A collapse on a continental scale
Around 8,200 years ago, a section of Norway's continental shelf gave way. Located about 100 kilometers off the Møre coast, a vast portion of the seabed failed. The event, known as the Storegga Slide, was not one event but a series of at least three massive submarine landslides. The main collapse occurred between 6225 and 6170 BCE.
The scale is difficult to comprehend. An estimated 2,900 to 3,500 cubic kilometers of sediment, mud, and rock cascaded into the deep Norwegian Sea. This mass of debris covers a seafloor area of about 95,000 square kilometers, a region comparable in size to Iceland. The failure occurred along a 290-kilometer stretch of the coastal shelf, leaving behind a massive scar on the ocean floor that remains one of the largest of its kind ever identified. The name "Storegga" is Old Norse for "great edge," a description of the colossal feature left behind.
The wave that washed away a world
The sudden displacement of such a colossal volume of material triggered a mega-tsunami across the North Atlantic. This was not a minor wave; models and geological evidence show its devastating reach. The Shetland Islands, directly in the tsunami's path, were struck by waves estimated to be over 20 meters high. The coast of Norway experienced run-up of 10-12 meters, while eastern Scotland was inundated by waves reaching 3-6 meters above the sea level of the time. Traces of the tsunami's sediment have been found as far away as Greenland. In Scotland, the tsunami's signature is a distinct layer of sand, discovered within ancient estuary muds in places like the Montrose Basin, sometimes up to 29 kilometers inland.
This event impacted the Mesolithic human populations of the era. At the time, a land bridge known as Doggerland connected Great Britain to mainland Europe. This low-lying plain, with lagoons and marshes, was a fertile hunting and fishing ground. While a gradual rise in sea level was already submerging Doggerland, the Storegga tsunami likely delivered a final, catastrophic blow, washing over the remaining land and its inhabitants. The event may have had a catastrophic impact on the coastal Mesolithic population.
A geological detective story
The precise trigger for the Storegga Slide is being studied by scientists, with several theories. One hypothesis is an earthquake. The region experienced significant seismic activity following the last ice age due to post-glacial rebound—the rising of the land after the immense weight of the ice sheets was removed. Such a quake could have destabilized the shelf.
Another theory centers on methane hydrates. These are ice-like structures of methane and water that are stable under high pressure and low temperatures in deep-sea sediments. A warming climate could have caused these hydrates to decompose, releasing vast quantities of methane gas. This gas release would have dramatically weakened the sediment structure, preparing it for collapse. A third possibility is simple sediment overload. As glaciers melted, rivers carried enormous loads of sediment to the continental shelf, which may have become over-steepened and unstable. It is likely that a combination of these factors—a loaded shelf, gas hydrates, and an earthquake by an earthquake—led to the collapse.