The images, taken January 21, 2013, by the European Space Agency’s (ESA) Mars Express, focus on the southeast segment of the giant volcano, which towers some 14 miles (22 kilometers) above the surrounding plains. This is more than double the height of Mauna Kea, the tallest volcano on Earth at 6 miles (10km), when measured from its oceanic base to summit.
Like Mauna Kea, Olympus Mons is a shield volcano, with gently sloping sides that extend outward at low angles. But unlike other shield volcanoes, it has an abrupt cliff edge, or scarp, separating it from the surrounding plains.
Lava flows cover the base of the volcano, punctuated by a handful of pointy and flat-topped blocks that were either rotated or uplifted during the collapse.
The transition from the towering heights of the volcano down onto the flat lava plain at the base of the scarp can be easily seen in the color-coded topography image.
Flows that ended before reaching the scarp did so with rounded tongues, as the lava cooled and crept to a stop.
Some lava flows are bounded by steep channel walls while others were contained in lava tubes. Zooming in to the top left portion of the flank in the leading image reveals one example of an ancient lava tube, its winding track partially exposed in channel segments where the roof of the tunnel has since collapsed.
Here, only two prominent features are visible: a “wrinkle ridge” in the lower center of the main image, which formed as lava cooled and contracted to buckle up and distort the surface, and a channel system that branches out into a horseshoe shape. This channel was likely carved by lava, but water may have once flowed here, too.
The occurrence of only a few small impact craters in this scene shows that it is relatively young compared with more heavily cratered regions elsewhere on Mars — the older the surface, the greater the exposure time to impact events by asteroids or comets.
For example, the vast lava plain surrounding the volcano truncates the majority of lava flows extending from the flanks, suggesting it is younger still and that it originated from a location outside this scene.
The volcanic region hosting Olympus Mons and several other large volcanoes is thought to have been active until tens of millions of years ago, relatively recent on the planet’s geological timescale that spans 4.6 billion years.