HRSC: Impact crater or supervolcano caldera?

At first glance, the region covered by this latest Mars Express image release appears to be pockmarked with impact craters. But the largest structure among them may hold a rather explosive secret: it could be remains of an ancient supervolcano. The images presented here were taken by the high-resolution stereo camera on ESA’s Mars Express on 26 November 2014, and focus on the Siloe Patera feature in the Arabia Terra region of Mars. Siloe Patera comprises two large nested craters, close to the centre of the main colour image. The outer rim measures about 40 x 30 km and, at its deepest point, the crater dips as low as 1750 m below the surrounding plains. Some scientists believe that Siloe Patera and a number of similar features in Arabia Terra are calderas, the collapsed centres of volcanoes. But not just any volcanoes: these are thought to be martian supervolcanoes…. [More at link]