Volcanic Alert Bulletin TON-2012/30 - Tongariro Volcano

22 November 2012, 11:45 am - Eruption update: activity decreased at Tongariro but risk remains high; Volcanic Alert Level remains at Level 2; Aviation Colour Code remains Orange

Activity at Tongariro has been at low level since yesterday’s eruption.

There remains a significant probability of sudden eruption within the next week.

After reviewing monitoring data, videos and images for yesterday's eruption at Tongariro, GNS Science confirms that the eruption lasted approx 5 minutes, with an ash column and plume being ejected 3-4 km above the Upper Te Maari crater.

An inspection flight will be made later today and GNS Science continues to closely monitor the situation.

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Watch the eruption recorded on GeoNet’s webcam

Background

The point of origin of yesterday’s eruption was similar to that from 6 August, 2012. During yesterday’s eruption, two small pyroclastic density currents were produced at the base of the column, to the West and North of the crater, and reached a limited distance of a few hundred metres downslope. These pyroclastic density currents are a mixture of ash, volcanic gas and atmospheric air flowing horizontally and being driven by gravity. Scientists believe that these were produced by part of the ash column not being energetic enough to rise, causing it to collapse at the base and flow downhill. There is no evidence at this stage of big blocks having been ejected far from the crater during the eruption.

From the preliminary examination of ash, GNS Science volcanologist Michael Rosenberg reported that “we haven't found any evidence yet of magma having reached the surface during the eruption”. More ash sampling and analyses by New Zealand volcanologists are planned or already underway.

There was no observed warning immediately prior to yesterday’s eruption. Future eruptions could also occur with little or no warning.

Aviation Colour Codes are based on four colours and are intended for quick reference only in the international civil aviation community. Code Orange indicates that a volcanic eruption is underway but with little or no ash being produced.

The Volcanic Alert Level ranges from 0 to 5 and defines the current status at a volcano. Level 2 indicates that a minor eruption has occurred.

Brad Scott, Nico Fournier
Volcanologists

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