New estimates of sulfur degassing and atmospheric mass-loading by the 934 AD Eldgjá eruption, Iceland

Abstract

The 934 AD Eldgjá basaltic flood lava eruption in southern Iceland is the largest on Earth in the last millennium. The Eldgjá fissures produced 19.6km3 of transitional basalt in a prolonged eruption that featured at least eight distinct episodes and may have lasted for 3–8 years. The atmospheric SO2 mass loading by Eldgjá is determined by new measurements of pre-eruption and residual sulfur contents in the products from all phases of the eruption. A pre-eruption sulfur content of ∼2150ppm indicates that the magma carried 232Mt of SO2 to the surface, where vent and lava flow degassing released 219Mt into the atmosphere. This value corresponds to a potential H2SO4-aerosol yield of ∼450Mt, increasing previous H2SO4-aerosol mass estimates by a factor of 2.6–4.5. Approximately 79% of the original sulfur mass was released at the vents, indicating ∼185Mt SO2 were discharged into the atmosphere above the Eldgjá fissures and carried aloft by the eruption columns to upper tropospheric and lower stratospheric altitudes (∼15km). Consequently, only ∼35Mt SO2 escaped from the lava into the lower troposphere. These estimates of the SO2 mass loading from Eldgjá make it the greatest known volcanic pollutant of recent history, exceeding that of 1783 AD Laki and 1815 AD Tambora eruptions by factors of 1.8 and 2.0–2.8, respectively. However, the intensity of climatic effects deduced by the Eldgjá event are not thought to have surpassed that of Laki or Tambora because the eruption was prolonged and subsequently the sulfur emissions were drawn out over several years. The lack of detailed historic records for this period make estimates of the effects of long term but significant release of SO2 (30–70Mt/yr) on the atmosphere uncertain.