Two directions

A Piece of Mars: Sometimes I just want to show the interior of a dune field, because it’s full of waves: ripples and dune crests, slip faces, all of which signs of movement. The dunes in this 0.67×0.47 km (0.41×0.29 mi) view have been made by two winds: one blowing from the top of the

Tortoise and hare

A Piece of Mars: There’s a lot of evidence for both fast and slow movement in this 480×270 m (0.3×0.17 mi) scene. The tortoise: The rippled surface at the top is high ground: the top of a dune. Wind pushes the ripples toward a steep sunlit slope, creating long thin, dark avalanches that slowly inch

Grainfall

A Piece of Mars: The dunes climbing over a rocky surface in this 0.96×0.54 km (0.6×0.34 mi) scene are mostly yellow because they’re covered (and therefore kept immobile) by dust. The crest of one dune, though, shows recent activity: dark sand has been pushed by the wind up the lower right side, and then shot

Light and dark

A Piece of Mars: This 0.96×0.54 km (0.6×0.34 mi) late winter scene is a study in contrast. The dark top half is uniformly rippled. This is the shady surface of the main windward side of one of Mars’ biggest dunes, in Kaiser crater. On the bottom is the sunlit side of the dune, strewn with

Stealth bomber dunes

A piece of Mars: These dunes look strangely triangular, a little bit like a flock of stealth bombers. Why? They’re two-faced barchans. Each flat face is an avalanche slope that faces downwind, formed by one of two distinct wind patterns that blow in this area (probably seasonally). Dunes like this can form on Earth, but

The looming dune

A piece of Mars: this 0.96×0.54 km (0.6×0.33 mi) scene shows a large, rippled dune that is slowly marching towards the upper right. The smooth striped band running from upper left to lower right is the slip face, where sand pushed by the wind eventually avalanches. Smaller scars show where slope failures (little landslides) have