Simulating the formation of overdeepenings with coupled ice, water, and sediment models

Abstract

Eyles identified Kvı́árjökull, an outlet of the icecap Öræfajökull, southeast Iceland, as an exemplar of the glaciated valley landsystem, emphasising rockfall debris supply, passive transport and reworking of a thick cover of supraglacial morainic till. In this paper, we take a fresh look at the sediments and landforms of Kvı́árjökull, focusing on clast form analysis to reconstruct primary transport pathways. New data demonstrate the importance of active transport of debris derived from the glacier bed. Substantial portions of the supraglacial debris cover can be traced back to englacial channel fill deposits or anomalously thick exposures of basal ice. These two types of sediments also make up much of Kvı́árjökull's large Neoglacial moraine rampart. We attribute the abundance of these non-rockfall sediments to the presence of a terminal overdeepening, and the switch from predominantly subglacial to predominantly englacial drainage that this induces. This hydrological switch enhances retention of debris within ice transport, preventing it from being washed away and making it available to feed ice-marginal moraine formation. The complexity of sediment transport processes observed at Kvı́árjökull and the contrast between it and alpine glaciers undermines any single concept of the glaciated valley landsystem; accordingly, we propose Kvı́árjökull as the type example of a distinct subclass, defined by its moderate relief, high-debris turnover, and drainage behaviour characteristic of an overdeepened basin.