Bulletin of Volcanology

, Volume 50, Issue 3, pp 194–209 | Cite as

Crystallization of Mount St. Helens 1980–1986 dacite: A quantitative textural approach

  • K. V. Cashman


Quantitative measurements of crystal size distributions (CSDs) have been used to obtain kinetic information on crystallization of industrial compounds (Randolph and Larson 1971) and more recently on Hawaiian basalts (Cashman and Marsh 1988). The technique is based on a population balance resulting in a differential equation relating the population densityn of crystals to crystal sizeL, i.e., at steady staten =no exp(−L/itGτ), whereno is nucleation density,G is the average crystal growth rate,τ is the average growth time, and the nucleation rateJ =noG. CSD (Inn vsL) plots of plagioclase phenocrysts in 12 samples of Mount St. Helens “blast” dacite and 14 samples of dacite from the 1980–1986 Mount St. Helens dome are similar and average = 9.6 (± 1.1) × 10−3 cm andno = 1−2 × 106 cm−4. Reproducibility of the measurements was tested by measuring CSDs of 12 sections cut from a single sample in three mutually perpendicular directions; precision of the size distributions is good in terms of relative, but not necessarily absolute values (± 10%). Growth and nucleation rates for plagioclase have been calculated from these measurements using time brackets ofτ = 30–150 years; growth ratesG are 3−10 × 10−12cm/s, and nucleation ratesJ are 5−21 × 10−6/cm3 s.G andJ for Fe-Ti oxides calculated from CSD data areG = 2−13 ± 10−13 cm/sec andJ = 7−33 × 10−5/cm3 s, respectively. The higher nucleation rate and lower growth rate of oxides resulted in a smaller average crystal size than for plagioclase. Sizes of plagioclase microlites (<0.01 mm) in the blast dacite groundmass have been measured from backscatter SEM photographs. Nucleation of these microlites was probably triggered by intrusion of material into the cone of Mount St. Helens in spring 1980. This residence time of 52 days gives minimum crystallization estimates ofG = 1−3 × 10−11 cm/s andJ = 9−16 × 1O3/cm3 s. The skeletal form of the microlites provides evidence for nucleation and growth at high values of undercooling (ΔT) relative to the phenocrysts. A comparison of nucleation and growth rates for the two crystal populations (phenocrysts vs microlites) suggests that while growth rate seems to be only slightly affected by changes inΔT, nucleation rate is a very strong function of undercooling. A comparison of plagioclase nucleation and growth rates measured in the Mount St. Helens dacite and in basalt from Makaopuhi lava lake in Hawaii suggests that plagioclase nucleation rates are not as dependent on composition. Groundmass textures suggest that plagioclase microphenocrysts crystallized at depth rather than in the conduit, in the dome, or after extrusion onto the surface. Most of this crystallization appears to be in the form of crystal growth (coarsening) of groundmass microphenocrysts at small degrees of undercooling rather than extensive nucleation of new crystals. This continuous crystallization in a shallow magmatic reservoir may provide the “overpressurization” needed to drive the continuing periodic domebuilding extrusions, which have been the pattern of activity at Mount St. Helens since December 1980.


Nucleation Rate Magmatic Reservoir Plagioclase Phenocryst Crystal Size Distribution Average Crystal Size 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Bennett JT, Krishnaswami S, Turekian KK, Melson WG, Hopson CA (1982) The uranium and thorium decay series nuclides in Mt. Helens effusives. Earth Plan Sci Lett 60:61–69Google Scholar
  2. Brandeis G, Jaupart C, Allegre CJ (1984) Nucleation, crystal growth and the thermal regime of cooling magmas. J Geophys Res 89:10161–10177Google Scholar
  3. Brandeis G, Jaupart C (1987) The kinetics of nucleation and crystal growth and scaling laws for magmatic crystallization. Contrib Mineral Petrol 96:24–34Google Scholar
  4. Carey S, Sigurdsson H (1985) The May 18, 1980 eruption of Mount St. Helens 2. Modeling of dynamics of the Plinian phase. Jl Geophys Res 90:2948–2958Google Scholar
  5. Cashman KV (1986) Crystal size distributions in igneous and metamorphic rocks. Unpubl PhD thesis, Johns Hopkins UniversityGoogle Scholar
  6. Cashman KV, Taggart JE (1983) Petrologic monitoring of 1981 and 1982 eruptive products from Mount St. Helens. Science 221:1385–1387Google Scholar
  7. Cashman KV, Ferry JM (1988) Crystal size distribution (CSD) in rocks and the kinetics and dynamics of crystallization III. Metamorphic crystallization. Contrib Mineral Petrol (Accepted)Google Scholar
  8. Cashman KV, Marsh BD (1988) Crystal size distribution (CSD) in rocks and the kinetics and dynamics of crystallization II. Makaopuhi lava lake. Contrib Mineral Petrol (Accepted)Google Scholar
  9. Chadwick WW, Swanson DA, Iwatsubo EY, Heliker CC, Leighley TA (1983) Deformation monitoring at Mount St. Helens in 1981 and 1982. Science 221:1378–1380Google Scholar
  10. Christiansen RL, Peterson DW (1981) Chronology of the 1980 eruptive activity. USGS Prof Paper 1250:17–30Google Scholar
  11. Criswell CW (1987) Chronology and pyroclastic stratigraphy of the May 18, 1980 eruption of Mount St. Helens, Washington. Jl Geophys Res 92:10237–10266Google Scholar
  12. Dowty E (1980) Crystal growth and nucleation theory and the numerical simulation of igneous crystallization. In: Hargraves RB (ed) The Physics of Magmatic Processes, Princeton pp 419–485Google Scholar
  13. Eichelberger JC, Hays DB (1982) Magmatic model for the Mount St. Helens blast of May 18, 1980. Jl Geophys Res 87:7727–7738Google Scholar
  14. Endo ET, Dzurisin D, Murray T, Syverson K (1987) The rate of magma ascent during dome building at Mount St. Helens (abstr) Hawaii symposium on How Volcanoes Work, Hilo, Hawaii p 33Google Scholar
  15. Friel JJ (1987) Computer-aided imaging of basaltic glass. Microbeam Analysis - 1987:325–326Google Scholar
  16. Friel JJ, Kacandes GH, Grandstaff DE, Ulmer GC (1986) Image analysis of an Icelandic basalt. Geol Soc Amer Abstracts with Programs 18:606Google Scholar
  17. Heliker CC (1984) Inclusions in the 1980–1983 dacite of Mount St. Helens, Washington. MS Thesis, Western Washington University, 185 ppGoogle Scholar
  18. Hoblitt RP, Miller CD, Vallance JW (1981) Origin and stratigraphy of the deposit produced by the May 18 directed blast. USGS Prof Paper 1250:401–419Google Scholar
  19. Kirkpatrick RJ (1977) Nucleation and growth of plagioclase, Makaopuhi and Alae lava lakes, Kilauea Volcano, Hawaii. Geol Soc Amer Bull 88:78–84Google Scholar
  20. Kirkpatrick RJ (1981) Kinetics of crystallization of igneous rocks. In: Lasaga AC, Kirkpatrick RJ (eds) Kinetics of Geochemical Processes, Reviews in Mineralogy vol. 8, pp 321–398Google Scholar
  21. Kuntz MA, Rowley PD, MacLeod NS, Reynolds RL, MacBroome LA, Kaplan AM, Lidke DJ (1981) Petrography and particle-size distribution of pyroclastic-flow ash-cloud, and surge deposits. USGS Prof Paper 1250:525–539Google Scholar
  22. Lipman PW, Morre JG, Swanson DA (1981a) Bulging of the north flank before the May 18 eruption - geodetic data. USGS Prof Paper 1250:143–155Google Scholar
  23. Lipman PW, Norton DR, Taggart JE, Brandt EL, Engleman EE (1981b) Compositional variations in 1980 magmatic deposits. USGS Prof. Paper 1250:631–640Google Scholar
  24. Lofgren GE (1980) Experimental studies on the dynamic crystallization of silicate melts. In: Hargraves RB (ed) The Physics of Magmatic Processes, Princeton, pp 487–551Google Scholar
  25. Marsh BD (1988) Crystal size distribution (CSD) in rocks and the kinetics and dynamics of crystallization I. Theory. Contrib Mineral Petrol (Accepted)Google Scholar
  26. Melson WG (1983) Monitoring the 1980–82 eruptions of Mount St. Helens: Compositions and abundances of glass. Science 221:1387–1391Google Scholar
  27. Moore JG, Albee WC (1981) Topographic and structural changes, March–July 1980 — photogrammetric data. USGS Prof Paper 1250:123–134Google Scholar
  28. Moore JG, Lipman PW, Swanson DA, Alpha TR (1981) Growth of lava domes in the crater, June 1980–January 1981. USGS Prof Paper 1250:541–547Google Scholar
  29. Moore JG, Sisson TW (1981) Deposits and effects of the May 18 pyroclastic surge. USGS Prof Paper 1250:421–438Google Scholar
  30. Naslund HR, Conrad HE, Urquhard J, Turner PA (1986) Computer simulation of apparent grain sizes in thin sections — applications to grain size variation in the Skaergaard Intrusion. (abst) EOS 67:384Google Scholar
  31. Randolph AD, Larson MA (1971) Theory of Particulate Processes. Academic Press, New York, 251 ppGoogle Scholar
  32. 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 90:2929–2947Google Scholar
  33. Saltykov SA (1967) The determination of the size distribution of particles in an opaque material from a measurement of the size distribution of their sections. In: Elias H (ed) Stereology. Proc 2nd Int Cong for Stereology, Springer, Berlin Heidelberg New York p 163Google Scholar
  34. Scandone R, Malone SD (1985) Magma supply, magma discharge and readjustment of the feeding system of Mount St. Helens during 1980. J Volcan Geotherm Res 23:239–262Google Scholar
  35. Shaw HR (1965) Comments on viscosity, crystal settling and convection in granitic magmas. Amer J Sci 263:120–152Google Scholar
  36. Swanson DA, Holcomb RT (1985) Regularities in the growth of Mount St. Helens' dome (abstr). Abstracts with Programs, Geol Soc Amer 17:411Google Scholar
  37. Swanson DA, Dzurisin D, Holcomb RT, Iwatsubo EY, Chadwick WW, Casadevall TJ, Ewert JW, Heliker CC (1987) Growth of the lava dome at Mount St. Helens, Washington (US), 1981–1983. Spec Pap Geol Soc Amer 212:1–16Google Scholar
  38. Underwood EE (1970) Quantitative Stereology. Addison-Wesley Massachusetts, 274 ppGoogle Scholar
  39. Wright TL, Okamura RT (1977) Cooling and crystallization of tholeiitic basalt, 1965 Makaopuhi lava lake, Hawaii. US Geol Surv Prof Paper 1004, 78 ppGoogle Scholar

Copyright information

© Springer-Verlag 1988

Authors and Affiliations

  • K. V. Cashman
    • 1
  1. 1.Department of Geological and Geophysical SciencesPrinceton UniversityPrincetonUSA

Personalised recommendations