Mt Ruapehu (2797m) is the North Island's highest mountain and one of the world’s most active volcanoes. One year-long eruption began in March 1945, spreading lava over Crater Lake and sending clouds of ash as far as Wellington. During the heavy ashfalls, hundreds of cases of ‘Ruapehu throat’ were reported. On Christmas Eve 1953, the crater-lake lip collapsed and an enormous lahar (volcanic mudflow) swept away everything in its path, including a railway bridge. A crowded train plunged into the river, killing 151 people, making it one of NZ’s worst tragedies.
Ruapehu also rumbled in 1969 and 1973, and significant eruptions occur with suspicious frequency. In 2007 a primary school teacher almost died when a rock was propelled through the roof of a trampers' shelter, crushing his leg.