[论文解读] Was Doggerland catastrophically flooded by the Mesolithic Storegga tsunami?

Jon Hill, Alexandros Avdis+3 more|White Rose Research Online (University of Leeds, The University of Sheffield, University of York)|Jul 18, 2017

Geology and Paleoclimatology Research被引用 4

一句话总结

本研究利用高分辨率数值海啸模型，评估了中石器时代Storegga海底滑坡是否引发了灾难性洪水，导致Doggerland被遗弃。结果表明，海啸可能仅造成中等程度的淹没——最大越岸高度达9米，洪水面积达2,000平方公里，与极端风暴潮相当，暗示海平面上升而非海啸才是Doggerland沉没及人类迁徙的主要原因。

ABSTRACT

Myths and legends across the world contain many stories of deluges and floods. Some of these have been attributed to tsunami events. Doggerland in the southern North Sea is a submerged landscape thought to have been heavily affected by a tsunami such that it was abandoned by Mesolithic human populations at the time of the event. The tsunami was generated by the Storegga submarine landslide off the Norwegian coast which failed around 8150 years ago. At this time there were also rapid changes in sea level associated with deglaciation of the Laurentide ice sheet and drainage of its large proglacial lakes, with the largest sea level jumps occurring just prior to the Storegga event. The tsunami affected a large area of the North Atlantic leaving sedimentary deposits across the region, from Greenland, through the Faroes, the UK, Norway and Denmark. From these sediments, run-up heights of up to 20 metres have been estimated in the Shetland Isles and several metres on mainland Scotland. However, sediments are not preserved everywhere and so reconstructing how the tsunami propagated across the North Atlantic before inundating the landscape must be performed using numerical models. These models can also be used to recreate the tsunami interactions with now submerged landscapes, such as Doggerland. Here, the Storegga submarine slide is simulated, generating a tsunami which is then propagated across the North Atlantic and used to reconstruct the inundation on the Shetlands, Moray Firth and Doggerland. The uncertainty in reconstructing palaeobathymetry and the Storegga slide itself results in lower inundation levels than the sediment deposits suggest. Despite these uncertainties, these results suggest Doggerland was not as severely affected as previous studies implied. It is suggested therefore that the abandonment of Doggerland was primarily caused by rapid sea level rise prior to the tsunami event.

研究动机与目标

• 评估Storegga海啸是否引发了南北海地区被淹没的中石器时代景观Doggerland的灾难性洪水。
• 通过整合古海深地形与沉积物证据与数值模拟，解决关于海啸规模及其对DoggerLand影响的相互矛盾的解释。
• 确定海啸是否为人类遗弃的主要驱动因素，或先前存在的快速海平面上升是否为占主导地位的因素。
• 通过将模型输出与设得兰群岛和莫里湾的沉积物进行比较，改进古淹没范围的重建。
• 评估由于古海深地形与滑坡源参数不确定性导致的当前模型局限性。

提出的方法

• 使用有限体积、深度平均的浅水模型模拟Storegga海底滑坡，以生成海啸波。
• 采用具有自适应网格加密的二维水动力模型，以解析复杂海岸动力学及在淹没地形上的淹没过程。
• 整合末次冰盛期后冰川融化与前冰川湖排水引起的相对海平面变化，以改善古环境背景。
• 利用设得兰群岛和莫里湾的沉积物作为约束条件，验证模型结果，将模拟的淹没范围与实际沉积物分布进行对比。
• 通过测试不同的滑坡源几何形态与海深重建方案，限制模型的不确定性。
• 通过计算越岸高度与洪水面积评估海啸对Doggerland的影响，并与风暴潮规模进行对比以提供背景参照。

实验结果

研究问题

• RQ1 根据某些考古学与地质学解释，Storegga海啸在多大程度上导致了Doggerland的灾难性洪水？
• RQ2 古海深地形与滑坡源参数的不确定性在多大程度上影响了模型对Doggerland海啸淹没范围的模拟结果？
• RQ3 设得兰群岛与莫里湾的沉积物是否与模拟的海啸越岸高度和淹没模式一致？
• RQ4 Doggerland的海啸波高是否足以造成广泛的人类迁徙，还是仅与极端风暴潮相当？
• RQ5 在Storegga事件之前快速的海平面上升是否在Doggerland遗弃过程中发挥了比海啸事件更重要的作用？

主要发现

• 模型预测Doggerland的最大海啸越岸高度为9米，事件期间最多有2,000平方公里（占陆地表面积的35%）被淹没。
• Doggerland的淹没程度与该地区极端风暴潮造成的淹没程度相当，表明海啸并非独特灾难性事件。
• 模型结果与设得兰群岛和莫里湾的沉积物表现出良好一致性，验证了模拟方法的可靠性。
• 本研究发现，古海深地形与滑坡源参数的不确定性导致估算的淹没范围低于沉积物所暗示的水平。
• 结果表明，Storegga事件前500年内快速的海平面上升很可能已造成大量洪水，是Doggerland被淹没和人类遗弃的主要驱动因素。
• 可变形滑动模型可能产生更大的波浪，但当前计算限制限制了其应用；本研究采用的刚性块体模型提供了保守估计。