Ruapehu 22/11/12: Likelihood of eruptions remains
Volcanic Alert Bulletin RUA-2012/02 - Ruapehu Volcano
22 November 2012, 12:00 pm - Likelihood of eruptions at Ruapehu remains; Volcanic Alert remains at Level 1; Aviation Colour Code remains Yellow
Yesterday GNS Science volcanologists visited the summit crater lake to sample the water and gas. Some provisional results should be available within a few days. GNS volcanologist Brad Scott said, “The lake remains similar to our last visit on 10 November. The lake is a uniform blue colour with very little convection and the temperature was only 19.5 °C. Everything looks quiet at the surface”.
Recent measurements at Ruapehu indicate that the likelihood of eruptions has increased and the observations yesterday don’t change this.
The Aviation Colour Code remains at Yellow and the Volcanic Alert Level remains at 1.
We are monitoring Ruapehu closely, but it often does not give any immediate warning that it is going to erupt.
Since late-October small earthquakes have been occurring about 5 km beneath the summit area of Ruapehu, but these may not be directly related to the high temperatures beneath Crater Lake as the earthquakes are much deeper.
A build-up of pressure beneath Crater Lake is thought to have caused the 2007 eruption and a smaller eruption in 2006.
We think that the temperature a few hundred metres beneath Crater Lake is about 800 °C, but the lake itself is only about 19-20 °C. This suggests the vent is partly blocked which may be leading to a pressure build-up beneath Crater Lake. A sudden release of the pressure may lead to an eruption.
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 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.