Skip to main content
SpringerLink
Log in

Crystallization of microlites during magma ascent: the fluid mechanics of 1980–1986 eruptions at Mount St Helens

  • Original Paper
  • Published:
Bulletin of Volcanology Aims and scope Submit manuscript

Abstract

Eruptions of Mount St Helens (Washington, USA) decreased in intensity and explosivity after the main May 18, 1980 eruption. As the post-May 18 eruptions progressed, albitic plagioclase microlites began to appear in the matrix glass, although the bulk composition of erupted products, the phenocryst compositions and magmatic temperatures remained fairly constant. Equilibrium experiments on a Mount St Helens white pumice show that at 160 MPa water pressure and 900°C, conditions deduced for the 8 km deep magma storage zone, the stable plagioclase is An47. The microlites in the natural samples, which are more albitic, had to grow at lower water pressures during ascent. Isothermal decompression experiments reported here demonstrate that a decrease in water pressure from 160 to 2 MPa over four to eight days is capable of producing the albitic groundmass plagioclase and evolved melt compositions observed in post-May 18 1980 dacites. Because groundmass crystallization occurs over a period of days during and after decreases in pressure, microlite crystallization in the Mount St Helens dacites must have occurred during the ascent of each magma batch from a deep reservoir rather than continuously in a shallow holding chamber. This is consistent with data on the kinetics of amphibole breakdown, which require that a significant portion of magma vented in each eruption ascended from a depth of at least 6.5 km (∼160 MPa water pressure) in a matter of days. The size and shape of the microlite population have not been studied because of the small size of the experimental samples; it is possible that the texture continues to mature long after chemical equilibrium is approached. As the temperature, composition, crystal content and water content of magma in the deep reservoir remained approximately constant from May 1980 to at least March 1982, the spectacular decrease in eruption intensity during this period cannot be attributed to changes in viscosity or density of the magma. Simple fluld mechanical considerations indicate, however, that the observed changes in mass flux of magma can be modelled by a five-fold decrease in conduit radius from 35 to 7 m, produced perhaps by plating of magma along the conduit walls. The decreased ascent rates which accompanied the decrease in conduit radius can explain the change from closed-system to open-system degassing and the shift from explosive to effusive eruptions during 1980.

This is a preview of subscription content, log in via an institution to check access.

Access this article

Log in via an institution

Subscribe and save

Springer+ Basic
$34.99 /Month
  • Get 10 units per month
  • Download Article/Chapter or eBook
  • 1 Unit = 1 Article or 1 Chapter
  • Cancel anytime
Subscribe now

Buy Now

Price excludes VAT (USA)
Tax calculation will be finalised during checkout.

Instant access to the full article PDF.

Institutional subscriptions

Similar content being viewed by others

References

  • Andersen DJ, Lindsley DH (1988) Internally consistent solution models for Fe−Mg−Mn−Ti oxides. Am Mineral 73:714–726

    Google Scholar 

  • Barker SE, Malone SD (1991) Magmatic system geometry at Mount St. Helens modelled from the stress field associated with post-eruptive earthquakes. J Geophys Res 96:11883–11894

    Google Scholar 

  • Barton PJ (1986) The relationship between seismic velocity and density in the continental crust — a useful constraint?. Geophys J Roy Astron Soc 87:195–208

    Google Scholar 

  • Carey S, Sigurdsson H (1985) The May 18, 1980 eruption of Mount St. Helens, 2: modeling of dynamics of the Plinian phase. J Geophys Res 90:2948–2958

    Google Scholar 

  • Casadevall TJ, Johnston DA, Harris DM, Rose WI Jr, Malinconico LL, Stoiber RE, Bornhorst TJ, Williams SN, Woodruff L, Thompson JM (1981) SO2 emission rates at Mount St. Helens from March 29 through December, 1980. In: Lipman PW, Mullineaux DR (eds) The 1980 Eruptions of Mount St. Helens. Washington. US Geol Surv Prof Pap 1250: 193–200

  • Cashman KV (1988) Crystallization of Mount St. Helens 1980–1986 dacite: a quantitative textural approach. Bull Volcanol 50:194–209

    Google Scholar 

  • Cashman KV (1992) Groundmass crystallization of Mount St. Helens dacite 1980–1986: a tool for interpreting shallow magmatic processes. Contrib Mineral Petrol 109:431–449

    Google Scholar 

  • Chadwick WW Jr, Archuleta RJ, Swanson DA (1988) The mechanics of deformation precursory to dome-building extrusions at Mount St. Helens 1981–1982. J Geophys Res 93:4351–4366

    Google Scholar 

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

    Google Scholar 

  • Deer WA, Howie RA, Zussman J (1963) Rock-Forming Minerals. 5 vols. Wiley, New York

    Google Scholar 

  • Endo ET, Dzurisin D, Swanson DA (1990) Geophysical and observational constraints for shallow ascent rates of dacitic magma at Mount St. Helens. In: Ryan MP (ed) Magma Transport and Storage. Wiley, Chichester, pp 317–334

    Google Scholar 

  • Eichelberger JC, Carrigan RC, Westrich HR, Price RH (1986) Non-explosive silicic volcanism. Nature 323:598–602

    Google Scholar 

  • Evarts RC, Ashley RP, Smith JG (1987) Geology of the Mount St. Helens area; record of discontinuous volcanic and plutonic activity in the Cascade arc of southern Washington. J Geophys Res 92:10155–10169

    Google Scholar 

  • Fink JH, Manley CR (1987) Origin of pumiceous and glassy textures in rhyolite flows and domes. Geol Soc Am Spec Pap 212:77–88

    Google Scholar 

  • Friedman JD, Olhoeft GR, Johnson GR, Frank D (1981) Heat content and thermal energy of the June dacite dome in relation to total energy yield, May–October 1980. In: Lipman PW, Mullineaux DR (ed) The 1980 Eruptions of Mount St. Helens, Washington, US Geol Surv Prof Pap 1250:557–567

  • Gerlach TM, Casadevall TJ (1986) Fumarole emissions at Mount St. Helens volcano, June 1980 to October 1981: degassing of a magma-hydrothermal system. J Volcanol Geotherm Res 28:141–160

    Google Scholar 

  • Hervig RL, Dunbar N, Westrich HR, Kyle PR (1989) Pre-eruptive water content of rhyolitic magmas as determined by ion microprobe analyses of melt inclusions in phenocrys. J Volcanol Geotherm Res 36:293–302

    Google Scholar 

  • Hurwitz S, Navon O (1994) Bubble nucleation in rhyolitic melts: experiments at high pressure, temperature and water content. Earth Planet Sci Lett 122:267–280

    Google Scholar 

  • Jachens RC, Spydell DR, Pitts GS, Dzurisin D, Roberts CW (1981) Temporal gravity variations at Mount St Helens, March–May 1980. In: Lipman PW, Mullineaux DR (eds) The 1980 Eruptions of Mount St Helens, Washington, US Geol Surv Prof Pap 1250:175–181

  • Jaupart C, Allegre CJ (1991) Gas content, eruption rate and instabilities of eruption regime in silicic volcanoes. Earth Planet Sci Lett 102:413–429

    Google Scholar 

  • Kirkpatrick RJ (1981) Kinetics of crystallization in igneous rocks. In: Lasaga AC, Kirkpatrick RJ (eds) Kinetics of Geochemical Processes. Mineral Soc Am Rev Mineral 8:321–398

  • Klug C, Cashman KV (1994) Vesiculation of May 18, 1980, Mount St. Helens magma. Geology 22:468–472

    Google Scholar 

  • Kuntz MA, Rowley PD, MacLeod NS, Reynolds RL, McBroome LA, Kaplan AM, Lidke DJ (1981) Petrography and particlesize distribution of pyroclastic-flow, ash-cloud, and surge deposits. In: Lipman PW, Mullineaux DR (eds) The 1980 Eruptions of Mount St Helens, Washington. US Geol Surv Prof Pap 1250:525–539

  • Lange RA, Carmichael ISE (1987) Densities of Na2O−K2O−CaO−MgO−FeO−Fe2O3−Al2O3−TiO2−SiO2 liquids: new measurements and derived partial molar properties. Geochim Cosmochim Acta 51:2931–2946

    Google Scholar 

  • Lees JM, Crosson RS (1989) Tomographic inversion for threedimensional velocity structure at Mount St. Helens using earthquake data. J Geophys Res 94:5716–5728

    Google Scholar 

  • Lipman PW, Norton DR, Taggart JE, Brandt EL, Engleman EE (1981) Compositional variations in 1980 magmatic deposits. In: Lipman PW, Mullineaux DR (eds) The 1980 Eruptions of Mount St Helens, Washington. US Geol Surv Prof Pap 1250:631–640

  • Lofgren GE (1976) Nucleation and growth of feldspar in dynamic crystallization experiments. Geol Soc Am Abstr 7:982

    Google Scholar 

  • Lofgren GE (1980) Experimental studies of the dynamic crystallization of silicate melts. In: Hargraves RB (ed) Physics of Magmatic Processes. Princeton University Press, pp 487–551

  • Lofgren GE, Donaldson CH, Williams RJ, Mullins O Jr, Usselman TM (1974) Experimentally reproduced textures and mineral chemistry of Apollo 15 quartz normative basalts. Proc 5th Lunar Sci Conf: 549–567

  • Marsh BD (1981) On the crystallinity, probability of occurrence, and rheology of lava and magma. Contrib Mineral Petrol 78:85–98

    Google Scholar 

  • Melson WG (1983) Monitoring the 1980–1982 eruptions of Mount St. Helens: compositions and abundances of glass. Science 221:1387–1391

    Google Scholar 

  • Melson WG, Hopson CA (1981) Preeruption temperatues and oxygen fugacities in the 1980 eruptive sequence. In: Lipman PW, Mullineaux DR (eds) The 1980 Eruptios of Mount St Helens, Washington. US Geol Surv Prof Pap 1250:641–648

  • Merzbacher C, Eggler DH (1984) A magmatic geohygrometer; application to Mount St. Helens and other dacitic magmas. Geology 12:587–590

    Google Scholar 

  • Metzner AB (1985) Rheology of suspensions in polymeric liquids. J Rheol 29:739–775

    Google Scholar 

  • Miller CD (1978) Holocene pyroclastic-flow deposits from Shastina and Black Butte west of Mount Shasta, California. US Geol Surv J Res 6:611–624

    Google Scholar 

  • Newhall CG, Melson WG (1983) Explosive activity associated with the growth of volcanic domes. J Volcanol Geotherm Res 17:111–131

    Google Scholar 

  • Newman S, Epstein S, Stolper E (1988) Water, carbon dioxide, and hydrogen isotopes in glasses from the ca. 1340 A.D. eruption of the Mono Craters, Ca: constraints on degassing phenomena and initial volatile content. J Volcanol Geotherm Res 35:75–96

    Google Scholar 

  • Nielsen CH, Sigurdsson H (1981) Quantitative methods of electron microprobe analysis of sodium in natural and synthetic glasses. Am Mineral 66:547–552

    Google Scholar 

  • Robie RA, Hemingway BA, Fisher JR (1978) Thermodynamic properties of minerals and related substances at 298.15 K and 1 bar pressure and at higher temperatures. US Geol Surv Bull 452:456 pp

    Google Scholar 

  • Rutherford MJ, Devine JD (1988) The May 18, 1980, eruption of Mount St Helens; 3. Stability and chemistry of amphibole in the magma chamber. J Geophys Res 93:11949–11959

    Google Scholar 

  • Rutherford MJ, Hill PM (1993) Magma ascent rates from amphibole breakdown: experiments and the 1980–1986 Mount St. Helens eruptions. J Geophys Res 98:19667–19685

    Google Scholar 

  • Rutherford MJ, Sigurdsson H, Carey S, Davis A (1985) The May 18, 1980, eruption of Mount St. Helens: 1. Melt composition and experimental phase equilibria. J Geophys Res 90:2929–2947

    Google Scholar 

  • Sarna-Wojcicki AM, Shipley S, Waitt RB, Durisin D, Wood SH (1981) Areal distribution, thickness, mass, volume, and grain size of air-fall ash from the six major eruptions of 1980. In: Lipman PW, Mullineaux DR (eds) The 1980 Eruptions of Mount St Helens, Washington, US Geol Surv Prof Pap 1250:577–600

  • Scandone R, Malone SD (1985) Magma supply, magma discharge and readjustment of the feeding systems of Mount St. Helens durng 1980. J Volcanol Geotherm Res 23:239–262

    Google Scholar 

  • Scheidegger KF, Federman AN, Tallman AM (1982) Compositional heterogeneity of tephras from the 1980 eruptions of Mount St. Helens. J Geophys Res 87:10861–10881

    Google Scholar 

  • Shaw HR (1965) Comments on viscosity, crystal settling, and convection in granitic magmas. Am J Sci 263:120–152

    Google Scholar 

  • Shaw HR (1972) Viscosities of magmatic silicate liquids; an empirical method of prediction. Am J Sci 272:870–893

    Google Scholar 

  • Smith DR, Leeman WP (1987) Petrogenesis of Mount St Helens dacitic magmas. J Geophys Res 92:10313–10334

    Google Scholar 

  • Stanley WD (1984) Tectonic study of Cascade Range and Columbia Plateau in Washington State based upon magnetotelluric soundings. J Geophys Res 89:4447–4460

    Google Scholar 

  • Stormer JC (1983) The effects of recalculation on estimates of temperature and oxygen fugacity from analyses of multi-component iron-titanium oxides. Am Mineral 68:586–594

    Google Scholar 

  • Swanson SE (1977) Relation of nucleation and crystal growth rate to the development of granitic textures. Am Mineral 62:966–978

    Google Scholar 

  • Swanson DA, Holcomb RT (1990) Regularities in growth of the Mount St Helens dacite dome 1980–1986. “In: Fink J (ed) The Mechanics of Lava Flow Emplacement and Dome Growth. IAVCEI Proc Volcanol 2:1–18

  • Swanson DA, Dzurisin D, Holcomb RT, Iwatsubo EY, Chadwick WW Jr, Casadevell TJ, Ewert JW, Helker CC (1987) Growth of the lava dome at Mount St. Helens, Washington (USA). Geol Soc Am Spec Pap 212:1–16

    Google Scholar 

  • Swanson SE, Naney MT, Westrich HR, Eichelberger JC (1989) Crystallization history of Obsidian Dome, Inyo Domes, California. Bull Volcanol 51:161–176

    Google Scholar 

  • Taylor BE, Eichelberger JC, Westrich HR (1983) Hydrogen isotopic evidence of rhyolitic magma degassing during shallow intrustion and eruption. Nature 306:541–545

    Google Scholar 

  • Weaver CS, Malone SD (1976) Mount St. Helens seismic events: volcanic earthquakes or glacial noises? Geophys Res Lett 3:197–200

    Google Scholar 

  • Westrich HR, Stockman HW, Eichelberger JC (1988) Degassing of rhyolitic magma during ascent and emplacement. J Geophys Res 93:6503–6511

    Google Scholar 

  • White FM (1986) Fluid Mechanics. 2nd edn. McGraw-Hill, New York, 732 pp

    Google Scholar 

  • Wildemuth CR, Williams MC (1984) Viscosity of suspensions modeled with a shear-dependent maximum packing fraction. Rheol Acta 23:627–635

    Google Scholar 

  • Williams DL, Abrams G, Finn C, Dzurisin D, Johnson DJ, Denlinger R (1987) Evidence from gravity data for an intrusive complex beneath Mount St Helens. J Geophys Res 92:10207–10222

    Google Scholar 

  • Wilson L, Sparks RSJ, Walker GPL (1980) Explosive volcanic eruptions IV. The control of magma properties and conduit geometry on eruption column on eruption column behaviour. Geophys J Roy Astron Soc 63:117–148

    Google Scholar 

Download references

Author information

Authors and Affiliations

  1. Department of Geological Sciences, Brown University, 02912, Providence, RI, USA

    C.-H. Geschwind & M. J. Rutherford

Authors
  1. C.-H. Geschwind
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. M. J. Rutherford
    View author publications

    You can also search for this author in PubMed Google Scholar

Rights and permissions

Reprints and permissions

About this article

Cite this article

Geschwind, CH., Rutherford, M.J. Crystallization of microlites during magma ascent: the fluid mechanics of 1980–1986 eruptions at Mount St Helens. Bull Volcanol 57, 356–370 (1995). https://doi.org/10.1007/BF00301293

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI: https://doi.org/10.1007/BF00301293

Key words

Search

Navigation