The English Channel tsunami of 27 June 2011 - a probable meteorological source
Abstract
On the 29 June 2011 the press reported a tsunami striking SW England between Penzance and Portsmouth two days earlier on the 27th. Initially, tidal anomalies of 20 cm were reported at Newlyn, around 30 cm at Plymouth and Weymouth, and 40 cm at Portsmouth. The tsunami flooded the Yealm Estuary at about 1030 bst as a 0.8 m bore flowing upriver. At St Michael's Mount people on the causeway suddenly found themselves knee deep in water as the sea level rose rapidly and reported their 'hair standing on end' before the water rose. At Marazion, the sea withdrew before the wave came in. Approximately 200 miles of coastline were affected. No earthquakes were reported on the 27th, so a massive landslide located off the southwest of England on the continental slope was suggested as the source. However, subsequent reporting of tidal anomalies and seiching, along the French Channel coast as far east as Calais, and along the Atlantic coast of the Bay of Biscay as far south as Spain and Portugal indicates that a geological cause of the tsunami, such as a submarine landslide, is unlikely. A meteorological origin for the tsunami is therefore most likely, with the source the convective, thundery activity extending between Portugal and the English Channel during the 26th and 27th June. Whereas the initial wave created by the weather conditions was small, additional enhancement caused by the Proudman effect, resulted in a ten-fold increase in wave height recorded at the gauges. The 'tsunami' wave of 0.8 m reported from the Yealm Estuary was probably lower (less than 0.5 m), and is attributed to a local convective source and resonance as the wave travelled into shallow water, probably due to the harbour effect. The anomalous differences in the timing of the tidal anomalies and tsunami at the different locations are attributed to the formation of several separate waves from different thundery cells as the area of convective activity travelled from Portugal to Brittany and then into the English Channel between 0000 and 1200 utc on the 27th. This is the first time that such regional anomalous tidal conditions were recorded in Spain, Britain and France, and positively identified as the result of a meteotsunami.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMNH21D..05T
- Keywords:
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- 4564 OCEANOGRAPHY: PHYSICAL / Tsunamis and storm surges;
- 4301 NATURAL HAZARDS / Atmospheric;
- 4330 NATURAL HAZARDS / Vulnerability