Nigg Valentin, Wohlwend Stephan, Hilbe Michael, Bellwald Benjamin, Fabbri Stefano C, de Souza Gregory F, Donau Florian, Grischott Reto, Strasser Michael, Anselmetti Flavio S
Institute of Geological Sciences and Oeschger Centre for Climate Change Research, University of Bern, Baltzerstrasse 1+3, 3012 Bern, Switzerland.
Geological Institute, ETH Zurich, Sonneggstrasse 5, 8092 Zürich, Switzerland.
Nat Hazards (Dordr). 2021;107(2):1069-1103. doi: 10.1007/s11069-021-04533-y. Epub 2021 Feb 8.
Large lacustrine mass movements and delta collapses are increasingly being considered as potential tsunamigenic sources and therefore hazardous for the population and infrastructure along lakeshores. Although historical reports document tsunami events in several lakes in Switzerland, and although the propagation of lake tsunamis has been studied by numerical wave modeling, only little is known about on- and offshore lacustrine tsunami deposits. In Lake Sils, Switzerland, a large prehistoric mass-movement deposit originating from the Isola Delta with a minimum estimated volume of 6.5 × 10 m and a basinal thickness of > 6 m in the seismic record has been identified by previous studies and radiocarbon dated to around 700 Common Era. Here, we combine (i) comprehensive sedimentological investigation of sediment cores recovered from the on- and offshore settings, (ii) mineralogical fingerprinting of the inflows from key catchments to characterize sediment provenance, and (iii) numerical tsunami modeling, to test the hypothesis of a tsunamigenic delta collapse in Lake Sils. We observe a clastic event deposit consisting of coarse-grained, fining-upward sand overlying an organic-rich peat deposit in the shallow water. This layer thins and fines landward on the coastal plain. Toward the deeper water (20-40 m), the deposit transforms into a thicker and more heterogeneous sediment package with multiple sequences of fining-upward sand and a well-pronounced clay cap at the top. Radiocarbon dating of the peat underlying the event deposit yields a maximum age of 225-419 calibrated Common Era. The tsunami models, which indicate wave heights reaching up to 5 m, simulate areas of inundation that coincide with the location of event deposits. Based on our results, we propose that the historically undocumented Isola Delta collapse generated a basin-wide tsunami that inundated the lakeshore, transporting large amounts of unconsolidated sediment along the lakeshore toward the coastal plain and into the deeper lake basin.
The online version of this article (10.1007/s11069-021-04533-y) contains supplementary material, which is available to authorized users.
大型湖相块体运动和三角洲坍塌越来越被视为潜在的海啸源，因此对湖岸沿线的人口和基础设施构成威胁。尽管历史报告记录了瑞士多个湖泊发生的海啸事件，并且尽管通过数值波浪模型研究了湖泊海啸的传播，但对于湖上岸线和近海的湖泊海啸沉积物却知之甚少。在瑞士的锡尔斯湖，先前的研究已经识别出一个源自伊索拉三角洲的大型史前块体运动沉积物，在地震记录中其估计最小体积为6.5×10⁶立方米，盆地厚度大于6米，放射性碳测年显示其年代约为公元700年左右。在这里，我们结合了以下几点：（i）对从湖上岸线和近海环境采集的沉积物岩芯进行全面的沉积学调查；（ii）对来自关键集水区的水流进行矿物学指纹分析，以确定沉积物来源；（iii）进行数值海啸建模，以检验锡尔斯湖发生海啸引发的三角洲坍塌这一假设。我们在浅水区观察到一个碎屑事件沉积层，由粗粒、向上变细的砂层覆盖在富含有机质的泥炭层之上。该层在海岸平原向陆地方向变薄且粒度变细。向更深水域（20 - 40米），该沉积物转变为一个更厚且更不均匀的沉积组合，有多个向上变细的砂层序列，顶部有一个明显的粘土层。对事件沉积层之下泥炭的放射性碳测年得出最大年龄为公元225 - 419年。海啸模型显示波高可达5米，模拟的淹没区域与事件沉积层的位置相符。基于我们的研究结果，我们提出，历史上未记载的伊索拉三角洲坍塌引发了一场全盆地范围的海啸，淹没了湖岸，将大量未固结的沉积物沿湖岸输送到海岸平原并进入更深的湖盆。
本文的在线版本（10.1007/s11069 - 021 - 04533 - y）包含补充材料，授权用户可获取。
