Debris avalanches caused by the collapse of volcanic flanks may permanently change the surrounding landscape and its drainage systems. Deposits of a two- to three-cubic-kilometer debris avalanche exposed along the Hautapu River about 50 km southeast of Mount Ruapehu, New Zealand, reflect the largest known collapse event of the stratovolcano, followed by a regrowth phase that produced pyroclastic eruptions and pumice-rich lahars.
The collapse most likely occurred due to magmatic unrest during the shift from a glacial to an interglacial climate. The debris avalanche inundated an area of more than 260 square kilometers, and was channelized within the proto-Hautapu catchment.
The subsequent pumiceous mass-wasting events continued to be confined to the proto-Hautapu River for another approx. ten thousand years.
At present the volcaniclastic deposits form a distinctive plateau on the highest topographic elevation within the river valley, while the Hautapu River incises into the underlying softer late Pliocene sediments.
Impacts of catastrophic volcanic collapse on the erosion and morphology of a distal fluvial landscape: Hautapu River, Mount Ruapehu, New Zealand M. Tost et al., Volcanic Risk Solutions, Massey University, Palmerston North 4442, New Zealand. Published online 26 Aug. 2014; http://dx.doi.org/10.1130/B31010.1.