The explosive eruption of Eyjafjallajökull, Iceland, between April and May 2010 deposited supraglacial tephra on the surfaces of glaciers across Iceland. While the initial effects of the eruption caused glacial melting, there may have been longer term effects on the remaining ice due to the presence of supraglacial airfall deposits. Cold supraglacial deposits can either enhance or hinder the underlying ablation rate in relation to that of a bare surface, depending on whether they are greater or less than a critical thickness. The critical thickness is the deposit thickness beneath which ablation is equal to that of a bare surface.
Streamflow data collected by the Icelandic Meteorological Office between 2005 and 2013 from rivers draining three glaciers in different parts of Iceland give an insight into the effects on glacial ablation of supraglacial tephra deposition from this eruption. Resulting changes in discharge vary depending on the location of the glaciers relative to that of the eruption source, and therefore in relation to airfall deposit thickness. Streamflow data from rivers draining glaciers close to the source of the Eyjafjallajökull 2010 eruption indicate that ablation was suppressed in the ablation season following the eruption, despite warm local air temperatures favouring enhanced melting. Comparison of the effects of supraglacial tephra deposits on the three glaciers at varying distances from the source vent indicate that the critical thickness for the tephra deposits lay between 0.1 and 5 mm.
Hobbs, L., Gilbert, J., Loughlin, S., & Lane, S. (2015, March). The effect on Icelandic glaciers of supraglacial deposition of tephra from the Eyjafjallajökull 2010 eruption. Presented at Volcano-ice and Icelandic Volcanism Conference 2015, Lancaster, UK