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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 110, B05402, doi:10.1029/2004JB003252, 2005

Discrete element simulations of gravitational volcanic deformation: 1. Deformation structures and geometries

Julia K. Morgan

Department of Earth Science, Rice University, Houston, Texas, USA


Patrick J. McGovern

Lunar and Planetary Institute, Houston, Texas, USA


Abstract

We have carried out two-dimensional particle dynamics simulations of granular piles subject to frictional Coulomb failure criteria to gain a first-order understanding of different modes of gravitational deformation within volcanoes. Under uniform basal and internal strength conditions, granular piles grow self-similarly, developing distinctive stratigraphies, morphologies, and structures. Piles constructed upon cohesive substrates exhibit particle avalanching, forming outward dipping strata and angle of repose slopes. Systematic decreases in basal strength lead to progressively deeper and steeper internal detachment faults and slip along a basal décollement; landslide forms grade from shallow slumps to deep-seated landslide and, finally, to axial subsidence and outward flank displacements, or volcanic spreading. Surface slopes decrease and develop concave up morphologies with decreasing décollement strength; depositional layers tilt progressively inward. Spatial variations in basal strength cause lateral transitions in pile structure, stratigraphy, and morphology. This approximation of volcanoes as Coulomb granular piles reproduces the richness of deformational structures and surface morphologies in many volcanic settings. The gentle slopes of Hawaiian volcanoes and Olympus Mons on Mars suggest weak basal décollements that enable volcanic spreading. High-angle normal faults, favored above weak décollements, are interpreted in both settings and may explain catastrophic sector collapse in Hawaii and broad aureole deposits surrounding Olympus Mons. In contrast, steeper slopes and shallow detachment faults predominate in the Canary Islands, thought to lack a weak décollement, favoring smaller, more frequent slope failures than predicted for Hawaii. The numerical results provide a useful predictive tool for interpreting dynamic behavior and associated geologic hazards of active volcanoes.

Received 23 June 2004; accepted 26 January 2005; published 12 May 2005.

Keywords: gravitational spreading; volcanotectonics; discrete element method (DEM).

Index Terms: 3070 Marine Geology and Geophysics: Submarine landslides; 8004 Structural Geology: Dynamics and mechanics of faulting (8118); 8020 Structural Geology: Mechanics, theory, and modeling; 8122 Tectonophysics: Dynamics: gravity and tectonics; 8168 Tectonophysics: Stresses: general.

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Citation: Morgan, J. K., and P. J. McGovern (2005), Discrete element simulations of gravitational volcanic deformation: 1. Deformation structures and geometries, J. Geophys. Res., 110, B05402, doi:10.1029/2004JB003252.