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Article Excerpt
Meteorological tsunamis, or meteo-tsunamis, are waves that possess tsunami characteristics but have a meteorological origin (Defant 1961; Rabinovich and Monserrat 1996, 1998; Bryant 2001; Gonzalez, Farreras, and Ochoa 2001). Tsunamis are characterized by their long wavelength and long-period nature; that is, the distance and time, respectively, between consecutive wave crests, often measured in kilometers and tens of minutes rather than in meters and seconds, as with most wind-generated waves, characteristics that enable shoaling tsunamis to grow in height at the shore and to penetrate relatively far inland. Various local names around the world describe meteorological tsunamis, such as rissaga in the Spain's Balearic Islands (Monserrat, Ibbetson, and Thorpe 1991), abiki in Japan's Nagasaki Bay (Hibiya and Kajiura 1982), marrobbio in Sicily (Candela and others 1999), Seebar in the Baltic Sea, and also, perhaps, "freak waves" (White and Fornberg 1998; Wu and Yao 2004).
Meteo-tsunamis have the same periods, spatial scales, physical properties, and destructive impacts as seismically generated tsunamis have when they refract and shoal along coasts (Bryant 2001; Monserrat, Vilibi, and Rabinovich 2006). Rogue waves are large meteorological waves that are infamous for sinking ships in the open sea and thus differ from tsunamis, which are of low amplitude in the open ocean, but rogue waves formed in coastal waters may be considered meteo-tsunamis if they take on tsunami-like characteristics (Kharif and Pelinovsky 2003).
A number of mechanisms can result in a meteo-tsunami. These include the passage of cyclones or hurricanes, frontal squalls, atmospheric pressure jumps (sudden changes in atmospheric pressure associated with thunderstorms), atmospheric gravity waves (vertical oscillations of air cells), tide-generated internal waves (Giese and others 1982), wave superposition (addition of overlapping wave-crest heights), interaction of wind and current, and atmospheric shock waves from volcanic activity (Rabinovich and Monserrat 1996; Lowe and de Lange 2000; Bryant 2001). These processes can generate tsunami-like waves if the disturbance propagates at the same speed as any surface ocean wave being generated (Monserrat, Vilibi, and Rabinovich 2006). Meteo-tsunamis are also very sensitive to resonance generated by local coastal geometry and topography, which, in enclosed inlets, bays, and harbors, can induce high-amplitude seiches; that is, standing waves that slosh back and forth across enclosed water bodies (Rabinovich and Stephenson 2004).
Coastal managers do not currently consider the coast of the British Isles to be at risk from meteo-tsunamis, but a review of historical large waves in southern Britain leads us to believe that the phenomenon does occur. This is particularly so within the enclosed basins of the Bristol Channel and the English Channel, sometimes with catastrophic consequences (Figure 1). Some authors have criticized the current coastal hazard planning in the United Kingdom for its lack of integration: It operates at the local or regional level and is usually conducted by local government authorities (Ballinger and others 2000). Coastal planners in the United Kingdom are more concerned with long-term, predictable hazards, such as coastal flooding, erosion, and sea-level rise, than with meteo-tsunamis, but evidence suggests that meteo-tsunamis should also be included in any coastal hazard assessment of these areas.
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METEO-TSUNAMI OCCURRENCES
Events included in this study share a key trait: one or more large waves that resemble a tsunami with no known associated seismic activity but with a possible meteorological explanation. However, the possibility exists, even with a meteoro-logical explanation, that some of these events may be due to distant seismic activity or a submarine landslide. The locations of places mentioned in this article are shown in Figure 2, and Table I summarizes the characteristics of meteo-tsunamis they experienced. We identified events through a survey of scientific and popular literature and of newspaper reports. Although the latter can provide valuable information, especially eye-witness statements, each report requires careful reading to avoid attributing credibility to statements that may be exaggerated or fabricated.
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TABLE I--SUMMARY OF METEO-TSUNAMI OCCURRENCES IN SOUTHERN BRITAIN DATE AREAS ORIGIN IMPACTS EFFECTED 23 November 1824 Chesil Beach Local Large wave and The Fleet gale/hurricane overtopped a gravel barrier and penetrated inland, destroying houses and a church and causing up to sixty deaths 23 April 1868 Burton Unknown, but not Villages Bradstock and associated with a inundated, Lyme Regis local storm waves up to 9 meters high 17 October 1883 Severn Unknown, but linked Large wave Estuary to a local storm overtopped sea defenses and flooded lowlands 18 August 1892 Yealm and Linked to a A series of Fowey thunderstorm/squall large waves Estuaries in the English damaged Channel boats 16 December 1910 Ilfracombe and Local gale Wave up to 9 the meters high surrounding struck area Ilfracombe and penetrated in land, causing damage 20 July 1929 Folkestone to Squall line in the Large wave Brighton English Channel struck beaches, killing two people 31 July 1996 Westward Ho! Probably a squall Large wave and line in the Bristol struck, Pembrokeshire Channel bowling people over up the beach at Westward Ho! and causing damage along the Pembroke coast 13 February 1979 Bristol Distant Atlantic A series of Channel and storm large, the western long-period English waves Channel overtopped coasts Chesil Beach and sea defenses
CHESIL BEACH AND THE FLEET (DORSET)
A storm on 23 November 1824 was marked by gale-or hurricane-force winds, according to some reports. One or more large waves with tsunami characteristics accompanied the storm and caused much damage and loss of life. Gordon Le Pard (1999) and Ian West (2008a, 2008b) provide accounts of the event that form the basis of the evidence we present. The Fleet is a lagoon sheltered behind the south-west-facing Chesil Beach gravel barrier (May 2003). During the 1824 storm a single giant wave overtopped, rather than breached, the gravel barrier from Chesil in the east, where it destroyed many fishermen's cottages and apparently killed fifty to sixty people. In Abbotsbury, to the west, the wave inundated back-barrier meadows to a depth of approximately 6.9 meters. Commemorative information regarding this event is on display at these locations and at the nearby coastal town of Weymouth, where the event badly damaged the seafront (Figure 3).
The most detailed accounts of the wave come from the village of East Fleet, in a small valley midway along the length of The Fleet lagoon (see Figure 3). What has been described as a tidal wave struck Fleet Church--also known as "Moonflect Church"--where a boy,
at six o'clock in the morning ... was standing, with other boys, by the gate near the cattle pound when he saw, rushing up...
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