This short article aims to simply describe the geology of the Caribbean islands. Without falling into the natural determinism that has long prevailed in Geography, we will present in a second part the influence that this particular geology may have had on the history, geography and economy of these islands in particular.
THE FORMATION OF THE CARIBBEAN ISLANDS.
Three main types of rock formations emerge at the Earth’s surface: sedimentary rocks (example: limestone), magmatic rocks (or igneous rocks, example: basalt) and metamorphic rocks (example: marble). Sedimentary rocks are the result of an accumulation of compacted fine particles (sediments). Magmatic rocks are formed by cooling the magma of volcanoes. Metamorphic rocks are derived from the transformation of the first two (crystallization or recrystallization), in the depths of the Earth, under the action of heat and/or pressure in particular (IMAGE). Logically, sedimentary rocks are dominant at the Earth’s surface (they outcrop), volcanic rocks are omnipresent just below, in the earth’s crust, and magmatic rocks are found primarily in the deepest depths. However, volcanism and especially tectonics can sometimes upset this order and bring metamorphic rocks (which are then subjected to erosion and disintegrate into sediments) to the surface; or conversely, bury sedimentary rocks in the depths, for example. In this second case, for example, a limestone rock will turn into marble under the influence of pressure and heat.
During the geological history of the Caribbean region, volcanoes first emerged from the ocean floor near the edge of the Caribbean plate: Central American volcanoes in the west, Greater Antilles volcanoes in the north, Lesser Antilles volcanoes in the east, and Dutch and Venezuelan island volcanoes in the south. It will be seen on the map that the Caribbean plate is separated from the North American plate by the Gonavian microplate, which is located exactly between northern Jamaica and southern Cuba, and which extends to cut Haiti off at its capital (hence the seismicity of this area) (IMAGE). Cuba and the Bahamas are actually on the North American plate. Sea level then changed over periods of millions of years (eustatism). When the level rises and the emerging volcano, or part of its relief, is a few metres below sea level, the coral develops. When sea level subsequently decreases (or when tectonics “pushes” the relief upwards), the coral layer emerges above the volcanic rock. This layer of coral then gradually transforms into sedimentary limestone rock. The volcanic rock formed a pointed relief (generally triangular, with a strong verticality). On the contrary, the sedimentary rock formed is characterized by its horizontality, determined by sea level during immersion (coral develops only in the surface water layer, and not after 30 meters of depth).
Thus, with a few exceptions and by simplifying as much as possible, the Caribbean islands can be described as volcanoes that have emerged more or less covered with sedimentary limestone rocks. If we wanted to establish a typology of the islands, this classification would therefore show a degradation starting from the most recent islands with a volcanic dominant (Dominica, Saint Vincent) to the oldest islands with a dominant limestone (Antigua and Barbuda, Anguilla). In the centre, we would find the double islands, which include both a predominantly volcanic and a predominantly calcareous part. Guadeloupe is the archetype with a young volcanic island (the Basse Terre), joined to an island with an older limestone predominance (the Grande Terre). The Lowland belongs to the arch of the recent volcanic islands of the Lesser Antilles (predominantly volcanic), which extends from Saba and Saint Kitts in the north to Granada in the south. Grande Terre, on the other hand, is connected to a second arch of ancient volcanic islands, covered with limestone as explained above, which extends from Saint-Martin in the North to Grande Terre and Désirade (IMAGE). In general, the islands of the Greater Antilles (Jamaica, Hispaniola, Cuba, Puerto Rico) are the most complex, with the presence, side by side, of regions dominated by volcanics and sediments, all of which have often been fractured and tilted by tectonics. The islands in the southern Caribbean basin (Aruba, Bonaire, Curacao and the Venezuelan islands) are generally islands of ancient volcanism with a dominant limestone dominance (such as the islands in the arc from Saint-Martin to La Désirade, mentioned above).