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Abstract

The Efate Pumice Formation (EPF) is the record of a major explosive eruption that occurred in the Vanuatu arc, southwestern Pacific, at about 1 Ma. The EPF is
the oldest stratigraphic unit of the Efate Island Group and consists of a succession of non-welded, trachydacitic pumice breccia and shard-rich sand and silt beds
with a minimum thickness of ~500 m and a minimum bulk volume of approximately 85 km3. The lower part (Efate Pumice Breccias) of the EPF comprises very thick beds composed almost exclusively of glassy, trachydacitic, pumice fragments with ragged terminations. In contrast, the upper part (Rentabau Tuffs) consists of up to 70 m of well-bedded and well-sorted shard-rich sand and silt. The
clast population of this upper part comprises >95 % glassy or formerly glassy shards, but fossil foraminifera are a ubiquitous and important non-volcanic component.
Some glass shards have blocky, equant shapes and arcuate fracture surfaces, features typically associated with the influence of external water during fragmentation, but most are cuspate and platy bubble-wall shards. Pyroclast morphologies indicate that the Efate Pumice Breccias were largely generated by magmatic-volatile-driven (dry), explosive fragmentation processes, and lithofacies
characteristics indicate deposition in below-storm-wave-base environments, from eruption-sourced, water-supported density currents of waterlogged pumice. The Rentabau Tuffs are interpreted to represent a change to hydromagmatic activity in response to waning discharge that allowed ingress of water (presumably seawater) to the vent(s).

Item Type:	Book Section
Authors/Creators:	Raos, AM and McPhie, J
Keywords:	pumice breccia, glass shard, submarine explosive eruption, Vanuatu, eruption-fed density current, hydromagmatic, pyroclastic
Publisher:	American Geophysical Union
DOI / ID Number:	https://doi.org/10.1029/140GM18
Item Statistics:	View statistics for this item

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