Two distinctly different terrain types are visible in this image of the northern lowlands of Mars.

An older, heavily cratered landscape has been inundated by much younger flows. The valley floors are filled with flows that have relatively smooth surfaces and very few superposed impact craters.

In contrast, the mesas and hills making up the older terrain have blocky surfaces, perhaps fragmented by ancient impacts. The smooth surfaces of the flows are punctuated by curved, subparallel fractures oriented transverse to the flow direction. These cracks resemble crevasses in terrestrial glaciers and were formed when the brittle solid crust of the flow fractured as it was dragged downstream. Detailed images such as this will help determine the role ice may have played in these flows.Written by: Paul Geissler   (3 February 2008)