Anthropogenic deforestation increases rockfall hazard in southern Christchurch, New Zealand.

Developing a robust chronology for mass-movement events is of crucial importance to understanding triggering mechanisms and assessing hazards. We constrain the emplacement time of four palaeorockfall boulders near Christchurch, New Zealand, using optically stimulated luminescence (OSL) of quartz and infrared stimulated luminescence dating (IRSL) of K-feldspar from colluvial loess deposits underlying and upslope of individual boulders. The quartz OSL and K-feldspar pIRIR 290 ages are all consistent with the stratigraphy and in excellent agreement with each other, indicating that all the boulders that overlie the in-situ loess and oldest loess colluvium unit must have been emplaced < 13 ka ago. A comparison of luminescence ages with cosmogenic 3 He surface-exposure ages from the surfaces of each boulder shows that two out of four boulders contain pre-deposition 3 He inheritance.Overall, the optical ages are consistent with both a prehistoric rockfall event at ~8-6 ka and a possible preceding event at ~14-13 ka, although the temporal resolution of the time of emplacement of individual boulders is ca. 3-5 ka. This resolution is not limited by age uncertainties but rather by the stratigraphy. This study is the first to show a successful application of luminescence dating to New

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Optical and radiocarbon dating of loessic hillslope sediments in New Zealand's South Island is used to constrain the timing of prehistoric rockfalls and associated seismic events, quantify spatial and temporal patterns of landscape evolution, and examine hillslope responses to climatic and anthropogenic forcing. Exploratory trenches adjacent to prehistoric boulders enable stratigraphic analysis of loess and loesscolluvium pre-and post-boulder emplacement sediments. Luminescence ages from colluvial sediments constrain timing of boulder emplacement to between ~3.0 and ~12.5 ka, well before the arrival of Polynesians (c. AD 1280) and Europeans (c. AD 1800) in New Zealand. Three phases of colluviation are revealed at the Rapaki study site, reflecting natural and anthropogenic-driven shifts in sedimentation and landscape evolution. Sediment accumulation rates increased considerably (>15 factor increase) following human arrival and associated anthropogenic burning of hillslope vegetation. Phytolith results suggest paleo-vegetation at Rapaki was compositionally variable and persisted under a predominantly cool temperature environment with warm-temperate elements. Palm phytolith abundances imply maximum climate warming during early (~12-11 ka) and late (~3-2 ka) Holocene phases. This study provides insights into the spatial and temporal patterns of hillslope evolution, highlighting the roles of climate change, earthquakes, and humans on surface processes.Keywords: rockfall, paleoseismicity, hillslope response, OSL, radiocarbon 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 2 patterns of hillslope evolution, highlighting the roles of climate change, earthquakes, and humans on surface processes.

We provide a summary of the surface fault ruptures produced by the Mw7.8 14 November 2016 Kaikōura earthquake, including examples of damage to engineered structures, transportation networks and farming infrastructure produced by direct fault surface rupture displacement. We also provide an overview of the earthquake in the context of the earthquake source model and estimated ground motions from the current (2010) version of the National Seismic Hazard Model (NSHM) for New Zealand. A total of 21 faults ruptured along a c.180 km long zone during the earthquake, including some that were unknown prior to the event. The 2010 version of the NSHM had considered multi-fault ruptures in the Kaikōura area, but not to the degree observed in the earthquake. The number of faults involved a combination of known and unknown faults, a mix of complete and partial ruptures of the known faults, and the non-involvement of a major fault within the rupture zone (i.e. the Hope Fault) makes this rupture an unusually complex event by world standards. However, the strong ground motions of the earthquake are consistent with the high hazard of the Kaikōura area shown in maps produced from the NSHM.

Abstract. To evaluate the geospatial hazard relationships between recent (contemporary) rockfalls and their prehistoric predecessors, we compare the locations, physical characteristics, and lithologies of rockfall boulders deposited during the 2010–2011 Canterbury earthquake sequence (CES) (n=185) with those deposited prior to the CES (n=1093). Population ratios of pre-CES to CES boulders at two study sites vary spatially from ∼5:1 to 8.5:1. This is interpreted to reflect (i) variations in CES rockfall flux due to intra- and inter-event spatial differences in ground motions (e.g., directionality) and associated variations in source cliff responses; (ii) possible variations in the triggering mechanism(s), frequency, flux, record duration, boulder size distributions, and post-depositional mobilization of pre-CES rockfalls relative to CES rockfalls; and (iii) geological variations in the source cliffs of CES and pre-CES rockfalls. On interfluves, CES boulders traveled approximately 100 to 250 m further downslope than prehistoric (pre-CES) boulders. This is interpreted to reflect reduced resistance to CES rockfall transport due to preceding anthropogenic hillslope de-vegetation. Volcanic breccia boulders are more dimensionally equant and rounded, are larger, and traveled further downslope than coherent lava boulders, illustrating clear geological control on rockfall hazard. In valley bottoms, the furthest-traveled pre-CES boulders are situated further downslope than CES boulders due to (i) remobilization of pre-CES boulders by post-depositional processes such as debris flows and (ii) reduction of CES boulder velocities and travel distances by collisional impacts with pre-CES boulders. A considered earth-systems approach is required when using preserved distributions of rockfall deposits to predict the severity and extents of future rockfall events.

The Schmidt hammer (SH) is widely used in geomorphology for relative‐ and calibrated‐exposure age dating surfaces and deposits within landforms. This study employs a laboratory‐based methodology to assess the effects of surface roughness, clast roundness, and clast volume on SH rebound values (R‐values) by analyzing samples from three modern depositional environments (i.e. river, alluvial fan, talus). Each environment contains clasts of Torlesse supergroup greywacke sandstones with distinct roundness and micro‐scale roughness characteristics. Roundness, surface roughness, and clast volume were all found to influence R‐values significantly. The R‐values from different deposit types are statistically significant and could potentially create an apparent age divergence of several thousand years for samples with the same exposure‐age. © 2020 John Wiley & Sons, Ltd.

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