Fragmentation has been proposed as an important dynamical process in the propagation of rock avalanches. The occurrence of an intense block fragmentation inside a rock avalanche traveling on smooth ...inclined terrain followed by a flat region (a geometry common to many landslides) is first studied numerically by means of a discrete element 2‐D code in which blocks are subjected to mutual collisions and impact with the terrain. This numerical model confirms that the locations where fragmentation is more likely to occur are those in correspondence of abrupt slope changes. We thus analyze this geometry of impact in two cases: low‐ and high‐impact energy. In the first case, where recent experimental data are available, a kinematic analysis shows that the energy released at impact causes high velocities of the smallest fragments, a highly probable scenario in rock avalanche dynamics. When the impact is so energetic to disintegrate the landslide, we find that explosive fragmentation at the slope break provides an extra horizontal boost to a rock avalanche via a peculiar mechanism coupling the geometry of the slope path to the dynamics of the rock avalanche. As a consequence, a net momentum gain (boost) results along the horizontal direction due to the terrain asymmetry. However, under normal field conditions, only when the slope angle is greater than 70° and fragmentation produces clasts of fairly uniform size, the momentum and runout distance are significantly enhanced. Allowing for a spectrum of fragment sizes and velocities, we find a relationship between the degree of fragmentation and the magnitude of the extra boost.
Key Points
Excessive runout of granular flows on steep slopes
Impact energy effect on rock fragmentation
Topographic and geometric effects on fragmentation and mobility
On 8th August 2017, a magnitude Ms 7.0 earthquake struck the County of Jiuzhaigou, in Sichuan Province, China. It was the third Ms ≥ 7.0 earthquake in the Longmenshan area in the last decade, after ...the 2008 Ms 8.0 Wenchuan earthquake and the 2013 Ms 7.0 Lushan earthquake. The event did not produce any evident surface rupture but triggered significant mass wasting. Based on a large set of pre- and post-earthquake high-resolution satellite images (SPOT-5, Gaofen-1 and Gaofen-2) as well as on 0.2-m-resolution UAV photographs, a polygon-based interpretation of the coseismic landslides was carried out. In total, 1883 landslides were identified, covering an area of 8.11 km2, with an estimated total volume in the order of 25–30 × 106 m3. The total landslide area was lower than that produced by other earthquakes of similar magnitude with strike-slip motion, possibly because of the limited surface rupture. The spatial distribution of the landslides was correlated statistically to a number of seismic, terrain and geological factors, to evaluate the landslide susceptibility at regional scale and to identify the most typical characteristics of the coseismic failures. The landslides, mainly small-scale rockfalls and rock/debris slides, occurred mostly along two NE-SW-oriented valleys near the epicentre. Comparatively, high landslide density was found at locations where the landform evolves from upper, broad valleys to lower, deep-cut gorges. The spatial distribution of the coseismic landslides did not seem correlated to the location of any known active faults. On the contrary, it revealed that a previously-unknown blind fault segment—which is possibly the north-western extension of the Huya fault—is the plausible seismogenic fault. This finding is consistent with what hypothesised on the basis of field observations and ground displacements.
In the morning of 23 August 2017, around 3×106 m3 of
granitoid rock broke off from the eastern face of Piz Cengalo, southeastern Switzerland.
The initial rockslide–rockfall entrained 6×105m3
of a ...glacier and continued as a rock (or rock–ice) avalanche before evolving into a
channelized debris flow that reached the village of Bondo at a distance of
6.5 km after a couple of minutes. Subsequent debris flow surges followed in
the next hours and days. The event resulted in eight fatalities along its
path and severely damaged Bondo. The most likely candidates for the water
causing the transformation of the rock avalanche into a long-runout debris
flow are the entrained glacier ice and water originating from the debris
beneath the rock avalanche. In the present work we try to reconstruct
conceptually and numerically the cascade from the initial rockslide–rockfall to the first debris flow surge and thereby consider two scenarios in
terms of qualitative conceptual process models: (i) entrainment of most of
the glacier ice by the frontal part of the initial rockslide–rockfall
and/or injection of water from the basal sediments due to sudden rise in
pore pressure, leading to a frontal debris flow, with the rear part largely
remaining dry and depositing mid-valley, and (ii) most of the entrained
glacier ice remaining beneath or behind the frontal rock avalanche and
developing into an avalanching flow of ice and water, part of which overtops
and partially entrains the rock avalanche deposit, resulting in a debris
flow. Both scenarios can – with some limitations – be numerically
reproduced with an enhanced version of the two-phase mass flow model
(Pudasaini, 2012) implemented with the simulation software r.avaflow, based
on plausible assumptions of the model parameters. However, these simulation
results do not allow us to conclude on which of the two scenarios is the more
likely one. Future work will be directed towards the application of a
three-phase flow model (rock, ice, and fluid) including phase transitions in
order to better represent the melting of glacier ice and a more appropriate
consideration of deposition of debris flow material along the channel.
The presence of trees along the slope and block fragmentation at impact strongly affect rockfall dynamics and hazard as a consequence. However, these phenomena are rarely simulated explicitly in ...rockfall studies. We performed rockfall simulations by using the 3D rockfall simulator Hy-Stone, modeling both the presence of trees and fragmentation through specific algorithms implemented in the code. By comparing these simulations with a more classical approach that attempts to account implicitly for such phenomena in the model parameters and by using a new probabilistic rockfall hazard analysis (PRHA) method, we were able to quantify the impact of these phenomena on the design of countermeasures and on hazard. We demonstrated that hazard changes significantly when accounting explicitly for these phenomena and that a classical implicit approach usually overestimates both the hazard level and the 95th percentile of kinetic energy, leading to an oversizing of mitigation measures.
Convolution neural network (CNN) is an effective and popular deep learning method which automatically learns complicated non-linear mapping from original inputs to given labels or ground truth ...through a series of convolutional layers. This study focuses on detecting landslides from high-resolution optical satellite images using CNN-based methods, providing opportunities for recognizing latent landslides and updating large-scale landslide inventory with high accuracy and time efficiency. Considering the variety of landslides and complicated backgrounds, attention mechanisms originated from the human visual system are developed for boosting the CNN to extract more distinctive feature representations of landslides from backgrounds. As deep learning needs a large number of labeled data to train a learning model, we manually prepared a landslide dataset which is located in the Bijie city, China. In the dataset, 770 landslides, including rock falls, rock slides, and a few debris slides, were interpreted by geologists from the satellite images and digital elevation model (DEM) data and further checked by fieldwork. The landslide data was separated into a training set that trains the attention boosted CNN model and a testing set that evaluates the performance of the model with a ratio of 2:1. The experimental results showed that the best F
1
-score of landslide detection reached 96.62%. The results also proved that the performance of our spatial-channel attention mechanism was fairly over other recent attention mechanisms. Additionally, the effectiveness of predicting new potential landslides with high efficiency based on our dataset is demonstrated.
We present a quantitative risk assessment (QRA) to guide decision-making for selection of rock fall protection strategies. The analysis corresponds to a section of highway near Canmore, Alberta, ...Canada; where rock falls are common. Environmental concerns, tourism, and economic activities overlap the project area, which increased the complexity of the decision-making process. QRA was adopted to improve highway user safety and minimize effects on natural, social, and economic environments. Uncertainty was associated with hazard and consequence quantification, and the study elicited plausible ranges of input variables for risk calculation. Expected and range in risk were calculated for current conditions and after mitigation. Individual risk to highway users was found to be low, following the limited exposure of any particular individual. Current total risk was calculated at 2.9 × 10
−4
probability of fatality and a plausible range between 2.0 × 10
−5
and 5.5 × 10
−3
. The slope protection configuration selected had a residual total risk between 9.0 × 10
−4
and 2.9 × 10
−6
, and a best estimate of 4.5 × 10
−5
. The risk levels were evaluated against criteria previously used in Canada and were considered an appropriate balance between project costs, public safety, environmental concerns, tourism, and economic activities after mitigation.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Indian Himalayas are home to numerous glacial lakes, which can pose serious threat to downstream communities and lead to catastrophic socioeconomic disasters in case of a glacial lake outburst flood ...(GLOF). This study first identified 329 glacial lakes of size greater than 0.05 km2 in the Indian Himalayas, and then a remote sensing‐based hazard and risk assessment was performed on these lakes. Different factors such as avalanche, rockfall, upstream GLOF, lake expansion, identification of the presence of ice cores, and assessment of the stability of moraine were considered for the hazard modeling. Further, a stochastic inundation model was applied to quantify the potential number of buildings, bridges, and hydropower systems that could be inundated by GLOF in each lake. Finally, the hazard parameters and downstream impact were collectively considered to determine the risk linked with each lake. A total of 23 lakes were identified as very high risk lakes and 50 as high‐risk lakes. The potential flood volumes associated with various triggering mechanisms were also measured and were used to identify the lakes with the most considerable risk, such as Shakho Cho and Khangchung Tso. This study is anticipated to support stakeholders and decision‐makers in identifying critical glacial lakes and make well‐informed decisions related to future modeling efforts, field studies, and risk mitigation measures.
Key Points
Avalanche trajectories suggest that 36 out of 329 glacial lakes are susceptible to dynamic failure via an avalanche entering the lake
Application of stochastic flood model reveals that 67 glacial lakes contain at least one hydropower system along their flow path
Indian Himalayas contain 23 critical glacial lakes, 17 of which are located in the state of Sikkim
The increasing availability of highly detailed and accurate three-dimensional (3D) geospatial data are currently pushing the 3D change detection analysis towards a new 3D mapping frame. In this ...paper, medium-term changes (8 years) at a coastal rocky cliff are quantified using and comparing 2.5D and 3D methods to estimate the volume of rockfalls and three datasets: one Terrestrial Laser Scanner (TLS) acquired in 2010 and two coincident Unmanned Aerial Vehicles (UAV: multirotor and fixed-wing) datasets acquired in 2018. Advantages and limitations of these techniques, platforms and methods are discussed and the role of Ground Control Points (GCPs) distribution was analysed. Maps of 3D changes were produced by means of the Multiscale-Model-to-Model Cloud-Comparison algorithm (M3C2). The volume of the eroded-deposited material was estimated using two 2.5D and one 3D approaches: 1) rasterizing M3C2 distances using a conventional top-view perspective, 2) rasterizing the M3C2 distances rotated and orientated with the
z
vector normal and, 3) for the largest rockfalls, the volume was estimated using the Poisson Surface Reconstruction (PSR) algorithm (3D). The 3D models produced using both UAV platforms showed cm-level accuracies with Root Mean Square Error (RMSE) of 0.02 and 0.03 m for the multirotor and the fixed-wing, respectively, and faithfully represented cliff geometry. GCP configuration analysis showed that, at least, two stripes of GCPs evenly distributed at different heights are necessary, but three are recommended. The spatial pattern of change between the TLS and the two UAVs datasets was similar. The quantification of the volume of the eroded-accumulated material (using the M3C2 distances and the two UAV datasets) resulted in significant differences as the fixed-wing underestimated the values calculated using the multirotor dataset. The 2.5D strategies used to quantify the volume of change underestimated the eroded volume of the largest rockfalls (compared to the PSR 3D method), which provided the most accurate volume estimates.
Weathering processes prepare and trigger rockfall, which is a key agent of alpine landscape evolution and a hazardous process. The relative importance of different weathering processes is hard to ...decipher; nevertheless, current knowledge assumes a dominant role of frost cracking in eroding alpine rockwalls. This study uses a laboratory approach to simulate volumetric expansion and ice segregation in four alpine rock samples, monitors crack deformation, and quantifies frost weathering efficacy. Our results show that short‐term volumetric expansion in cracks provides stresses up to 10 MPa over hours, while long‐term ice segregation causes stresses of 1 MPa over days. While volumetric expansion in fall can reach critical fracture levels, volumetric expansion in early summer and ice segregation rather approaches subcritical fracture propagation levels. We conclude that subcritical crack propagation is the dominant antecedent process of rockfall initiation, which can be amplified by rare critical cracking due to volumetric expansion.
Plain Language Summary
Weathering processes reduce the strength of alpine rockwalls over time and can cause rockfall events. It is widely assumed that the freezing of water to ice is the dominant weathering process. Theoretical stresses exerted by frost weathering processes are higher than the strengths of the strongest rocks. Unfortunately, freezing in nature occurs often in combination with wetting and drying or cooling and the effects of freezing are hard to decipher from these processes. Therefore, we simulate the freezing of rock samples in the laboratory, where we can control conditions and try to isolate the freezing effects. For our simulations, we cut an artificial crack into a rock sample, fill this crack up with water, and cool the rock to freeze the water infill to ice. Frost weathering works by short‐term volumetric expansion during freezing of water or long‐term ice segregation. Both processes produce stresses that result in crack widening which we record. Our results show that the ice stresses are far below the strength of rocks. To crack the rock, you need repetitive freezing that with time increases the length of the crack rather than one big freezing event breaking the rock at once.
Key Points
Short‐term volumetric expansion and long‐term ice segregation mostly produce ice pressures below intact rock strength
Generated ice stresses are below intact fracture toughness of rocks and frost weathering proceeds by subcritical cracking
Frost weathering processes in conjunction with thermomechanical stresses will respond to climate change
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