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Preview: Permafrost and Periglacial Processes

Permafrost and Periglacial Processes

Wiley Online Library : Permafrost and Periglacial Processes

Published: 2018-01-01T00:00:00-05:00


Sorted patterned ground in a karst cave, Ledenica pod Hrušico, Slovenia


Patterned ground is a characteristic periglacial landform in polar and alpine environments but has not been systematically studied in karst caves. Here we characterize the periglacial environment and sorted stripes within the Ledenica pod Hrušico ice cave, western Slovenia. The stripes were mapped, sediment depth and grain size were measured, and cave and outside air temperatures were monitored together with ground temperatures. Eleven sorted stripes of coarse limestone debris had developed on 1 m thick silt-rich sediment, underlain by limestone bedrock. Silt-rich cave sediments can accumulate as insoluble carbonate residue or during flood events, whereas coarse debris may result from frost shattering. Cold winter air entered the ice cave, but little air exchange occurred during summer, when the cave air temperature slowly rose to a maximum of 5°C. Winter temperature oscillations propagated efficiently to the snow-free cave floor. Fourteen freeze-thaw cycles were observed at the patterned-ground surface during winter 2015/2016 and may cause the differential frost heaving necessary for sediment sorting. Such periglacial conditions and mixtures of silty and coarse sediments can produce sorted patterns in karst caves.

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Kinematic investigations on the Furggwanghorn Rock Glacier, Switzerland


Many thermo-hydro-mechanical parameters and their interactions influence the creep behaviour of rock glaciers, with the result that the kinematics of rock glaciers are complex and not fully understood. An interdisciplinary project began in 2010 to investigate the physical ground conditions and any climatic dependence of a fast-moving rock glacier below the Furggwanghorn peak, in the Turtmann Valley of the Swiss Alps. Remote sensing and subsurface instrumentation (in-place inclinometers and temperature sensors), together with ground and airborne geophysical methods, reveal the creep rate and the hydrological and thermal conditions of the rock glacier. The Furggwanghorn rock glacier exhibits displacements in the order of metres per year and showed substantial surface changes at a minimal ground temperature slightly below 0°C. A detailed three-dimensional kinematic ground model shows the internal structure and shear surfaces, indicating past creep behaviour and failure mechanisms. The results suggest that observed seasonal changes in the creep rate of the rock glacier did not depend directly on the temperature at depth, but were very likely controlled by hydrological processes.

Erosion and sediment transfer processes at the front of rapidly moving rock glaciers: Systematic observations with automatic cameras in the western Swiss Alps


When connected to torrential channels, the fronts of active rock glaciers constitute important sediment sources for gravitational transfer processes. In this study, a 2013–16 time series of in situ webcam images from the western Swiss Alps was analyzed to characterize the erosion processes responsible for sediment transfer at the front of three rapidly moving rock glaciers and their temporal behavior. The main erosion processes comprised rock fall, debris slide, superficial flow and concentrated flow. These processes were induced by (i) changes of the frontal slope angle produced by rock glacier advance, and (ii) increases in water content of the sediments at the rock glacier front due to melt processes and rainfall. Erosion almost ceased during winter, when the front was frozen and snow-covered. The onset of snowmelt triggered an active period of high-frequency erosion events. After the melt period, sediment transfer continued as occasional rock falls, while other erosion processes occurred only during or following rainfall events. Intense regressive erosion phases that triggered debris flows were rare and occurred when enhanced snowmelt and/or recurring rainfall induced substantial groundwater flow on the debris slopes directly below the rock glacier fronts.

Validation of simulated temperature profiles at rock walls in the eastern alps (Dachstein)


While rock temperature is a key factor for many geomorphic phenomena in high mountains, assessing the small-scale temperature distribution remains challenging. We adapted the program package WUFI®, originally designed to calculate energy and moisture fluxes in building walls, for modeling natural rock faces. We determined physical rock properties and local meteorological parameters as input data for the simulations at rock walls in the Dachstein Mountains, Austria, and calculated annual temperature fluctuations at the surface and at 3, 10, 30, 50 and 100 cm depth, including different elevations, aspects and slope angles. Thirty-seven temperature sensors inserted into drillholes of different depths at ten locations (altitudes from 2300 to 2700 m) were used to validate the simulation. Additionally, surface temperatures were determined from infrared images; these were calibrated for surface emissivity using further temperature sensors. Simulated temperatures and sensor data show very good agreement, with a mean correlation coefficient of 0.94, and the validation of surface temperatures by thermal imaging also delivered good results (r > 0.9). This means that the WUFI software can be used to model complex temperature distributions in natural rock wall settings, thus making it a valuable tool for geomorphological investigations.

Long-term changes in the ground thermal regime of an artificially drained thaw-lake basin in the Russian European north


Long-term (1982–1995) observations of the ground thermal regime of a drained thaw-lake basin in the Pechora Lowlands of the Russian European north revealed a high spatial and temporal variability in the ground temperature response to artificial drainage. The thermal response was controlled by the atmospheric climate and by evolution of the landsurface following drainage. Observed changes in permafrost conditions were related to three climatic subperiods identified from air and ground temperature trends. The first (1982–1984) was characterized by gradual ground cooling associated with partial formation of permafrost patches under the initial stage of formation of marshy meadows. The second (1985–1987) involved strong ground cooling, resulting in the formation of a subsurface permafrost layer beneath most of the basin. The third (1988–1995) was marked by a gradual increase in annual mean ground temperature, promoting partial permafrost degradation under marshy meadows and willow stands. Initially, newly aggraded permafrost remained under peat mounds and tundra meadows. The spatial pattern of permafrost change can be attributed to heterogeneous landsurface evolution and variable snow thickness. Four distinct ground temperature regimes are distinguished: (i) thawed ground, (ii) deep permafrost, (iii) unstable permafrost and (iv) stable permafrost.

Fine-scale influences on thaw depth in a forested peat plateau landscape in the Northwest Territories, Canada: Vegetation trumps microtopography


The influence of vegetation and microtopography on fine-scale variability of thaw depth is largely unknown but potentially important for improving modeling of ecosystem–permafrost interactions. To elucidate their influence, we measured tree density, shrub cover and cryptogam presence (lichen and bryophyte) on forested permafrost peat plateaus in the discontinuous permafrost zone in the southern Northwest Territories, Canada. Greater tree density was associated with shallower thaw depth (approximately one quarter of the variance), whereas shrub cover had a negligible influence on thaw depth. Cryptogam species influenced thaw depth, with greater thaw depth associated with Sphagnum than with Cladonia (a difference on the order of 10%). Greater thaw depth occurred beneath hummocks than beneath hollows (a difference also on the order of 10%). Together, canopy cover, cryptogam species and microforms contribute to a variation of roughly half the variance in thaw depth in the peat plateau landscape.