A tectonic aneurysm is an isolated zone of extreme uplift and exhumation rates. This forms when uplift from local tectonics are combined with very weak crust and uplift from a river anticline. When a major river flows over an area of tectonic uplift, the erosion from the river will erode the uplifted material. This will cause extremely rapid exhumation along the major rivers, of up to 10 mm per year. Within the Himalaya there are two tectonic aneurysms, each on one of the two syntaxis of the orogenic belt: Nanga Parbat in the west and Namche Barwa in the east. These tectonic aneurysms form in similar ways to river anticlines, but with extreme erosion rates and very weak and ductile crust. The syntaxis mark the end of the Himalayan orogen on either side and define the location of two large rivers, the Indus and the Yarlung Tsangpo River. The syntaxis on either side of the Himalaya are dominated by a strike slip fault zone, instead of a compressional thrust faulting, as in the rest of the orogen. In the west the Indus River flows through the Nanga Parbat and in the east the Yarlung Tsangpo River flows through the Namche Barwa. The very high erosion rates of these two rivers is coupled with weak, hot, thin, dry, crust to form areas of extreme uplift and exhumation.