Two successive landslides within a month started in October 11, 2018, and dammed twice the Jinsha River at the border between Sichuan Province and Tibet in China. Both events had potential to cause ...catastrophic flooding that would have disrupted lives of millions and induced significant economic losses. Fortunately, prompt action by local authorities supported by the deployment of a real-time landslide early warning system allowed for quick and safe construction of a spillway to drain the dammed lake. It averted the worst scenario without loss of life and property at least one order of magnitude less to what would have been observed without quick intervention. Particularly, the early warning system was able to predict the second large-scale slope failure 24 h in advance, along with minor rock falls during the spillway construction, avoiding false alerts. This paper presents the main characteristics of both slope collapses and damming processes, and introduces the successful landslide early warning system. Furthermore, we found that the slope endured cumulative creeping displacements of > 40 m in the past decade before the first event. Twenty-five meter displacement occurred in the year immediately before. The deformation was measured by the visual interpretation of multitemporal satellite images, which agrees with the interferometry synthetic aperture radar (InSAR) measurement. If these had been done before the emergency, economic losses could have been reduced further. Therefore, our findings strengthen the case for the deployment of systematic monitoring of potential landslide sites by integrating earth observation methods (i.e., multitemporal satellite or UAV images) and in situ monitoring system as a way to reduce risk. It is expected that this success story can be replicated worldwide, contributing to make our society more resilient to landslide events.
Rock slope stability is a key research issue in geotechnical engineering. Weak layer is a distinct feature distinguishing the rock slopes from soil types, and its existence considerably controls the ...slope stability. Taking in to account the differences in mineral composition, sedimentary conditions, stress history and other geological processes, the physical and mechanical parameters of rock mass generally show certain spatial variability. On the other hand, for slope failures such as landslides, rockfall and debris flows, earthquake is one of the main triggering factors. In this paper, an efficient framework is presented to evaluate the stability of the rock slope with weak layers considering spatial variability of rock mass strength properties under seismic loading. A rock slope model with weak layer is established, followed by modeling of both the spatial variability of cohesion (c) as well as friction angle (ϕ) of rock material and weak layer characterized by random field method. Random seismic loading is applied via the pseudo-static method. The Latin Hypercube Sampling (LHS) is adopted to calculate the failure probability of rock slope. The results indicate that the spatial variability of weak layer has more influence on the slope stability than that of rock material, and the influence of seismic randomness cannot be neglected. In addition, under different seismic loadings, the spatial variability of weak layers and seismic randomness have different effects on slope failure probability.
•Framework proposed to evaluate seismic stability of rock slopes considering spatial variability.•Highlighting the effect of weak layer on failure probability.•Considering seismic randomness and spatial variability simultaneously.•Sensitivity analysis of the influence of various parameters on failure probability under different seismic loadings.
A strong earthquake (Mw=6.4) occurred in NW Peloponnesus, Greece, on June 8, 2008. The focal mechanism shows a transcurrent kinematics, and based on aftershocks distribution the causative fault is a ...dextral strike-slip NNE-SSW trending structure. The shock generated severe secondary environmental effects like rock-falls and liquefaction phenomena inducing structural damages and ground failures mainly along the fault strike. Evidence of liquefaction was observed in the area of Kato Achaia and Roupakia villages, while rock-falls were triggered mainly close to the epicentre at the foothills of the Skolis Mountain. Based on a quantitative methodological approach, the ground deformation and failures generated by the event have been investigated. In particular, based on an immediate post-event survey, we mapped in detail the distribution of the earthquake-induced ground failures, defining the areas prone to liquefaction and their associated potential. Moreover, a rock-fall hazard zonation in the area of Skolis Mountain has been developed based on the shadow angle approach, confirming the validity of the safety run-out distance models.
A database of fatalities caused by natural hazard processes in Switzerland was compiled for the period between 1946 and 2015. Using information from the Swiss flood and landslide damage database and ...the Swiss destructive avalanche database, the data set was extended back in time and more hazard processes were added by conducting an in-depth search of newspaper reports. The new database now covers all natural hazards common in Switzerland, categorised into seven process types: flood, landslide, rockfall, lightning, windstorm, avalanche and other processes (e.g. ice avalanches, earthquakes). Included were all fatal accidents associated with natural hazard processes in which victims did not expose themselves to an important danger on purpose. The database contains information on 635 natural hazard events causing 1023 fatalities, which corresponds to a mean of 14.6 victims per year. The most common causes of death were snow avalanches (37 %), followed by lightning (16 %), floods (12 %), windstorms (10 %), rockfall (8 %), landslides (7 %) and other processes (9 %). About 50 % of all victims died in one of the 507 single-fatality events; the other half were killed in the 128 multi-fatality events. The number of natural hazard fatalities that occurred annually during our 70-year study period ranged from 2 to 112 and exhibited a distinct decrease over time. While the number of victims in the first three decades (until 1975) ranged from 191 to 269 per decade, it ranged from 47 to 109 in the four following decades. This overall decrease was mainly driven by a considerable decline in the number of avalanche and lightning fatalities. About 75 % of victims were males in all natural hazard events considered together, and this ratio was roughly maintained in all individual process categories except landslides (lower) and other processes (higher). The ratio of male to female victims was most likely to be balanced when deaths occurred at home (in or near a building), a situation that mainly occurred in association with landslides and avalanches. The average age of victims of natural hazards was 35.9 years and, accordingly, the age groups with the largest number of victims were the 20–29 and 30–39 year-old groups, which in combination represented 34 % of all fatalities. It appears that the overall natural hazard mortality rate in Switzerland over the past 70 years has been relatively low in comparison to rates in other countries or rates of other types of fatal accidents in Switzerland. However, a large variability in mortality rates was observed within the country with considerably higher rates in Alpine environments.
We performed a passive seismic monitoring of the La Praz ∼14,000 m3 unstable slope (French Alps) spanning over 10 years. During the last 6 months prior to collapse, we detected a clear 24% decrease ...in the slope's fundamental resonance frequency, f0, caused by a reduction in overall rock mass stiffness. The combined study of f0 and slope deformation suggested the alternating importance of sudden brittle failure processes versus more ductile phases with possible sliding. Seismic monitoring revealed slope damage that remained ambiguous or undetected with ground surface deformation monitoring, and highlighted critical periods with intense damage. Only some of these critical damage periods could be related to clear external forcing factors such as intense rainfall episodes. These new insights into rock slope's structural condition at depth represent an asset for future monitoring systems. Surface deformation and passive seismic stiffness tracking combined could reveal active slopes with ongoing damage processes.
Plain Language Summary
Forecasting the time of rockfalls is of critical importance for risk mitigation operators in order to preserve the safety of persons and the integrity of infrastructure. Most monitoring systems are based on ground deformation measurements, which may fail when the surface motion does not accurately reflect changes in slope stiffness with time. In this work, we used a seismic sensor that passively recorded ground vibrations on top of a ∼14,000 m3 unstable slope. We detected a significant decrease in the slope's first resonance frequency (−24%) during the 6 months preceding complete collapse. We also revealed details of slope damage processes acting within the slope, showing sudden breakage phases alternating with smoother deformation and sliding phases. These processes would not have been suspected with slope deformation monitoring alone. The use of a new parameter that combines passive seismic tracking and surface deformation measurements could help revealing active slopes with ongoing damage processes. This inovative approach represents an asset for future practical rock slope monitoring.
Key Points
We observed a 24% decrease in rock slope fundamental frequency during the 6 months preceding a ∼14,000 m3 collapse
New insights into slope degradation processes revealed the alternate control of two damage regimes with contrasting rate
Results revealed slope damage phases that would not have been suspected on the basis of slope deformation monitoring alone
Rockfall remains a prominent hazard for transportation corridors worldwide. Recent studies have shown promising results in resolving the relationships between rockfall activity and triggers, ...including in some cases detecting precursor activity prior to failure, which could have implications to improving safety and performance of transportation corridors. The aim of this study is to better understand rockfall failure processes and triggers for cut slopes in interbedded sedimentary rock through a long-term study using photogrammetry data with high spatiotemporal frequency. The combination of daily data, high-precision rockfall volume estimation, and 22-month monitoring duration is unique among studies that evaluate rockfall triggers and allows us to derive insights into differences in rockfall triggering between blocks of different volumes. The data collected allowed the relative frequency of rockfalls of different volumes to be well-constrained for volumes ranging from 0.01 m3 up to 76 m3 (the largest event that occurred during the monitoring period). A quantitative comparison between precipitation and rockfall activity established that precipitation was the primary trigger for rockfall at the site, with only 1.4% of 24-h photo intervals without precipitation having at least one rockfall, as compared to 25.0% of photo intervals with precipitation (and 57.1% of photo intervals with at least 5 mm of precipitation). The marginal impact of additional rainfall above 8 mm per 24-h period on rockfall probability was negligible among all rockfalls observed, whereas the probability of the largest rockfalls at the site (> 1 m3) occurring continued to increase as a function of precipitation up to 20 mm per 24-h period. Detailed analysis of change data leading up to the largest (76 m3) rockfall observed illustrated the progressive failure mechanism of the block, including observations of forward toppling motion and smaller precursor rockfalls around its perimeter. This rockfall was also used for a proof-of-concept demonstration of the potential for a spatiotemporal rockfall density metric to be used to help identify areas of potential hazard. Ultimately, the findings from this study contribute to knowledge on rockfall processes outside alpine regions, which have historically been less well-studied.
Rockwall erosion by rockfall is largely controlled by frost weathering in high alpine environments. As alpine rock types are characterized by crack‐dominated porosity and high rock strength, frost ...cracking observations from low strength and grain supported pore‐space rocks cannot be transferred. Here, we conducted laboratory experiments on Wetterstein limestone samples with different initial crack density and saturation to test their influence on frost cracking efficacy. We exposed rocks to real‐rockwall freezing conditions and monitored acoustic emissions as a proxy for cracking. To differentiate triggers of observed cracking, we modeled ice pressure and thermal stresses. Our results show initial full saturation is not a singular prerequisite for frost cracking. We also observe higher cracking rates in less‐fractured rock. Finally, we find that the temperature threshold for frost cracking in alpine rocks falls below −7°C. Thus, colder, north‐exposed rock faces in the Alps likely experience more frost cracking than southern‐facing counterparts.
Plain Language Summary
Freezing results in the formation of ice that exerts stresses on fracture walls and draws in additional moisture to supply further growth and break down rocks, a process termed frost cracking. Frost cracking drives much erosion and rockfall in alpine environments. Here we test hypotheses from prior work about how frost cracking is impacted by saturation and rock properties. We exposed rock samples of different strength and saturation to identical freezing conditions in laboratory experiments. We monitored rock temperature and acoustic emissions (AE), assuming frost cracking produces the recorded AE hits. We find that initial full saturation is not required for frost cracking, as water transport is enhanced by fractures in alpine rocks. Furthermore, rock with initial higher short‐term strength showed more frost cracking because, we infer, of stiffness properties that make these rocks more brittle compared to lower strength rocks. Frost cracking occurred at a wide range of temperatures below freezing and was highest between −9 and −7°C. We thus conclude that frost cracking is most impacted by temperature and rock short‐term strength. In Alpine environments, this may result in more frost cracking and rockfall on colder north‐facing rockwalls than warmer southern exposures.
Key Points
Initial saturation levels do not limit the efficacy of ice segregation in fractured alpine rocks
Rock initial crack density impacts rock stiffness and thermal properties and thus frost cracking efficacy
The “frost cracking window” temperature range is dependent on rock strength and crack‐controlled porosity in alpine rocks
In the growing field of Geoheritage, Geoconservation, Geo-education and Geotourism, there is a need to manage sites of geoheritage significance. While there is some great geology in nature available ...to appreciate for scenic value, education, tourism and research, many locations need to be protected from people and commercialism (e.g. the Iridium layer at the K/T boundary in Gubbio, Italy, the Ediacaran fauna in South Australia, the Burgess Shale in Canada or the zircon crystals at Jack Hills, among many others), and some locations need hazard management to protect people (e.g. continuously collapsing cliffs that have potential to be hazardous via rock falls, or slippery slopes, or high cliffs that are treacherous, or 'king waves' on rocky shores). The concept of the '8Gs' is intended as a policy-style guidance that logically and progressively links Geology and Geoheritage through a series of steps to Geo-education and Geotourism. There is a logical progression from Geology the Science, through to Geoheritage and the identification of sites of geoheritage significance, to the establishment of Geosites/Geoparks, Geoconservation, leading to Geomanagement, Geo-education and Geotourism. Geomanagement needs to be undertaken prior to the use of sites for Geo-education and Geotourism. In relation to Geomanagement, sites need to be investigated for safety issues, and for the protection of their geological features. Geodiversity, the eighth 'G', is outside the progression but plays an important part in underpinning biodiversity. There is also a need to address and manage geodiversity in a given region or specific site to help understand and manage biodiversity.
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