Mt Ruapehu volcanic unrest drops to moderate - eruption still possible, Geonet says

Mt Ruapehu, seen here in 2018, has had a continued period of moderate volcanic unrest this year. Photo / Supplied

The level of volcanic unrest at Mt Ruapehu has decreased from heightened to moderate, but it can still erupt at any moment.

GNS Science reported volcanic tremor strength at Mt Ruapehu has declined to weak levels over the past week.

The volcanic alert level will stay at level 2 which indicated the primary hazards are those expected during volcanic unrest: steam discharge, volcanic gas, earthquakes, landslides, and hydrothermal activity.

While level 2 was mostly associated with volcanic unrest hazards, Mt Ruapehu is an active volcano and has the potential to erupt with little or no warning.

The aviation colour code remains yellow.

The Crater Lake (Te Wai ā-moe) temperature is 28C and has continued to slowly cool over the past three to four weeks.

There has also been an increase in overflow of the lake due to the heavy rainfall.

Although gas measurement flights could not happen in the past few weeks because of the weather, the last relatively high sulphur dioxide and carbon dioxide measurements were consistent with a continued period of moderate volcanic unrest at Mt Ruapehu.

GNS Science staff would carry out more frequent aerial observations and gas measurements when weather conditions were suitable.

What now?

According to GNS, the most likely outcome in the next three weeks of the ongoing unrest was either minor eruptive activity confined to the lake basin or no eruption.

Minor eruptions may generate lahars - dangerous volcanic mudflows - in the Whangaehu River.

The next likely scenario was a larger eruption that impacted the summit plateau with volcanic surges.

This could generate lahars in multiple catchments, similar to what was seen after the September 2007 eruption, or like those in June 1969.

An eruption of this size would cause life-threatening hazards on the summit plateau and in valleys impacted by lahars.

The chance of a prolonged eruptive episode or a larger eruption, with wider ashfall impacts that happened in 1995 and 1996, is higher than it was before the start of elevated unrest in March.

However, this was unlikely within the next three weeks.

Such an eruption would most likely only follow a sequence of smaller eruptions.