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High magma decompression rates at the peak of a violent caldera-forming eruption (Lower Pumice 1 eruption, Santorini, Greece)

Citation

Simmons, JM and Carey, RJ and Cas, RAF and Druitt, TH, High magma decompression rates at the peak of a violent caldera-forming eruption (Lower Pumice 1 eruption, Santorini, Greece), Bulletin of Volcanology, 79 Article 42. ISSN 0258-8900 (2017) [Refereed Article]

Copyright Statement

Copyright 2017 Springer-Verlag Berlin Heidelberg

DOI: doi:10.1007/s00445-017-1120-1

Abstract

We use the deposit sequence resulting from the first catastrophic caldera collapse event recorded at Santorini (associated with 184ka Lower Pumice 1 eruption), to study the shallow conduit dynamics at the peak of caldera collapse. The main phase of the Lower Pumice 1 eruption commenced with the development of a sustained buoyant eruption column, producing a clast-supported framework of rhyodacitic white pumice (LP1-A). The clasts have densities of 310740kgm−3, large coalesced vesicles that define unimodal size distributions and moderate to high vesicle number densities (1.2נ1091.7נ109cm−3). Eruption column collapse, possibly associated with incipient caldera collapse, resulted in the development of pyroclastic flows (LP1-B). The resulting ignimbrite is characterised by rhyodacitic white pumice with a narrow density range (250620kgm−3) and moderate to high vesicle number densities (1.3נ1092.1נ109cm−3), comparable to clasts from LP1-A. An absence of deep, basement-derived lithic clast assemblages, together with the occurrence of large vesicles and relatively high vesicle number densities in pumice from the fallout and pyroclastic flow phases, suggests shallow fragmentation depths, a prolonged period of bubble nucleation and growth, and moderate rates of decompression prior to fragmentation (711MPas−1). Evacuation of magma during the pyroclastic flow phase led to under-pressurisation of the magma reservoir, the propagation of faults (associated with the main phase of caldera collapse) and the formation of 20m thick lithic lag breccias (LP1-C). Rhyodacitic pumices from the base of the proximal lithic lag breccias show a broader range of density (330990kgm−3), higher vesicle number densities (4.5נ1091.1נ1010cm−3) and higher calculated magma decompression rates of 1528MPas−1 than pyroclasts from the pre-collapse eruptive phases. In addition, the abundance of lithic clasts, including deeper, basement-derived lithic assemblages, records the opening of new vents and a deepening of the fragmentation surface. These data support numerical simulations which predict rapid increases in magma decompression and mass discharge rates at the onset of caldera collapse.

Item Details

Item Type:Refereed Article
Keywords:caldera eruption, volcano, Santorini
Research Division:Earth Sciences
Research Group:Geology
Research Field:Volcanology
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Earth Sciences
Author:Carey, RJ (Dr Rebecca Carey)
Author:Cas, RAF (Professor Ray Cas)
ID Code:116468
Year Published:2017
Funding Support:Australian Research Council (DE150101190)
Web of Science® Times Cited:2
Deposited By:Earth Sciences
Deposited On:2017-05-10
Last Modified:2017-06-29
Downloads:0

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