Pressure is building up in the Crater Lake on Mt Ruapehu, increasing the likelihood of an eruption in the coming weeks, scientists say.
GNS Science said recent measurements taken on the volcano over the last few weeks indicated that eruptions were more likely “over the next weeks to months”.
The Aviation Colour Code has increased from green to yellow as a warning for those flying over the region, but the Volcanic Alert Level remained at level 1.
Pressure was believed to be building up under the Crater Lake, and a sudden release of that pressure may lead to an eruption.
“We are monitoring Ruapehu closely, but it often does not give any immediate warning that it is going to erupt,” GNS Science Duty Volcanologist Steven Sherburn said.
GNS Science believed the temperature a few hundred metres beneath the crater was about 800 degrees Celsius but the lake itself was only 20degC.
“This suggests the vent is partly blocked which may be leading to a pressure build-up beneath Crater Lake.”
Small earthquakes have been occurring about 5 kilometres beneath the summit of Ruapehu since late October, GNS said.