Glacier retreat and landform production on an overdeepened glacier foreland: The debris-charged glacial landsystem at Kvíárj?kull, Iceland

摘要

Glacier recession and landform development in a debris-charged glacial landsystem characterized by an overdeepening is quantified using digital photogrammetry, digital elevation model (DEM) construction and mapping of the Icelandic glacier Kvíárj?kull for the period 1945-2003. Melting of ice-cores is recorded by surface lowering rates of 0·8myr~(-1) (1945-1964), 0·3myr~(-1) (1964-1980), 0·015myr~(-1) (1980-1998) and 0·044myr~(-1) (1998-2003). The distribution/preservation of pushed and stacked ice-cored moraine complexes are determined by the location of the long-term glacial drainage network in combination with retreat from the overdeepening, into which glacifluvial sediment is being directed and where debris-rich ice masses are being reworked and replaced by esker networks produced in englacial meltwater pathways that bypassed the overdeepening and connected to outwash fans prograding over the snout. Recent accelerated retreat of Kvíárj?kull, potentially due to increased mass balance sensitivity, has made the snout highly unstable, especially now that the overdeepening is being uncovered and the snout flooded by an expanding pro-glacial, and partially supraglacial, lake. This case study indicates that thick sequences of debris-charged basal ice/controlled moraine have a very low preservation potential but ice-cored moraine complexes can develop into hummocky moraine belts in de-glaciated terrains because they are related to the process of incremental stagnation, which at Kvíárj?kull has involved periodic switches from transport-dominant to ablation-dominant conditions. Glacier recession is therefore recorded temporally and spatially by two suites of landforms relating to two phases of landform production which are likely typical for glaciers occupying overdeepenings: an early phase of active, temperate recession recorded by push moraines and lateral moraines and unconfined pro-glacial meltwater drainage; and a later phase of incremental stagnation and pitted outwash head development initiated by the increasing topographic constraints of the latero-frontal moraine arc and the increasing importance of the overdeepening as a depo-centre.