The three Storegga Slides ( no, Storeggaraset) are amongst the largest known

submarine landslide Submarine landslides are marine landslides that transport sediment across the continental shelf and into the deep ocean. A submarine landslide is initiated when the downwards driving stress (gravity and other factors) exceeds the resisting str ...

s. They occurred at the edge of Norway's continental shelf in the

Norwegian Sea The Norwegian Sea ( no, Norskehavet; is, Noregshaf; fo, Norskahavið) is a marginal sea, grouped with either the Atlantic Ocean or the Arctic Ocean, northwest of Norway between the North Sea and the Greenland Sea, adjoining the Barents Sea to ...

, approximately 6225–6170

BCE Common Era (CE) and Before the Common Era (BCE) are year notations for the Gregorian calendar (and its predecessor, the Julian calendar), the world's most widely used calendar era. Common Era and Before the Common Era are alternatives to the or ...

. The collapse involved an estimated length of coastal shelf, with a total volume of of debris, which caused a

tsunami A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater exp ...

in the

North Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the "Old World" of Africa, Europe an ...

Description

Storegga (

Norwegian Norwegian, Norwayan, or Norsk may refer to: *Something of, from, or related to Norway, a country in northwestern Europe * Norwegians, both a nation and an ethnic group native to Norway * Demographics of Norway *The Norwegian language, including ...

: ''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 landslides, which triggered very large

s 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 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 Montrose Basin is a nearly circular tidal basin which makes up part of the estuary of the River South Esk and which sits just inland of the town of Montrose in Angus on the east coast of Scotland. The basin is protected by a number of designat ...

, the Firth of Forth 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 Methane clathrate (CH4·5.75H2O) or (8CH4·46H2O), also called methane hydrate, hydromethane, methane ice, fire ice, natural gas hydrate, or gas hydrate, is a solid clathrate compound (more specifically, a clathrate hydrate) in which a large amo ...

, 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 In biogeography, a land bridge is an isthmus or wider land connection between otherwise separate areas, over which animals and plants are able to cross and colonize new lands. A land bridge can be created by marine regression, in which sea leve ...

known to archaeologists and geologists as

Doggerland Doggerland was an area of land, now submerged beneath the North Sea, that connected Britain to continental Europe. It was flooded by rising sea levels around 6500–6200 BCE. The flooded land is known as the Dogger Littoral. Geological sur ...

linked

Britain Britain most often refers to: * The United Kingdom, a sovereign state in Europe comprising the island of Great Britain, the north-eastern part of the island of Ireland and many smaller islands * Great Britain, the largest island in the United King ...

Denmark ) , song = ( en, "King Christian stood by the lofty mast") , song_type = National and royal anthem , image_map = EU-Denmark.svg , map_caption = , subdivision_type = Sovereign state , subdivision_name = Kingdom of Denmark , establish ...

and the

Netherlands ) , anthem = ( en, "William of Nassau") , image_map = , map_caption = , subdivision_type = Sovereign state , subdivision_name = Kingdom of the Netherlands , established_title = Before independence , established_date = Spanish Netherl ...

across what is now the southern

North Sea The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea, epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the ...

. 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 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 A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betwe ...

, 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