The Acheron rock avalanche deposit, Canterbury, New Zealand: Age and implications for dating landslides

Abstract

New radiocarbon ages for wood samples retrieved from the base of the Acheron rock avalanche near Porters Pass, Canterbury, show a clustering of ages between 1370 and 1101 yr BP. This is significantly dissimilar to the established radiocarbon age of 500 ±69 yr BP (NZ547), from weathering-rind thickness measurements and from lichen studies. This contradiction impacts on current calibrations of lichenometric and weathering-rind dating methods, which has serious implications for landslide and earthquake dates based on them. A 500-600 yr BP earthquake event along the Porters Pass-Amberley Fault Zone has been dated in an adjacent trench and is consistent with previous dates but does not correspond to the Acheron rock avalanche emplacement as previously proposed. The landslide may have been caused by either a Porters Pass Fault event (1100-800 yr BP) or by the better-constrained Round Top event (1010 + 50 yr BP) on the Alpine Fault. © 2012 The Royal Society of New Zealand.