Volcanic Alert Bulletin RUA-2013/01 - Ruapehu Volcano

5 March 2013, 10:30am - Ruapehu unrest continues, apparent deep temperatures show decline; Volcanic Alert remains at Level 1; Aviation Colour Code remains Yellow.

Results from the on-going monitoring of the Ruapehu Crater Lake are showing that the temperatures at depth have started to decline. While they remain elevated, the declining trend is now confirmed. However the Crater Lake temperature remains static at 22-25°C, indicating that a partial blockage between the deeper hydrothermal system and the Crater Lake remains. Because of this blockage and the resulting potential to increase pressure at depth over time, Ruapehu remains in an elevated level of unrest.

The Volcano Alert Level remains at 1 and the Aviation Colour Code at Yellow.

Gas data from January and February show emission rates of 15-25 tonnes per day SO2 and around 650 tonnes per day CO2. These are within the usual range of emissions measured at Ruapehu. Seismicity remains low, characterised by weak volcanic tremor and some shallow earthquakes. Visual observations in the last few weeks have sometimes shown areas of discolouration in the lake. These are relatively common and are thought to reflect internal convection processes within the lake.

GNS Science volcanologist Brad Scott said, “Our analysis is still showing high temperatures exist beneath the lake, but these have decreased in the last month. We think there is still a partial blockage between the deep and shallow systems as the lake temperature has remained steady. The relatively low temperature of the Crater Lake, since March 2012, is one of the longest periods of low lake temperature we have recorded.”

If the sealed zone fails suddenly an eruption could occur, probably with little or no warning. If it fails more gradually then the pressure released would be more gradual and the likelihood of an eruption would be less.

GNS Science continues to closely monitor Ruapehu through the GeoNet project.


Ruapehu Crater Lake is well known for its cyclic temperature variations. In a normal temperature cycle the lake temperature varies between around 15-45°C over a period of 9-12 months. Eruptions in 1988, 2006, and 2007 are believed to have occurred as a result of sudden failure of a seal beneath the Crater Lake. GNS Science has a monitoring site at the Crater Lake which measures the temperature and level of the lake water and transmits the data via satellite.

The Volcanic Alert Level ranges from 0 to 5 and defines the current status at a volcano. Level 1 indicates a departure from typical background surface activity.

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 a volcano is experiencing signs of elevated unrest above known background levels.

The GeoNet project is funded by EQC and provides monitoring for all of New Zealand’s volcanoes.

Craig Miller
Duty Volcanologist

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