HR: 15:10h
AN: V13F-07 INVITED     [Abstracts]
TI: Gravitational Collapse of Lava Domes Triggered by Volcanic Fluids
AU: * Elsworth, D
EM: elsworth@psu.edu
AF: Earth and Mineral Sciences, Penn State University, University Park, PA 16802 United States
AU: Voight, B
V13F-07 AF: Earth and Mineral Sciences, Penn State University, University Park, PA 16802 United States
AU: Taron, J
V13F-07 AF: Earth and Mineral Sciences, Penn State University, University Park, PA 16802 United States
AU: Thompson, G
V13F-07 AF: British Geological Survey, Keyworth, Nottingham, NG12 5GG United Kingdom
AU: Vinciguerra, S
V13F-07 AF: Osservatorio Vesuviano, Istituto Nazionale di Geofisica e Vulcanologia, Naples, ITA 80124 Italy
AU: Simmons, J
V13F-07 AF: ExxonMobil Exploration Company, 233 Benmar, Houston, TX 77060 United States
AB: Excess fluid pressures exert important controls on the stability of lava domes and of the flanks of volcanoes. Migrating overpressures reduce the shear strength of the edifice and may control the timing, morphology, and energetics of failure. Excess pressures may be developed both directly from magma degassing, and indirectly from the interaction of magma with infiltrating rainwater or groundwater. Interior gases influence the strength of the volcanic pile, and hence its stability, in at least two ways. In the fractured and solidified outer carapace high gas contents reduce effective stresses and concomitantly lower shear strength. In the dome interior, magmas which avoid the off-gassing of volatiles exhibit a low and primarily cohesive strength. Signatures of these various processes are evident in the extensive record of collapses which chart the episodic growth and destruction of the lava dome at Soufriere Hills volcano, Montserrat. Mechanisms include (1) interior pressurization by magma degassing, (2) the interaction of rainwater with the hot dome rind, and (3) the segregation of magmas extruded into the dome resulting in a relatively weak and potentially gas overpressured core. The influence of gas overpressures applied interior to a brittle carapace is typified by the response to episodes of cyclic inflation, where collapse may be delayed and may be triggered at inferred pressures below the peak reached in the prior cycle. Similar influences on timing, and in collapse style are present for rainfall-triggered events where deluges beyond a given intensity and duration are required to promote failure, and the style of collapse is influenced by the antecedent conditions of gas pressurization within the lava dome. In all instances, interior gas overpressures or the presence of a segregated plastic core are both viable mechanisms to promote a switch between shallow instability of the dome carapace to deep transaction of the dome core. Such switching to a more hazardous and mobile failure mode may occur absent the usual seismic, geodetic, or chemical signatures which herald a collapse event, and poses special challenges in monitoring for hazard assessment.
DE: 8414 Eruption mechanisms and flow emplacement
DE: 8488 Volcanic hazards and risks
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005