Rock slope instability and erosion: toward improved process understanding (original) (raw)

Slope failures and erosion rates on a glacierized high-mountain face under climatic changes

Earth Surface Processes and Landforms, 2013

In this study, rapid topographic changes and increased erosion rates caused by massive slope failures in a glacierized and permafrost-affected high-mountain face were investigated with respect to the current climatic change. The study was conducted at one of the highest periglacial rock faces in the European Alps, the east face of Monte Rosa, Italy. Pronounced changes in ice cover and repeated rock and ice avalanche events have been documented in this rock wall since around 1990. The performed multitemporal comparison of high-resolution digital terrain models (DTMs) complemented by detailed analyses of repeat photography represents a unique assessment of topographic changes and slope failures over half a century and reveals a total volume loss in bedrock and steep glaciers in the central part of the face of around 25 Â 10 6 m 3 between 1988 and 2007. The high rock and ice avalanche activity translates into an increase in erosion rates of about one order of magnitude during recent decades. The study indicates that changes in atmospheric temperatures and connected changes in ice cover can induce slope destabilization in high-mountain faces. Analyses of temperature data show that the start of the intense mass movement activity coincided with increased mean annual temperatures in the region around 1990. However, once triggered, mass movement activity seems to be able to proceed in a self-reinforcing cycle, whereby single mass movement events might be strongly influenced by short-term extreme temperature events. The investigations suggest a strong stability coupling between steep glaciers and underlying bedrock, as most bedrock instabilities are located in areas where surface ice has disappeared recently and the failure zones are frequently spatially correlated and often develop from lower altitudes progressively upwards.

Legacies of catastrophic rock slope failures in mountain landscapes

Earth-Science Reviews, 2008

This review examines interpretive issues relating to catastrophic, long-runout landslides in the context of large numbers of recently discovered late Quaternary events. It links relevant research in landslide science, including some novel or hitherto-ignored complexities in the nature and role of these events, to broader concerns of mountain geomorphology. Attention is drawn to mountain ranges known to have large concentrations of events. In particular, discoveries in three regions are singled out; the Karakoram Himalaya, the coastal mountains of northwestern North America, and the Southern Alps of New Zealand. In each region, many new events, or previously unrecognized complexities, have been identified in the past decade or two. Research on the sedimentology and geomorphology of prehistoric, eroded deposits has been critical to identifying rock avalanches, including many that were formerly attributed to other processes. Discoveries of rock avalanches in the ancient stratigraphic record have helped with the field recognition of rock-avalanche materials and in developing facies models of deposits with complex emplacement histories. The stratigraphic record also provides insights into interactions of streaming rock debris with deformable substrates. Such interactions are responsible for "landslide-tectonized" forms and transformation of rock avalanches into debris flows. Of special interest are runout geometries involving the interactions of rock avalanches with topography or substrate materials, and travel over glaciers. Other emerging issues relate to reconstruction of detachment-zone geometries, and slow, deep-seated slope movements that may trigger catastrophic failure. Most previous landslide studies have focused on individual events or general models, whereas the questions addressed here arise from a comparative approach emphasizing common and contrasting features among events in sets and in different regions. The scale and frequency of landslides in the regions of interest mean they have an important role in denudation, regional landform development, watershed evolution, and Quaternary environmental change. A major developmental factor, largely neglected, is persistent disturbance of high mountain fluvial systems by many successive landslides. Damming of streams and subsequent breaching of landslide barriers strongly influence inter-montane sedimentation and denudation, with particular significance in post-, para-, and inter-glacial contexts. Although an individual landslide appears as a "catastrophe" lasting only a minute or two, its legacy can persist as a morphogenetic influence for millennia or tens of millennia through disturbance of other processes. The influence is permanently felt; in effect, multiple events make the event a "normal" one in regions such as the three considered here.

Physical modelling of rainfall- and snowmelt-induced erosion of stony slope underlain by permafrost

Earth Surface Processes and Landforms, 2011

Physical modelling experiments have been carried out in a cold room to test on a small scale, the effects of water supply during the thaw of an experimental slope with permafrost. Permafrost was maintained at depth and a thin active layer was frozen and thawed from the surface. Data from the experiments relate to two different conditions, first with moderate rainfall, and second with heavy rainfall during the thaw period.

Weathering as a Predisposing Factor to Slope Movements

2010

Recognition of weathering as a primary process in the development of landforms dates back at least to the late 19th and early 20th century, as indicated by several contributions from various countries (e.g. Cortese 1895;; nevertheless, it was only in the second half of the last century that systematic studies on weathering and related topics such as geomorphology, engineering geology and petrography were carried out. In a recent review paper Ehlen found through an on-line search more than 9000 hits where the term 'weathering' was used, dating from the mid-1950s to the beginning of the 21st century. Such a huge number of citations clearly demonstrates the attention that the scientific community has dedicated to the in-place breakdown of rocks by chemical, physical and biological processes. However, despite the high frequency of landslides and erosional phenomena in weathered materials, and the damage and casualties they repeatedly cause, not very much is known about the direct and indirect relationships between weathering and slope

Enhanced rock-slope failure following ice-sheet deglaciation: timing and causes.

Earth Surface Processes and Landforms, 2014

The temporal pattern of rock-slope failures (RSFs) following Late Pleistocene deglaciation on tectonically stable terrains is controversial: previous studies variously suggest (1) a rapid response due to removal of supporting ice ('debuttressing'), (2) a progressive decline in RSF frequency, and (3) a millennial-scale delay before peak RSF activity. We test these competing models through beryllium-10 ( 10 Be) exposure dating of five closely-spaced quartzite RSFs on the Isle of Jura, Scotland, to establish the relationship between timing of failure and those of deglaciation, episodes of rapid warming and periods of rapid glacio-isostatic uplift. All five dated RSFs occurred at least 720-2240 years after deglaciation, with the probability of failure peaking~2 ka after deglaciation, consistent with millennial-scale delay model . This excludes debuttressing as an immediate cause of failure, though it is likely that time-dependent stress release due to deglacial unloading resulted in progressive development of failure planes within the rock. Thaw of permafrost ice in joints is unlikely to have been a prime trigger of failure as some RSFs occurred several centuries after the onset of interstadial warming. Conversely, the timespan of the RSFs coincides with the period of maximum glacio-isostatic crustal uplift, suggesting that failure was triggered by uplift-driven seismic events acting on fractured rock masses. Implications of this and related research are: (1) that retreat of the last Pleistocene ice sheets across tectonically-stable mountainous terrains was succeeded by a period of enhanced rock-slope failure due to deglacial unloading and probably uplift-driven seismicity; (2) that the great majority of RSFs in the British Isles outside the limits of Loch Lomond Stadial (= Younger Dryas) glaciation are of Lateglacial (pre-Holocene) age; and (3) numerous RSFs must also have occurred inside Loch Lomond Stadial (LLS) glacial limits, but that runout debris was removed by LLS glaciers.

Slope Dynamics and Climate Change Through Indirect Interactions

The rapid variation of climate can cause direct changes in slope dynamics due to a modified rainfall regime. Variations in evapotranspiration regime determines changes in soil moisture, modifies shrinking-swelling cycles, creeping, surface mass movement, and soil erosion, including gully erosion. All these effects can be considered as direct consequences of any climate modification. Besides them, other indirect effects should be considered to fully determine climate change impact on slope dynamics. This is the case of the effects of climate change on vegetation, that strongly controls slope instability phenomena. Here we will concentrate on the effect of increased danger due to forest fire, and in particular we discuss the changes in the hydrogeological hazard linked to the effect of drought on wild fires in a case-study in Umbria (Italy), mainly considering field observations and simulations with LANDPLANER (LANDscape, Plant, LANdslide and ERosion) model. This study shows that when...

Monitoring and modeling of slope response to climate changes

2008

Shallow slides are often triggered by climate effects. An understanding of the slope failure conditions and effective remedial measures can be achieved by comprehensive field monitoring of climatic and hydrologic changes and the consequent changes in slope responses. Two contributions from two different geographic regions are presented to gain understanding of the complex phenomena involved in slope failure studies. In the first part Alonso et al., contributes theoretical analysis of a stochastic model for the reliability of planar slides in a partially saturated soil, subjected to a rainfall history described as a time series and then presents a case history of shallow mudslides triggered by a Mediterranean climate, analyzed by means of a coupled hydro-mechanical modeling tool. The joint saturated-unsaturated consideration of the slide is necessary to understand field data. In the second part Rahardjo et al., contributes field monitored data from three residual soil slopes in Singapore and demonstrates how field monitored data on climatic, hydrologic, and slope variables were used to evaluate slope responses under subtropical Singapore climate.

Hydro-mechanical interactions of a rock slope with a retreating temperate valley glacier

2021

• We monitored subsurface pore pressures and micrometer scale strain in a rock slope during strong glacial retreat caused by climate warming • We identified thermo-hydromechanical drivers for reversible deformation and irreversible rock mass damage acting at various timescales • Slope damage intensity can be related to landslide spatial and temporal distribution