Data from instruments on the currently orbiting Mars Global Surveyor (MGS) suggest that as an alternative interpretation to lacustrine deposits, widespread sediments on Mars may be tephra deposits of variable age, formed in part by volcano-ice interactions. The materials are often associated with outcrops of mapped geological units that have each been previously interpreted as volcanic ash deposits with identified, but unconfirmed possible volcanic vents. Spectral investigation indicates that although some outcrops are basaltic, many show moderate to high concentrations of andesite, a composition at which large explosive eruptions may be possible. In addition, many outcrops are in areas suspected to be water/ice rich. On Earth, magma and groundwater can react to create violent explosive eruptions. Observations from MGS support a pyroclastic mechanism of deposition and show some morphologies consistent with volcano-ice interactions, including subaqueous eruptions. Perhaps MGS data are finally producing more definitive evidence of the widespread tephra that were predicted to be likely in the reduced atmospheric pressure of Mars.
