Erosion and Sedimentation on the Island of Surtsey
In this paper Birgir Vilhelm Óskarsson and his co-authors present data from a photogrammetric study, which uses aerial photography to survey and map the surface of Surtsey. It examines the rates of erosion and sedimentation on the island since eruptions terminated in 1967. The study generated three new DEMs (Digital Elevation Model), which include two scanned aerial photography images from 1967 and 1974 and a third composed of high-resolution close-range images from a 2019 survey. The 2019 survey flights can be viewed at https://www.ni.is/en/research/monitoring-and-research/surtsey/surtsey-3d . The study revised the estimated total volumes of the volcanic lithologies on the surface of Surtsey. It shows that the initial volume of the subaerial lava flows has decreased from 70 × 10 6 m 3 to 58 × 10 6 m 3 over the past 52 years. It also quantifies volumes and rates of erosion and sedimentation.
Looking at the volume differences between the DEM models, differences in elevation between the two time frames can be determined. The 1967 – 1974 DEM shows that the southern lava fields underwent extensive erosion. The northwestern areas of the tephra and tuff cones also showed erosion on their inner flanks, sediment accumulation at their bases, and mass wasting in their upper rims and northern flanks. The DEM model shows that the southeastern boulder terrace underwent sedimentation, only to be completely eroded away in 1968. It verified that a negative area inside the Surtur tuff cone was caused by the collapse of a small intra-crater scoria cone, whose remains can still be seen within the larger Surtur structure. The 1967 – 2019 DEM shows some similar features, such as the extensive erosion of the southern lava fields and the continued recession and migration of the northern sediment spit. It also reveals advanced erosion and sedimentation in certain areas: pronounced erosion on the eastern side and sediment accumulation on the cones’ eastern and northern flanks as well as within craters.
Images of the models showing erosion features in Surtsey from the Iceland Institute of Natural History monitoring and research study (https://www.ni.is/en/research/monitoring-and-research/surtsey). A) The NW side of Surtsey shows erosion scars in the Surtungur tuff cone. Field of view is about 800 m. B) The SW side of Surtsey shows sea caves forming in the tuff cone and at the contact between the tuff cone and the lava flows. Field of view is about 600 m.
Elevation differences from the 1967–1974 and 1974–2019 DEMs show the main geomorphic changes in Surtsey since the end of the eruption in 1967. The colors give the values in meters of material eroded (red) or deposited (blue). The thickness in meters for selected locations (crosses) is shown for reference. Stippled lines show the areal change since 1967 and arrows the respective years between them (Óskarsson et al. 2020).
The surface of Surtsey has undergone rapid erosion of uncompacted and unconsolidated tephra by wind and runoff erosion along with mass wasting. Erosion rates were high in the early post-eruption years but the rates decreased over time. Estimates from these erosion rates and other studies predict that in about 100 years Surtsey will become a crag of basaltic tuff similar to the other crags within the Vestmannaeyjar archipelago of volcanic islands.
Citation
Óskarsson, B.V., Jónasson, K., Valsson, G., and Belart, J. M. C., 2020, Erosion and sedimentation in Surtsey island quantified from new DEMs: Surtsey Research, v. 14, p. 63–77, doi:10.33112/surtsey.14.5.
