The Veiðivötn 1477 CE basaltic Plinian eruption: retrieving source parameters through field work and 1D physical plume modelling

Abstract In this study, we investigate the dynamics of the Veiðivötn 1477 CE (V1477) Plinian eruption in Iceland, which produced a bulk volume of ~ 10.8 km 3 of basaltic tephra dispersed over half of Iceland (~ 53,000 km 2 ), reaching at least as far as Greenland and Scandinavia. Despite available data on total tephra volume, dispersion and petrology, the exact eruption source parameters remain poorly understood. We present the results of a new field study on the V1477 including deposit dispersal, thickness, and pumice texture, size and density. Calculations from field data give a total dense rock equivalent volume of 4.3 ± 0.2 km 3 , a plume height of ~ 30 km. Injecting our field-based data in a 1D physical plume model allows us to estimate a MER of 2.6 (± 1.3) × 10 8 kg/s, and a minimum volatile content of 2 wt.% to maintain the stable plume. However, petrological measurements show that the Veiðivötn fissure swarm basaltic magmas commonly contain insufficient volatile to drive such column height. This discrepancy can be explained by our observations which argue in favour of a dry magmatic fragmentation feeding a high momentum jet rising through external shallow water, followed by (i) steam enrichment of the plume, enhancing plume height, and (ii) passive secondary fragmentation of the larger clasts into ash by cooling induced by the interaction of the jet edges with external shallow water. Based on our field-based reconstruction, the V1477 eruption is estimated at VEI 5-6, corresponding to a Plinian to phreato/ultra-Plinian event.