Geografisk Tidsskrift, Bind 82 (1982)

Zonation of permafrost indicators in Swedish Lappland

ANDERS RAPP

Side 37

Rapp, Anders: Zonation of permafrost indicators in Swedish Lappland.
Geografisk Tidsskrift 82: 37-38. Copenhagen, October 15,
1982.

The distribution of three permafrost indicators in the Kiruna bisko region is described. The indicators are: palsa bogs, large non-sorted polygons, »tundra polygons«, and small thermokarst ponds. All three types of features can be traced on aerial photographs, and are of considerable interest as indicators of their environment, particulary the local climate.

Anders Rapp, professor, fil. dr. Dep. of Physical Geography, University
of Lund. Sölvegatan 13, Lund, Sweden.

SUMMARY

The mountain range and its eastern foreland in northernmost Sweden has occurrences of discontinuous permafrost. The new geomorphological maps in scale 1:250000 contain much information on the distribution of permafrost indicators and are used for this study of the zonation of three types of permafrost indicators in the Kiruna-Abisko region. These indicators are: palsa bogs, large non-sorted polygons called »tundra polygons« on the maps, and small thermokarst ponds (map symbol: »collapsed pingos«). Palsas are clear indicators of actual permafrost in peat bogs. They mainly occur in a zone east of the mountain front and in the eastern mountain valleys at low altitudes below 600 m a.5.1., with mean annual air temperatures roughly below -I°C and thin snow cover. Ground temperatures of -2°C at 8 m depth have been measured (Knutsson, 1980). Many large non-sorted polygons have been discovered in north Scandinavia during the last 20 years. In Swedish Lappland they occur mainly above the tree line in flat areas of till or outwash in wind-exposed valley bottoms from 650 to 1000 m a.s.l. in the eastern, continental mountain zone. The polygons have in some cases fossil wedge casts over actual permafrost or no permafrost. In the latter case they may be soil wedge polygons, not indicating former permafrost cf. Friedman et.al. 1971.

»Collapsed pingos« or small thermokarst ponds are a rare
feature which may indicate actual permafrost in earth
mounds of wet sites in high altitudes.

All three types of features can be traced on aerial photographs, and are of considerable interest as indicators of their environment, particularly the local climate. They should be studied in more detail for a better understanding of permafrost and its fluctuations in the discontinuous zone.


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Fig. 1. Map of the distribution of discontinuous permafrost in northern Scandinavia. The limits of the zone of palsa bogs are based on maps by Melander, 1976 and later, and Rapp & Clark, 1971 for Sweden, Seppälä, 1979 for Finland, and Åhman, 1977 for Norway. Black squares mark the sites of large non-sorted polygons (tundra polygons) in the Swedish mountains. Dotted lines are mean annual air temperature lines of O°C and -1 °C in Sweden, period 1901-1930. Fig. 1. Kort visende udbredelsen af diskontinuert permafrost i Nordskandinavien.

RESUMÉ

Bjergkæden og dens østlige forland i Nordsverige indeholder forekomster af diskontinuert permafrost. De nye geomorfologiske kort (1:250000) indeholder megen information om udbredelsen af permafrostindikatorer i Kiruna-Abisko området. Permafrostindikatorerne er følgende: moser med palser, store usorterede polygoner, »tundra polygoner«, og små søer dannet som et termokarstfænomen (på kortene angivet som sammensunkne pingos). Palser er et klart tegn på recent permafrost i tørvemoser. De optræder især i en zone øst for bjergkæden samt i dale i bjergenes østlige del. Forekomsterne ligger lavt, mindre end 600 m.0.h., de er karakteriseret ved en gennemsnitlig lufttemperatur lavere end -I°C samt et tyndt snedække. Jordtemperaturer på -2°C er målt i 8 mt's dybde. Store usorterede polygoner er påvist i Nordskandinavien gennem de seneste 20 år. I Svensk Lappland optræder de hovedsagelig over trægrænsen i jævne områder bestående af till eller smeltevandssedimenter, beliggende i vindexponerede dales bund, i højder fra 650 til 1000 m.o.h. i det østlige, kontinentale bjergområde. Polygonerne indeholder i nogle tilfælde fossile wedge casts. Nogle steder findes derunder recent permafrost, andre steder ikke. I sidstnævnte tilfælde kan polygonerne være soil wedge polygoner, som ikke er tegn på permafrost. Sammensunkne pingos eller små termokarst søer er sjældne fænomener, der kan angive tilstedeværelse af recent permafrost i earth mounds på fugtige, højtliggende steder.

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Fig. 2. Map of zones of permafrost indicators in the Kiruna-Abisko region, N. Sweden. The map is based on Melander, 1976 and 1977, and on own observations. Grey tone indicates areas above 600 m a.5.1., which is the approximate birch forest limit in this region. Key: 1 = lake. 2 = groups of palsas. 3 = area of large non-sorted polygons. 4 = thermokarst ponds (»collapsed pingo«). 5 = mountain summit and altitude in meters. 6 = supposed neotectonic faults. 7 = area above 600 m altitude. 8 = town. 9 = road. 10 = glacier, p = permafrost revealed by drilling or excavation. Fig. 2. Kort visende zoneringen <2//?e/-ma/ro.s?/nüf/A:a?orer /' Kiruna området, Nordsverige. Kortet er baseret på Melander (1976,1977), samt på egne observationer.

Alle tre indikatorer kan iagttages på flyfotos, og er af væsentlig interesse som indikatorer for omgivelsernes miljø, og specielt det lokale klima. De bør studeres detaljeret, for derved at opnå et bedre kendskab til permafrosten samt dennes fluktuationer i zonen med diskontinuert permafrost.

LITERATURE

Friedman, J. D., Johansson, C. E., Oskarsson, N., Svensson, H., Thorarinsson, S. and Williams, R. S., 1971: Observations on Icelandic polygon surfaces and palsa areas. Photo interpretation and field studies. Geogr. Annaler 53 A.

Knutsson, S., 1980: Permafrost i Norgevägen. Byggmästaren 10/

80.

Melander, O. 1976: Geomorfologiska kartbladet 29 J Kiruna. SNV
PM 741.

Melander, O. 1977: Geomorfologiska kartbladet 30 I Abisko, etc.
SNV PM 857.

Melander, O. 1977: Geomorfologiska kartbladet 30 J. Rensjön.
SNV PM 858.

Rapp, A. and Clark, M., 1971: Large non-sorted polygons in Pad-

jelanta National Park, Swedish Lappland. Geogr. Annaler 53 A.
Seppälä, M. 1979: Recent palsa studies in Finland. Acta Univ. Oul.

A 82. Geol. 3. Oulu, Finland.

Åhman, R. 1977: Palsar i Nordnorge. Medd. Lunds Univ. Geogr.
Inst. LXXVIII