The eruptions of Oraefajokull 1362 (Iceland) and Lanzarote 1730-36 (Canary Islands) : sulphur emissions and volcanology

This thesis presents new data on the volcanology, erupted volumes, and sulphur emissions of the AD 1362 Orӕfajokull eruption and the AD 1730-36 Lanzarote eruption, and relates these findings to their atmospheric and environmental impacts. The Orӕfajokull eruption was an explosive Plinian event with high eruption columns (~30 Ian) that produced an extensive tephra-fall and a small pyroclastic flow deposit (~2 km3 total volume). In contrast, the Lanzarote eruption was a long-lasting basaltic fissure eruption involving Hawaiian and Strombolian fire fountain activity (eruption plumes 8-16 km high) generating a scoria fall deposit and lava flows (~5 km3 total volume). Chapter 1 introduces the effects of volcanic gas release, and highlights the importance of SO2. In chapter 2, I provide a critical assessment of the petrologic method used to estimate the sulphur release from a volcanic eruption. The petrologic method uses the difference in sulphur concentrations between melt inclusions and matrix glasses, measured by electron microprobe, scaled to the mass of erupted magma, and corrected for the magma crystal content. I show that it provides estimates for sulphur degassing from non-arc, basaltic, reduced magmas that are similar to independent satellite measurements (TOMS). Using this technique, the AD 1362 Orӕfajokulll eruption is estimated to have released only ~0.6 Mt of SO2 into the stratosphere - supported by lack of an ice core acidity peak. The major environmental hazard resulting from this eruption was large volumes of pumice and ash injected into the upper atmosphere and its subsequent fallout over a wide area (chapter 3). The Lanzarote eruption released at least 45 Mt of SO2. This was determined using a new technique based on the correlation between S and incompatible element (K, P, Ti) ratios (S/I); knowing this ratio the original S content of a degassed liquid can be calculated from its concentration of I. The release of SO2 from the Lanzarote eruption is shown to have caused significant climatic perturbations - as demonstrated in the climate proxy record (chapter 4).