collapse events; and (6) estimating the long-term eruption rates of composite volcanoes. 2. Geologic setting 2.1. Regional geology Volcanism in central North Island, New Zealand, is associated with westward subduction of oceanic crust of the Pacific Plate at ~45 mm yr-1 beneath the Australian Plate along the Hikurangi Trench system (Fig. 1; Cole and Lewis, 1981; Reyners et al., 2006; DeMets et al., 2010). Most arc-related volcanism is manifested in the Taupo Volcanic Zone (TVZ), a rifting arc active since 2 Ma, which comprises northern and southern segments dominated by andesite-dacite composite cones and a rhyolite-dominated central segment (Wilson et al., 1995). The southern TVZ segment comprises the prominent Tongariro and Ruapehu composite volcanoes as well as several smaller inactive volcanic edifices, which collectively form the Tongariro Volcanic Centre (Fig. 1; Cole, 1978). Rifting and extension in the southern TVZ occurs at a direction of ~115° and a rate of 2.3 ± 1.2 mm yr-1 (Villamor and Berryman, 2006a). This motion is manifested by the 40 km-wide Mount Ruapehu graben, which is bounded by the Rangipo and Raurimu faults to the east and west, respectively, and by the NE-striking Karioi and the ENE-striking Ohakune fault sets to the south (Fig. 1; Villamor and Berryman, 2006b). Ruapehu volcano sits on late Tertiary sediments and Mesozoic basement rocks ('greywacke'). The latter are generally inferred to be part of the Kaweka Terrane, a Jurassic greywacke-argillite sequence of felsic composition that outcrops in the ranges east of the Rangipo Fault (Adams et al., 2009; Lee et al., 2011; Price et al., 2015). An index map of Ruapehu with geographical features referred to throughout the text is provided in Fig. 2. 2.2. Volcanological overview Ruapehu is New Zealand's largest active andesite volcano, with a ~150 km 3 edifice surrounded by a volcaniclastic ring plain of similar volume (Hackett and Houghton, 1989; Gamble et al., 2003). The flanks of the edifice are composed of lava flows and autobreccias

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Calculation of surface exposure ages, using in situ cosmogenic nuclides, requires accurate knowledge of local production rates. Here, we report the first attempt to calibrate cosmogenic 3 He production in the south-west Pacific region. We present a new radiocarbon chronology that precisely dates the emplacement of the Murimotu Formation, a large debris avalanche deposit in central North Island, New Zealand (ca. 830 m asl; 39˚S), which occurred 10.4-10.6 cal ka BP. Measurements of cosmogenic 3 He in pyroxene separated from large andesitic blocks exposed during this event yield a sea-level high-latitude production rate of 120 AE 12 atoms g À1 a À1 ('Lm' scaling). This is consistent with a recent global compilation, comprised predominantly of calibration sites located in the Northern Hemisphere. Thus, we conclude that the globally compiled cosmogenic 3 He production rate is valid in the south-west Pacific. Using independent, proximal calibrations of cosmogenic isotopes

Geological records of mountain glacier fluctuations provide useful evidence for tracing the magnitude and rate of past temperature change. In this study, we present air temperature reconstructions for the last glacial termination in New Zealand derived using snowline reconstructions and numerical glacier modelling. We target the Arthur's Pass moraines in the Otira River catchment, which have previously been dated to the Lateglacial using cosmogenic 10Be. Recalculation of these exposure ages using a locally calibrated 10Be production rate indicates that these moraines formed ca. 16–14 ka. Our glacier modelling experiments and snowline reconstructions exhibit good agreement and show that the Arthur's Pass moraines formed in a climate that was 2.2–3.5 °C colder than present. Combining our results with other, proximal glacier records shows that ice in this catchment retreated ca. 50 km from the coastal plain to the main divide during the interval 17–15 ka, in response to a temperature increase of at least ca. 3 °C. Over half of this retreat occurred after the glacier had withdrawn from an overdeepened basin. Thus, we conclude that temperature increase was the primary driver of widespread and rapid glacier retreat in New Zealand at the onset of the last glacial termination.

Abstract. Quantitative palaeoclimate reconstructions provide data for evaluating the mechanisms of past, natural climate variability. Geometries of former mountain glaciers, constrained by moraine mapping, afford the opportunity to reconstruct palaeoclimate, due to the close relationship between ice extent and local climate. In this study, we present results from a series of experiments using a 2-D coupled energy balance-ice flow model that investigate the palaeoclimate significance of Last Glacial Maximum moraines within nine catchments in the central North Island, New Zealand. We find that the former ice limits can be simulated when present-day temperatures are reduced by between 4 and 7 • C, if precipitation remains unchanged from present. The spread in the results between the nine catchments is likely to represent the combination of chronological and model uncertainties. The majority of catchments targeted require temperature decreases of 5.1 to 6.3 • C to simulate the former glaciers, which represents our best estimate of the temperature anomaly in the central North Island, New Zealand, during the Last Glacial Maximum. A decrease in precipitation of up to 25 % from present, as suggested by proxy evidence and climate models, increases the magnitude of the required temperature changes by up to 0.8 • C. Glacier model experiments using reconstructed topographies that exclude the volume of post-glacial (< 15 ka) volcanism generally increased the magnitude of cooling required to simulate the former ice limits by up to 0.5 • C. Our palaeotemperature estimates expand the spatial coverage of proxy-based quantitative palaeoclimate reconstructions in New Zealand. Our results are also consistent with independent, proximal temperature reconstructions from fossil groundwater and pollen assemblages, as well as similar glacier modelling reconstructions from the central Southern Alps, which suggest air temperatures were ca. 6 • C lower than present across New Zealand during the Last Glacial Maximum.