Images and caption contributed by Dr. Lori Fenton.
A yardang is a topographical feature that has been carved out of a surface by the wind. The word is derived from the Turkic word yar, which means ridge or steep bank. On Earth they are most commonly found in deserts where there is a sand supply, which abrades the surface when moved by the wind, and soft sedimentary rocks that the sand easily erodes. Over time, the sand wears down the surface into beautiful streamlined shapes that are aligned with the prevailing sand-moving winds.
Image 1: Emmenides Dorsum on Mars. Image captured with the Thermal Emission Imaging System visual camera (THEMIS VIS V12350012), taken on Sept. 26, 2004. Yardangs reveal that this surface has been wind-sculpted and planed off by ~450 m.
Image 1 shows a region on Mars called Emmenides Dorsum, a high flat plain about 1000 km southwest of Olympus Planitia. The many long, needle-like features are yardangs that have been cut into an easily eroded (possibly sedimentary) unit. There are several small buttes and mesas that are erosional remnants, indicating the level of a former surface that has since been almost entirely stripped away by sand abrasion. A shadow measurement from one of the buttes indicates that ~450 m of sediment has been removed from this surface. Some of the mesas have a circular shape, suggestive of former craters. This indicates that the former high surface remained uneroded long enough for a few craters to impact it.
Image 2: The Lut Desert, Iran. The image is a Digital Globe image from Google Earth. To find this location in Google Maps type the following coordinates into the 'Find...' bar and display the 'satellite' image: 30° 35' 38.78" N, 58° 16' 0.25" E. You may need to zoom out to see the image.
The second image shows yardangs in the Lut Desert of Iran. These yardangs are of comparable size to the martian yardangs in Image. 1. The dark material in the lanes between the yardangs is sand that is traveling downwind to a sand sea south of this yardang field. In this case, the sand that has eroded the surface is still present and actively changing the landscape. In the martian case, the sand may be long gone, reflecting an ancient climate regime in which winds were strong and sand was plentiful.
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