A genetic classification of the palsa-like mounds in Western Canada
DOI:
https://doi.org/10.26485/BP/1998/37/9Keywords:
palsa-like landform, ice content, peat, climate changeAbstract
In Western Canada, there appear to be five main groups of true palsa-like landforms. Floating palsas are developed entirely in peat and float like an iceberg. They exhibit increased ice content due to addition of meteoric water, but are under 60 cm high. Minerogenic palsas are developed in a thin peat cover, with the permafrost extending down into the mineral substrate. They represent the bulk of the palsas and their height is dependent on the expansion due to water changing to ice in their core. 2-4 m is typical, with ice contents up to 90% by volume in some layers. Lithalsas are developed entirely in a mineral substrate at sites where fen peat cannot develop. They go through a different sequence of stages and can develop a cover of ericaceous peat. A typical mature lithalsa has an average ice content of over 60% in its core, and its height and shape are similar to those of a minerogenic palsa.
Floating peat plateaus differ from palsas by having a fiat top rising only 1-2 m above the fen. The icy core is limited to the peat and contains less H20 than the surrounding unfrozen peat. Air has replaced some of the water so that it floats considerably higher than the floating palsas. Where the icy core of a peat plateau extends down into a mineral substrate, an anchored peat plateau is produced. Since the rate of peat formation on the mound is half that in the fen, the anchored peat plateaus slowly drown and are eventually destroyed without the intervention of a climatic change.
These true palsa-like landforms can be mimicked by other processes, e.g. intrusion of water producing pingos or seasonal frost mounds. Other examples described include permafrost that has subsequently developed in a blanket bog on a slope, and thermokarst caused by melting snow at the foot of slopes in areas of continuous permafrost. These are not considered to be palsa mounds, since palsas are regarded as distinct from other types of permafrost.
References
Åhman, R., 1977 - Palsar i Nordnorge. Meddelanden Fran Lunds Universitets Geografiska Institution Adhandlingar, 78; 165 pp.
Brown, R. J. E., 1970 - Occurrence of permafrost in Canadian peatlands. Proceedings, 3rd International Peat Congress, Quebec. National Research Council of Canada, Ottawa; p. 174-181.
Dionne, J. C., 1978 - Formes et phénomènes périglaciares en Jamésie, Québec subarctique. Géographie Physique et Quaternaire, 32; p. 187-247.
Dionne, J. C., 1984 - Palses et limites méridionales du pergélisol dans l'hemisphère nord: le cas de Blanc/Sablon, Québec. Géographie Physique et Quaternaire, 38; p. 165-184.
Fosgren, B., 1966 - Tritium determinations in the study of palsa formation. Geografiska Anna/er, 48a; p. 102-110.
Fosgren, B., 1968 - Studies of palsas in Finland, Norway and Sweden, 1964-1966. Biul. Peryglacjalny, 17; p. 117-123.
Fries, T., Bergström, E., 1910 - Nígra iakttagelser öfver palsar och deras förekomst i nordligaste Sverige. Geol. Fören. Forhandl., 32, Stockholm.
Harris, S. A., 1988 - Observations on the redistribution of moisture in the active layer and permafrost. Proceedings, 5th International Permafrost Conference, Trondheim, Norway. Tapir Press, Trondheim. Vol. 1; p. 364-369.
Harris, S. A., 1989 - Landforms and ground ice as evidence of the source of H2O in permafrost. Progress in Physical Geography, 13; p. 367-390.
Harris, S. A., 1993 - Palsa/like mounds developed in a mineral substrate, Fox Lake, Yukon Territory. Proceedings, 6th International Conference on Permafrost, Beijing, 1; p. 238-243.
Harris, S. A., Nyrose, D., 1992 - Palsa formation in floating peat and related vegetation cover as illustrated by a fen bog in the Macmillan Pass, Yukon Territory, Canada. Geografiska Annaler, 74A; p. 349-362.
Harris, S. A., Schmidt, I. H.., 1994 - Permafrost aggradation and peat accumulation since 1200 years B.P. in peat plateaus at Tuchitua, Yukon Territory (Canada). Journal of Paleolimnology, 12; p. 3-17.
Harris, S. A., Schmidt, I. H., Krouse, H. R., 1992 - Hydrogen and oxygen isotopes and the origin of ice in peat plateaus. Permafrost and Periglacial Processes, 3; p. 19-27.
Harris, S. A., Waters, N. M., Krouse, H. R., 1993 - Hydrogen and oxygen isotopes and the origin of ice in peat plateaus: Reply. Permafrost and Periglacial Processes, 4; P·. 269-275.
Lagarec, D., 1982 - Cryogenic mounds as indicators of permafrost conditions, northern Quebec. In: Proceedings 4th Canadian Permafrost Conference, N.R.C., Ottawa; p. 43-48.
Mackay, J. R., 1993 - The growth of pingos, western Arctic coast, Canada. Canadian Journal of Earth Sciences, 10; p. 979-1004.
Mackay, J. R., 1979 - Pingos of the Tuktoyaktuk Peninsula area, Northwest Territories. Géographie Physique et Quaternaire, 33; p. 3-61.
Magnusson, N. H., Lundqvist, G., Granhind, E., 1957 - Sveriges Geologi (Svenska Bokforiaget, Stockholm). In: Muskeg and the Northern Environment in Canada. N. W.Radforth and C. O. Brawner, Eds., University of Toronto Press, Toronto; p. 63-81.
Müller F., 1959 - Beobachtungen - ber Pingos. Meddelelser om Groenland, 153; 127 pp.
Nelson, F. E., Hinkel, K. M., Outcalt, S. I., 1991 - Palsa-scale frost mounds. In: Periglacial Geomorphology, J. C. Dixon, A. D. Abrahams, Eds., Chichester; p. 305-325.
Payette, S., Seguin, M. K., 1979 - Les buttes minérales cryogènes dans les bosses terres de la rivière au Feuilles, Nouveau-Québec. Géographie Physique et Quaternaire, 33; p.339-358.
Pissart, A., 1967 - Les pingos de l'île Prince Patrick (76ON 120OW). Geographical Bulletin, 9; p. 189-217.
Porsild, A. E., 1938 - Earth mounds in unglaciated Arctic Northwest America. Geographical Review, 28; p. 46-58.
Radforth, N. W., Bellamy, D. J., 1973 - A pattern of muskeg: a key to continental waters. Canadian Journal of Earth Sciences, 10; p. 1420-1430.
Schunke, E., 1983 - Aktuelle Palsabildung in der Subarktis und ihre klimatischen Bedingungen. Abhandl. d. Akademie d. Wiss. Göttingen, Math.-Phys. Klasse, Dritte Folge 35; p. 19-33.
Seppälä M., 1980 - Stratigraphy of a silt-cored palsa, Atlin Region, British Columbia, Canada. Arctic, 33; p. 357-365.
Seppälä, M., 1986 - The origin of palsas. Geografiska Annaler, 68A; p. 141-147.
Svensson, H., 1964 - Structural observations in the minerogenic core of a pals. Särtryck Fran Lunds Universitets Geografiska Institution , 17, Arsbok, 1964; p. 138-142.
Thorarisson, S., 1951 - Notes on patterned ground in Iceland, with particular reference to the Icelandic "flas". Geografiska Annaler, vol. 33; p. 144-156.
Wahl, H. E., Fraser, D. B., Harvey, R. C., Maxwell, J. B., 1987 - Climate of the Yukon. Environment Canada, Atmospheric Environment Service. Climatological Studies, 40; 323 pp.
Washburn, A. L., 1983a - Palsas and continuous permafrost. Permafrost 4th International Conference Proceeding, National Academy Press, Washington. Vol. l; p. 1372-1377.
Washburn, A. L., 1983b - What is a palsa? Abhandl. d. Akademie d. Wiss. Göttingen, Math.-Phys. Klasse, 35; p. 34-47.
Zoltai, S. C., Tarnocai, C., 1971 - Properties of a wooded palsa in Northern Manitoba. Arctic and Alpine Research, 3; p. 115-129.
Zoltai, S. C., Vitt, D. H., 1990 - Holocene climatic change and the distribution of peatlands in western interior Canada. Quaternary Research, 33; p. 231-240. a minerogenic wooded palsa in northern Manitoba (Zoltai, Tarnocai, 1971)
