Dark streaks are thought to be caused by the removal of a thin veneer of dust, revealing a darker surface beneath. The materials may or may not be the same; in general, the more finely a given substance is divided, the higher its albedo. Dark streaks have been observed to develop and change significantly in short amounts of time, which is consistent with the speed at which erosion of a thin dust layer could occur. Dark streaks are almost always associated with craters or topographic obstructions, in whose wake turbulence will enhance erosion. The two frames shown were taken only 30 (Earth) days apart. (Location: Latitude -30.7°, Longitude 119°.
(a) Viking photograph 603A08, NGF orthographic version, red filter. (b) Viking photograph 639A67, NGF rectilinear version, red filter.)