Mt Ruapehu's crater lake is heating up, according to measurements taken by GNS science volcanologists this week.

Duty volcanologist Michael Rosenberg says Crater Lake (Te Wai ā-moe) has responded to volcanic earthquakes beneath Mt Ruapehu.

"In response to the sequence of seismic events recorded last week beneath Mt Ruapehu, volcanologists have collected water samples from the crater lake and measured volcanic gases in the plume. Seismic data have been analysed in detail."

The amounts of carbon dioxide (CO2) and sulphur gases (SO2 and H2S) have increased since the last measurements on February 7, 2020.

"However, the values are not at all unusual and are within the ranges measured over the past year. Water samples are being analysed this week, with chemistry results expected by next week.

"New analysis of last week's volcanic earthquakes defines a source area 3km beneath the summit of Ruapehu, which is normal for seismic activity at Ruapehu.

"Volcanic tremors increased in strength briefly last weekend, then declined during the week, and has now increased again to similar levels."

In response to the earthquakes last week, Michael says Crater Lake (Te Wai ā-moe) has slowly heated from 24ºC and is currently at 30ºC.

"Upwelling of grey sediment and sulphur slicks on the lake surface were observed during our visit last week. The lake is being mixed and is overflowing through the usual outlet channel.

"The flow of gases and hydrothermal fluids though the lake show that the underlying vent area is open."

He says it's not unusual to observe volcanic earthquakes at Ruapehu and similar episodes of increased seismic activity and gas flux were observed during March 2018 and 2019, September 2017 and April 2016. None of these resulted in a sustained increase in volcanic unrest.

The Volcanic Alert Level remains at Level 1. The Volcanic Alert Level reflects the current level of volcanic activity and is not a forecast of future activity.

There is no change in the Aviation Colour Code from Green.