Tongariro's Te Māri craters erupted in November 2012, blasting ash and steam 2km into the air. Photo / Supplied
Tongariro's Te Māri craters erupted in November 2012, blasting ash and steam 2km into the air. Photo / Supplied
Tongariro National Park has three volcanoes and one of them - Ruapehu - is second only to Whakaari/White Island for eruption danger.
There will always be some volcanic risk for people using the park, Conservation Department (DOC) Central North Island director of operations Damian Coutts said. He has the powerto close part or all of the park if risk level rises.
Tongariro National Park has a volcanologist and public safety ranger as part of its team.
Whakaari/White Island and Ruapehu have been responsible for most of GeoNet's volcanic alert bulletins over the past four years.
Ruapehu is usually on volcanic alert level (VAL) 1, which signifies minor unrest.
Whakaari/White Island erupted unexpectedly at VAL 2 (moderate to heightened unrest) on December 9. There were 47 people ashore at the time. Some were killed and others badly burned.
This disaster may prompt more safety precautions, Coutts said, but there are already robust procedures in place for Tongariro National Park.
People are advised not to enter the crater basin at Ruapehu's summit at all. If VAL 1 rises toward 2 they are advised not to enter its summit hazard zone. When VAL 2 (moderate to heightened unrest with increased likelihood of an eruption) is reached, the summit hazard zone is closed.
Ruapehu eruptions can cause lahars onto parts of the Whakapapa ski area. When they happen, sirens sound and voice messages warn skiers to leave the valleys for higher ground.
The alarm system is tested weekly, and also during the winter in a combined exercise with GNS and ski operator RAL.
Ruapehu had major eruptions in 1995 and 1996, and it has had at least 60 minor eruptions since 1945. In 2007, one of the minor eruptions critically injured climber William Pike, who was in the crater's Dome Shelter. Pike's leg was crushed by debris and had to be amputated below the knee. He has since returned many times to Ruapehu.
When the Tongariro Alpine Crossing is closed there are warning signs at its approaches. Photo / Supplied
The Ngauruhoe and Tongariro volcanoes are usually at VAL 0 (no volcanic unrest). When they start heading toward VAL 1, road signs are activated at approaches to the Tongariro Alpine Crossing and stakeholders meet.
If the alert level rises to 1 or 2, the whole crossing is closed. Volcanic alert levels 3, 4 and 5 are for minor, moderate and major eruptions.
The Te Māri Craters on Mt Tongariro erupted twice in 2012, in August and November. The eruptions damaged Ketetahi Hut and the Tongariro Alpine Crossing track but nobody was hurt.
After Whakaari and Ruapehu, the volcano in the northern Kermadec Islands is probably New Zealand's most active. It erupted suddenly in March 2006, killing a DOC observer.
