8150 years, 10 to 20-metre-high tsunami invaded the north of Europe. The Shetland Islands and the coast of Norway have been particularly affected. The cause of the tsunami was the Storegga landslide, 300-2000 metres below the level of the sea. Submarine landslides are often much more important than the landslides on land. The Storegga landslide destroyed an area larger than Scotland and the hardware today covers hundreds of kilometres on the seabed. Searching for the causes of these landslides is much more difficult under the water as on land, because of their inaccessibility.
A group of scientists from Kiel and Bremen have now discovered a potential cause of the landslides off the coasts of Mauritania and the results have been published in the international journal of research in Geology. They have combined the drilling results with the seismic data and were able to show that a certain stratification of the seabed has been responsible for at least one slide in this region.
“submarine landslides occur on very low slope, often with gradients as low as 1 or 1.5 degrees,”, says the lead author, Dr Morelia Urlaub of the GEOMAR Helmholtz Centre for Ocean Research Kiel. The slope in the Storegga slide area, for example, was 1.6 degrees. The landslide was studied off the coast of Mauritania, Cap Blanc, had a maximum slope of 2.8 degrees. When a layer is replaced, all of the layers overlying move to the bottom of the slope. It is difficult to determine the composition of this particular layer, because it is destroyed with the landslide.
In the case of the landslide off Mauritania, the researchers have had the chance. In the immediate vicinity of the failure region of Cap Blanc, landslides, parts of the slope are still intact. So, Dr. Urlaub has been pleased to note that the ocean Drilling Program (today: International Ocean Discovery Program) has taken samples of sediments in exactly this area. “We have been able to use these old 1980s hearts to seek the low point of the slope,”, she said. The combination of these drilling and seismic data have shown that the slope had slide where a clay layer overlies a layer of ooze consisting of the remains of fossil planktonic organisms.
This plankton out of the mud consists mainly of diatoms. These phytoplankton organisms form shells of silica. In certain phases of the Earth’s history, large amounts of diatoms form, the shells of which, after death, sink to the bottom of the sea and of the form of thick layers.
Since diatom ooze seems to be a common characteristic of north-west off the coast of Africa, as observed in the seismic data, the authors speculate that this phenomenon is also the reason why other mega-slides in the region. Thus, the assumptions for the Cap Blanc slide could be transferred to other areas of the region. The results of this study can help to identify areas that are prone to landslides.
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