Observation of the mini-tsunami off Cornwall on 27 June by French tide gauges.

 

A mini-tsunami was observed on Monday 27 June 2011 off Cornwall. It was also seen in certain Southern English estuaries in the form of a small wave rising in the direction of the current in the same way as a tidal bore (see video below).

This mini-tsunami was observed by the French RONIM tide gauge network and the English tide gauge network in the English Channel and the Atlantic. 10 to 30 cm high port seiches were measured at several locations, probably due to this event. The period of these oscillations was between a few minutes and a few tens of minutes and varied according to the configuration of each port. No seismic activity was reported on the date in question by the relevant bodies so the event may have been gravitational (landslide) or meteorological in origin (atmospheric pressure gradient, sea states etc.) in the case of a "meteo- tsunami".

The English press reported that a premium of 0.2 m was recorded by the Newlyn tide gauge, it is 0.3 m and 0.4 m in Plymouth to Portsmouth.

sleac.org :

Marigram Newlyn

Marigram Newlyn

Marigram Plymouth

Marigram Plymouth

Tide gauge observations in metropolitan France :

The ports are placed in the order in which the phenomenon occurred.

Station Tide curve Estimate time of arrival Estimated maximum amplitude
Le Conquet
Marigram Le conquet
05h50 TU (07h50 local) 15cm à 07h30 TU (09h30 local)
Concarneau
Marigram Concarneau
06h00 TU (08h00 local) 20cm à 09h50 TU (11h50 local)
Les sables d'Olonne
Marigram Les sables d'Olonne
06h20 TU (08h20 local) 18cm à 21h50 TU (23h50 local)
Saint-Malo
Marigram Saint Malo
06h30 TU (08h30 local) 14cm à 06h45 TU (08h45 local)
Le Crouesty
Marigram Le Crouesty
06h40 TU (08h40 local) 16cm à 09h00 TU (11h00 local)
La Rochelle
Marigram La Rochelle
07h30 TU (09h30 local) 16cm à 15h10 TU (17h10 local)
Cherbourg
Marigram Cherboug
09h25 TU (11h25 local) 15cm à 10h45 TU (12h45 local)
Saint Jean de Luz
Marigram Saint Jean de Luz
10h45 TU (15h45 local) 8cm à 18h45 TU (20h45 local)
Le Havre
Marigram Le Havre
10h55 TU (12h55 local) 14cm à 16h10 TU (18h10 local)
Dieppe
Marigram Dieppe
11h50 TU (13h50 local) 19cm à 19h55 TU (21h55 local)
Boulogne sur mer
Marigram Boulogne
12h30 TU (14h30 local) 13cm à 17h30 TU (19h30 local)
Calais
Marigram Calais
13h00 TU (15h00 local) 18cm à 17h40 TU (19h40 local)

 

The estimated times of arrival appear to show a propagation of the phenomenon: The wave would appear to have taken 5 hours to travel from Le Conquet to Saint Jean de Luz at the far end of the Bay of Biscay and approximately 7 hours to reach Calais via the English Channel. There was no seiche of any noticeable amplitude in Roscoff..

Tracings of records schedules by the atmospheric pressure tide gauges are given below:

track in the Channel

track in the Channel

track in the Atlantic coast

track in the Atlantic coast

 

 

News links :

-The Telegraph : Landslide causes tsunamis off the coast of Cornwall, 29 juin 2011 (en anglais) ;

-The Guardian : Mild tsunami strikes Cornish coast, shifting water levels 'in a flash', 29 juin 2011 (en anglais) ;

-BBC news : Underwater landslide likely cause of 'mild tsunami', 29 juin 2011 (en anglais) ;

-Daily Mail : The hair-raising truth about the Cornish tsunami triggered by under-sea earthquake, 1er juillet 2011 (en anglais) ;

-Hydro international : Small Tsunami in English Channel, 4 juillet 2011 (en anglais).

First interpretations and conclusions :

-British Geological Survey, Tsunami or meteotsunami ?, South West England, June 2011

Links to display real time tide gauge data :

-Marégraphes anglais sur le site UK National Tidal and Sea Level Facility ;

-Marégraphes anglais sur le site Sea Levels along the European Atlantic Coastline (SLEAC) ;

-Marégraphes français sur le site IOC sea level station monitoring facility.

Bibliography :

Ardhuin F., E. Devaux, L. Pineau-Guillou (2010). Observation et prévision des seiches sur la côte Atlantique française, XIièmes Journées Nationales "Génie Civil - Génie Côtier", 22-24 juin 2010, Sables d'Olonne, pp. 1-8, DOI:10.5150/jngcgc.2010.001-A.

Haslett, S.K., Mellor, H.E. and Bryant, E.A., 2009. Meteo-tsunami hazard associated with summer thunderstorms in the United Kingdom. Physics and Chemistry of the Earth, Parts A/B/C, 34(17–18) : 1016–1022.

Haslett, S. K. and Bryant, E. A. : Meteorological Tsunamis in Southern Britain : An Historical Review, Geographical Review, Volume 99, Issue 2, pages 146–163, April 2009, DOI : 10.1111/j.1931-0846.2009.tb00424.x

Haslett, S. K. and Bryant, E. A. : Historic tsunami in Britain since AD 1000 : a review, Nat. Hazards Earth Syst. Sci., 8, 587-601, doi:10.5194/nhess-8-587-2008.

Monserrat, S., Vilibić, I., and Rabinovich, A. B. : Meteotsunamis : atmospherically induced destructive ocean waves in the tsunami frequency band, Nat. Hazards Earth Syst. Sci., 6, 1035-1051, doi:10.5194/nhess-6-1035-2006.

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