Volcanic Alert Bulletin TON-2012/34 - Tongariro Volcano

Published: Mon Nov 26 2012 2:30 PM

Volcanic Alert BulletinTON-2012/34
Mon Nov 26 2012 2:30 PM; Tongariro Volcano
Volcanic Alert Level remains at 1
Aviation Colour Code remains at Yellow

No further volcanic activity has occurred since the eruption on Wednesday. Gas flux has decreased and seismic activity remains low. GNS Science continues to closely monitor the situation.

GNS volcanologist Brad Scott said; “GNS Science has now lowered the Volcanic Alert Level from Level 2 to Level 1. This is based on the lack of further eruptions, no volcanic ash in the plume, decrease in gas output and continuing minor seismic activity. Conditions are now similar to before the November 21 eruption. The Aviation Colour Code remains at Yellow”.

While we were able to recognise the onset of the state of unrest at Te Maari, we cannot recognise useful precursors to eruptions like last week. Over the next week, the scenario considered most likely is that there may be further eruptions and these could occur with no warning.

Despite the reduced gas output a gas odour can expected downwind from Tongariro.

Background

GNS Science usually measures volcanic gas output from a plane. Gas sensors installed inside the aircraft can detect and quantify the amount of Carbon Dioxide (CO2 ), Sulphur Dioxide (SO2) and Hydrogen Sulphide (H2S). Successful gas flights are dependent on suitable weather conditions. Such conditions are often not very favourable at Tongariro. The Sulphur Dioxide (SO2) sensors can be operated from a vehicle driving along a road beneath the plume, but we do not obtain such a complete data set as flying. Yesterday’s Sulphur Dioxide (SO2) measurements were vehicle based.

Examination of the ash confirms there are small amounts of fresh volcanic glass in the eruption deposit, being consistent with the inferred presence of molten material at shallow depth below Te Maari. This is consistent with other observations from the August eruption and observations since then like the gas flux. We do not see evidence for substantial recharge of the system beneath the Upper Te Maari crater.

GNS Science uses a range of tools to monitor volcanoes. Seismometers record earthquakes, GPS stations record ground swelling. Acoustics sensors record air-waves such as those produced by an eruption. A new acoustic sensor was added at on Tongariro on Friday.

The Volcanic Alert Level ranges from 0 to 5 and defines the current status at a volcano. Level 1 indicates volcanic unrest, with departures from background levels.

Aviation Colour Codes are based on four colours and are intended for quick reference only in the international civil aviation community. Code Yellow indicates that volcanic activity has decreased significantly but continues to be closely monitored.

Brad Scott, Nico Fournier Volcanologists