6 CARIBB. MAR. STUD., SPECIAL EDITION, 2007 there is plate collision or subduction, coastal form may also be variable, partly from volcanic activity and partly from the elevation of deposits of marine origin. including palcorccfs, ancient beach rock, and sandstones. The littoral (area close to the shoreline) is typically the most densely populated region of all Caribbean countries and has been much perturbed by human settlement. entirely or primalily of the territorial seas and exclusive economic zones of two or more coastal States.' 2.4 Plate Tectonics, Seismic Activity, and Volcanism The distinctive shape of the Caribbean Sea and the arc of islands surrounding it relate closely to the tectonics of the region·--thc position of the dynamic plates of the Earth·s crust and the boundaries between them. Figure 2.1 shows that all of the islands, with the exception or the Bahamas, lie close to the boundary of a fonnation known as the Caribbean Plate. It is moving eastward with respect to the adjacent North American and South American plates at a rate of approximately 20 mm/yr (Miller ct al. 2005). 2.2 The Shallow Sub-littoral The characteristics of the shallow sub-littoral (the area below the low-tide mark) again vary with geological history. Adjacelll to continental landmasses and larger islands there is generally a wide shallow sub-littoral or shelt: This may be seen in various places, such as off northcm South America, ofl' Nicaragua and Honduras, parts of Cuba, and the Bahamas. Many small countries of the Lesser Antilles, however, hnvc narrow island shelves and are surrounded by deep water. 2.3 Bathymetry The fonn of the Caribbean basin Boor is highly folded, with many ridges and troughs. The most prominent ridge is that between Nicaragua and the Greater Antilles, along which the island of Jamaica emerges. On either side of this prominent are deep troughs that extend down to depths of about 5,000 metres. There nrc several smaller ridges and rises, notably the Cayman Ridge south of Cuba, the Beata Ridge south of Hispaniola, and the Aves Ridge running north from Venezuela, These ridges cflcctively separate the deep-water masses of the Caribbean Sea into three prominent basins. There arc two notable deep troughs in the Caribbean Sea, the Cayman Trough south of Cuba and the Puerto Rico Trench north of Puerto Rico and Hispaniola. A linal prominent feature of the bathymetry (the shape of the ocean 11oor) of the Caribbean Sea is the Great Bahama Bank, with its extensive shallows and low-lying islands. There arc also many other less prominent ridges and basins that convey a picture of highly irregular contours to the Boor of the Sen, and a separation of the deepwater masses, The overall picture projected is of a Sea largely enclosed by the landmasses of South and Central America and the Greater Antilles, with comparatively narrow passages bet ween the Lesser and Greater Antilles, connecting it with the Atlantic Ocean. Therefore the Caribbean Sea is a semi-enclosed sea which, according to Article 122 of the 1982 United Nations Convention on the Law of the Sen (UNCLOS), is defined as 'a gulf, basin or sea surrounded by two or more States and connected to another sea or the ocean by a narrow outlet or consisting Seismic activity caused by the movement between the plates is generated along these boundaries. Along the Northern margin, including areas close to Jamaica and the Virgin Islands, moderate earthquakes of shallow depth arc generated. Ncar the plate boundaries there is also activity caused by movement within the plates themselves: for example, in the Northern Caribbean earthquakes arc caused by intemal deformation in a slab of the North American Plate. Concentrations of these earthquakes occur at depths of up to 300 km (Fig. 2.2). Seismic events in the Eastern Caribbean arc principally associated with a subduction zone" at the junction of the Caribbean and the North American plates. The North American Plate dips from East to West beneath the Caribbean Plate along a north·-south line just cast of the main island arc. Earthquakes are also concentrated in the Leeward Islands due to movement within the Caribbean Plate and in the region north-west of Trinidad, where the plate boundary changes direction. The pattern of earthquakes along the boundaries of the Caribbean Plate (Fig. 2.1) illustrates that except lor the Bahamas, Cuba, and the Yucatan Peninsula of Mexico; the countries surrounding the Caribbean Sea arc prone to si.b'11ilicant earthquake hazards (Fig. 2.2). This is perhaps one of the three distinctive and defining features of the Caribbean region. 2.5 Climate and Circulation Given its latitude, the Caribbean Sea and the adjacent littoral coastal landmasses have a wet tropical climate with 9 A subduction zone is a region \\·here two tectonic plntcs converge, with one sliding undcmcmh the other towurds the mohcn nH:k of the Eurth's nmntlc. II is typically associated with vulcanic <tctivity am.! c:Jrthquakcs. -27-