Permafrost aggradation caused by tephra accumulation over snow-covered surfaces: Examples from the Hekla-2000 eruption in Iceland

Abstract

The relationship between explosive volcanic eruptions and permafrost aggradation is discussed at a regional (Hekla volcano, Iceland, 63°59′N 19°40′W) and a global scale. During the most recent Hekla eruption in winter 2000, tephra buried the adjacent winter snow cover. Observations of denivation landforms, excavated sections and active-layer thickness were carried out 15 to 77 months after the eruption. Results show that the combination of climate that favours permafrost and a thin layer of tephra is sufficient to reduce the sub-tephra snow ablation substantially, possibly even to zero, causing aggradation of the surface and preserving massive ground ice and permafrost. Based on these observations, a conceptual model for permafrost aggradation related to tephra accumulation was developed. On a global scale, about one third of all active volcanoes seems to be located in permafrost-favourable areas, suggesting that explosive volcanic eruptions may be significant for permafrost aggradation. Copyright © 2007 John Wiley & Sons, Ltd.