High intensity rainstorms and geological hazards: Cyclone Alison, March 1975, Kaikoura, New Zealand

Abstract

In the 48-hour period from 9 am (NZST) on 11 March 1975, much of the coastal area surrounding Kaikoura, South Island, New Zealand, was severely damaged by high intensity (4 to 12 hour duration) rainfalls resulting from the passage of Cyclone Alison. Extensive regolith mass movements of the debris slide — avalanche — flow types occurred within the steep coastal catchments, and rapid stream aggradation and erosion caused damage in excess of NZ$ 1 million to railway and highway installations. The geologic and geomorphic setting of the Kaikoura area is such that similar ‘catastrophic’ events have almost certainly occurred during geologically recent times, and can be expected to recur in the future. The computed return period for the high intensity rainfalls accompanying Cyclone Alsion exceeds 200 years at the Kaikoura Peninsula meteorological station (Tomlinson, 1975), but there are obvious economic and engineering limitations to the minimisation of future damage.