HR: 1340h
AN: V53A-1542    [Abstracts]
TI: Integrating Fragmentation Criteria with Dynamic Conduit Models: the Significance of Syn-eruptive Bubble Expansion in Vulcanian Explosions
AU: * Diller, K
EM: kristi.diller@asu.edu
AF: Arizona State University, Dept. of Geological Sciences, Tempe, AZ 85287-1404 United States
AU: Clarke, A
EM: amanda.clarke@asu.edu
AF: Arizona State University, Dept. of Geological Sciences, Tempe, AZ 85287-1404 United States
AU: Voight, B
EM: voight@ems.psu.edu
AF: Pennsylvania State University, Dept. of Geosciences, University Park, PA 16802 United States
AU: Neri, A
EM: neri@pi.ingv.it
AF: Istituto Nazionale di Geofisica e Vulcanologia, Via della Faggiola 32, Pisa, PSA I-56126 Italy
AB: Vulcanian eruptions are short-lived explosions resulting from a sudden decompression of a pressurized, vesiculated magma, which typically fragment and evacuate only a portion of the conduit. However, simple models show that unless some fraction of the total gas pressure in the vesiculated magma is relieved between explosion initiation and arrival of the fragmentation wave, runaway fragmentation and sustained eruption result. Therefore, in order to predict depth of fragmentation and eruptive mass, we explore mechanisms of syn-explosion pressure relief. We do so by combining analytical models of permeable gas loss, bubble growth in response to instantaneous decompression, and experimentally determined fragmentation criterion (Spieler et al., 2004, Earth Planet. Sci. Lett. 226: 139-148) with 1D numerical models of conduit flow. Pressure relief from permeable gas loss is not significant, unless, due to the fragmentation process itself, syn-eruptive system permeability exceeds values measured in natural samples by three orders of magnitude. On the other hand, significant gas pressure can be relieved during the short time scales of Vulcanian eruptions via syn-eruptive bubble growth. After testing several formulations, our preferred model considers bubble growth in an infinite melt (Barclay et al., 1995, Bull. Volc. 57: 422-431) and the influence of bulk viscosity (Lejeune & Richet, 1995, JGR 100 B3: 4215-4229). Resulting depth of fragmentation and mass erupted are consistent with field observations of the 1997 Vulcanian eruptions at Soufrière Hills volcano, Montserrat (Druitt et al., 2002, Geo. Soc. of London, Mem. 21: 281-306). The generalized theory can be applied to other volcanoes, allowing valuable prediction of eruptive volume of Vulcanian explosions and providing a simple means of estimating initial conditions for multi-phase models of explosive eruptions. This work highlights the significance of syn-eruptive processes in controlling eruption scale.
DE: 8414 Eruption mechanisms and flow emplacement
DE: 8428 Explosive volcanism
DE: 8434 Magma migration and fragmentation
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005