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The MW 7.8 14 November 2016 Kaikoura Earthquake generated more than 20,000 mapped landslides and about 200 significant landslide dams. Besides the immediate hazard from the landslides, cracked ground, landslide debris and landslide dams also pose longer-term risk to infrastructure, because if the landslides and debris remobilise and the dams breach, they could generate future debris flows and floods. These in turn, could sever transport routes and further damage infrastructure, adversely impacting the post-earthquake economic recovery of the region. The goal of this short-term project was to collect perishable (ephemeral) data on landslides and landslide dams generated by the earthquake. Currently there are more than 20,000 landslide source areas in the landslide inventory. Key findings from the landslide inventory are: 1) the number of large landslides (with source areas ≥10,000 m2) triggered by the Kaikoura Earthquake is fewer than the number of similar sized landslides triggered by other similar magnitude earthquakes in New Zealand; 2) the largest landslides (with volumes from 5 to 20 M m3) occurred either on or within 2,500 m of the 24 mapped faults that ruptured to the surface; and 3) the landslide density within 2,500 m of a mapped surface fault rupture is as much as three times higher than those densities farther than 2,500 m from a ruptured fault. Around 200 significant landslide dams generated by the earthquake have now been mapped and combined with data from past New Zealand and overseas landslide dams. These data have been used to develop a regional-scale, empirically-based tool to assess the post-formation likelihood of dam failure (breaching), which can be used for future landslide dam generating events. Many of the larger dams have also been investigated in detail and dam-breach models have been calibrated from back-analysing their failure. (auth)

An approximately 25,500 m³ debris avalanche occurred on the 23rd January 2019 from the coastal cliffs of Cape Kidnappers, Hawke’s Bay. The debris avalanche was observed by multiple bystanders, and seriously injured two tourists. The tourists were walking along the beach, which forms the public accessway to the Gannet Colony at Cape Kidnappers – a popular tourist attraction in the Hawke’s Bay. The cliff collapse occurred within a conglomerate unit located in the upper 50 m of the cliff. The site has been the location of previous failures with a significant debris avalanche occurring from the lower half of the cliff in the 2015. The remnants of the 2015 debris deposit were still present at the base of the cliff on the 23rd January 2019, with the 2015 deposit acting as a ramp, allowing the 23rd January 2019 debris avalanche debris to travel further. ‘Small’ precursory rockfalls were observed sporadically through the week prior to the 23rd January 2019 event. There was no discernible trigger for the debris avalanche, with no seismicity and limited rainfall recorded in the week prior. Marine erosion at the toe of the slope may have been a contributing factor in the 2015 failure. The most likely cause of 23rd January debris avalanche is upward propagation of cliff failure through time. The final cause of failure would be the culmination of cliff material weakening through time (due to weathering processes such as saltwater wetting and drying and failure surface development in response to ongoing stress relief). As the strength of the material decreases and the failure propagates, ‘low’ apparently benign environmental stresses can act as a trigger for final failure. Several smaller rockfalls have occurred after the 23rd January 2019 debris avalanche, including a 10,000 m³ debris avalanche located to the east of the 23rd January debris avalanche. This subsequent cliff failure narrowly missed two tourists who were walking along the beach below (the beach and accessway were closed at the time). Anecdotal evidence, field observations, and aerial LiDAR analysis all indicate that landslides of a similar size, or smaller, occur regularly along this 7 km long section of coastal cliffs between Clifton and Black Reef. However, the baseline risk users of the beach accessway are exposed to is unknown. As such, the logical next step would be to undertake a quantitative risk assessment to quantify this baseline risk. (auth)

Fluid flow in the high-temperature (300 C), andesite-hosted Rotokawa geothermal reservoir (Taupo Volcanic Zone (TVZ), New Zealand) is largely controlled by fractures and faults but their geometries are still poorly understood. The aim of this study is to measure and derive geometric parameters characterising fractures in andesitic formations in order to use these as input for dis-crete fracture network models (DFN) and predictive fluid flow models of the Rotokawa geothermal reservoir. We make use of two complementary fracture datasets. (1) The fracture geometry in-trinsic to andesitic formations are studied on outcrops at Mt Ruapehu (TVZ volcano), with the measurement of c. 200 fractures along a 100 m long scanline, and the acquisition of a Terrestrial Laser Scanner (TLS) scan acquired over the entire outcrop. (2) Fracture orientation, width and spacing are determined for three acoustic borehole televiewer (BHTV) logs and 33 m of cores from the Rotokawa Geothermal Field. Two types of fractures are observed at the Mt Ruapehu outcrop. The majority of fractures form sub-vertical cooling joints. The TLS scan samples six dip directions suggesting an hexagonal section typical of basaltic lava flows. The scanline survey did not fully sample the six directions. The preliminary analysis of fracture length on the scanline survey highlights the high degree of fracture connectivity and a weak spatial clustering. A subset of the fractures are sub-horizontal, highly clustered and are aligned with possible changes of crystallinity, viscosity and flow banding within the flow. Further analysis is required to make firm conclusions about the fracture length and spacing. Fractures are conchoidal which enhances the fracture linkages, which cannot be easily quantified from scanline surveys and will be evaluated on the TLS scans. The BHTV and core analysis reveals that fractures within the reservoir are predominantly steeply dipping and NE SW-striking, parallel to the trend of the maximum horizontal compressive stress (S Hmax) and the rift axis. Fractures in the reservoir are preferentially oriented with respect to the in-situ stress and the tectonic faults but may be locally inherited from cooling joints and fractures associated with the internal fabric of the lava flows. BHTV logs indicate that the 8 50 mm wide fractures follow an exponential distribution. The log-normal, power-exponential or power-law distributions have similar likelihoods for fracture spacing of 0.005 50 m. Low spacing are best fitted by either an exponential, gamma or power-exponential distribution. This change at c. 1 m spacing may correspond to the threshold at which fracture interaction occurs. The lithological controls on the fractures is observed at both the outcrop and core scale, with fracture being less numerous and more tortuous in breccias than in massive lava. The breccias are typically more permeable than the massive interior, and offer lateral and vertical connectivity in reservoirs. Breccias also affect the propagation of the fractures due to their heterogeneity. Integrating these observations into fracture models will be fundamental to the prediction capability of the fracture models of the Rotokawa andesitic reservoir. Observations made at Ruapehu and Rotokawa have wide implication for the successful development of geothermal resources in volcanic-hosted geothermal reservoirs. non-peer-reviewed