Erosion and sedimentation in Surtsey island quantified from new DEMs

We present data from a photogrammetric study on Surtsey island that generated three new DEMs andorthoimages, two from scanned aerial images from 1967 and 1974 and one from high-resolution closerange images from a survey in 2019. DEM differencing allowed for quantification of the erosion and thesedimentation in the island since 1967. Of the subaerial volcanics, about 45% of the lava fields have erodedaway but only about 16% of the tuff cones. The prevailing SW coastal wave erosion is evident from theerosive pattern in Surtsey, and the cumulative loss of the coastal margins amounts to 28±0.9x106 m3 since1967, with the current average erosion rate of 0.4±0.02x106 m3/yr. Wind deflation and runoff erode the tuffcones and the sediments at the flanks of the cones, with the total volume loss amounting to 1.6±0.2x106 m3and the current erosion rate of 0.03±0.004x106 m3/yr. A rapid decline in erosion rates characterized the firstyears post-eruption, and the coastal erosion rate during the winter of 1967–68 was about 5–6 times higherthan the current erosion rate due to the thinner and less cohesive nature of the lava apron at the edge of theshelf. The cones eroded at a rate about 2–3 times higher during the first years due to the uncompacted andunconsolidated nature of the cones at that time. The 2019 area of 1.2 km2 and an extrapolation of the currenterosion rate fits well with the projected erosion curve of Jakobsson et al. (2000) with the island becoming atuff crag after approximately 100 years.