Olympus Mons, found near the Martian equator, is the largest volcano in the solar system. At a height of 25 km, it rises three times taller than Mount Everest’s height above sea level. Mons has a very gentle slope. It is up to 550 km at its base. The edge of the volcano’s base is marked by a basal cliff that is 6 km high in some places, but has been eradicated by the overflow of lava in the Martian past.
Olympus Mons is the result of many thousands of basaltic lava flows. The extraordinary size of the volcano has been attributed to the lack of tectonic plate movement on the planet. The lack of movement allows the Martian crust to remain fixed in place over a magma hotspot allowing repeated, large lava flows. Many of these flows have levees along their edges. The cooler, outer margins of the flow solidify, forming the levees and leaving a central trough of molten, flowing lava.
Picture Credit : Google