The significance of volcanic ash fall for Earth’s glaciers

Hobbs, L.K.; Gilbert, J.S.; Lane, S.J.

Abstract

Worldwide glacier mass changes are key indicators of global climatic change [1]. The effect of volcanic air fall, which may enhance or hinder ablation depending primarily on deposit thickness, is a potentially important driver of glacial change. Below a critical thickness, lowering of surface albedo by deposits increases ice ablation, while above this threshold heat conduction to the ice is reduced sufficiently that ablation decreases and ice becomes insulated from solar radiation (e.g.[2], [3]). The influence of such deposits is important when assessing climate variation using glacier fluctuations, and should also be taken into account when assessing past glacial advances and retreats with respect to climate in volcanic regions [3].
Air fall deposits have high potential to affect Earth’s glaciers as they are capable of covering many thousands of square kilometres, depending on the magnitude and explosivity of the source eruption, and are therefore widespread in a way that local scree and glacial debris deposits are not. Thicknesses vary from several metres in close proximity to the source vent, to sub-monolayer coverings in very distal locations with grading from coarse to extremely fine with increasing distance from the volcano. Multiple tephra layers may develop within ice as ash is deposited from periodic eruptions, which may be rapidly buried and therefore not affect ablation rates until some time after deposition.
Comparison of the positions of Earth’s glaciers to those of the 1545 active volcanoes listed by [4] shows that locations of these features often coincide. Of these volcanoes, 281 (18.2%) have ice/snow cover, while 229 (14.8%) are sufficiently close to ice bodies to potentially affect them. At present, 70 volcanoes (4.5% of the total listed) are known to have caused ash deposition on ice in historical times (with further occurrences over the last 30,000 years demonstrated in Antarctic ice cores). This must be a minimum figure due to the current lack of formal documentation of the occurrence of ash deposition on glaciers.

• Presentation Conference Type: Poster
• Conference Name: Volcanic and Magmatic Studies Group Conference
• Start Date: Jan 5, 2011
• End Date: Jan 7, 2011
• Acceptance Date: Nov 26, 2010
• Publication Date: Jan 7, 2011
• Peer Reviewed: Peer Reviewed
• Keywords: volcanic ash fall, Earth's glaciers
• Public URL: https://uwe-repository.worktribe.com/output/966101
• Publisher URL: https://www.vmsg.org.uk/events/abstracts/2011_cambridge.pdf
• Additional Information: Title of Conference or Conference Proceedings : Volcanic and Magmatic Studies Group Conference 2011