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Emplacement of the 18 May 1980 lateral blast deposit ENE of Mount St. Helens, Washington

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Abstract

Facies variations east-northeast of Mount St. Helens preserve a record of depositional processes in the 18 May 1980 lateral blast cloud. This paper reports new field, grain-size and component data from the ENE sector of the timber-blowdown zone and presents a model for blast flow and sedimentation. The first-erupted ejecta was rich in juvenile components and extends to the distal blowdown limit. The last-erupted ejecta was rich in accidental lithics and reached no further than a few kilometres from the mountain due to waning discharge. The blast cloud was a turbulent stratified flow which transported and deposited sediment in the manner of a ‘high-density’ turbidity current. The possibility that the blast was emplaced as a giant shearing fluidised bed is not favoured by compositional zoning patterns. Depositional conditions were strongly influenced by the rate of suspended-load fallout from the blast. Within about 8 km from vent rapid sedimentation caused deposition under moderate to high concentration conditions and formation of a basal hindered-settling zone able to detach gravitationally and drain into local depressions. The resulting proximal facies resembles a low-aspect-ratio ignimbrite. Fines depletion in the proximal facies is attributed to a combination of residual turbulence and rapid gas escape during particle settling and compaction through the hindered-settling zone. Component data suggest that the blast head played no significant role in the generation of fines depletion in the blast deposit as suggested by previous workers. With increasing distance from vent the rate of particle fallout declined and sedimentation took place under increasingly dilute and tractional conditions, building up antidune-like bedforms. Wavelengths of these bedforms range from 20 to <1 m, and decrease away from vent. There is a systematic relationship between antidune migration direction and depositional slope. The transition from proximal (ignimbrite-like) to distal (surge-like) facies suggests a possible gradation in transport and deposition processes between conventional pyroclastic surges and high-velocity pyroclastic flows.

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References

  • Allen JRL (1982) Sedimentary structures. Their character and physical basis. Volume II. Elsevier, Amsterdam 663 pp

    Google Scholar 

  • Allen JRL, Leeder MR (1980) Criteria for the instability of upper-stage plane beds. Sedimentology 27:209–217

    Google Scholar 

  • Barwis JH, Hayes MO (1985) Antidunes on modern and ancient washover fans. J Sediment Petrol 55:907–916

    Google Scholar 

  • Brantley SR, Waitt RB (1988) Interrelations among pyroclastic surge, pyroclastic flow, and lahars in Smith Creek Valley during first minutes of 18 May 1980 eruption of Mount St. Helens, USA. Bull Volcanol 50:304–326

    Google Scholar 

  • Chough SK, Sohn YK (1990) Depositional mechanics and sequences of base surges, Songaksan tuff ring, Cheju Island, Korea. Sedimentology 37:1115–1135

    Google Scholar 

  • Criswell CW (1987) Chronology and pyroclastic stratigraphy of the May 18, 1980, eruption of Mount St. Helens, Washington. J Gepphys Res 92:10237–10266

    Google Scholar 

  • Crowe BM, Fisher RV (1973) Sedimentary structures in base-surge deposits with special reference to cross-bedding, Ubehebe Craters, Death Valley, California. Geol Soc Am Bull 84:663–682

    Google Scholar 

  • Davies R (1968/69) The experimental study of the differential settling of particles in suspension at high concentrations. Powder Tech 2:32–42

    Google Scholar 

  • Fisher RV (1986) Systems of transport and deposition within pyroclastic surges: evidence from Mount St. Helens, Washington. EOS Trans Am Geophys Union 67:1246

    Google Scholar 

  • Fisher RV (1990) Transport and deposition of a pyroclastic surge across an area of high refift: the 18 May 1980 eruption of Mount St. Helens, Washington. Geol Soc Am Bull 102:1038–1054

    Google Scholar 

  • Fisher RV, Waters AC (1970) Base surge bedforms in maar volcanoes. Am J Sci 268:157–180

    Google Scholar 

  • Fisher RV, Wlicken HX, Hoblitt RP (1987) May 18, 1980, Mount St. Helens deposits in South Coldwater Creek, Washington. J Geophys Res 92:10267–10283

    Google Scholar 

  • Folk RL, Ward WC (1957) Brazos River bar, a study in the significance of grain-size parameters. J Sediment Petrol 27:3–26

    Google Scholar 

  • Ghosh JK, Mazumder BS, Saha MR, Sengupta S (1986) Deposition of sand by suspension currents: experimental and theoretical studies. J Sediment Petrol 56:57–66

    Google Scholar 

  • Greer MR, Yancey HF (1938) Expression and interpretation of the size composition of coal. Am Inst Min Met Eng Tech 948:250–269

    Google Scholar 

  • Hand BM (1974) Supercritical flow in density currents. J Sediment Petrol 44:637–648

    Google Scholar 

  • Hand BM, Bartberger CE (1988) Leeside sediment fallout patterns and the stability of angular bedforms. J Sediment Petrol 58:33–43

    Google Scholar 

  • Hoblitt RP, Miller CD (1984) Comment on ‘Mount St. Helens 1980 and Mount Pelee 1902 — flow or surge?’. Geology 12:692–693

    Google Scholar 

  • Hoblitt RP, Miller DC, Vallance JE (1981) Origin and stratigraphy of the deposits produced by the May 18 directed blast. In: Lipman PW, Mullineaux DR (eds) The 1980 eruptions of Mount St. Helens, Washington, US Geol Surv Prof Pap 1250:401–419

  • Jopling AV, Richardson EV (1966) Backset bedding developed in shooting flow in laboratory experiments. J Sediment Petrol 36:821–825

    Google Scholar 

  • Kieffer SW (1981) Fluid dynamics of the May 18 blast at Mount St. Helens. In: Lipman PW, Mullineaux DR (eds) The 1980 eruptions of Mount St. Helens, Washington, US Geol Surv Prof Pap 1250:379–400

  • Kieffer SW, Sturtevant B (1988) Erosional furrows formed during the lateral blast at Mount St. Helens, May 18, 1980. J Geophys Res 93:14793–14816

    Google Scholar 

  • Komar PD, Wang C (1984) Processes of selective grain transport and the formation of placers on beaches. J Geol 92:637–655

    Google Scholar 

  • Lindsey JF (1968) The development of clast fabrics in mudflows. J Sediment Petrol 38:1242–1253

    Google Scholar 

  • Lowe DR (1982) Sediment gravity flows: II. Depositional models with special reference to the deposits of high-density turbidity currents. J Sediment Petrol 52:279–297

    Google Scholar 

  • Lowe DR (1988) Suspended-load fallout rate as an independent variable in the analysis of current structures. Sedimentology 35:765–776

    Google Scholar 

  • Malin MC, Sheridan MF (1982) Computer-assisted mapping of pyroclastic surges. Science 217:637–640

    Google Scholar 

  • Middleton GV (1965) Antidune cross-bedding in a large flume. J Sediment Petrol 35:922–927

    Google Scholar 

  • Middleton GV (1967) Experiments on density and turbidity currents. III. Deposition of sediment. Can J Earth Sci 4:475–505

    Google Scholar 

  • Middleton GV, Hampton MA (1973) Sediment gravity flows: mechanics of flow and deposition. In: Middleton GV, Bouma AH (eds) Turbidites and deep water sedimentation. SEPM Short Course Notes. pp 1–38

  • Middleton GV, Neal WJ (1990) Experiments on the thickness of beds deposited by turbidity currents. J Sediment Petrol 59:297–307

    Google Scholar 

  • Moore JG, Rice CJ (1984) Chronology and character of the May 18, 1980, explosive eruptions of Mount St. Helens. National Academy of Sciences, Special Volume on Explosive Volcanism pp 133–142

  • Moore JG, Sisson TW (1981) Deposits and effects of the May 18 pyroclastic surge. In: Lipman PW, Mullineaux DR (eds) The 1980 eruptions of Mount St. Helens, Washington, US Geol Surv Prof Pap 1250:421–438

  • Nir A, Acrivos A (1990) Sedimentation and sediment flow on inclined surfaces. J Fluid Mech 212:139–153

    Google Scholar 

  • Pantin HM, Leeder MR (1987) Reverse flow in turbidity currents: the role of interal solitons. Sedimentology 34:1143–1155

    Google Scholar 

  • Paola C, Wiele SM, Reihart MA (1989) Upper-regime parallel lamination as the result of turbulent sediment transport and low-amplitude bed forms. Sedimentology 36:47–59

    Google Scholar 

  • Phillips CR, Smith TN (1971) Modes of settling and relative settling velocities in two-species suspensions. Ind Eng Chem Fundam 10:581–587

    Google Scholar 

  • Postma G (1986) Classification for sediment gravity-flow deposits based on flow conditions during sedimentation. Geology 14:291–294

    Google Scholar 

  • Postma G, Nemec W, Kleinspehn KL (1988) Large floating clasts in turbidites: a mechanism for their emplacement. Sediment Geol 58:47–61

    Google Scholar 

  • Rees AI (1983) Experiments on the production of a transverse grain alignment in a sheared dispersion. Sedimentology 30:437–448

    Google Scholar 

  • Rosenbaum JG, Waitt RB (1981) Summary of eyewitness accounts of the May 18 eruption. In: Lipman PW, Mullineaux DR (eds) The 1980 eruptions of Mount St. Helens, Washington, US Geol Surv Prof Pap 1250:53–67

  • Rosi M (1990) Comment on “May 18, 1980, Mt. St. Helens deposits in South Coldwater Creek, Washington” by RV Fisher, HX Glicken, RP Hoblitt (1987). Bull Volcanol 52:66–68

    Google Scholar 

  • Sallenger AH Jr (1979) Inverse grading and hydraulic equivalence in grain-flow deposits. J Sediment Petrol 49:553–562

    Google Scholar 

  • Schmincke H-U, Fisher RV, Waters AC (1973) Antidune and chute and pool structures in the base surge deposits of the Laacher See area, Germany. Sedimentology 20:553–574

    Google Scholar 

  • Sigurdsson H, Carey SN, Fisher RV (1987) The 1982 eruption of El Chichon volcano, Mexico (3): physical properties of pyroclastic surges. Bull Volcanol 49:467–488

    Google Scholar 

  • Simpson JE (1987) Gravity currents: in the environment and the laboratory. Ellis Horwood Ltd, Chichester, 244 pp

    Google Scholar 

  • Slingerland RL (1977) The effects of entrainment on the hydraulic equivalence relationships of light and heavy minerals in sands. J Sediment Petrol 47:753–770

    Google Scholar 

  • Sohn YK, Chough SK (1989) Depositional processes of the Suwolbong tuff ring, Cheju Island (Korea). Sedimentology 36:837–855

    Google Scholar 

  • Sparks RSJ (1976) Grain size variations in ignimbrites and implications for the transport of pyroclastic flows. Sedimentology 23:147–188

    Google Scholar 

  • Sparks RSJ, Moore JG, Rice CJ (1986) The initial giant umbrella cloud of the May 18, 1980, explosive eruption of Mount St. Helens. J Volcanol Geotherm Res 28:257–274

    Google Scholar 

  • Steidtmann JR (1982) Size-density sorting of sand-size spheres during deposition from bedload transport and implications concerning hydraulic equivalence. Sedimentology 29:877–883

    Google Scholar 

  • Todd SP (1989) Stream-driven, high-density gravelly traction carpets: possible deposits in the Trabeg Conglomerate Formation, SW Ireland and some theoretical considerations of their origin. Sedimentology 36:513–530

    Google Scholar 

  • Valentine GA (1987) Stratified flow in pyroclastic surges. Bull Volcanol 49:616–630

    Google Scholar 

  • Waitt RB (1981) Devastating pyroclastic density flow and attendant airfall of May 18 — stratigraphy and sedimentology of deposits. In: Lipman PW, Mullineaux DR (eds) The 1980 eruptions of Mount St. Helens, Washington, US Geol Surv Prof Pap 1250:439–458

  • Waitt RB (1984) Comment on ‘Mount St. Helens 1980 and Mount Pelee 1902 — flow or surge?’ Geology 12:693

    Google Scholar 

  • Waitt RB, Dzurisin D (1981) Proximal air-fall deposits from the May 18 eruption — stratigraphy and field sedimentology. In: Lipman PW, Mullineaux DR (eds) The 1980 eruptions of Mount St. Helens, Washington, US Geol Surv Prof Pap 1250:601–616

  • Walker GPL (1985) Origin of coarse lithic breccias near ignimbrite source vents. J Volcanol Geotherm Res 25:157–171

    Google Scholar 

  • Walker GPL, McBroome LA (1983) Mount St. Helens 1980 and Mount Pelee 1902 — flow or surge? Geology 11:571–574

    Google Scholar 

  • Walker GPL, Morgan LA (1984) Reply on ‘Mount St. Helens 1980 and Mount Pelee 1902 — flow or surge?’ Geology 12:693–695

    Google Scholar 

  • Walker GPL, Self S, Froggatt PC (1981) The ground layer of the Taupo ignimbrite: a striking example of sedimentation from a pyroclastic flow. J Volcanol Geotherm Res 10:1–11

    Google Scholar 

  • Wilson CJN (1980) The role of fluidization in the emplacement of pyroclastic flows: an experimental approach. J Volcanol Geotherm Res 8:231–249

    Google Scholar 

  • Wilson CJN (1985) The Taupo eruption, New Zealand. II. The Taupo ignimbrite. Philos Trans R Soc London A 314:299–310

    Google Scholar 

Download references

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Druitt, T.H. Emplacement of the 18 May 1980 lateral blast deposit ENE of Mount St. Helens, Washington. Bull Volcanol 54, 554–572 (1992). https://doi.org/10.1007/BF00569940

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