Slope Profile of Slope Streaks Indicate an Energetic Triggering Mechanism

Abstract

There are several active geologic processes on Mars today one of which is the formation of slope streaks. Slope streaks are a widespread and relatively common process that were first observed as dark fan-shaped features with lobed ends in Viking Orbiter images taken in 1977 (Morris, 1982; Ferguson and Lucchitta, 1984). Investigation of repeat images identified slope streaks as relatively low-albedo features that vary in width (up to 200 m wide) and length (up to a few kilometers long) (Sullivan et al., 2001). Although it was assumed that the slope streaks formed on steep slopes >20°, the slopes were not resolved due to the resolution limit of the data. Slope streaks have been found to form in high-albedo dusty regions on Mars, concentrated around the equator between 39°N and 28°S (Sullivan et al., 2001; Schorghofer and King, 2011; Heyer et al., 2019). Additionally, slope streaks have been observed to fade over decades and high-albedo slope streaks have also been observed (interpreted to be faded slope streaks) (Schorghofer et al., 2007). The formation of slope streaks has previously been observed to be inconsistent spatially and temporally (Schorghofer and King, 2011); however, more recent research has identified seasonal variations of formation, with the highest rates of formation occurring in the fall (near Ls 190) (Heyer et al., 2019). There are many proposed formation mechanisms for slope streaks that fall into either a dry or wet mechanism category. The dry mechanism involves a granular flow triggered by a disturbance mechanism (e.g. dust devil or meteorite impact), while a wet mechanism would indicate a debris flow triggered by a phase change of H2O (e.g. melting of ice to trigger groundwater discharge). Research presented here investigates the slope profiles of identified slope streaks to further understand and constrain the formation mechanism. We investigated 13 well-monitored slope streak sites. Using Arcmap we identified slope streaks within each site with a polyline. For each site we identified CTX stereopairs, processed each image using the Integrated Software for Imagers and Spectrometers (ISIS3), and then used Ames Stereo Pipeline (ASP) to create digital elevation models (DEM) for each site. In Arcmap using the DEMs and the polylines for each slope streak we extracted the slope profiles to determine the starting and stopping slope of each slope streak and then average slope of the entire slope streak. Results indicate that on average slope streaks starts at a slope of 24° and end on a slope of 16° with the ending slope decreasing with increasing flow distance. Also, the majority of slope streaks start on a slope <30°, which is near the dynamic angle of repose. The low start angle and the decreasing stop angle with flow distances indicates an energetic triggering mechanism may be necessary to create a slope streak. Recent research from Heyer et al. (2020) identified dust devil tracks that appear to have triggered slope streaks, supporting our results that are most consistent with a dry and energetic triggering mechanism.