NEWS

Volcanic Alert Bulletin: Tongariro Alert Level Remains at Level 2

Thursday 22 November 2012, 3:38PM
By Wairoa District Council
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Activity at Tongariro has been at low level since yesterday’s eruption. The Volcanic Alert Level remains at 2 and the Aviation Colour Code at Orange.

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 min, with an ash column and plume being ejected 3-4 km above the Upper Te Maari crater.

The eruption was recorded by GeoNet’s webcam and a video of the eruption can be found on the GeoNetNZ channel at the following URL:

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

Background:

The point of origin of yesterday’s eruption was similar to that from August 6, 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 meters 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 collapsing 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 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 immeditately 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.