Apr 18 2011 - Ruapehu Volcano

The temperature of the Crater Lake has decreased to around 33 - 34 °C from a peak of 41 °C in March 2011. Other monitored indicators in recent weeks also suggest a slow decrease of activity.

While activity seems to be decreasing overall and there are no data to suggest an imminent eruption, the volcano remains in a state of elevated unrest above the typical background level. Therefore the Aviation Colour Code remains at Yellow and the Volcanic Alert Level remains at Level 1.

The current heating phase of the Crater Lake, which started in October 2010, appears to be declining. The temperature of the lake peaked at 41 °C on March 1 and fluctuated around 38 - 39 °C during that month. Over the past two weeks, the Crater Lake temperature has decreased and is now fluctuating around 33 - 34 °C.

Since April 4, observations by GNS Science show a general decrease in activity, with lower CO₂ gas flux, less seismicity, little change in the Crater Lake water chemistry and cessation of lake overflow accompanying the start of the cooling trend.

Despite the reduced activity Ruapehu remains at a slightly elevated level of unrest and the Aviation Colour Code therefore remains at Yellow.

If atmospheric conditions are suitable steam may still be seen above the crater, and if lake sediments on the lake floor are disturbed by the gas and heat flow into the lake, the lake colour may change.

GNS Science volcanologists continue to monitor this and other volcanoes. Ruapehu remains an active volcano and future eruptions may occur with little or no warning.

The Volcanic Alert Level remains at Level 1 (departure from typical background surface activity, signs of unrest). The Volcanic Aviation Colour Code remains at Yellow (elevated unrest above the typical background).

Nico Fournier
GeoNet Duty Volcanologist

Brad Scott
Volcano Surveillance Coordinator