On the floor of this crater where there are no dunes, the ice forms an uninterrupted layer.
On the dunes however, dark streaks form as surface material from below the ice is mobilized and deposited on top of the ice. In some cases this mobile material probably slides down the steep face of the dune, while in other cases it may be literally blown out in a process of gas release similar to removing a cork from a champagne bottle.

Image is less than 1 km (less than 1 mile) and is 3165 km (196 mi) above the surface. For full image including scale bars and additional information, visit the source link.

NASA/JPL/UArizona Larger image