Unique emerald lake in the crater of an extinct volcano Ruapehu can be found in Tongariro National Park, New Zealand. Following Ruapehu’s eruptions in 1995, a layer of unconsolidated material called tephra formed a dam on the crater rim preventing the natural gradual flow of water out of the lake. The lake breached the dam in mid 2007 creating a lahar. The event was predicted, and well planned for, so there were no major consequences. In some years when the acicidy levels in the lake are low it is possible to “bath” in the crater lake. Though this is unadvisable as Mt Ruapehu is a active volcano which erupts on average every 10-20 years.