VOLCANIC AND THERMAL ACTIVITY
New Zealand's active volcanoes are confined to the Taupo Volcanic Zone, a belt which extends from Tongariro National Park to White Island. Ruapehu (9,175 ft) is the highest peak in the North Island and carries its only permanent snowfield, within which is a hot crater lake. Since 1889 more than 12 steam eruptions and four ash eruptions have been recorded. That of 1945 began with the appearance of a lava dome which displaced the lake, after which intermittent eruptions continued until 1947, leaving a deep crater. The lake had previously overflowed into the Whangaehu River through a tunnel beneath the surrounding ice, but it refilled to a higher level because of a barrier of scoria and debris from the eruption. On 24 December 1953 this carried away, precipitating a flood or lahar down the Whangaehu, which destroyed the railway bridge at Tangiwai and engulfed an express train with the loss of 151 lives. Smaller floods occurred previously in 1861, 1895, 1889, and 1925.
At the north-west foot of Ruapehu are a tourist hotel, the Chateau Tongariro, and numerous accommodation buildings erected by tramping and ski clubs. A ski lift takes passengers to the foot of the Whakapapa Glacier.
Ngauruhoe (7,504 ft) is a subsidiary cone of Tongariro. There have been more than 60 eruptions since it was first seen by Europeans in 1839; there was a lava flow in 1870, another in 1949, and 17 in 1954. Some of these were preceded by hot avalanches. It has a perfectly shaped cone which is 3,000 ft high, with a truncated summit a quarter of a mile across.
Tongariro (6,458 ft) is a large multiple volcano with several craters within a summit 3 miles in diameter. Four of these have erupted within historic time, the largest eruption being that of Te Mari in 1896.
The above three volcanoes and their surroundings were constituted as Tongariro National Park in 1894 following a gift to the New Zealand Government of 6,500 acres in 1887 by Te Heuheu Horonuku. Ngauruhoe was first climbed by J. C. Bidwill in 1839, and Ruapehu crater lake was first seen by J. P. Maxwell and G. Beetham in 1879.
On 10 June 1886 Mount Tarawera suddenly erupted violently. A line of craters was blasted across its three domes, ejecting blocks, scoria, and ash over a wide area, the noise of the detonations being heard in Auckland. The eruption extended progressively along the line into Rotomahana, where steam-blast eruptions destroyed the Pink and White Terraces and showered debris over the surrounding country. About 100 people lost their lives. It is now known that Tarawera had lain dormant for about 900 years since a previous eruption had spread pumice around.
White Island, in the Bay of Plenty, is an active volcano on the summit of a large submarine volcanic edifice about 15 miles in diameter. It has been continuously active since first seen and named by Captain Cook in 1769. Several craters emit large quantities of steam and, occasionally, ash. In 1914 a landslide from the crater rim produced a mud flow which destroyed a number of buildings and killed the sulphur workers on the island.
In addition to the active volcanoes, there is geological and radiocarbon-dating evidence that the following districts have experienced volcanic activity within the past few hundreds or thousands of years, and further eruptions there may be expected. In the Auckland district 63 points of eruption have been recognised, and the youngest of these, Rangitoto, is only about 750 years old. They include basaltic scoria cones, flows, tuff rings, and maars. Basaltic cones of age comparable with some of the younger Auckland ones are found in the Kaikohe – Bay of Islands and Whangarei districts. In Taranaki the last eruption from Mount Egmont occurred about 350 years ago.
The most violent of all the eruptions of the past few thousand years took place at Taupo about 1,830 years ago, when pumice was erupted over several thousand square miles. Previous eruptions have occurred in the same locality. Other pumice eruptions have occurred in the Maroa and Okataina volcanic centres, the latter including Tarawera. These places remain as potential danger spots.