Olympus Mons Mons aureole deposits (discussed below). Olympus Mons lies at the edge of the Tharsis bulge, an ancient vast volcanic plateau likely formed by the end of the Noachian Period. During the Hesperian, when Olympus Mons began to form, the volcano was located on a shallow slope that descended from the high in Tharsis into the northern lowland basins. Over time, these basins received large volumes of sediment eroded from Tharsis and the southern highlands. The sediments likely contained abundant Noachian-aged phyllosilicates (clays) formed during an early period on Mars when surface water was abundant, and were thickest in the northwest
Olympus Mons large lava lake. Using geometric relationships of caldera dimensions from laboratory models, scientists have estimated that the magma chamber associated with the largest caldera on Olympus Mons lies at a depth of about below the caldera floor. Crater size-frequency distributions on the caldera floors indicate the calderas range in age from 350 Mya to about 150 Mya. All probably formed within 100 million years of each other. Olympus Mons is asymmetrical structurally as well as topographically. The longer, more shallow northwestern flank displays extensional features, such as large slumps and normal faults. In contrast, the volcano's steeper southeastern side has