NDLI: Flank spreading and collapse of weak-cored volcanoes

Content Provider	Springer Nature Link
Author	Cecchi, Emmanuelle Wyk de Vries, Benjamin Lavest, Jean Marc
Copyright Year	2004
Abstract	Volcanoes subjected to hydrothermal activity develop weak cores as a result of alteration and due to elevated pore pressures. Edifices constructed at the angle of repose of volcanoclastics, or at even more gentle slopes, respond to internal weakening by initially deforming slowly, but may then collapse catastrophically. Such a process has so far been described for only a few volcanoes, such as Casita, Nicaragua; however, the conditions for flank spreading are widespread and many, if not most volcanoes should suffer some alteration-related flank spreading. We provide analogue models that characterise the structure — surface deformation fields and internal structures — of a spreading flank. Deformation creates a characteristic concave-convex-concave flank profile producing structures such as basal thrusts, summit normal faults, grabens and strike-slip relay faults. Three deformation regimes are found: a ‘pit collapse’ regime is associated with very small volumes of ductile material located far from the edifice surface. This would not appear in nature, as time for deformation is greater than the lifetime of a volcano, unless very low rock viscosities are present. The other two regimes are flank spreading regimes, one symmetric and one asymmetric. The latter is the most common, as most volcanic structures are asymmetrical in form and in distribution of physical properties. The deformation is controlled by altered region dimensions, volume and position relative to the edifice, and to a lesser extent by its shape. As the flanks spread, landslides are created, initially on the steepened portion, but also from fault scarps. Major flank collapse may occur leading to explosive hydrothermal decompression and to a debris avalanche rich in hydrothermally altered material. We provide several new examples of volcanoes that have structures and morphologies compatible with flank spreading. We suggest that it is a common feature, important in the tectonics and hazards of many volcanoes.
Starting Page	72
Ending Page	91
Page Count	20
File Format	PDF
ISSN	02588900
Journal	Bulletin of Volcanology
Volume Number	67
Issue Number	1
e-ISSN	14320819
Language	English
Publisher	Springer-Verlag
Publisher Date	2004-08-18
Publisher Place	Berlin/Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Gravitational deformation Analogue modelling Hydrothermal alteration Edifice weakening Flank spreading Volcano instability Collapse
Content Type	Text
Resource Type	Article
Subject	Geochemistry and Petrology

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