A representation of the Tharsis Ridge, showing the altitude of the volcanoes compared to the surrounding areas. The elevated southern hemisphere is also shown. From Mars Global Surveyor.
Click on image for full size

The Tharsis Ridge

This image, taken from the Mars Global Surveyor mission (MGS), 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 by all spacecraft visiting Mars, including recent ones by Mars Pathfinder and Mars Global Surveyor have indicated that this region of Mars is actually a giant bulge, as shown in the picture. The picture also shows how much higher the southern hemisphere of Mars is than the rest of the planet.

The Ridge probably formed somewhat late in Mars' history. This means that Mars probably had a late warming period, which created the Ridge, with it's volcanoes. The Ridge may have been built in a manner similar to the volcanic rises of Venus, namely by a rising hot balloon of material from the deep interior, which formed land on the surface. The cratering record suggests that after this period of activity, all volcanic activity on Mars ceased.

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more


A "mantle plume" is a bubble of material which rises to the surface layers from the deep interior of the planet. The plume is the red portion shown in the drawing to the left. Such plumes are thought to...more

Plume Volcanism

The Hawaiian Islands are an example of the way some volcanoes are made. A rising hot bubble of material finds it's way into the crust of the Earth from the deep interior, and erupts material unto the surface....more

Mars Global Surveyor Measures Martian Global Hemispheres

Mars Global Surveyor carries an instrument which measures the heights of things. This instrument is called an altimeter, or "altitude-meter". The picture to the left shows Mars Global Surveyor's measurement...more

The Viking Missions

The Viking I and Viking 2 missions were designed to both orbit Mars and land and make exploratory observations on the planet's surface. At this stage in the history of the exploration of Mars, scientists...more

The History of Martian Volcanism

During its earliest history, Mars was bombarded with asteroid-like boulders leftover from the formation of Mars. The impacts of these boulders caused the surface of Mars to become warm enough for continents...more

The Climate of Mars

The unusual climate of Mars makes Mars not quite right for life as we know it on Earth. If the climate were warm enough, water would not freeze into the ground but vaporize into the atmosphere. Lots of...more

The Martian Lithosphere

Like the Earth's lithosphere, the Martian lithosphere is the not-so-rigid part of the crust of Mars which is cooler than the interior of Mars somewhat like the film on top of a cup of hot cocoa. On Earth,...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA