ERUPTIVE DYNAMICS OF THE "CITLALTÉPETL PUMICE" AT CITLALTÉPETL VOLCANO, EASTERN MEXICO

Abstract

Citlaltépetl (Pico de Orizaba) is Mexico's highest (5675 m a.s.l.) potentially active volcano, which is presently in a dormant state. Between 9.0 and 8.5 ky B.P., a sequence of volcanic eruptions occurred at Citlaltépetl volcano as part of the most explosive Holocene episode. This sequence is associated with the deposition of an intercalation of pumice fallout and scoria and pumice-rich pyroclastic flow deposits, named here as "Citlaltépetl Pumice" (C.P.). Detailed stratigraphic and petrographic correlation of over 100 measured sections, in conjunction with the analysis of the physical characteristics of the juvenile and lithic portions of each main layer of the sequence, provided the basis to reconstruct the eruptive episodes and to assert the eruptive dynamics of the whole sequence, which was divided into eight main eruptions separated by three brief periods of quiescence. The eruption sequence started with a phreatic phase that soon developed into a bread-crusted, bomb-bearing phase. This was followed by a sequence of vigorous Plinian explosive eruptions separated by brief periods of repose and a short dome-collapse activity. It was followed by another cycle of alternated scoria pyroclastic flows-forming and Plinian activity. This eruptive sequence shows the complexity of single eruptive events with alternated contrasting styles suggested by the compositional differences between the pyroclastic flow and fallout products. © 2006 Elsevier B.V. All rights reserved.