Geology
The volcanic massif, often referred to as simply Tongariro, has a height of 1,978 metres (6,490 ft). It first erupted 275,000 years ago. The volcano consists of at least 12 cones. Ngauruhoe, while often regarded as a separate mountain, is geologically a cone of Tongariro. It is also the most active vent, having erupted more than 70 times since 1839, the last episode in 1973 to 1975.
Activity has also been recorded at other vents in recent history. Te Māri Craters erupted in 2012, for the first time since 1897. Red Crater last erupted ash in 1926 and contains active fumaroles. There are many explosion craters on the massif; water has filled some of these to form the Blue Lake and the Emerald Lakes.
Andesitic eruptions tend to form steep stratovolcanoes with layers of both lava and tephra, including mountains such as Tongariro. The high altitude and severe alpine climate between March and October cause snowfall in the winter, and rain can freeze, causing verglass (with commercial ski-fields at neighbouring Mount Ruapehu), while in the mid to late summer, the mountains can be bare apart from odd patches of snow in south-facing gullies. Of all North Island regions, the Volcanic Plateau is closest to having a continental climate.
Read more about this topic: Mount Tongariro