Mount Ruapehu - WikiHQ

Severe weather incidents

Weather conditions can be changeable over the day, and mountain visitors are advised to be prepared and carry basic survival equipment. Severe weather has claimed several lives over the years, including a party of five NZ Army soldiers and one RNZN naval rating, caught in a week-long storm while undergoing winter survival training in 1990. The same storm also trapped an experienced Japanese mountaineer when the weather unexpectedly closed in on him, but he built a snow cave and sheltered in it until he was rescued days later. In 2008 extreme weather resulted in about 2000 visitors being evacuated from Whakapapa skifield, with cars being led down the mountain in groups of five. About 100 cars were left at the skifield overnight.

Geology

Ruapehu is a composite andesitic stratovolcano located at the southern end of the Taupō Volcanic Zone and forming part of the Tongariro Volcanic Centre. Volcanism at Ruapehu is caused by the subduction of the Pacific Plate under the Australian Plate at the Hikurangi Trough to the east of the North Island. Ruapehu has erupted from multiple craters over its lifetime, however, only one crater is presently active, a deep crater at the southern end of the summit plateau which is filled with hot, acidic water, dubbed Crater Lake (Te Wai ā-moe). The lake water currently covers separate north and central vents.

Ruapehu sits on a basement of Mesozoic greywacke overlain by a thin layer of sediments of the Wanganui Basin, composed of sands, silts, shell beds, and limestone. It has not been clearly established when Ruapehu first began erupting, only that eruptions began at least 250,000 years ago and possibly as early as 340,000 years ago. Ruapehu has been built in four distinct stages of relatively intense eruptive activity followed by periods of relative quiet. Each of these four stages of activity has left behind distinct rock formations, named the Te Herenga Formation (erupted 250,000–180,000 years ago), the Wahianoa Formation (erupted 160,000–115,000 years ago), the Mangawhero Formation (erupted 55,000–15,000 years ago), and the Whakapapa Formation (erupted 15,000–2,000 years ago). Activity is characterized by cyclic heating and cooling of the lake over periods of 6–12 months. Each heating cycle is marked by increased seismic activity under the crater and is accompanied by increased emission of volcanic gases, indicating that the vents under Crater Lake are open to gas escape. Subsequently, andesitic clasts found 100 km southwest of Ruapehu, near Whanganui, demonstrate that volcanism was likely present in the Ruapehu area 340,000 years ago.

Beginning approximately 55,000 years ago, a third phase of cone-building eruptions began, creating the Mangawhero Formation. This formation was erupted onto the eroded Wahianoa Formation in two phases: the first occurring 55,000–45,000 years ago and the second 30,000–15,000 years ago. The Mangawhero Formation can be found over most of modern Ruapehu, and it forms most of the mountain's high peaks as well as the Turoa skifield.</small>

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Lava flows that have been erupted from Ruapehu since the last glacial maximum are called the Whakapapa Formation. These flows all erupted between 15,000 and 2,000 years ago from a number of different craters on the summit of Ruapehu as well as from craters on the northern and southern flanks of the mountain.

Approximately 10,000 years ago, a series of major eruptions occurred, not just on Ruapehu, but also at the Tama Lakes between Ruapehu and Tongariro volcanoes. This period of intense eruptions is called the Pahoka-Mangamate event and is thought to have lasted between 200 and 400 years. On Ruapehu, lava was erupted from Saddle Cone—a flank crater on the northern slopes—and from another crater on the southern slopes. This southern crater erupted three times, and lava flows from this crater travelled nearly 14 km to the south. Accordingly, most of the cone and ring-plain is older than 10,000 years.

In recorded history, these eruptions have occurred about 50 years apart, in 1895 (lahar), 1945 and 1995–1996. A lava dome was observed in Crater Lake on 19 March but was destroyed in a series of explosive eruptions over the following week. A second, larger lava dome appeared in May, which continued to grow over the following months and had emptied Crater Lake of water by July.

After eruptions subsided in late December, Crater Lake slowly began refilling, with a "boiling lake" already filling the bottom of the crater by mid-January.

A larger phreatic eruption occurred at 3:59 a.m. on 24 April 1975, blasting rocks up to 1.6 km northwest of the crater, against the wind, and depositing ash more than 100 km to the southeast. Nine minutes of seismic activity preceded the eruption, but crater dilation had been measured two weeks earlier. Nearly half of the water in Crater Lake was erupted into the air, which subsequently rained down onto the summit, generating lahars down several river valleys. Lahars which travelled down the Whakapapa and Manganui o te Ao rivers entered the Whanganui River and poisoned it, which affected much of the aquatic life downstream. Additionally, the lahars damaged ski installations on the Whakapapa ski field, several bridges and hydroelectric tunnel intakes, but no loss of life occurred.

Three days later, on the morning of 27 April, Ruapehu erupted again. A series of five eruptions occurred between 7:10 a.m. and 10:18 a.m., sending surges of mud, rocks, and ash northwards across the summit plateau and producing eruption columns up to 500 m high. A minor eruption occurred on 26 April, which sent waves against the walls of the crater and damaged some monitoring equipment there. A second eruption on 29 June destroyed the equipment and produced a lahar. Chemical analysis showed that magma was interacting with water under the lake.

thumb|300px|Crater Lake and Tahurangi, the highest peak (top right) in 2016. The 1996 tephra dam is the bluish dark area at lake edge directly below Tahurangi.

Following this, activity died off until 15 June 1996 when renewed seismic activity was recorded. This was followed by eruptions on 17 and 18 June which once again emptied the partially refilled Crater Lake of water. Strombolian eruptions occurred on 27 June and throughout July and August, producing eruption columns more than 10 km high and shooting rocks 1.4 km from the crater. Ash in the Tongariro River also damaged the intake turbines at the Rangipo power station, and ash clouds caused airport closures as far away as Auckland and Wellington. The eruptions also caused closures to the three ski fields on the mountain, costing the region an estimated $100 million in lost revenue.

Both the 1995 and 1996 eruptions were filmed and streamed to the internet via a custom-built 'volcano-cam', possibly the first such camera in the world. The website hosting the feed during the 1996 eruption received up to 4000 hits an hour.

Lahar danger

After the 1996 eruption it was recognised that a catastrophic lahar could again occur when Crater Lake burst the volcanic ash dam blocking the lake outlet as it did in 1953. In 1997, the government proposed digging a trench through the blockage in the wall of Crater Lake, but this was plan was opposed by conservation groups and Māori. A Ngāti Rangi spokesman noted that the mountain was sacred, and said: "as far as we are concerned if these things [lahars] do happen well we step aside. Let them go past".

Other plans considered were building a stop bank on the Desert Road, or creating an early-warning system, which would be much more expensive than digging a trench. In 2001, the Eastern Ruapehu Lahar Alarm and Warning System (ERLAWS) system was installed on the mountain to detect a crater wall collapse and alert the relevant authorities. It began operating in 2002. The lake gradually filled with snowmelt and had reached the level of the hard rock rim by January 2005. The lahar finally occurred on 18 March 2007 (see below).

2006 and 2007 activity

Ruapehu erupted at 10:24 p.m. on 4 October 2006. The small eruption was marked by a magnitude 2.9 volcanic earthquake and sent waves 4– tall crashing into the wall of the crater. No ash was erupted into the atmosphere, and the eruption is presumed to have occurred entirely underwater.

thumb|300px|Fresh lahar channels scar Ruapehu's eastern slopes, 2007.

At 11:22 a.m. 18 March 2007, the tephra dam which had been holding back Crater Lake burst, sending a lahar down the mountain. An estimated 1.9–3.8 million cubic metres of mud, rock, and water travelled down the Whangaehu river.

At 8:16 p.m. on 25 September 2007, volcanic tremor was detected underneath Ruapehu, which was followed at 8:26 p.m. by an explosive surtseyan eruption. The explosive phase of the eruption lasted for less than a minute and blasted ash, mud, and rocks northward, reaching to about 2 km from Crater Lake. Two climbers were caught in the eruption at Dome Shelter, an alpine hut approximately 600 m from the crater, when the hut was struck by the surge.

The eruption initiated lahars down the Whangaehu valley and the Whakapapa skifield. ERLAWS detected the lahars in the Whangaehu valley. A snow groomer on the Whakapapa skifield narrowly avoided being caught in the lahar there. Since then, Crater Lake has continued its regular cycle of heating and increased gas emissions, although with periods of sustained high temperatures that occurred in 2011, 2016 and 2019.

Since 2019, seismic unrest and volcanic activity have decreased. In 2020, the temperature of the crater lake had risen to . In May of 2022, lake temperatures peaked at . Between May 2022 and September 2025, lake temperatures have steadily decreased, however, substantial amounts of volcanic gas continue to be released. This demonstrates that an open pathway persists between the magma source and the lake, allowing gas to escape and reducing the likelihood of pressure buildup beneath the crater. Scientists interpret this behavior as shorter durations of volcanic gas entering the lake. Other monitoring indicators—including earthquakes, tremor, gas emissions, and lake chemistry—are all within normal ranges.

Eruptions at Ruapehu are expected to continue as they have for the past 2,000 years, with frequent minor eruptions and more significant events every 20–30 years, although the possibility of larger events like the Pahoka-Mangamate event cannot be ruled out. An eruption warning system operates in the ski field to warn skiers in the event of another eruption. Lahars also represent a significant hazard to surrounding river valleys, particularly the Whangaehu River, which is crossed by national highways, the North Island Main Trunk railway line, and electricity transmission lines.

GNS Science continuously monitors Ruapehu using a network of seismographs, GPS stations, microphones and webcams. Chemical analysis of the water in Crater Lake is regularly undertaken along with airborne gas measurements. Live data can be viewed on the GeoNet website.

Recreational

The mountain, as part of Tongariro National Park is host to a wide range of recreational activities.

Skiing

Since the first ski field developments in 1923, Ruapehu has had three ski areas developed, Whakapapa on the north-western side, Tūroa on the south western slopes, and a club Tukino field on the east of the mountain. The commercial developments have not been a consistent success, with at least two business failures by 2023. While as of 2001, Mount Ruapehu had the largest total ski area in New Zealand, developments in the South Island may see by 2025 the establishment there of the largest single commercial ski area in New Zealand. A 60-year concession for commercial ski field operation was granted to the then operator of the Whakapapa ski field, in 2015. After the operator went into receivership in 2023 a new operator has expressed interest in taking over the Whakapapa concession. From April 2024, Tūroa operated by Pure Tūroa Limited has a limited ten year concession.

Winter access to the mountain, car parks and ski fields has restrictions.

Climbing and walking

There are multiple walking tracks and routes on the mountain's slopes. Alpine huts are provided for trampers and climbers. These are mainly owned by private clubs. Blyth Hut, Lupton Hut (private), Mangaehuehu Hut, Mangaturuturu Hut, Rangipo Hut, and Whangaehu Hut on the mountain are potentially listed as available for use by the Department of Conservation. Campsites also exist on the slopes of the mountain.

Waihohonu Hut

thumb|Waihohonu Hut

Waihohonu Hut is a historic cabin located in the Tongariro National Park. The cabin was constructed in 1904 and is now the oldest extant mountain hut in New Zealand. It was registered as a category 1 historic building with Heritage New Zealand in 1993. It was used early in its history as a stop over for stage coaches.

Ethel Birchclimbed the mountain in 1881 the first European woman to do so

References

External links

The 1996 Ruapehu Eruption Images and Information from Michigan Technological University
Volcanic Hazards at Ruapehu Volcano – from GNS Science
Volcano Camera – Mt Ruapehu – hourly photographs from GeoNet
2012 Warning from the Department of Conservation
Ruapehu Eruption resources blog continuous since 1995 with new activity reported as it happens
GeoNet New Zealand Alert Bulletins