Widespread occurrence of ephemeral funnel hoarfrost and related air ventilation in coarse‐grained sediments of a relict rock glacier in the seckauer tauern range, austria

Abstract

Kellerer-Pirklbauer, A., Pauritsch, M. and Winkler, G., 2015. Widespread occurrence of ephemeral funnel hoarfrost and related air ventilation in coarse-grained sediments of a relict rock glacier in the Seckauer Tauern Range, Austria.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 Schöneben Rock Glacier. 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.

Investigating groundwater flow components in an Alpine relict rock glacier (Austria) using a numerical model

“…The estimated hydraulic conductivity of the SRG (Table 1) is in good agreement with findings of Pauritsch et al (2015) and Winkler et al (2016a). Nevertheless, the winter base flow cannot be reproduced correctly in the calibration period with either of the applied aquifer bases.…”

“…This layer is supposed to represent glacial sediment deposits (probably morainic sediments), which would be in agreement with the findings at an active rock glacier, where moraine deposits have been encountered in two drill cores at its base (Krainer et al 2015). The hydraulic properties of the layer at the base of the Schöneben rock glacier were additionally estimated by Pauritsch et al (2015) using analytical models of sloping aquifers by focusing on winter base flow data. The derived hydraulic conductivity on the order of 10 −5 m/s is consistent with findings of Winkler et al (2016a).…”

“…The surface of the SRG is covered by coarse-grained, blocky material consisting of gneissic rocks ranging from cubic decimeters to a few cubic meters. The characteristic morphology with distinct collapse structures (i.e., caused by the melting of the ice and the resulting loss in volume), the partial vegetation cover (mainly grasses and dwarf pines) and the low slope gradient of the rock glacier front indicate that the SRG can be assumed to be a relict rock glacier, which is supported by an average water temperature above 2.2°C at the spring emerging at the front of the rock glacier (Kellerer-Pirklbauer et al 2015;Winkler et al 2016a).…”

Long‐term monitoring of sporadic permafrost at the eastern margin of the European Alps (Hochreichart, Seckauer Tauern range, Austria)

“…However, as shown by continuous ground temperature measurements at this rock glacier (stars in Figure i; relevant data series shown in Figure c of ref. ), the ground thermal conditions on the dates of measurements were not in equilibrium. A very cold period of up to −20°C in the first half of February 2012 severely and enduringly affected the thermal regime of all five ground temperature measurement sites (and hence the entire rock glacier).…”

“…Ground and air temperature have also been monitored since 2011 at the Dürr valley and the Schöneben cirque, respectively (Figure , white stars, 10 monitoring sites in the two valleys). Temperature monitoring at these two areas focuses on hydrological issues, although the cooling effect of the blocky layer is also considered . Relevant thermal results from these two areas are considered in the discussion.…”