Rockfall Debris Research Articles

New insights on gravity flow dynamics during submarine canyon flushing events

Millions of tons of material are flushed through submarine canyons during infrequent high-magnitude events, transporting coastal sediment to the deep ocean. However, observations related to individual canyon flushing events are challenging due to the destructive nature and infrequency of flushing events. The impacts of one of the largest gravity flows in the past decade were documented in Kaikōura Canyon, Aotearoa−New Zealand, where >1 km3 of sediment was mobilized by the 2016 CE Kaikōura earthquake (Mw 7.8). We present new high-resolution (<1 m) multibeam data collected with an autonomous underwater vehicle (AUV) along the Kaikōura Canyon axis, together with side-scan sonar and seafloor video imagery. These data sets reveal a wide range of erosional and depositional features that were not previously identified. Eroded bedrock and deep erosional structures are found in the upper canyon, including linear grooves, and rockfall debris (>5-m-diameter boulders). This erosional area transitions downcanyon to coarse-grained depositional bedforms, including cyclic steps and gravel waves (average wavelengths of 250 m and wave heights of ∼20 m), covering the mid- and lower canyon. Our observations provide high-resolution field-based evidence of (1) flow transformation, from a debris flow to a high-density turbidity current; and (2) variations of flow dynamics within turbidity currents both across- and downcanyon, during an infrequent, high-energy canyon flushing event. This research offers new insights into the processes that create and shape nearshore bedrock-incising submarine canyons.

Rockfall Kinematics from Massive Rock Cliffs: Outlier Boulders and Flyrock from Whitney Portal, California, Rockfalls

ABSTRACT Geologic conditions and topographic setting are among the most critical factors for assessing rockfall hazards. However, other subtle features of rockfall motion may also govern the runout of rockfall debris, particularly for those sourced from massive cliffs where debris can have substantial momentum during transport. Rocks may undergo collisions with trees and talus boulders, with the latter potentially generating flyrock—launched rock pieces resulting from boulder collisions that follow distinctively different paths than the majority of debris. Collectively, these intricacies of rockfall kinematics may substantially govern the hazards expected from rockfall to both persons and infrastructure located beneath steep cliffs. Here, we investigate the kinematics, including outlier boulder and flyrock trajectories, of seismically triggered rockfalls on 24 June 2020 that damaged campground facilities near Whitney Portal, CA, a heavily used outdoor recreation gateway to the Sierra Nevada mountains. Our results, obtained in part by rockfall runout model simulations, indicate that outlier boulder trajectories resulted from opportunities provided by less steep terrain beyond the talus edge. The influence of trees, initially thought to have served a protective capacity in attenuating rockfall energy, appears to have been negligible for the large boulder volumes (>50 m3) mobilized, although they did potentially deflect the trajectory of flyrock debris. Rockfall outlier boulders from the event were comparable in volume and runout distance to prehistoric boulders located beyond the talus slope, thereby providing some level of confidence in the use of a single rockfall shadow angle for estimating future rockfall hazards at the site.

Rockfall susceptibility and runout in the Valley of the Kings

The UNESCO world heritage site Valley of the Kings or Wadi el-Moluk (وادي الملوك) near Luxor, Egypt, hosts unique burial places of Egyptian kings and royals from the New Kingdom (c. 1539–1075 BCE) and attracts about 0.5 to 2 million tourists per year. Very steep to subvertical cliffs of Thebes Limestone surround the Valley of the Kings. The rock mass is cut by frequent joints and faults making the cliff walls prone to rockfalls. However, only few rockfall debris are found in the valley, likely due to natural remobilisation by flood events and artificial clearings and excavation works that rendered the natural debris cover over the millennia. This work focuses on rockfall susceptibility and runout and makes use of new high-resolution landscape surface models utilising terrestrial laser scanning. We investigated rockfall release areas by exploring rock mass fractures at 23 cliff segments and analysed the kinematics of potential rockfalls. Furthermore, we estimated potential rockfall deposition areas with CONEFALL supported by nine numerical simulations of single rockfall events using Rockyfor3D. We found that nearly 4500 m2 (26%) of the public walking paths and 24 out of 64 tomb entrance areas locate within potential rockfall runout zones.

Geotechnical slope stability and rockfall debris related safety assessments of rock cuts adjacent to a rail track using aerial photogrammetry data analysis

Transportation infrastructure facilitates the accessibility and mobility of goods, people, and services through its vast network spanning across the USA. The departments of transportation (DOT) agencies face many challenges in monitoring and maintaining these infrastructure assets for continuing their service and operations, especially those located adjacent to slopes in rural and remote areas. Mobilizing and conducting traditional infrastructure inspections in those conditions can be laborious and time-consuming. Also, the unstable or highly weathered rock slopes pose significant rockfall hazards due to the moisture content, intrusion, and temperature changes, transpired over a period of time, causing weathering and rockfalls, ultimately resulting in debris accumulation. Recently, unmanned aerial vehicles (UAVs) in conjunction with close-range photogrammetry techniques are being researched and used ubiquitously for infrastructure monitoring applications in and around mountainous regions. In this study, a rock-cut located in a remote terrain where a rail track was passing through was aerially inspected and imaged for performing a comprehensive safety assessment and analysis to evaluate the stability of rock-cut and ways to assess rockfall safety zones and boundaries. A unique approach was developed by leveraging the aerial mapping and data compilation along with an immersive three-dimensional visualization of slopes for conducting stability analysis followed by the evaluation of rockfall debris zones adjacent to rail tracks. Successful assessments conducted in this study indicate that the methodologies will benefit the transportation agencies in effectively monitoring and managing transportation infrastructure adjacent to hilly terrains and ensure the maintenance of safe clearance zones needed to safeguard the public and property.

Hydropower Infrastructure Performance after the 2015 Gorkha, Nepal, Earthquake Sequence

Hydropower infrastructure, the primary source of electricity in Nepal, experienced severe damage following the 2015 Gorkha earthquake sequence, resulting in a 15% loss in the country's energy production. The performance of hydropower infrastructure during and after the sequence was one of the unique focuses of the Geotechnical Extreme Events Reconnaissance (GEER) study. The GEER team visited damaged hydropower projects along the Trishuli and Sunkoshi rivers by road and on foot, along with the ongoing 465-MW Upper Tamakoshi hydropower project by helicopter. The primary cause of damage to the hydropower infrastructure was landslide and rockfall debris falling on powerhouses, penstocks, and dam structures. Moreover, landslides blocked road access to many sites, delaying necessary repairs to damaged structures and resumption of power generation. Power production in Nepal before and after the 2015 Gorkha earthquake sequence, seismic performance of visited hydropower projects, and short- and long-term effects, together with residual risks for Nepal's hydro-power infrastructure, are discussed in this paper.

Scottish landform examples 44: the Dirc Mhòr meltwater gorge

ABSTRACTThe Dirc Mhòr gorge in the central Grampian Highlands is 1.1 km long, ∼250 m wide and up to 110 m deep, and is incised in granite bedrock. It is the largest of several bedrock gorges that are incised into spurs, cols or plateau margins in the area, and its present catchment area is negligible. The floor of the gorge is covered by coarse rockfall debris, and the sides of the gorge are mantled by talus accumulations; surface water flow is absent. The gorge is inferred to have evolved over several glacial-interglacial cycles, with subglacial meltwater erosion deepening the gorge under successive ice sheets, and paraglacial rockwall collapse widening the gorge during intervening interglacial periods. Subglacial erosion may also have contributed to gorge enlargement as it widened.

The chronology of human and animal presence in the decorated and sepulchral cave of Cussac (France)

In this article, we present a first synthesis of the chronology of Cussac Cave (Dordogne, SW France). This deep cavern (1.6 km), discovered in 2000, is very well preserved (e.g. intact floors) and thus favorable to research, especially given its rare association of parietal art and human remains, deposited in at least three locations. The scientific team working since 2009 presents here a first diachronic reconstruction of the natural (geological, biological) and anthropogenic (cultural, spiritual) elements relevant to the sectors of the cave accessible for study. In addition to the nuclear dating methods commonly used in karst contexts and decorated sites (U–Th and 14C for speleothems, 14C-AMS for organic materials, bone and charcoal), we drew upon other disciplines to determine the relative chronology of the events that occurred in the cave: geosciences (karstology, sedimentary geology, geoarchaeology), biological anthropology, paleontology, zooarchaeology, anthracology, ichnology, lithic and osseous technology, and of course, the study of parietal art. Their integrated study enabled us to define a coherent and global chronological framework. The results confirm that bears frequented the cavity several times before any human incursions. Humans later ventured into the cave after it had already undergone several phases of karstogenesis, collapse, sedimentation, erosion and concretion formation. The nuclear methods and relative dating methods employed concur in favor of the hypothesis of human incursions only during the Middle Gravettian period, approximately 28–29,000 cal BP, to carry out spiritual, graphic and sepulchral activities. After the cave was abandoned by Gravettian people, some final sedimentary and biological events occurred (partial flooding, concretion formation, presence of mesofauna and microfauna, etc.), but were insufficient to significantly modify the decorated and sepulchral sanctuary. Later human frequentations (Late Glacial, Late Magdalenian, Late Neolithic) are quantitatively anecdotal and, most importantly, were limited to the cave porch and vestibular areas, which were sealed-off from the internal zone by rockfall debris and Late Glacial or Holocene concretion formations.

Rainfall Induced Rock-Fall Debris Avalanche in October 2010, at Kwande Local Government Area of Benue State, Nigeria

Abstract This study explains the causes and the mechanism of the landslide occurrence at Kwande local Government Area of Benue, Nigeria in 2010. Although there was no fatality or any damage in the area, a large area of farmland was destroyed, trees were uprooted and a normal stream course was also disturbed. To study and understand the landslide event, a combination of geotechnical investigations and statistical data were used. These parameters were applied to a numerical model to simulate the causes of the landslide. Results of the geotechnical investigations made on samples taken from the area, showed average maximum dry density value of 1.6kg/m3, and average optimum moisture content value of 14%, hence the low to moderate density is indicative of a soil that can easily disperse. Also the triaxial compression test showed an angle of internal friction and cohesion values averaging around 14.82° and 25kPa respectively, and these low values indicate that the shear strength of the soil was reduced, due to the combined effect of increase in slope gradient, and high precipitation intensity which increased to a monthly value of 145mm before the landslide. The simulation result showed that the factor of safety value was 1.158, which is still close to the value for an incipient failure. Hence the results shown can be used in predicting the mechanisms and areas of possible landslides, as well as the causes of such soil deformations, and as such, safety measures could be taken against the reoccurrence of landslides in the area.

Rangewide glaciation in the Sierra Nevada, California

The 600-km-long Sierra Nevada underwent extensive Pleistocene glaciation except for its southernmost 100 km. Presently, ∼1700 small glaciers and ice masses near the crest of the range occur above 3250 m in elevation; these covered an area of ∼50 km 2 in 1972. Fourteen of the largest glaciers decreased by about one half in area during the period from 1900 to 2004. Rock glaciers, generally glacial ice covered by 1–10 m of rockfall debris, occur in about the same span of the range as ice and permanent snowfields. They are, on average, lower by 200–300 m, apparently because of the insulating layer of rocky rubble that protects their internal ice from the sun’s heat and from wind. The principal Pleistocene glacial stages are the Sherwin (ca. 820 ka), Tahoe (170–130 and ca. 70 ka), Tioga (14–28 ka), and Recess Peak (13 ka). Some 7040 glacial lakes, produced primarily by quarrying from bedrock, were mostly exposed after recession of the Tioga glacial stage. The lakes largely mark the area of primary snow accumulation. Below the lower limit of the lakes, ice flowed downward into river-cut canyons, forming major trunk glaciers within the zone of ablation. The range is in general a westward-tilted block upfaulted on its east side. Therefore, the main late Pleistocene trunk glaciers (Tahoe/Tioga) west of the crest extend 25–60 km, whereas those east of the crest extend only 5–20 km. Because of higher precipitation northward, glacial features such as the toes of existing glaciers and rock glaciers, as well as the late season present-day snowline, all decrease in elevation northward. Likewise, the elevation of the lower limit of glacial lakes, an indication of the zone of snow accumulation during the late Pleistocene, decreases about the same degree. This similarity suggests that the overall climate patterns of the late Pleistocene, though cooler, were similar to those of today. The east slope glaciers show a similar northward depression, but they are ∼500–1000 m higher. The upper part of the glacial system was erosive over a broad highland area as the evenly distributed ice in the accumulation zone moved to lower elevation. The abundant lake basins record this erosive action. The lower part of the glacier system was largely confined to major preexisting river canyons in which melting dominated. The average of rangewide estimates of the equilibrium line altitude (ELA)—the boundary between the upper snow and ice accumulation zone and the lower ablation zone—of many late Pleistocene glaciers parallels, and is only 200–300 m above, the altitude of the lower limit of the lakes. Hence, the lake zone provides a means of estimating the ELA.

Simulating the formation of overdeepenings with coupled ice, water, and sediment models

Eyles identified Kvı́árjökull, an outlet of the icecap Öræfajökull, southeast Iceland, as an exemplar of the glaciated valley landsystem, emphasising rockfall debris supply, passive transport and reworking of a thick cover of supraglacial morainic till. In this paper, we take a fresh look at the sediments and landforms of Kvı́árjökull, focusing on clast form analysis to reconstruct primary transport pathways. New data demonstrate the importance of active transport of debris derived from the glacier bed. Substantial portions of the supraglacial debris cover can be traced back to englacial channel fill deposits or anomalously thick exposures of basal ice. These two types of sediments also make up much of Kvı́árjökull's large Neoglacial moraine rampart. We attribute the abundance of these non-rockfall sediments to the presence of a terminal overdeepening, and the switch from predominantly subglacial to predominantly englacial drainage that this induces. This hydrological switch enhances retention of debris within ice transport, preventing it from being washed away and making it available to feed ice-marginal moraine formation. The complexity of sediment transport processes observed at Kvı́árjökull and the contrast between it and alpine glaciers undermines any single concept of the glaciated valley landsystem; accordingly, we propose Kvı́árjökull as the type example of a distinct subclass, defined by its moderate relief, high-debris turnover, and drainage behaviour characteristic of an overdeepened basin.

Sediment dynamics below retreating cliffs

ABSTRACTThe retreat of cliffs may constitute the dominant erosional response to base‐level fall in arid settings underlain by horizontally‐bedded sedimentary rock. These vertical cliffs typically loom above a relatively straight bedrock slope (‘plinth’) that is mantled with a thin layer of sediment and perched near the angle of repose. In detail, a plinth consists of a system of quasi‐parallel ridges and channels. We ask how the sediment supplied from a retreating cliff influences the erosion of the plinth hillslopes and channels, and how this affects the rate of cliff retreat. Motivated by field observations and high‐resolution topographic data from two sites in western Colorado, we develop a two‐dimensional (2D), rules‐based numerical model to simulate the erosion of channels draining a plinth and diffusive erosion of the intervening interfluves. In this model, retreat of a cliffband occurs when the height of the vertical cliff exceeds a threshold due to incision by channels on the plinth below. Debris derived from cliff retreat is distributed over the model plinth according to the local topography and distance from the source. This debris then weathers in place, and importantly can act to reduce local bedrock erosion rates, protecting both the plinth and ultimately the cliff from erosion. In this paper, we focus on two sets of numerical model experiments. In one suite, we regulate the rate of rockfall to limit the cliff retreat rate; in most cases, this results in complete loss of the plinth by erosion. In a second suite, we do not impose a limit on the cliff retreat rate, but instead vary the weathering rate of the rockfall debris. These runs result in temporally steady cliff‐plinth forms and retreat rates; both depend on the weathering rate of the debris. Copyright © 2011 John Wiley & Sons, Ltd.

The use of ablation‐dominated medial moraines as samplers for 10Be‐derived erosion rates of glacier valley walls, Kichatna Mountains, AK

AbstractWe use cosmogenic 10Be concentrations in amalgamated rock samples from active, ice‐cored medial moraines to constrain glacial valley sidewall backwearing rates in the Kichatna Mountains, Alaska Range, Alaska. This dramatic landscape is carved into a small ∼65 Ma granitic pluton about 100 km west of Denali, where kilometer‐tall rock walls and ‘cathedral’ spires tower over a radial array of over a dozen valley glaciers. These supraglacial landforms erode primarily by rockfall, but erosion rates are difficult to determine. We use cosmogenic 10Be to measure rockwall backwearing rates on timescales of 103–104 years, with a straightforward sampling strategy that exploits ablation‐dominated medial moraines.A medial moraine and its associated englacial debris serve as a conveyor system, bringing supraglacial rockfall debris from accumulation‐zone valley walls to the moraine crest in the ablation zone. We discuss quantitatively several factors that complicate interpretation of cosmogenic concentrations in this material, including the complex scaling of production rates in very steep terrain, the stochastic nature of the rockfall erosion process, the unmixed nature of the moraine sediment, and additional cosmogenic accumulation during transport of the sediment.We sampled medial moraines on each of three glaciers of different sizes and topographic aspects. All three moraines are sourced in areas with identical rock and similar sidewall relief of ∼1 km. Each sample was amalgamated from 25 to 35 clasts collected over a 1‐km longitudinal transect of each moraine. Two of the glaciers yield similar 10Be concentrations (∼1·6–2·2 × 104 at/g) and minimum sidewall slope‐normal erosion rates (∼0·5–0·7 mm/yr). The lowest 10Be concentrations (8 × 103 at/g) and the highest erosion rates (1·3 mm/yr) come from the largest glacier in the range with the lowest late‐summer snowline. These rates are reasonable in an alpine glacial setting, and are much faster than long‐term exhumation rates of the western Alaska Range as determined by thermochronometric studies. Copyright © 2010 John Wiley & Sons, Ltd.

Some observations on the formation of an active pronival rampart at Grunehogna Peaks, Western Dronning Maud Land, Antarctica

AbstractSummer observations of the morphology and the debris accumulation processes at an actively forming pronival rampart at Grunehogna Peaks, Western Dronning Maud Land, Antarctica demonstrate that rockfall debris accumulation is causing downslope (outward) rampart extension even though the distal slope is not at the angle of repose. Field experiments show that the vast majority of rocks can traverse a stable firn surface to reach the proximal slope of the rampart and more than half end up on the distal slope or beyond. The formation processes indicate that the morphological characteristics and environmental conditions under which such features develop may be more varied than conceived in current models. Consequently, caution must be employed when fossil ramparts are used to infer palaeo‐environmental conditions. Copyright © 2010 John Wiley & Sons, Ltd.

Talus structure and evolution on sandstone mountains in NW Scotland

Twelve gully-wall sections excavated in the upper rectilinear slope of three talus accumulations in NW Scotland reveal a common stratigraphy, similar to that previously described elsewhere in upland Britain: a lower unit of in situ rockfall debris and an upper unit of debris-flow and/or slopewash deposits, often overlying or intercalated with buried organic soils. The upper unit indicates downslope reworking of sediments derived from the top of the talus. Radiocarbon dating of buried organic soils implies that the onset of talus reworking was asynchronous, and occurred before 6.6—7.0 cal. kyr BP at one site (roughly 5.0 kyr after deglaciation) but after c. 2.7 cal. kyr BP at another. A general model for talus evolution in upland Britain is proposed, based on the geomorphological, stratigraphic and dating evidence of this and earlier studies. This comprises: (1) initial accumulation of rockfall debris within a few millennia following deglaciation; (2) near-cessation of rockfall accumulation and development of gullies near the talus crest, with concomitant redistribution of eroded talus sediments on the upper slope by debris flows and slopewash; (3) downslope extension of gullies with associated erosion of both talus and overlying debris-flow and slopewash deposits, and redistribution of these sediments as slope-foot debris cones. This sequence can be explained as an intrinsic response to diminution of paraglacial rockfall inputs, and does not necessarily imply any change in climate, frequency of extreme rainstorm events or other extrinsic effects.

Late Holocene debris cone development and vegetation and land-use history in the Pasture Beck valley, Lake District, NW England

SUMMARY Investigations of a sedimentary sequence exposed in the distal margin of a small debris cone in the valley of Pasture Beck, eastern Lake District, have yielded detailed information concerning the time and nature of cone aggradation phases and the local vegetation and land-use history. Radiocarbon dates from two buried peat beds indicate that the cone surface was generally stable from the late 8 th to the early 13 th centuries AD (1165–736 cal. BP). An interlude of colluvial gravel deposition interrupted peat accumulation and was probably the result of a single short-lived event. Gravel-dominated beds represent deposition of reworked rockfall debris and glacial drift by cohesionless debris flows, whereas finer-grain beds are probably the result of sheet-flows derived by washout of fines from debris-flow deposits. The stratigraphic evidence indicates that the minerogenic sediments accumulated in quick succession. Pollen and charcoal data from peat samples reveal intensification of land-use before burial of the peats by minerogenic sediments. It is proposed that landscape instability was associated first with Norse-Irish settlement and woodland clearance, and later, probably, to the expansion of upland pastures and more intensive grazing in the 13 th century AD. When the Pasture Beck data is considered along with information from elsewhere in the British Isles, it is apparent that not all patterns of Late Holocene landscape change in upland areas can be ascribed to a single cause.

Bedrock slope evolution in saltrock terrain

Saltrock is a highly soluble terrain-forming material and, over short periods of time under predominantly solutional erosion processes, shows readily measurable change. It provides an analogue for landform evolution on less rapidly soluble materials such as limestone and gypsum. Saltrock erosion in a Mediterranean environment is observed with erosion pins on both solid outcrop and rockfall debris. Erosion of the salt terrains is very closely related to rainfall events. Surface lowering rates of up to 20 mm per 100 mm rainfall are observed, representing an annualised rate of ca 100 mm a−1 (= 10 m per century or 100 m per millennium). Clear relationships, which are described by bivariate polynomial equations, exist between slope angle and erosion rate. Slope evolution is then modelled with these equations, to reveal good correspondence with the small-scale landforms present at the field sites.

Numerical simulation of debris flows triggered from the Strug rock fall source area, W Slovenia

Abstract. The Strug landslide was triggered in December 2001 as a rockslide, followed by a rock fall. In 2002, about 20 debris flows were registered in the Kosec village; they were initiated in the Strug rock fall source area. They all flowed through the aligned Brusnik channel, which had been finished just before the first debris flow reached the village in April 2002. Debris flow events were rainfall-induced but also governed by the availability of rock fall debris in its zone of accumulation. After 2002 there was not enough material available for further debris flows to reach the village. Nevertheless, a decision was reached to use mathematical modeling to prepare a hazard map for the village for possible new debris flows. Using the hydrological data of the Brusnik watershed and the rheological characteristics of the debris material, 5 different scenarios were defined with the debris flow volumes from 1000 m3 to a maximum of 25 000 m3. Two mathematical models were used, a one-dimensional model DEBRIF-1D, and a two-dimensional commercially available model FLO-2D. Due to the lack of other field data, data extracted from available professional films of debris flows in 2002 in the Kosec village were used for model calibration. The computational reach was put together from an 800-m long upstream reach and 380-m long regulated reach of the Brusnik channel through the village of Kosec. Both mathematical models have proved that the aligned Brusnik channel can convey debris flows of the volume up to 15 000 m3. Under the most extreme scenario a debris flow with 25 000 m3 would locally spill over the existing levees along the regulated Brusnik channel. For this reason, additional river engineering measures have been proposed, such as the raising of the levees and the construction of a right-hand side sedimentation area for debris flows at the downstream end of the regulated reach.

Sediment production and delivery from recent large landslides and earthquake-induced rock falls in the Upper Soča River Valley, Slovenia

Landsliding not only changes the morphology of the terrain but is also an effective factor in sediment production. Extreme events such as earthquake-induced large rock falls or rainfall-induced landslides may, during the event itself or in a period after it, greatly increase the sediment delivery and river sediment transport. The effects of strong earthquakes and large landslides on sedimentation are evident in the Upper Soča River basin, NW Slovenia. The annual sediment production in the headwaters of this typical alpine valley in western Slovenia is estimated to average>1000 m3 km−2 a−1. In the last few years, two large landslides triggered there were of comparable volume but differed regarding sediment delivery to the fluvial network. The 2000 Stože landslide at 1.5 million m3 was a debris flow that delivered more than 1 million m3 to the Koritnica River. The Strug complex landslide was initiated in 2001 by a rock slide and soon amounted to an estimated volume of 310,000 m3. In 2002, it released over 20 rainfall-induced debris flows on the order of 100 to 1000 m3 to the fluvial system.In mountainous terrain in the headwaters of the Upper Soča River, slope failures may occur during strong earthquakes depending on the event magnitude. The earthquake of April 12, 1998 (MS 5.6) caused more than 100 failures, among them 50 rock falls. About 260,000 m3 of rock fall material will remain on hill slopes with no potential of reaching the river network, while an estimated volume of 480,000 m3 may be released to watercourses in a longer period during extreme events. About 200,000 m3 of rock fall debris was deposited in areas from where the material was released to watercourses during rainfall events. As a consequence of the 1998 earthquake, hyperconcentrated flows were observed during floods in some torrential tributary channels of the Upper Soča River. After the earthquake of July 12, 2004 (MS 4.9), 50 rather superficial slope failures including 38 rock falls were registered. From 2000 until 2004, more than 150,000 m3 sediments were dredged from the Upper Soča River channel.

Strug landslide in W Slovenia: A complex multi-process phenomenon

Large rock slides frequently cause secondary unstable phenomena. Many such instability processes happened after December 2001, when the Strug rockslide estimated at 95,000 m 3 was triggered above the Koseč village near Kobarid in the Julian Alps, W Slovenia. It was initiated at the contact between high permeable calcareous rocks (Cretaceous scaglia) thrusted over nearly impermeable clastic rocks (Cretaceous flysch). Soon after the rockslide initiation, a rock fall with a volume of 45,000 m 3 was initiated within the rockslide. The kinetic push of the rock fall caused the movement of a translational soil landslide with a volume of 180,000 m 3 that partially slipped into the torrential ravine of the Brusnik Stream. After a sudden drop of 15 m in December 2001, the rockslide average velocity exponentially slowed down to less than 10 m/year till the end of 2002, and came to a practical stillstand in 2003. After the rainfall in spring 2002, small debris flows made of clayey gravels with a volume of up to 1000 m 3 started to flow from the zone of accumulation of the rock fall over the soil landslide to and along the channel of the Brusnik Stream. In 2002, more than 20 debris flow events were registered. The statistical analysis of the measured local rainfall intensities showed that debris flows were initiated at daily rainfall reaching from 20 to 30 mm, depending on the antecedent precipitation. This value may be taken as a specific hydrologic threshold for this site. Because in 2003 no more debris flows were registered, a conclusion was drawn that debris flow events were rainfall-induced but governed on the same time by the availability of rock fall debris in its zone of accumulation.

The origin and evolution of footslope ramps in the sandstone desert environment of south-west Jordan

In the Cambrian–Ordovician sandstones of south-west Jordan, the spectacular scenery that has developed under arid conditions includes the presence of low-angle (<10°) ramp slopes lying beneath vertical cliffs and running down to adjacent wadi beds or playas. The ramps are depositional features built of fine debris with occasional larger clasts and may be mantled by weathered boulders in their upper parts. These ramps are especially well displayed in the Ishrin Sandstone, but seem to be the landforms rarely, if ever reported from desert environments. The analysis of ramp geomorphology and sedimentology, and of rock slopes above the ramps, strongly suggests that most of the material that makes up the ramps is provided by catastrophic rockfalls. Rockfall debris is subjected to efficient salt weathering and quickly disintegrates into easily transported fine-grained material which, redistributed by surface wash, builds the ramps. The uniqueness of the ramps arises from a combination of lithological and environmental factors, the former accounting for the high frequency of rockfalls in the Ishrin sandstone, the latter being responsible for the efficacy of salt weathering and surface wash.