Volcano-ice interactions at Prestahnúkur, Iceland: Rhyolite eruption during the last interglacial-glacial transition

• Published in: Annals of Glaciology
• Main Authors: McGarvie, D. W., Stevenson, J. A., Burgess, R., Tuffen, H., Tindle, A. G.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2007
• Subjects: Prestahnúkur; Annals of Glaciology; Ice Sheet; Iceland
• Online Access: https://research.manchester.ac.uk/en/publications/3a2b7f22-7d06-418d-a919-f95357c4dedf; https://doi.org/10.3189/172756407782282453

Prestahnúkur is a 570 m high rhyolite glaciovolcanic edifice in Iceland's Western Rift Zone with a volume of 0.6 km3. Uniform whole rock, mineral and glass compositions suggest that Prestahnúkur was constructed during the eruption of one magma batch. Ar-Ar dating gives an age of 89 ± 24 ka, which implies eruption during the transition (Oxygen Isotope substages 5d to 5a) between the Eemian interglacial and the Weichselian glacial period. Prestahnúkur is unique among published accounts of rhyolite tuyas because a base of magmatically-fragmented tephra appears to be absent. Instead, basal exposures consist of glassy lava lobes and coarse hyaloclastite, above which are single and multiple lava sheets with matrix-supported basal breccias and hyaloclastite upper carapaces. Steepening ramp structures at sheet termini are interpreted as ice-contact features. Interactions between erupting magma and water/ice have affected all lithologies. A preliminary model for the construction of Prestahnúkur involves an effusive subglacial eruption between 2-19 years duration which never became emergent, into an ice sheet over 700 m thick. If 700 m of ice had built up during this interglacial-glacial transition, this would corroborate models arguing for the swift accumulation of land-based ice in rapid response to global cooling.