Ancient Rockslide Research Articles

Frictional heating and thermal effects of ancient rockslide sedimentology: a case study of the Dora Kamiyama Rockslide and implications for dynamic reconstruction

Frictional heating and thermal effects of ancient rockslide sedimentology: a case study of the Dora Kamiyama Rockslide and implications for dynamic reconstruction

Hydrological control shift from river level to rainfall in the reactivated Guobu slope besides the Laxiwa hydropower station in China

Landslides are common geohazards associated with natural drivers such as precipitation, land degradation, toe erosion by rivers and wave attack, and ground shaking. On the other hand, human alterations such as inundation by water impoundment or rapid drawdown may also destabilize the surrounding slopes. The Guobu slope is an ancient rockslide on the banks of the Laxiwa hydropower station reservoir (China), which reactivated during the reservoir impoundment in 2009. We extracted three-dimensional surface displacements with azimuth and range radar interferometry using European Space Agency's Copernicus Sentinel-1 and German Aerospace Center's TerraSAR-X data during 20152019. The upper part of the Guobu rockslide is characterized by toppling and is mostly subsiding with maximum rates over 0.4 m/yr and 0.7 m/yr in the vertical and horizontal directions, respectively. During filling of the reservoir prior to 2014, there was a long-wavelength in-phase response between rising reservoir level and GPS-observed increased slope movements. After the reservoir water level stabilized from 2015 to 2019, the slide movement became seasonal and we see a correlation between rainfall and landslide movement. These observations suggest that the slide motion is now primarily controlled by rainfall. The spatiotemporal landslide displacements allow us to estimate the hydraulic diffusivity of the rock mass, to be on the order (~1.05 × 10‐7 m2/s) and the thickness of the moving rock mass (~200 m). Our results demonstrate that InSAR is a useful tool for monitoring the rockslide movement as a function of seasonal precipitation.

Multiple geophysical investigations to characterize massive slope failure deposits: application to the Balta rockslide, Carpathians

SUMMARYOrigins of ancient rockslides in seismic regions can be controversial and must not necessarily be seismic. Certain slope morphologies hint at a possible coseismic development, though further analyses are required to better comprehend their failure history, such as modelling the slope in its pre-failure state and failure development in static and dynamic conditions. To this effect, a geophysical characterization of the landslide body is crucial to estimate the possible failure history of the slope. The Balta rockslide analysed in this paper is located in the seismic region of Vrancea-Buzau, Romanian Carpathian Mountains and presents a deep detachment scarp as well as a massive body of landslide deposits. We applied several geophysical techniques on the landslide body, as well as on the mountain crest above the detachment scarp, in order to characterize the fractured rock material as well as the dimension of failure. Electrical resistivity measurements revealed a possible trend of increasing fragmentation of rockslide material towards the valley bottom, accompanied by increasing soil moisture. Several seismic refraction surveys were performed on the deposits and analysed in form of P-wave refraction tomographies as well as surface waves, allowing to quantify elastic parameters of rock. In addition, a seismic array was installed close to the detachment scarp to analyse the surface wave dispersion properties from seismic ambient noise; the latter was analysed together with a colocated active surface wave analysis survey. Single-station ambient noise measurements completed all over the slope and deposits were used to further reveal impedance contrasts of the fragmented material over in situ rock, representing an important parameter to estimate the depth of the shearing horizon at several locations of the study area. The combined methods allowed the detection of a profound contrast of 70–90 m, supposedly associated with the maximum landslide material thickness. The entirety of geophysical results was used as basis to build up a geomodel of the rockslide, allowing to estimate the geometry and volume of the failed mass, that is, approximately 28.5–33.5 million m3.

The Influence of External Digital Elevation Models on PS-InSAR and SBAS Results: Implications for the Analysis of Deformation Signals Caused by Slow Moving Landslides in the Northern Apennines (Italy)

Advanced interferometric synthetic aperture radar (InSAR) postprocessing, like persistent scatterer InSAR (PS-InSAR), offers the possibility to investigate slow moving landslides, where standard interferometry is problematic. These advanced algorithms involve the analysis of a series of SAR acquisitions in both time and space. One input that requires particular attention for landslide applications is the external digital elevation model (DEM) that is used to correct the interferograms for the topographic phase term. When multiple elevation data sets are available for a given study area, it is difficult to decide which one should be used. In this paper, we test the sensitivity of PS-InSAR/Small Baseline Subset (SBAS) results to different DEMs. The study area is located in the Northern Apennines of Italy, where chaotic clay shales and fine-grained flysch host slow-moving earth flows and ancient rock slides. $C$ -band (Envisat) and $X$ -band (Cosmo-SkyMed) data are processed with different DEMs. We describe a simple framework to statistically analyze the influence of these models on the final PS-InSAR/SBAS results. We find that individual interferograms do not vary much depending on the DEM, while the results from PS-InSAR and SBAS analysis do vary. This is likely caused by the way the DEM error is estimated. We find also that the quality of the DEM is more important than the resolution and that $X$ -band InSAR data are more sensitive to the choice of the DEM than $C$ -band. The significance of the results is discussed with reference to two landslide areas.

Alpine landslide risk scenario: run-out modelling using a 3D approach

Rockslides of considerable volume developing on the flanks of narrow alpine valleys represent a significant hazard for the potential of river damming and consequent sudden discharge of water.A limestone rock mass of about 650,000 m3 endangers a portion of the upper course of Tagliamento River valley in north-eastern Italy.This section of the valley is prone to detachment of rock landslides due to its structural setting and it has a history of landslide damming: in the literature two huge events are widely documented and a third event is identified and described in this paper. The ancient detachment crown and the corresponding deposit can be observed in the portion of slope adjacent to the unstable rock mass.This paper deals with the run-out model of the unstable rock mass using a Smoothed Particles Hydrodynamics (SPH) model implemented in the DAN3D code. In order to select the appropriatematerial parameters, the ancient rockslide was back-analysed. Subsequently, the parameters were applied to the present unstable portion of the slope to determine the location and dimensions of the deposit that could be formed.It is demonstrated that the deposit has the potential to create a natural dam across the Tagliamento River that would form a 500,000 m3 lake. Although the lake will have limited dimensions, this would represent a very high risk for the downstream villages and infrastructures in case of a sudden collapse of the natural dam.

Back analysis of an ancient rockslide at Lake Fundudzi, Limpopo Province, South Africa

A massive rockslide occurred in the Soutpansberg Mountains of the Limpopo Province ~20,000 years ago that blocked the course of the eastern flowing Mutale River forming Lake Fundudzi, which is the only known true inland lake in South Africa. The landslide occurred in the northwestward dipping and highly jointed Fundudzi Formation of the Soutpansberg Group. The failed slope was observed to be a homogenous jointed sandstone rock slope which is quartzitic in places. Cluster analysis, which uses fuzzy clustering in Rocscience Dips, revealed three major joint sets (JS1, S0 and JS3) in the rock mass with an average dip and dip direction of 85°/237°, 15°/283° and 73°/157°, respectively. The main failure plane best correlated with JS3, which dips towards the lake. The kinematic analysis also revealed that the mechanism of failure was planar which is in agreement with site observations. The strong rock material classification of the sandstone from a laboratory index and mechanical tests was one of the indicators that failure could have been mostly structurally controlled. The technique of back-analysis was employed using RocPlane in order to investigate the geotechnical conditions that may have resulted in failure. The results obtained from the sensitivity analysis in RocPlane showed that the joint roughness coefficient (JRC) followed by the residual basic friction angle (ϕ r) were the main influential shear strength parameters on the factor of safety, F, as opposed to the joint wall compressive strength (JCS) which has very little impact on F for the range of values considered. Results from back-analysis show a range of possible combinations of JRC and ϕ r values under different groundwater and seismic conditions. Whilst the groundwater shows more impact than the seismic coefficient, the field evidence points to seismic activity as a more plausible trigger than groundwater. This study shows the usefulness of back-analysis techniques in assessing various conditions of failure that may have resulted in ancient rockslides. Although it may not result in a unique set of geotechnical parameters that may have resulted in failure, it, however, gives an insight into probable causes of failure and, thus, can be useful in mitigation of future failures.

Partial reactivation of a huge deep-seated ancient rock slide: recognition, formation mechanism, and stability

Abstract. About 18 years ago, a large-scale discontinuous layer in properties and colour was found in the new Fengjie town at the shore of the Three Gorges Reservoir area in China. There are many resettled residents and buildings on the sloping area, the safety of which is potentially affected by this layer, so it has become the focus of attention. Before this study started there were two viewpoints regarding the origin of this layer. One was that is was from a huge ancient slide and the other was that is was from a fault graben. In order to find out how it was formed and to be able to carry out a stability analysis of the slope the authors have carried out a research program, including geological field investigations and mapping, a deep drilling hole, a geotechnical centrifuge model test, and a simulation analysis. The results of the research led to the conclusion that the layer is the sliding plane of a huge deep-seated ancient rock slide, which we called the Sanmashan landslide. An important argument for the conclusion is the recognition of a regional compressive tectonic stress field in this area, which cannot lead to the formation of a fault graben because it needs a tensional tectonic stress field. Moreover, numerous unique geological features, sliding marks, and other relics of the ancient slide have been discovered in the field. The formation process of the ancient slide could be repeated in a large geotechnical centrifuge model test. The test shows that a deformation and failure process of "creep–crack–cut" has occurred. The type of the ancient slide can be classified as a "successive rotational rock slide". Finally, the role of seepage in the stability of the Sanmashan landslide has been analysed. Our final conclusions are that, during rainfall and filling–drawdown cycles in the Three Gorges Reservoir, the Sanmashan landslide as a whole is dormant and stable and the secondary landslides in the toe area of the slope are presently stable but can be reactivated. This research provides an important basis for the remedial measures and land use planning in the new Fengjie town, and a well-documented case history for researchers worldwide.

Gravity-induced rock mass damage related to large en masse rockslides: Evidence from Vajont

The Vajont landslide is a well-known, reservoir-induced slope failure that occurred on 9 October 1963 and was characterized by an ‘en masse’ sliding motion that triggered various large waves, determining catastrophic consequences for the nearby territory and adjacent villages. During the Vajont dam construction, and especially after the disaster, some researchers identified widespread field evidence of heavy rock mass damage involving the presumed prehistoric rockslide and/or the 1963 failed mass. This paper describes evidence of heavy gravitational damage, including (i) folding, (ii) fracturing, (iii) faulting, and (iv) intact rock disintegration. The gravity-induced rock mass damage (GRMD) characterizes the remnants of the basal shear zone, still resting on the large detachment surface, and the 1963 failed rock mass. The comprehensive geological study of the 1963 Vajont landslide, based on the recently performed geomechanical survey (2006–present) and on the critical analysis of the past photographic documentation (1959–1964), allows us to recognize that most GRMD evidence is related to the prehistoric multistage Mt. Toc rockslide. The 1963 catastrophic en masse remobilization induced an increase to the prehistoric damage, reworking preexisting structures and creating additional gravity-driven features (folds, fractures, faults, and rock fragmentation). The gravity-induced damage was formed during the slope instability phases that preceded the collapse (static or quasi-static GRMD) and also as a consequence of the sliding motion and of the devastating impact between the failed blocks (dynamic GRMD). Gravitational damage originated various types of small drag folds such as flexures, concentric folds, chevron, and kink-box folds, all having a radius of 1–5m. Large buckle folds (radius of 10–50m) are related to the dynamic damage and were formed during the en masse motion as a consequence of deceleration and impact processes that involved the sliding mass. Prior to failure, unstable rock slopes can be affected by diffuse newly formed gravity-driven joints that are absent in the surrounding area and within the underlying bedrock, as the Vajont case history demonstrates (joint sets J9 and J10). These fractures, caused by critical tensile and shear stresses, represent an important mechanical clue to recognizing, on a geological basis, the instability condition of a rock slope under investigation. Owing to its complex geological evolution, the Vajont landslide is an outstanding example to help learn about cumulative GRMD effects that can accumulate over time when an ancient rockslide is further remobilized by a sudden en masse sliding motion.

The Hungtsaiping landslides: from ancient to recent

A large and deep-seated landslide at Hungtsaiping was triggered by the 1999 Chi-Chi earthquake with the magnitude of 7.3. Extensive site investigations for the landslide were conducted including field reconnaissance, geophysical exploration, borehole logs, and laboratory experiments. Thick colluvium was found around the landslide area and indicated the occurrence of a large ancient landslide. The Hungtsaiping area involves at least two large landslides events, an ancient rockslide and the 1999 colluvium slide. With the consideration of a source collapse mass, the two landslides in sequence are reasonably reproduced by the distinct element modeling. The modeling is calibrated by rock mass strength behavior through a procedure with the Hoek–Brown failure criterion, statistical experimental design, and optimization techniques. The mechanism of the 1999 landslide that cannot be revealed by the underground exploration data alone is clarified. The proposed procedure enables a rational and efficient way to determine micro-parameters for the distinct element modeling of landslides.

Ancient, giant rockslides, Sinking Creek Mountain, southern Appalachians, Virginia

Giant rockslides and slumps are recognized over a large part of the east limb of the Sinking Creek anticline, a southern Appalachian fold. The slides are among the largest such features known in the Appalachians and are found within 15 km of the active Giles County, Virginia, seismic zone. The zone of rockslides, identified by anomalous topography and geologic structures, is about 25 km long and 1.0 km wide. Downslope transport, ranging from 0.5 to 1.0 km, of at least 100 million m 3 of Silurian sandstones and shales can be identified. During sliding, bedding within individual blocks, as much as 5.0 km long, has undergone 30° to 90° rotation about a horizontal axis. The displaced masses have undergone extensive erosion and dissection and may be only remnants of previously more extensive slides. Secondary features associated with the rockslides include breakaway scarps, slope reversals, sag ponds, and slide breccias. The recognition of these features, which might be mistaken for remnants of an Alleghanian thrust sheet, suggests that examination of similar settings throughout the southern and central Appalachian Valley and Ridge province might disclose additional examples of large ancient rockslides.

The Howell Creek Structure -- A Paleogene Rock Slide in the Southern Canadian Rocky Mountains

ABSTRACT The Howell Creek structure exposes an area of Upper Cretaceous sandstones and shales surrounded by Paleozoic limestones in the southern Canadian Rocky Mountains. Since its discovery, the structure has become widely known as a tectonic window in which the usual relationships between overthrust and subthrust strata have been modified by later faulting. Recent road works and a forest fire have created new exposures which show that the Howell Creek structure is an ancient rock slide, emplaced during or shortly after the phase of extension faulting that followed the early Tertiary deformation of the Front Ranges of the Rocky Mountains.