Vertical plan view of the horst and graben landscape of Ascuris Planum
Vertical plan view of the horst and graben landscape of Ascuris Planum
This 200 by 80-kilometre section of Ascuris Planum is a textbook example of the parallel ridges referred to as a ‘horst and graben’ structure. These are created by tectonic forces. If a rigid, brittle rock crust is stretched, due to rising subsurface material, for example, the surface above undergoes tension. If the tensile stress rises above a certain limit, the crust breaks up along steeply sloping fracture surfaces, creating a ‘fault zone’. If the crust continues to expand, large blocks of rock slide down the fracture surfaces several hundred metres, or even one to two thousand metres, forming a tectonic graben. The blocks left standing on both sides now tower above the landscape and form the associated horsts.
