Bougainville is the principal island of the northern group of the Solomon Islands . It is approximately 190km long by 50 km wide. An island of great natural beauty, it features a steep mountain range, in parts more than 2,500 metres high. The soil is mainly volcanic. Mt Bagana at 200m is an active volcano. The Keriaka limestone plateau, south of Mt Balbi contains Benua Cave, 4,500,000m 3 , one of the largest underground caverns in the world.

Bougainville has relatively little flat land except in the northern and coastal areas. Its fertile areas coupled with rainfall which rises to 5000mm a year in the mountain areas, allows copra and cocoa to be grown successfully as commercial crops. Until 1989, more copper, copra and cocoa were exported from Bougainville than from any other place in Papua New Guinea .