Recent Rockfalls Research Articles

Rockfall Hazard and Risk Assessment Along a Transportation Corridor in the Nera Valley, Central Italy

Rockfalls are a common type of fast-moving slope failures, and in many countries they represent the primary cause of landslide fatalities. We present a methodology to ascertain rockfall hazard and to determine the associated risk along transportation networks. The proposed methodology is based on the combined analysis of the recurrence of rockfall events, determined from historical information, the frequency-volume statistics of rockfalls, obtained from inventories of recent rockfall triggering events, and the results of a physically based, spatially distributed rockfall simulation model used to determine rockfall hazard. The available information on rockfall hazard is combined in a Geographic Information System with a map of the transportation network to identify the road sections potentially subject to rockfalls. Information on the location and type of rockfall defensive measures, including revetment nets, elastic fences, concrete walls, and artificial tunnels, is used to estimate the efficacy of the defensive structures and to determine the level of the residual rockfall risk along the roads. To illustrate the methodology, we discuss an application in a 48-km2 area in the Nera River valley, in the Umbria Region of central Italy, where rockfalls are abundant, and where considerable investments were recently made to mitigate rockfall risk.

Distribution of precarious rocks at the Nevada Test Site: Comparison with ground motion predictions from nuclear tests

Precarious rocks have been proposed as ground motion seismoscopes that have been in place thousands of years, thereby providing important constraints on seismic hazard estimates. Numerous precarious rocks exist in the region of large nuclear explosions at Nevada Test Site (NTS). Ground motion recordings from nuclear tests have provided regression equations for ground acceleration and ground velocity as a function of distance and explosion yield for comparison with constraints from precarious rocks. Very near large NTS explosions, there are no precarious rocks or semiprecarious rocks. Cliff faces are shattered and numerous recent rockfalls have fresh white surfaces covered by caliche: proof that the rockfalls have been caused by the explosions. As the distance from the explosions increases and the contours for predicted ground motion decrease, fewer and fewer rockfalls are observed, some semiprecarious rocks begin to appear, and finally, numerous precarious rocks are found with no evidence of recent rockfalls. To quantify the calibration of precarious rocks and ground motion we (1) do field tests on the rocks to determine the quasi‐static and dynamic toppling accelerations, (2) carry out computer tests using estimates of waveforms from NTS explosions, and (3) compare the results with ground motions predicted by empirical regressions for nuclear explosions. We conclude that these comparisons provide an important validation of the precarious rock methodology and an approximate validation of preliminary estimates of toppling accelerations.

Examples of recent rockfalls from basalt cliffs in Northern Ireland

Two examples of recent rockfalls from basalt cliffs in Northern Ireland are described and some trigger mechanisms suggested. The Downhill rockfall of June 2002 resulted in derailment of the Londonderry-Belfast train and occurred following two months of above average rainfall. The Trostan rockfall(s) has (have) resulted in basalt boulders accumulating on the track bed of a late nineteenth century mineral railway, the track having been removed by 1900. Rockfall timing(s) and cause(s) are not known with certainty but the possibility of distant seismic activity acting as a trigger mechanism is introduced. Both examples exceed in magnitude rockfall events recorded elsewhere on the Ulster basalts, and demonstrate the unstable nature of basalt cliffs and the hazards posed to transport routes engineered along their base.

The influence of environmental and lithologic factors on rockfall at a regional scale: an evaluation using GIS

Analysis of the spatial distribution of rockfall deposits at a regional scale (over an area of 250 km 2 of northern Spain) using a cartographic database supported by a Geographic Information System (GIS) reveals several relationships between rockfall activity and environmental variables. Recent rockfall activity is inferred when recent scree is preserved at the bottom of the rock slopes. In order to identify the slope source areas of the scree we have mapped the deposit's drainage basin, applying topographic criteria, and we have combined these basins with the rock slopes map. A method for setting the basin boundaries automatically will replace manual cartography. This method is based on algorithms available within many commercial software programs and originally planned to analyse the behaviour of fluids over a topographic surface. The results obtained by combining the rockfall area source map with the geology and DTM show the relationships between the distribution of rockfall deposits and lithology, elevation and slope of the rockwall and a strong control of the joint type and density. Elevation influence on rockfall has been associated with climatic variations with elevation. Other variables, such as orientation, show complex influences that are difficult to interpret.

Investigations regarding Alpine talus slopes using ground‐penetrating radar (GPR) in the Bavarian Alps, Germany

AbstractThe applicability of ground‐penetrating radar (GPR) for the investigation of loose debris was tested at two sites (Viererkar and Zugspitzplatt). A pulseEKKO 100 GPR system equipped with 25 MHz antennae was utilized. The aim of the investigation was to record the base of the debris layer, and thereby acquire an estimation of the backweathering rates of the adjacent rockwalls. The study areas are situated in the Northern Alps near the German–Austrian border. The sites are characterized by steep limestone rockwalls and extensive talus accumulations. A total of six profiles was surveyed.The method is suitable and effective for a quick survey in this dry, high‐ohmic substrate. The GPR system was able to deliver information about the subsurface stratigraphy to c. 70 m depth. The boundary line to the bedrock was discovered – depending upon the profile surveyed −5 to 25 m below the surface. The base of the debris material sometimes shows no distinct reflection. Buried features (V‐shaped furrows, zones overdeepened by ice action, geological structures) could be detected. Arched structures well below the talus–bedrock interface can be interpreted as drainage systems in the karstic bedrock. A thick scree layer of Late Glacial age was separated from a thinner layer on the talus surface, which was related to the Holocene.The backweathering rates were fixed by a calculation of talus volume to c. 100 mm/103 a during the Holocene (Viererkar) and 150–300 mm/103 a (Zugspitzplatt). The detrital formation in north‐exposed sites is twice as intense as in south‐exposed sites. These results match the rates of recent rockfall in the same area of investigation. The calculated backweathering for the late glacial period is 150–730 mm/103 a.The magnitude of the calculated rockwall retreat lies well within the range of previous measurements. The discrepancy between some weathering rates highlights the fact that recent and past relief formation must be differentiated. Otherwise recent removal rates may be overestimated. Copyright © 2001 John Wiley & Sons, Ltd.

Geological Evaluation of West Virginia Landslides

The major urban areas of West Virginia have been mapped for landslides at a scale of 1:24,000 under an Appalachian Regional Commission (ARC) grant. The mapping covered 36 quadrangles where recent landslides, old landslides, rockfalls, and slide-prone areas were identified. With a landslide density of 18 per square mile covering on average 11 acres each, consideration of several geological factors that are understandable to decisionmakers and the general public was warranted. From this database, a random selection of 2,416 landslides were analyzed using 12 geological map factors to ascertain the conditions associated with past failures and attempt to assess future risk. Three natural factors associated with the sampled landslides appear to be critical for the evaluation of future risks: rock formation, soil series, and slope percent. These factors, when normalized for their actual areal distribution, provide an inexpensive, preliminary assessment of the hazard prior to any financial investment or development decision. For example, if an area has one high-risk factor, building regulations may be required to meet certain additional requirements. As the number of high-risk factors increase, perhaps with consideration given to moderate or low-risk factors, these requirements would change accordingly. Examples of landslides and this normalization procedure for several areas in West Virginia are discussed. Landslide reduction techniques will also be presented.

Ancient and recent landslides and rockfalls in the Skiby zone of the south-east carpathians and geological regularities of their formation

Complex overthrust structures of the Skiby zone in the Ukrainian Carpathians and intensive differentiated neotectonic movements resulted in the development both of old and recent landslides of up to dozens of millions of cubic metres in volume. The landslides occur in terrigenous flysch complexes of Cretaceous and Paleogene age. One of these landslides of about 10–12 million m3 took place in June 1969 in the valley of the Black Cheremosh. Landslides of plastic character (earthflows) are common in this region; their origin depends on the ground-water conditions of slopes. Landslides of any type are characterized from the point of view of the relationship of their occurrence to tectonic structures, geomorphological elements, zone of weathering and ground-water conditions.

Recent Rock Fall a Trifling Incident in Niagara's History

Recent Rock Fall a Trifling Incident in Niagara's History