Shaking under Mt Ruapehu 'moderate to strong' as crater lake cools

Monday, 28 December 2020

Shaking under Mt Ruapehu is now “moderate to strong” despite a cooling of the crater lake.

The Volcanic Alert Level was raised to Level 2 last week after the crater lake’s temperature increased to 43C.

Since then, the lake’s water has cooled slightly to 41C, according to an update from GNS Science on Monday.

An airborne view of the Crater Lake on top of New Zealand's largest active volcano, Mt Ruapehu.

However, the level of volcanic tremor continues to be moderate to strong, and several shallow earthquakes have been recorded.

* Mt Ruapehu crater lake temperature rising

A view of the crater lake from the summit.

* Ruapehu's crater lake warms up

Since 2007, the lake temperature has exceeded 40C on seven occasions.

GNS Science has reported several volcanic earthquakes, the largest (M2.2) occurring on Boxing Day underneath the volcano.

Volcanic earthquakes of this size are uncommon and the combination with elevated tremor and high lake temperature indicate “moderate to heightened volcanic unrest”, the institute said in a statement.

“We continue to closely monitor Ruapehu, and this week we will attempt a gas flight to measure volcanic gas emissions. We will also attempt to sample the water at the crater lake for further chemical analyses. Together, these will help identify processes occurring at depth beneath the volcano.”

Level 2 indicates the primary hazards are those expected during volcanic unrest; steam discharge, volcanic gas, earthquakes, landslides and hydrothermal activity.

The Aviation Colour Code remains at yellow. The colour code system is based on four ascending activity levels – green, yellow, orange and red – and is intended to provide the international civil aviation community with information about volcanic activity and the potential presence of volcanic ash in the atmosphere.