The similarity of fluidized ejecta blankets of double-layer ejecta (DLE) craters and long run-out landslides: morphometry and modeling

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The combined and comparative analysis of impact craters on Mars and Earth was a reasonable and successful way to investigate the effects of volatiles on the excavation process during impact cratering. Main questions raised in this former application could be answered. It could be demonstrated via three-dimensional reconstruction that the Ries crater´s ejecta blanket contains a massive intermediate rampart and is morphometrically similar to the Martian double layer ejecta (DLE) craters. Abundant indicators for the presence of water during deposition and flow were found in two boreholes of the Ries ejecta blanket. The fundamental flow kinematics as well as the spatial and temporal relationship of the ejecta layer deposition of DLE craters could be solved. In the course of the project it became obvious that the inner and outer ejecta layers move in different landslide modes. While the inner ejecta layer is formed by a translational slide that emanates from the crater rim and overruns the proximal parts of the outer ejecta facies the outer more fluid-rich layer moves in a debris flow or debris avalanche mode. We observed a strong topographic and morphologic resemblance between these ejecta facies, and Martian landslides as well as terrestrial long run-out rock avalanches. A first-order feature of the inner layer of DLE ejecta layers and landslides are radial (longitudinal) ridges and grooves parallel to the flow direction. Although such striations appear to be a fundamental phenomenon of fast mass movements their formation is so far poorly understood. We believe that their formation is key to understand the flow mechanism. Their geometry and spacing may even allow to constrain physical parameters of the flow. In the continuation project we will develop a mathematical model based on Voellmy´s equations that is aimed to simulate their formation. A rigorous morphometric analysis provides the basis of input parameters to that model. Likewise characteristic is the formation of extensional furrows and compressive ridges perpendicular to the flow that off-set the radial/longitudinal ridges and grooves. These features develop during the final increments of the flow when the moving masses regain strength. Our morphometric analysis includes these features. The outcome of this proposal is twofold and far-reaching: (i) The comparative quantitative morphometric analysis of surface features of ejecta blankets of DLE craters and landslides will prove or disprove the landslide characteristics of DLE craters. (ii) The fundamental phenomenon of the formation of longitudinal ridges and grooves on fast moving rock masses will be explained.