Pits, Hollows and Viscous Flow

The mid-latitudes of Mars are draped with deposits of water ice and dust on the order of tens of meters thick. The deposits are preserved to varying degrees, depending on latitude and the degree of dust cover that insulates and protects the ice from subliming away. These mantling deposits are thought to have been mobilized from the polar caps and redeposited from the atmosphere millions of years ago during periods when Mars' axial tilt was higher than it is today.