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11.
The occurrence of wet-snow avalanches is, in general, poorly understood. For 20 years (winters of 1975–1976 to 1994–1995),
the avalanche activity has been observed in the Dischma valley near Davos (Eastern Swiss Alps). The study area comprises a
large starting zone of north-easterly aspect (2,300 m a.s.l.) with several avalanche paths. We have analyzed the occurrence
data in combination with meteorological and snowpack data collected at an elevation of 2,090 m a.s.l. During the 20-year observation
period, almost 800 wet-snow avalanches were observed, about 4.5 times more loose snow avalanches than slab avalanches. Considering
both types of avalanches jointly, snow depth, precipitation and air temperature showed the highest correlation with avalanche
activity. Most loose snow avalanches occurred when air temperature was high and/or after a precipitation period. Slab avalanches
occurrence was primarily related to warm air temperatures and snowpack properties such as the isothermal state and the existence
of capillary barriers. Radiation did not show up as a significant variable. The results suggest that in a transitional snow
climate wet-snow avalanches are, as dry snow avalanches, often related to precipitation events, and that wet slab instability
strongly depends on snowpack properties in relation to warming of the snowpack and melt water production. 相似文献
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The tracking performance of High Sensitivity Global Positioning System (HSGPS) receivers under avalanche deposited snow was
investigated. Two field trials were held during April 2006 in the Canadian Rocky Mountains to study the factors affecting
GPS signals and positioning performance for avalanche rescue. The PLAN Group at the University of Calgary has developed the
miniature Global Navigation Asset Tracker (GNAT™) which integrates the SiRFstar III HSGPS receivers with a microcontroller,
onboard flash storage and a 2.4 GHz Zigbee radio modem. The test systems were placed down a 6 cm hole bored in avalanche deposited
snow for 2.5 h with data collected at 1 Hz. Post-mission analysis showed average GPS signal attenuation of approximately 11
to 13 dB within the first 1.5 m of avalanche debris. Sufficient GPS signals for positioning were received by GPS receivers
buried in 2.7 m of avalanche deposited snow. Methods of improving the GPS position beneath the avalanche debris were investigated,
resulting in horizontal position RMS values of 7.4 and 2.8 m at depths of 2.0 and 2.68 m respectively. 相似文献
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15.
The Pebble Creek Formation (previously known as the Bridge River Assemblage) comprises the eruptive products of a 2350 calendar
year B.P. eruption of the Mount Meager volcanic complex and two rock avalanche deposits. Volcanic rocks of the Pebble Creek
Formation are the youngest known volcanic rocks of this complex. They are dacitic in composition and contain phenocrysts of
plagioclase, orthopyroxene, amphibole, biotite and minor oxides in a glassy groundmass. The eruption was episodic, and the
formation comprises fallout pumice (Bridge River tephra), pyroclastic flows, lahars and a lava flow. It also includes a unique
form of welded block and ash breccia derived from collapsing fronts of the lava flow. This Merapi-type breccia dammed the
Lillooet River. Collapse of the dam triggered a flood that flowed down the Lillooet Valley. The flood had an estimated total
volume of 109 m3 and inundated the Lillooet Valley to a depth of at least 30 m above the paleo-valley floor 5.5 km downstream of the blockage.
Rock avalanches comprising mainly blocks of Plinth Assemblage volcanic rocks (an older formation making up part of the Mount
Meager volcanic complex) underlie and overlie the primary volcanic units of the Formation. Both rock avalanches are unrelated
to the 2350 B.P. eruption, although the post-eruption avalanche may have its origins in the over-steepened slopes created
by the explosive phase of the eruption. Much of the stratigraphic complexity evident in the Pebble Creek Formation results
from deposition in a narrow, steep-sided mountain valley containing a major river.
Received: 20 January 1998 / Accepted: 29 September 1998 相似文献
16.
Bayesian stochastic modelling for avalanche predetermination: from a general system framework to return period computations 总被引:1,自引:1,他引:0
N. Eckert E. Parent M. Naaim D. Richard 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(2):185-206
Stochastic models are recent but unavoidable tools for snow avalanche hazard mapping that can be described in a general system
framework. For the computation of design return periods, magnitude and frequency have to be evaluated. The magnitude model
consists of a set of physical equations for avalanche propagation associated with a statistical formalism adapted to the input–output
data structure. The friction law includes at least one latent friction coefficient. The Bayesian paradigm and the associated
simulation techniques assist considerably in performing the inference and taking estimation errors into account for prediction.
Starting from the general case, simplifying hypotheses allows computing the predictive distribution of high return periods
on a case-study. Only release and runout altitudes are considered so that the model can use the French database. An inversible
propagation model makes it possible to work with the latent friction coefficient as if it is observed. Prior knowledge is
borrowed from an avalanche path with similar topographical characteristics. Justifications for the working hypotheses and
further developments are discussed. In particular, the whole approach is positioned with respect to both deterministic and
stochastic hydrology. 相似文献
17.
Changes in mountain landscape can affect avalanche activity, causing changes in risk, potentially enhanced by a transition of the socio-environmental system and its underlying dynamics. Thus, integrative approaches combining biophysical and social sciences are required to assess changes in risk in all its dimensions. This study proposes a holistic methodology combining land cover change detection using advanced image processing techniques, geohistorical investigations and qualitative modelling of risk changes in order to infer the evolution of avalanche risk and its drivers in the upper Maurienne (French Alps) from 1860 to 2017. Results show that a continuous increase of forested areas associated with the retraction of agro-pastoral zones followed a period of land abandonment and depopulation. However, reforestation within avalanche paths remains largely incomplete and mostly absent in the majority of release areas, making a decrease in avalanche occurrence and propagation unlikely. This, combined with marked urban sprawl partially concentrated in avalanche prone areas, locally increased the exposure of residential settlements to avalanches. Hence, even if new defense structures have been set up, our analysis indicates that avalanche risk in the upper Maurienne increased through the study period. Even if local specificity related to physical dissimilarities and/or distinguished socio-economic trends always exist, our results may be valid for many high alpine valleys. Our approach is also transferable to other natural hazards, notably in wider mountain environments, as a contribution to the elaboration of effective adaptation strategies in a context of increasing risks related to combined climate change and socio-economic transitions. 相似文献
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19.
Peter Höller 《Natural Hazards》2009,48(3):399-424
During the last 50 years, an average of 30 persons per year was killed by avalanches in Austria. About one-third of all avalanche
fatalities occurred as a result of so-called ‘catastrophic avalanches’. ‘Catastrophic avalanches’ are spontaneously released
avalanches that affect villages and cause damage to property (buildings, roads and other infrastructure). The biggest avalanche
events in Austria were in 1950/1951 (135 fatalities), in 1953/1954 (143 fatalities) and in February 1999, when 38 persons
were killed in Galtür and Valzur. This article deals with an analysis of nine major avalanche cycles in the last 55 years.
An avalanche cycle in this article is defined as 50 recorded avalanches of at least size 3 in two days and/or 5 persons killed
in villages within two days. The basis of this study are the well-documented records from Fliri (1998), who analysed natural
disasters in the western part of Austria and the Trentino, including floods, mudflows, earthquakes and avalanches. The meteorological
data were taken from two relevant observation sites in the northern part of the Austrian Alps, from two sites in an intermediate
and continental region, respectively and from one site in the southern part of the Austrian Alps. Atmospheric patterns were
analysed by using weather charts for the relevant periods. Both the meteorological data and the weather charts were provided
by the Central Institute for Meteorology and Geodynamics (ZAMG). It was found that there was a major cycle every 6 years (on
average). Two-thirds of all investigated cycles were characterised by a continuous increase of snow depth over a period of
at least three days. In only three periods (1975, 1986, 1988), daily extreme values could be observed. More than 40% of all
the cycles occurred in January. In two-thirds, a north-westerly oriented frontal zone was responsible for the formation of
a major cycle. The remaining cycles were released by low-pressure areas over Central Europe and the Mediterranean Sea, respectively. 相似文献
20.
Peter Höller 《Natural Hazards》2007,43(1):81-101
At all times natural hazards like torrents or avalanches pose a threat to settlements and infrastructures in the Austrian
Alps. Since 1950 more than 1,600 persons have been killed by avalanches in Austria, which is on average approximately 30 fatalities
per year. In particular, the winter periods 1950/1951 and 1953/1954 stand out with more than 100 fatalities. Those events
led to an increase of avalanche control programmes in the following decades. While from the 1950s to the 1970s emphasis was
placed on permanent measures (technical structures, afforestations, hazard zoning ...) additional programmes such as avalanche
warning and forecasting have supplemented avalanche control measures in the last decades. Current research is focused on avalanche
simulation, risk management and the influence of the forest on avalanche formation. An important area of future research is
to develop improved methods for avalanche forecasting and to intensify the investigation of the dynamics of avalanches. 相似文献