ROLES OF GROUND ICE, MAGMATIC VOLATILES, AND IMPACT-TRIGGERING ON A VERY RECENT AND HIGHLY EXPLOSIVE VOLCANIC ERUPTION ON MARS

Volcanic activity on Mars has been dominantly effusive. The existence of a young (<1 Ma), well-preserved pyroclastic deposit from an explosive volcanic eruption along a segment of the Cerberus Fossae fissures, overlying the effusive lava flows making up the bulk of Elysium Planitia, provides a unique opportunity to better understand the dynamics of explosive volcanic eruptions on Mars. The pyroclastic deposit is symmetric around the fossa, mantles the surface, and has an estimated volume similar to moderate to highly explosive volcanic eruptions on the Earth. Based on the deposit characteristics, evidence of ground ice in the pore space of the underlying martian regolith, and the recent history of aqueous floods in Elysium Planitia, we suggest that melting of ice-saturated regolith by an intruded magma-filled dike, and the subsequent entrainment of this water may have played a key role in magma fragmentation and generation of the pyroclastic deposit. Using a transient heat conduction model with moving boundary conditions to track the ice melting fronts, we find that for the typical estimates of water:magma mass ratio required for similar terrestrial volcanic eruptions, the time scales of the entrainment of water-laden regolith reasonably match the likely eruption durations. Our results support the possibility that ground water derived from the melting of ice in the martian regolith might have caused magma fragmentation due to a molten fuel coolant type interaction. We also assess the possible effect of magmatic volatiles and crystals on the explosivity of the eruption using conduit flow model of multiphase magma under martian conditions, and find that for reasonable range of dissolved water content, explosive magma fragmentation might have been possible. Using scaling analysis, we further show that the eruption might have been triggered by the nearby Zunil crater-forming impact. The young age of the deposit and our model results suggest that the associated volcano-tectonic activity may still be active today in Elysium Planitia on Mars.