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Union Hall Alamy Stock Photo
something in the water

Experts puzzled by unusual tidal activity off southern coast

Video footage shows the tide rapidly draining and flooding again.

EXPERTS HAVE SAID that the cause of unusual tidal activity off the coast of Cork is something of a mystery.

The phenomenon occurred on Saturday afternoon when harbours at Union Hall in west Cork rapidly drained, dropping 70cm in just five minutes before quickly flooding again.

A spokesperson for the Marine Institute told The Journal that it was one of several similar occurrences off the coast of Wexford and Pembrokeshire in Wales.

“The tide was seen to be travelling in the wrong direction and in some instances with several reversals of flow observed.

“Such rare events are usually driven by a factor or a number of factors that may lead to an unusual event, but in this case the causes are not immediately clear.”

The Marine Institute has been in contact with other monitoring organisations and will collaborate with others to review various data sets with the aim of determining the cause of the “reverse” tide.

“In particular, the high resolution met-ocean data from the M3 & M5 Data Buoys stationed off the south coast will be analysed in detail once they are recovered in coming months to identify any unique meteorological conditions that might have led or contributed to this event.”

Gerard McCarthy, an oceanographer at Maynooth University, said that typical rate of change for tides is one centimetre per minute.
He wrote on Twitter:

Tsunami in West Cork? At 1540 on Saturday last, at low tide, harbours in West Cork abruptly drained. Union Hall saw water levels drop 70 cm in 5 mins. Normal tides change at about 1 cm per minute. In the aftermath, there was some big seiching.

A seiche is a standing wave oscillating in a body of water.

McCarthy also refuted suggestions that the waves were caused by an offshore earthquake near the Portuguese island of Sao Jorge in the Azores.

“There were ~2.7 magnitude tremors near the Azores at 8.30+10.30 GMT. 2.7 is small in terms of generating a tsunami. The Azores is 1000 km from W Cork so it would have travelled at 125–170 km/hour—slow by tsunami standards.”

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