Sorted Paterned in Karst Caves: Development and Potential for Permafrost Research


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julia.boike [ at ] awi.de

Abstract

One of the most distinctive periglacial landscape landforms is patterned ground. Although usually found in mountains or in polar regions, it has also been reported from several karst caves in Slovenian Dinaric Mountains and Alps, Swiss Jura Mountains and West Carpathian Mountains in Slovakia but never studied in detail. Ledenica pod Hrušico ice cave lies on a karst plateau at an elevation of about 800 m. It consists of a spacious 20 m deep shaft, debris cone and two small passages. One of the passages contains fine sediments, which are mixed with limestone debris. Sorted stripes are present on an inclined slope of this passage. Twelve 20-50 cm wide stripes of coarse limestone debris developed on fine cave sediment. The grain size of the fine sediment is predominantly silty (80 %), which makes it very susceptible to frost heaving. A geoelectrical survey and drilling revealed one metre sediment thickness. Several freeze-thaw cycles occur at the sediment ground surface in winter due to cave temperature fluctuations. Cave air temperature measurements show that surface air enters the cave only when its temperature drops below the cave air temperature, which results in preferentially cold and oscillating winter temperatures and the formation of a cool air pool in the summer. Karst caves can contain significant amounts of silty sediments that accumulated during flood events when the cave was situated in the floodwater zone or can originate from fine rock weathering. Frost shattering of parent bedrock is a potential source for coarse debris. The cold climatic conditions that result from cave morphology sustain low ground temperatures in summer and cause freeze-thaw cycles in winter, which result in frost heaving that causes sediment sorting. Barka Cave lies close to Snežnik Mountain at an elevation of 1100 m. It is a 20 m deep and 50 long oval collapse doline with locally overhanging walls. Sorted patterned ground developed on vegetation free floor under these walls. Especially characteristic are sorted circles with diameters ranging between 40 to 70 cm. Frost heave and needle ice length up to 10 cm were observed during freezing conditions. A wide grain size range of sediment (gravel and sand) present on sorted circles enables tracking of ground movements with surface from motion technique. Absence of snow and vegetation makes karst caves unique places for monitoring of ground movements caused by ground freezing. Sorted patterned ground in karst caves can thus help to reveal cryoturbation mechanisms that are responsible for large organic carbon storage in soils underlain by permafrost..



Item Type
Conference (Conference paper)
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Primary Division
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Peer revision
Not peer-reviewed
Publication Status
Published
Event Details
1st Southern Hemisphere Conference on Permafrost, 04 Dec 2019 - 14 Dec 2019, Queenstown, New Zealand.
Eprint ID
50847
Cite as
Obu, J. , Kosutnik, J. , Overduin, P. , Boike, J. and Blatnik, M. (2019): Sorted Paterned in Karst Caves: Development and Potential for Permafrost Research , 1st Southern Hemisphere Conference on Permafrost, Queenstown, New Zealand, 4 December 2019 - 14 December 2019 .


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