Effects of Density Driven Deformation within Volcanic Edifices Using Discrete Element Simulations

We have carried out 2-D numerical simulations that investigate density-driven deformation in volcanic edifices similar to those in Hawaii and Olympus Mons. Located within volcanoes are a series of magma chambers, reservoirs, and conduits where magma travels and collects. As a magma cools, dense minerals, including olivine, are fractionated out and collect at the base of magma chambers, building thick accumulations called cumulates. These hot and dense materials can flow ductily due to stresses imparted by gravity. The gravitational spreading of cumulates within volcanoes causes internal and surficial deformation that may include faulting, subsidence of summit regions, and possibly flank instability. Using the discrete element method (DEM), we have modeled the effects of dense cumulate within volcanic edifices by creating granular piles subject to a Coulomb frictional rheology, containing central cores of dense, low friction materials. As the volcanoes grow, the presence and outward movement of the dense cumulate produces distinctive structures and stratigraphy. “Reference volcanoes”, or granular piles lacking internal cumulate, yield stratigraphic layers with low dips and nearly planar flank slopes near the angle of repose. Volcanoes with internal cumulates exhibit shield-shaped profiles with inward dipping strata, summit “calderas" and wide perimeter regions of thrust faulting. By varying the density of the internal cumulate and the coefficients of friction between the volcano and the base, we obtained a range of volcanic shapes that vary from broad, shallowly sloping flanks to narrow, steep surface slopes. While the simulations illustrate a variety of gravity driven deformation features, they appear to successfully reproduce certain deformational characteristics that are prevalent on both Olympus Mons and Hawaiian volcanoes, including subsidence near volcanic summits, proximal normal faulting, surficial landslides, and distal thrusting.