1. Arctic Centre, University of Lapland, FI-96101 Rovaniemi, and Dept. of Geophysics, University of Oulu, FI-90014 Oulu, Finland,
2. Arctic Centre, University of Lapland, FI-96101 Rovaniemi, Finland;
3. Dept. of Geomorphology, University of Silesia, PL-41-200 Sosnowiec, Poland;
4. Institute of Geophysics, Polish Academy of Sciences, PL-01-452 Warsaw, Poland.