Martian megaflood‐triggered chaos formation, revealing groundwater depth, cryosphere thickness, and crustal heat flux

Abstract

Ravi Vallis is an outflow channel complex that emerged from Aromatum Chaos, a region of collapsed ground in Xanthe Terra, Mars. I propose that the megaflood that carved Ravi Vallis incised the crust more than 700 m, penetrated the cryosphere, and triggered the release of groundwater and genesis of secondary chaos zones in the deepest parts of the channel system. Discharge rates of 4 × 106 to 5 × 107 m3 s−1 are estimated for early overland flooding. Assuming bank‐full flow would yield unrealistic discharge rates of >3 × 108 m3 s−1. Waning stage flooding in an inner channel had a discharge rate on the order of ≲1 × 106 m3 s−1. The cryosphere thickness and groundwater depth are estimated as the sum of the channel incision depth and the thickness of residual cryosphere beneath the channel floor that could be disrupted by high artesian pressure. The surface elevation (−1231 m) of a transient water body in Aromatum Chaos would have controlled the maximum potentiometric heads in confined aquifers to the east. Where Iamuna Chaos was spawned, the floor of Ravi Vallis would have experienced upward hydraulic pressures of ≤2.4 MPa, enough to rupture a basaltic rock layer ≤255 m thick. At the time of the flood the cryosphere thickness and groundwater depth would have been 700 to 1000 m at this location on the equator, indicating a relatively cold, long‐term climate trend similar to that of present‐day Mars. The crustal heat flux likely exceeded 50 mW m−2 at Iamuna Chaos. If deep lakes existed at that time in the ancestral Valles Marineris, their ice covers are estimated to have been less than 3 km thick. The fluvial incision and groundwater breakout model described here can fully account for the inception of Iamuna Chaos, Oxia Chaos, and a smaller unnamed chaos. Therefore a locally enhanced crustal heat flux was not required to initiate the formation of these chaotes.