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The influence of edifice slope and substrata on volcano spreading.

Delcamp, Audray and van Wyk de Vries, Benjamin and James, Mike R. (2008) The influence of edifice slope and substrata on volcano spreading. Journal of Volcanology and Geothermal Research, 177 (4). pp. 925-943. ISSN 0377-0273

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Abstract

Gravitational volcano spreading is caused by flow of weak substrata due to volcanic loading, and is now a process known to affect many edifices. The process produces extension in the upper edifice, evidenced by gräben and normal faults, and compression at the base, seen in strike–slip faults and thrusts. Where spreading is identified, host volcanoes have a range of fault densities, variable rift and gräben shapes, and different degrees of structural asymmetry. Previous studies have suggested a link between edifice shape and structure and the proportion of brittle to ductile material in the substrata or lower edifice. We study this link using refined sand cone analogue models standing on a brittle–ductile/sand–silicone substrata. Two scenarios have been investigated, the first mainly represents oceanic volcanoes with a ductile layer within the edifice (type I), where there is an outer ductile free surface. The second represents most continental volcanoes that have ductile substrata (type II). We apply the model results to natural examples and develop quantitative relationships between slope, brittle–ductile ratio fault density, spreading rate and structural style. Displacement fields calculated from stereophotogrammetry show significant differences between different slope models. We find that more faults are produced when the cone is initially steeper, or when the brittle substratum is thinner. However, the effect of the brittle layer dominates over that of slope. The strike–slip movements are found to be an essential feature in the spreading mechanism and the gräben are in fact transtensional features. Strike–slip and graben faults make a conjugate flower pattern. The structures produced are well-organised for type II edifices, but they are poorly organised for type I models. Type I models represent good analogues for oceanic volcanoes that are commonly affected by large slumps bounded by an extensional zone and lack of well-formed sector gräben. The well-observed connection between oceanic volcano rifts and large landslide-slumps is confirmed to be a consequence of spreading.

Item Type: Article
Journal or Publication Title: Journal of Volcanology and Geothermal Research
Uncontrolled Keywords: volcano spreading ; edifice morphology ; sector Gräben ; faulting ; oceanic volcano
Subjects: G Geography. Anthropology. Recreation > GE Environmental Sciences
Departments: Faculty of Science and Technology > Lancaster Environment Centre
ID Code: 27743
Deposited By: Mr Richard Ingham
Deposited On: 23 Oct 2009 10:58
Refereed?: Yes
Published?: Published
Last Modified: 26 Jul 2012 16:42
Identification Number:
URI: http://eprints.lancs.ac.uk/id/eprint/27743

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