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Abstract
This paper examines the occurrence of ephemeral hoarfrost crystals at funnel openings (funnel hoarfrost) detected between large blocks at the surface of the presumably relict chöneben ock lacier. Field mapping on 25 November 2011 identified 51 individual funnel openings with notable hoarfrost crystals distributed over the entire rock glacier. Hoarfrost was no longer detectable a few days after the initial mapping campaign. At least in the period 20–25 November 2011 temperature conditions at the rock glacier surface were favourable for hoarfrost formation and preservation as indicated by different types of measurements. A period of 24–48 h of hoarfrost‐suitable weather conditions would have been sufficient to form the observed hoarfrost if crystal growth rates of 2–4 mm h−1 are assumed. The void systems with funnel hoarfrost seem to be rather localised and limited in horizontal (10s of metres) and vertical (some metres) extent. Presumably the observed funnel hoarfrost was caused by the so‐called chimney effect, although no larger reversible air circulation systems with warm air exhalation were identified. Continuous ground temperature data from several sites at the rock glacier surface (period November 2011–December 2012) showed that hoarfrost sites are cooler and thermally buffered compared with non‐hoarfrost sites at similar elevations. This seems to be related to the decoupling of the air above the rock glacier and the pore air during periods of atmospheric warming. Only the combination of specific micro‐climatic (temperature/humidity), geometric (open void systems) and sedimentological (grain size/sediment structure) conditions allow the formation of the ephemeral funnel hoarfrost at this rock glacier.
Acknowledgement
This study was carried out within the framework of the project Water Resources of Relict Rock Glaciers co‐funded by the Federal Government of Styria and the European Regional Development Fund (ERDF). Please visit http://www.uni‐graz.at/hydro‐blogle for more information on the project. GIS data have been provided by the Federal Government of Styria, administrative office GIS‐Steiermark. Climate data were kindly provided by the Federal Government of Styria, Hydrological Service. Andreas Pilz is thanked for fieldwork assistance. Ground temperature data from the neighbouring Reichart Cirque and daily photographs from the remote digital camera at Feistererhorn are collected within a long‐term monitoring program of the Department of Geography and Regional Science, University of Graz. The manager of this monitoring network is the first author of this paper. The monitoring network was initiated during the project ALPCHANGE – Climate Change and Impacts in Southern Austrian Alpine Regions funded by the Austrian Science Fund/FWF through project no. FWF P18304‐N10. Reynald Delaloye, Xavier Bodin and two anonymous reviewer are very much thanked for their constructive comments on earlier versions of this paper.
This paper is dedicated to Sarah Eulenstein, who was born during the preparation period of this paper and who is the third child of the first author.
Additional information
Notes on contributors
Andreas Kellerer‐pirklbauer
Andreas Kellerer‐Pirklbauer, Institute for Earth Sciences, University of Graz, Heinrichstrasse 26, A‐8010 Graz, Austria, and Department of Geography and Regional Science, University of Graz, Heinrichstrasse 36, A‐8010 Graz, Austria
E‐mail: [email protected]
Marcus Pauritsch
Marcus Pauritsch and Gerfried Winkler, Institute for Earth Sciences, University of Graz, Heinrichstrasse 26, 8010 Graz, Austria
E‐mail: [email protected]; [email protected]