The AD 1362 Öræfajökull eruption, S.E. Iceland: Physical volcanology and volatile release

• Published in: Journal of Volcanology and Geothermal Research
• Main Authors: Sharma, Kirti, Self, Stephen, Blake, Stephen, Thordarson, Thorvaldur, Larsen, Gudrun
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: 2008
• Subjects: Greenland; Greenland ice core; ice core; Iceland
• Online Access: https://oro.open.ac.uk/12911/; https://doi.org/10.1016/j.jvolgeores.2008.08.003

The explosive rhyolitic eruption of Öræfajökull volcano, Iceland, in AD 1362 is described and interpreted based on the sequence of pyroclastic fall and flow deposits at 10 proximal locations around the south side of the volcano. Öræfajökull is an ice-clad stratovolcano in south central Iceland which has an ice-filled caldera (4–5 km diameter) of uncertain origin. The main phase of the eruption took place over a few days in June and proceeded in three main phases that produced widely dispersed fallout deposits and a pyroclastic flow deposit. An initial phase of phreatomagmatic eruptive activity produced a volumetrically minor, coarse ash fall deposit (unit A) with a bi-lobate dispersal. This was followed by a second phreatomagmatic, possibly phreatoplinian, phase that deposited more fine ash beds (unit B), dispersed to the SSE. Phases A and B were followed by an intense, climactic Plinian phase that lasted 8–12 h and produced unit C, a coarse-lapilli, pumice-clast-dominated fall deposit in the proximal region. At the end of Plinian activity, pyroclastic flows formed a poorly-sorted deposit, unit D, presently of very limited thickness and exposed distribution. Much of Eastern Iceland is covered with a very fine distal ash layer, dispersed to the NE. This was probably deposited from an umbrella cloud and is the distal representation of the Plinian fallout. A total bulk fall deposit volume of 2.3 km3 is calculated ( 1.2 km3 DRE). Pyroclastic flow deposit volumes have been crudely estimated to be < 0.1 km3. Maximum clast size data interpreted by 1-D models suggests an eruption column 30 km high and mass discharge rates of 108 kg s− 1. Ash fall may have taken place from heights around 15 km, above the local tropopause ( 10 km), with coarser clasts dispersed below that under a different wind regime. Analyses of glass inclusions and matrix glasses suggest that the syn-eruptive SO2 release was only 1 Mt. This result is supported by published Greenland ice-core acidity peak data that also suggest very minor sulphate ...