A tsunami sweeps across an ancient sea floor at Larne, Northern Ireland

At Larne, Northern Ireland, the effects of the tsunami that swept across the area 200 million years ago can be seen clearly in the rocks exposed on the shore.

The lower part of this picture shows the top of the seismite, with the originally horizontal layers highly disturbed by the original earthquake shock and by the effects of the subsequent tsunami which it generated. The first, and most violent, waves of the tsunami would have scoured the sea floor, ripping up and reburying chunks of still soft sediment from the top of the seismite. The pale banded lumps amongst the darker sediment in the lower half of the picture probably represent some of these ripped-up chunks of sea floor.

In the top third of the picture the layering is undisturbed and conspicuous pale ripples can be seen; these get smaller in successively higher layers. They formed as the water of the shallow sea in this area sloshed to and fro during the waning stages of the tsunami's journey across the region.