Mauritius is located in the Indian Ocean about 800km east of Madagascar and 2,000 km off the nearest point of the African mainland and is considered the most accessible island in the Indian Ocean. This small sub-tropical island occupies an area of 1864 km2 and was shaped by two series of volcanic eruptions millions of years ago. Mauritius is mostly of volcanic formation and is almost entirely surrounded by coral reefs. A coastal plain, widest in the north, rises sharply to a 1,500 ft high plateau bordered by three mountain ranges - the Black River Range, the Grand Port Range, and the Moka Range. The longest river is the Grand River South East, about 25 miles in length.