Ruapehu eruption more likely
Mount Ruapehu's crater lake (AAP)
By 3 News online staff
An eruption at Mount Ruapehu is growing increasingly likely, say GNS Science volcanologists.
The agency has today raised its colour-coded aviation alert level from green to yellow to reflect changes in the mountain’s crater lake.
“We have been measuring changes at Ruapehu over the last few weeks and believe these changes make eruptions more likely over the next weeks to months,” GNS duty volcanologist Steve Sherburn said in a statement.
"We think that the temperature a few hundred metres beneath Crater Lake is about 800degC, but the lake itself is only about 20degC. 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."
The aviation colour code is a four-colour reference which indicates potential hazards around a volcano. A yellow level indicates “signs of elevated unrest above known background levels”.
GNS last raised the Ruapehu alert level in April 2011, as volcanologists noticed an increase in water temperature in the volcano's crater lake, as well as seismic activity and changes in volcanic gas output. GNS lowered the alert level in May 2011 as the lake's temperature declined.
Ruapehu’s last eruption came occurred in 2007, an activity which lasted for around seven minutes and caused two lahar flows.