Over the past eight days, the temperature at Mt Ruapehu’s Crater Lake (Te Wai ā-moe) has risen further from ~32 °C to ~36 °C. Our modelling suggests that the temperature rise corresponds to about ~460 MW of heat entering the lake. Temperature and heat input are within the typical range for a heating cycle.

Volcanic tremor levels remain elevated and, after a slight increase over the past week, are now amongst the highest levels we have seen over the past nine years.

Crater Lake water and gas sampling and an airborne gas flight were completed last week. Analysis of the lake water and gas samples do not indicate significant changes in the geothermal system feeding into the lake. The amount of gas released through the lake has increased from the previous measurements but remains within the typically observed long term trends. The crater lake has changed to a battleship grey colour as upwelling waters have disturbed sediments on the lake floor. Sulphur slicks are present on the lake surface.

The results to date are typical for the beginning of a heating cycle with the exception that tremor values are unusually high. Current data indicate that normal processes seen at the crater lake are occurring. Gas and fluids from the shallow magma under the volcano are interacting with the crater lake geothermal system, causing heating of the lake, volcanic tremor, and increases in gas emission at the surface.

The interpretation of this activity is consistent with elevated volcanic unrest and therefore the Volcanic Alert Level remains at Level 2. The Aviation Colour Code remains at Yellow.

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 Volcanic Alert Level reflects the current level of elevated volcanic unrest. The Volcanic Alert Level should not be used to forecast future activity. However, at Volcanic Alert Level 2, eruptions are usually more likely than at Volcanic Alert Level 1.

Volcanic Alert Level 2 indicates the primary hazards are those expected during volcanic unrest; steam discharge, volcanic gas, earthquakes, landslides and hydrothermal activity. While Volcano Alert Level 2 is mostly associated with volcanic unrest hazards, eruptions can still occur with little or no warning.

For information on access to the Mt Ruapehu area, please visit the Department of Conservation’s websites on volcanic risk in Tongariro National Park and follow their Facebook page for further updates.

GNS Science and its National Geohazards Monitoring Centre continue to closely monitor Mt Ruapehu for further changes.

Yannik Behr

Duty Volcanologist

Media Contact: 021 574 541 or media@gns.cri.nz

Footnote: You might notice we've made a tweak to the name of these bulletins - from Volcanic Alert Bulletin to Volcanic Activity Bulletin. We've done this because we think it better reflects the purpose of these Bulletins, which can also include more general updates. Any queries, please let us know at media@gns.cri.nz