The Crater Lake (Te Wai ā-moe) temperature has been rising and is now 43ºC. During a gas flight last week, the lake was observed to be a uniform grey colour which shows it is well-mixed. There is some flow over the outlet. The gas output through the crater lake has also increased markedly in response to this heating cycle. The amounts of carbon dioxide (CO2) and sulphur gases (SO2 and H2S) in the plume are the largest measured in the past two decades. The continued flow of gases and hydrothermal fluids though the lake shows that the underlying vent area is open.

Volcanic tremor is being produced as short-lived pulses that coincide with increased gas passing through the crater lake and its plumbing system. Modelling of energy input into the lake has shown increase during the past month from around 200 MW to around 400 MW. Since 2007 Crater Lake temperature has exceeded 40 °C a number of times, without leading to an eruption. However. the combination of the increased lake temperature, volcanic tremor and gas output have motivated the Alert Level change.

The Volcanic Alert Level has been raised to Level 2. The Volcanic Alert Level reflects the current level of volcanic activity. Mt Ruapehu is an active volcano and has the potential to erupt with little or no warning when in a state of volcanic unrest. The Aviation Colour Code is changed to Yellow.

The Volcanic Alert Level reflects the current level of volcanic unrest or activity and is not a forecast of future activity. Volcanic Alert Level 2 indicates the primary hazards are those expected during volcanic unrest; steam discharge, volcanic gas, earthquakes, landslides and hydrothermal activity. While Volcano Alert Level 2 is mostly associated with environmental hazards, eruptions can still occur with little or no warning.

GNS Science and the National Geohazards Monitoring Centre continue to closely monitor Mt Ruapehu for further signs of activity. GeoNet monitors Mt Ruapehu via a network of seismic and acoustic sensors, GPS receivers, sensors in the lake and visits to the lake area and gas flights.

Mike Rosenberg Duty Volcanologist Media Contact: 021 574 541 or media@gns.cri.nz