The Maninjau caldera was formed by a volcanic eruption estimated to have occurred around 52,000 years ago. Deposits from the eruption have been found in a radial distribution around Maninjau extending up to to the east, to the southeast, and west to the present coastline. The deposits are estimated to be distributed over and have a volume of. The caldera has a length of and a width of.
The lake
Lake Maninjau has an area of, being approximately long and wide. The average depth is, with a maximum depth of. The natural outlet for excess water is the Antokan river, located on the west side of the lake. It is the only lake in Sumatra which has a natural outlet to the west coast. Since 1983, this water has been used to generate hydroelectric power for West Sumatra, generated around 68 MW at maximum load. Most of the people who live around Lake Maninjau are ethnically Minangkabau. Villages on the shores of the lake include Maninjau and Bayur. Maninjau is a notable tourist destination in the region due to its scenic beauty and mild climate. It is also a site for paragliding.
Local fishing and agriculture
Two endemic species collected from the lake for local consumption and for export to markets outside the crater are pensi, a species of small mussel, and palai rinuak, a type of small fish. One method of preparing palai rinuak is to grill a mixture of the fish along with coconut and spices, wrapped in a banana leaf. The lake is used for aquaculture, using karamba floating net cages. The technique was introduced in 1992 and, by 1997, there were over 2,000 cage units with over 600 households engaged. Each cage may have 3-4 production cycles each year. There is evidence of pollution around some karamba areas. On the edge of the lake, land use includes rice fields in the swamps and the lower slopes. The villages are bordered uphill by a large belt of forest-like tree gardens, which dissolve into the upper montane forest on the steepest parts of the slopes up to the ridge of the caldera. The tree gardens include three typical components:
