LAUSR

Abstract Geological records of past glacier extent can yield important constraints on the timing and magnitude of pre-historic climate change. Here we present a cosmogenic 3He moraine chronology from Mt. Ruapehu in central North Island, New Zealand that records fluctuations of New Zealand's northernmost glaciers over the last 14,000 years. In the Mangaehuehu Glacier catchment, exposure ages and geomorphic observations at our most distal moraine site, relative to the current glacier margin, show that glacial retreat during the last glacial termination was interrupted by one or more readvances between 14 and 11 ka. Further up-valley, moraine boulders deposited at 4.5 ka indicate that glaciers were more extensive during the mid-Holocene than at any later time. The youngest exposure ages in our study, 150–450 years, constrain the formation of moraines situated within 500 m from the present-day Mangaehuehu Glacier terminus. These ages are in agreement with historic sources that show the glacier close to these moraine limits approximately 100 years ago. Overall our data show that glaciers on Mt. Ruapehu retreated c. 3 km since 14 ka, in response to a net rise in the local equlibrium line altitude of c. 400 m. The magnitude of post-industrial snowline rise and glacier retreat on Mt. Ruapehu is also consistent with instrumental temperature data that record approximately 0.9 ∘C of warming during the 20th century.