Internal structure and permafrost characteristics of the rock glaciers of southern carpathians (romania) assessed by geoelectrical soundings and thermal monitoring

Abstract

Six rock glaciers in the outhern arpathians have been investigated by means of geoelectrical soundings in order to detect their internal stratigraphy and the existence of frozen sediments. In the case of three relict rock glaciers, the electrical resistivity measurements indicated a typical internal structure. Low resistivity values (<10-kΩm) which are typical of unfrozen fine‐grained materials were obtained, but high resistivity values (25–240-kΩm) measured in the ietroasa, Ieşu and ietrele rock glaciers denote the presence of sediments cemented by interstitial ice and ice lenses. Based on the moderate resistivity values, the ice content is probably low to medium in the upper portion of these rock glaciers, that is, above 2040 m.

At two sites (ietroasa and ăiuga rock glaciers), ground surface temperature evolution was monitored using digital dataloggers. Mean annual ground surface temperature and regime throughout the winter were extracted from the recordings and confirmed the probability of permafrost occurrence in ietroasa rock glacier. In the Ieşu and ietrele rock glaciers, measurements of bottom temperatures of the winter snow cover were performed in March 2012. Considering the thick active layer, the reduced ice content and the presence of scarce vegetation on their surface it could be assumed that the permafrost exists in marginal conditions in the outhern arpathians. The ground ice in permafrost is produced by the groundwater freezing or by snow banks buried by coarse angular boulders following large rockfalls.

Key words:

• rock glaciers
• permafrost
• geoelectrical soundings
• thermal measurements
• Southern Carpathians

Acknowledgements

We would like to thank Jan Boelhouvers, Martin Hoelzle, Ole Humlum and an anonymous reviewer for their constructive comments on an earlier version of this manuscript. Also, we are grateful to Yanni Gunnell for improving the English of the manuscript. Finally, the authors are grateful to numerous students from the Department of Geography, West University of Timişoara for their committed help in carrying and installing the heavy equipment in the field.