The surface evolution of Mars with emphasis on hydrologic and volcanic processes

Mars' surface had been influenced and sculpted by a variety of geologic and geomorphic processes. The Mars Global Surveyor (MGS) mission, in orbit around Mars since 1997, has been instrumental in construction and evaluation of hypotheses regarding the surface evolution of the planet. Earlier missions revealed valley networks that were suggestive of fluvial erosion. However, the importance of surface versus subsurface flow has long been debated. MGS data have given insight into the timing, degree, and mechanism of fluvial resurfacing. High-resolution topographic data have shown a heavily degraded landscape hosting numerous erosional remnants that are evidence for continental-scale denudation on substantial portions of the highlands. Further, reanalysis of many highland valley systems has revealed an order of magnitude increase in the number of valleys, total valley length, and drainage density than previously mapped. In light of new data, it is likely that surface runoff (and by inference precipitation) played an important role in the sculpting of large regions of the martian landscape early in the planet's history. Subsurface fluid flow has also been important throughout much of Mars' history. A key example is the Terra Meridiani hematite deposit near the martian equator. Regional geologic mapping utilizing several data sets has indicated that circulation of Fe-rich water through existing volcanic deposits is likely responsible for this extensive, dark plain with a unique mineral signature. Volcanism has been a paramount aspect of martian surface evolution and this process has been active throughout much of the planet's history. MGS data have shown a correlation between widely spaced, equatorial layered deposits that have many characteristics consistent with a widespread, episodic, subaerial source of fine-grained material. Thinning of deposits with increasing distance from the massive magmatic complex known as the Tharsis rise suggests that much of these materials may be volcanic ash flows and air fall from explosive eruptions in this region. In summary, MGS data allows for evaluation of the importance of many processes responsible for shaping the surface of Mars. This understanding is essential to unravel the geologic, hydrologic, and climatic histories of Mars.