View of the western part of the upper reaches of Nirgal Vallis
View of the western part of the upper reaches of Nirgal Vallis
Nirgal Vallis stretches 700 kilometres across the southern Martian Highlands; north is to the right in the image. The shape of the main valley and its remarkably short side valleys is somewhat unusual when compared to the morphology of most river valleys on Earth. The cross section of the valley is a striking U-shape, with very steep scarps several hundred metres high at the sides and a flat, broad valley floor. Particularly striking are the two impact craters that are almost identical in size, but which have eroded in very different ways. These can be seen at the bottom right and upper left edges of the image. Each measures approximately 20 kilometres across. Partially lobular ejecta blankets can be clearly seen around both craters. The highland plain in which Nirgal Vallis was created by the outflow of water consists of solidified, low-viscosity flood basalts.
