Recent extreme slope failures in glacial environments: effects of thermal perturbation

This paper describes recent exceptional slope failures in high-mountain, glacial environments: the 2002 Kolka–Karmadon rock–ice avalanche in the Caucasus, a series of ice–rock avalanches on Iliamna Volcano, Alaska, the 2005 Mt. Steller rock–ice avalanche in Alaska, and ice and rock avalanches at Monte Rosa, Italy in 2005 and 2007. Deposit volumes range from 10⁶ to 10⁸ m³ and include rock, ice and snow. Here we focus on thermal aspects of these failures reflecting the involvement of glacier ice and permafrost at all sites, suggesting that thermal perturbations likely contributed to the slope failures. We use surface and troposphere air temperatures, near-surface rock temperatures, satellite thermal data, and recent 2D and 3D thermal modeling studies to document thermal conditions at the landslide sites. We distinguish between thermal perturbations of volcanic-geothermal and climatic origin, and thermal perturbations related to glacier–permafrost interaction. The data and analysis support the view that recent, current and future climatic change increases the likelihood of large slope failures in steep glacierized and permafrost terrain. However, some important aspects of these settings such as the geology and tectonic environment remain poorly understood, making the identification of future sites of large slope instabilities difficult. In view of the potentially large natural disasters that can be caused by such slope failures, improved data and understanding are needed.     

A robust debris-flow and GLOF risk management strategy for a data-scarce catchment in Santa Teresa,Peru

The town of Santa Teresa (Cusco Region, Peru) has been affected by several large debris-flow events in the recent past, which destroyed parts of the town and resulted in a resettlement of the municipality. Here, we present a risk analysis and a risk management strategy for debris-flows and glacier lake outbursts in the Sacsara catchment. Data scarcity and limited understanding of both physical and social processes impede a full quantitative risk assessment. Therefore, a bottom-up approach is chosen in order to establish an integrated risk management strategy that is robust against uncertainties in the risk analysis. With the Rapid Mass Movement Simulation (RAMMS) model, a reconstruction of a major event from 1998 in the Sacsara catchment is calculated, including a sensitivity analysis for various model parameters. Based on the simulation results, potential future debris-flows scenarios of different magnitudes, including outbursts of two glacier lakes, are modeled for assessing the hazard. For the local communities in the catchment, the hazard assessment is complemented by the analysis of high-resolution satellite imagery and fieldwork. Physical, social, economic, and institutional vulnerability are considered for the vulnerability assessment, and risk is eventually evaluated by crossing the local hazard maps with the vulnerability. Based on this risk analysis, a risk management strategy is developed, consisting of three complementing elements: (i) standardized risk sheets for the communities; (ii) activities with the local population and authorities to increase social and institutional preparedness; and (iii) a simple Early Warning System. By combining scientific, technical, and social aspects, this work is an example of a framework for an integrated risk management strategy in a data scarce, remote mountain catchment in a developing country.     

The 2020 glacial lake outburst flood process chain at Lake Salkantaycocha (Cordillera Vilcabamba,Peru)

Glacial lakes represent a threat for the populations of the Andes and numerous disastrous glacial lake outburst floods (GLOFs) occurred as a result of sudden dam failures or dam overtoppings triggered by landslides such as rock/ice avalanches into the lake. This paper investigates a landslide-triggered GLOF process chain that occurred on February 23, 2020, in the Cordillera Vilcabamba in the Peruvian Andes. An initial slide at the SW slope of Nevado Salkantay evolved into a rock/ice avalanche. The frontal part of this avalanche impacted the moraine-dammed Lake Salkantaycocha, triggering a displacement wave which overtopped and surficially eroded the dam. Dam overtopping resulted in a far-reaching GLOF causing fatalities and people missing in the valley downstream. We analyze the situations before and after the event as well as the dynamics of the upper portion of the GLOF process chain, based on field investigations, remotely sensed data, meteorological data and a computer simulation with a two-phase flow model. Comparison of pre- and post-event field photographs helped us to estimate the initial landslide volume of 1–2 million m³. Meteorological data suggest rainfall and/or melting/thawing processes as possible causes of the landslide. The simulation reveals that the landslide into the lake created a displacement wave of 27 m height. The GLOF peak discharge at the dam reached almost 10,000 m³/s. However, due to the high freeboard, less than 10% of the lake volume drained, and the lake level increased by 10–15 m, since the volume of landslide material deposited in the lake (roughly 1.3 million m³) was much larger than the volume of released water (57,000 m³, according to the simulation). The model results show a good fit with the observations, including the travel time to the uppermost village. The findings of this study serve as a contribution to the understanding of landslide-triggered GLOFs in changing high-mountain regions.

     

The challenge to detect and attribute effects of climate change on human and natural systems

Future scenarios of the energy system under greenhouse gas emission constraints depict dramatic growth in a range of energy technologies. Technological growth dynamics observed historically provide a useful comparator for these future trajectories. We find that historical time series data reveal a consistent relationship between how much a technology’s cumulative installed capacity grows, and how long this growth takes. This relationship between extent (how much) and duration (for how long) is consistent across both energy supply and end-use technologies, and both established and emerging technologies. We then develop and test an approach for using this historical relationship to assess technological trajectories in future scenarios. Our approach for “learning from the past” contributes to the assessment and verification of integrated assessment and energy-economic models used to generate quantitative scenarios. Using data on power generation technologies from two such models, we also find a consistent extent - duration relationship across both technologies and scenarios. This relationship describes future low carbon technological growth in the power sector which appears to be conservative relative to what has been evidenced historically. Specifically, future extents of capacity growth are comparatively low given the lengthy time duration of that growth. We treat this finding with caution due to the low number of data points. Yet it remains counter-intuitive given the extremely rapid growth rates of certain low carbon technologies under stringent emission constraints. We explore possible reasons for the apparent scenario conservatism, and find parametric or structural conservatism in the underlying models to be one possible explanation.     

Ice thawing,mountains falling—are alpine rock slope failures increasing?

Many high‐mountain environments of the world have seen dramatic changes in the past years and decades. Glaciers are retreating and downwasting, often at a dramatically fast pace, leaving large amounts of potentially unstable debris, moraines and rock slopes behind. Although in the main invisible to the eye of an observer, permafrost, i.e. rock and debris with permanent zero or subzero temperatures, is thawing. Several slopes have become unstable and landslides potentially related to permafrost degradation have received wide‐ranging attention from both scientists and the media. A number of those landslides can be related to the effects of recent changes in the cryosphere, which are ultimately driven by changes in climatic parameters, in particular temperature and precipitation.     

Landslides and increased debris-flow activity: A systematic comparison of six catchments in Switzerland

An increase in debris-flow frequency is expected in steep Alpine catchments after the occurrence of a large landslide, such as a rock avalanche. Herein we describe changes in debris-flow activity following increases in sediment availability due to landslides, or accelerated rock-glacier movement, for five catchments in the Swiss Alps, the Spreitgraben, Schipfenbach, Bondasca, Riascio, and Dorfbach catchments. Documentation on debris-flow activity is available from both before and after the landslide that generated the new sediment deposits. Data from nearby meteorological stations were used to explore possible changes in rainfall activity, and how the intensity and duration of rainfall events may have changed. In all cases there was a considerable increase in debris-flows frequency for one to eight years following the landslide. The annual number of days with debris-flow activity following the landslide was similar to that observed for the Illgraben catchment, where many such landslides occur annually. No clear change in precipitation totals preceding debris flows was apparent for the Riascio catchment, suggesting that the increase in frequency of debris flows is related to the increase in the amount of sediment that can be readily mobilized. In the two cases where rainfall data were available on an hourly basis, no systematic changes in the intensity or duration of rainfall related to debris-flow triggering were apparent, as shown by the close-clustering of storms on the intensity-duration plots. Following the sediment-generating event, an initial and sudden increase of the sediment yield was observed, followed by a decrease over time towards pre-disturbance values. The response of the catchments appears to be related to the amount of debris-flow activity prior to the landslide: sediment yield from catchments with frequent debris flows prior to the landslide activity did not increase as dramatically as in catchments where debris-flow activity was less common prior to the landslide. © 2018 John Wiley & Sons, Ltd.     

Database of glacial lake outburst floods (GLOFs)–IPL project No. 179

This article summarises activities and preliminary results of the International Programme on Landslides Project no. 179 “Database of glacial lake outburst floods (GLOFs)”. This project is planned for 3 years (2013–2015); the main objectives of the first year are (1) to create an online database and (2) to select collaborating partners. A survey of existing and relevant documents, information and organisations has been initiated along with the creation of a website (www.glofs-database.org) and the establishment of international collaboration. The first preliminary results show regional differences in various attributes of GLOF events (e.g. triggers, chronological distribution). These differences should be taken into consideration in regionally focused methods of hazard assessment, mitigation and consequently risk management.     

Lake outburst and debris flow disaster at Kedarnath,June 2013: hydrometeorological triggering and topographic predisposition

Heavy rainfall in June 2013 triggered flash flooding and landslides throughout the Indian Himalayan state of Uttarakhand, killing more than 6000 people. The vast majority of fatalities and destruction resulted directly from a lake outburst and debris flow disaster originating from above the village of Kedarnath on June 16 and 17. Here, we provide a systematic analysis of the contributing factors leading to the Kedarnath disaster, both in terms of hydrometeorological triggering and topographic predisposition. Topographic characteristics of the lake watershed above Kedarnath are compared with other glacial lakes across the north-western Himalayan states of Uttarakhand and Himachal Pradesh, and implications for glacier lake outburst hazard assessment in a changing climate are discussed. Our analysis suggests that the early onset of heavy monsoon rainfall (390 mm, June 10–17) immediately following a 4-week period of unusually rapid snow cover depletion and elevated streamflow was the crucial hydrometeorological factor, resulting in slope saturation and significant run-off into the small seasonal glacial lake. Between mid-May and mid-June 2013, snow-covered area above Kedarnath decreased by around 50 %. The unusual situation of the lake being dammed in a steep, unstable paraglacial environment but fed entirely from snowmelt and rainfall within a fluvial dominated watershed is important in the context of this disaster. A simple scheme enabling large-scale recognition of such an unfavourable topographic setting is introduced. In view of projected 21st century changes in monsoon timing and heavy precipitation in South Asia, more emphasis should be given to potential hydrometeorological triggering of lake outburst and debris flow disasters in the Himalaya.     

Unraveling driving factors for large rock–ice avalanche mobility

Large rock–ice avalanches have attracted attention from scientists for decades and some of these events have caused high numbers of fatalities. A relation between rock slope instabilities in cold high mountain areas and climate change is currently becoming more evident and questions about possible consequences and hazard scenarios in densely populated high mountain regions leading beyond historical precedence are rising. To improve hazard assessment of potential rock–ice avalanches, their mobility is a critical factor. This contribution is an attempt to unravel driving factors for the mobility of large rock–ice avalanches by synthesizing results from physical laboratory experiments and empirical data from 64 rock–ice avalanches with volumes >1x10⁶ m³ from glacierized high mountain regions around the world. The influence of avalanche volume, water and ice content, low‐friction surfaces, and topography on the apparent coefficient of friction (as a measure of mobility) is assessed. In laboratory experiments granular ice in the moving mass was found to reduce bulk friction up to 20% while water led to a reduction around 50% for completely saturated material compared with dry flows. Evidence for the effects of water as a key driving factor to enhance mobility was also found in the empirical data, while the influence of the ice content could not be confirmed to be of much relevance in nature. Besides liquefaction, it was confirmed that mobility increases with volumes and that frictional surface characteristics such as flow paths over glaciers are also dominant variables determining mass movement mobility. Effects of the topography along the flow path as well as channeling are assumed to be other critical factors. The results provide an empirical basis to roughly account for different path and flow characteristics of large rock–ice avalanches and to find appropriate ranges for friction parameters for scenario modeling and hazard assessments. Copyright © 2011 John Wiley & Sons, Ltd.