Late-Pleistocene and Holocene mountain permafrost geomorphology of Norway and Iceland.

Abstract

The combined effect of glacial and periglacial processes on landscape evolution has recently been termed the ‘cryoconditioning’ of landscapes, and largely affect the Fennoscandian landmass. Further, the distribution of permafrost both temporally and spatially during and after the last glaciation affect the overall geomorphic expression. In this thesis the product of landscape evolution is investigated in terms of the geomorphic imprint of glacial and periglacial processes, where the interactions between glaciers and permafrost have been particularly focussed upon. Whereas the glacial variations over the Holocene are relatively well known the same is not the case for the permafrost distribution.

As a starting point, inventories of landforms indicating present and former permafrost were compiled for mainland Norway and northern Iceland. The main findings from the inventories were (1) a low abundance of landforms in Norway and a high abundance of landforms in Iceland probably due to differences of bedrock competence, (2) an apparent change in processes leading to rock glacier formation occurred in mid-Holocene from a dry, periglacial regime characterizing early-Holocene to a humid, glacially-dominated regime in mid- to late-Holocene, and (3) warm and maritime permafrost regions are dominated by permafrost landforms formed by the influence of glaciers. For Iceland the occurrence of relict rock glaciers at sea level imply a possible earlier deglaciation or alternatively a less extensive Last Glacial Maximum (LGM) than commonly accepted.

As a second step, modelling of permafrost variations over the Holocene was performed in depth and spatially, using a 1D heat flow model and a 2D equilibrium model (CryoGRID1.0). During the warm Holocene Thermal Maximum (HTM) the permafrost survived at high altitudes in southern Norway, whereas during the ‘Little Ice Age’ (LIA) the permafrost reached its greatest extent both in depth and spatially. From these results altitudinal zones of permafrost ages was suggested, analogous to age patterns for Arctic permafrost. From the Neoglaciation until present, the potential of glacier-permafrost interactions has been large.

Thirdly, a case study of the currently very small glacier, or glacieret, Omnsbreen which formed and largely disappeared during the LIA was studied in terms of glacial geomorphic evidence for permafrost interaction. Modelled permafrost distribution for the LIA suggest permafrost presence in the Omnsbreen surroundings during its formation and decay, and the landform assemblage present at Omnsbreen is considered representative for mountain glaciers terminating into permafrost. Permafrost is currently only present sporadically in the Omnsbreen surroundings, and the glacier and permafrost underwent a parallel disintegration.

The current geomorphic expression of Norway and northern Iceland is significantly affected by long-term interactions between the glacial, subglacial and ground thermal regimes.