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Did magma ascent rate control the explosive-effusive transition at the Inyo volcanic chain, California?

¹ Department of Mineral Sciences, Smithsonian Institution, P.O. Box 37012, NHB-119, Washington, D.C. 20013-7012, USA
² Department of Geological Sciences, University of Texas, 1 University Station C1100, Austin, Texas 78712-0254, USA

Rhyolitic eruptions often begin explosively and then shift to extrusions of lava. It is widely believed that the style of eruption is dependent on magma flow rate within the conduit, fast ascent leading to explosive eruption and slow ascent favoring effusive behavior. Currently, the velocity of rhyolite magma flowing in a conduit is unknown, and therefore eruption models remain untested against geologic evidence of magma ascent. We show that explosively erupted rhyolite magma from the Inyo volcanic chain ascended slowly (centimeters per second), at same rates as the dome-building phases. We propose that the explosive-effusive transition sub-Plinian rhyolite eruptions is governed by the alleviation of exsolved volatile pressure in the shallow conduit rather than the magma flow rate.

Key Words: microlites • pumice • magma ascent • decompression experiments