Jamaica - Geography
Jamaica lies 145 kilometers south of Cuba and 160 kilometers west of Haiti (see fig. ___, frontispiece, and fig.___, Jamaica. Administrative Divisions.). Its capital city, Kingston, is about 920 kilometers southeast of Miami. At its greatest extent, Jamaica is 235 kilometers long, and it varies between 35 and 82 kilometers wide. With an area of 10,911 square kilometers, Jamaica is the largest island of the Commonwealth Caribbean and the third largest of the Greater Antilles, after Cuba and Hispaniola (the island containing the Dominican Republic and Haiti). The Pedro Banks, an area of shallow seas extending generally east to west for over 160 kilometers, lie southwest of Jamaica. A cluster of cays (low islands or reefs--see Glossary) are associated with the banks. To the southeast lie the Morant Cays, fifty-one kilometers from Morant Point, the easternmost point of Jamaica.
Jamaica and the other islands of the Antilles evolved from an arc of ancient volcanoes that rose from the sea billions of years ago. During periods of submersion, thick layers of limestone were laid down over the old igneous and metamorphic rock. In many places, the limestone is thousands of feet thick. The country can be divided into three landform regions: the eastern mountains, the central valleys and plateaus, and the coastal plains (see fig. ___, Jamaica. Topography).
The highest area is that of the Blue Mountains. These eastern mountains are formed by a central ridge of metamorphic rock running northwest to southeast from which many long spurs jut to the north and south. For a distance of over 3 kilometers, the crest of the ridge exceeds 1,800 meters. The highest point is Blue Mountain Peak at 2,256 meters. The Blue Mountains rise to these elevations from the coastal plain in the space of about sixteen kilometers, thus producing one of the steepest general gradients in the world. In this part of the country, the old metamorphic rock reveals itself through the surrounding limestone.
To the north of the Blue Mountains lies the strongly tilted limestone plateau forming the John Crow Mountains. This range rises to elevations of over 1,000 meters. To the west, in the central part of the country, are two high rolling plateaus: the Dry Harbour Mountains to the north and the Manchester Plateau to the south. Between the two, the land is rugged and here, also, the limestone layers are broken by the older rocks. Streams that rise in the region flow outward and sink soon after reaching the limestone layers.
The limestone plateau covers two-thirds of the country, so that karst formations dominate the island. Karst is formed by the erosion of the limestone in solution. Sinkholes, caves and caverns, disappearing streams, hummocky hills, and terra rosa (residual red) soils in the valleys are distinguishing features of a karst landscape; all these are present in Jamaica. To the west of the mountains is the rugged terrain of the Cockpit Country, one of the world's most dramatic examples of karst topography.
The Cockpit Country is pockmarked with steep-sided hollows as much as fifteen meters deep and separated by conical hills and ridges. This area of the country was once known as the "Land of Look Behind," because Spanish horsemen venturing into this region of hostile runaway slaves were said to have ridden two to a mount, one rider facing to the rear to keep a precautionary watch. Where the ridges between sinkholes in the plateau area have dissolved, flat-bottomed basins or valleys have been formed that are filled with terra rosa soils, some of the most productive on the island. The largest basin is the Vale of Clarendon, eighty kilometers long and thirty-two kilometers wide. Queen of Spains Valley, Nassau Valley, and Cave Valley were formed by the same process.
The coastline of Jamaica is one of many contrasts. The northeast shore is severely eroded by the ocean. There are many small inlets in the rugged coastline, but no coastal plain of any extent. A narrow strip of plains along the northern coast offers calm seas and white sand beaches. Behind the beaches is a flat raised plain of uplifted coral reef.
The southern coast has small stretches of plains lined by black sand beaches. These are backed by cliffs of limestone where the plateaus end. In many stretches with no coastal plain, the cliffs drop 300 meters straight to the sea. In the southwest, broad plains stretch inland for a number of kilometers. The Black River courses seventy kilometers through the largest of these plains. The swamplands of the Great Morass and the Upper Morass fill much of the plains. The western coastline contains the island's finest beaches, stretching for more than six kilometers along a sandbar at Negril.
Two types of climate are found on Jamaica. An upland tropical climate prevails on the windward side of the mountains, whereas a semiarid climate predominates on the leeward side. Warm trade winds from the east and northeast bring rainfall throughout the year. The rainfall is heaviest from May to October, with peaks in those two months. The average rainfall is 196 centimeters per year. Rainfall is much greater in the mountain areas facing the north and east, however. Where the higher elevations of the John Crow Mountains and the Blue Mountains catch the rain from the moisture-laden winds, rainfall exceeds 508 centimeters per year. Since the southwestern half of the island lies in the rain shadow of the mountains, it has a semiarid climate and receives fewer than 762 millimeters of rainfall annually.
Temperatures are fairly constant throughout the year, averaging 25°C to 30°C in the lowlands and 15°C to 22°C at higher elevations. Temperatures may dip to below 10°C at the peaks of the Blue Mountains. The island receives, in addition to the northeast trade winds, refreshing onshore breezes during the day and cooling offshore breezes at night. These are known on Jamaica as the "Doctor Breeze" and the "Undertaker's Breeze," respectively.
Jamaica lies at the edge of the hurricane track; as a result, the island usually experiences only indirect storm damage. Hurricanes occasionally score direct hits on the islands, however. In 1980, for example, Hurricane Allen destroyed nearly all Jamaica's banana crop.
Although most of Jamaica's native vegetation has been stripped in order to make room for cultivation, some areas have been left virtually undisturbed since the time of Columbus. Indigenous vegetation can be found along the northern coast from Rio Bueno to Discovery Bay, in the highest parts of the Blue Mountains, and in the heart of the Cockpit Country.
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