SLOPE MOVEMENTS IN THE CORDILLERA BLANCA REGION, PERU

Detailed geologic mapping, aerial photograph interpretation, exploratory borings made for instrument installation, and seismic refraction lines delineated five modes of slope movement near the Canon del Pato Hydroelectric Project in the Cordillera Blanca Region of Peru. The bedrock in the area is comprised of shale with interbedded fine-grained sandstone that has undergone contact metamorphism (related to the intrusion of the Cordillera Blanca Batholith) to hornfels and quartzite. Five modes or mechanisms of slope movement were identified: 1) movement of colluvium above the bedrock, 2) chaotic rock falls related to movement along foliation joints, 3) translational sliding of rock blocks with minimal rotation along foliation joints, 4) sliding of rock blocks along relict bedding planes, and 5) sliding along zones of shearing and brecciation related to the batholith intrusion. Movement related to any of these mechanisms can be experienced as a result of gravity, aluviones, rainfall events, high water levels in the river at the base of the slope, and seismic events. Mode 5 movement is presently impacting one of the two intake structures for the hydroelectric project and the other movement modes have the potential to affect the project.