Strong earthquakes of 22 May 1960 produced three large landslides which blocked the outlet of Lago Riñihue, 65 kilometers east of the city of Valdivia, Chile. The lake level rose 26.5 meters before water began discharging through artificially constructed canals during the last week in June, 1960. The largest landslide involved about 30 million cubic meters of unconsolidated sediments, the intermediate landslide about 6 million cubic meters, and the smallest landslide about 2 million cubic meters.
The surface of rupture of the largest landslide is within an 80-meter sequence of Pleistocene lake clays. The clays are underlain by till and overlain by outwash sands and gravels. Movement of the landslide is interpreted as having been principally block gliding and lateral spreading. Secondary landslides within the larger landslide were produced by rotational slumping, debris falls, and earth flows.
Several ancient landslides exist in the vicinity of Lago Riñihue, the largest involving more than 100 million cubic meters of unconsolidated sediments. Many of the older landslides also were probably triggered by earthquakes.