Of volcanic origin, Réunion consists mostly of rugged mountains and short torrential rivers. It is located about 450 mi (724 km) east of Madagascar, in the Indian Ocean. First explored by Portuguese navigators in the 16th century, the island of Réunion, then uninhabited, was taken as a French possession in 1642. African slaves were imported first to work coffee and then sugar plantations; with the abolition of slavery in 1848, indentured laborers from Indochina, India, and East Africa were brought in. In 1947, Réunion became an overseas department of France.