Following a thorough review of recent monitoring data GNS Science has confirmed that it believes Ruapehu remains at a heightened level of unrest and that an eruption is more likely than normal.
GNS Science head volcanologist Gill Jolly said, “Our analysis is still showing higher than normal temperatures beneath the crater lake. We think this reflects a partially sealed zone a few hundred metres beneath the lake which might be causing a pressure build up behind it. That pressure would make an eruption more likely than normal.”.
“It doesn't mean that an eruption is inevitable”, said Dr Jolly. “If the sealed zone fails suddenly an eruption could occur, probably with little or no warning. If it fails more gradually then the pressure would probably be released more slowly and the likelihood of an eruption would revert to normal”.
“We never have the whole story so there is always uncertainty in our assessment of what might happen at volcanoes. It's like detective work without all the clues. But when we see something that might increase the chance of an eruption we have to be more cautious”, said Dr Jolly.
The crater lake is quiet and its temperature has remained relatively low, 20 - 25 degrees Celsius, since March. Our understanding of the situation is consistent with these observations.
GNS Science continues to closely monitor Ruapehu through the GeoNet project.
Eruptions in 1988, 2006, and 2007 are believed to have occurred as a result of sudden failure of a seal beneath the crater lake.
Small earthquakes 3-5 km beneath the crater lake in late-October and early-November have now stopped. It is not clear if those earthquakes were related to the high temperatures estimated a few hundred metres beneath the lake.
GNS Science has a monitoring site at the crater lake which regularly sends back the temperature of the lake water.
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.
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.
Brad Scott, Steven Sherburn