The three Storegga Slides ( no, Storeggaraset) are amongst the largest known submarine landslides. They occurred at the edge of Norway's

continental shelf A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an island ...

in the Norwegian Sea, approximately 6225–6170 BCE. The collapse involved an estimated length of coastal shelf, with a total volume of of debris, which caused a tsunami in the North Atlantic Ocean.

Description

Storegga ( Norwegian: ''Great Edge'') is located at the edge of Norway's continental shelf in the Norwegian Sea, north-west of the Møre coast. In around 6200 BCE, structural failures of the shelf caused three underwater

landslide Landslides, also known as landslips, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, deep-seated grade (slope), slope failures, mudflows, and debris flows. Landslides occur in a variety of ...

s, which triggered very large tsunamis in the North Atlantic Ocean. The collapses involved an estimated length of coastal shelf, with a total volume of of debris. Based on

carbon dating Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for determining the age of an object containing organic material by using the properties of radiocarbon, a radioactive isotope of carbon. The method was dev ...

of plant material recovered from sediment deposited by the tsunamis, the latest incident occurred around approximately 6225–6170 BCE. In Scotland, traces of the subsequent tsunami have been recorded, with deposited sediment being discovered in Montrose Basin, the

Firth of Forth The Firth of Forth () is the estuary, or firth, of several Scottish rivers including the River Forth. It meets the North Sea with Fife on the north coast and Lothian on the south. Name ''Firth'' is a cognate of ''fjord'', a Norse word meani ...

up to inland and above current normal tide levels.

Possible mechanism

A possible triggering mechanism is thought to have been an earthquake that induced a catastrophic expansion of methane clathrate, a solid compound consisting of large amounts of methane suspended within a crystal water structure that forms in deep oceans under extremely high pressure. If removed from a high-pressure, low-temperature environment, one cubic metre of solid methane clathrate expands to 164 cubic metres of gaseous methane. If such an expansion occurred, it may have weakened the integrity of the surrounding rock sufficiently to trigger the slide. Another theory is that over time, streams from melting glaciers had carried trillions of tons of sediment to the edge of the continental shelf, where it accumulated in many layers. In this case, a trigger such as an earthquake could have caused a large area of seafloor to collapse into the deep Norwegian sea, thus carrying the enormous volume of accumulated sediment along with it.

Impact on human populations

Storegga tsunami deposits, Montrose basin (Maryton)

At, or shortly before, the time of the Second Storegga Slide, a land bridge known to archaeologists and geologists as Doggerland linked Britain, Denmark and the Netherlands across what is now the southern North Sea. This area is believed to have included a coastline of lagoons, marshes, mudflats and beaches, and to have been a rich hunting, fowling and fishing ground populated by

Mesolithic The Mesolithic (Greek: μέσος, ''mesos'' 'middle' + λίθος, ''lithos'' 'stone') or Middle Stone Age is the Old World archaeological period between the Upper Paleolithic and the Neolithic. The term Epipaleolithic is often used synonymous ...

human cultures. Vincent Gaffney, "Global Warming and the Lost European Country"
/ref> Although Doggerland was permanently submerged through a gradual rise in sea level, it has been hypothesized that coastal areas of both Britain and mainland Europe, extending over areas which are now submerged, would have been temporarily inundated by a tsunami triggered by the Storegga Slide. This event would have had a catastrophic impact on the Mesolithic population at the time. A 2021 study found that about of Scotland's northern and eastern coastline were affected, with water encroaching inland. With present-day populations and sea levels, a similar event today could devastate and destroy seafront and port areas of Arbroath, Stonehaven, Aberdeen, Inverness, Wick, and Montrose. While the tsunami caused by the Second Storegga Slide would have been devastating for those within the run-in zone, ultimately the tsunami was neither universally catastrophic nor the reason behind the inundation of the last vestiges of Doggerland.

Future slides

Storegga has been thoroughly investigated as part of the preparation activities for the Ormen Lange gas field off the coast of Norway. The prevalent conclusion is the slide was caused by glacial deposits left behind after the previous glacial period, making any recurrence only possible following a new ice age. After facts and arguments supporting this conclusion were published in 2004, the development of the Ormen Lange gas field was considered unlikely to increase the risk of triggering a new slide.

References

External links

BBC: The moment Britain became an island, 14 February 2011
Historical geology Landslides in Norway Geology of Norway 7th millennium BC Natural disasters in Scotland Tsunamis Norwegian Sea North Sea