Dust storms are not the only aeolian activity observed on Mars; dust devils have also been seen. They are common in many areas on Earth and are caused by a temperature instability in the lower atmosphere due to strong solar heating of the surface. The hot air rises and cooler air rushes in to replace it, often forming a small vortex. On Earth, dust devils can become large enough to cause minor damage to buildings, etc.; these on Mars are even bigger. The dust devils and their shadows are marked by arrows in (a); the same area without the dust devils is shown in (b). The vertical black-and-white arrows denote the same feature in each view. The vertical streaks and regularly spaced dots in (a) are photographic artifacts.
Location: Latitude 40.3°, Longitude 144.7°, in Arcadia Planitia. (a) Viking photograph 038B25, NGF orthographic version, clear filter. (b) Viking photograph 112A25, NGF orthographic version, green filter.