Like the frozen waves of an ocean, the chains of hills in Lycus Sulci (the ‘furrows of Lycia’) cover the Amazonis Planitia lowlands that lie to the northwest of the Olympus Mons volcano. This undulating area, characterised by long ridges and intervening valleys, stretches for hundreds of kilometres. This image is approximately 50 kilometres wide in the foreground. The characteristic undulating appearance of this landscape was probably created by compressing and spreading out of rock masses mobilised by lava flows as they were pushed over the landscape. Over time, this effect was accentuated by the erosion of less resistant material between the ridges.