Airborne measurements of SO2 of the Fagradalsfjall eruption in Iceland with remote sensing

The eruption begun after an intensive earthquake activity in the volcanic system of Reykjanes that opened up several kilometer long underground dike crossing the plate boundary of Reykjanes at an angle of around 22°. Quakes of varying intensity caused material damage in the township of Grindavik, the major population center in the neighborhood. The eruption came on March 20th, with put any clear warning, a magma eruption without much ash formation but when reaching the surface, the magma released gasses in a magnitude similar to other volcanic eruption of this type, e.g., Holuhraun (magma from Bardarbunga) 2014 and Surtsey 1963 - 1967. A characteristic SO2 emission in this eruption was measured 6kg/sec of SO2 from each m3 of magma or 2 o/ o o. This is similar to what was observed in the Holuhraun airborne observation campaign and corresponds very well to the estimates for Surtsey. The composition of the volcanic gas is similar too, the main constituent is water, often 90 - 55% of the total gas flow. The magma is 1200 - 1300 °C hot and comes from a very deep source about 20 km down. The possibility exists that the eruption goes on for a long time, widens the conduit and increases in output. An airborne measurement campaign was conducted in a light airplane, TF-VTR, by Dr. Gylfi Arnason, Reykjavik University (RU) with a mobile remote sensing DOAS instrumentation specially adapted for use in this airplane from the Duesseldorf University of Applied Sciences (HSD), Germany. This observation technology has been used with good results during volcanic events in Europe, Japan and America. Four sorties were carried out, measuring the column load of SO2 by flying under the plume in several traverses, each giving about 20 measurements of the SO2 column load. The results are compared to other measurement results from IMO (Icelandic Meteorological Institute) and UI (University of Iceland) and results from previous campaigns 2014 and 1963 - 67 and found similar. In the beginning the eruption output was steady at 5 m3/sec but was increasing in output magnitude and pulsating, making gas flux estimations more difficult. A steady plume in a steady wind follows the dispersion model developed by the authors, but the pulsating plume creates large puffs with high gas concentrations and increased hazards for nearby populations centers. Gas accumulation in a large clouds during calm weather, observed during the 2014 Holuhraun event, does also happen here and increases the risk of serious pollution events. This seriously hampers the possibility of using modeling results only to estimate gas pollution risks, and stresses the need for monitoring the gas flow by airborne measurements of the propagation of the plumes, puffs and accumulated clouds that may threaten the neighborhood.