The AD 930 long-runout Round Top debris avalanche, Westland, New Zealand

Abstract

A major landslide from the faulted range front between the Toaroha and Hokitika Rivers, central Westland, New Zealand, probably resulted from an earthquake on the Alpine Fault at AD 930 ± 50 yr. The 550 m high asymmetric scarp on Round Top, through which the Alpine Fault trace passes, is the source of a deposit of avalanche debris with a volume of c. 45 Mm3 spread over an area of more than 5 km2. The avalanche, which flowed more than 4 km from its source overan alluvial plain, is an example of a life-threatening hazard which has not previously been given adequate attention in Westland. Here, I describe the internal fracturing and faulting of the hummocky deposit, and compare its 570 m vertical fall and 4800 m runout distance with another nearby avalanche. © 1998 Taylor & Francis Group, LLC.