A major rockfall and debris slide on the Lyell Glacier, South Georgia

A major rockfall occurred near the summit of Paulsen Peak (1877 m) and initiated a slide of rock, firn, and ice debris 4 km down the Lyell Glacier, South Georgia, through a total vertical height of approximately 1630 m. From a seismic record it is calculated that the average velocity of the rockfall and slide was 60 km h-1. The excessive travel distance of the slide is explained by a grain flow mechanism in a fluid medium of suspended particles. Large quantities of windborne dust were deposited over 110 km2 downwind. By comparison of the slide volume with that of supraglacial debris elsewhere on the glacier, it is estimated that the rockfall represents a minimum of 93 years' "normal" subaerial erosion. Similar high-magnitude, low-frequency processes could play an important role in cirque formation. The distribution of the slide debris is not related to direct glacier transport, and its extensive spread some 2 km beyond the equilibrium line may influence the mass balance of the glacier.

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