Tephra Influence on Glacier Ablation on Iceland since 2010
Supraglacial particles are known for their impact on glacier energy and mass balance. Thin layers of aerosols deposited on the glacier reduce the albedo, increase absorbed global radiation and enhance ablation whereas thick layers tend to have insulating effects. Grain size and chemical composition of the particle cover play an important role in determining the intensity of these influences. Large scale, non-insulating particle covers may originate from either atmospheric black carbon (ABC) deposition or fallout of volcanic ashes. Deposition of fine-grained and thin layers of ABC extends over large areas showing a rather uniform pattern on the regional scale. Volcanic ashes may also be deposited over regional-scale areas but show a high spatial variability of thicknesses. The heterogeneous dispersal of volcanic ashes complicates glacier wide influence assessments. Hence and so far, most related studies focused on the influence of ABC deposition. The influences of volcanic ash fall, in contrast, have hardly been studied, even though active volcanism and extensive glacierized areas coincide in various regions of the world. In 2010 and 2011 two major eruptions of Eyjafjalljökull and Grímsvötn volcanos spread tephra over large parts of the Icelandic ice caps. Due to the rather easy accessibility of these areas and the availability of related data they represent an ideal opportunity for a study of the influences of volcanic tephra deposits on glacier mass balance.
The aim of the project was to develop a spatially distributed approach for modeling of the influences of supraglacial tephra deposits on glacier mass balance that is able to cope with the spatiotemporal inhomogeneities of these deposits regarding thickness and chemical composition on a regional scale. The model was applied to the two recent Icelandic eruptions and the induced changes in mass balance of Vatnajökull, Myrdalsjökull and Eyjafjallajökull ice caps. The approach not only relied on time invariant data of tephra thickness but also accounted for the temporal variability of this quantity. By this means, the project provided a continuous chain of transfer functions between, as explicants, the interior, micro-scale forcing by grain-size distribution and chemical composition of deposited tephra and the exterior forcing by meteorological conditions and, as resultant, the macro-scale changes in glacier ablation and mass balance. Besides the closing of the gap in scientific knowledge regarding ice-volcano interactions in this respect, the project also created a potentially valuable tool for the purpose of hazard mitigation after volcanic eruptions in glacierized regions. The modeling approach facilitates a fast quantification of changes in ablation and runoff in subsequent river systems after volcanic eruptions. This might be important for the protection of infrastructure and settlements in affected regions.
|Dipl.-Geol. Rebecca Möller|
|Prof. Peter Kukla|
|Prof. Christoph Schneider|