Tongariro (6,458 ft), after which Tongariro National Park is named, is a truncated multiple volcano 9 miles long and 5 miles wide at its base with a summit 5 miles long and 2 miles wide. It is a multiple volcano in that the broad summit contains a considerable number of small craters including North Crater, South Crater, Central Crater, West Crater, Red Crater, Te Mari Craters, and Oturere Crater. It appears likely that these are later centres of activity within the rim of the remains of an earlier multiple volcano disrupted by explosion and collapse. A reconstruction of the form of the old volcano suggests that there were four craters forming an elongated volcano aligned north-west. On the northern slopes of Tongariro are a number of small explosion craters. Since 1840 there have been eruptions from three centres on Tongariro. Red Crater erupted ash in 1855 and steam in 1859. Variations of considerable extent in steam emissions, still continuing, have been reported. Te Mari consists of two craters. The lower, called Sulphur Lagoon, is filled with water and, according to the Maoris, has been frequently active in the past. The upper, formed during an eruption in 1869, emitted ash up to 1896 but since then its only activity has been fumarolic. A lava flow was erupted from the upper crater, probably in the 1880s.
To the west of Te Mari and somewhat lower (4,500 ft) is an area of fumaroles and hot springs, Ketetahi. Although Sir George Grey claimed to have reached the summit of Tongariro on 31 December 1866, it was probably Ngauruhoe that he climbed, seeing nothing but mist. The first definite ascent was made by Sir James Hector on 23 November 1867. Earlier attempts by travellers to climb the mountain were frustrated by the Maoris who regarded it as tapu.