Journal: Natural Hazards and Earth System Sciences Discussions

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Copernicus

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2013 - 201932020 - 20223
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Publications 1 - 6 of 6
  • Impact of topography on in-situ soil wetness measurements for regional landslide early warning – a case study from the Swiss Alpine Foreland
    Item type: Working Paper
    Wicki, Adrian; Lehmann Grunder, Peter Ulrich; Hauck, Christian; et al. (2022)
    Natural Hazards and Earth System Sciences Discussions
    Recent studies have demonstrated the potential of in-situ soil wetness measurements to predict regional shallow landslides. Increasing availability of monitoring data from sensor networks provides valuable information for developing future regional landslide early warning systems (LEWSs), however, most existing monitoring sites are located on flat terrain. The question arises, if the representativeness for regional landslide activity would improve if sensors were installed on a landslide-prone hillslope? To address this, two soil wetness monitoring stations were installed at close proximity on a steep slope and on a flat location in the Napf region (Northern Alpine Foreland of Switzerland), and measurements were conducted over a period of 3 years. As both sites inhibit similar lithological, vegetation and precipitation characteristics, soil hydrological differences can be attributed to the impact of topography and hydrogeology. At the sloped site, conditions were generally wetter and less variable in time, and evidence was found for temporary lateral water transport along the slope. These differences were systematic and could be reduced by considering relative soil moisture changes. The application of a statistical landslide forecast model showed that both sites were equally able to distinguish critical from non-critical conditions for landslide triggering, which demonstrates the value of existing monitoring sites in flat areas for the application in LEWSs.
  • Co-detection of micro seismic activity as early warning of gravitational slope failure
    Item type: Working Paper
    Faillettaz, Jérome; Funk, Martin; Beutel, Jan; et al. (2018)
    Natural Hazards and Earth System Sciences Discussions
    We developed a new strategy for Disaster Risk Reduction for gravitational slope failure: We propose a simple method for real-time early warning of gravity-driven failures that considers and exploits both the heterogeneity of natural media and characteristics of acoustic emissions attenuation. This method capitalizes on co-detection of elastic waves emanating from micro-cracks by a network of multiple and spatially distributed sensors. Event co-detection is considered as surrogate for large event size with more frequent co-detected events marking imminence of catastrophic failure. In this study we apply this method to a steep rock glacier/debris slope and demonstrate the potential of this simple strategy for real world cases, i.e. at slope scale. This low cost, robust and autonomous system provides a well adapted alternative/complementary solution for Early Warning Systems.
  • Origin of the power-law exponent in the landslide frequency-size distribution
    Item type: Working Paper
    Jafarimanesh, Ahoura; Mignan, Arnaud; Danciu, Laurentiu (2018)
    Natural Hazards and Earth System Sciences Discussions
    Landslide statistics is characterized by a power-law frequency-size distribution (FSD) with power exponent α centered on 2.2–2.4, independently of the landslide trigger. So far, the origin of the α-value, critical to probabilistic hazard assessment, remains hypothetical. We present a generic landslide cellular automaton (LSgCA) based on the rules of Self Organized Criticality and on the Factor of Safety (FS) concept. We show that it reproduces the power-law FSD for realistic parameter ranges (i.e. cohesion, soil unit weight, soil thickness, angle of friction, slope angle, pore water pressure) with LSgCA simulations yielding α = 2.17±0.49, which is in agreement with α = 2.21±0.53 obtained from an updated meta-analysis of the landslide literature. The parameter α remains stable despite changes in the landslide triggering process, with the trigger only influencing the spatial extent of the landslide initiation phase defined from an FS contour. Furthermore, different FS formulations do not significantly alter the results. We find that α is constrained during the initiation phase of the landslide by the fractal properties of the topography, as we observed a positive correlation between fractal dimension and α while α did not change during the propagation phase of the LSgCA. Our results thus suggest that α can be estimated directly from the FS map for probabilistic landslide hazard assessment. However full modeling (including the propagation phase) would be required to combine the spatial distributions of landslide and exposure in probabilistic risk analysis.
  • Computational snow avalanche simulation in forested terrain
    Item type: Working Paper
    Teich, Michaela; Fischer, Jan-Thomas; Feistl, Thomas; et al. (2013)
    Natural Hazards and Earth System Sciences Discussions
    Two-dimensional avalanche simulation software operating in three-dimensional terrainis widely used for hazard zoning and engineering to predict runout distances andimpact pressures of snow avalanche events. Mountain forests are an effective biologicalprotection measure; however, the protective capacity of forests to decelerate or even to stop avalanches that start within forested areas or directly above the treeline isseldom considered in this context. In particular, runout distances of small- to medium-scale avalanches are strongly influenced by the structural conditions of forests inthe avalanche path. We present an evaluation and improvement of a novel forestdetrainment function implemented in the avalanche simulation software RAMMS for avalanche simulation in forested terrain. The new approach accounts for the effect offorests in the avalanche path by detraining mass, which leads to a deceleration andrunout shortening of avalanches. The relationship is parameterized by the detrainmentcoefficientK(Pa) accounting for differing forest characteristics. We variedKwhensimulating 40 well-documented small- to medium-scale avalanches which released in and ran through forests of the Swiss Alps. Analyzing and comparing observed andsimulated runout distances statistically revealed values forKsuitable to simulate thecombined influence of four forest characteristics on avalanche runout: forest type,crown closure, vertical structure and surface roughness, e.g. values forKwere higherfor dense spruce and mixed spruce-beech forests compared to open larch forests at the upper treeline. Considering forest structural conditions within avalanche simulationwill improve current applications for avalanche simulation tools in mountain forest andnatural hazard management.
  • Pre-collapse motion of the February 2021 Chamoli rock-ice avalanche, Indian Himalaya
    Item type: Working Paper
    Van Wyk de Vries, Maximillian; Bhushan, Shashank; Jacquemart, Mylène; et al. (2021)
    Natural Hazards and Earth System Sciences Discussions
    On the 7th of February 2021, a large rock-ice avalanche triggered a debris flow in Chamoli district, Uttarakhand, India, leaving over 200 dead or missing. The rock-ice avalanche originated from a steep, glacierized north-facing slope. In this work, we assess the precursory signs exhibited by this slope prior to the catastrophic collapse. We evaluate monthly slope motion from 2015 to 2021 through feature tracking of high-resolution optical satellite imagery. We then combine these data with a time series of pre- and post-event DEMs, which we use to evaluate elevation change over the same area. Both datasets show that the 26.9 Mm3 collapse block moved over 10 m horizontally and vertically in the five years preceding collapse, with particularly rapid motion occurring in the summers of 2017 and 2018. We propose that the collapse results from a combination of snow-loading in a deep headwall crack and permafrost degradation in the heavily jointed bedrock. Our observation of a clear precursory signal highlights the potential of satellite imagery for monitoring the stability of high-risk slopes. We find that the timing of the Chamoli rock-ice avalanche could likely not have been forecast from satellite data alone.
  • Variable hydrograph inputs for a numerical debris-flow runout model
    Item type: Working Paper
    Mitchell, Andrew; Zubrycky, Sophia; McDougall, Scott; et al. (2021)
    Natural Hazards and Earth System Sciences Discussions
    Debris flows affect people and infrastructure around the world, and as a result, many numerical models and modelling approaches have been developed to simulate their impacts. Observations from instrumented debris-flow channels show that variability in inflow depth, velocity and discharge in real debris flows is much higher than what is typically used in numerical simulations. However, the effect of this natural variability on numerical model outputs is not well known. In this study, we examine the effects of using complex inflow time series within a single-phase runout model utilizing a Voellmy flow-resistance model. The interactions between model topography and flow-resistance were studied first using a simple triangular hydrograph, which showed simulated discharges change because of local slopes and Voellmy parameters. Next, more complex inflows were tested using time series based on 24 real debris-flow hydrographs initiated from three locations. We described a simple method to scale inflow hydrographs by defining a target event volume and maximum allowable peak discharge. The results showed a large variation in simulated flow depths and velocities arising from the variable inflow. The effects of variable inflow conditions were demonstrated in simulations of two case histories of real debris flows, where the variation in inflow leads to significant variations in the simulation outputs. The real debris-flow hydrographs were used to provide an indication of the range of impacts that may result from the natural variability in inflow conditions. These results demonstrate variation in inflow conditions can lead to reasonable estimates of the potential variation in impacts.
Publications 1 - 6 of 6