Petrologic constraints on the decompression history of magma prior to Vulcanian explosions at the Soufrière Hills volcano, Montserrat

Amanda Clarke, S. Stephens, R. Teasdale, R. S J Sparks, K. Diller

Research output: Contribution to journalArticle

76 Citations (Scopus)

Abstract

A series of 88 Vulcanian explosions occurred at the Soufrière Hills volcano, Montserrat, between August and October, 1997. Conduit conditions conducive to creating these and other Vulcanian explosions were explored via analysis of eruptive products and one-dimensional numerical modeling of magma ascent through a cylindrical conduit. The number densities and textures of plagioclase microlites were documented for twenty-three samples from the events. The natural samples all show very high number densities of microlites, and > 50% by number of microlites have areas < 20 μm2. Pre-explosion conduit conditions and decompression history have been inferred from these data by comparison with experimental decompressions of similar groundmass compositions. Our comparisons suggest quench pressures < 30 MPa (origin depths < 2 km) and multiple rapid decompressions of > 13.75 MPa each during ascent from chamber to surface. Values are consistent with field studies of the same events and statistical analysis of explosion time-series data. The microlite volume number density trend with depth reveals an apparent transition from growth-dominated crystallization to nucleation-dominated crystallization at pressures of ∼ 7 MPa and lower. A concurrent sharp increase in bulk density marks the onset of significant open-system degassing, apparently due to a large increase in system permeability above ∼ 70% vesicularity. This open-system degassing results in a dense plug which eventually seals the conduit and forms conditions favorable to Vulcanian explosions. The corresponding inferred depth of overpressure at 250-700 m, near the base of the dense plug, is consistent with depth to center of pressure estimated from deformation measurements. Here we also illustrate that one-dimensional models representing ascent of a degassing, crystal-rich magma are broadly consistent with conduit profiles constructed via our petrologic analysis. The comparison between models and petrologic data suggests that the dense conduit plug forms as a result of high overpressure and open-system degassing through conduit walls.

Original languageEnglish (US)
Pages (from-to)261-274
Number of pages14
JournalJournal of Volcanology and Geothermal Research
Volume161
Issue number4
DOIs
StatePublished - Apr 1 2007

Fingerprint

Volcanoes
degassing
Degassing
pressure reduction
decompression
volcanoes
magma
Explosions
explosions
explosion
ascent
Open systems
volcano
plugs
histories
overpressure
history
Crystallization
density (number/volume)
crystallization

Keywords

  • conduit dynamics
  • conduit modelling
  • explosive eruptions
  • quench pressure
  • Vulcanian

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics

Cite this

Petrologic constraints on the decompression history of magma prior to Vulcanian explosions at the Soufrière Hills volcano, Montserrat. / Clarke, Amanda; Stephens, S.; Teasdale, R.; Sparks, R. S J; Diller, K.

In: Journal of Volcanology and Geothermal Research, Vol. 161, No. 4, 01.04.2007, p. 261-274.

Research output: Contribution to journalArticle

@article{d36aef8c8f8c4df192bb39245096c355,
title = "Petrologic constraints on the decompression history of magma prior to Vulcanian explosions at the Soufri{\`e}re Hills volcano, Montserrat",
abstract = "A series of 88 Vulcanian explosions occurred at the Soufri{\`e}re Hills volcano, Montserrat, between August and October, 1997. Conduit conditions conducive to creating these and other Vulcanian explosions were explored via analysis of eruptive products and one-dimensional numerical modeling of magma ascent through a cylindrical conduit. The number densities and textures of plagioclase microlites were documented for twenty-three samples from the events. The natural samples all show very high number densities of microlites, and > 50{\%} by number of microlites have areas < 20 μm2. Pre-explosion conduit conditions and decompression history have been inferred from these data by comparison with experimental decompressions of similar groundmass compositions. Our comparisons suggest quench pressures < 30 MPa (origin depths < 2 km) and multiple rapid decompressions of > 13.75 MPa each during ascent from chamber to surface. Values are consistent with field studies of the same events and statistical analysis of explosion time-series data. The microlite volume number density trend with depth reveals an apparent transition from growth-dominated crystallization to nucleation-dominated crystallization at pressures of ∼ 7 MPa and lower. A concurrent sharp increase in bulk density marks the onset of significant open-system degassing, apparently due to a large increase in system permeability above ∼ 70{\%} vesicularity. This open-system degassing results in a dense plug which eventually seals the conduit and forms conditions favorable to Vulcanian explosions. The corresponding inferred depth of overpressure at 250-700 m, near the base of the dense plug, is consistent with depth to center of pressure estimated from deformation measurements. Here we also illustrate that one-dimensional models representing ascent of a degassing, crystal-rich magma are broadly consistent with conduit profiles constructed via our petrologic analysis. The comparison between models and petrologic data suggests that the dense conduit plug forms as a result of high overpressure and open-system degassing through conduit walls.",
keywords = "conduit dynamics, conduit modelling, explosive eruptions, quench pressure, Vulcanian",
author = "Amanda Clarke and S. Stephens and R. Teasdale and Sparks, {R. S J} and K. Diller",
year = "2007",
month = "4",
day = "1",
doi = "10.1016/j.jvolgeores.2006.11.007",
language = "English (US)",
volume = "161",
pages = "261--274",
journal = "Journal of Volcanology and Geothermal Research",
issn = "0377-0273",
publisher = "Elsevier",
number = "4",

}

TY - JOUR

T1 - Petrologic constraints on the decompression history of magma prior to Vulcanian explosions at the Soufrière Hills volcano, Montserrat

AU - Clarke, Amanda

AU - Stephens, S.

AU - Teasdale, R.

AU - Sparks, R. S J

AU - Diller, K.

PY - 2007/4/1

Y1 - 2007/4/1

N2 - A series of 88 Vulcanian explosions occurred at the Soufrière Hills volcano, Montserrat, between August and October, 1997. Conduit conditions conducive to creating these and other Vulcanian explosions were explored via analysis of eruptive products and one-dimensional numerical modeling of magma ascent through a cylindrical conduit. The number densities and textures of plagioclase microlites were documented for twenty-three samples from the events. The natural samples all show very high number densities of microlites, and > 50% by number of microlites have areas < 20 μm2. Pre-explosion conduit conditions and decompression history have been inferred from these data by comparison with experimental decompressions of similar groundmass compositions. Our comparisons suggest quench pressures < 30 MPa (origin depths < 2 km) and multiple rapid decompressions of > 13.75 MPa each during ascent from chamber to surface. Values are consistent with field studies of the same events and statistical analysis of explosion time-series data. The microlite volume number density trend with depth reveals an apparent transition from growth-dominated crystallization to nucleation-dominated crystallization at pressures of ∼ 7 MPa and lower. A concurrent sharp increase in bulk density marks the onset of significant open-system degassing, apparently due to a large increase in system permeability above ∼ 70% vesicularity. This open-system degassing results in a dense plug which eventually seals the conduit and forms conditions favorable to Vulcanian explosions. The corresponding inferred depth of overpressure at 250-700 m, near the base of the dense plug, is consistent with depth to center of pressure estimated from deformation measurements. Here we also illustrate that one-dimensional models representing ascent of a degassing, crystal-rich magma are broadly consistent with conduit profiles constructed via our petrologic analysis. The comparison between models and petrologic data suggests that the dense conduit plug forms as a result of high overpressure and open-system degassing through conduit walls.

AB - A series of 88 Vulcanian explosions occurred at the Soufrière Hills volcano, Montserrat, between August and October, 1997. Conduit conditions conducive to creating these and other Vulcanian explosions were explored via analysis of eruptive products and one-dimensional numerical modeling of magma ascent through a cylindrical conduit. The number densities and textures of plagioclase microlites were documented for twenty-three samples from the events. The natural samples all show very high number densities of microlites, and > 50% by number of microlites have areas < 20 μm2. Pre-explosion conduit conditions and decompression history have been inferred from these data by comparison with experimental decompressions of similar groundmass compositions. Our comparisons suggest quench pressures < 30 MPa (origin depths < 2 km) and multiple rapid decompressions of > 13.75 MPa each during ascent from chamber to surface. Values are consistent with field studies of the same events and statistical analysis of explosion time-series data. The microlite volume number density trend with depth reveals an apparent transition from growth-dominated crystallization to nucleation-dominated crystallization at pressures of ∼ 7 MPa and lower. A concurrent sharp increase in bulk density marks the onset of significant open-system degassing, apparently due to a large increase in system permeability above ∼ 70% vesicularity. This open-system degassing results in a dense plug which eventually seals the conduit and forms conditions favorable to Vulcanian explosions. The corresponding inferred depth of overpressure at 250-700 m, near the base of the dense plug, is consistent with depth to center of pressure estimated from deformation measurements. Here we also illustrate that one-dimensional models representing ascent of a degassing, crystal-rich magma are broadly consistent with conduit profiles constructed via our petrologic analysis. The comparison between models and petrologic data suggests that the dense conduit plug forms as a result of high overpressure and open-system degassing through conduit walls.

KW - conduit dynamics

KW - conduit modelling

KW - explosive eruptions

KW - quench pressure

KW - Vulcanian

UR - http://www.scopus.com/inward/record.url?scp=33847618392&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=33847618392&partnerID=8YFLogxK

U2 - 10.1016/j.jvolgeores.2006.11.007

DO - 10.1016/j.jvolgeores.2006.11.007

M3 - Article

AN - SCOPUS:33847618392

VL - 161

SP - 261

EP - 274

JO - Journal of Volcanology and Geothermal Research

JF - Journal of Volcanology and Geothermal Research

SN - 0377-0273

IS - 4

ER -