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Emissions of SO2 by volcanic eruptions have been shown to be important for short-term environmental and climate changes. Stratospheric sulphur mass-loading by explosive silicic eruption is commonly considered to be the principal forcing factor for these changes. The SO2 emissions from basaltic flood lava eruptions have not featured strongly in the discussions on volcano-climate interactions, notwithstanding the fact that basaltic magma is typically richer in sulphur (by a factor of two to four), than silicic magmas, as well as the evidence of widespread atmospheric impact associated with historical flood lava eruption.

Fourteen Holocene flood lava eruptions are known from the Veidivötn, Grimsvötn, and Katla volcanic systems of the Eastern Volcanic Zone in South Iceland, which include the three largest of its kind in Iceland; the 1783-1784 Laki, 934-40 Eldgjá, and c.8600 years bp Thjórsá events. We present new data on the sulphur content in melt inclusions from the Veidivotn system and use this information, along with existing inclusion data from the Grímsvötn and Katla volcanic systems, to establish an empirical method for estimating the sulphur mass release from these basaltic flood lava eruptions. The results show that these eruptions released a total of c.700 Mt SO2 into the atmosphere in four 600- to 850-year-long eruption periods. During each period, between 98 and 328 Mt SO2 were emitted into the atmosphere, and the mass loadings from individual eruptions ranged from 5 to 210 Mt SO2. These flood lava eruptions are likely to have resulted in widespread atmospheric perturbations and, by analogy with the 1783-1784 Laki eruption, the effects of the largest eruptions may have been felt on a hemispheric scale.

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