Segara Anak is a crater lake in the caldera that formed during the explosive volcanic eruption of Mount Samalas in 1257. The caldera is next to Mount Rinjani on Lombok Island in Indonesia. "Segara Anak" means "child of the sea" and refers to the blue lake's resemblance to the sea. The volcanic cone Gunung Barujari is at the eastern end of the lake and is responsible for its crescent shape. The lake temperature is 20-22 C, which is 5 - 7 C-change higher than normal for a lake at its altitude. Hot magma below the lake is responsible for this anomaly. Gas bubbles escape from the lake floor, helping the lake to have a pH of 7–8. The surface of Segara Anak is 2004 m above mean sea level (AMSL) and is Indonesia's second-highest caldera lake with an active volcano. The peak of Gunung Baru Jari is 2376 m AMSL. The lake covers 45 km2, with dimensions of 7.5 by, and has a maximum depth of 230 m.

Fish breeding

There were no fish in Segara Anak. In 1969, volcanologists from the Geological Society of London examined the lake and recommended the cultivation of fish. In 1985, the Nusa Tenggara Barat provincial government began breeding fish in the lake. The fish bred rapidly and the lake became home to millions of tilapia and carp. Segara Anak is today a popular spot for fishing, and some locals make a living from this.

Mount Samalas

The estimated height of Mount Samalas before its 1257 eruption was 4200 m. According to a 2013 study, the eruption destroyed the mountain by ejecting up to 10 mi3 of Dense rock equivalent or 200 km3 of rock into the atmosphere. The eruption was one of the largest during the last few thousand years, with a probable Volcanic Explosivity Index of 7. The eruption may have been the cause of decreased global temperatures for a few years and may have even been a triggering factor for the Little Ice Age.