Mount Ruapehu, or just Ruapehu, is an active stratovolcano, situated at the southern end of the Taupo Volcanic Zone. It is 23 kilometres northeast of the town of Ohakune and 40 kilometres southwest of the southern shore of Lake Taupo.

Ruapehu is the highest point on the North Island of New Zealand. Ruapehu contains three major peaks: Tahurangi (2,797m), Te Heuheu (2,755m) and Paretetaitonga (2,751m). Ruapehu is frequently active, and is one of the largest active volcanoes in New Zealand. It is part of Tongariro National Park.

The name Ruapehu is Maori for pit of noise or exploding pit.

Volcanic Activity

The volcano has erupted in 1861, 1895, 1903, 1945, 1969, 1971, 1975, 1988, 1995 and 1996.

Between eruptions, a crater lake forms from melting snow. Where an eruption has deposited a tephra dam across the lake's outlet, the dam may collapse after the lake has risen above the level of its normal outlet, causing a mud flow known as a lahar.

A lahar on December 24, 1953 caused the Tangiwai disaster, with the loss of 151 lives, when the Tangiwai railway bridge, across the Whangaehu river, collapsed just before an express train crossed the bridge while the lahar was in full flood. It was already known that the river had partially undermined one of the bridge piers and it is believed that the lahar finished the job, causing the bridge to collapse. Although warned of the collapsed bridge, the train driver was unable to stop the train in time.

Major Volcanoes of New Zealand

Spectacular eruptions occurred during 1995 and 1996. Ruapehu had been showing signs of increased activity since late November 1994, with elevated Crater Lake temperatures and a series of eruptions that increased in intensity over about 9 months. Several lahar were observed, both in the Whangaehu river and other areas of the mountain between September 18 and September 25 1995, indicating the Crater lake was being emptied by the eruptions. The Department of Conservation immediately issued hazard warnings and advised all people to keep off the mountain. This eruption also ended the ski season on the mountain. The eruption cloud also disrupted air travel, occasionally closing airports and the central north island airspace. Episodic eruptions continued until the end of November 1995.

Within hours of a major eruption during the night being reported on September 25 1995, news media were trying to get live video of the eruption and amateur photographers had published eruption images on the World Wide Web. A webcamera, dubbed the world's first "VolcanoCam", was also set up. Since then Ruapehu has been monitored by at least one and sometimes several volcanocams.

Another, smaller, eruption phase began on the morning of June 17, 1996, again the mountain was closed to visitors and the skifields were closed for the season, this time before they even opened.

After the 1996 eruption, it was recognised that a catastrophic lahar could again occur when the crater lake burst the volcanic ash dam blocking the lake outlet. This is the same mechanism that caused the 1953 lahar. The lake has been gradually filling with snowmelt since 1996 and by January 2005 the lake had reached the level of the hard rock rim. As the water level continues to rise, so does the likelihood of the lahar being triggered. The lahar is unlikely to occur prior to the 2005/06 summer. Authorities are currently planning for managing this event safely when it occurs.

Ski Fields

Ruapehu has two commercial skifields, Whakapapa on the northern side and Turoa on the southern slope. The private Tukino field is located on the east of the mountain. The season is generally from July to October but depends on snow and weather conditions. Both skifields are accessible by car and chairlifts, with beginners to advanced skiing slopes. Limited accommodation and refreshments are available at Top O'the Bruce — the car park at the top of Bruce Road — and at the entry to Whakapapa, as well as elsewhere on the mountain. Alpine huts are also provided for trampers and climbers.

Weather

Weather conditions can be changeable over the day, and mountain visitors are advised to be prepared and carry basic survival equipment. Although severe weather is unusual and generally forecast, it has claimed several lives over the years, including a party of soldiers undergoing winter survival training. During the same storm a Japanese tourist was trapped in a snow cave for several days after he made the shelter when the weather unexpectedly closed in on him. On July 5, 2003 about 350 skiers and 70 skifield staff were trapped on the mountain overnight at Top O'the Bruce when a sudden snow storm blew up and within a few minutes made the access road too dangerous to descend. They spent the night in relative comfort and all safely descended the next morning. Such rapidly changing conditions are typical of the weather on New Zealand mountains.

External links

• The 1996 Ruapehu Eruption (http://www.geo.mtu.edu/volcanoes/new.zealand/ruapehu/) Images and Information from Michigan Technical University (http://www.mtu.edu/)
• Volcanic Hazards at Ruapehu Volcano (http://www.gns.cri.nz/what/earthact/volcanoes/nzvolcanoes/ruabookprint.htm) - from the Institute of Geological and Nuclear Sciences Limited (http://www.gns.cri.nz/)
• Volcano Camera - Mt Ruapehu (http://www.geonet.org.nz/ruapehu.html) - hourly photographs from GeoNet (http://www.geonet.org.nz/)
• Mt Ruapehu Crater Lake Lahar Threat Response (http://www.doc.govt.nz/Whats-New/Issues/Mt-Ruapehu-Crater-Lake/index.asp) from the Department of Conservation (http://www.doc.govt.nz/)
• Mt Ruapehu - Crater Lake Status (http://www.ew.govt.nz/enviroinfo/hazards/naturalhazards/volcano/craterlake.htm) from Environment Waikato (http://www.ew.govt.nz/)
• Peakware World Mountain Encyclopedia - Ruapehu (http://www.peakware.com/encyclopedia/peaks/ruapehu.htm)