This image shows dark sand dunes in Chasma Boreale. Chasma Boreale is a giant trough that cuts into the north polar ice cap for 570 kilometers (350 miles) forming a broad valley bordered by stacked layers of ice. A portion of the north polar ice cap is visible at the northern edge of the trough in the upper portion of the image.

Many dark toned sand dunes march down the trough under the wind’s direction. The sand dunes visible here are barchan dunes. Barchan dunes are also commonly found on Earth, and are crescent-shaped with a steep slip face bordered by horns oriented in the downwind direction. Barchan dunes form by uni-directional winds and thus are good indicators of the dominant wind direction. In this case, the dunes indicate that the direction of the strongest winds are parallel to the chasma walls, roughly east to west. The dark material composing the dunes could be volcanic ash or is possibly dark sand eroding out of the polar layered materials.

Written by: Maria Banks   (19 November 2008)

More info and image formats at http://hirise.lpl.arizona.edu/PSP_010169_2650

Image: NASA/JPL/University of Arizona