Wednesday 8 August 2012

Eruption on Mount Tongariro.

On Monday 6 August 2012, at 11.50 pm local time (11.50 am GMT), an eruption occurred on the Te Māri Crater on Mount Tongariro on New Zealand's North Island, according to GNS Science. The eruption comprised of a steam plume which rose a kilometer into the air, carrying a considerable amount of rock and ash with it, with reports of boulders being thrown up to 1.5 km and ash falls across a large area east of the summit. There are no reports of any casualties, but people have been evacuated from the area around the volcano and several airports closed temporarily.

Steam Plume above Mount Tongariro. Hawke's Bay Regional Council.

The eruption was probably caused by a build up and release of high-pressure steam within the volcano, and now that the pressure has been released there is unlikely to be a repeat of the incident. However the heat source that created the storm may lead to further activity, particularly if it is an injection of new magma into the chamber beneath the volcano, which could potentially erupt as lava at the surface.

The volcano suffered a number of small Earth tremors in July, which may have been a sign of magma rising beneath the summit, though it had been quiet in the week running up to the eruption, which seems to have caught some people out, with the eruption widely reported as 'unpredicted'. This has also been reported as the first eruption in over a hundred years, or the first eruption since 1897, neither of which is true, the volcano having last erupted on 4 July 1977, when it produced a column of steam and ash that rose 900 m above the summit. Several other eruptions occurred in 1974 & 1975. The Te Māri Crater has not been active since the 1890s, but this cannot be seen as a separate volcano, and it is entirely possible that this eruption will be a prelude to eruptions from another crater.

An eruption on 19 February 1975 that produced a dense, ash-laden cloud and through blocks 20 m across hundreds of meters into the air. Ian Nairn/New Zealand Geological Survey/Smithsonian Global Volcanism Program.

Tongariro is a complex volcano with over a dozen craters, that has been erupting for over 275 000 years. Like all of New Zealand's volcanoes it is fed by the subduction of the Pacific Plate beneath the Australian. As the Pacific Plate sinks into the Earth's interior beneath New Zealand it is partially melted by the friction and heat of the planets interior. Some of the melted material then rises through the overlying Australian Plate, fueling the volcanoes of New Zealand.

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