Mount Ruapehu (Māori: [ˈɾʉaˌpɛhʉ]; English ) is an active stratovolcano at the southern end of the Taupō Volcanic Zone and North Island volcanic plateau in New Zealand. It is 23 km (14 mi) northeast of Ohakune and 23 km (14 mi) southwest of the southern shore of Lake Taupō, within Tongariro National Park. The North Island's major ski resorts and only glaciers are on its slopes. Ruapehu, the largest active volcano in New Zealand, has the highest point in the North Island and has 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 water between major eruptions, being known as Crater Lake (Māori: Te Wai ā-moe). The name Ruapehu means "pit of noise" or "exploding pit" in Māori.
Geography Ruapehu is located in the centre of the North Island of New Zealand, 23 km (14 mi) northeast of Ohakune, New Zealand, and 23 km (14 mi) southwest of the southern shore of Lake Taupō, within Tongariro National Park. Ruapehu is the largest and southernmost volcano in the national park, with an estimated volume of 110 km3. The volcano is surrounded by a ring plain of volcanic material, made from lahar deposits, ash fall, and landslide debris. There are three access routes to Ruapehu, and each access route leads to one of the three skifields that are found on its slopes. State Highway 48 leads to Whakapapa Village at the base of the mountain, and from there an access road leads up the mountain to Iwikau Village at the base of the Whakapapa skifield on the northwestern bumpy hilly slopes. An access road from Ohakune leads to Turoa skifield on the southwestern slopes, and a four-wheel drive track leads from the Desert Road (State Highway 1) to the Tukino skifield on the eastern slopes. Ruapehu's active crater, dubbed Crater Lake (Te Wai ā-moe), is situated at the southern end of the Summit Plateau, and as the name suggests, is filled with a warm, acidic lake. The lake's outlet is at the head of the Whangaehu Valley, where the Whangaehu River arises. The Whangaehu River is notorious for destructive lahars caused by Ruapehu's eruptions. In historic times, eruptions have built tephra dams across the outlet on several occasions, most recently in 1945 and 1996. These dams failed in 1953 and 2007 respectively, causing an outburst of Crater Lake each time, which sent destructive lahars down the river. The 1953 lahar was the cause of the Tangiwai disaster, a railway accident in which 151 people died. Even larger lahars occurred in 1862 and 1895.
Glaciers A total of 18 glaciers have been recognised on Ruapehu, of which six are named. Two glaciers are found in the active crater: one on the north side of the crater under Paretetaitonga Peak and another one to the south, and these are New Zealand's only crater glaciers. Most of the ice on Ruapehu is contained in only three of its glaciers: the Whangaehu, Summit Plateau, and Mangatoetoenui glaciers. The Summit Plateau glacier is not a glacier in the true sense, but rather an ice field that fills an extinct volcanic crater, and the ice there reaches more than 130 m thick. The Whangaehu glacier feeds the Whangaehu River, and the Mangatoetoenui glacier is one of the principal sources of the Waikato River, which arises as a series of streams on Ruapehu's eastern slopes. On the western side of the mountain, many of the streams that arise there, such as the Whakapapa and Manganui o te Ao rivers, feed the Whanganui River.
Ruapehu's glaciers are situated at the northern limit for the formation of permanent ice in New Zealand, and thus they are extremely sensitive to changes in climate. Surveys of the glaciers undertaken since 1955 have found that the glaciers have all been thinning and retreating, with the exception of the northern crater glacier, which thickened and lengthened after the 1953 outburst of Crater Lake lowered the lake water level.
Climate Ruapehu has a polar tundra climate (Köppen: ET) on the upper slopes, with average temperatures ranging from −4 to 15 °C (25 to 59 °F) in summer and −7 to 7 °C (19 to 45 °F) in winter, depending on elevation and cloudiness. On the lower slopes, Ruapehu has a subpolar oceanic climate (Köppen: Cfc). The prevalent wind direction in the region is westerly or northwesterly, and gale force conditions (i.e. wind speeds higher than 33 kn (61 km/h)) are common on the mountain. Rainfall is higher on the western flanks of Ruapehu than the eastern flanks due to the rain shadow effect. Whakapapa Village receives an average of 2,200 mm of rain per year, whereas the Rangipo Desert to the east of Ruapehu receives slightly more than 1,500 mm of rain annually. Snow falls on average as low as 1,500 m elevation.
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. Extreme weather conditions have caused visitors to be trapped on the mountain in the past. In 2003, about 350 visitors to Whakapapa skifield and 70 staff had to stay overnight in various lodges at Iwikau village (small village at the top of mountain road) after a snow storm made the road too dangerous to descend. 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
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