Abstract

In October 1981 a mass of rock and soil having an estimated volume of 500,000 m3 fell as a rock fall-avalanche from a steep slope 800 m high near the head of Olokele Canyon on the island of Kauai, Hawaii. Boulders were launched into the air from a bench on the slope for a downstream distance of about 850 m. The velocity of the avalanche was rapidly diminished by impact against the valley sides, and it became a muddy debris flow that traveled 4.6 km downstream, severely eroding the valley sides. The volume of debris deposited on the canyon bottom is estimated to be 2,500,000 m3, or about four times the volume derived from the slope. Slope failure is attributed to gradual undercutting and loss of shear strength in beds of weathered ash and to joints in a thick basaltic cap rock.

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