The likelihood of Mt Ruapehu erupting has increased - with temperature changes indicating eruptions were "more likely over the next weeks to months".
GNS duty volcanologist Steven Sherburn said yesterday temperatures a few hundred metres beneath the volcano's crater lake were about 800C, but the lake itself was only about 20C. "This suggests the vent is partly blocked which may be leading to a pressure build-up beneath the crater lake," Dr Sherburn said. "A sudden release of the pressure may lead to an eruption."
The Aviation Colour Code has increased from Green to Yellow. Code Yellow indicates a volcano is experiencing signs of elevated unrest above known background levels.
Drifting ash from the Mt Tongariro eruption on August 7 this year forced Hawke's Bay airport to close for a day, cancelling 14 inbound and 14 outbound flights. About 500 passengers were affected after Air New Zealand deemed the risk too great to ignore.
The ash also grounded Skyline Aviation services - including the air ambulance and Lowe Corporation Rescue Helicopter.