This image from NASA Mars Odyssey shows Pavonis Mons, one of the three huge Tharsis volcanoes, encircled on the west side by a series of arcuate ridges. How these features were formed is still unknown.
This image from NASA Mars Odyssey shows Pavonis Mons, one of the three huge Tharsis volcanoes, encircled on the west side by a series of arcuate ridges. How these features were formed is still unknown.