Exploratour - The Surface of Mars
Tharsis Ridge
This picture shows the Tharsis Ridge, the green/blue area in the middle of the picture, as well as a portion of the southern hemisphere of Mars. The green areas are higher than the surroundings, and the yellow/white regions, which are actually Martian volcanoes, are the highest of all. The red line in the picture is the spacecraft measurement which indicates just how large the regions are compared to one another.
The Tharsis Ridge is a region about twice the size of the United States (8000 km), and is where many of the volcanoes of Mars are found. Measurements have shown that this region of Mars is actually a giant bulge, as shown in the picture.
The Ridge may have been built in a manner similar to the volcanic rises of Venus, namely by a rising hot plume from the deep interior, which formed land on the surface. The Ridge formed somewhat late in Mars' history. This means that Mars probably had a late warming time, which created the Ridge.