Fluvial and Coastal Landforms and Processes

Rivers and streams cause lateral and vertical erosion of ice-cored terraces and moraines by thermo-erosional undercutting, removing the debris-cover and exposing the permafrost. Most large rivers have a braided morphology due to the high sediment load and large diurnal and seasonal fluctuations in discharge common for glacio-nival flow regimes.

Taliks (unfrozen zones with groundwater movement in permafrost environments) are believed to exist below most valley rivers. When glaciers override an outwash plain, such as during a surge event, proglacial open taliks (i.e. taliks in contact with the active layer) may become closed taliks overlain by isolating glacier ice and underlain by relict permafrost. Such closed taliks have important consequences for the formation and development of subglacial drainage systems, and they may be identified by proglacial upwelling and winter discharge. They may also be important for whether a coupling of glacier ice and relict permafrost occurs.

Naled (plural naledi; also referred to as icing and aufeis) is an extrusive stratified ice accretion formed when successive water discharge inundates the valley floor during the cold season. Perennial naled assemblages are common on Disko Island and are often related to ordinary or homothermal springs (spring naled), alluvial fans, and upwelling on outwash plains (river naled) (Humlum, 1979; Humlum and Svensson, 1982). No reports of naled associated with pingos have been made to date. Naled formed as a consequence of winter discharge from glacier portals or through taliks below glacier termini (glacier naled) seems to be linked to surge-type glaciers (Yde and Knudsen, 2005). During the surge event of Kuannersuit Glacier an at least 3 m thick glacier naled was produced in front of the glacier during the winter of 1997/1998. The advancing glacier transferred longitudinal compressive stresses onto the proglacial naled, while a high hydraulic pressure below the naled caused an upward pressure, resulting in failure and stacking of large faulted naled blocks in front of the glacier (Yde et al., 2005b; Roberts et al., 2009). This landform is termed thrust-block naled. Glacier naled associated with surge events may be debris-rich relative to other types of naled, containing a significant amount of clay. Also, the observations at Kuannersuit Glacier indicate that proglacial naled may be incorporated into the basal ice of advancing glaciers.

Coastal erosion occurs as tidewater undercutting of rocks and marine terraces. Along the beaches of Disko Island a debris-rich tidal platform ice-foot forms each winter, reducing the erosional and depositional effects of waves and affecting coast morphology and sedimentology (Nielsen, 1982). Raised marine terraces and beach ridges are widespread, and the highest marine limits are between 80 - 120 m (Weidick and Bennike, 2007).

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  • kaarle weckman
    What is fluvial and coastal landforms?
    4 years ago

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