  Hesperian chaotic terrains have been recognized as the source of outflow
channels formed by catastrophic outflows. Four main scenarios have been
proposed for the formation of chaotic terrains that involve different amounts
of water and single or multiple outflow events. Here, we test these scenarios
with morphological and structural analyses of imagery and elevation data for
Aram Chaos in conjunction with numerical modeling of the morphological
evolution of the catastrophic carving of the outflow valley. The morphological
and geological analyses of Aram Chaos suggest large-scale collapse and
subsidence (1500 m) of the entire area, which is consistent with a massive
expulsion of liquid water from the subsurface in one single event. The combined
observations suggest a complex process starting with the outflow of water from
two small channels, followed by continuous groundwater sapping and headward
erosion and ending with a catastrophic lake rim collapse and carving of the
Aram Valley, which is synchronous with the 2.5 Ga stage of the Ares Vallis
formation. The water volume and formative time scale required to carve the Aram
channels indicate that a single, rapid (maximum tens of days) and catastrophic
(flood volume of 9.3?104 km3) event carved the outflow channel. We conclude
that a sub-ice lake collapse model can best explain the features of the Aram
Chaos Valley system as well as the time scale required for its formation.
