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Wairakei Research Centre

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Wairakei

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New Zealand

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VOLCANIC ALERT BULLETIN: Tong – 12/23

1230pm Monday, 27 August 2012

Tongariro Volcano Volcanic Alert Level 1

Aviation Colour Code: Yellow

Revised Eruption Phenomena Map for Te Maari, Tongariro It has been two weeks since the issue of a first phenomena map for the current volcano unrest period in the Te Maari area of Tongariro. As stated with that first release, the map will be revised as further scientific data, modelling and interpretation become available. The science advisory group for this eruption, convened by GNS Science, have agreed that the volcanic phenomena map should now be updated as the result of further discussion and scientific input. In addition to GNS scientists, Department of Conservation, Massey, Canterbury, Victoria, Otago and Waikato universities have all provided input. The following updates have been made to the phenomena map. This replaces all previous map versions: (1) The 3km summit hazard zone is now based around the August 6th eruption source. Eruptions from other existing vents, or the generation of new vents, are now considered unlikely without any further precursory activity (not as yet detected). The geological and historical record, past magma geochemistry and current monitoring data were all considered along with the existing vent locations and any other potential source-area(s). (2) The map title has been updated to reflect the narrowing of the summit hazard zone, now focussed on the Te Maari area specifically. (3) A cartographic change to make the map easier to read. All of summit hazard zone has been shaded red, with the flow hazard zone in yellow, only shown beyond the fringes of the red. Text on the map has been modified to explain some flow hazard exists in the summit hazard zone. (4) The blue line representing the stream catchment currently containing a debris flow deposit has been thickened with explanation text added noting that there is a risk of remobilisation of debris flow deposits there. Other stream lines within the flow hazard zone have also been thickened somewhat and the legend now explains that these are all streams with some elevated flow hazard.

(5) The previous active volcanic vents on Tongariro have been colour coded as being active in the past 27,000 years (red open circle), or past 500 years (solid red circle) to help with highlighting eruptions in the most active recent vents. Taupo Civil Defence says the map update reinforces the advice for motorists not to stop along SH46. Debris from the recent eruption is blocking streams, meaning a significant volume of water has built up at various places. Taupo Civil Defence emergency manager Phil Parker said: "Signs erected by NZTA are in place reminding people not to stop anywhere on SH46. Additional warning signage is also in place near a culvert on the highway, as this would carry the majority of any debris flows should the main debris dam collapse. NZTA has contractors monitoring the area extremely closely." Mr Parker said devices to monitor movement in the main debris dam have been installed and are being tested by Massey University. “Further work is planned to improve our understanding of the debris dams and how far material might go if the largest one collapses. At this stage, the debris would not be expected to affect any buildings but could affect SH46 within about 15 minutes of a collapse. We will review our advice – and what we plan to do - once we have the results of further analysis.” Contacts: GNS Science; Dr Gill Jolly, Head of Volcanology Department Dr Graham Leonard, Volcanologist Emergency management and Civil Defence; Phil Parker, Taupo District Council Stephen Ward, Waikato Regional Council