barchan

December 27, 2013

Wintery dune

A piece of Mars: A single dune sits on the surface of Mars, not too far from the north pole. It’s early spring, but this far north the dune is still covered in white CO2 frost (as well as a […]
October 25, 2013

Are you being oblique?

A piece of Mars: Barchan, or crescent dunes, are generally thought to form from winds blowing from a single direction. Reality isn’t usually that nice. Here are two barchans with crescent-shaped slip faces on their eastern (right) sides, indicating that […]
September 4, 2013

Martian sports

A piece of Mars: In the center are two dark dunes, racing one another to jump over hurdles formed of older, now inactive dunes (or maybe those bright things are ripples, we still don’t know for sure). The dune in […]
January 11, 2013

Bright and dark sand on a dune

A piece of Mars: A lovely little dune is right at the edge of this image, trying its best to migrate into the center of the frame. The bright sickle-shaped part of the dune is its slip face, where sand […]
December 6, 2012

Crescents and ripples

A piece of Mars: A lonely dune slowly makes its way (towards the upper right) across a plain. Well, look closer, it’s not all that lonely. Surrounding it on the plain are smaller streaks that are ripples, which also once […]
July 14, 2012

Barely a dune

A piece of Mars: What makes a dune different from a random pile of sand? Usually the requirement is that it has a “slipface”, a steep avalanching slope. The central dune in the image here has a small one, making […]
July 11, 2012

Wrapping around

A piece of Mars: Dunes near the north pole of Mars form in a very cold environment. Winter ice continually tries to stop them in their tracks, which makes for unusually rounded dunes like these. (HiRISE ESP_027451_2635)
May 13, 2012

One perfect barchan on Mars

A piece of Mars: In nature most dunes pile on one another or strongly influence each other. But occasionally, like a perfect flower or crystal, you find a perfectly shaped dune. Here is a crescentic dune, called a “barchan”, formed […]