THARSIS

Tharsis region of Mars. A number of volcanoes are visible in this picture, which is a composite of enormous domed volcanic province on Mars. The name was initially given to a bright region mapped from Earth. After detailed geologic mapping by the U.S. Mariner 9 planetary probe in 1972, the lava plain was called Tharsis Planitia. The plain is some 4,800 km (2,980 miles) across and rises to an elevation of about 6 km (3.7 miles) above the mean radius of Mars. It is capped by several shield volcanoes that stand 24 km (about 15 miles) or higher. These volcanoes are the largest known in the solar system. Olympus Mons is the most noteworthy of the group. False-colour picture of Memnonia Fossae, near Tharsis. The craters in the Patterns of roughly radial valleys and fractures emerge from Tharsis, and lava-flow units can be recognized on its surface. Lava ages are estimated from crater counts to be about one to three billion years old, but some individual volcanic features may be younger. The Tharsis dome may have been formed both by uplift and by the buildup of lava flows. Dynamical analyses suggest that the Martian axial tilt was altered by the formation of the Tharsis bulge, with an ensuing climate change over the entire planet. This is supported in that the Tharsis region is little-modified by the winding channels characteristic of older Martian regions. Such channels may have been cut by flowing water under pre-Tharsis climatic conditions. The post-Tharsis Martian axial tilt may have caused more of the water to become permanently frozen.