Slow Ruapehu temperature rise hints at risky pressure build up at volcano

Monday, 28 March 2022

Mt Ruapehu’s crater lake Te Wai ā-moe – the volcanic alert level remains at 2 but there’s a hint of pressure building up inside the mountain, which could increase the chances of an eruption and the aviation colour code has been elevated to yellow.

Slower-than-expected temperature rises at Mt Ruapehu’s crater lake, Te Wai ā-moe, suggests a vent beneath it may be partially blocked, potentially increasing the chances of an eruption.

While the volcanic alert level remains at 2, the aviation colour code around the mountain has now been increased to yellow, indicating to aircraft operators that they need to take activity at Ruapehu into greater account.

Two weeks ago, the lake entered a new heating cycle, accompanied by strong levels of volcanic tremor, or earthquakes.

An update Monday from GeoNet said the temperature in the lake has continued to rise slowly to about 32 degrees C. “Strong tremor has continued throughout this heating period,” GNS duty volcanologist Geoff Kilgour said in a statement.

* Increased likelihood of eruption at Mt Ruapehu, move to alert level 2

* Ruapehu in slow volcanic warm up

The slow heating had been hindered by heavy rainfall at the volcano and an influx of cold water into the lake.

While signs were that gas is fluxing through the system, the slower-than-expected increase in lake temperature suggests a partial blockage may exist in the vent beneath the lake, preventing the hot gas from entering the lake.

“This could allow pressure to build up within the volcano,” said Kilgour.

Asked if such a blockage and resulting pressure would increase the chance of an eruption, Kilgour said: “Yes, it does. Gas is still able to go through but not particularly quickly. If that pressure build-up continues…that’s when we might expect an eruption to occur.”

The update from GeoNet said interpretation of this activity is consistent with elevated volcanic unrest and therefore the volcanic alert level remains at Level 2. But Kilgour said the raising of the aviation colour code to yellow reflected the ongoing nature of the situation.

Mt Ruapehu is an active volcano and has the potential to erupt with little or no warning when in a state of elevated volcanic unrest, the update said, adding that at Level 2, eruptions are usually more likely than at Level 1.

Potential hazards at Level 2 include steam discharge, volcanic gas, earthquakes, landslides and hydrothermal activity.

GNS Science and the National Geohazards Monitoring Centre will be continuing to closely monitor the maunga for further changes.