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Université de Fribourg

Dynamics in debris-flow activity on a forested cone — A case study using different dendroecological approaches

Bollschweiler, Michelle ; Stoffel, Markus ; Schneuwly, Dominique M.

In: Catena, 2008, vol. 72, no. 1, p. 67-78

Dendrogeomorphological analyses of trees affected by debris flows have regularly been used to date past events. However, this method has always been limited to forested cones where trees registered the impact of previous events. The minimum age dating of trees growing in the debris deposits can, in contrast, provide information on the latest possible moment of past activity. In this paper, we...

Université de Fribourg

Evidences of winter ascending air circulation throughout talus slopes and rock glaciers situated in the lower belt of alpine discontinuous permafrost (Swiss Alps)

Delaloye, Reynald ; Lambiel, Christophe

In: Norwegian Journal of Geography

The winter ascending circulation of air throughout an accumulation of coarse slope sediments (the so-called chimney effect) facilitates the cooling of the ground and even the occurrence of permafrost in the lower part of a deposit. Simultaneously, any freezing is unlikely to occur in the upper part. The chimney effect has been reported to date mainly for cold and sometimes perennially frozen...

Université de Fribourg

Altitudinal differences in flower traits and reproductive allocation

Fabbro, Thomas ; Körner, Christian

In: Flora - Morphology, Distribution, Functional Ecology of Plants, 2004, vol. 99(1), p. 70

We tested whether alpine plants increase their effort to attract pollinators to compensate for assumed pollinator scarcity at high altitude. A three times larger fraction of the shoot was allocated to flowers in alpine plants (30 species, 2700m asl) compared to lowland plants (20 species, 600m asl), while leaf mass fraction did not differ between the altitudes. At high elevation, a three times...

Université de Fribourg

Geomorphology of the Hérens valley (Swiss Alps)

Lambiel, Christophe ; Maillard, Benoît ; Kummert, Mario ; Reynard, Emmanuel

In: Journal of Maps, 2016, vol. 12, no. 1, p. 160–172

This paper presents a geomorphological map of the Hérens valley in the Western Swiss Alps. With an area of 270 km2 and altitudes ranging from 470 to 4357 m a.s.l., this valley is one of the main secondary catchments of the Upper Rhône valley. The high differences in altitudes, combined with a varied geology, create an important geomorphic diversity. The main processes active in mountain...

Université de Fribourg

Internal structure and permafrost distribution in two alpine periglacial talus slopes, Valais, Swiss Alps

Scapozza, Cristian ; Lambiel, Christophe ; Baron, Ludovic ; Marescot, Laurent ; Reynard, Emmanuel

In: Geomorphology, 2011, vol. 132, no. 3-4, p. 208-221

In order to determine the spatial extension and the characteristics of permafrost within alpine talus slopes, two sites located in the western part of the Swiss Alps were studied using borehole drilling and electrical resistivity tomography (ERT) profiles. Three boreholes were drilled along an upslope–downslope transect in both talus slopes. In both sites, frozen sediments are present only in...

Université de Fribourg

Gap‐filling algorithm for ground surface temperature data measured in permafrost and periglacial environments

Staub, Benno ; Hasler, Andreas ; Noetzli, Jeannette ; Delaloye, andReynald

In: Permafrost and Periglacial Processes, 2017, vol. 28, no. 1, p. 275–285

Ground surface temperatures (GST) are widely measured in mountain permafrost areas, but their time series data can be interrupted by gaps. Gaps complicate the calculation of aggregates and indices required for analysing temporal and spatial variability between loggers and sites. We present an algorithm to estimate daily mean GST and the resulting uncertainty. The algorithm is designed to...

Université de Fribourg

Analyzing rockfall activity (1600–2002) in a protection forest—a case study using dendrogeomorphology

Stoffel, Markus ; Schneuwly, Dominique M. ; Bollschweiler, Michelle ; Lièvre, Igor ; Delaloye, Reynald ; Myint, Moe ; Monbaron, Michel

In: Geomorphology, 2005, vol. 68(3-4), p. 224

For the first time, dendrogeomorphology has been used to investigate spatial and temporal variations of rockfall activity in a protection forest. We report results of 564 cores from 135 severely injured Larix decidua Mill. trees on the west-facing Täschgufer slope, Swiss Alps. While trees sampled reached an age of 297 years on average, the oldest one attained breast height in AD 1318. For...

Université de Fribourg

Seasonal timing of rockfall activity on a forested slope at Täschgufer (Swiss Alps) – a dendrochronological approach = Saisonale Steinschlagverteilung auf einem bewaldeten Hang im Täschgufer (Schweizer Alpen) – ein dendrochronologischer Ansatz.

Stoffel, Markus ; Lièvre, Igor ; Monbaron, Michel ; Perret, Simone

In: Zeitschrift für Geomorphologie, 2005, vol. 49(1), p. 89-106

Dendrochronology was used to study 25 years of rockfall activity on a forested slope at Täschgufer, Täsch (Swiss Alps). We introduce a new approach by evaluating the initiation of callous tissue and resin duct formation after rockfall occurrence to determine the seasonal timing of events. Results from 270 stem discs of 18 Larix decidua Mill. trees show distinct seasonal differences in rockfall...

Université de Fribourg

Unraveling the patterns of late Holocene debris-flow activity on a cone in the Swiss Alps: chronology, environment and implications for the future

Stoffel, Markus ; Conus, Delphine ; Grichting, Michael A. ; Lièvre, Igor ; Maître, Gilles

In: Global and Planetary Change, 2008, vol. 60, no. 3-4, p. 222-234

Debris-flow activity on the forested cone of the Ritigraben torrent (Valais, Swiss Alps) was assessed from growth disturbances in century-old trees, providing an unusually complete record of past events and deposition of material. The study of 2246 tree-ring sequences sampled from 1102 Larix decidua Mill., Picea abies (L.) Karst. and Pinus cembra ssp. sibirica trees allowed reconstruction of 123...

Université de Fribourg

Tree-ring reconstruction of debris-flow events leading to overbank sedimentation on the Illgraben cone (Valais alps, Switzerland)

Stoffel, Markus ; Bollschweiler, Michelle ; Leutwiler, Astrid ; Aeby, Patrick

In: The Open Geology Journal, 2007, vol. 2, p. 18-29

Dendrogeomorphological analyses of trees affected by debris flows have regularly been used to date past events. However, while previous studies in the Swiss Alps have focused primarily on granitic and gneissic debris-flow material and on Larix decidua Mill. and Picea abies (L.) Karst. trees, they have – at the same time – widely disregarded torrents dominated by finely fractured calcareous...