Mount Ruapehu
| Mount Ruapehu |
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Mount Ruapehu, or just Ruapehu, is an active stratovolcano at the southern end of the Taupo Volcanic Zone in New Zealand. It is 23 kilometres northeast of Ohakune and 40 kilometres southwest of the southern shore of Lake Taupo, within Tongariro National Park. The North Island's major skifields and only glaciers are on its slopes.
Ruapehu is one of the world's most active volcanoes[1]and the largest active volcano in New Zealand. It is the highest point in the North Island and includes three major peaks: Tahurangi (2,797 m), Te Heuheu (2,755 m) and Paretetaitonga (2,751 m). The deep, active crater is between the peaks and fills with a crater lake between major eruptions.
Volcanic activity
Ruapehu is largely composed of andesite and began erupting at least 250,000 years ago. In recorded history, major eruptions have been about 50 years apart,[1] in 1895, 1945 and 1995-1996. Minor eruptions are frequent, with at least 60 since 1945. Some of the minor eruptions in the 1970s generated small ash falls and lahars (mudflows) that damaged skifields.[2]
Between major eruptions, a warm acidic crater lake forms, fed by melting snow. Major eruptions may completely expel the lake water. Where a major eruption has deposited a tephra dam across the lake's outlet, the dam may collapse after the lake has refilled and risen above the level of its normal outlet, the outrush of water causing a large lahar.
1945 eruption and aftermath
The 1945 eruption emptied the crater lake and dammed the outlet with tephra. The crater slowly refilled with water, until on December 24 1953 the tephra dam collapsed causing a lahar in the Whangaehu River. The lahar 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 it while the lahar was in full flood. It was already known that the river had partially undermined one of the bridge piers and 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 and 6 of the carriages fell into the river.
1995-96 eruptions
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 nine 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 people to keep off the mountain, thus ending the ski season. The eruption cloud 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 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. 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. Authorities are currently planning for managing this event safely when it occurs.
2006 eruption
Ruapehu last erupted at 10.30pm on 4 October 2006. The small eruption created a volcanic earthquake of magnitude 2.8, sending a water plume 200 m into the air and 6-m waves crashing into the wall of the crater.[3]
2007 Lahar
After months of speculation and controversy, on 18 March 2007 the crater lake burst, sending a lahar down the mountain.[1]
Ski fields
Ruapehu has two commercial skifields, Whakapapa on the northern side and Turoa on the southern slope. They are the two largest ski fields in New Zealand, with Whakapapa the larger. The private Tukino field is 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, and elsewhere on the mountain. Alpine huts are 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 descended safely the next morning. Such rapidly changing conditions are typical of the weather on New Zealand mountains.
See also
Notes
- ^ a b New Zealand Department of Conservation. "Crater Lake". Retrieved 2006-10-23.
- ^ New Zealand Department of Conservation. "Central North Island Volcanoes". Retrieved 2006-10-23.
- ^ "Scientists confirm Mt Ruapehu eruption". Retrieved 2006-10-23.
External links
- The 1996 Ruapehu Eruption Images and Information from Michigan Technical University
- Volcanic Hazards at Ruapehu Volcano - from GNS Science
- Volcano Camera - Mt Ruapehu - hourly photographs from GeoNet
- Mt Ruapehu Crater Lake Lahar Threat Response from the Department of Conservation
- Ruapehu Guide, photos, links
- Mt Ruapehu - Crater Lake Status from Environment Waikato
- Peakware World Mountain Encyclopedia - Ruapehu