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Ambiguous landscape histories can arise from equivocal or incomplete geomorphological, sedimentological or geochronological evidence. In this study, we apply quantitative analyses to robustly assess the origin and age of a field of rounded mounds, known as 'The Hillocks'. Using clast analysis, the sediment is shown to be consistent with a landslide origin but inconsistent with other glacial sediments in the region. Cosmogenic 10Be exposure age dating suggests The Hillocks formed ~8 ka. Ground‐penetrating radar reveals that the deposit rests upon deltaic foreset beds; combined with topographical data, we calculate a deposit volume of ~15–27 M m3, consistent with the estimated volume of the proposed source area. Overall, our data support a rock avalanche origin, indicating that by 8 ka the valley was ice‐free at The Hillocks' location, and the level of Lake Wakatipu was lower than 340 m asl by this time. The Dart River delta shoreline was situated somewhere between The Hillocks and the present day shoreline at that time, and has prograded at a maximum average rate of 1 m a−1 since ~8 ka. These findings are significant given the lack of landforms by which to constrain glacial or post‐glacial landscape histories in this region of New Zealand. Copyright © 2019 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Rock avalanches are common in mountainous regions that are tectonically active. They are capable of forming natural dams of uncertain persistence that have significant impacts on the river system over wide spatial scales and possibly over geological time scales. Here we combine field data and digital elevation model (DEM) analysis to show the response of Ram Creek, New Zealand, to 28 years of sediment dispersion following the 1968 emplacement of a co-seismic, rock-avalanche dam that breached catastrophically in 1981. The results show a system that has not attained equilibrium, being unable to move the quantity of dam-derived sediments, and will likely not attain equilibrium before the next major sediment input; it is in a state of persistent disturbance where localised reworking dominates. Erosion in Ram Creek is focussed on lateral bevelling and bedrock gorge widening rather than vertical incision to keep pace with tectonic uplift. Importantly for studies of tectonic geomorphology, this widening — which if sustained will form a strath terrace — does not represent a period of reduced uplift. Stream metrics (concavity and steepness) are unable to differentiate the identified rock-avalanche-induced knickpoint from tectonic and lithological knickpoints. [ABSTRACT FROM AUTHOR]

A large rock avalanche fell from the slope below Hillary Ridge of Aoraki/Mount Cook at 21:32 (New Zealand Standard Time (NZST) = UTC + 12 h) on Monday 14 July 2014. About 0.9 million m of indurated greywacke collapsed from a >60° slope at 43.6165°S 170.1427°E between 2600 and 2920 m, without warning or apparent trigger. The avalanche of rock debris crossed Noeline Glacier névé, entraining snow and ice debris, before passing through an icefall, accelerating down steepening slopes and ended on Hooker Glacier. A small mountaineering shelter sited on a topographic high within the avalanche path was damaged but not completely destroyed. Covering a total fall of 1600 m and travel distance of 3.9 km, the avalanche angle of reach was 24°. The deposit of rock, snow and ice debris covers 1.4 million m. Airborne dust travelled at least 6 km. The event was recorded by the national seismograph network, as a M2.6 earthquake with the strongly emergent characteristics of a large avalanche. [ABSTRACT FROM AUTHOR]

Catastrophic deep-seated rock slope failures (RSFs; e.g., rock avalanches) can be particularly useful proxies for fault rupture and strong ground motion, and currently represent an underappreciated hazard of earthquakes in New Zealand. This study presents observations of the previously undescribed Cascade rock avalanche (CRA), a c. 0.75 km single-event, long-runout, catastrophic failure interpreted to have been coseismically triggered by a large to great earthquake c. 660 AD on the Alpine Fault. Despite its size and remarkable preservation, the CRA deposit has been previously identified as a terminal moraine and fault-damaged outcrop, highlighting the common misinterpretation of similar rock avalanche deposits. Comparisons are drawn between the CRA and other Alpine Fault-attributed rock avalanches, such as the better-studied c. 860 AD Round Top rock avalanche, to re-assess coseismic rock avalanche hazard. Structural relationships indicate the rock mass comprising the CRA may have formerly been a portion of a larger (c. 3 km) RSF, before its catastrophic collapse on a deep-seated gravitational collapse structure (sackung). Sackungen and RSFs are common throughout the Southern Alps and other mountainous regions worldwide; in many cases, they should be considered potential precursors to catastrophic failure events. Two masses of rock in the Cascade River Valley show precursory signs of potential catastrophic failures of up to c. 2 km; a similar mass may threaten the town of Franz Josef. [ABSTRACT FROM AUTHOR]

Abstract: Volcanic domes may be emplaced rapidly and with few hazardous consequences, even at the summit of large stratovolcanoes. In this study the most recent activity of Mt. Taranaki in New Zealand is shown to have been a passive effusion of a c. 5.9millionm3 lava dome with minor associated explosions and little syn-eruptive hazard. This event, the Sisters eruption, appears to have been unrecorded by local indigenous populations but likely occurred between A.D. 1785 and 1820. The magma erupted is chemically distinct from the preceding A.D. 1755 Tahurangi eruption. Based on breakdown of hornblende crystal rims, the Sisters magma was probably only four days outside the hornblende stability field before cooling, and the magma ascended its last four km along a conduit at rates of 0.012ms−1. Based on dome surface morphology, a relatively low-viscosity magma is inferred. The dome remained in a metastable state for up to 70years following the eruption; eventually generating a large, cool (<350°C) collapse of at least 2millionm3 of rock, forming a highly hazardous mass flow that travelled over 5km. Factors contributing to the post-eruption dome instability include: its emplacement onto a steep flank of unconsolidated breccia or talus, possible oversteepening, fracturing due to spreading and subsidence, rapid cooling during heavy rain, and a hydrothermally altered inner core. The likely trigger for the collapse was a heavy rainstorm or an earthquake. Volcanic domes in the summit regions of volcanoes must be considered metastable and a potential source for hazardous, non-eruption related mass flows for many decades following their emplacement. [Copyright &y& Elsevier]

Rock slope failure (RSF) occurs in different contexts but is typically reported either as (i) single-category inventories or (ii) single-site geotechnical monographs. Few studies have sought to evaluate the spatial incidence of all modes of RSF conjointly, and to infer scenarios of regional landscape evolution from observed patterns of cumulative rock slope overstressing. Here we present the results of a systematic inventory of rock avalanches, rockfalls, rockslides, and gravitational rock slope deformations in the Western Alps (France, Italy, Switzerland) conducted using satellite imagery made available in Google Earth as a detection tool, and aided by preliminary ground-truth checks. The inventory totals 1416 montane RSFs, impacting 9.1% of the study area. Underpinned by GIS tools, the study further examines the spatial distribution of RSF with consideration for (i) predisposing factors (typically: lithology, geological structure), and (ii) preparatory factors (geomorphological process regimes that drives a given slope segment to the point of failure). The latter encompass slower variables (e.g., long-term crustal stress regime, cumulative residence time above equilibrium line altitudes) and faster variables (e.g., short-span glacier-related stresses, permafrost thaw, seismicity). RSF density patterns helped to define seven RSF super-hotspots (large diversity of RSF modes, up to 50% of displaced rock masses/unit area), which define the most intensely overstressed areas of the Western Alps. These super-hotspots occur at sites where highly dynamic, thick, warm-based glaciers above the equilibrium line either intersected (middle Maurienne) or followed the strike of (middle Isère) N-S bands of highly susceptible lithologies and structures during the Quaternary. The widespread incidence of rock slope deformation (cumulative area: 1760 km2, i.e., nearly 3 times the total of the other three RSF categories combined) appears further correlated with the low tectonic activity of the orogen and with its areas dominated by an extensional tectonic regime west of the Penninic Frontal Thrust. This contrasts with seismically active orogens, e.g., New Zealand's Southern Alps, where rock slope deformation is scarce compared to rock avalanches and shallow landslides. • A new inventory of 1416 rock slope failures (RSF) in the Western Alps is presented. • RSF size and failure mode are analysed in relation to climatic and geological variables. • Regionally, hotspots of extreme slope stress are dominated by rock slope deformation. • Spatial patterns of slope overstressing put landscape evolution in a new perspective. • The slope evolution cycle is contrasted with that of New Zealand's Southern Alps. [ABSTRACT FROM AUTHOR]