Global Dust Storm. The early stages in the development of the first global dust storm were observed by Viking Orbiter 2 in the Thaumasia region. It shows an area several thousand kilometers wide seething with turbulent clouds of dust. This storm spread rapidly to higher altitudes, and suspended dust obscured much of the planet for a period of 50 days. Increased solar heating as Mars nears perihelion is thought to provide the energy that creates these large-scale disturbances.
North is to the upper right.