Weathering, blockfields, and fracture systems and the implications for long-term landscape formation: Some evidence from lyngen and øksfordjøkelen areas in North Norway

The basic geomorphology of two mountain areas in North Norway (ca 70° N) is outlined. The region has remnants of the Palaeic surface of the North Scandes, which are now seen as a summit accordance. Some of these summits have extensive plateaus on which blockfields containing fines (ca. 20%) and suites of clay minerals are found. These have been interpreted as pre-glacial weathering sequences. Laboratory investigations on a block of removed rock show no freeze-thaw weathering products, and chemical weathering is restricted to the outer few millimeters of faces exposed by joints. This lack of weathering is attributed to the paucity of micro-cracks in the intact rock. Block production appears to be controlled by spacing of intersecting cracks and joints at about the meter scale. The time periods and climatic conditions required for the accumulation of clays and the depth of the blockfield points to pre-Quaternary weathering. This view is supported by comparison with other investigations in Scandinavia. The inheritance of the pre-Quaternary elements in a "glacial" landscape is discussed in light of an appreciation of a more holistic long-term view of landscape development. The failure of Pleistocene ice caps to remove the summit blockfield is attributed to either cold-based ice and/or the removal of ice in ice streams, leaving any ice covering summits as ineffective in glacial erosion.