Eruptive Stratigraphy And The Transport And Deposition Of Pyroclastic Material From The Caldera-Forming Eruption Of Volcan Ceboruco, Nayarit, Mexico

Abstract

The ~1000 A.D. eruption of Volcan Ceboruco produced 3--4 km<super>3</super> of rhyodacitic to dacitic magma erupted as the Jala Pumice, forming a 3.7-km-wide caldera. The tephra sequence consists of alternating Plinian fall and pyroclastic surge deposits, and a series of lithic-rich pyroclastic flow deposits. The latter are known as the Marquesado and North-Flank Pyroclastic Flow deposits. Stratigraphic evidence and results of a comprehensive analysis of accidental lithic and pumice populations constrain the timing of caldera collapse, and the emplacement of the pyroclastic flow deposits to the end of the Jala Pumice. Mass accumulation calculations of particles from fall layers display sedimentation patterns consistent with deposition from dilute and turbulent currents with low particle concentration. Pyroclastic flow and surge deposits likely resulted from density-stratified currents, with a basal region of relatively high particle concentration, and an upper dilute layer that transports particles in turbulent suspension. <p>