Polygenetic nature of a rhyolitic dome and implications for hazard assessment:: Cerro Pizarro volcano, Mexico

Rhyolitic domes are commonly regarded as monogenetic volcanoes associated with single, brief eruptions, in contrast to andesitic or dacitic domes that usually show a complex evolution including alternating long periods of growth and explosive destruction. Rhyolitic domes are characterized by short-lived successions of pyroclastic and effusive activity associated with a series of discrete eruptive events that apparently last on the order of years to decades or perhaps up to centuries. Cerro Pizarro, a rhyolitic dome in the eastern Mexican Volcanic Belt, is a relatively small (similar to 1.1 km(3)), isolated volcano that shows aspects of polygenetic volcanism including long-term repose periods (similar to 50-80 ky) between eruptions, chemical variations over time, and a complex evolution of alternating explosive and effusive eruptions, including a cryptodome phase, a sector-collapse event and prolonged erosional processes. This eruptive behavior provides new insights into how rhyolite domes may evolve, in contrast to the traditional models of rhyolitic domes as short-lived, monogenetic systems. A protracted, complex evolution bears important implications for hazard assessment if reactivation of an apparently extinct rhyolitic dome must be seriously considered. (C) 2008 Elsevier B.V. All rights reserved.