The explosive, basaltic Katla eruption in 1918, south Iceland II. Isopach map, ice cap deposition of tephra and layer volume

Due to poor preservation and lack of proximal tephra thickness data, no comprehensive isopach map has existed for the layer from major eruption Katla volcano in 1918. We present such a obtained by combining existing data on 1918 soil profiles with newly acquired 590 km2 My?rdalsjökull ice cap which covers caldera its outer slopes. A 20–30 m surface vents is inferred photos taken 1919. The greatest thicknesses presently observed, 30–35 cm, occur where outcrops lowermost parts ablation areas Kötlujökull Sólheimajökull outlet glaciers. fallout location within exposed both glaciers, as estimates balance velocities imply lateral transport since ~15 km Kötlujökull, ~11 about 2 Sléttjökull. Calculations thinning during this indicate that layers were respectively over 1.2 thick they fell while insignificant broad northern lobe K1918 an estimated volume 0.95+/-0.25 km3 (corresponding 1.15+/-0.30x10**12 kg) whereof 50% My?rdalsjökull. About 90% land 10% sea south southeast volcano. estimate contains only part total erupted it excludes water-transported pyroclasts any material may have been left glacier bed at vents. While three main dispersal axes can be defined (N, NE SE), distribution complex shape reflecting period variable wind directions intensity. In terms airborne tephra, largest explosive Iceland silicic Askja 1875.