Conduit Evolution during the 1992 Eruptive Sequence at Mt. Spurr, Alaska

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EAR-0229655CashmanThe upward migration of magma through shallow conduits plays an important role in volcanic activity, as the physical changes that magma undergoes during ascent may determine the style and intensity of the resulting eruption. However, little is known about the shapes of volcanic conduits, their evolution through the course of an eruption, or the effect of conduit shape on rates of magma ascent. We propose to analyze conduit evolution during the 1992 eruptions of Mt. Spurr, Alaska, by using individual earthquakes to determine the stress field around the conduit for different phases of the eruptive sequence. This work will both complement and test results from the numerous seismic and petrologic studies already completed on the Spurr eruptive sequence. We are particularly interested in determining the stress state of the conduit during (1) the ten months of activity leading up to the first explosive event, (2) the intra-eruptive period [June - September 1992], and (3) the post-eruptive period. Evaluation of these three time periods will allow us to evaluate conditions of magma ascent prior to eruptive activity, examine the response of the conduit to individual eruptions, and test the hypothesis that seismic swarms in November and December of 1992 were actually eruptions that "failed" because a solidified plug had formed at shallow levels. Our results will thus both provide insight into the 1992 eruptions at Mt. Spurr and aid development of a general model of stress field response to episodes of magma migration. Additionally, we will compare our results with those from a stress field study of dike emplacement at nearby Iliamna Volcano with the hope of shedding light on conditions that either promote or hinder propagation of intruding magma to the surface, thus improving interpretations of future seismic crises in volcanic regions.