Phreatic explosion at Ruapehu in 1992. Photo by Christian Treber . Mt. Ruapehu is a stratovolcano on the North Island of New Zealand. It has erupted about 50 times since 1861. At the top of the volcano there is an acidic crater lake.
Most eruptions are phreatic , involving steam explosions caused by the contact of lava and water.
The most recent major phreatic eruption was in 1975. A ground inspection on 17 September at the Ruapehu Volcano discovered an actively convecting lake at 58 degrees C with sulfur slicks. Steam plumes were evident and thought to be due to the cool weather and a hot lake emitting steam. Between 21-26 August, elevated tremor culminated in a series of volcanic earthquakes on 26 August. No eruptions occurred.