Imagine you are walking along the coast of eastern Scotland, when suddenly you notice the sea rapidly retreating- like a low tide but much more pronounced. Around you, fish are left slithering, gasping for air and writhing on the sand, such is the speed of retreat of the water. You stay for a while, pondering this phenomenon, when suddenly in the distance you hear a roaring noise. Looking north, you see a gigantic wall of water approaching. Where it crashes into the coast there is a terrific noise, as if whole swathes of land are being ripped away in one sudden movement. The noise gets louder and louder until it is terrifying in its intensity. Suddenly the water is rushing towards you, shoving rocks and trees ahead of it as if they were children's toys.

Couldn't happen here?

Calamities such as this, particularly when attributed to somewhere in the UK, seem sensational - fictional even. It would seem that such things could not possibly happen in this part of the world. However, such an event did occur a long time ago, and there is scientific evidence to suggest that it could re-occur some time in the future.

Strange things happen at sea

Around 7,500 years ago, two enormous disturbances¹ occurred at sea between Norway and Scotland in a region is known today as the Storegga area. Huge sections of the continental shelf fell away into deeper waters, affecting an underwater region of 88,000 square kilometres - similar in size to mainland Scotland itself. In each case, it is believed that an earthquake may have triggered the slides, and that an explosive release of methane from gas-hydrates² greatly amplified the collapse. Huge amounts of energy were transferred into the sea water itself, resulting in two separate tsunamis of gargantuan proportions.

The science bit

A tsunami³, is a long-amplitude wave that occurs infrequently around the world as a result of massive disturbances at sea such as earthquakes, landslides, volcanic eruptions or meteorite strikes. Tsunamis are deceptive: in deep sea they propagate very quickly through the water while not reaching any significant height. However, it is when the waves hit the continental margins that the real fun begins. The waves slow down, but in order to maintain energy their height increases dramatically. By the time the waves hit land they may be several metres high. Tsunamis have been known to travel all the way across oceans, causing damage thousands of kilometres away from the point of origination.

Water, water everywhere

Such was the effect of the Storegga tsunamis. Huge waves radiated out from the slide area, first hitting the west coast of Norway with unimaginable force, then in short order Shetland Islands, the Faeroe Islands, Orkney, northern Scotland and Iceland. There is evidence that the waves reached as far south as eastern England, which was fully connected to the European mainland at that time. The cataclysms would have wreaked an enormous trail of destruction, with evidence showing that the waves were at least 10m high in many places.

How do we know?

Even though the tsunamis happened a long time ago, there is quite a lot of corroborative evidence of their occurrence from studies in different locations along the North Sea coast. The coastline has changed greatly since then. Because of the weight of the ice sheets during the last Ice Age, much of Scotland and Scandinavia was somewhat lower than it is today. Since then, the land has been rising gently back to its original position; resulting in raised beaches in many coastal areas. Naturalists discovered unexpected layers of sand and marine sediment within peat layers in these raised beds. Detailed analysis confirmed that the sediment was deposited rapidly. Radiocarbon dating was able to date these layers to around 7,500 years ago; and differences in the layers confirmed that at least two separate events occurred during this period. There is also evidence that human lives may have been lost in the cataclysms, as at least two stone-age settlements have been found just under the sand layers along the Norwegian and Scottish coasts⁴. What is even more remarkable is that older layers of rapid sea inundations were discovered, dating back 30,000 years and more. The Storegga tsunamis were not an isolated occurrence.

Finale or Encore?

The Storegga incidents give our present age some cause for concern. First of all, it makes it clear that north-western Europe is not immune from major disaster and that it may happen again, despite the fact that it is one of the most geologically stable areas on the planet. Disaster early-warning systems, such as those that exist in Japan, may not be such a bad idea given the number of people who would be affected were it to happen. Secondly, even though few people would see a re-occurrence as imminent, the very fact that it might occur in the future should have a bearing on major planning decisions, such as the positioning of nuclear power stations and toxic waste facilities. Thirdly there is a concern that we do not yet know enough about the causes of the tsunamis at a time when gas and oil drilling⁵ is about to occur in the very area of the Storegga disaster.

Related Links

3-D bathymetric image of the Storegga area.

BBC news report on the Storegga slides.

Why killer waves are so hard to detect.