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Rapid, giant landslides, or sturzstroms, are among the most powerful natural hazards on Earth. They have minimum volumes of ∼106–107 m3 and, normally preceded by prolonged intervals of accelerating creep, are produced by catastrophic and deep-seated slope collapse (loads ∼1–10 MPa). Conventional analyses attribute rapid collapse to unusual mechanisms, such as the vaporization of ground water during sliding. Here, catastrophic collapse is related to self-accelerating rock fracture, common in crustal rocks at loads ∼1–10 MPa and readily catalysed by circulating fluids. Fracturing produces an abrupt drop in resisting stress. Measured stress drops in crustal rock account for minimum sturzstrom volumes and rapid collapse accelerations. Fracturing also provides a physical basis for quantitatively forecasting catastrophic slope failure. [Copyright &y& Elsevier]

A geotechnical investigation has been carried out on a large volume landslide in the Stambach Valley on the slopes above the town of Bad Goisern, Austria. Undrained loading has been considered as a means of triggering a large volume debris flow. The initiation of this landslide has been linked with the collapse of rock pillars from the rock face of Zwerchwand onto the head of the flow. The concept of pore tensions resulting from stress relief has been used to account for the time delays of up to 10 months between the loading and the reactivation of the debris flow. [Copyright &y& Elsevier]

Abstract: This paper considers the role that microseismic ground displacements may play in fracturing rock via cyclic loading and subcritical crack growth. Using a coastal rock cliff as a case study, we firstly undertake a literature review to define the spatial locations that may be prone to microseismic damage. It is suggested that microseismic weakening of rock can only occur in ‘damage accumulation zones’ of limited spatial extent. Stress concentrations resulting from cliff height, slope angle and surface morphology may nucleate and propagate a sufficiently dense population of microcracks that can then be exploited by microseismic cyclic loading. We subsequently examine a 32-day microseismic dataset obtained from a coastal cliff-top location at Staithes, UK. The dataset demonstrates that microseismic ground displacements display low peak amplitudes that are punctuated by periods of greater displacement during storm conditions. Microseismic displacements generally display limited preferential directivity, though we observe rarely occurring sustained ground motions with a cliff-normal component during storm events. High magnitude displacements and infrequently experienced ground motion directions may be more damaging than the more frequently occurring, reduced magnitude displacements characteristic of periods of relative quiescence. As high magnitude, low frequency events exceed and then increase the damage threshold, these extremes may also render intervening, reduced magnitude microseismic displacements ineffective in terms of damage accumulation as a result of crack tip blunting and the generation of residual compressive stresses that close microcracks. We contend that damage resulting from microseismic ground motion may be episodic, rather than being continuous and in (quasi-)proportional and cumulative response to environmental forcing. A conceptual model is proposed that describes when and where microseismic ground motions can operate effectively. We hypothesise that there are significant spatial and temporal limitations on effective microseismic damage accumulation, such that the net efficacy of microseismic ground motions in preparing rock for fracture, and hence in enhancing erosion, may be considerably lower than previously suggested in locations where high magnitude displacements punctuate ‘standard’ displacement conditions. Determining and measuring the exact effects of microseismic ground displacement on damage accumulation and as a trigger to macro-scale fracture in the field is not currently possible, though our model remains consistent with field observations and conceptual models of controls on rockfall activity. [Copyright &y& Elsevier]

Abstract: The processes of change on near-vertical coastal cliffs have been quantified using terrestrial photogrammetry and laser scanning. The approach allows discrete rockfall geometry to be measured, and source located in three dimensions. This paper presents the analysis of an inventory of over 100000 discrete rockfalls, recorded from the Liassic coast at Staithes, North Yorkshire (UK), where a rock face area of over 16000 m2 has been monitored over a 20 month period. The data obtained on three-dimensional scar geometry and source position give an insight into rockfall characteristics from a range of rock types, cliff heights and geometries. Multiple failure mechanisms such as overhang collapse, constant spalling, fragmentation and large scale, coherent rockfalls have been observed and related to rock-type controlled processes on the rock face. The spatially referenced rockfall scar data are used to assess the influence of environmental controls on variable rock mass properties, such as rock type, structure and cliff geometry. Analysis of rockfall magnitude–frequency reveals notable similarities between coastal rockfalls and inventories from non-coastal environments. The resolution of the monitoring data allows quantification of rockfalls down to volumes of 1.25×10−4 m3 to be consistently sampled and measured. This complete magnitude–frequency relationship suggests that rather than evolving exclusively through isolated, sporadic losses, coastal cliff geomorphology reflects interconnected processes in which each rockfall is part of a continuum of change to the rock face. Further detailed assessment of the rock face reveals the control of the pre-failure morphology on subsequent failure patterns, for example, the quantity of rock protrusion from the cliff is positively correlated with subsequent failure volume. The continuum of activity and the controls on failure identified within these data suggest that the episodic behaviour of coastal cliffs previously assumed may have been overstated by coarser resolution monitoring data. The findings improve our understanding of the evolution of coastal cliffs and highlight areas for further research into both cliff processes and the character of rock slope failures in general. [Copyright &y& Elsevier]

Abstract: The Fu-shan long-term ecological site is one of Taiwan''s mid-altitude forest drainage basins. This study provides an estimation of the denudation rate for two small catchments within that site. Data upon which the estimation is based include topographic maps, site surveys, and measurements on bed, dissolved, and suspended loads over the period from 1998 to 2000. The result indicates that typhoons and storm rainfalls, as well as geomorphic and ancestral conditions, have major impacts on hydrological and sediment regimes of these drainage basins. The total sediment output measured at Weir No. 1 indicates a denudation rate of ∼2.7mm per year, which is 53% of the figure calculated from the data measured at Weir No. 2. Since the geological settings in these basins are similar, the result is a demonstration of the nonlinear relationship between basin areas and sediment production. In Basin No. 1, 90% of the total sediment output is dissolved load. However, this figure plunges to 42% in Basin No. 2, in contrast with the fact that the runoff per unit area in Basin No. 2 is 35% higher than that in Basin No. 1. The denudation rates of these two drainage basins are relatively high in comparison with those from other areas around the world. [Copyright &y& Elsevier]