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Deformed symmetrical volcanoes

¹ Dipartimento di Scienze della Terra—A. Desio, Università degli Studi di Milano, via Mangiagalli 34, 20133 Milano, Italy
² National Institute of Geological Science, Velasquez Street, Corner C.P. Garcia, University of the Philippines, Quezon City 1101, Philippines

Analog modeling of volcanic cones traversed by strike-slip faulting was conducted, and the cones were analyzed for deformation characteristics. The study shows that symmetrical volcanoes that have undergone basal strike-slip offset may be deformed internally without manifesting any change in their conical shape. Volcanoes deformed by strike-slip faulting may already have well-developed fractures in their interior, yet still appear as a symmetrical cone, exhibiting concentric contours when viewed on a topographic map. Moreover, slight changes in the basal shape of the cone induced by strike-slip movement can be restored by the relatively faster resurfacing and reshaping processes from the deposition of younger eruptive products. These findings pose a subtle but significant point in the assessment of volcanic landslide hazards: not all perfect cones are undisturbed. The detection of concealed deformation is important because fractures induce further instability in volcanoes and act as slip planes during volcano-collapse events. There are many examples of symmetrical volcanoes in nature. The faultless appearance of such perfect cones can be misleading, which requires careful attention in hazards assessment.

Key Words: analog model • digital photogrammetry • volcano instability • strike-slip faulting • Mount St. Helens • Galeras volcanic complex • Mayon volcano

This article has been cited by other articles:

				G. Norini, L. Capra, G. Groppelli, and A.M.F. Lagmay Quaternary sector collapses of Nevado de Toluca volcano (Mexico) governed by regional tectonics and volcanic evolution Geosphere, October 1, 2008; 4(5): 854 - 871. [Abstract] [Full Text] [PDF]