Why the seafloor starts moving

February 13, 2018

8150 years ago, a 10-20 meter high tsunami overran northern Europe. The Shetland Islands and the coast of Norway were hit particularly hard. The cause ofthe tsunami was the Storegga landslide, 300-2000 meters below sea level. Submarine landslides are often much larger than landslides onshore. The Storegga landslide affected an area larger than Scotland and the material today covers hundreds of kilometers on the seabed. Searching for the causes of such landslides is much more difficult underwater than on land due to their inaccessibility.

A group of scientists from Kiel and Bremen have now discovered a potential cause of landslides off the coast of Mauritania and published the results in the international research journal Geology. They combined results from drilling with seismic data and were able to show that a certain stratification of the seafloor was responsible for at least one slide in this region.

"Submarine landslides happen on very shallow slopes, often with gradients as low as 1or 1.5 degrees," says lead author Dr. Morelia Urlaub from the GEOMAR Helmholtz Center for Ocean Research Kiel. The slope in the Storegga slide area, for example, had 1.6 degrees. The landslide studied off the Mauritanian Cap Blanc had a maximum slope of 2.8 degrees. When a layer gives way, all overlying layers move down 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 were lucky. In the immediate vicinity of the failed area of the Cap Blanc landslide parts of the slope are still intact. Thus, Dr. Urlaub was happy to note that the Ocean Drilling Program (today: International Ocean Discovery Program) had sampled the sediment exactly in this area. "We were able to use these old 1980s cores to look for the weak point in the slope," she says. The combination of this drilling and seismic data showed that the slope was slipping just where a clay layer overlies ooze made up of the remains of fossil planktonic organisms.

This plankton mud mainly consists of diatoms. These phytoplankton organisms form shells out of silica. In some phases of the Earth's history, large amounts of diatoms form, the shells of which, after dying, sink to the bottom of the sea and form thick layers.

Since diatomaceous oozes appear to be a common feature off the Northwest African coast as observed in seismic data, the authors assume that this phenomenon is also the reason for other mega-slides in the region. Thus, the assumptions for the Cap Blanc slide could be transferred to other areas of the region. The outcome of this study may therefore help to identify areas, which are prone to landslides
-end-


Helmholtz Centre for Ocean Research Kiel (GEOMAR)

Related Landslides Articles from Brightsurf:

Simple actions can help people survive landslides
Simple actions can dramatically improve a person's chances of surviving a landslide, according to records from 38 landslides in the US and around the world.

Landslides have long-term effects on tundra vegetation
Landslides have long-term effects on tundra vegetation, a new study shows.

Most landslides in western Oregon triggered by heavy rainfall, not big earthquakes
Deep-seated landslides in the central Oregon Coast Range are triggered mostly by rainfall, not by large offshore earthquakes.

FSU researcher detects unknown submarine landslides in Gulf of Mexico
A Florida State University researcher has used new detection methods to identify 85 previously unknown submarine landslides that occurred in the Gulf of Mexico between 2008 and 2015, leading to questions about the stability of oil rigs and other structures, such as pipelines built in the region.

Climate change could trigger more landslides in High Mountain Asia
More frequent and intense rainfall events due to climate change could cause more landslides in the High Mountain Asia region of China, Tibet and Nepal, according to the first quantitative study of the link between precipitation and landslides in the region.

Martian landslides not conclusive evidence of ice
Giant ridges on the surface of landslides on Mars could have formed without ice, challenging their use by some as unequivocal evidence of past ice on the red planet, finds a new UCL-led study using state-of-the-art satellite data.

Ground failure study shows deep landslides not reactivated by 2018 Anchorage Quake
Major landslides triggered by the 1964 magnitude 9.2 Great Alaska earthquake responded to, but were not reactivated by, the magnitude 7.1 Anchorage earthquake that took place 30 November 2018, researchers concluded in a new study published in Seismological Research Letters.

Rice irrigation worsened landslides in deadliest earthquake of 2018 finds NTU study
Irrigation significantly exacerbated the earthquake-triggered landslides in Palu, on the Indonesian island of Sulawesi, in 2018, according to an international study led by Nanyang Technological University, Singapore (NTU Singapore) scientists.

Precursors of a catastrophic collapse
The flanks of many island volcanoes slide very slowly towards the sea.

Quick reconnaissance after 2018 Anchorage quake reveals signs of ground failure
A day after the Nov. 30, 2018, magnitude 7 earthquake in Anchorage, Alaska, US Geological Survey scientists Robert Witter and Adrian Bender had taken to the skies.

Read More: Landslides News and Landslides Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.