eruptions at an andesitic volcano - Sakurajima Volcano, Japan, K. Ishihara high-level magma transport at Mount Etna volcano, as deduced from ground deformation measurements, J.B. Murray changing styles of effusive eruption of Mount Etna since 1600 A D, J.W. Hughes et al.

@book{openalexw597459718,
    author = "Ryan, Michael P. and from Source to Eruption Site, Storage",
    title = "Magma transport and storage",
    year = "1990",
    booktitle = "Wiley eBooks",
    abstract = "Part 1 Heat and mass transport in magmatic systems: a compaction model for melt transport in the earth's asthenosphere - The basic model, applications, A.C. Fowler hot spots, swells and mantle plumes, P. Olson magma waves and diapiric dynamics, J.A. Whitehead an experimental study of melt migration in an olivine-melt system, G.N. Riles, Jr. and D.L. Kohlstedt solidification and melting along dykes by the laminar flow of basaltic magma, P.M. Bruce and H.E. Huppert on the role of laminar and turbulent flow in buoyancy driven magma fractgures, D.L. Turcotte computer simulations of explosive volcanic eruptions, K.H. Wohletz and G.A. Valentine the in-situ thermal transport properties and the thermal structure of Mount Saint Helens eruptive units. M.P. Ryan et al. Part 2 Transport structure, mechanics and dynamics of magmatic systems: melt extraction from mantle peridotites: hydrofracturing and porous flow, with consequences for oceanic ridge activity, A. Nicolas on the physical nature of the Icelandic magma transport system, M.P. Ryan dynamics of Drafla Caldera North Iceland - 1975-1985, J.A. Ewart et al magma generation in the upper mantle inferred from seismic measurements in peridotite at high pressure and temperature, H. Sato and I.S. Sacks differences in magma storage in different volcanic environments as revealed by seismic tomography - Silicic volcanic centers and subduction-related volcanoes, H.M. Iyer geophysical and observational constraints for ascent rates of dacitic magma at Mount Saint Helens, E.T. Endo et al pressure sources and induced ground deformation associated with explosive eruptions at an andesitic volcano - Sakurajima Volcano, Japan, K. Ishihara high-level magma transport at Mount Etna volcano, as deduced from ground deformation measurements, J.B. Murray changing styles of effusive eruption of Mount Etna since 1600 A D, J.W. Hughes et al.",
    openalex = "W597459718"
}

The June 15, 1991 eruption of Mt. Pinatubo, one of the largest eruptions in the world this century, deposited 5-7 cubic kilometers of pumiceous pyroclastic-flow deposits and about 0.2 cubic kilometers of tephra-fall deposits on the slopes of the volcano. Decreases in infiltration capacity and evapotranspiration caused by the eruption and its deposits have increased the rate and magnitude of surface runoff production, and the new deposits provide a vast supply of highly credible sediment.

@misc{doi103133wri924039,
    author = "Pierson, T. C. and Janda, R. J. and Umbal, J.V. and Daag, A.S.",
    title = "Immediate and long-term hazards from lahars and excess sedimentation in rivers draining Mount Pinatubo, Philippines",
    year = "1992",
    abstract = "The June 15, 1991 eruption of Mt. Pinatubo, one of the largest eruptions in the world this century, deposited 5-7 cubic kilometers of pumiceous pyroclastic-flow deposits and about 0.2 cubic kilometers of tephra-fall deposits on the slopes of the volcano. Decreases in infiltration capacity and evapotranspiration caused by the eruption and its deposits have increased the rate and magnitude of surface runoff production, and the new deposits provide a vast supply of highly credible sediment.",
    url = "https://doi.org/10.3133/wri924039",
    doi = "10.3133/wri924039",
    openalex = "W2166087291",
    references = "doi10102990eo00386, doi101029gm027, doi101029gm027p0157, doi10108002626668909491318, doi10108002626668909491338, doi1011475sabo197337210, doi1023072050272, doi103133b1241i, doi103133b965a"
}

Recent 1980–1986 Mount St. Helens dacites contain the phenocryst assemblage, plagioclase, amphibole, low‐Ca pyroxene, magnetite, ilmenite, and rare high‐Ca pyroxene, which indicates that they all originated from an 8 km deep reservoir at 900°±20°C with X H 2O = 0.67 in fluid according to experimental data. Iron‐titanium oxide phenocryst compositions indicate that all post May 18 dacitic magmas erupted at 900°±20°C except for the final lava extrusion in October 1986; the magma reservoir may have cooled to 866°C by October 1986. Amphiboles in the post May 18, 1980, magma contain one or more amphibole populations characterized by reaction rims of different thicknesses. The development of the amphibole reaction rims in these rocks is a response to water loss from the coexisting melt during an approximately adiabatic ascent from a deep reservoir. Constant P and T and isothermal decompression experiments show that during a 900°C constant rate decompression from 8 km to the surface, no reaction rim develops on amphibole in 4 days, a 10‐μm rim develops in 10 days, and a 35‐μm rim develops in 20 days. These experimental data and histograms of rim widths in 1980–1986 Mount St. Helens dacites show that post May 18 eruptions are composed in large part of magma represented by a population of thin‐rimmed amphiboles, magma which ascended from the deep (8 km) reservoir in 6 to 10 days. The remainder of each sample consists of magma containing amphiboles with reaction rims ranging from 14 to 60 μm, magma which apparently spent from 8 to 25 days along the conduit margins before being mixed thoroughly (millimeter scale) into the erupting magma. The mixing in a viscous, slowly ascending dacite may be enhanced by its flow through partially crystallized magma emplaced earlier and by the evolution and loss of a large vesicle population. The experimental calibration of amphibole reaction rim width versus decompression time yields average ascent velocities for post May 18 dacites of about 15–30 m/h for magma represented by the thick‐rimmed amphiboles and from 35 to 50 m/hr for magma represented by the thin‐rimmed crystals. An ascent rate of >66 m/h is indicated for the May 18, 1980, eruption, which contains amphiboles with no reaction rims. The volume of endogenous dome growth which preceded extrusion of magma newly derived from the deep source region suggests that the effective conduit volume beneath Mount St. Helens in 1981–1982 was equivalent to a cylinder 8 km long and 8–9 m in radius.

@article{doi10102993jb01613,
    author = "Rutherford, M. J. and Hill, Peter M.",
    title = "Magma ascent rates from amphibole breakdown: An experimental study applied to the 1980–1986 Mount St. Helens eruptions",
    year = "1993",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "Recent 1980–1986 Mount St. Helens dacites contain the phenocryst assemblage, plagioclase, amphibole, low‐Ca pyroxene, magnetite, ilmenite, and rare high‐Ca pyroxene, which indicates that they all originated from an 8 km deep reservoir at 900°±20°C with X H 2O = 0.67 in fluid according to experimental data. Iron‐titanium oxide phenocryst compositions indicate that all post May 18 dacitic magmas erupted at 900°±20°C except for the final lava extrusion in October 1986; the magma reservoir may have cooled to 866°C by October 1986. Amphiboles in the post May 18, 1980, magma contain one or more amphibole populations characterized by reaction rims of different thicknesses. The development of the amphibole reaction rims in these rocks is a response to water loss from the coexisting melt during an approximately adiabatic ascent from a deep reservoir. Constant P and T and isothermal decompression experiments show that during a 900°C constant rate decompression from 8 km to the surface, no reaction rim develops on amphibole in 4 days, a 10‐μm rim develops in 10 days, and a 35‐μm rim develops in 20 days. These experimental data and histograms of rim widths in 1980–1986 Mount St. Helens dacites show that post May 18 eruptions are composed in large part of magma represented by a population of thin‐rimmed amphiboles, magma which ascended from the deep (8 km) reservoir in 6 to 10 days. The remainder of each sample consists of magma containing amphiboles with reaction rims ranging from 14 to 60 μm, magma which apparently spent from 8 to 25 days along the conduit margins before being mixed thoroughly (millimeter scale) into the erupting magma. The mixing in a viscous, slowly ascending dacite may be enhanced by its flow through partially crystallized magma emplaced earlier and by the evolution and loss of a large vesicle population. The experimental calibration of amphibole reaction rim width versus decompression time yields average ascent velocities for post May 18 dacites of about 15–30 m/h for magma represented by the thick‐rimmed amphiboles and from 35 to 50 m/hr for magma represented by the thin‐rimmed crystals. An ascent rate of >66 m/h is indicated for the May 18, 1980, eruption, which contains amphiboles with no reaction rims. The volume of endogenous dome growth which preceded extrusion of magma newly derived from the deep source region suggests that the effective conduit volume beneath Mount St. Helens in 1981–1982 was equivalent to a cylinder 8 km long and 8–9 m in radius.",
    url = "https://doi.org/10.1029/93jb01613",
    doi = "10.1029/93jb01613",
    openalex = "W2002132035",
    references = "doi101007bf00278003"
}

Mount St. Helens, 50 km to the west of Mount Adams and the main Cascade volcanic chain, is only 80 km above the subducting oceanic lithosphere. The elevated temperatures off the subducting slab, because of the close proximity of the Juan de Fuca Ridge to the trench,may induce slab melting at a depth of ∼80 km. Dacites from Mount St. Helens have geochemical compositions off magmas that are derived by direct partial melting of metamorphosed basalts at high pressure, i.e., relatively high AI (Al2O3 > 15% at 70% SiO2), low Y and Yb (because of garnet and amphibole stability in the source), low Sc, and high Sr and Eu. Trace element modeling of the partial melting of mid-oceanic ridge basalt (MORB) from the Juan de Fuca Ridge that yields a hornblende eclogite residue can reproduce the Mount St. Helens data (results off the model are quite distinct from data derived from the Mount Adams volcanic rocks). In contrast, Mount Adams is ∼135 km above the subducting slab and is associated with normal arc magmatism believed to be derived from the mantle above the subducting plate. The Cascade are has been active in its present locality, because of oblique subduction, for the past 7 m.y. The major volcanoes along the arc have existed for at least 500 ka, but Mount St. Helens has existed for <40 ka. We suggest that the subducting plate may have reached elevated temperatures, because of the approach of North America to the Juan de Fuca Ridge, at ∼40 ka, which initiated melting of the slab.

@article{doi1011300091761319930210547mshpeo23co2,
    author = "Defant, Marc J. and Drummond, Mark S.",
    title = "Mount St. Helens: Potential example of the partial melting of the subducted lithosphere in a volcanic arc",
    year = "1993",
    journal = "Geology",
    abstract = "Mount St. Helens, 50 km to the west of Mount Adams and the main Cascade volcanic chain, is only 80 km above the subducting oceanic lithosphere. The elevated temperatures off the subducting slab, because of the close proximity of the Juan de Fuca Ridge to the trench,may induce slab melting at a depth of ∼80 km. Dacites from Mount St. Helens have geochemical compositions off magmas that are derived by direct partial melting of metamorphosed basalts at high pressure, i.e., relatively high AI (Al2O3 > 15\% at 70\% SiO2), low Y and Yb (because of garnet and amphibole stability in the source), low Sc, and high Sr and Eu. Trace element modeling of the partial melting of mid-oceanic ridge basalt (MORB) from the Juan de Fuca Ridge that yields a hornblende eclogite residue can reproduce the Mount St. Helens data (results off the model are quite distinct from data derived from the Mount Adams volcanic rocks). In contrast, Mount Adams is ∼135 km above the subducting slab and is associated with normal arc magmatism believed to be derived from the mantle above the subducting plate. The Cascade are has been active in its present locality, because of oblique subduction, for the past 7 m.y. The major volcanoes along the arc have existed for at least 500 ka, but Mount St. Helens has existed for <40 ka. We suggest that the subducting plate may have reached elevated temperatures, because of the approach of North America to the Juan de Fuca Ridge, at ∼40 ka, which initiated melting of the slab.",
    url = "https://doi.org/10.1130/0091-7613(1993)021<0547:mshpeo>2.3.co;2",
    doi = "10.1130/0091-7613(1993)021<0547:mshpeo>2.3.co;2",
    openalex = "W2044394940",
    references = "doi1010160016703778902223, doi1011300091761319920201011cateot23co2"
}

Mount Rainier is potentially the most dangerous volcano in the Cascade Range because of its great height, frequent earthquakes, active hydrothermal system, and extensive glacier mantle. Many debris flows and their distal phases have inundated areas far from the volcano during postglacial time. Two types of debris flows, cohesive and noncohesive, have radically different origins and behavior that relate empirically to clay content. The two types are the major subpopulations of debris flows at Mount Rainier. The behavior of cohesive flows is affected by the cohesion and adhesion of particles; noncohesive flows are dominated by particle collisions to the extent that particle cataclasis becomes common during near-boundary shear. Cohesive debris flows contain more than 3 to 5 percent of clay-size sediment. The composition of these flows changed little as they traveled more than 100 kilometers from Mount Rainier to inundate parts of the now-populated Puget Sound lowland. They originate as deep-seated failures of sectors of the volcanic edifice, and such failures are sufficiently frequent that they are the major destructional process of Mount Rainier's morphologic evolution. In several deposits of large cohesive flows, a lateral, megaclast-bearing facies (with a mounded or hummocky surface) contrasts with a more clay-rich facies in the center of valleys and downstream. Cohesive flows at Mount Rainier do not correlate strongly with volcanic activity and thus can recur without warning, possibly triggered by non-magmatic earthquakes or by changes in the hydrothermal system. Noncohesive debris flows contain less than 3 to 5 percent clay-size sediment. They form most commonly by bulking of sediment in water surges, but some originate directly or indirectly from shallow slope failures that do not penetrate the hydrothermally altered core of the volcano. In contrast with cohesive flows, most noncohesive flows transform both from and to other flow types and are, therefore, the middle segments of flow waves that begin and end as flood surges. Proximally, through the bulking of poorly sorted volcaniclastic debris on the flanks of the volcano, flow waves expand rapidly in volume by transforming from water surges through hyperconcentrated stream flow (20 to 60 percent sediment by volume) to debris flow. Distally, the transformations occur more slowly in reverse order - from debris flow, to hyperconcentrated flow, and finally to normal streamflow with less than 20 percent sediment by volume. During runout of the largest noncohesive flows, hyperconcentrated flow has continued for as much as 40 to 70 kilometers. Lahars (volcanic debris flows and their deposits) have occurred frequently at Mount Rainier over the past several thousand years, and generally they have not clustered within discrete eruptive periods as at Mount St. Helens. An exception is a period of large noncohesive flows during and after construction of the modern summit cone. Deposits from lahar-runout flows, the hyperconcentrated distal phases of lahars, document the frequency and extent of noncohesive lahars. These deposits also record the following transformations of debris flows: (1) the direct, progressive dilution of debris flow to hyperconcentrated flow, (2) deposition of successively finer grained lobes of debris until only the hyperconcentrated tail of the flow remains to continue downstream, and (3) dewatering of coarse debris flow deposits to yield fine-grained debris flow or hyperconcentrated flow. Three planning or design case histories represent different lengths of postglacial time. Case I is representative of large, infrequent (500 to 1,000 years on average) cohesive debris flows. These flows need to be considered in long-term planning in valleys around the volcano. Case II generalizes the noncohesive debris flows of intermediate size and recurrence (100 to 500 years). This case is appropriate for consideration in some structural design. Case III flows are

@article{doi103133pp1547,
    author = "Scott, Keith and Vallance, James W. and Pringle, Patrick T.",
    title = "Sedimentology, Behavior, and Hazards of Debris Flows at Mount Rainier, Washington",
    year = "1995",
    journal = "USGS professional paper",
    abstract = "Mount Rainier is potentially the most dangerous volcano in the Cascade Range because of its great height, frequent earthquakes, active hydrothermal system, and extensive glacier mantle. Many debris flows and their distal phases have inundated areas far from the volcano during postglacial time. Two types of debris flows, cohesive and noncohesive, have radically different origins and behavior that relate empirically to clay content. The two types are the major subpopulations of debris flows at Mount Rainier. The behavior of cohesive flows is affected by the cohesion and adhesion of particles; noncohesive flows are dominated by particle collisions to the extent that particle cataclasis becomes common during near-boundary shear. Cohesive debris flows contain more than 3 to 5 percent of clay-size sediment. The composition of these flows changed little as they traveled more than 100 kilometers from Mount Rainier to inundate parts of the now-populated Puget Sound lowland. They originate as deep-seated failures of sectors of the volcanic edifice, and such failures are sufficiently frequent that they are the major destructional process of Mount Rainier's morphologic evolution. In several deposits of large cohesive flows, a lateral, megaclast-bearing facies (with a mounded or hummocky surface) contrasts with a more clay-rich facies in the center of valleys and downstream. Cohesive flows at Mount Rainier do not correlate strongly with volcanic activity and thus can recur without warning, possibly triggered by non-magmatic earthquakes or by changes in the hydrothermal system. Noncohesive debris flows contain less than 3 to 5 percent clay-size sediment. They form most commonly by bulking of sediment in water surges, but some originate directly or indirectly from shallow slope failures that do not penetrate the hydrothermally altered core of the volcano. In contrast with cohesive flows, most noncohesive flows transform both from and to other flow types and are, therefore, the middle segments of flow waves that begin and end as flood surges. Proximally, through the bulking of poorly sorted volcaniclastic debris on the flanks of the volcano, flow waves expand rapidly in volume by transforming from water surges through hyperconcentrated stream flow (20 to 60 percent sediment by volume) to debris flow. Distally, the transformations occur more slowly in reverse order - from debris flow, to hyperconcentrated flow, and finally to normal streamflow with less than 20 percent sediment by volume. During runout of the largest noncohesive flows, hyperconcentrated flow has continued for as much as 40 to 70 kilometers. Lahars (volcanic debris flows and their deposits) have occurred frequently at Mount Rainier over the past several thousand years, and generally they have not clustered within discrete eruptive periods as at Mount St. Helens. An exception is a period of large noncohesive flows during and after construction of the modern summit cone. Deposits from lahar-runout flows, the hyperconcentrated distal phases of lahars, document the frequency and extent of noncohesive lahars. These deposits also record the following transformations of debris flows: (1) the direct, progressive dilution of debris flow to hyperconcentrated flow, (2) deposition of successively finer grained lobes of debris until only the hyperconcentrated tail of the flow remains to continue downstream, and (3) dewatering of coarse debris flow deposits to yield fine-grained debris flow or hyperconcentrated flow. Three planning or design case histories represent different lengths of postglacial time. Case I is representative of large, infrequent (500 to 1,000 years on average) cohesive debris flows. These flows need to be considered in long-term planning in valleys around the volcano. Case II generalizes the noncohesive debris flows of intermediate size and recurrence (100 to 500 years). This case is appropriate for consideration in some structural design. Case III flows are",
    url = "https://doi.org/10.3133/pp1547",
    doi = "10.3133/pp1547",
    openalex = "W1484627669",
    references = "doi10100797836426975939, doi1010160040195171900382, doi1010160169555x91900278, doi1010160377027384900027, doi101029tr035i006p00951, doi101086627271, doi101130reg7p1, doi102110pec79270075, openalexw1555930968, openalexw1598633756"
}

iv evolves. While some exposures are better than they were when Harry mapped the deposit, others no longer exist.

@article{doi103133ofr96677,
    author = "Glicken, Harry",
    title = "Rockslide-debris avalanche of May 18, 1980, Mount St. Helens Volcano, Washington",
    year = "1996",
    journal = "Antarctica A Keystone in a Changing World",
    abstract = "iv evolves. While some exposures are better than they were when Harry mapped the deposit, others no longer exist.",
    url = "https://doi.org/10.3133/ofr96677",
    doi = "10.3133/ofr96677",
    openalex = "W2130485868",
    references = "openalexw2167464155, openalexw2623958108"
}

The frequency‐magnitude distribution of earthquakes, characterized using the b ‐value, is examined as a function of space beneath Mount St. Helens (1988–1996), and Mt. Spurr (1991–1995). At Mount St. Helens, two volumes of anomalously high b (b > 1.3) can be observed at depths of 2.6–3.6 km below the crater floor and below 6.4 km. These anomalies coincide with (1) the depth of vesiculation of ascending magma, and (2) the suggested location of a magma chamber at Mount St. Helens. Study of Mt. Spurr reveals an area of high b ‐value (b ≥ 1.3) at a depth of about 2.3–4.5 km below the crater floor of the active vent Crater Peak. We propose that the higher material heterogeneity in the vicinity of a magma chamber or conduit due to vesiculation of the ascending magma is the main cause of the increased b ‐value at shallow depths. Alternatively, interaction of magma with groundwater may have increased pore pressure and lowered the effective stress. The deeper anomaly at Mount St. Helens is likely caused by high thermal stress gradients in the vicinity of the magma chamber. Our results indicate that detailed mapping of the frequency‐magnitude distribution can be used as a tool to trace vesiculation and locate active magma chambers.

@article{doi10102996gl03779,
    author = "Wiemer, Stefan and McNutt, Stephen R.",
    title = "Variations in the frequency‐magnitude distribution with depth in two volcanic areas: Mount St. Helens, Washington, and Mt. Spurr, Alaska",
    year = "1997",
    journal = "Geophysical Research Letters",
    abstract = "The frequency‐magnitude distribution of earthquakes, characterized using the b ‐value, is examined as a function of space beneath Mount St. Helens (1988–1996), and Mt. Spurr (1991–1995). At Mount St. Helens, two volumes of anomalously high b (b > 1.3) can be observed at depths of 2.6–3.6 km below the crater floor and below 6.4 km. These anomalies coincide with (1) the depth of vesiculation of ascending magma, and (2) the suggested location of a magma chamber at Mount St. Helens. Study of Mt. Spurr reveals an area of high b ‐value (b ≥ 1.3) at a depth of about 2.3–4.5 km below the crater floor of the active vent Crater Peak. We propose that the higher material heterogeneity in the vicinity of a magma chamber or conduit due to vesiculation of the ascending magma is the main cause of the increased b ‐value at shallow depths. Alternatively, interaction of magma with groundwater may have increased pore pressure and lowered the effective stress. The deeper anomaly at Mount St. Helens is likely caused by high thermal stress gradients in the vicinity of the magma chamber. Our results indicate that detailed mapping of the frequency‐magnitude distribution can be used as a tool to trace vesiculation and locate active magma chambers.",
    url = "https://doi.org/10.1029/96gl03779",
    doi = "10.1029/96gl03779",
    openalex = "W1967379622",
    references = "doi101007bf00278003"
}

The effects of isolation on primary succession are poorly documented. I monitored vegetation recovery on two Mount St. Helens lahars (mud flows) with different degrees of isolation using contiguous plots. Seventeen years after the eruption, species richness was stable, but cover continued to increase. That isolation affects community structure was confirmed in several ways. The dominance hierarchies of the lahars differed sharply. Detrended correspondence analysis on Lahar I showed a trend related to distance from an adjacent woodland, whereas vegetation on Lahar II was relatively homogeneous. Spectra of growth forms and dispersal types also differed. Lahar I was dominated by species with modest dispersal ability, while Lahar II was dominated by species with better dispersal. Variation between plots should decline through time, a prediction confirmed on Lahar II. Lahar I remained heterogeneous despite having developed significantly higher cover. Here, the increasing distance from the forest has prevented plots from becoming more homogeneous. At this stage of early primary succession, neither lahar is converging towards the species composition of adjacent vegetation. This study shows that isolation and differential dispersal ability combine to determine initial vegetation structure. Stochastic effects resulting from dispersal limitations may resist the more deterministic effects of competition that could lead to floristic convergence.

@article{moral1998early,
    author = "Moral, Roger del",
    title = "Early succession on lahars spawned by Mount St. Helens",
    year = "1998",
    journal = "American Journal of Botany",
    abstract = "The effects of isolation on primary succession are poorly documented. I monitored vegetation recovery on two Mount St. Helens lahars (mud flows) with different degrees of isolation using contiguous plots. Seventeen years after the eruption, species richness was stable, but cover continued to increase. That isolation affects community structure was confirmed in several ways. The dominance hierarchies of the lahars differed sharply. Detrended correspondence analysis on Lahar I showed a trend related to distance from an adjacent woodland, whereas vegetation on Lahar II was relatively homogeneous. Spectra of growth forms and dispersal types also differed. Lahar I was dominated by species with modest dispersal ability, while Lahar II was dominated by species with better dispersal. Variation between plots should decline through time, a prediction confirmed on Lahar II. Lahar I remained heterogeneous despite having developed significantly higher cover. Here, the increasing distance from the forest has prevented plots from becoming more homogeneous. At this stage of early primary succession, neither lahar is converging towards the species composition of adjacent vegetation. This study shows that isolation and differential dispersal ability combine to determine initial vegetation structure. Stochastic effects resulting from dispersal limitations may resist the more deterministic effects of competition that could lead to floristic convergence.",
    url = "https://doi.org/10.2307/2446417",
    doi = "10.2307/2446417",
    number = "6",
    openalex = "W2118210219",
    pages = "820-828",
    volume = "85",
    references = "doi10100797894009406116, doi101007978940095526419, doi10100797894009919727, doi101038371065a0, doi101046j15231739199206040513x, doi1018900012965819970780081cirlag20co2, doi1023071218728, doi1023071938349, doi1023071939377, doi1023071942661"
}

The complexity of flow and wide variety of depositional processes operating in subaqueous density flows, combined with post‐depositional consolidation and soft‐sediment deformation, often make it difficult to interpret the characteristics of the original flow from the sedimentary record. This has led to considerable confusion of nomenclature in the literature. This paper attempts to clarify this situation by presenting a simple classification of sedimentary density flows, based on physical flow properties and grain‐support mechanisms, and briefly discusses the likely characteristics of the deposited sediments. Cohesive flows are commonly referred to as debris flows and mud flows and defined on the basis of sediment characteristics. The boundary between cohesive and non‐cohesive density flows (frictional flows) is poorly constrained, but dimensionless numbers may be of use to define flow thresholds. Frictional flows include a continuous series from sediment slides to turbidity currents. Subdivision of these flows is made on the basis of the dominant particle‐support mechanisms, which include matrix strength (in cohesive flows), buoyancy, pore pressure, grain‐to‐grain interaction (causing dispersive pressure), Reynolds stresses (turbulence) and bed support (particles moved on the stationary bed). The dominant particle‐support mechanism depends upon flow conditions, particle concentration, grain‐size distribution and particle type. In hyperconcentrated density flows, very high sediment concentrations (>25 volume%) make particle interactions of major importance. The difference between hyperconcentrated density flows and cohesive flows is that the former are friction dominated. With decreasing sediment concentration, vertical particle sorting can result from differential settling, and flows in which this can occur are termed concentrated density flows. The boundary between hyperconcentrated and concentrated density flows is defined by a change in particle behaviour, such that denser or larger grains are no longer fully supported by grain interaction, thus allowing coarse‐grain tail (or dense‐grain tail) normal grading. The concentration at which this change occurs depends on particle size, sorting, composition and relative density, so that a single threshold concentration cannot be defined. Concentrated density flows may be highly erosive and subsequently deposit complete or incomplete Lowe and Bouma sequences. Conversely, hydroplaning at the base of debris flows, and possibly also in some hyperconcentrated flows, may reduce the fluid drag, thus allowing high flow velocities while preventing large‐scale erosion. Flows with concentrations <9% by volume are true turbidity flows (sensu Bagnold, 1962), in which fluid turbulence is the main particle‐support mechanism. Turbidity flows and concentrated density flows can be subdivided on the basis of flow duration into instantaneous surges, longer duration surge‐like flows and quasi‐steady currents. Flow duration is shown to control the nature of the resulting deposits. Surge‐like turbidity currents tend to produce classical Bouma sequences, whose nature at any one site depends on factors such as flow size, sediment type and proximity to source. In contrast, quasi‐steady turbidity currents, generated by hyperpycnal river effluent, can deposit coarsening‐up units capped by fining‐up units (because of waxing and waning conditions respectively) and may also include thick units of uniform character (resulting from prolonged periods of near‐steady conditions). Any flow type may progressively change character along the transport path, with transformation primarily resulting from reductions in sediment concentration through progressive entrainment of surrounding fluid and/or sediment deposition. The rate of fluid entrainment, and consequently flow transformation, is dependent on factors including slope gradient, lateral confinement, bed roughness, flow thickness and water depth. Flows with high and low sediment concentrations may co‐exist in one transport event because of downflow transformations, flow stratification or shear layer development of the mixing interface with the overlying water (mixing cloud formation). Deposits of an individual flow event at one site may therefore form from a succession of different flow types, and this introduces considerable complexity into classifying the flow event or component flow types from the deposits.

@article{doi101046j13653091200100360x,
    author = "Mulder, Thierry and Alexander, Jan",
    title = "The physical character of subaqueous sedimentary density flows and their deposits",
    year = "2001",
    journal = "Sedimentology",
    abstract = "The complexity of flow and wide variety of depositional processes operating in subaqueous density flows, combined with post‐depositional consolidation and soft‐sediment deformation, often make it difficult to interpret the characteristics of the original flow from the sedimentary record. This has led to considerable confusion of nomenclature in the literature. This paper attempts to clarify this situation by presenting a simple classification of sedimentary density flows, based on physical flow properties and grain‐support mechanisms, and briefly discusses the likely characteristics of the deposited sediments. Cohesive flows are commonly referred to as debris flows and mud flows and defined on the basis of sediment characteristics. The boundary between cohesive and non‐cohesive density flows (frictional flows) is poorly constrained, but dimensionless numbers may be of use to define flow thresholds. Frictional flows include a continuous series from sediment slides to turbidity currents. Subdivision of these flows is made on the basis of the dominant particle‐support mechanisms, which include matrix strength (in cohesive flows), buoyancy, pore pressure, grain‐to‐grain interaction (causing dispersive pressure), Reynolds stresses (turbulence) and bed support (particles moved on the stationary bed). The dominant particle‐support mechanism depends upon flow conditions, particle concentration, grain‐size distribution and particle type. In hyperconcentrated density flows, very high sediment concentrations (>25 volume\%) make particle interactions of major importance. The difference between hyperconcentrated density flows and cohesive flows is that the former are friction dominated. With decreasing sediment concentration, vertical particle sorting can result from differential settling, and flows in which this can occur are termed concentrated density flows. The boundary between hyperconcentrated and concentrated density flows is defined by a change in particle behaviour, such that denser or larger grains are no longer fully supported by grain interaction, thus allowing coarse‐grain tail (or dense‐grain tail) normal grading. The concentration at which this change occurs depends on particle size, sorting, composition and relative density, so that a single threshold concentration cannot be defined. Concentrated density flows may be highly erosive and subsequently deposit complete or incomplete Lowe and Bouma sequences. Conversely, hydroplaning at the base of debris flows, and possibly also in some hyperconcentrated flows, may reduce the fluid drag, thus allowing high flow velocities while preventing large‐scale erosion. Flows with concentrations <9\% by volume are true turbidity flows (sensu Bagnold, 1962), in which fluid turbulence is the main particle‐support mechanism. Turbidity flows and concentrated density flows can be subdivided on the basis of flow duration into instantaneous surges, longer duration surge‐like flows and quasi‐steady currents. Flow duration is shown to control the nature of the resulting deposits. Surge‐like turbidity currents tend to produce classical Bouma sequences, whose nature at any one site depends on factors such as flow size, sediment type and proximity to source. In contrast, quasi‐steady turbidity currents, generated by hyperpycnal river effluent, can deposit coarsening‐up units capped by fining‐up units (because of waxing and waning conditions respectively) and may also include thick units of uniform character (resulting from prolonged periods of near‐steady conditions). Any flow type may progressively change character along the transport path, with transformation primarily resulting from reductions in sediment concentration through progressive entrainment of surrounding fluid and/or sediment deposition. The rate of fluid entrainment, and consequently flow transformation, is dependent on factors including slope gradient, lateral confinement, bed roughness, flow thickness and water depth. Flows with high and low sediment concentrations may co‐exist in one transport event because of downflow transformations, flow stratification or shear layer development of the mixing interface with the overlying water (mixing cloud formation). Deposits of an individual flow event at one site may therefore form from a succession of different flow types, and this introduces considerable complexity into classifying the flow event or component flow types from the deposits.",
    url = "https://doi.org/10.1046/j.1365-3091.2001.00360.x",
    doi = "10.1046/j.1365-3091.2001.00360.x",
    openalex = "W2120162798",
    references = "doi101007bf00301484, doi101016s0012825297818582, doi101017s0022112089000340, doi10102997rg00426, doi101046j136530912000047s1062x, doi101086626171, doi101086627725, doi101086629747, doi101098rspa19540186, doi101111j136530911983tb00702x, doi101130reg7p1, doi101146annurevearth25185, doi101306212f7f312b2411d78648000102c1865d, doi1013065ceadd7616bb11d78645000102c1865d, doi1013065d25cc7916c111d78645000102c1865d, doi10130674d723b52b2111d78648000102c1865d, doi10130674d7262b2b2111d78648000102c1865d, doi102110scn8403, doi102475ajs25012849, nardin1979a, normark1978fan, openalexw1570283708"
}

Abstract. An intense lateral blast devastated Mount St. Helens in 1980, but forest understory species survived in some north‐slope ‘refugia’. We explored the effects of refugia on colonization of barren pumice in 1997 and 1998, 18 yr after the eruption. The seed rain of 23 colonizers came mostly from populations that had previously established in refugia. Parachutists had small, vagile seeds, parasailors had winged seeds, and tumblers were blown along the ground. The latter two groups are heavier and dispersed more slowly, but are more likely to survive. The proportion of the vegetation represented by wind‐dispersed species increased with distance from refugia. Parachutist's density declined with time and proximity to refugia. As vegetation adjacent to refugia developed, populations of parasailors and tumblers expanded, foreshadowing their dominance in more remote pumice. Refugia played a critical role in determining the rate and course of succession by providing fertile islands that permitted pioneers and dry meadow species to establish near barren pumice. Species that survived in refugia played a negligible role in colonization. This study showed that when refugia contrast sharply with new substrates, they accelerate recovery by facilitating the invasion of pioneer species.

@article{doi101111j165411032003tb02195x,
    author = "Fuller, R.N. and del Moral, R.",
    title = "The role of refugia and dispersal in primary succession on Mount St. Helens, Washington",
    year = "2003",
    journal = "Journal of Vegetation Science",
    abstract = "Abstract. An intense lateral blast devastated Mount St. Helens in 1980, but forest understory species survived in some north‐slope ‘refugia’. We explored the effects of refugia on colonization of barren pumice in 1997 and 1998, 18 yr after the eruption. The seed rain of 23 colonizers came mostly from populations that had previously established in refugia. Parachutists had small, vagile seeds, parasailors had winged seeds, and tumblers were blown along the ground. The latter two groups are heavier and dispersed more slowly, but are more likely to survive. The proportion of the vegetation represented by wind‐dispersed species increased with distance from refugia. Parachutist's density declined with time and proximity to refugia. As vegetation adjacent to refugia developed, populations of parasailors and tumblers expanded, foreshadowing their dominance in more remote pumice. Refugia played a critical role in determining the rate and course of succession by providing fertile islands that permitted pioneers and dry meadow species to establish near barren pumice. Species that survived in refugia played a negligible role in colonization. This study showed that when refugia contrast sharply with new substrates, they accelerate recovery by facilitating the invasion of pioneer species.",
    url = "https://doi.org/10.1111/j.1654-1103.2003.tb02195.x",
    doi = "10.1111/j.1654-1103.2003.tb02195.x",
    openalex = "W4238340471",
    references = "moral1998early"
}

Abstract. An intense lateral blast devastated Mount St. Helens in 1980, but forest understory species survived in some north-slope ‘refugia’. We explored the effects of refugia on colonization of barren pumice in 1997 and 1998, 18 yr after the eruption. The seed rain of 23 colonizers came mostly from populations that had previously established in refugia. Parachutists had small, vagile seeds, parasailors had winged seeds, and tumblers were blown along the ground. The latter two groups are heavier and dispersed more slowly, but are more likely to survive. The proportion of the vegetation represented by wind-dispersed species increased with distance from refugia. Parachutist's density declined with time and proximity to refugia. As vegetation adjacent to refugia developed, populations of parasailors and tumblers expanded, foreshadowing their dominance in more remote pumice. Refugia played a critical role in determining the rate and course of succession by providing fertile islands that permitted pioneers and dry meadow species to establish near barren pumice. Species that survived in refugia played a negligible role in colonization. This study showed that when refugia contrast sharply with new substrates, they accelerate recovery by facilitating the invasion of pioneer species.

@article{doi1016581100923320030140637trorad20co2,
    author = "Fuller, R.N. and del Moral, R.",
    title = "The role of refugia and dispersal in primary succession on Mount St. Helens, Washington",
    year = "2003",
    journal = "Journal of Vegetation Science",
    abstract = "Abstract. An intense lateral blast devastated Mount St. Helens in 1980, but forest understory species survived in some north-slope ‘refugia’. We explored the effects of refugia on colonization of barren pumice in 1997 and 1998, 18 yr after the eruption. The seed rain of 23 colonizers came mostly from populations that had previously established in refugia. Parachutists had small, vagile seeds, parasailors had winged seeds, and tumblers were blown along the ground. The latter two groups are heavier and dispersed more slowly, but are more likely to survive. The proportion of the vegetation represented by wind-dispersed species increased with distance from refugia. Parachutist's density declined with time and proximity to refugia. As vegetation adjacent to refugia developed, populations of parasailors and tumblers expanded, foreshadowing their dominance in more remote pumice. Refugia played a critical role in determining the rate and course of succession by providing fertile islands that permitted pioneers and dry meadow species to establish near barren pumice. Species that survived in refugia played a negligible role in colonization. This study showed that when refugia contrast sharply with new substrates, they accelerate recovery by facilitating the invasion of pioneer species.",
    url = "https://doi.org/10.1658/1100-9233(2003)014[0637:trorad]2.0.co;2",
    doi = "10.1658/1100-9233(2003)014[0637:trorad]2.0.co;2",
    openalex = "W2069751725",
    references = "moral1998early"
}

@article{doi101007s004450060109y,
    author = "Belousov, Alexander and Voight, B. and Belousova, Marina",
    title = "Directed blasts and blast-generated pyroclastic density currents: a comparison of the Bezymianny 1956, Mount St Helens 1980, and Soufrière Hills, Montserrat 1997 eruptions and deposits",
    year = "2007",
    journal = "Bulletin of Volcanology",
    url = "https://doi.org/10.1007/s00445-006-0109-y",
    doi = "10.1007/s00445-006-0109-y",
    openalex = "W2025160966",
    references = "crandell1987deposits, doi101007bf00302002, doi101007bf01073511, doi1010160377027384900027, doi101038323598a0, doi101093petrology41121, doi101111j1365246x1980tb02613x, doi101306212f7f312b2411d78648000102c1865d, doi103133pp1444, doi105860choice352778, doi107551mitpress119930030017, openalexw1587261652, openalexw2100680228, openalexw597459718"
}

Abstract The 1918 eruption of the glacially capped Katla volcano, southern Iceland, generated a violent jökulhlaup, or glacial outburst flood, inundating a large area of Mýrdalssandur, the proglacial outwash plain, where it deposited ca 1 km 3 of volcaniclastic sediment. The character of the 1918 jökulhlaup is contentious, having been variously categorized as a turbulent water flow, a hyperconcentrated flow or as a debris flow, based on localized outcrop analysis. In this study, outcrop‐based architectural analyses of the 1918 deposits reveal the presence of lenticular and tabular bedsets associated with deposition from quasi‐stationary antidunes and down‐current migrating antidunes, and from regular based bedsets, associated with transient chute‐and‐pool bedforms, all of which are associated with turbulent, transcritical to supercritical water flow conditions. Antidune wavelengths range from 24 to 96 m, corresponding to flow velocities of 6 to 12 m sec −1 and average flow depths of 5 to 19 m. This range of calculated flow velocities is in good agreement with estimates made from eyewitness accounts. Architectural analysis of the 1918 jökulhlaup deposits has led to an improved estimation of flow parameters and flow hydraulics associated with the 1918 jökulhlaup that could not have been achieved through localized outcrop analysis. The observations presented here provide additional sedimentological and architectural criteria for the recognition of deposits associated with transcritical and supercritical water flow conditions. The physical scale of sedimentary architectures associated with the migration of bedforms is largely dependent on the magnitude of the formative flow events or processes; sedimentary analyses must therefore be undertaken at the appropriate physical scale if reliable interpretations, regarding modes of deposition and formative flow hydraulics, are to be made.

@article{doi101111j13653091200700931x,
    author = "Duller, Robert A. and Mountney, Nigel P. and Russell, Andrew J. and CASSIDY, NIGEL C.",
    title = "Architectural analysis of a volcaniclastic jökulhlaup deposit, southern Iceland: sedimentary evidence for supercritical flow",
    year = "2008",
    journal = "Sedimentology",
    abstract = "Abstract The 1918 eruption of the glacially capped Katla volcano, southern Iceland, generated a violent jökulhlaup, or glacial outburst flood, inundating a large area of Mýrdalssandur, the proglacial outwash plain, where it deposited ca 1 km 3 of volcaniclastic sediment. The character of the 1918 jökulhlaup is contentious, having been variously categorized as a turbulent water flow, a hyperconcentrated flow or as a debris flow, based on localized outcrop analysis. In this study, outcrop‐based architectural analyses of the 1918 deposits reveal the presence of lenticular and tabular bedsets associated with deposition from quasi‐stationary antidunes and down‐current migrating antidunes, and from regular based bedsets, associated with transient chute‐and‐pool bedforms, all of which are associated with turbulent, transcritical to supercritical water flow conditions. Antidune wavelengths range from 24 to 96 m, corresponding to flow velocities of 6 to 12 m sec −1 and average flow depths of 5 to 19 m. This range of calculated flow velocities is in good agreement with estimates made from eyewitness accounts. Architectural analysis of the 1918 jökulhlaup deposits has led to an improved estimation of flow parameters and flow hydraulics associated with the 1918 jökulhlaup that could not have been achieved through localized outcrop analysis. The observations presented here provide additional sedimentological and architectural criteria for the recognition of deposits associated with transcritical and supercritical water flow conditions. The physical scale of sedimentary architectures associated with the migration of bedforms is largely dependent on the magnitude of the formative flow events or processes; sedimentary analyses must therefore be undertaken at the appropriate physical scale if reliable interpretations, regarding modes of deposition and formative flow hydraulics, are to be made.",
    url = "https://doi.org/10.1111/j.1365-3091.2007.00931.x",
    doi = "10.1111/j.1365-3091.2007.00931.x",
    openalex = "W1764022448",
    references = "doi101007bf00301484"
}

Uncertainty remains on the origin of distal mass deposition maxima observed in many recent tephra fall deposits. In this study the link between ash aggregation and the formation of distal mass deposition maxima is investigated through reanalysis of tephra fallout from the Mount St. Helens 18 May 1980 (MSH80) eruption. In addition, we collate all the data needed to model distal ash sedimentation from the MSH80 eruption cloud. Four particle size subpopulations were present in distal fallout with modes at 2.2 Φ, 4.2 Φ, 5.9 Φ, and 8.3 Φ. Settling rates of the coarsest subpopulation closely matched predicted single‐particle terminal fall velocities. Sedimentation of particles <100 μ m was greatly enhanced, predominantly through aggregation of a particle subpopulation with modal diameter 5.9 ± 0.2 Φ (19 ± 3 μ m). Mammatus on the MSH80 cloud provided a mechanism to transport very fine ash particles, with predicted atmospheric lifetimes of days to weeks, from the upper troposphere to the surface in a matter of hours. In this mechanism, ash particles initiate ice hydrometeor formation high in the troposphere. Subsequently, the volcanic cloud rapidly subsides as mammatus develop from increased particle loading and cloud base sublimation. Rapid fallout occurs as the cloud passes through the melting level in a process analogous to snowflake aggregation. Aggregates sediment en masse and form the distal mass deposition maxima observed in many recent volcanic ash fall deposits. This work provides a data resource that will facilitate tephra sedimentation modeling and allow model intercomparisons.

@article{doi1010292008jb005756,
    author = "Durant, A. J. and Rose, William I. and Sarna‐Wojcicki, Andrei M. and Carey, S. and Volentik, A. C.",
    title = "Hydrometeor‐enhanced tephra sedimentation: Constraints from the 18 May 1980 eruption of Mount St. Helens",
    year = "2009",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "Uncertainty remains on the origin of distal mass deposition maxima observed in many recent tephra fall deposits. In this study the link between ash aggregation and the formation of distal mass deposition maxima is investigated through reanalysis of tephra fallout from the Mount St. Helens 18 May 1980 (MSH80) eruption. In addition, we collate all the data needed to model distal ash sedimentation from the MSH80 eruption cloud. Four particle size subpopulations were present in distal fallout with modes at 2.2 Φ, 4.2 Φ, 5.9 Φ, and 8.3 Φ. Settling rates of the coarsest subpopulation closely matched predicted single‐particle terminal fall velocities. Sedimentation of particles <100 μ m was greatly enhanced, predominantly through aggregation of a particle subpopulation with modal diameter 5.9 ± 0.2 Φ (19 ± 3 μ m). Mammatus on the MSH80 cloud provided a mechanism to transport very fine ash particles, with predicted atmospheric lifetimes of days to weeks, from the upper troposphere to the surface in a matter of hours. In this mechanism, ash particles initiate ice hydrometeor formation high in the troposphere. Subsequently, the volcanic cloud rapidly subsides as mammatus develop from increased particle loading and cloud base sublimation. Rapid fallout occurs as the cloud passes through the melting level in a process analogous to snowflake aggregation. Aggregates sediment en masse and form the distal mass deposition maxima observed in many recent volcanic ash fall deposits. This work provides a data resource that will facilitate tephra sedimentation modeling and allow model intercomparisons.",
    url = "https://doi.org/10.1029/2008jb005756",
    doi = "10.1029/2008jb005756",
    openalex = "W2074885278",
    references = "doi101007bf00302002"
}

Abstract Submarine sediment density flows are one of the most important processes for moving sediment across our planet, yet they are extremely difficult to monitor directly. The speed of long run‐out submarine density flows has been measured directly in just five locations worldwide and their sediment concentration has never been measured directly. The only record of most density flows is their sediment deposit. This article summarizes the processes by which density flows deposit sediment and proposes a new single classification for the resulting types of deposit. Colloidal properties of fine cohesive mud ensure that mud deposition is complex, and large volumes of mud can sometimes pond or drain‐back for long distances into basinal lows. Deposition of ungraded mud (T E‐3) most probably finally results from en masse consolidation in relatively thin and dense flows, although initial size sorting of mud indicates earlier stages of dilute and expanded flow. Graded mud (T E‐2) and finely laminated mud (T E‐1) most probably result from floc settling at lower mud concentrations. Grain‐size breaks beneath mud intervals are commonplace, and record bypass of intermediate grain sizes due to colloidal mud behaviour. Planar‐laminated (T D) and ripple cross‐laminated (T C) non‐cohesive silt or fine sand is deposited by dilute flow, and the external deposit shape is consistent with previous models of spatial decelerating (dissipative) dilute flow. A grain‐size break beneath the ripple cross‐laminated (T C) interval is common, and records a period of sediment reworking (sometimes into dunes) or bypass. Finely planar‐laminated sand can be deposited by low‐amplitude bed waves in dilute flow (T B‐1), but it is most likely to be deposited mainly by high‐concentration near‐bed layers beneath high‐density flows (T B‐2). More widely spaced planar lamination (T B‐3) occurs beneath massive clean sand (T A), and is also formed by high‐density turbidity currents. High‐density turbidite deposits (T A, T B‐2 and T B‐3) have a tabular shape consistent with hindered settling, and are typically overlain by a more extensive drape of low‐density turbidite (T D and T C,). This core and drape shape suggests that events sometimes comprise two distinct flow components. Massive clean sand is less commonly deposited en masse by liquefied debris flow (D CS), in which case the clean sand is ungraded or has a patchy grain‐size texture. Clean‐sand debrites can extend for several tens of kilometres before pinching out abruptly. Up‐current transitions suggest that clean‐sand debris flows sometimes form via transformation from high‐density turbidity currents. Cohesive debris flows can deposit three types of ungraded muddy sand that may contain clasts. Thick cohesive debrites tend to occur in more proximal settings and extend from an initial slope failure. Thinner and highly mobile low‐strength cohesive debris flows produce extensive deposits restricted to distal areas. These low‐strength debris flows may contain clasts and travel long distances (D M‐2), or result from more local flow transformation due to turbulence damping by cohesive mud (D M‐1). Mapping of individual flow deposits (beds) emphasizes how a single event can contain several flow types, with transformations between flow types. Flow transformation may be from dilute to dense flow, as well as from dense to dilute flow. Flow state, deposit type and flow transformation are strongly dependent on the volume fraction of cohesive fine mud within a flow. Recent field observations show significant deviations from previous widely cited models, and many hypotheses linking flow type to deposit type are poorly tested. There is much still to learn about these remarkable flows.

@article{doi101111j13653091201201353x,
    author = "Talling, Peter J. and Masson, Douglas G. and Sumner, E. J. and Malgesini, G.",
    title = "Subaqueous sediment density flows: Depositional processes and deposit types",
    year = "2012",
    journal = "Sedimentology",
    abstract = "Abstract Submarine sediment density flows are one of the most important processes for moving sediment across our planet, yet they are extremely difficult to monitor directly. The speed of long run‐out submarine density flows has been measured directly in just five locations worldwide and their sediment concentration has never been measured directly. The only record of most density flows is their sediment deposit. This article summarizes the processes by which density flows deposit sediment and proposes a new single classification for the resulting types of deposit. Colloidal properties of fine cohesive mud ensure that mud deposition is complex, and large volumes of mud can sometimes pond or drain‐back for long distances into basinal lows. Deposition of ungraded mud (T E‐3) most probably finally results from en masse consolidation in relatively thin and dense flows, although initial size sorting of mud indicates earlier stages of dilute and expanded flow. Graded mud (T E‐2) and finely laminated mud (T E‐1) most probably result from floc settling at lower mud concentrations. Grain‐size breaks beneath mud intervals are commonplace, and record bypass of intermediate grain sizes due to colloidal mud behaviour. Planar‐laminated (T D) and ripple cross‐laminated (T C) non‐cohesive silt or fine sand is deposited by dilute flow, and the external deposit shape is consistent with previous models of spatial decelerating (dissipative) dilute flow. A grain‐size break beneath the ripple cross‐laminated (T C) interval is common, and records a period of sediment reworking (sometimes into dunes) or bypass. Finely planar‐laminated sand can be deposited by low‐amplitude bed waves in dilute flow (T B‐1), but it is most likely to be deposited mainly by high‐concentration near‐bed layers beneath high‐density flows (T B‐2). More widely spaced planar lamination (T B‐3) occurs beneath massive clean sand (T A), and is also formed by high‐density turbidity currents. High‐density turbidite deposits (T A, T B‐2 and T B‐3) have a tabular shape consistent with hindered settling, and are typically overlain by a more extensive drape of low‐density turbidite (T D and T C,). This core and drape shape suggests that events sometimes comprise two distinct flow components. Massive clean sand is less commonly deposited en masse by liquefied debris flow (D CS), in which case the clean sand is ungraded or has a patchy grain‐size texture. Clean‐sand debrites can extend for several tens of kilometres before pinching out abruptly. Up‐current transitions suggest that clean‐sand debris flows sometimes form via transformation from high‐density turbidity currents. Cohesive debris flows can deposit three types of ungraded muddy sand that may contain clasts. Thick cohesive debrites tend to occur in more proximal settings and extend from an initial slope failure. Thinner and highly mobile low‐strength cohesive debris flows produce extensive deposits restricted to distal areas. These low‐strength debris flows may contain clasts and travel long distances (D M‐2), or result from more local flow transformation due to turbulence damping by cohesive mud (D M‐1). Mapping of individual flow deposits (beds) emphasizes how a single event can contain several flow types, with transformations between flow types. Flow transformation may be from dilute to dense flow, as well as from dense to dilute flow. Flow state, deposit type and flow transformation are strongly dependent on the volume fraction of cohesive fine mud within a flow. Recent field observations show significant deviations from previous widely cited models, and many hypotheses linking flow type to deposit type are poorly tested. There is much still to learn about these remarkable flows.",
    url = "https://doi.org/10.1111/j.1365-3091.2012.01353.x",
    doi = "10.1111/j.1365-3091.2012.01353.x",
    openalex = "W1934469433",
    references = "dejong1972flysch, doi1010160012825283900223, doi1010160037073880900524, doi1010160040195171900382, doi101016jmarpetgeo200301003, doi101016jmarpetgeo200309001, doi101016jmarpetgeo200902012, doi101016s0012825297818582, doi101016s0264817299000112, doi10102900eo00168, doi10102997rg00426, doi101046j13653091200100360x, doi101086625710, doi101086629606, doi101098rspa19540186, doi101098rsta20061810, doi101098rstl18830029, doi101111j136530911976tb00051x, doi101111j136530911977tb00122x, doi101111j13653091200801019x, doi101111j13653091200901073x, doi101146annurevfluid121108145618, doi1013062f9182e316ce11d78645000102c1865d, doi10130674d7262b2b2111d78648000102c1865d, doi102110sedred200434, nardin1979a, openalexw1570283708, openalexw580680426"
}

@article{doi101007s0044501610953,
    author = "Gardner, James E. and Andrews, B. J. and Dennen, R. L.",
    title = "Liftoff of the 18 May 1980 surge of Mount St. Helens (USA) and the deposits left behind",
    year = "2016",
    journal = "Bulletin of Volcanology",
    url = "https://doi.org/10.1007/s00445-016-1095-3",
    doi = "10.1007/s00445-016-1095-3",
    openalex = "W2565756080",
    references = "openalexw2167464155"
}