Volcanic Alert Bulletin: NGA 2015/02 - Ngauruhoe Volcano

Published: Tue Mar 31 2015 1:58 PM

Volcanic Alert BulletinNGA 2015/02
Tue Mar 31 2015 1:58 PM; Ngauruhoe Volcano
Volcanic Alert Level remains at 1
Aviation Colour Code Green

Seismic activity around Ngauruhoe has remained slightly elevated this last week. Visits were made to install additional seismic equipment and measure fumarole temperatures. Ngauruhoe unrest continues: Volcanic Alert Level 1

The Volcanic Alert Level was raised to Level 1 from Level 0 on March 20 in response to the changes in earthquake activity, indicating minor volcanic unrest. The GeoNet seismographs around Mt Ngauruhoe have continued to record earthquake activity. Our analyses indicate these earthquakes are shallow, occurring at depths of less than about 5 km. Since March 1 the number of events per day has ranged from 1 to 67, which is similar to previous episodes between 2006 and 2010.

We have visited the summit crater and eastern outer rim to measure fumarole temperatures and obtain thermal IR images (see below). GNS Science gas chemist Agnes Mazot commented, “the temperatures in the summit crater and on the outer eastern rim are unchanged from our previous visit in January 2015. The maximum temperature measured was 87 °C, on the outer eastern rim. The temperatures in this area have ranged 81 to 87 °C over the last 17 years”. Thermal IR (InfraRed) images are one method of mapping heat flow over large areas, some of which may not be accessible. The image below shows part of the inner north wall of the summit crater. Collecting repeat images will allow us to ascertain if there are any changes. The warmest area is the white area near the centre of the image, being 35 °C.

Thermal IR image and visual image of the inner north wall of the summit crater, 27 March 2015.a

Thermal IR image and visual image of the inner north wall of the summit crater, 27 March 2015.a

Thermal IR image and visual image of the inner north wall of the summit crater, 27 March 2015.bThermal IR image and visual image of the inner north wall of the summit crater, 27 March 2015.

Thermal IR image and visual image of the inner north wall of the summit crater, 27 March 2015.bThermal IR image and visual image of the inner north wall of the summit crater, 27 March 2015.

The current change at Ngauruhoe indicates the volcano has entered a state of volcanic unrest, like we have recorded several times in the last 30 years. No previous periods of unrest have resulted in a volcanic eruption. The outcome of this unrest is more likely than not that there will be no eruption in the short term, like during the 2006-2010 unrest.

The last significant eruption at Ngauruhoe was in 1975. Earthquakes are not unusual near Ngauruhoe but it is some time since we last recorded significant numbers or events above magnitude 1. Similar numbers, but smaller events occurred in December 2014. Other swarms of earthquakes near Ngauruhoe occurred in 1983, 1991, 1994, 1995 and again 2006-2010, but otherwise Ngauruhoe usually has little earthquake activity. We continue to monitor Ngauruhoe closely and will release updated information as it is available or necessary. The Volcanic Alert Level ranges from 0 to 5 and defines the current status at a volcano.

The Aviation Colour Code for Ngauruhoe is Green. Aviation Colour Codes are based on four colours and are intended for reference only in the international civil aviation community.

Information Contact: Brad Scott Volcanologist 07 3748211