Abstract
AbstractA decade of high-resolution monitoring has revealed extensive activity in fresh Martian gullies. Flows within the gullies are diverse: they can be relatively light, neutral or dark, colourful or bland, and range from superficial deposits to 10 m-scale topographic changes. We observed erosion and transport of material within gullies, new terraces, freshly eroded channel segments, migrating sinuous curves, channel abandonment, and lobate deposits. We also observed early stages of gully initiation, demonstrating that these processes are not merely modifying pre-existing landforms. The timing of activity closely correlates with the presence of seasonal CO2 frost, so the current changes must be part of ongoing gully formation that is driven largely by its presence. We suggest that the cumulative effect of many flows erodes alcoves and channels, and builds lobate aprons, with no involvement of liquid water. Instead, flows may be fluidized by sublimation of entrained CO2 ice or other mechanisms. The frequent activity is likely to have erased any features dating from high-obliquity periods, so fresh gully geomorphology at middle and high latitudes is not evidence for past liquid water. CO2 ice-driven processes may have been important throughout Martian geological history and their deposits could exist in the rock record, perhaps resembling debris-flow sediments.
Highlights
We suggest a related alternative, in which gas generation occurs via two effects within a mix of sediment and CO2 ice tumbling down a gully
Extensive activity is occurring in Martian gullies today, including formation of a host of geomorphic features often associated with water
The flows seen within Martian gullies may resemble those produced by aqueous processes because they are fluidized to some extent, likely by gas generated from entrained CO2 frost
Summary
Landforms on Mars resemble water-formed features on Earth, with channels transporting material from an alcove to a depositional apron. We compare these frost data with observations of gully activity and its morphological effects, expanding the survey of Dundas et al. Such flows may be minor activity that was distinct because of contrast with traces of frost, analogous to the more obvious flows over frost observed elsewhere (Fig. 7), but produce changes that are minimal at HiRISE resolution in well-illuminated images.
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