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

Scapozza, Cristian; Lambiel, Christophe; Baron, Ludovic; Marescot, L.; Reynard, Emmanuel

doi:10.1016/j.geomorph.2011.05.010

Cited by 84 publications

(92 citation statements)

References 46 publications

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“…Onaca et al (2015) indicate this as an important effect for the maintenance of permafrost in the Retezat Mountains (Romania), where permafrost occurs at sites with MAGST below 0 • C, BTS lower than −3 • C and ground freezing index higher than 600 • days. Snow avalanche and rock and debris fall events have also been shown to be responsible for burial of snow and ice at the base of talus slopes, even at low altitudes (see for example Scapozza et al, 2011, or Kenner et al, 2017. Such buried ice may be preserved for long periods of time, below the climate boundary of permafrost, and acts as a heat sink promoting lower GST and may thus explain the conditions observed at T3.…”

Section: Discussionmentioning

confidence: 99%

New observations indicate the possible presence of permafrost in North Africa (Djebel Toubkal, High Atlas, Morocco)

2017

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Abstract. Relict and present-day periglacial features have been reported in the literature for the upper reaches of the High Atlas mountains, which is the highest range in North Africa (Djebel Toubkal -4167 m a.s.l.). A lobate feature in the Irhzer Ikhibi south at 3800 m a.s.l. has been previously interpreted as an active rock glacier, but no measurements of ground or air temperatures are known to exist for the area. In order to assess the possible presence of permafrost, we analyse data from June 2015 to June 2016 from two air temperature measurement sites at 2370 and 3210 m a.s.l. and from four ground surface temperature (GST) sites at 3220, 3815, 3980 and 4160 m a.s.l. to characterize conditions along an altitudinal gradient along the Oued Ihghyghaye valley to the summit of the Djebel Toubkal. GSTs were collected at 1 h intervals, and the presence of snow cover at the monitoring sites was validated using Landsat 8 and Sentinel-2 imagery. Two field visits allowed for logger installation and collection and for assessing the geomorphological features in the area. The results show that snow plays a major role on the thermal regime of the shallow ground, inducing important spatial variability. The lowest site at 3220 m had a thermal regime characterized by frequent freeze-thaw cycles during the cold season but with few days of snow. When snow settled, the ground surface remained isothermal at 0 • C , indicating the absence of permafrost. The highest sites at 3980 and 4160 m a.s.l. showed very frequent freeze-thaw cycles and a small influence of the snow cover on GST, reflecting the lack of snow accumulation due to the wind-exposed settings on a ridge and on the summit plateau. The site located at 3815 m in the Irhzer Ikhibi south valley had a cold, stable thermal regime with GST varying from −4.5 to −6 • C from December to March, under a continuous snow cover.The site's location in a concave setting favours wind-driven snow accumulation and lower incoming solar radiation due to the shading effect of a ridge, inducing the conservation of a thick snow pack. The stable and low GSTs are interpreted as a strong indicator of the probable presence of permafrost at this site, which is an interpretation supported by the presence of lobate and arcuate features in the talus deposits. We present first results and further observations using geophysics, and borehole measurements are foreseen. This is the first time that probable permafrost has been reported from temperature observations in the mountains of North Africa.

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Section: Discussionmentioning

confidence: 99%

New observations indicate the possible presence of permafrost in North Africa (Djebel Toubkal, High Atlas, Morocco)

2017

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“…Schneider et al, 2013). Additionally, the lower pore space volume can generally lower the ground ice volume, which can develop by freezing of unconfined water (Scapozza et al, 2011;Vonder Mühll et al, 2000). The non-crystalline origin of the talus material can be listed as another factor which influences the local resistivity regime (Etzelmüller et al, 2006).…”

Section: Range Of Resistivity Valuesmentioning

confidence: 99%

“…thickness of the active layer, frost table topography, ice content) can be highly heterogeneous within small distances and can vary within single landform units (Schneider et al, 2013;Langston et al, 2011;Scapozza et al, 2011;Kneisel, 2010a). This is due to complex interactions between small-scale surface conditions (e.g.…”

Section: Introductionmentioning

confidence: 99%

Internal structure of two alpine rock glaciers investigated by quasi-3-D electrical resistivity imaging

Emmert

Kneisel

2017

The Cryosphere

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Abstract. Interactions between different formative processes are reflected in the internal structure of rock glaciers. Therefore, the detection of subsurface conditions can help to enhance our understanding of landform development. For an assessment of subsurface conditions, we present an analysis of the spatial variability of active layer thickness, ground ice content and frost table topography for two different rock glaciers in the Eastern Swiss Alps by means of quasi-3-D electrical resistivity imaging (ERI). This approach enables an extensive mapping of subsurface structures and a spatial overlay between site-specific surface and subsurface characteristics. At Nair rock glacier, we discovered a gradual descent of the frost table in a downslope direction and a constant decrease of ice content which follows the observed surface topography. This is attributed to ice formation by refreezing meltwater from an embedded snow bank or from a subsurface ice patch which reshapes the permafrost layer. The heterogeneous ground ice distribution at Uertsch rock glacier indicates that multiple processes on different time domains were involved in the development. Resistivity values which represent frozen conditions vary within a wide range and indicate a successive formation which includes several advances, past glacial overrides and creep processes on the rock glacier surface. In combination with the observed topography, quasi-3-D ERI enables us to delimit areas of extensive and compressive flow in close proximity. Excellent data quality was provided by a good coupling of electrodes to the ground in the pebbly material of the investigated rock glaciers. Results show the value of the quasi-3-D ERI approach but advise the application of complementary geophysical methods for interpreting the results.

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“…Lugon et al, 2004;Otto and Sass, 2006;Ribolini et al, 2010;Scapozza et al, 2011), as well as for analysing the internal structure and ice occurrences (e.g. Delaloye and Lambiel, 2005;Lambiel and Pieracci, 2008;Morard, 2011).…”

Section: Introductionmentioning

confidence: 99%

A spatial and temporal analysis of different periglacial materials by using geoelectrical, seismic and borehole temperature data at Murtèl–Corvatsch, Upper Engadin, Swiss Alps

et al. 2013

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Abstract. Different geophysical investigations, such as electrical resistivity tomography (ERT) and refraction seismic tomography (RST), allow for an improved characterization of subsurface conditions in mountain permafrost areas. The knowledge of the permafrost internal composition constitutes a major prerequisite for climate-related modelling studies, for detailed hazard or local infrastructure assessments. To detect the smallscale variations of permafrost characteristics and its varying sensitivity to climate influencing factors, two ERT and RST monitoring profiles were installed in 2009 at two different sites called Chastelets and Murtèl forefield located in the Murtèl-Corvatsch area, Upper Engadin, eastern Swiss Alps. The geophysical profiles extend over four existing boreholes and are characterized by strong small-scale variations of surface as well as subsurface structures such as bedrock, fine material or coarse debris. Here we present ERT measurements carried out in a bimonthly interval during the years of 2009 to 2012 and RST measurements which were performed once a year, normally in August, during the same period. Based on these data sets the so-called four-phase model, based on petrophysical relationships, was applied to determine the volumetric fractions of ice, water and air within the heterogeneous ground, resulting in a relatively precise description of the subsurface material around the existing boreholes.The observations revealed a permafrost occurrence at the Chastelets rock glacier with an estimated icesaturated layer of at least 10 m thickness and the detection of a thawed layer with increased water content in the lower frontal part of the rock glacier within an area of fine material. In the area of the Murtèl forefield the analysis revealed strongly weathered bedrock, which is in the upper part covered by a pronounced layer of coarse debris establishing a thermal regime which is able to sustain permafrost beneath. In addition, the high temporal ERT measurements revealed a seasonal formation of ice during wintertime within the coarseas well as the fine-grained active layer zones. It can be concluded that the combination of existing borehole temperature measurements, the ERT/RST measurements and the application of the four-phase model resulted in an in-depth view of the investigated area, which is a major prerequisite for future modelling studies allowing for a better treatment of the present small-scale spatial ground variabilities.

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

Cited by 84 publications

References 46 publications

New observations indicate the possible presence of permafrost in North Africa (Djebel Toubkal, High Atlas, Morocco)

New observations indicate the possible presence of permafrost in North Africa (Djebel Toubkal, High Atlas, Morocco)

Internal structure of two alpine rock glaciers investigated by quasi-3-D electrical resistivity imaging

A spatial and temporal analysis of different periglacial materials by using geoelectrical, seismic and borehole temperature data at Murtèl–Corvatsch, Upper Engadin, Swiss Alps

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