HR: 0800h
AN: V51A-04    [Abstracts]
TI: The 1943-1952 Eruption of Parícutin Volcano - the Pyroclastic Record
AU: * Cashman, K
EM: cashman@uoregon.edu
AF: University of Oregon, Department of Geological Sciences, Eugene, OR 97403-1272, United States
AU: Pioli, L
EM: lpioli@uoregon.edu
AF: University of Oregon, Department of Geological Sciences, Eugene, OR 97403-1272, United States
AU: Rosi, M
EM: rosi@dst.unipi.it
AF: Universita di Pisa, Dipartimento di Scienze della Terra via S. maria, 53, Pisa, 56126, Italy
AU: Erlund, E
EM: eerlund@uoregon.edu
AF: University of Oregon, Department of Geological Sciences, Eugene, OR 97403-1272, United States
AU: Delgado Granados, H
EM: hugo@geofisica.unam.mx
AF: Instituto de Geofisica, UNAM, Departamento de Vulcanologia Av. Universidad 3000, Coyoacan, 04510, Mexico
AU: Wallace, P
EM: pwallace@uoregon.edu
AF: University of Oregon, Department of Geological Sciences, Eugene, OR 97403-1272, United States
AB: The 1943-1952 eruption of Parícutin volcano, Michoacan, is famous for the compositional evolution preserved in successive lava flows. The physical nature of the eruption is less well known, despite the remarkable observational record that was obtained during its nine years of activity. We have revisited both the tephra deposits and the observational accounts with the goal of reconstructing, from a modern perspective, the nature of the ‘cineritic' activity that serves as Walker's (1973) type example of a violent strombolian eruptive style. We have described sixteen tephra sections around the volcano. Only very proximal sections preserve the late (post-1946) andesitic tephra sequence and associated breadcrust bombs. The tephra sequence preserved in medial to distal sites varies more with direction than with distance, not surprising given the strong variations in prevailing wind directions in this region. (1) Southern sections preserve a complex basal lapilli sequence comprising thin alternating black (enriched in lithics and scoria) and tan (enriched in vesicular tephra) layers; analysis of the vesicular tephra shows it to have a more primitive composition than the earliest erupted lava. These basal layers are overlain by a coarse ash layer, consistent with observations of a persistent weak plume to the SW that accompanied early lava effusion and cone growth. The ash is overlain by a thick sequence of intercalated lapilli and ash. To the north, an ash bed forms the deposit base and is again overlain by alternating lapilli and ash; to the east, alternating beds of lapilli and ash mark the base of the section. We interpret this widespread lapilli and ash sequence to have been deposited during the ‘heavy cineritic phase' of activity that extended from mid-March through the summer of 1943. Lapilli are homogeneous basaltic andesite with the same bulk composition as lava erupted during this time period. Unique to eastern sections is a pronounced tan vesicular tephra in the middle of the sequence that may represent deposits associated with a change in activity in late1943 to continuous lava emission and strombolian explosions from a flank vent on the NE side (the Sapichu vent). The correspondence of the preserved tephra sequence with both contemporaneous accounts and the chemical stratigraphy provided by analysis of lava flows allows us to make some generalizations about the violent strombolian eruptive style. All tephra deposits, proximal to distal, are characterized by alternating layers of ash and lapilli, consistent with accounts of eruption styles varying from explosions (‘tubular' eruptions) to more prolonged ash-laden ‘blasts' to ‘gaseous' eruptions of white vapors (Luhr and Simkin 1993). Moreover, the protracted nature of the eruptive activity means that individual marker beds can be traced only along depositional axes, such that traditional methods of whole-deposit characterization are not applicable. Finally, from the hazards perspective, it is important to note that although both the average magma supply rate and tephra emissions decreased with time, the strength of individual explosions increased with the onset of Vulcanian activity during the last several months.
DE: 8414 Eruption mechanisms and flow emplacement
DE: 8428 Explosive volcanism
DE: 8488 Volcanic hazards and risks
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2007 Joint Assembly