Impact of Ashfalls from Eyjafjallajökull and Grímsvötn Volcanoes on Glacier Ablation on Iceland – a Field Experiment

Abstract:

The albedo of glaciers may be altered by deposition of light-absorbing aerosols, which consequently has an impact on their energy- and mass balance. Icelandic volcanoes have produced frequent eruptions within the recent past that spread tephra over extensive areas. The glaciers of Iceland are thus an ideal location for studies related to the influence of supraglacial tephra layers on ablation.

The two latest subglacial eruptions that induced considerable amounts of ashfall over major Icelandic ice caps were the one of Eyjafjallajökull in April and May 2010 and the one of Grímsvötn in May 2011. The different chemical compositions of the ashes produced by those two eruptions are also noticeable in their distinct thermal properties.

In summer 2015, a field experiment was conducted on western Vatnajökull ice cap. In this experiment, the influence of volcanic tephra from both eruptions on surface ablation is monitored by automated measurements. Artificial plots with varying types and thicknesses of tephra were installed on the glacier. Two types of pristine tephra were compared. One was sampled from inside the caldera of Eyjafjallajökull volcano and one from rocky outcrops at the southern caldera rim of Grímsvötn volcano. Tephra thickness across the different artificial plots ranged from 0.5 to 200 mm. The surface ablation on the plots was continuously monitored by automated measurements. For selected plots, additionally changes of the albedo and the temperature profile through the tephra layer were measured. An automatic weather station was set up for continuous meteorological monitoring.

We here present first results from this field experiment. Analyses of the overall variability of surface ablation with tephra thickness are shown alongside with indications of dependencies on meteorological conditions, mainly solar radiation and rainfall. Special emphasis is placed on highlighting differences between the effects of the two different types of tephra.