Freak west Cork tides not caused by marine earthquake, experts say

Experts say that unusual tidal conditions which left some West Cork locals fearful when they saw water levels drop dramatically over the weekend is due to fast-moving weather fronts rather than an earthquake at sea.

Scores of people in Union Hall and Courtmacsherry harbours watched last Saturday as rapidly dropping water levels left boats stranded and caused concern among locals that a tsunami could be heading towards them.

However, weather and marine experts believe that the event, which was felt as far away as France, Cornwall and Wales, was caused by a meteotsunami, a phenomenon during which high waves are provoked by fast-moving weather rather than by an earthquake at sea.

Prof Frédéric Dias, a principal investigator with MaREI, the Science Foundation Ireland centre for energy, climate and marine research and innovation at University College Cork, said investigations were under way.

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“What is interesting is that it is not a local phenomenon, it is more global. It was in fact felt in France as well. It looks like it was due to an atmospheric disturbance, with effects that can be amplified locally,” Prof Dias told The Irish Times.

Dr Gerard McCarthy, oceanographer with Irish Climate Research and Analysis UnitS (Icarus) in the Department of Geography at Maynooth University, said he believed the most likely cause of the phenomenon was probably a meteotsunami rather than an earthquake or landslide.

“There was a small earthquake recorded near the Azores,” he said, “but it was likely too small and too far away to have an impact on the Irish coast to anything like the extent we saw in Union Hall and Courtmacsherry.”

Dr McCarthy said the Union Hall and Courtmacsherry harbours are regularly affected by seiching, a regular oscillation of tidal currents caused by atmospheric pressure.

“Seiching is basically water moving backwards and forwards and this happens in both of these bays normally. My best guess is that this regular seiching coincided with a dramatic and sudden change in atmospheric pressure somewhere out over the Atlantic off the coast of West Cork.

“If you imagine someone dropping a large volume of water straight down on the sea, that’s the kind of effect we are talking about. That pressure combined with the regular to and fro of water in those bays could have created a dramatic and unusual effect like the one we saw.”

Such events occur regularly around the Irish coast, but are more common during the winter, he said. “It’s something that can happen anywhere but if you get the right combination of factors all together, you can see something quite dramatic occurring like what happened along the West Cork coast at the weekend.”

One witness at Courtmacsherry, charter boat operator David Edwards, said: “The water was rushing out like a river. I’d never seen anything like it before. The first thing you think is ‘tsunami’.”

In Union Hall, Adrian Nowotynski was mooring his boat when the phenomenon struck.

“It was going out so fast that my boat was keeled on the bottom and so were a number of yachts and fishing trawlers and I’ve never seen that before. My first instinct was it must be an earthquake somewhere, nobody had ever seen the like of it in Union Hall before,” he said.