By David Neave, Leibniz Universität Hannover
The 1783–1784 Laki Fires in southern Iceland were one of the largest and most destructive basaltic eruptions to have been witnessed first-hand. The eruption generated about 15 km3 of near-homogenous lava, blanketed Iceland and much of the North Atlantic region in a toxic haze and is implicated in the death of least a quarter Iceland’s population by famines. The eruption also took place over a period of eight months, orders of magnitude longer than most explosive eruptions. The length of fissure eruptions like the Laki Fires thus prompts questions about magma reservoir dynamics: was the magma assembled in a single event immediately before eruption or in a step-wise manner over many months?
By analysing the textures of rock samples collected throughout the eruption we found that the crystal proposals and crystal size distributions show that the efficiency of crystal entrainment varied greatly during the eruption. We also estimated that crystal residence times in the erupted melt were much shorter than the total eight-month duration of the eruption. The erupted magma was thus assembled incrementally, which has important implications understanding and monitoring the long-term behaviour of plumbing systems feeding basaltic fissure eruptions.
David Neave is a postdoc at the Leibniz Universität Hannover, Germany. His current research into magma mixing is funded by the German Research Foundation (DFG). He is primarily interested in combining observations from natural and experimental systems to understand how basaltic magmas are assembled and stored in the crust. You can read more about Laki here: https://doi.org/10.2138/am-2017-6015CCBY