The Cordillera Blanca Fault is a large normal fault stretching about 200 kilometres along the western foot of the Cordillera Blanca in the Peruvian Andes, home to some of the highest peaks in the tropics. Unlike most Andean faults it is extensional, dropping the Callejón de Huaylas valley down relative to the towering glaciated range to the east.
Its steep, west-facing scarp is one of the clearest active normal-fault scarps in the world, slicing across glacial deposits and offsetting moraines to show that it has moved repeatedly since the last ice age. The extension is thought to reflect the gravitational collapse and uplift of the exceptionally high, thickened crust of the range.
The fault has produced large prehistoric earthquakes recorded in its offset landforms, and it poses a serious hazard to the densely populated Callejón de Huaylas, including the city of Huaraz. The region is also infamous for the 1970 Ancash disaster, whose shaking unleashed a deadly ice-and-rock avalanche onto the town of Yungay.