Lake Rotorua

The Rotorua Caldera is one of several large volcanoes located in the Taupo Volcanic Zone on the North Island of New Zealand. Its last major eruption was about 240,000 years ago. At this time, the Mamaku ignimbrite, covering about 4000 square km, was deposited. After the eruption, the magma chamber underneath the volcano collapsed. The circular depression left behind is the current caldera, about 22 km (14 mi) in diameter and now occupied by Lake Rotorua. Mokoia Island, close to the centre of the lake, is a rhyolite dome. There are other domes like Hinemoa Point, Ngongotaha, Pohaturoa and Pukeroa. The most recent magmatic eruption occurred less than 25,000 years ago, creating some of the smaller lava domes. There is also much geothermal activity.

• http://en.wikipedia.org/wiki/Lake Rotorua