An extensive permanent snowfield and the possible occurrence of permafrost in till in the Ridnitšohkka area, Finnish Lapland

Abstract

An area of permanent snow and frozen ground was studied at the end of summer seasons during the years 1990-1993 near the summit of Ridnitv sohkka fell, which at 1317 m a.s.l. is the second highest peak in Finland. The eastern flank of Ridnitv sohkka has the most extensive area of permanent snow (3 km 2) in Finland, while the summit region represents the highest single area of basal till devoid of vegetation cover and displaying patterned ground features. The ground penetrating radar results show that the form of the snowfield does not conform to the topography of the underlying bedrock and reveal the presence of several continuous reflectors dipping down-slope. Observations based on drilling and a single test pit indicate that the snowfield is 6.2 m thick and that it contains discontinuous lenses or layers of ice from 2 to 30 mm in thickness. Plant material from the depth of 4.05 m in the drilling core yielded a radiocarbon age of 35 years, while variations in the size of lichens growing at the edge of the snowfield indicated that the snowfield was of considerably greater extent some 100 to 150 years ago. The results suggest that the snowfield has been stable for a relatively long period but the "residence time" of snow in the snowfield is rather short, presumably less than 100 years and possibly only a few decades. Percussion drilling on the Ridnitv sohkka summit plateau, situating 1290 m a.s.l., revealed that the till was frozen at the depth of 1.9 m at the end of July 1993. Discovery of frozen till shows that frozen ground can locally survive from one season to the next, while the extent of the permanent snowfield and vegetationfree patterned ground suggest that the conditions favourable for permafrost might have existed over wider areas.

Neoglacial activity in Finland: dating the evidence from glaciolacustrine sediment sequences in the Halti-Ridnitšohkka region

“…The basal till at the Ridnitšohkka summit plateau is devoid of vegetation cover and displays patterned ground features. At the end of July during several summer seasons (in 1994, 2004, 2005), frozen ground conditions have been found in the till overburden (Hirvas et al, 2000;. Typical morphological features of the summit slopes are solifluction terraces and lobes.…”

“…During the past few years, this region has experienced decreased amounts of snow precipitation, and the snowfield has barely survived. Simultaneously, the frozen till (permafrost) conditions have spread on the Ridnitšohkka summit plateau (from 1.9 m below the ground surface at the end of July in 1991 to 0.85 m in 2005), probably because of the decreased insolating effect of the snow cover (Hirvas et al, 2000;.…”