Dunes not in the global dune database
When the martian surface is eroded, pretty things emerge
July 25, 2016Fossil dunes
August 8, 2016
A Piece of Mars: Ten years ago I participated in a global survey of martian dunes. But we missed a few dune fields, like these beauties. They’re small, low, and in rugged terrain, which made them difficult to spot in the lower resolution data set we used. I keep a list of dune fields we’ll have to add if we get a chance to update the database. This scene is 0.96.0.54 km (0.6×0.34 mi) wide. (HiRISE ESP_043582_1555, NASA/JPL/Univ. of Arizona)
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Wow! Really, really lovely. I’ve had a look at the full Hirise image. Those are probably rippunes covering the dunes, something like the ones on Namib where they are, as here, noted to have very nearly the same width on all the dune surfaces, though they vary in height and shape – from sinuous to quite linear. I couldn’t find a slip face on any of the dunes in the full image. I understand that dunes without slip faces are are rare type on Earth and the presence of avalanching is normally a part of what we mean by a dune. Are we sure we should be calling these dunes? Maybe they don’t need any big slip faces if the individual rippunes have their own, but if these turn out to be that different in the way they move then maybe they’ll need a new name anyway.
Many of the dunes seem to be situated in particular places in the rocky landscape, with their north-west margins against projecting rock. There are several smaller rippune covered areas in craters and other small depressions. I think that some of these will expand into dunes which probably don’t move downwind but rather grow larger and “live” near the depression where they were “born”. Its hard to explain the strong spatial correlation with the bedrock topography unless these “dunes” are anchored in one place.