Periglacial Weathering Processes

In many of the major valleys large blocks of rocks have been detached from the walls and are now occupying the valley slopes (Pedersen et al., 2001). In Kuannersuit Kuussuat (Kuannersuit Valley), there are no obvious signs of glacial abrasion on the relocated blocks, although they have been eroded by fluvial processes. This leads to the preliminary interpretation that the large detachments are a paraglacial phenomenon related to pressure-release on valley walls during the deglaciation of the Wisconsin ice cap covering Disko Island. Talus deposits on valley slopes are often found in relation to ice-cored terraces, ice-cored moraines, tills or rock glaciers, although evidence of recent mass wasting events occur, i.e. on the western valley slope at the head of Kuannersuit Kuussuat. Mass wasting events in the narrow Vaigat Strait may also cause tsunamis, which lead to erosion and deposition along the northeastern shores of Disko Island.

Mechanical breakdown enhanced by frequent freeze-thaw cycles leads to rock shattering and formation of regolith deposits. Field observations on Disko Island support the notion by Mackay (1999) that rock types with schistosity facilitate water access and, hence, shatter more frequently. On an outwash plain formed by the Sorte Hak glaciers around 1940, the basaltic stones are generally unbroken or slightly shattered (Figure 5), whereas all observed shale stones have been heavily shattered (Figure 6). Observations on the outwash plain in front of Kuannersuit Glacier suggest that shale stones shatter explosively within one or a few years in this environment.

Figure 6. Explosively shattered shale stone incorporated into the surface of an outwash plain on top of buried glacier ice, Kuannersuit Kuussuat (Kuannersuit Valley). Camera etui for scale.
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Figure 7. Oblique view of ice-wedge polygons associated with thermal contracting cracking, Bl^sedalen.

Chemical weathering rates have not been quantified in non-glacierized catchments on Disko Island, but solute provenance estimations from Kuannersuit Glacier (Yde et al., 2005 a) indicate relatively high chemical weathering yields compared to non-basaltic environments. Suspended sediment loads in rivers and streams are also relatively high due to glacial erosion and abundant unconsolidated sediments on valley floors (Rasch et al., 2003; Knudsen et al., 2007), which cause high sedimentation rates in the inner parts of fjords (Gilbert et al., 1998, 2002; M0ller et al., 2001).

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