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Armelle Decaulne - One of the best experts on this subject based on the ideXlab platform.
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a century long Snow Avalanche chronology reconstructed from tree rings in parâng mountains southern carpathians romania
Quaternary International, 2016Co-Authors: Olimpiu Pop, Flaviu Meseșan, Armelle Decaulne, Ionelageorgiana Gavrilă, Gheorghe Rosian, Iulian Horea Holobâcă, Titu AnghelAbstract:Abstract Snow Avalanches are common processes on steep slopes of the alpine and subalpine belts in Parâng Mountains (Southern Carpathians, Romania). The increasing tourism activities in these high mountain areas expose tourists to a high level of hazard especially in the Avalanche prone areas, where the past Avalanche activity is poorly documented. Snow Avalanches also affect coniferous and mixed forests, offering the opportunity to analyze disturbed trees and date past events with a one-year resolution. In this work, we present the results of the dendrogeomorphic reconstruction in terms of frequency and spatial extent of past Snow Avalanches occurred in the past along the Zăvoaie Avalanche path located on the NE slope of Parângul Mic peak (2519 m a.s.l.). A total of 57 Norway spruce ( Picea abies (L.) Karst.) disturbed by Snow Avalanches was sampled, and their growth reactions (scars, callous tissues, compression wood and traumatic resin ducts) identified within tree-rings served as basis for establishing a calendar of past events with one-year resolution. The analysis of tree-rings allows reconstruction of a minimum of 12 Avalanche events spanning 1900–2013. In the absence of historic documented events (except in the case of the 1997 event), dendrogeomorphic methods are a reliable tool to reconstruct the Snow Avalanche activity within the studied path. These results provide a better understanding of the local Snow Avalanche frequency, magnitude and return periods. These may be included in the present hazard mitigation planning or future decision making in this area, in order to reduce exposure of tourists and related infrastructure to this hazard.
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a 100 year extreme Snow Avalanche record based on tree ring research in upper bodalen inner nordfjord western norway
Geomorphology, 2014Co-Authors: Armelle Decaulne, Katja Laute, Ólafur Eggertsson, Achim A. BeylichAbstract:Abstract This paper analyses with the help of tree-ring studies the recurrence of extreme Snow Avalanches in a path situated in the upper Bodalen valley and originating from an outlet glacier of the Jostedalsbreen ice cap. By analysing tree-ring patterns of 91 trees, four extreme Snow-Avalanche events, extending over the entire valley floor and up to a distance of 800 m from the foot of the slope, are clearly highlighted during the 20th century and at the beginning of the 21st century. Return periods of 15 to 20 years for the most extreme events are extracted from the analyses, and recurrence intervals of 10 to 15 years for Avalanches presenting distinct deposition lobes uphill of the distal torrent. Results obtained by tree-ring analyses are successfully compared with available documents at different spatial and temporal scales. Rock-face Snow-Avalanche occurrences in the area, of small to medium size, are associated with heavy wintry precipitation combined with strong winds. However this normal situation is not valid for extreme Snow Avalanches crossing the path investigated in the paper, which result from the outlet glacier located in the starting zone; this glacier commands spatial and inter-annual variations of Snow accumulation in the departure zone.
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a first dendrogeomorphologic approach of Snow Avalanche magnitude frequency in northern iceland
Geomorphology, 2012Co-Authors: Armelle Decaulne, Ólafur Eggertsson, Þorsteinn SæmundssonAbstract:Abstract The paper examines the potential of dendrogeomorphic analyses to deliver a one-year resolution chronology of Snow-Avalanche winters in Northern Iceland, at the scale of a colluvial cone covered with European White Birch trees and shrubs ( Betula pubescens Ehrh.). Reconstruction of the Avalanche history is performed using tree-ring analyses. Determination of the most reliable growth disturbance (class 1 of growth eccentricity) and applying a tempering index value with threshold 10% of trees responding in the same year and at least two trees affected, Avalanche-activity years are highlighted, resulting in 52 Avalanche winters. Amongst those, 5 winters have activity index over 40%, indicating major years. Calculation of frequency of similar growth disturbances at each tree provides a return period ranging from 4.2 to 19 years. Inferred spatial extent of Snow-Avalanche events induces flow-like Snow Avalanches with limited extent around the tree-less parts of the cone with a return period under 6 years; the cone is totally covered and the distal tree-limit over-passed with a return period of 15–20 years.
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A first dendrogeomorphologic approach of Snow Avalanche magnitude-frequency in
2012Co-Authors: Armelle Decaulne, Ólafur EggertssonAbstract:article i nfo The paper examines the potential of dendrogeomorphic analyses to deliver a one-year resolution chronology of Snow-Avalanche winters in Northern Iceland, at the scale of a colluvial cone covered with European White Birch trees and shrubs (Betula pubescens Ehrh.). Reconstruction of the Avalanche history is performed using tree-ring analyses. Determination of the most reliable growth disturbance (class 1 of growth eccentricity) and applying a tempering index value with threshold 10% of trees responding in the same year and at least two trees affected, Avalanche-activity years are highlighted, resulting in 52 Avalanche winters. Amongst those, 5 winters have activity index over 40%, indicating major years. Calculation of frequency of similar growth disturbances at each tree provides a return period ranging from 4.2 to 19 years. Inferred spatial extent of Snow-Avalanche events induces flow-like Snow Avalanches with limited extent around the tree-less parts of the cone with a return period under 6 years; the cone is totally covered and the distal tree-limit over- passed with a return period of 15-20 years.
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distribution and frequency of Snow Avalanche debris transfer in the distal part of colluvial cones in central north iceland
Geografiska Annaler Series A-physical Geography, 2010Co-Authors: Armelle Decaulne, Þorsteinn SæmundssonAbstract:This paper emphasizes the importance of studying diffuse rock debris accumulation in the far distal part of colluvial cones with the aim of de- fining the spatial distribution and frequency of ex- treme Snow Avalanches. These deposits are located at some distance from the slope and have rarely been described in the literature. The field based methods used in this study confirm the Snow- Avalanche origin of these deposits by (i) character- izing the distribution of the deposits along the col- luvial cones and to their furthest extent, some way from the foot of the slope, and (ii) clearly defining the orientation of the long axis of the furthest and largest boulders as parallel with the main cone axis. A relative age of the deposits is obtained by assess- ing the vegetation cover of the boulder surfaces and by measuring the rock hardness using a Schmidt hammer. The study concludes that there were fre- quent extreme Snow Avalanches which have oc- curred since the Little Ice Age, and that they have decreased in magnitude during the past decade.
Markus Stoffel - One of the best experts on this subject based on the ideXlab platform.
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Impacts of land-cover changes on Snow Avalanche activity in the French Alps
Anthropocene, 2020Co-Authors: Robin Mainieri, Nicolas Eckert, Markus Stoffel, Adrien Favillier, Jérôme Lopez-saez, Taline Zgheib, Pauline Morel, Mélanie Saulnier, Jean-luc Peiry, Christophe CoronaAbstract:Abstract Dendrogeomorphic analyses provide long and continuous chronologies of mass movements that are useful for the detection of trends related to climate change. Socio-environmental changes can, however, induce non-stationarities. This study addresses the following questions: (1) How does the evolution of forest cover induce non-stationarities in tree-ring based reconstructions of Snow Avalanche activity? (2) How are trends inherent to tree-ring approaches distinguishable from real fluctuations in Avalanche activity? Using dendrogeomorphic techniques, we reconstructed Snow Avalanches in six adjacent paths in the French Alps. Results show two distinct trends in process activity between 1750 and 2016. In the southern paths, the frequency of Snow Avalanches increased sharply in the 1970s. The distribution of tree ages, as well as old topographic maps, allow an attribution of this trend to the destruction of large parts of the forest stand by a large Snow Avalanche in the 1910−20 s. This extreme event induced a sudden change in the capability of newly colonizing trees to record subsequent Snow Avalanches. In the northern paths, by contrast, progressive afforestation starting in the mid-19th century, as well as colonization of the release areas after World War II, resulted in a strong reduction in Snow Avalanche activity since the 1930s. Even if global warming remains a possible additional driver of Snow Avalanche activity at the study sites, the rural exodus and the abatement of pastoral practices during the 19th and 20th centuries are the main explanations for the observed trends in process activity. Results also illustrate a need to clarify the complex interrelations among forest evolution, global warming, social practices, and the process activity itself when interpreting trends in mass movements.
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Climate warming enhances Snow Avalanche risk in the Western Himalayas
Proceedings of the National Academy of Sciences of the United States of America, 2018Co-Authors: Juan Antonio Ballesteros-cánovas, Jaime Madrigal-gonzález, Daniel Trappmann, Nicolas Eckert, Markus StoffelAbstract:Ongoing climate warming has been demonstrated to impact the cryosphere in the Indian Himalayas, with substantial consequences for the risk of disasters, human well-being, and terrestrial ecosystems. Here, we present evidence that the warming observed in recent decades has been accompanied by increased Snow Avalanche frequency in the Western Indian Himalayas. Using dendrogeomorphic techniques, we reconstruct the longest time series (150 y) of the occurrence and runout distances of Snow Avalanches that is currently available for the Himalayas. We apply a generalized linear autoregressive moving average model to demonstrate linkages between climate warming and the observed increase in the incidence of Snow Avalanches. Warming air temperatures in winter and early spring have indeed favored the wetting of Snow and the formation of wet Snow Avalanches, which are now able to reach down to subalpine slopes, where they have high potential to cause damage. These findings contradict the intuitive notion that warming results in less Snow, and thus lower Avalanche activity, and have major implications for the Western Himalayan region, an area where human pressure is constantly increasing. Specifically, increasing traffic on a steadily expanding road network is calling for an immediate design of risk mitigation strategies and disaster risk policies to enhance climate change adaption in the wider study region.
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testing dendrogeomorphic approaches and thresholds to reconstruct Snow Avalanche activity in the făgăras mountains romanian carpathians
Quaternary Geochronology, 2015Co-Authors: Patrick Chiroiu, Markus Stoffel, Alexandru Onaca, Petru UrdeaAbstract:Snow Avalanches are a widespread natural phenomenon in steep mountain environments, where they modulate landscapes and frequently disturb forest stands. Such disturbances in trees have been used since the 1970s to retrospectively date Avalanches, study their extent and reach, as well as to document their triggers. Although virtually every dendrogeomorphic paper is still based on the concepts established by Shroder (1978), important methodological improvements have been achieved in the field ever since and more particularly over the last decade. This study therefore reports on recent methodological progress and employs three different approaches (i.e. Shroder index value and Kogelnig-Mayer weighted index value) and different sets of signals in trees (i.e. inclusion of tangential rows of traumatic resin ducts as evidence of past avalanching) to record Snow Avalanche activity. Using 238 increment cores from 105 Picea abies (L.) Karst trees which colonize a Snow Avalanche path in the Romanian Carpathians, we illustrate possibilities and limitations of the different approaches for the period covered by the chronologies (1852–2013). In addition, we sampled 30 undisturbed P. abies trees from a forest stand north of the Avalanche path, where no geomorphic disturbance was identified, so as to build a reference tree-ring chronology. The three Avalanche chronologies constructed with the disturbed trees allow identification of past process activity, but results differ quite considerably in terms of Avalanche frequency, number of reconstructed events and their temporal distribution. Depending on the approach used, 15 to 20 Snow Avalanches can be reconstructed, with the best results being obtained in the dataset including tangential rows of traumatic resin ducts. The addition of this anatomical feature, formed after mechanical impact enlarges the number of growth disturbances by 43.5%, and can thus explain the increase of reconstructed Avalanches by one-third as compared to the results of the chronology using the “conventional” Shroder approach.
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a new tree ring based semi quantitative approach for the determination of Snow Avalanche events use of classification trees for validation
Arctic Antarctic and Alpine Research, 2013Co-Authors: Romain Schlappy, Nicolas Eckert, Markus Stoffel, Christophe Corona, Vincent Jomelli, Delphine Grancher, Daniel Brunstein, Michael DeschatresAbstract:Abstract On forested paths, dendrogeomorphology has been demonstrated to represent a powerful tool to reconstruct past activity of Avalanches, an indispensable step in Avalanche hazard assessment. Several quantitative and qualitative approaches have been shown to yield reasonable event chronologies but the question of the completeness of tree-ring records remains debatable. Here, we present an alternative semi-quantitative approach for the determination of past Snow Avalanche events. The approach relies on the assessment of the number and position of disturbed trees within Avalanche paths as well as on the intensity of reactions in trees. In order to demonstrate that no bias was induced by the dendrogeomorphic expert, we carry out a statistical evaluation (Classification and Regression Trees, or CART) of the approach. Results point to the consistency and replicability of the procedure and to the fact that the approach is not restricted to the identification of high-magnitude Avalanches. Evaluation of the ...
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possibilities and limitations of dendrogeomorphic time series reconstructions on sites influenced by debris flows and frequent Snow Avalanche activity
Arctic Antarctic and Alpine Research, 2011Co-Authors: Barbara Kogelnigmayer, Markus Stoffel, Michelle Schneuwlybollschweiler, Johannes Hubl, Florian RudolfmiklauAbstract:Past debris-flow and Snow Avalanche activity was assessed for the Reiselehnrinne (Tyrol, Austria) using growth disturbances in growth-ring series of 372 Norway spruce (Picea abies (L.) Karst.) trees. Determination of events was performed by analyzing (a) the number and (b) intensity of growth disturbances within tree-ring series and (c) the spatial distribution of affected trees. Differentiation of debris flow from Snow Avalanche events was based on the intra-annual position of scars, callus tissues or tangential rows of traumatic resin ducts, and on the spatial distribution of trees with simultaneous reactions in the tree-ring series. We introduce a weighting factor to substantiate the dating of past process activity in a comprehensive way and to compare individual events as to their intensity and total number of tree-ring responses. The accuracy of the dendrogeomorphic assessment was then evaluated by comparing the reconstructed event frequency with chronologies available for the Reiselehnrinne. Comparison of tree-ring with historical data demonstrated clearly that the reconstructed event frequency contains the majority of past debris flow and Snow Avalanche events in the Reiselehnrinne, but that dating of events is not always possible, especially if they are clustered in time or have a limited spread on the cone.
Achim A. Beylich - One of the best experts on this subject based on the ideXlab platform.
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Potential effects of climate change on future Snow Avalanche activity in western Norway deduced from meteorological data
Geografiska Annaler Series A-physical Geography, 2018Co-Authors: Katja Laute, Achim A. BeylichAbstract:ABSTRACTThe formation of Snow Avalanches is controlled by the complex interaction between terrain characteristics, Snowpack and meteorological conditions. Accordingly, Snow Avalanches exhibit a high sensitivity to climatic variations. This study focuses on the possible effects of climatic variations on Snow Avalanche activity within one of Norway’s most Snow Avalanche-prone areas. We have statistically analyzed long-term homogenized meteorological data from seven official meteorological stations, three of them with a long-term record of 120 years (1896–2015). In addition, gained results and insights from a four-year (2009–2012) high-resolution Snow Avalanche monitoring investigation conducted in the same study area are incorporated. Potential effects and overall implications of a changing Snow Avalanche activity are discussed. Statistical analyses show an increasing trend for both air temperature and precipitation with an accelerated increase for the last 30 years for the core winter period. A tendency fo...
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Environmental Controls and Geomorphic Importance of a High-Magnitude/Low-Frequency Snow Avalanche Event in Bødalen, Nordfjord, Western Norway
Geografiska Annaler Series A-physical Geography, 2014Co-Authors: Katja Laute, Achim A. BeylichAbstract:Snow Avalanches are common phenomena in western Norway. During the winter–spring period 2011/2012 an extreme Snow Avalanche occurred within the upper valley part of a steep and glacier-connected mountain catchment (Bodalen) in western Norway. Compared with annually occurring regular Snow Avalanches, so-called ‘extreme Snow Avalanche events’ are more difficult to monitor and to study as they are characterized by recurrence intervals often longer than a decade. Morphometric and meteorological controls of a high-magnitude/low-frequency Snow Avalanche event, its geomorphic effects as well as its related relative role in mass transport compared with the annually monitored Snow Avalanche activity within the Bodalen catchment were explored. Maximum values of Snow height, velocity and pressure were predicted by applying a numerical run-out simulation. The formation of this Snow Avalanche resulted from the combination of extraordinary meteorological conditions and a favourable morphometric setting of the source area. The Snow Avalanche path covered a total distance of 2900 m, including a stretch of 850 m where the Snow Avalanche slid downwards on top of the Bodalsbreen outlet glacier. Within the run-out zone, directly located in front of the Bodalen outlet glacier, 2032 stones with b-axes >5 cm were remobilized which corresponds to a total transferred debris mass of 460 t. Compared with annually occurring Snow Avalanches within the Bodalen drainage basin the relative importance of extreme-sized Snow Avalanches is comparably low with respect to direct erosion and sediment transfer along rockwalls at higher slope areas. However, extreme-sized Snow Avalanches play a significant role with respect to the remobilization of debris/sediment at lower slope areas as well as to down-valley transport of sediment, including recognizable transfers of debris into the main stream channels of the drainage basin system whenever extreme Snow Avalanches reach the main channel.
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a 100 year extreme Snow Avalanche record based on tree ring research in upper bodalen inner nordfjord western norway
Geomorphology, 2014Co-Authors: Armelle Decaulne, Katja Laute, Ólafur Eggertsson, Achim A. BeylichAbstract:Abstract This paper analyses with the help of tree-ring studies the recurrence of extreme Snow Avalanches in a path situated in the upper Bodalen valley and originating from an outlet glacier of the Jostedalsbreen ice cap. By analysing tree-ring patterns of 91 trees, four extreme Snow-Avalanche events, extending over the entire valley floor and up to a distance of 800 m from the foot of the slope, are clearly highlighted during the 20th century and at the beginning of the 21st century. Return periods of 15 to 20 years for the most extreme events are extracted from the analyses, and recurrence intervals of 10 to 15 years for Avalanches presenting distinct deposition lobes uphill of the distal torrent. Results obtained by tree-ring analyses are successfully compared with available documents at different spatial and temporal scales. Rock-face Snow-Avalanche occurrences in the area, of small to medium size, are associated with heavy wintry precipitation combined with strong winds. However this normal situation is not valid for extreme Snow Avalanches crossing the path investigated in the paper, which result from the outlet glacier located in the starting zone; this glacier commands spatial and inter-annual variations of Snow accumulation in the departure zone.
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Morphometric and meteorological controls on recent Snow Avalanche distribution and activity at hillslopes in steep mountain valleys in western Norway
Geomorphology, 2014Co-Authors: Katja Laute, Achim A. BeylichAbstract:Abstract Snow Avalanches are common phenomena in Norway. Controlling factors of Snow Avalanche distribution and activity, and the relative importance of Snow Avalanches regarding contemporary sedimentary mass transfers were explored within two steep, parabolic-shaped and glacier-connected tributary valleys (Erdalen and Bodalen) in western Norway. Mapping of distribution, extent and the entire path lengths of Snow Avalanches was combined with spatial data analysis (GIS and DEM computing) of morphometric controls. The timing and frequency of Snow Avalanches were explored by correlating meteorological data with high-resolution monitoring data of Snow Avalanche events. Sediment masses annually transferred by Snow Avalanches along hillslopes and from hillslopes into stream channels were estimated. A high inter-annual variability of Avalanche activity and a wide spectrum of Avalanche sizes and types ranging from small to extreme-sized events were found for the four-year investigation period 2009–2012. Spatial distribution of Snow Avalanches is governed by the topographical factors valley orientation, slope aspect, relative slope height and rockwall morphometry whereas timing and frequency of Snow Avalanches are controlled by Snowfall intensity, periods with strong winds combined with a prevalent wind direction or sharp air temperature changes within short time periods. Snow Avalanches represent one of the dominant denudational processes and have a high relative importance regarding sedimentary mass transfers within the two mountain valleys Erdalen and Bodalen in western Norway.
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The EuroDendro project -Snow-Avalanche frequency and magnitude in European Middle Mountain unravelled by dendrogeomorphological analyses
2010Co-Authors: Armelle Decaulne, Katja Laute, Achim A. Beylich, Ó. Eggertsson, Þ. Sæmundsson, Olympiu Pop, Emmanuelle Defive, Sébastien LarrueAbstract:The EuroDendro project aims to detect the signal of recent Snow-Avalanche activity within the analyses of tree rings. In mountain areas, even middle mountains, Snow Avalanches are a common process & pose serious hazards & risks in recently occupied sectors, either for residence or recreation purposes. Where (i) geomorphological evidence of Snow-Avalanche occurrence are scarce, (ii) historical records are poor & (iii) trees are colonizing part of the slopes, tree-ring analyses appear as a good alternative to reveal the recent Snow-Avalanche history. The dendromorphological approach consists in a survey of the investigated areas to inventory damages that affect the morphology of the tree: tilting of the trunk, presence of scars on the trunk, topped trees. Such a survey enables mapping the most frequent Snow-Avalanche paths, helping to: locate the maximum potential damages estimate the runout distances appreciate the lateral dispersion of the events The EuroDendro project is very interested in: (i) broad-leaved trees, which attracted seldom attention in dendrogeomorphology related to Snow-Avalanche activity: birch (Betula pubescens) in N Iceland birch (Betula pubescens) & alder (Alnus) in W Norway beech (Fagus sylvatica) in NE Cantal-France (ii) coniferous trees in little explored areas where broad-leaved trees are unavailable: spruce (Picea abies) in Central Romania Core extractions in c & d directions, i.e. parallel to the main flux lines, on both the uphill & the downhill sides of the tree Core analyses on a Lintab measurement table, enabling tree-rings counting, location & dating of growth disturbances (narrow & large rings) & reaction wood formation. The EuroDendro project investigates four main areas, some of them in connection with other scientific frameworks. The investigated areas are located in: xx (A) Northern Iceland, in the Dalsmynni valley, the Ljósavatn-skarð pass & the southern Fnjóskadalur valley, (B) Western Norway, at the bottom of Nordfjord, in Erdalen & Bødalen, (C) Central Romania, in the Southern Carpathians, in the Bâlea valley, Făgărăş massif, (D) Central France, in the Northeastern valleys of the Cantal massif. xx All these areas are characterised by steep slopes, harsh wintry conditions, known frequent Snow-Avalanche activity, a relative remotness & a tree-cover on talus & cones. A B C D The Fjnóskadalur site, Iceland © Armelle Decaulne The Bâlea site, Romania © Armelle Decaulne The Erdalen site, Norway © Armelle Decaulne The Cantal site, France © Emmanuelle Defive © GoogleEarth Study sites location Recurrent Snow Avalanches strongly influence the growth of the birches that develop typical tilted trunks (Ljósavatnskarð, Iceland). © Armelle Decaulne Slow growth Samples from the lower track & upper runout zones Broad-leaved trees => tension wood on the strained side of the trunk => asymmetrical growth Reference growth from outside the Snow-Avalanche influence area isolate the role of climatic accident & insect attacks Location of the reaction wood date recurrent events over the last 80 years, with a different distribution Young trees could indicate: (i) recent Snow-Avalanche activity drop at valley level (ii) change in grazing zones Well-defined areas of felled trees = recent major Snow-Avalanche events Reference growth = average of all cores extracted in c-d directions Samples from the lower runout zones Bødalen: sudden drop of tree growth in 2000 = major Avalanche felled the tree Erdalen: recurrent avalanchy winters post-1995, severe from 2000 & especially in 2002 & 2006 Reference curve built from straight spruces sampled below the path Narrow path with poor tree cover, even in the distal runout zone Most of the trees are very young (+/-30 years) Reaction wood formation on the downhill side = recurrent stress due to Snow-Avalanche activity. Oldest trees signal several avalanchy periods, especially from 1920s to early 1950s again during the 1980s. Spatial distribution of major impact areas affecting trees in the Bødalen valley, Norway. Background image is © Norwegian land survey Main dendrogeomorphological investigated paths in the Bødalen valley, Norway. © Katja Laute Map of the tree morphology, reflecting damages due to Snow-Avalanche occurrence on a colluvial cone in the Dalsmynni valley, Iceland. Background images are © skipulag.is Birches felled by a Snow Avalanche in the Bødalen valley, Norway. © Armelle Decaulne Topped & tilted spruce in the distal part of the path, Romania. © Armelle Decaulne Asymetric branch distribution on a spruce in Romania. © Armelle Decaulne Scars on the trunk & main branches in the Snow-Avalanche path. © Armelle Decaulne Tilting, scars & topping Tilting & scars Main areas of felled trees Main areas of damaged shrubs Tilting 200 m
Nicolas Eckert - One of the best experts on this subject based on the ideXlab platform.
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Impacts of land-cover changes on Snow Avalanche activity in the French Alps
Anthropocene, 2020Co-Authors: Robin Mainieri, Nicolas Eckert, Markus Stoffel, Adrien Favillier, Jérôme Lopez-saez, Taline Zgheib, Pauline Morel, Mélanie Saulnier, Jean-luc Peiry, Christophe CoronaAbstract:Abstract Dendrogeomorphic analyses provide long and continuous chronologies of mass movements that are useful for the detection of trends related to climate change. Socio-environmental changes can, however, induce non-stationarities. This study addresses the following questions: (1) How does the evolution of forest cover induce non-stationarities in tree-ring based reconstructions of Snow Avalanche activity? (2) How are trends inherent to tree-ring approaches distinguishable from real fluctuations in Avalanche activity? Using dendrogeomorphic techniques, we reconstructed Snow Avalanches in six adjacent paths in the French Alps. Results show two distinct trends in process activity between 1750 and 2016. In the southern paths, the frequency of Snow Avalanches increased sharply in the 1970s. The distribution of tree ages, as well as old topographic maps, allow an attribution of this trend to the destruction of large parts of the forest stand by a large Snow Avalanche in the 1910−20 s. This extreme event induced a sudden change in the capability of newly colonizing trees to record subsequent Snow Avalanches. In the northern paths, by contrast, progressive afforestation starting in the mid-19th century, as well as colonization of the release areas after World War II, resulted in a strong reduction in Snow Avalanche activity since the 1930s. Even if global warming remains a possible additional driver of Snow Avalanche activity at the study sites, the rural exodus and the abatement of pastoral practices during the 19th and 20th centuries are the main explanations for the observed trends in process activity. Results also illustrate a need to clarify the complex interrelations among forest evolution, global warming, social practices, and the process activity itself when interpreting trends in mass movements.
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Climate warming enhances Snow Avalanche risk in the Western Himalayas
Proceedings of the National Academy of Sciences of the United States of America, 2018Co-Authors: Juan Antonio Ballesteros-cánovas, Jaime Madrigal-gonzález, Daniel Trappmann, Nicolas Eckert, Markus StoffelAbstract:Ongoing climate warming has been demonstrated to impact the cryosphere in the Indian Himalayas, with substantial consequences for the risk of disasters, human well-being, and terrestrial ecosystems. Here, we present evidence that the warming observed in recent decades has been accompanied by increased Snow Avalanche frequency in the Western Indian Himalayas. Using dendrogeomorphic techniques, we reconstruct the longest time series (150 y) of the occurrence and runout distances of Snow Avalanches that is currently available for the Himalayas. We apply a generalized linear autoregressive moving average model to demonstrate linkages between climate warming and the observed increase in the incidence of Snow Avalanches. Warming air temperatures in winter and early spring have indeed favored the wetting of Snow and the formation of wet Snow Avalanches, which are now able to reach down to subalpine slopes, where they have high potential to cause damage. These findings contradict the intuitive notion that warming results in less Snow, and thus lower Avalanche activity, and have major implications for the Western Himalayan region, an area where human pressure is constantly increasing. Specifically, increasing traffic on a steadily expanding road network is calling for an immediate design of risk mitigation strategies and disaster risk policies to enhance climate change adaption in the wider study region.
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Physical and societal statistics for a century of Snow-Avalanche hazards on Sakhalin and the Kuril Islands (1910-2010)
Journal of Glaciology, 2014Co-Authors: E.a. Podolskiy, K. Izumi, V.e. Suchkov, Nicolas EckertAbstract:The analysis of historical Avalanche data is important when developing accurate hazard maps. The record of Snow-Avalanche disasters on Sakhalin and the Kuril Islands is incomplete, due to the historical division into periods of Japanese and Russian rule. Here we combine and analyze data from Japanese and Russian sources to reconstruct a continuous record of Avalanche catastrophes in the region from 1910 to 2010. Despite the relatively small scale of the majority of catastrophic Avalanches, with a total vertical drop 238 injuries have occurred in 275 incidents over a 100 year period (two-thirds of those killed were Japanese). This death toll is higher than that in Canada, New Zealand or Iceland, or non-recreational fatalities in France. A wave of Avalanche disasters (1930s-60s) following intense colonization of Sakhalin and the Kuril Islands is evident. Although this 'wave' could be considered a local issue of the past, many presently developing countries may face similar situations. The fatality rate has decreased over time, due to social factors, and differs from that of any other region, in its absence of deaths through recreational activities. Although in recent years the fatality rate is lower than that of Iceland or the USA, the per capita Avalanche casualty rate on Sakhalin and the Kuril Islands remains among the highest in the world.
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a new tree ring based semi quantitative approach for the determination of Snow Avalanche events use of classification trees for validation
Arctic Antarctic and Alpine Research, 2013Co-Authors: Romain Schlappy, Nicolas Eckert, Markus Stoffel, Christophe Corona, Vincent Jomelli, Delphine Grancher, Daniel Brunstein, Michael DeschatresAbstract:Abstract On forested paths, dendrogeomorphology has been demonstrated to represent a powerful tool to reconstruct past activity of Avalanches, an indispensable step in Avalanche hazard assessment. Several quantitative and qualitative approaches have been shown to yield reasonable event chronologies but the question of the completeness of tree-ring records remains debatable. Here, we present an alternative semi-quantitative approach for the determination of past Snow Avalanche events. The approach relies on the assessment of the number and position of disturbed trees within Avalanche paths as well as on the intensity of reactions in trees. In order to demonstrate that no bias was induced by the dendrogeomorphic expert, we carry out a statistical evaluation (Classification and Regression Trees, or CART) of the approach. Results point to the consistency and replicability of the procedure and to the fact that the approach is not restricted to the identification of high-magnitude Avalanches. Evaluation of the ...
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Optimal design of Snow Avalanche passive defense structure using extreme value run-out models
2011Co-Authors: Pascale Favier, Nicolas Eckert, D. Bertrand, M. NaaimAbstract:In order to protect elements at risk (humans, roads, houses, etc.) against Snow Avalanche hazard, civil engineering structures can be used such as dams or mounds. Generally, the design of such defense structures is based on the definition of a reference hazard used to define the potential loading applied. These approaches remain insufficient for their optimal design. The minimization of expected total costs is an interesting alternative that generalizes costbenefit approaches to a continuous decision variable. Hazard magnitude must though be evaluated with care, and extreme value theory is a natural framework to work within. In this study, we expand previous work devoted to the optimal design of the height of an Avalanche dam by risk minimization. The magnitude of an Avalanche is assumed to be represented by its run-out distance, the most critical value. A simple Peak Over Threshold model is used to represent the number and the magnitude of run-outs exceeding the dam, but the exponential distribution is replaced by the Generalised Pareto Distribution more consistent with the extreme value theory. Total costs are evaluated as the sum of construction costs and damages to buildings of various value and position. An application on a real case study illustrates the approach. Statistical and decisional considerations are proposed to quantify the risk. For instance, a baseline risk function is considered and its influence on the decisional variable is shown. Optimal design results, obtained under both Classical and Bayesian paradigms, are compared and discussed.
Perry Bartelt - One of the best experts on this subject based on the ideXlab platform.
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A Reverse Dynamical Investigation of the Catastrophic Wood-Snow Avalanche of 18 January 2017 at Rigopiano, Gran Sasso National Park, Italy
International Journal of Disaster Risk Science, 2021Co-Authors: Barbara Frigo, Bernardino Chiaia, Perry Bartelt, Igor Chiambretti, Margherita MaggioniAbstract:On 18 January 2017 a catastrophic Avalanche destroyed the Rigopiano Gran Sasso Resort & Wellness (Rigopiano Hotel) in the Gran Sasso National Park in Italy, with 40 people trapped and a death toll of 29. This article describes the location of the disaster and the general meteorological scenario, with field investigations to provide insight on the Avalanche dynamics and its interaction with the hotel buildings. The data gathered in situ suggest that the Avalanche was a fluidized dry Snow Avalanche, which entrained a sligthtly warmer Snow cover along the path and reached extremely long runout distances with braking effect from mountain forests. The Avalanche that reached the Rigopiano area was a “wood-Snow” Avalanche—a mixture of Snow and uprooted and crushed trees, rocks, and other debris. There were no direct eyewitnesses at the event, and a quick post-event survey used a numerical model to analyze the dynamics of the event to estimate the pressure, velocity, and direction of the natural flow and the causes for the destruction of the hotel. Considering the magnitude and the damage caused by the event, the Avalanche was at a high to very high intensity scale.
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quantification of basal friction for technical and silvicultural glide Snow Avalanche mitigation measures
Natural Hazards and Earth System Sciences, 2014Co-Authors: Thomas Feistl, Peter Bebi, L Dreier, Marc Hanewinkel, Perry BarteltAbstract:Abstract. A long-standing problem in Avalanche engineering is to design defense structures and manage forest stands such that they can withstand the forces of the natural Snow cover. In this way, glide-Snow Avalanches can be prevented. Ground friction plays a crucial role in this process. To verify existing guidelines, we collected data on the vegetation cover and terrain characteristics of 101 glide-Snow release areas in Davos, Switzerland. We quantified the Coulomb friction parameter μm by applying a physical model that accounts for the dynamic forces of the moving Snow in the stauch zone. We investigated the role of glide length, slope steepness and friction in Avalanche release. Our calculations revealed that the slope angle and slab length for smooth slopes correspond to the technical guidelines for defense structure distances in Switzerland. Artificial defense structures, built in accordance with guidelines, prevent glide-Snow Avalanche releases, even when the terrain is smooth. Slopes over 40 m in length and 45° in steepness require a ground friction of μm = 0.7 corresponding to stumps or tree regeneration to ensure protection. Forest management guidelines that define maximum forest gap sizes to prevent glide-Snow Avalanche release neglect the role of surface roughness and therefore underestimate the danger on smooth slopes.
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Snow Avalanche hazard modelling of large areas using shallow water numerical methods and gis
Environmental Modelling and Software, 2007Co-Authors: Urs Gruber, Perry BarteltAbstract:Snow Avalanches threaten settlements and roads in steep mountainous areas. Hazard mitigation strategies apply numerical models in combination with GIS-based methods to determine run out distances and pressure maps of Snow Avalanches in three-dimensional terrain. The Snow Avalanche modelling system is usually applied to study single Avalanche tracks. In this paper we investigate the application of a numerical modelling system for large area hazard analysis. We begin by briefly presenting the depth-averaged equations governing Avalanche flow. Then, we describe the statistical and GIS-based methods that are applied to define the initial fracture depths and release areas for Snow Avalanche modelling. We discuss the calibration of the Avalanche model friction coefficients for extreme Avalanches in function of altitude, Avalanche size and topography. Seven test sites with areas between 100 and 350km^2, that are well distributed over the different Snow climates and elevation ranges of Switzerland, were used to calibrate the model by comparing the simulation results with historic Avalanche events and existing Avalanche hazard maps. We then show how the Avalanche modelling system was applied over the mountainous region of Switzerland (25,000km^2) to delineate forests with protective function against Avalanches.
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calculating dense Snow Avalanche runout using a voellmy fluid model with active passive longitudinal straining
Journal of Glaciology, 1999Co-Authors: Perry Bartelt, B Salm, U GruberAbstract:A quasi-one-dimensional dense-Snow Avalanche model has been developed to predict Avalanche runout and flow velocity in a general two-dimensional terrain. The model contains three different dense-Snow-Avalanche flow laws. These are: (1) a Voellmy-fluid flow law with longitudinal active/passive straining, (2) a Voellmy-fluid flow law advanced by Russian researchers in which the Coulomb-like dry friction is limited by a yield stress, and (3) a modified Criminale-Ericksen-Filby fluid model proposed by Norwegian researchers. The application of the Voellmy-fluid law with active/passive straining to solve practical Avalanche-dynamics problems is evaluated by applying the model to simulate laboratory experiments and field case-studies. The model is additionally evaluated by comparing simulation results using the Russian and Norwegian models. In a final analysis the influence of the initial conditions on Avalanche runout is investigated. We conclude that the model resolves many of the shortcomings of the Voellmy-Salm model, which is traditionally used in Switzerland to predict Avalanche runout. Furthermore, since the model contains the three well-calibrated parameters of the Swiss Guidelines on Avalanche calculation it can be readily applied in practice. We discuss why we believe the Russian and Norwegian models are not ready for practical application. Finally, we show that many problems remain, such as the specification of the initial release conditions. We conclude that numerical models require a more detailed description of initial fracture conditions.
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Geomorphological Hazards and Disaster Prevention - Review and future challenges in Snow Avalanche risk analysis
Geomorphological Hazards and Disaster Prevention, 1Co-Authors: Michael Bründl, Jürg Schweizer, Perry Bartelt, Margreth Keiler, Thomas GladeAbstract:Background Snow Avalanches pose a major threat to alpine communities because they affect safety in villages and on traffic routes. Therefore, dealing with Avalanche danger has a long tradition in Alpine countries. In most countries, Avalanches contribute only to a small degree to the overall risk of a country. For Switzerland, for example, Avalanche risk represents only 2% of all risks (BABS, 2003). Snow Avalanche formation, geomorphology and land use planning Snow Avalanches are a type of fast-moving mass movement. They can also contain rocks, soil, vegetation or ice. Avalanche size is classified according to its destructive power (McClung and Schaerer, 2006). A medium-sized slab Avalanche may involve 10,000 m 3 of Snow, equivalent to a mass of about 2,000 tons (Snow density 200 kg/m 3 ). Avalanche speeds vary between 50 and 200 km/h for large dry Snow Avalanches, whereas wet slides are denser and slower (20–100 km/h). If the Avalanche path is steep, dry Snow Avalanches generate a powder cloud. There are different types of Snow Avalanches (Table 5.1), and in particular two types of release: loose Snow Avalanches and slab Avalanches. Loose Snow Avalanches start from a point, in a relatively cohesionless surface layer of either dry or wet Snow. Initial failure is analogous to the rotational slip of cohesionless sands or soil, but occurs within a small volume ( 3 ) in comparison to much larger initiation volumes in soil slides.