The 11-km-long Inyo volcanic chain consists of 6 magmatic and more than 15 phreatic eruptive centers alined along a north-trending fracture. About 0.8 km3 of rhyolitic-rhyodacitic magma erupted along the chain during at least 3 eruptive episodes during the past several thousand years. Pyroclastk deposits make up about 40% of this volume. The chemical similarities, timing of eruptions, and alinement of magmatic and phreatic vents indicate that the third eruptive episode, about 650-550 yr ago, occurred when a vertical, tabular, silicic magma body was emplaced at a shallow depth. A similar dikelike intrusion may explain an increase in seismicity and deformation in the south moat of Long Valley caldera. Events about 650-550 yr ago at the Inyo chair provide a model for possible events during future eruptions in the south moat of the caldera.

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