Great Red Island, Madagascar
The southwestern area of Madagascar - the fourth largest island in the world - is highlighted in this Envisat image. The rivers Morondava, Maharivo, Mangoky and Onilahy are shown, respectively, emptying into the Indian Ocean in the Mozambique Channel. The green coloured body of water visible just below the Mangoky River is Lake Ihotry.
Madagascar was once attached to the African mainland but broke away more than 150 million years ago. The island is divided into east and west by the Hauts Plateaux mountain chain, located in the central highlands, that runs north to south through the country. The Mangoky River rises in the central highlands and stretches westerly some 564 kilometers through the vertical-running Bemaraha Plateau, the coastal plain and the Mangoky Delta, which has an area of 1 547 sq km, before flowing into the channel. The capital, Antananarivo, is also located in the central highlands.
The Isalo National Park, which is located to the right in the image in the burnt orange area halfway between the Mangoky and Onilahy rivers, was created in 1962 and covers around 81 000 hectares. The mountain is characterised by eroded sandstone, which much of dates back to the Jurassic period, according to the conservation organization WWF.
Madagascar is often referred to as the â€˜Great Red Island' because of the appearance of its red laterite soil, which was once covered with green rainforest before slash-and-burn techniques introduced for farming caused heavy erosion.
Madagascar's coastline contains some 3540 km of coral reef systems, with the majority found on the west coast. Fifty-two km of true barrier reefs are located in the Toliara region, which is located just to the north of the Onilahy River. The reef system from Toliara to Morombe, located on the coast left of Lake Ihotry, is considered one of the most extensive reef systems in the western Indian Ocean region.
Coral reefs worldwide are increasingly under threat from coral bleaching, where the algae is expelled from the coral tissue, progressively losing its colour and eventually dying. The precise reason for coral bleaching is unknown but the phenomenon is associated with increased water temperatures, low salinity and high sunlight levels.
A study by Conservation International carried out earlier this month along Madagascar's south-western coast showed damage to these reef systems from coral bleaching believed to be caused by rising sea temperatures.
Envisat's Medium Resolution Imaging Spectrometer (MERIS) acquired this image on 8 August 2006, working in Full Resolution mode to yield a spatial resolution of 300 metres.