HR: 15:25h
AN: V13F-08 INVITED     [Abstracts]
TI: Particle Dynamics Simulations of Gravitational Volcanic Deformation
AU: * Morgan, J K
EM: morganj@rice.edu
AF: Rice University, Dept Earth Science, MS-126, 6100 Main St, Houston, TX 77005 United States
AU: McGovern, P J
EM: mcgovern@lpi.usra.edu
AF: Lunar and Planetary Institute, 3600 Bay Area Blvd, Houston, TX 77058 United States
AB: Although active volcanoes are subject to dynamic forcing due to magmatic intrusion, eruption, and seismicity, gravitational loading plays a determining role in volcano deformation. A wide spectrum of gravitationally driven phenomena has been documented on volcanic edifices, including catastrophic debris avalanches, shallow slumps, deep seated landslides, and volcanic spreading. To gain a first order understanding of the different modes of gravitational deformation within volcanoes, we have carried out 2-D particle dynamics simulations of dry granular piles subject to Coulomb (frictional) failure criteria. Internal friction of the pile was fixed at 0.6; basal friction coefficients ranged from 0.3 to 0.1, with a reference case of a cohesive non-sliding substrate. Under steady-state conditions, the granular piles grow self-similarly, developing distinctive deformation structures, layer stratigraphies, and morphologies, indicative of the mechanical state of the granular pile. Systematic decreases in basal strength lead to progressively deeper and steeper internal detachment faults that intersect the decollement and allow outward displacement of the lower flanks. Surface slopes decrease with decreasing basal strength, eventually producing broadly concave-upward flank morphologies. Landslide forms grade from avalanches, to shallow slumps, deep-seated landslides, and finally, axial subsidence and outward flank displacements, i.e., volcanic spreading. Our results can be readily explained by examining traction stresses along a weak decollement, which increase away from the axis of the pile due to topographic loading. Basal slip occurs when traction shear stresses reach the Coulomb failure criterion, which occurs closer to the pile axis for lower basal strength conditions. Lateral sliding of the lower flanks enables downward displacement of a wedge shaped slump above a favorably oriented detachment. Remarkably, this approximation of volcanoes as Coulomb granular piles reproduces the richness of deformational structures and slope morphologies found in many volcanic settings. The gentle slopes of Hawaiian volcanoes and Olympus Mons on Mars suggest weak basal decollements that enable volcanic spreading. High-angle normal faults, favored above weak decollements, are interpreted in both settings, and 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, which lack a weak d‚collement, favoring smaller, more frequent slope failures than predicted for Hawaii. Arc volcanoes built upon highly irregular substrates may exhibit mixed modes of deformation in space and time. These numerical models provide us with a useful predictive tool for interpreting dynamic behavior and associated geologic hazards of active volcanoes.
DE: 3070 Submarine landslides
DE: 8004 Dynamics and mechanics of faulting (8118)
DE: 8020 Mechanics, theory, and modeling
DE: 8488 Volcanic hazards and risks
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005