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Rock Avalanche in Robinson Crater
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Rock Avalanche in Robinson Crater

December 5, 2012
An impact crater changes its shape with time by various degradation processes, such as wall slumping, infilling with ejecta deposits from nearby impacts, and volcanic activities. Rock avalanches as shown in today's featured image also contribute to modifying crater shape little by little. Multiple tongue shaped flow fronts in this image evoke liquid (Newtonian) flow features, especially mudflows. Similar features have been found on Mars, and are interpreted to represent recent mudflows. Water is not stable on the Moon's surface (except perhaps as ice in permanently shadowed craters), so these flows are dry (granular) rock slides. Perhaps some of the flow features on Mars thought to indicate wet mudflows are really dry granular flows? Northern slope inside Robinson crater. LROC NAC M114259768R, 0.52 m/pixel, image width is 620 m, sun light is from right side. Slope direction is from top to the bottom of the image [NASA/GSFC/Arizona State University].