Distribution of large rock avalanche deposits in the central Southern Alps, New Zealand

Deposits from 46 Holocene rock avalanches, with volumes ranging from 1 000 000 m 3 to 500 000 000 m 3 , have been identified from aerial photographs of the Southern Alps between Arthur's Pass and Mt Cook. The rock avalanches occur mainly in the eastern Southern Alps, in Torlesse Supergroup rocks. Rock avalanches are rare in schist terrain. Rock avalanching is a significant slope process in the Southern Alps. In the last 2000 years, 19 large rock avalanches have moved about 1 000 000 000 m 3 of material; equivalent to an areally averaged erosion rate of 100 t/km 2 per year, although the material is seldom moved far from its source. Rock avalanche deposits may be a significant sediment source for major rivers in the Southern Alps. The average annual yield of 36 000 t from a rock avalanche in the Jollie River is more than the measured annual sediment yield of the river.