Island of Mahé

Position of center of photo (Lat/Long): [-4.680556/55.481667]

The granitic islands are the peaks of the submarine Mascarene Plateau, a continental formation theorized to be either a part of Africa separated when Asia began to drift away from the original single continent of Gondwanaland, or the remnants of a microcontinent that existed up to the beginning of the Tertiary Period, approximately 50 million years ago. The granitic islands are characterized by boulder-covered hills and mountains as high as 940 meters rising abruptly from the sea. Elsewhere, narrow coastal plains extend to the base of the foothills. Extensively developed coral reefs are found mainly on the east coasts because of the southwest trade winds and equatorial current. Ninety-nine percent of the population is located on the granitic islands, and most are on Mahé.

The coralline islands differ sharply from the granitic in that they are very flat, often rising only a few feet above sea level. They have no fresh water, and very few have a resident population. Many, like Île aux Vaches, Île Denis, the Amirante Isles, Platte Island, and Coetivy Island are sand cays upon which extensive coconut plantations have been established. Some of the coralline islands consist of uplifted reefs and atolls covered with stunted vegetation. Several of these islands have been important breeding grounds for turtles and birds, as well as the sites of extensive guano deposits, which formerly constituted an important element of the Seychellois economy but now for the most part are depleted. Aldabra Islands, the largest coralline atoll with an area greater than Mahé, is a sanctuary for rare animals and birds.

The climate of Seychelles is tropical, having little seasonal variation. Temperatures on Mahé rarely rise above 29 C. or drop below 24 C. Humidity is high, but its enervating effect is usually ameliorated by prevailing winds. The southeast monsoon from late May to September brings cooler weather, and the northwest monsoon from March to May, warmer weather. High winds are rare inasmuch as most islands lie outside the Indian Ocean cyclone belt; Mahé suffered the only such storm in its recorded history in 1862. Mean annual rainfall in Mahé averages 2,880 millimeters at sea level and as high as 3,550 millimeters on the mountain slopes. Precipitation is somewhat less on the other islands, averaging as low as 500 millimeters per year on the southernmost coral islands. Because catchment provides most sources of water in Seychelles, yearly variations in rainfall or even brief periods of drought can produce water shortages. Small dams have been built on Mahé since 1969 in an effort to guarantee a reliable water supply, but drought can still be a problem on Mahé and particularly on La Digue.