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Generation of a debris avalanche and violent pyroclastic density current on 26 December (Boxing Day) 1997 at Soufrière Hills Volcano, Montserrat

By
R. S. J. Sparks
R. S. J. Sparks
Department of Earth Sciences, University of Bristol, Bristol, BS8 1RJ, UK
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J. Barclay
J. Barclay
Department of Environment Sciences, University of East Anglia, Norwich, NR4 7JT, UK
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E. S. Calder
E. S. Calder
Department of Earth Sciences, University of Bristol, Bristol, BS8 1RJ, UK
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R. A. Herd
R. A. Herd
British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK
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J-C. Komorowski
J-C. Komorowski
Observatoire de Guadeloupe, Institut de Physique du Globe, Guadeloupe, French Antilles
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R. Luckett
R. Luckett
British Geological Survey, Murchision House, West Mains Road, Edinburgh, EH9 3LA, UK
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G. E. Norton
G. E. Norton
British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK
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L. J. Ritchie
L. J. Ritchie
Centre for Volcanic Studies, University of Luton, Park Square, Luton, LU1 3JU, UK
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B. Voight
B. Voight
Department of Geosciences, Penn State University, University Park, PA 16802, USA
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A. W. Woods
A. W. Woods
BP Institute, Madingley Rise, Cambridge University, Cambridge CB3 0EZ, UK
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Published:
January 01, 2002

Abstract

Growth of an andesitic lava dome at Soufrière Hills Volcano, Montserrat, beginning in November 1995, caused instability of a hydrothermally altered flank of the volcano. Catastrophic failure occurred on 26 December 1997, 14 months after the instability was first recognized. Two months before failure a dome lobe had extruded over the unstable area and by 25 December 1997 this had a volume of 113 × 106m3. At 03:01 (local time) the flank rocks and some dome talus failed and generated a debris avalanche (volume 46 × 106 m3). Between 35 and 45 × 106 m3 of the dome then collapsed, generating a violent pyroclastic density current that devastated 10 km2 of southern Montserrat. The failure of the flank and dome formed two adjacent bowl-shaped collapse depressions. The most intense activity lasted about 11.6 minutes. The hummocky debris avalanche deposit is composed of a mixture of domains of heterolithic breccia. The pyroclastic density current had an estimated peak velocity of 80–90 ms−1, and minimum flux of 108 kg s−1. The current was largely erosional on land with most deposition out at sea. Destructive effects included removal of houses, trees and large vehicles, and formation of a scoured surface blackened by a thin (3–4 mm) layer of tar. Two discrete depositional units formed from the pyroclastic density current, each with a lower coarse-grained layer and an upper fine-grained stratified layer. These deposits are overlain by an ashfall layer related to buoyant lofting of the current. Flank failure is attributed to loading of hydrothermally weakened rocks by the dome. The generation of the pyroclastic density current is attributed to failure and explosive disintegration of the dome, involving release and violent expansion of gases initially at high pore pressures.

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Contents

Geological Society, London, Memoirs

The Eruption of Soufrière Hills Volcano, Montserrat from 1995 to 1999

T. H. Druitt
T. H. Druitt
Université Blaise Pascal, Clermont-Ferrand, France
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B. P. Kokelaar
B. P. Kokelaar
University of Liverpool, UK
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Geological Society of London
Volume
21
ISBN electronic:
9781862393967
Publication date:
January 01, 2002

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