142 publications from this institution
The influence of tsunamis on the submarine environment was virtually unknown before the 2004 Indian Ocean Tsunami, which hit the coastlines of many countries around the Indian Ocean, and the 2011 Tōhoku Tsunami, which mainly hit coastlines of Japan. When triggered by a tsunami, sediment can be redeposited over wide areas onshore, but especially offshore. Recent advances in seafloor mapping considerably improved the identification of offshore areas that were influenced by a tsunami and helped to find suitable locations for sampling and investigating recent and ancient subaquatic tsunami deposits. Tsunami-influenced deposits are observed from shallow marine environments to water depths below 1000m. The application of a range of proxy methods to analyze sediment-surface samples and sediment cores in different case studies worldwide showed that tsunami deposits can be identified and distinguished from storm-generated and flash flood deposits in subaquatic sediment cores. One particular conclusion from this research is, that the preservation potential of tsunami deposits increases with water depth.
Tunnel valleys are assumed to form near the margin of ice sheets. Hence, they can be used to reconstruct the dynamics of former ice margins. The detailed formation and infill of tunnel valleys, however, are still not well understood. Here, we present a dense grid of high‐resolution 2D multi‐channel reflection seismic data from the German sector of the southeastern North Sea imaging tunnel valleys in very great detail. Three tunnel valley systems were traced over distances ranging between 11 and 21 km. All tunnel valleys are completely filled and buried. They differ in incision depth, incision width and number of incisions. The tunnel valleys cut 130–380 m deep into Neogene, Palaeogene and Cretaceous sediments; they show a lower V‐shaped and an upper U‐shaped morphology. For individual tunnel valleys, the overall incision direction ranges from east–west to northeast–southwest. Two tunnel valleys intersect at an oblique angle without reuse of the thalweg. These valleys incise into a pre‐existing glaciotectonic complex consisting of thrust sheets in the northwest of the study area. The analysis of the glaciotectonic complex and the tunnel valleys leads us to assume that we identified several marginal positions of (pre‐)Elsterian ice lobes in the southeastern North Sea.
Marine sand and gravel resources receive an increasing interest, leading to greater quantities of dredged material. Nevertheless, knowledge concerning negative impacts on adjacent coastal sediment transport systems and the duration necessary for the physical regeneration of extraction sites is scarce. Here we assess time scales of regeneration of three extraction sites situated in the Baltic Sea by investigating sonographic data sets covering several years. We incorporate data from other extraction sites and compare the results by applying a shore-normal zonation of the shoreface. Hence, limiting depths of the upper and lower shorefaces are calculated from wave statistics. From our comparisons we conclude that the time scales of regeneration are most profoundly determined by the position of the extraction site relative to the seaward limit of the shoreface. Locating extraction sites well beyond this limit therefore implies a slow regeneration. In contrast, material extractions on the upper shoreface may exhibit a fast regeneration, but negative impacts on the coastal sediment budget cannot be excluded. Additional factors controlling the velocity of regeneration are the depth of the extraction as well as the character and availability of the potential material for regeneration. As a consequence, there is no ideal location for marine sediment extraction. The appropriate place should be a well-balanced compromise allowing fast regeneration together with a minimised impact on the coastal sediment budget.
No abstract is provided for this article.
Southeast Asian deltas are highly threatened areas for flooding as a response to the combined effects of natural compaction and subsidence exacerbated by human impacts, e.g. oil, gas and water extraction, retention of sediment discharge due to river damming and sand mining, land use changes, sea-level rise and storm-induced water-level setup. Tide-induced water-level fluctuations on different time- and spatial scales, seasonal variations of freshwater runoff and sea-level setup can amplify the impact of sea-level rise and of storm surges on the coastal environment and its inhabitants. Moreover, increasing populations accompanied by growing societal demands can lead to further pressure on delta areas. For the Vietnamese Mekong Delta (VMD) and the Saigon-Dong Nai River (SGDNR), rates of subsidence of several cm/yr have already been determined, but for the coastal area, which is most vulnerable to sea-level rise and storm surges, a lack of detailed spatial and temporal information of this parameter exists. To assess the influence of tide- and water-level fluctuations, records from 11 stations, from the tectonically stable position Vung Tau north of the SGDNR entry to Ganh Hao in the southern VMD, were analyzed. The results reveal a relative sea-level rise at Vung Tau reaching 2.2 ± 0.3 mm/yr for the period from 1987 to 2015, while along the VMD those rates show a spatially variation from 5.6 ± 0.3 mm/yr at Ben Trai to 13.5 ± 0.7 mm/yr at My Thanh. Considering Vung Tau as tectonically stable, these numbers indicate subsidence rates of the coastal sections along the VMD ranging from 3.4 ± 0.3 mm/yr to 11.3 ± 0.7 mm/yr. It is likely that the rates of subsidence along the coast of VMD have accelerated since 2005. They are not only up to 4 times higher than the mean sea-level rise but are variable along the whole SGDNR estuary and the VMD East Sea coastline. Additionally, the importance of daily, fortnightly and seasonal water level fluctuations due to tides and atmospheric influence, which are acting on top of the long-term relative sea-level rise, is shown. Especially the identified regional variations make these data valuable for setting regional priorities for protection strategies to mitigate riverine and marine flooding, especially when both coincide.
No abstract is provided for this article.
