Tidal Surge / Tsunami, South Coasts of Devon & Cornwall on Monday 27th June 2011

I first heard about the 'tsunami' on Radio Cornwall on Monday evening, but hadn't heard anything since, besides an eyeball report from the river Tamar at Millbrook.

First noticed at about 9am (which would be the same time as Monday morning's low tide) by both tourists and bait diggers at St Michaels Mount, the Looe Harbour Master later reported seeing a tidal surge of 4-5 ft entering the Looe river. There were also reports of a 'tidal bore' reported travelling up the river Plym, in addition to tidal surges in Devon, Dorset and also Hampshire.

St Michael's Mount, Cornwall

Tide anomolies measuring the surge were recorded in Newlyn, Plymouth and Portsmouth.

Technically, it was a tsunami, as it was thought to have been caused by an underground landslide rather than lunar tide related, such as a tidal bore, although the British Geological society confirmed there were was no seismic activity in UK waters.

It is not the first time Cornwall has been hit by a Tsunami. On the 1st of November, 1755, the Great Lisbon Earthquake which resulted in the near total destruction of Lisbon, sent waves of up to 10ft towards Cornwall, arriving 4 hours after the quake struck.

Maybe next time, I'll have one of these ready, and see if we can catch muddy barrels.

Tsunami waves are different to storm generated windwaves in that it is their wavelength and not their height which causes the sometimes devastating effects. Whilst a typical windblown wave may have a wavelength of 30m and height on average of say 2m, a tsunami may have a wavelength of 100's of kms, but a smaller wave height, making them difficult to detect. This explains the drawback effect where the sea appears to recede hundreds of meters preceding the tsunami where the trough hits land first, as was captured so dramatically on film during the Boxing Day Tsunamis. The longer wavelength is also the reason why the tsunami wave continues to rush inland far further than normal storm or wind generated waves before receding, typically the cause of devastation to areas near the coastline.

Amateur video footage of a tidal surge at the river Yealm was caught on camera and shown here:

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