Identifying Martian gully evolution
Martian gullies are small-scale, geologically recent features characterized by the alcove-channel-apron morphology associated with flows with a component of liquid water. Theories advanced to explain Martian gully formation include groundwater processes and melting of near-surface ice due to climate variation. Gullies are often associated with ‘mantling terrain’ that drapes topography at mid to high latitudes and which has been proposed to be ice-rich.
We have morphologically classified Martian gullies into four groupings according to whether they form solely within the mantle (Type A), erode into ‘bedrock’ (Type B), and by how well developed they appear (1 or 2). Orientation, length, geological setting and latitude were also recorded, as well as whether more than one generation of gullies formed on a given slope (labelled ‘reactivated’).
About 25% of gullies form solely within the mantle; these are generally shorter than gullies that erode bedrock and the morphologically simplest gullies (A1) are the shortest. We present latitude and orientation trends for the most recent episode of gully formation. We suggest that this recent activity is probably controlled by either deposition of ice-rich material or degradation of pre-existing ice-rich material.
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The latest Mars missions are returning data of unprecedented fidelity in their representation of the martian surface. New data include images with spatial resolution better than 30 cm per pixel, stereo imaging-derived terrain models with one meter postings, high-resolution imaging spectroscopy, and RADAR data that reveal subsurface structure. This book reveals how this information is being used to understand the evolution of martian landscapes, and includes topics such as fluvial flooding, permafrost and periglacial landforms, debris flows, deposition and erosion of sedimentary material, and the origin of lineaments on Phobos, the larger martian moon. Contemporary remote sensing data of Mars, on a par with those of Earth, reveal landscapes strikingly similar to regions of our own planet, so this book will be of interest to Earth scientists and planetary scientists alike. An overview chapter summarising Mars’ climate, geology and exploration is included for the benefit of those new to Mars.