Assessing glacier retreat and landform production at the ‘debris-charged’ snout of Kvíárjökull, Iceland

Abstract

Iceland is a critical location for the study of glacier fluctuations and landform production in response to climate change due to its diverse glacial legacy and its archive of aerial photographs that provide accurately dated records of glacier retreat and landform evolution from 1945. This study focuses on Kvíárjökull, an outlet glacier of the Öræfajökull ice cap in southeast Iceland, recently classified as a ‘debris-charged glacier landsystem’. Digital photogrammetry was applied on five sets of aerial photographs from 1945 to 2003 in order to produce Digital Elevation Models from which measurements of morphometric change within the glacier snout and foreland were made. This analysis was combined with field assessments and geomorphological mapping to investigate the evolution of landforms from complex debris transport pathways and the impact of ice marginal dynamics on moraine evolution.

The temporal pattern of retreat of Kvíárjökull correlates with fluctuations in air temperature with a lag of about 10 years compared to other Icelandic glaciers. Ice-marginal pushing during lateral fluctuations of the snout results in the construction of push moraine ridges and the destruction of controlled moraine derived from englacial debris concentrations. Accelerated snout retreat between 1998 and 2003 exceeded the rate of increase in air temperature and is attributed to the growth of proglacial and supraglacial lakes associated with high rates of backwasting. Backwasting of ice cores consumes ridges of high relief, thus, reducing the preservation of controlled moraine ridges. A model for the de-icing of ice-cored moraines is presented in which ice-cores remain in the landscape for up to 83 years after detachment from the glacier snout.

A debris-charged glacier landsystem model is presented in which hummocky moraine complexes comprise three process-sediment-landform associations: chaotic hummocky moraine, with minor elements of linearity resulting from the stagnation of controlled moraine; heavily channelized moraine complexes; and, most prevalent, discontinuous push moraine ridges formed during ice-marginal pushing. A time series of five 1:10,000 geomorphological maps illustrates the evolution of this landsystem and provides an unprecedented record of cryospheric change.