Olympus Mons

Olympus Mons lies on Mars in the Tharsis region. Encyclopaedia Britannica describes its central edifice as about 22 kilometres high and 700 kilometres across, with an outward-facing escarpment reaching as much as 10 kilometres above the surrounding terrain. Such measurements depend on the reference elevation used on Mars. NASA identifies it as the largest volcano in the Solar System.

The volcano's wide profile and gently sloping flanks are characteristic of a shield volcano. NASA describes Olympus Mons as having been built by fluid lava that accumulated over time. The relatively stable Martian crust, together with a long period of volcanic construction, helps explain how a volcano could grow to such an exceptional size; the detailed history is a subject of planetary-geology research.

At the summit is a large, nested caldera. A U.S. Geological Survey map describes six overlapping collapse pits that together measure approximately 65 by 80 kilometres, along with wrinkle ridges, graben and lava-flow features. These mapped structures indicate a complex sequence of volcanic activity and changes to the summit. The caldera is a collapse feature, not a single simple crater.

Olympus Mons has been studied using spacecraft images, topographic measurements and geological mapping. Images from the European Space Agency's Mars Express spacecraft have documented the volcano, while the U.S. Geological Survey's detailed caldera map integrates surface and topographic evidence. Because direct field sampling has not taken place there, interpretations rely on remote observations and comparative planetary geology.