Laki

The Volcano:

The Lakagígar crater row, along which the AD 1783 Laki eruption took place, is located within the Grímsvötn volcanic system in the Eastern Volcanic Zone (EVZ) of Iceland between the glaciers of Mýrdalsjökull and Vatnajökull, in an area of fissures which run in a south-west to north-east direction. The name Laki actually corresponds to a mountain which sits in the middle of the crater row. The EVZ is the most magmatically productive of the neovolcanic zones in Iceland, accounting for 79% of the magma volume erupted in Iceland in historic time (Thordarson & Larsen, 2007) and has been active for at least 2-3 Ma (Sæmundsson, 1974). GPS studies indicate that spreading rates along the EVZ are variable, with faster spreading in the north than in the south (e.g. La Femina et al., 2005), where the rift is propagating southwestwards under the Vestmannæyjar (Steinthorsson et al., 1985). Laki is located in the faster spreading northern portion of the EVZ where tholeiites are erupted. Alkali basalts are erupted in the slower spreading southern portion (Jakobsson, 1979). Notably, volcanism in the EVZ is characterised by large fissure eruptions. The ~19.1 km³ AD 934-938 Eldgjá eruption in the Katla system, and the 15.1 km³AD 1783-1784 Laki eruption (Thordarson & Larsen, 2007) are the largest volume fissure eruptions which have been directly observed in historical time.

Thordarson & Self (1993) provide a detailed description of the physical volcanology and timeline of the Laki eruption, known locally as the Skaftáreldar (Skaftár Fires). The eruption took place over approximately 8 months from June 1783 to February 1784 as part of a 2 year long volcano-tectonic episode in the Grímsvötn volcanic system. The eruption occurred on a 27 km long series of 10 en echelon fissures which opened in a step-wise fashion from southwest to northeast. Opening of each fissure is considered as a distinct phase of eruption. Each phase was characterised by a short period of high fire fountaining, which gave way to lower fountaining and finally lava effusion. Fissures I-V opened to the southwest of Laki Mountain, from which the eruption gets its name, and fissures VI-X to the northeast. During phases I-V lava was channelled from its source in the highlands down the Skaftá river gorge onto the Siða coastal plain (Fig. 1). During phases VI-X lava was largely channelled down the Hverfisfljót river gorge. The lava eventually covered an area of ~600 km². Detailed studies of shallow degassing and lava flow emplacement have been undertaken by Thordarson et al. (1996) and Guilbaud et al. (2007).

The eruption is of particular importance becasue of the 122 Mt of SO₂ emitted during the eruption which is thoguht to have had severe effects of the climate on local to hemispheric scales resulting in cooling in the northern hemisphere of 1.3°C (Thordarson & Self, 2003). Emissions of HF and SO₂ also lead to the the death of over 50% of Iceland’s livestock population, leading to famine which killed approximately 25% of the population.

CVG Research on Laki:

• Neave, D. A., Passmore, E., Maclennan, J., Fitton, G. & Thordarson, T. (2013). Crystal-Melt Relationships and the Record of Deep Mixing and Crystallization in the AD 1783 Laki Eruption, Iceland. Journal of Petrology, doi:10.1093/petrology/egt027.
• Passmore, E., Maclennan, J., Fitton, G. & Thordarson, T. (2012). Mush disaggregation in basaltic magma chambers: Evidence from the AD 1783 Laki Eruption. Journal of Petrology, doi:10.1093/petrology/egs061.

Key References on Laki:

• Bindeman, I.N., Sigmarsson, O. & Eiler, J. (2006). Time constraints on the origin of large volume basalts derived from O-isotope and trace element mineral zoning and U-series disequilibria in the Laki and Grímsvötn volcanic system. Earth and Planetary Science Letters 245, 245-259.
• Guilbaud, M.-N., Blake, S., Thordarson, T. & Self, S. (2007). Role of Syn-eruptive Cooling and Degassing on Textures of Lavas from the AD 1783-1784 Laki Eruption, South Iceland. Journal of Petrology 48, 1265-1294.
• Sigmarsson, O., Condomines, M., Grönvold, K & Thordarson, T. (1991). Extreme magma homogeneity in the 1783-84 Lakagigar eruption: origin of a large volume of evolved basalt in Iceland. Geophysical Research Letters 18, 2229-2232.
• Thordarson, T. & Self, S. (1993). The Laki (Skaftár Fires) and Grímsvötn eruptions in 1783-1785. Bulletin of Volcanology 55, 233-263.
• Thordarson, T., Self, S., Oskarsson, N. & Hulsebosch, T. (1996). Sulfur, chlorine, and fluorine degassing and atmospheric loading by the 1783-1784 AD Laki (Skaftár Fires) eruption in Iceland. Bulletin of Volcanology 58, 205-225.
• Thordarson, T. & Self, S. (2003). Atmospheric and environmental effects of the 1783-1784 Laki eruption: a review and reassessment. Journal of Geophysical Research 108, D1.
• Thordarson, T. & Larsen, G. (2007). Volcanism in Iceland in historical time: Volcano types, eruption styles and eruptive history. Journal of Geodynamics 43,118-152.

CVG expert:
John Maclennan
Margaret Hartley
David Neave
Clive Oppenheimer
Marie Edmonds