Planetary scientists suspect that the landslides started several 100 million years ago, when large amounts of lava flowed down Olympus Mons. The flows probably deposited on bedrock that contained large amounts of water in the form of ice. The volcanic heat melted this ice, so that the rim areas of the volcano became unstable, broke off and partly slid away. During the collapse, huge rockfalls and landslides dropped from the lower slopes of the shield volcano over hundreds of kilometers of the surrounding volcanic plains. The characteristic crumpled appearance likely resulted during the landslide as material slid away from the volcano and became compressed or pulled apart as it travelled across the surface. Over time, wind erosion of weaker material between the peaks accentuated this effect. The hills and ridges are also covered by fine wind-blown dust. Single aureole landslides can be some hundred meters thick. Due to the superposition of several slides, thickness of more than 2000 m can be reached. This indicates, that multiple collapse events took place. These phases of activity can also be seen in the HRSC observation (see annotated image). Here, the deposit showing a large fracture is overlying the older landslide deposit which ends in the smooth plains.