Landsliding on the Paeroa Fault at Te Kopia

Abstract

The Paeroa Fault scarp in the Te Kopia area has a maximum vertical expression of 525 m. Three rhyolitic ignimbrites derived from the Whakamaaru caldera are exposed. These are the source rocks for numerous debris flow deposits. Thermal fluids have interacted with these rocks for a prolonged period. Alteration marginal to the now active thermal area is dominated by mordenite, which replaces volcanic glass and pumice clasts within the ignimbrites. This is a common feature within all the debris flow deposits exposed at Te Kopia. Other slope deposits are dominated by silicified tuffaceous sediments sourced fkom the Huka Falls Formation, and are identified as hydrothermal eruption breccias. Debris flows, rockfall, earth flows and block sliding are the active slope processes, each producing a distinctive geomorphology and spatial distribution. Mordenite and other hydrothermal minerals probably had an important effect in creating the debris flows.