Origin of the valley networks on Mars: a hydrological perspective

The geomorphology of the martian valley networks is examined from a hydrolo gical perspective for the compatibility with an origin by rainfall, globall y higher heat flow, and localized hydrothermal systems. Comparison of morph ology and spatial distribution of valleys on geologic surfaces with terrest rial fluvial valleys suggests that most martian valleys are probably not in dicative of a rainfall origin, nor are they indicative of formation by an e arly global uniformly higher heat flow. In general, valleys are not uniform ly distributed within geologic surface materials as are terrestrial fluvial valleys. Valleys tend to form either as isolated systems or in clusters on a geologic surface unit leaving large expanses of the unit virtually untou ched by erosion. With the exception of fluvial valleys on some volcanoes, m ost martian valleys exhibit a sapping morphology and do not appear to have formed along with those that exhibit runoff morphology. In contrast, terres trial sapping valleys form from and along with runoff valleys. The isolated or clustered distribution of valleys suggests localized water sources were important in drainage development, Persistent groundwater outflow driven b y localized, but vigorous hydrothermal circulation associated with magmatis m, volcanism, impacts, or tectonism is, however, consistent with valley mor phology and distribution, Snowfall From sublimating ice-covered lakes or se as may have provided an atmospheric source of water for the formation of so me valleys in regions where the surface is easily eroded and where localize d geothermal/hydrothermal activity is sufficient to melt accumulated snowpa cks. (C) 2001 Elsevier Science B.V. All rights reserved.