ESA’s Mars Express mission aimed a high-resolution stereo camera (HRSC) at the most imposing volcano on Mars. reveals its spectacular surroundings and turbulent past.
Mars is home to the largest volcanoes in the solar system. The tallest of these is Olympus Mons, a giant shield volcano discovered by NASA’s Mariner 9 spacecraft in 1971. Olympus Mons (Olympus Mountain) is 21.9 km high at its summit. about 2.5 times higher than Mount Everest on Earth above sea level.
The Mariner scientists observed not only the summit of Olympus Mons, but also its surroundings and noted a “halo” that stretched hundreds of kilometers from the base of the volcano. This halo, in turn, surrounds the volcano’s “basal escarpment,” an immediate boundary around Olympus Mons. which is remarkably steep and in some places reaches a height of up to seven kilometers.
These new images reveal a wrinkled structure called Lycus sulci at the edges of the halo; The volcano itself is off the image, lower left (southeast), many hundreds of kilometers away.
The halo, shown particularly well in this 2004 NASA Mars Orbiter Laser Altimeter image and in the context map accompanying this new Mars Express release, tells the story of how the lower flanks of Olympus Mons catastrophically collapsed several hundred million years ago.
Large amounts of lava once flowed down the volcano, causing landslides that tumbled down its flanks onto bedrock, in this case a bedrock containing ice and water.
Choking lava melted this ice and made it unstable. As a result, the cliff edge of Mount Olympus broke and partially slid off. This collapse took the form of massive rockfalls and landslides that tumbled down and spread far across the surrounding plains.
As the landslides moved away from Olympus and across the surface of Mars, they were alternately compressed and stretched; they wrinkled and separated. This created the characteristic folds seen in these new images of Lycus sulci, as ESA reports.
After its formation, Lycus Sulci became even more apparent over time as winds whipped across the Martian surface and eroded the material. This wind also picked up dust, carried it across the length and breadth of Mars, and later spread this fine sand over nearby hills and ridges.
Individual landslides like those at Olympus Mons can be several hundred meters thick. But for this giant, which suffered multiple colossal and intersecting collapses, they can be up to two kilometers thick.
This landslide overlap is clearly visible in the annotated image. The wrinkled terrain to the right of the painting predates the overlying folds to the left, which flowed down the slopes of the volcano later in Martian history.
Despite their extraterrestrial dimensions, the volcanoes on Mars bear similarities to those on Earth. Similar landslides—in type, if not magnitude—are seen around the volcanic islands of Hawaii and the Canary Islands, which have experienced large rock falls in the past.
Another feature that highlights the truly immense proportions of Olympus Mons can be seen in Yelwa Crater on the right of the image. Although dwarfed by the giant Lycus Sulci, this crater is more than 8 km in diameter, putting it just below the height of Mount Everest above sea level.
Located more than 1,000 kilometers from the top of Mount Olympus, Yelwa Crater shows how far destructive landslides traveled from the volcano’s flanks before settling down.