The researchers managed to map in detail one of the largest underwater landslides of the world, the Stad Slidein the Norwegian Sea. The “mega landslide”, 360 m thick, was triggered well 400,000 years agoprobably due to an earthquake; his volume equal to 4300 km3 and his extension of 46,500 km2comparable to that of Switzerland, suggest that it generated a tsunami. Studying submarine landslides is difficult but very important because they can have serious consequencesfor example generating very high waves and damaging submarine cables. Furthermore, their numbers could increase with current climate change.
What was discovered with the map of the Stad Slide underwater landslide: causes and characteristics
The Stad Slide, off the west coast of Norway, is the largest of the five “mega landslides” that have occurred in the area over the last 3 million years. Despite having a volume of 4300 km3 and one maximum thickness of 360 mwas only identified ten years ago because its deposits are located approximately 1 km deep below the seabed marine. At the time, only 5% of the landslide had been mapped, but now researchers have managed to map it in extensive detail.
This was possible using seismic reflection data collected between 2014 and 2018, obtained by sending sound waves from a ship towards the seabed and measuring how these were reflected; such measurements reveal the properties of the seabed and the nature of sedimentary layers that are located below it. It was thus discovered that the landslide is made up of layers of coarse sediments alternating with layers of fine sediments. Precisely this difference between the characteristics of the sediments could have created conditions favorable to the detachment of the material. The landslide would have developed in the form of a debris flow along the slope that connects the continental shelf to the actual seabed. The enormous quantity of debris that fueled the landslide was produced by ancient glacierswhich with their erosive force tore large volumes of fragments from the bedrock as they flowed over it, and then deposited them. The trigger of the landslide would instead be attributed to earthquakes caused by the so-called “post-glacial rebound“, which consists in the lifting of the lithosphere following the melting of the overlying ice. In the case of the Stad Slide, the landslide occurred in different phasesas evidenced by its stepped profile. Moving a similar amount of material it may have generated a large tsunamialthough it is difficult to find evidence of this.
Why it is important to study underwater landslides
Submarine landslides can be much larger than landslides on land. Despite their size, however, they are difficult to locate and map, and therefore our knowledge about it is limited. The goal, in the future, is to acquire more information on underwater landslides since their consequences can also be serious. As well as causing tsunamithese events can involve submarine cables which carry global Internet traffic, for a total extension of 1.4 million kilometers. Breakage of these cables causes enormous inconvenience and repair costs. Just think of what happened in 2008 off the coast of Alexandria in Egypt, when the damage to a submarine cable caused a loss of tens of millions of euros, cutting off the Internet connection to 75 million people in the Middle East. Even on seabed of our peninsuladuring earthquakes or river floods, submarine landslides occur which channel along the canyons of the continental slope and erode the seabed with their large volumes of debris. The climate change currently underway, which is causing increasingly rapid melting of the ice, could increase the risk of these events occurring.
