Snow Avalanche Paths Research Articles

Identifying and interpreting regional signals in tree-ring based reconstructions of snow avalanche activity in the Goms valley (Swiss Alps)

One of the purposes of dendrogeomorphic studies is to provide long and continuous reconstructions of mass movements and to detect climate-induced trends in process activity. The development of regional chronologies—in which information from different sites are aggregated—is often needed to identify process–climate relations and to overcome local-scale specificities, sparse data available for individual sites and to extract a signal that is common to a larger region and possibly driven by past climate fluctuations or large-scale environmental changes. Yet, such chronologies are scarce and consensus neither exists on how to compile local data at the regional scale nor on the methods to be used to extract a common signal. In the case of snow avalanches, existing regional tree-ring studies typically included less than ten paths, and they discriminated years of high/low avalanche activity based on a regional index representing the proportion of disturbed trees in any given year. However, such an index does not account for potential non-stationarities in local tree-ring reconstructions such as e.g., time-varying sample size, decreasing dendrogeomorphic potential of trees after the occurrence of an extremely large, devastating avalanche or socio-environmental changes. Here we combine a dendrogeomorphic approach to reconstruct snow avalanche events in 11 paths located in the Goms valley (Swiss Alps) with an innovative statistical modelling approach. For each path, we compute reconstructions using a 4-step procedure to disentangle potential effects of snow avalanches from disturbance pulses in trees caused by climatic or other exogenous factors. We then process the regional dataset (spanning the period 1766–2014) within a Bayesian hierarchical spatio-temporal framework specifically designed to homogenise time series of avalanche events by i) removing trends related to the decreasing number of living trees back in time and ii) inferring robust trends in mean annual/regional avalanche activity in time and space. This contribution has the merit to introduce a methodological approach allowing rigorous extraction of common, average avalanche signals from snow avalanche paths characterized by heterogeneous process activity. Despite its stringency, we show that 11 avalanche paths may not suffice to yield a signal that is independent from the selection of couloirs. As a result, the approach also does not highlight a clear climatic control of snow avalanche activity but rather points to a complex, yet combined impact of afforestation and management strategies on reconstructed avalanches.

Brief communication: Weak control of snow avalanche deposit volumes by avalanche path morphology

Abstract. Snow avalanches are a major component of the mountain cryosphere, but little is known about the factors controlling the variability of their deposit volumes. This study investigates the influence of avalanche path morphology on ca. 1500 deposit volumes recorded between 2003 and 2018 in 77 snow avalanche paths of the French Alps. Different statistical techniques show a slight but significant link between deposit volumes and path mean elevation and orientation, with contrasted patterns between winter and spring seasons. The limited and partially non-linear nature of this control may result from the combined influence on the genesis of deposit volumes of mean path activity, climate conditions, and mechanical thresholds determining avalanche release.

Snow avalanche hazard prediction using machine learning methods

Snow avalanches are among the most destructive natural hazards threatening human life, ecosystems, built structures, and landscapes in mountainous regions. The complexity of snow avalanche modelling has been discussed in many studies, but its modelling is not well-documented. Snow avalanche modeling in this study was done using three main categories of data, including avalanche occurrence locations, meteorological factors, and terrain characteristics. Two machine learning models, namely support vector machine (SVM) and multivariate discriminant analysis (MDA), were employed. A ratio of 70 to 30 of data was considered for calibrating and validating the models. Results indicated that both models had an excellent performance in snow avalanche modeling (area under curve, AUC > 90), although hits and misses analysis demonstrated the superior performance of MDA. Sensitivity analysis indicated that the topographic position index, slope, precipitation, and topographic wetness index were the most effective variables for modeling. A snow avalanche map indicated that the high snow avalanche hazard zone was mostly near the streams and was matched with hillsides around the water pathways. Findings of study can be helpful for land use planning, to control snow avalanche paths, and to prevent the probable hazards induced by it, and it can be a good reference for future studies on modeling snow avalanche hazards.

Calculating snow-avalanche return period from tree-ring data

The return period is a key element used for snow-avalanche characterization. To calculate the return period, historical data regarding past snow-avalanche activity are required. In mountain areas where past snow avalanches are poorly documented, dendrogeomorphic approaches constitute a reliable method for the reconstruction of past snow avalanches at the temporal scale of living trees. This paper presents an automated method for calculating the snow-avalanche return period using a digital elevation model and the location of the trees disturbed by every reconstructed snow-avalanche occurrence. Unlike the existing method, the method we propose requires neither the calculation of return period for every sampled tree nor the use of interpolation. This new method is based on the determination of spatial extent for every past snow-avalanche occurrence using the upslope area algorithm. The number of past snow-avalanche occurrences is calculated for every pixel of the path. The chronology length is divided by the number of past snow-avalanche occurrences to obtain the return period. In the present paper, both the proposed method and the existing method are applied to calculate the return period for three confined snow-avalanche paths located in Parâng Mountains, part of the Romanian Carpathians. Results are compared and discussed.

Geomorphological conditions of snow avalanches in the Tatra Mountains

Snow avalanches are substantial processes of the natural environment and the denudation system in high mountains, with their activity depending on topoclimate, relief and snow conditions. The aim of the present research was to recognise the geomorphological conditions for snow avalanche activity in the Tatra Mountains by analysing the relationship between relief and avalanche path features for the area encompassing the whole of the massif – both the Polish and Slovak parts of the Tatras. Maps of snow avalanches that occurred in the recent past, aerial photos and a digital terrain model were used to make a map of avalanche paths, with the starting zone, avalanche track and accumulation zone specified within each snow avalanche path. For each type of designated unit of snow avalanche track, a morphometric analysis was performed, taking into account slope aspect and inclination. More than 3,770 avalanche paths were identified whose number, morphometric features and altitudinal range differ between individual parts of the Tatra Mountains, corresponding to relief. The length of avalanche paths reaches up to 3,138 m, with paths located about 200 m higher in the High Tatras than in other parts of the massif. The average area of the starting zone in the High Tatras is half the size of that in the Western Tatras, while the number of accumulation zones is double the size. Based on a statistical analysis, the interrelations between slope exposure, slope inclination and length of avalanche path, as well as size of starting zones, were established. It was found that the length of avalanche tracks and the size of avalanche starting zones both decrease with increasing slope inclination.

Application of timberline morphometric analysis for detecting snow avalanche paths: A case study of the Tatra Mountains

The upper forest limit is principally controlled by climate factors, mainly temperature but locally also other factors, such as snow avalanches, debris flows, and wind throw. Therefore, the timberline course may be use as a proxy of these drivers. The aim of the study was to employ the morphometric features of the upper forest limit for remote detection of avalanche paths. We introduced the Morphometric Avalanche Index (MAI), which combine simple parameters such as: Perimeter Development, Altitudinal Difference, Elongation Ratio, Area, and the existence forest patches. This tool was tested in four valleys in the Tatra Mountains, wherein 103 known avalanche paths. The employment of MAI resulted in remote identification of 90% of avalanche paths existing and acknowledged in this region. Additionally 28 avalanche paths that had not been previously indicated as such were detected.

Environmental controls and geomorphic importance of a high‐magnitude/low‐frequency snow avalanche event in bødalen, nordfjord, western norway

Snow avalanches are common phenomena in western orway. 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 (ødalen) in western orway. 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 ødalen 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 Bødalsbreen outlet glacier. Within the run‐out zone, directly located in front of the ødalen 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 ødalen 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.

Testing dendrogeomorphic approaches and thresholds to reconstruct snow avalanche activity in the Făgăraş Mountains (Romanian Carpathians)

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.

Geomorphology of snow avalanche impact landforms in the southern Canadian Cordillera

Snow avalanche impact landforms (SAILs) are typically elliptical‐shaped depressions bounded by an arcuate ridge located at the base of avalanche paths. The geomorphology of these features is controlled by the topography of the avalanche path, the availability of unconsolidated debris in the impact area and the ability of the avalanche impacts to displace the available debris in the direction of avalanche flow. Ground‐based snow avalanches move debris by bulldozing, and airborne snow avalanches move sediment by excavation on impact.This paper reports on the geomorphology, and surface age and stability of three SAILs in the southern Canadian Cordillera. Dendrochronology and lichenometry were used to date geomorphic activity at the sites. Evidence of present SAIL stability suggests they result from episodic, high‐magnitude avalanche impact events over many hundreds of years. All three landforms share common morphologies: a water‐filled bowl‐shaped depression distally bounded by an arcuate ridge‐oriented transverse to the avalanche path. Despite sharing many attributes, field investigations revealed that the origin of each SAIL was a function of the local variations in snow avalanche path topography and availability of unconsolidated debris in the impact area. The snow avalanche path associated with the Blackhorn site has a gentle gradient, which suggests that this SAIL is a result of ground‐based avalanches. The SAIL at Spoon Lake appears to be a consequence of a resistant geologic feature that focuses snow avalanches in the impact area and results in explosive excavation. The morphology of the snow avalanche track at Peyto Lake causes large snow avalanches to become airborne prior to impacting and excavating an impact pool. All three SAILs examined in this paper are historically persistent landforms and these observations support previous findings indicating that SAILs require hundreds of years to develop.

Dendrogeomorphology as a tool to unravel snow-avalanche activity: Preliminary results from the Fnjóskadalur test site, Northern Iceland

Snow avalanches are a major hazard for many settlements and transportation corridors in northern Iceland. At many sites the occurrence of snow avalanches during the past century has not been recorded. Visible damage, such as tilting, scars and decapitation of trees and shrubs (Betula pubescens) growing on colluvial cones in a remote area in Central North Iceland clearly identifies snow-avalanche paths of a given magnitude and frequency. An analysis of tree-ring data was made using the chronology of ring sizes and wood reaction in snow-avalanche tracks subject to frequent avalanches. Abnormal growth, correlated with abrupt increases or decreases in growth rates, is related to snow-avalanche impact. The preliminary results provide reliable dendrogeomorphological data that show the spatial extent and frequency of snow avalanches in the study area. Further investigation that includes a broader sampling strategy and dendrochronological laboratory analysis is required.

An Assessment of Snow Avalanche Paths and Forest Dynamics Using Ikonos Satellite Data

Ikonos panchromatic and multispectral satellite data were acquired in October 2000 and August 2002 for a test area along US Highway 2, the southern border of Glacier National Park (GNP), Montana, USA. The research goals were to map snow avalanche paths and to characterize vegetation patterns in selected paths for longitudinal (i.e., source, track, and runout) and transverse (i.e., inner, flanking, outer) zones as part of a study of forest dynamics and nutrient flux from paths into terrestrial and aquatic systems. In some valleys, as much as 50 percent of the area may be covered by snow avalanche paths, and as such, serve as an important carbon source servicing terrestrial and aquatic ecosystems. Snow avalanches move woody debris down‐slope by snapping, tipping, trimming, and excavating branches, limbs, and trees, and by injuring and scaring trees that remain in‐place. Further, snow avalanches alter the vegetation structure on paths through secondary plant succession of disturbed areas. Contrast and edge enhancements, Normalized Difference Vegetation Index (NDVI), and the Tasseled Cap greenness and wetness transformations were used to examine vegetation patterns in selected paths that were affected by high magnitude snow avalanches during the winter of 2001-2002. Using image transects organized in longitudinal patterns in paths and in forests, and transects arranged in transverse patterns across the sampled paths, the Tasseled Cap transforms (and NDVI values) were plotted and assessed. Preliminary results suggest that NDVI patterns are different for paths and forests, and Tasseled Cap greenness and wetness patterns are different for longitudinal and transverse zones that describe the morphology of snow avalanche paths. The differentiation of paths from the background forest and the characterization of paths by morphometric zones through remote sensing has implications for mapping forest disturbances and dynamics over time and for large geographic areas and for modeling nutrient flux in terrestrial and aquatic systems.

Power‐laws and snow avalanches

This paper presents evidence of frequency‐size power‐laws in several groups of snow avalanche paths. Other natural hazards, such as earthquakes and forest fires, exhibit similar power‐law relationships. In addition, an analysis of the response of one group of snow avalanche paths to storms through time demonstrates a power‐law between the response of the system and the binned frequency of those responses. Our results, as well as our experience with these complex, non‐linear systems, are consistent with self‐organized criticality. The practical implication of this work is that the frequency‐size relationship for small and medium sized avalanches may be useful for quantifying the risk of large snow avalanches within a group of avalanche paths.

ENVIRONMENTAL CHANGE IN GLACIER NATIONAL PARK, MONTANA: AN ASSESSMENT THROUGH REPEAT PHOTOGRAPHY FROM FIRE LOOKOUTS

This paper describes a largely unrecognized source of panoramic photographs from the 1930s for fire lookouts in the American West, and uses a set of those photographs from Glacier National Park (GNP), Montana, to illustrate landscape changes through rephotography. We rephotographed 360° panoramas from nine of the same fire lookouts and qualitatively and quantitatively compared the nature and amount of landscape change from 1935 to the late 1990s. Notable changes included drastic glacial recession, infilling of snow-avalanche paths, forest succession as a result of fire-suppression policies, upward advance of treeline, and pressures on the Park periphery resulting from anthropogenic developments. Geomorphic changes in general were less distinct than biogeographic changes. [Key words: Repeat photography, environmental change, Glacier National Park (GNP), Rocky Mountains, Montana.]

Effects of increased cloud-cover on a montane forest landscape

Abstract:Although increased cloud-cover may reduce global temperature response to trace gas emissions, it is an important climatic change from an ecological perspective. For plants, cloud-cover reduces photosynthesis and alters establishment; these effects differ among species. The differential effects may be modified, however, by pattern at the landscape level, such as forest edges. Here we include cloud-cover and the edge effects of a snow avalanche path in a simulation of the dynamics of a montane forest using a spatially explicit implementation of the JABOWA-FORET model. Cloud cover is simulated by a 10% reduction in ambient light. Alternately we forced constant full sunlight, constant mortality for conifers, or both, on a strip of simulated cells in order to maintain an avalanche path. Higher light levels maintained on the path allow the persistence of shade-intolerant species that otherwise decline under a scenario of increased cloud-cover (deciduous proportion on 800 cells changes from 0.19 to 0.11...

Influence of snow patterns and snow avalanches on the alpine treeline ecotone

Abstract. Snow avalanches, snow accumulation, and snow ablation patterns were mapped and analyzed to assess their impact on the three‐dimensional position, composition (closed canopy forest, open canopy forest, meadow, krummholz, and non‐vegetated surfaces), and spatial structure of the Alpine Treeline Ecotone (ATE) in a portion of Glacier National Park, Montana, USA. Multitemporal Landsat Multispectral Scanner data were processed to derive snow accumulation and ablation patterns throughout a snow season. Landsat Thematic Mapper data were processed and combined with aerial photo interpretations for discerning and characterizing snow avalanche paths. Transition matrices were used to assess the change in the state of snow cover conditions, whereas multiple regression analyses were used to examine the position and character of snow avalanche paths. The analyses were framed and implemented within a geographic information system (GIS) approach. Results indicate a snowmelt pattern progressing from zonal to azonal; influence of local site and situation factors in snow accumulation and ablation patterns; and the importance of topography, geologic structure, and lithology in defining the starting elevation and source area of snow avalanche paths. Finally, a conceptual process is presented where sites affected by stresses and disturbances are analyzed at a local spatial scale for analysis through a deterministic model, whereas regional stresses and disturbances are assessed through remote sensing and GIS approaches for analysis through empirical models.

SITE CHARACTERISTICS OF DEBRIS FLOWS AND THEIR RELATIONSHIP TO ALPINE TREELINE

Over 150 debris flows in eastern Glacier National Park, Montana, were mapped from a combination of aerial photograph analysis and fieldwork, and categorized as to site characteristics that are suggestive of causal processes. The debris-flow sites were digitized and entered into an integrated geographic information system for subsequent analysis. Principal components analysis was carried out to assess which terrain characteristics exert the most influence over debris-flow location. The greatest number of mapped debris flows were debris torrents occurring within the confines of snow-avalanche paths, followed by snow-patch debris flows, debris torrents unassociated with snow-avalanche paths, and moraine debris flows. Elevation, snow potential, and snow distribution exerted the greatest control over debris-flow location. The impact of debris flows into the alpine treeline ecotone was especially pronounced in two valleys, but debris flows act to depress treeline below its climatic optimum throughout the valley...

Zonas de aludes en la Vallferrera: Clasificación y riesgo geomorfológico

Avalanche areas in the Vallferrera: classification and geomorphological risk. The Vallferrera basin is located in the western Catalonian Pyrenees, bordering on Andorra. In this area, a study of the snow avalanche path characteristics has been done starting from two points of view (MASES 1991): Firstly, a description and a classification of the different morphologies of the snow avalanche paths have been done. We have compared their distribution with some intrinsic parameters of the basin, like lithology, preexistent relief, etc. It has been observed that the different morphologies of the snow avalanche paths are the results of their adaptation to the pre-existent glacial relief. Secondly, the snow avalanche risk has been analyzed at the Vallferrera basin. There have been identified four zones of high risk, due to the interference between the avalanches and the social structure.

Lithologic, Structural, and Topographic Influences on Snow-Avalanche Path Location, Eastern Glacier National Park, Montana

Abstract We examine the roles of lithology, structure, and topography as determinants of the location and morphology of snow-avalanche paths in east-central Glacier National Park, Montana. Most models of avalanche path location emphsize topographic interactions with prevailing winds and ignore the role of geologic influences. Landsat Thematic Mapper digital data, covering the study area, were enhanced through a combination of directional and nondirectional spatial filters, principal components analysis, and channel ratioing to delineate the relationships between lithology, structure, topography, and avalanche-path location. We used GIS technology to examine these spatial relationships. Fieldwork confirmed the remote sensing and GIS interpretations. More than 50 percent of the snow-avalanche paths are located directly beneath a widespread diorite sill, and roughly 25 percent and 20 percent of the additional paths were associated with topographic couloirs (probably structurally controlled) and structural lineaments respectively. Structural patterns also influenced slope aspect of the paths. Morphometric differences between these paths and those from a larger, previous study group are attributed to local climatic differences on opposite sides of the Continental Divide.

A statistical analysis of tree-ring dating in conjunction with snow avalanches: Comparison of on-path versus off-path responses

Tree-rings were collected from snow-avalanche paths in Colorado, and from positions away from avalanche paths. The rings were examined for morphological responses to avalanche-induced trauma. Use of the Chi-square statistic revealed a significant difference in the number of morphological responses from on-path versus off-path positions. A high number of on-path trees were definitely damaged by avalanche impact in 1973; a lower number of trees from off-path positions illustrated morphologic ring-responses from random, nonavalanche, events in the same year.

Snow Avalanche Path Terrain and Vegetation, Glacier National Park, Montana

Snow avalanche paths are major geomorphic features in the Rocky Mountains of Glacier National Park, Montana. They are the most common and geographically widespread form of mass-wasting in the central portion of the park. Field work and aerialphoto studies identified over 800 such paths in the study area. Other mass-wasting phenomena are also common.