English: Ascraeus Mons is the northernmost of three volcanos near the equator of the planet Mars. This Mars Global Surveyor Mars Orbiter Camera image shows the wall on one of the calderae at the summit of the large volcano, Ascraeus Mons. A caldera is a large depression formed by collapse after magma in a volcano is erupted from or withdrawn to a greater depth. After collapse, the wall of this caldera was further modified by downslope movement of debris and it was pelted by small meteors to form a scattering of small craters. This image is located near 11.6°N, 104.6°W, and covers an area about 3 km (1.9 mi) across. The picture is illuminated by sunlight from the lower left.