Tongariro Volcano Alert Level Raised 20/7/12

Jul 20 2012, 1:30 pm - Tongariro Volcano

Volcanic Alert Bulletin TON-2012/01 - Earthquake activity, Mount Tongariro: Alert Level raised from Level 0 to Level 1; Aviation Colour Code changed to Yellow

Small volcanic earthquakes have been recorded beneath Mount Tongariro. The sequence started on July 13, but soon declined, restarting on July 18 and increasing in number on July 19 and 20. These indicate unrest at Tongariro and give reason to change the Volcanic Alert Level to Level 1 and the Aviation Colour Code to Yellow.

As part of our routine monitoring of seismic activity we have recorded several volcanic earthquakes at Mount Tongariro since July 13. These earthquakes are small (magnitudes <2.5) and have only been well recorded by a few of the seismometers in our permanent network. The earthquakes cluster in a zone between Emerald Crater and the Te Māri craters at 2-7km depth.

To better understand the significance of these earthquakes we are planning to:

• deploy portable seismic recorders around the epicentres of the earthquakes;

• conduct sampling of selected hot springs, crater lakes and fumaroles in the area.

Our historic seismic data has shown that these small volcanic earthquakes are common at Tongariro, but usually only occur at an average rate of 2 per year. We have recorded more than 20 since July 13. Seismic activity indicating unrest was last detected at Tongariro during 2001. Our routine volcano monitoring also includes the chemistry of the lakes, springs and fumaroles on Tongariro. These were last sampled in May 2012. The samples collected in May show no anomalies.

Mount Tongariro is a volcanic complex that lies to the north of Ngauruhoe. It consists of numerous craters and vents. Te Māri craters lie about two kilometres east of Ketetahi hot springs on the north side of Mount Tongariro. The Te Māri craters are the last craters to be active on Tongariro. Ash eruptions have been recorded from Tongariro from 1855 to 1897, as well as unconfirmed activity in 1926-27.

Volcano Alert Level has changed from 0 to 1
Aviation Colour Code has changed from Green to Yellow

GNS Science volcanologists are monitoring the unrest and further information will be released as necessary.

Brad Scott
Volcanologist

ENDS

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