Inferno Crater Lake is a large hot spring located in the Waimangu Volcanic Rift Valley on the North Island of New Zealand, and the largest geyser-like feature in the world. The actual geyser is not visible, as it plays underwater at the bottom of the lake, however, fumaroles are visible on the lake's shore and the rock wall behind it.
The water temperature in the lake ranges from 35 to 80 °C (95 to 176 °F), with acidity up to pH 2.2, and lake levels that vary up to 12 metres (39 ft), following a complicated 38-day cycle that includes an overflow stage. White silica deposits grow up to the overflow level, and the lake's colour is a result of finely divided silica suspended in the water. At low water levels the lake can be a dull grey colour, changing to an intensely sky blue colour at higher lake levels, in particular after the overflow stage.
Inferno Crater was blasted out of the side of the locally prominent Mt Haszard as part of the 1886 Mount Tarawera eruption, which opened several craters along a 17-kilometre (11 mi) rift stretching southwest from Mount Tarawera to the nearby Southern Crater. Inferno Crater's trumpet-shaped lake bed is up to 30 metres (98 ft) deep when the lake is full, which is also when it reaches its highest temperature.
According to en.wikipedia