Tuesday 23 October 2018

Boulders caused by waves, not tsunami

The enormous boulders found at Annagh Head
The enormous boulders found at Annagh Head
Caroline Crawford

Caroline Crawford

Giant boulder deposits off the west coast were not caused by a tsunami but the sheer force of Atlantic storms.

The centuries-old deposits in Annagh Head, Co Mayo, were long thought to be tsunamites, caused by an unknown tsunami.

However, research shows they are the result of Atlantic waves of up to 30 metres over hundreds of years.

Scientists from NUI Galway and Oxford University compared the boulderite deposits in Annagh Head with similar tsunamites in New Zealand.

Data shows that a coastline in an area in the North Island of New Zealand was produced by a 12-13 metre-high tsunami in one hour.


But researchers used field, historical and oceanographic data to argue the origin of the boulders at Annagh Head, which exceed 50 tonnes, were the result of ferocious Atlantic storm waves.

They used a computer simulation which predicted that north-east Atlantic storms, which have produced waves of over 60 metres, can produce boulderites that cannot be distinguished from tsunamites when size alone is considered.

Co-author of the study, Professor Paul Ryan from Earth and Ocean Sciences at NUI Galway, said: "This study shows the enormous power of storm waves battering the foreshore over centuries."

The findings were published in the leading journal 'Proceedings of the National Academy of Sciences'.

Irish Independent

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