Relationship Between Magma Recharge and Eruption Revealed Through In Situ Geochemical Fingerprinting and Crystal Size Distribution Analysis

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EAR-0073884BohrsonThe process of magma recharge, which is intrusion of hotter magma into the base of a magma reservoir, is thought to be a catalyst for some volcanic eruptions. Newly intruded and standing magma may mix, and by one of a number of mechanisms, vesiculation may occur. Vesiculation leads to increased pressure in the magma reservoir, which, in turn, may lead to eruption. Previous work suggests that the degree of explosivity of the eruption may be critically dependent on the rate of intrusion and volume of recharge magma: slow intrusion of relatively small volumes of recharge magma may lead to gentle eruption whereas rapid intrusion of relatively large volumes of recharge magma may cause explosive eruption. These contrasting scenarios predict that the associated volcanic deposits may record differences in the extent and style of magma mixing and in the timing of recharge relative to eruption. The 1915 eruption of Lassen, a volcanic center located in northeastern California, is an extremely well-documented eruption in which recharge is hypothesized as the eruption catalyst. For volcanic products of this eruption, the chemical fingerprint of magma mixing will be determined using in situ laser-ablation ICP-MS, and the location of formation, crystallization history, and residence times of crystals will be determined from crystal size distribution analysis. Together, these data will reveal the timing of the recharge event relative to eruption and will also permit a description of the fluid dynamics of mixing in this reservoir. Through studies such as this one, quantitative constraints on the timing between recharge and eruption and on the relationships among recharge rate, recharge volume and explosivity will emerge. Such information will lead to enhanced understanding of dynamics and timing of volcanic eruptions.