Shallow-storage conditions for the rhyolite of the 1912 eruption at Novarupta, Alaska

Recent studies have proposed contrasting models for the plumbing system tha t fed the 1912 eruption of Novarupta, Alaska. Here, we investigate the cond itions under which the rhyolitic part of the erupted magma last resided in the crust prior to eruption. Geothermometry suggests that the rhyolite was held at similar to 800-850 degreesC, and analyses of melt inclusions sugges t that it was fluid saturated and contained similar to4 wt% water. Hydrothe rmal, water-saturated experiments on rhyolite pumice reveal that at those t emperatures the rhyolite was stable between 40 and 100 MPa, or a depth of 1 .8-4.4 km. These results suggest that pre-eruptive storage and crystal grow th of the rhyolite were shallow; if the rhyolite ascended from greater dept hs, it did so slowly enough for unzoned phenocrysts to grow as it passed th rough the shallow crust.