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Textured gullies

ESP_038389_1105_0.501xA piece of Mars. These are gullies on a martian hillside (upslope is to the upper right). Water may be what forms the channels, carrying soil and rocks downslope. The textured pattern of the lower slope is caused by the wind forming ripples on loose sediment that has been transported partway down the hill. (HiRISE ESP_038389_1105, NASA/JPL/Univ. of Arizona)

Rivers of freezing gas

ESP_038399_0945_1.0xA piece of Mars: This 600×450 m (1969×1476 ft) polar scene shows sinuous channels 2-8 m (7-26 ft) wide carved out of ice-filled and ice-covered terrain. They’re not formed by flowing water, but instead by flowing gas that gets trapped under thick winter ice. The pressure of the underground gas builds until it explodes, forcing its way out, and carrying brown soil with it. Local winds blow the soil downwind (to the upper right), forming distinctive streaks. This happens every year on Mars. Awesome. (HiRISE ESP_038399_0945, NASA/JPL/Univ. of Arizona)

A way through

ESP_037494_1685_0.575xA piece of Mars: Wind ha blown the dark, rippled sand between jagged hills, from top to bottom in this frame (663 m or 2175 ft across). Regardless of the terrain, sand finds a way to get through — just like at the beach, it manages to get everywhere. (HiRISE ESP_037494_1685, NASA/JPL/Univ. of Arizona)

Huge wind-made cliffs

PSP_006694_1895_16384ppdA piece of Mars: Topography in color is draped over an image of a windblown cliff. The entire shape of the landscape here was formed by wind, from the large 400 m (1312 ft) tall zigzag cliff, to the small streamlined shapes in the valley. Even the deep gorge that looks like a stream channel was formed by winds, all blowing toward the upper left. (HiRISE PSP_006694_1895 NASA/JPL/Univ. of Arizona, HRSC ESA/DLR/FU Berlin)

Mars is watching you…

ESP_037995_1755_0.589xA piece of Mars: This looks like a pair of eyes looking at us. It’s really some small brown hills, two of which (the “eyes”) are surrounded by dark gray sand that has blown into scours as the wind interacts with the topography of the hills. It’s a great way to tell what direction the strongest winds blow here: from the bottom to the top of the frame (the frame is 509×382 m or 1670×1253 ft). (HiRISE ESP_037995_1755, NASA/JPL/Univ. of Arizona)

Almost a dune

ESP_038117_1385_1.0x A Piece of Mars: This field of 2 m wide sand ripples has a dark splotch in the middle (the scene is 300×225 m or 984×738 ft). The splotch is the peak of a low hill that straddles the classification gap between proper dunes and simple drifts of sand. Maybe it was a dune that has been modified down to this bump, or maybe it’s a drift that could grow into a dune, if enough sand blew in and accumulated on it. (HiRISE ESP_038117_1385, NASA/JPL/Univ. of Arizona).

Lumpy bumpy dunes

ESP_037203_2555_1.0xA piece of Mars: These funny shaped dunes were formed by winds blowing from two directions – one from the top of the frame and one from the upper right. Both winds make steep slopes (slip faces) on the downwind (lee) sides of the dunes. With enough sand supply, the “point” between the slip faces will continue to extend toward the lower left as the two winds take turns driving the sand back and forth. (HiRISE ESP_037203_2555, NASA/JPL/Univ. of Arizona)

Changing winds

PSP_002387_1985_1.0xA piece of Mars: There are two sets of ripples here: tan ones and gray ones, each oriented to a different wind (scene is 300×225 m, or 984×738 ft). The gray ones sit on top of the tan ones, so the gray ones are younger. Now come the fun questions: why the different colors? Are they made out of different material (and if so, why), or are the older tan ones different because the gray sediment has weathered to tan over time? (HiRISE PSP_002387_1985, NASA/JPL/Univ. of Arizona)

Missing bedrock

ESP_017173_1715_32768ppdA piece of Mars: Wind flow on Mars can be quite dramatic. Here, a single wind-sculpted hill stands 1.5 km (0.93 mi) wide and 600 m (1970 ft) high (color shows elevation). That sounds big, but vastly larger is the volume of material that has been removed to form it. A sandy ridge forming a “bow shock” indicates present-day winds still blow in the same direction. (HiRISE ESP_017173_1715, NASA/JPL/Univ. of Arizona)

Martian waves

ESP_037200_1765_0.501xA piece of Mars: The swirly candy stripes in these big dark dunes are layers inside that have been made visible by wind erosion (the scene is 1.5×0.9 km, or 0.93×0.56 mi). It’s rare to see the inside structure of dunes like this, but these are being eroded by wind blowing from the upper right. For similar examples on Earth, check out The Wave. (HiRISE ESP_037200_1765, NASA/JPL/Univ. of Arizona)