Erosion in Madagascar—
Dramatic evidence of the catastrophic erosion of northwestern Madagascar is revealed in this near-vertical, June 1983 photograph of the rapidly expanding Betsiboka River Delta. The removal of the native forest for cultivation and pastureland during the past 50 years has led to massive annual soil losses approaching 112 tons per acre (250 metric tons per hectare) in some regions of the island, the largest amount recorded anywhere in the world. The photograph provides convincing evidence of the result of this process, as the effects of water erosion are seen throughout the 1,544-square-mile (4000-square-kilometer) land surface area of the photograph. The delta continues to build toward the mouth of Bombetoka Bay, which enters the Mozambique Channel.
As a result of rapid and unregulated deforestation, the eroded watershed of the Betsiboka River in NW Madagascar (16.0N, 46.5E) debouches into a large estuary, the Bay of Bombeteka. The immense sediment loads coming down the river have resulted in the silting of of the estuary since 1947 when the port facility of Majunga was moved from inland to the coast to prevent oceangoing ships from running aground.
Photo #: STS007-3-58 Date: Jun. 1983
Geographic Region: MADAGASCAR
Feature: BETSIBOKA RIVER DELTA
The Betsiboka Estuary on the northwest coast of Madagascar is the mouth of Madagascar’s largest river and one of the world’s fast-changing coastlines. Nearly a century of extensive logging of Madagascar’s rainforests and coastal mangroves has resulted in nearly complete clearing of the land and fantastic rates of erosion. After every heavy rain, the bright red soils are washed from the hillsides into the streams and rivers to the coast. Astronauts describe their view of Madagascar as "bleeding into the ocean." One impact of the extensive 20th century erosion is the filling and clogging of coastal waterways with sediment, a process that is well illustrated in the Betsiboka estuary. In fact, ocean-going ships were once able to travel up the Betsiboka estuary, but must now berth at the coast.
A bad situation is made worse when tropical storms bring severe rainfall, greatly accelerating the rates of erosion. As an illustration, astronauts aboard the International Space Station documented widespread flooding and a massive red sediment plume flowing into the Bestiboka estuary and the ocean in the wake of Tropical Cyclone Gafilo, which hit northern Madagascar on March 7 and 8, 2004. A comparative image (ISS007-E-14344) taken in September 2003 shows normal water levels in the estuary.
Despite the heavy coastal flooding in the top image, new coastal developments can be seen. The Mahajanga Aquaculture Development Project, a joint venture between Madagascar and the Japan International Cooperative Agency, strings along the coastal region at the mouth of the estuary (inset images). This project is a shrimp farm and has been developed since 1999. Successive images taken by astronauts show increasing numbers of ponds constructed between 2000 and the present. Coastal aquaculture projects are frequently controversial, pitting the protection and viability of coastal ecosystems (especially rapidly disappearing mangrove environments) against badly needed industry in developing countries.
Photo #: ISS008-E-19233 Date: Mar. 2004
Geographic Region: MADAGASCAR
Feature: BETSIBOKA RIVER DELTA, MAJUNGA
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