Mount Ruapehu's Crater Lake

Mount Ruapehu, or just Ruapehu, is an active stratovolcano at the southern end of the Taupo Volcanic Zone in New Zealand. It is 23 kilometres northeast of Ohakune and 40 kilometres southwest of the southern shore of Lake Taupo, within Tongariro National Park. The North Island's major skifields and only glaciers are on its slopes.

Ruapehu is one of the world's most active volcanoes and the largest active volcano in New Zealand. It is the highest point in the North Island and includes three major peaks: Tahurangi (2,797 m), Te Heuheu (2,755 m) and Paretetaitonga (2,751 m). The deep, active crater is between the peaks and fills with a crater lake between major eruptions.

Tongariro National Park is the oldest national park in New Zealand, located in the central North Island. It has been acknowledged by UNESCO as one of the 28 mixed cultural and natural World Heritage Sites.

Tongariro National Park was the fourth national park established in the world. The active volcanic mountains Ruapehu, Ngauruhoe, and Tongariro are located in the centre of the park.

There are a number of Māori religious sites within the park and the summits of Tongariro, including Ngauruhoe and Ruapehu, are tapu (sacred). The park includes many towns around its boundary including Ohakune, Waiouru, Horopito, Pokaka, Erua, National Park Village, Whakapapa skifield and Turangi.

A crater lake is a lake that forms in a volcanic crater or caldera, such as a maar; less commonly and with lower association to the term a lake may form in an impact crater caused by a meteorite. Sometimes lakes which form inside calderas are called caldera lakes, but often this distinction is not made. Crater lakes covering active (fumarolic) volcanic vents are sometimes known as volcanic lakes, and the water within them is often acidic, saturated with volcanic gases, and cloudy with a strong greenish color. Lakes located in dormant or extinct volcanoes tend to have fresh water, and the water clarity in such lakes can be exceptional due to the lack of inflowing streams and sediment.