In mid-2010, several smaller barchan dunes are approaching the Carretera from the south.

The orientation of the barchan dunes suggest that they were generated by northeasterly winds.

Smaller barchan dunes often bump into larger ones from behind because they move faster and are carried by winds blowing in one direction.

Any kind of dune, from very fine ripples underfoot to truly gargantuan barchan dunes.

Simple barchan dunes may stretch from meters to a hundred meters or so between the tips of the horns.

Barchan dunes have been observed on Mars, where the thin atmosphere produces winds strong enough to move sand and dust.

A barchan dune will tend to form from a mound of sand, the development envisaged by Bagnold being as follows.

All Vastitas Borealis was barchan dunes, made of black garnet sand."

Barchan dunes are produced by strong winds blowing across a level surface, and are crescent-shaped with the concave side away from the wind.

Small simple barchan dunes and large mega-barchans are common at the margins of Olympia Undae and in areas where the sand cover is thin.

Simple barchan dunes may appear as larger, compound barchan or megabarchan dunes, which may migrate with the wind.

Barchan dunes are also found in the south of the Special Region of Yogyakarta, Indonesia, the largest being at Parangkusumo Beach.

The Great Sand Dunes National Park in the American state of Colorado has spectacular examples of barchan dunes.

Immediately north of the drill, the crests of the great barchan dunes still stuck out of the ice-first as a bumpy beach, then as hundreds of crescent islands.

Under the wind, free snow particles accumulate and drift similarly to barchan dunes of sand, and the resulting drifting snow shapes are also popularly referred to as "barchans".

Olympia Undae contains a variety of dune forms and wind-related (aeolian) depositional features, including sand sheets, transverse dunes, simple barchan dunes, mega-barchans, and complex barchanoid ridges.

As barchan dunes migrate, smaller dunes outpace larger dunes, bumping into the rear of the larger dune and eventually appear to punch through the large dune to appear on the other side.

For many square miles the unimpeded wind had indeed built up great transverse dunes-frozen waves in a burning ocean-but there were harder patches, too, and here the sand had been pushed into the crescent shapes of barchan dunes, all neatly pointing downwind.

Looking down at the ice chaos Nadia suddenly remembered what the land had looked like on that first trip, the endless hills and hollows, the funnel-like alases, the great black barchan dunes, the incredible laminated terrain in the last sands before the polar cap ... all gone now, overwhelmed by ice.