HR: 15:40h
AN: A43D-11 INVITED     [Abstracts]
TI: Sulphur Release from Holocene Basalt Eruptions in the East Volcanic Zone, Iceland
AU: * Thordarson, T
EM: thor.thordarson@ed.ac.uk
AF: School of Geosciences, The University of Edinburgh, Grant Institute, The Kings Buildings, West Mains Road, Edinburgh, EH9 3JW, United Kingdom
AB: SO₂ emissions by basaltic eruptions are significant contributors of atmospheric sulfur because of high initial sulfur contents in basaltic magmas. The Eastern Volcanic Zone (EVZ) is a young (<3 m.y. old) and developing rift zone in south central Iceland, characterized by basaltic volcanism. It is the most productive of the currently active volcanic zones, with >205 km³ of basaltic magma erupted in the Holocene. Subaerial fissure eruptions account for 130 km³ (63%) of the magma volume and ~80 km³ was expelled in subglacial eruptions at the Katla, Grimsvotn and Bardarbunga volcanoes. Fourteen flood lava eruptions account for about 87 km³ (44%) of the total magma volume or 74% of the subaerial production. The three largest Holocene flood lava eruptions in Iceland, the 1783-84 Laki (15 km³), 934-40 Eldgja (20 km³), and ~8500 BP Thjorsa (22 km³) events, all occurred within the EVZ. The magnitude of these three events is underpinned by the volume of magma expelled, which is about 28% of the Holocene magma output. Flood lava eruptions are prolonged eruptions (months to years) characterized by recurring eruption episodes. Each episode begins with a short-lived explosive subplinian phase, supporting >10 km high eruption columns, followed by a longer lasting lava effusion phase. The bulk of the sulphur is vented into the atmosphere by the explosive phases and therefore prolonged flood lava eruptions can maintain elevated H₂SO₄ aerosols loading for periods of months to years. Petrologic estimates indicates that the fourteen EVZ flood lava eruptions emitted ~700 megatons (Mt) SO₂ into the atmosphere in four 600- to 850-year-long eruption periods occurring at 8-9 ka, 6-7ka, 3-4 ka and 0.2-1.1ka BP. Between 98 and 328 Mt SO₂ were emitted in each eruption period, with 5 to 210 Mt SO₂ mass loading by individual eruptions. Consequently, and analogous to the 1783-84 Laki eruption, the effects of these eruptions may have been felt on a hemispheric scale for several years. Over the last 9000 years basaltic eruptions within the EVZ have released ~1500 Mt of SO₂ into the atmosphere, which on an annual basis equates ~10% of the current global volcanic sulfur flux. About 30% of this sulfur mass is background emissions because it was produced by small explosive subglacial eruptions that have occurred at a steady rate of 10-15 eruptions/century throughout the Holocene. The rest of this sulfur mass was released periodically by subaerial fissure eruptions, including the contribution from the EVZ flood lava events. This is, however, a minimum estimate for the total Holocene SO₂ emissions by EVZ volcanism because (1) the volume figures given here for the erupted magma volumes are conservative estimates, (2) it ignores the possible SO₂ contribution by degassing of unerupted magma, and (3) does not take into account the contributions from the intermediate (andesite) and silicic (dacite to rhyolite) eruptions to the sulfur emissions, which make up >15% of the erupted Holocene magma volume in the EVZ.
DE: 0370 Volcanic effects (8409)
DE: 1605 Abrupt/rapid climate change (4901, 8408)
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 3362 Stratosphere/troposphere interactions
DE: 8408 Volcano/climate interactions (1605, 3309)
SC: Atmospheric Sciences [A]
MN: 2007 Joint Assembly