File:Ascraeus Mons Caldera - CTX-CRISM - Flickr - jccwrt.png

The eastern rim of Ascraeus Mons' 24 km wide summit caldera. The caldera is thought to have formed relatively recently in Martian history, with estimates placing it at 100 million years old. The drainage of magma from beneath the summit caused the floor of the caldera (top left) to drop nearly 4 km relative to the surrounding summit region (bottom right). The rocks were torn during the caldera collapse, which formed nesting concentric fractures several hundred meters high.

At 18,225 m above Mars' "sea level" (a reference point where the atmosphere is dense enough that water vapor, liquid water, and gas are in equilibrium at 0C), Ascraeus Mons is Mars' second tallest mountain after Olympus Mons (21,285 m). It is the northern end of a chain of three volcanoes collectively known as the Tharsis Montes. These volcanoes are probably fed by long-lived hot spots in the Martian mantle, and have been active throughout the planet's history.

This image uses 40m/px color imagery collected with the Mars Reconnaissance Orbiter's CRISM imaging spectrometer and 5m/px monochrome imagery collected with the orbiter's CTX camera. The CRISM image was taken on November 9, 2010, and the CTX image was taken on September 9, 2012.