Recent research supports the view that a tsunami occurred widely in the northern North Sea and adjacent areas of the Atlantic Ocean at around 6,000 BC. The event is known to have altered coastlines and probably affected coastal populations, but its greatest significance today appears to be in the sediments it deposited, which provide a stratigraphic marker horizon of value to geologists and archaeologists alike.
‘Tsunami’ is a word adopted by geologists to describe a sea surface disturbance seen in a series of waves. A tsunami may originate on the sea floor, such as in land movement along a fault or in a landslide, or in a volcanic explosion. It may also be caused by the impact of a meteorite on the sea surface. The tsunami waves spread away from the area of the event. Places in their path often experience an initial drawdown of water before the first wave arrives. The size and number of the waves depend upon the nature and scale of the cause, together with the depth of the sea and the shape (bathymetry) and composition of the sea floor. Out at sea, tsunami waves may be no more than a metre or two high, but they grow as they reach shallow water and have been known to reach heights of over 30 metres. Although not much higher than the greatest storm waves, they are of a much longer period, travel faster and involve much greater energy. They can occur in all oceans and seas of the world. Some indication of the devastation big tsunamis achieve is shown in the photograph of a demolished church (below).
Evidence for a North Sea and Atlantic tsunami consists of deposits lying within Holocene (post-glacial) sediments landward of the present day coastline. Such sediments are found where land has risen after glacial ice sheet decay (isostatic uplift) more than the sea level. The map (below) depicts locations where the deposits have been found, together with the area of the likely cause of the tsunami, the second Storegga slide.
