Olympus Mons is a shield volcano on Mars and it is the largest volcano in the Solar System. Located in the Tharsis region of the planet along with three other large volcanoes, Olympus Mons measures an incredible 27 km in height and is 3 times taller than Mount Everest. It is about 500 km in diameter. The mountain was formed from a single hotspot that flowed for thousands, if not millions, of years. The lack of plate tectonics that allowed this unhindered flow also prevented massive pressure buildups that would have blown the top off of the volcano, decreasing its overall height.