Mt Ruapehu volcanic alert level lowered to 1

GNS says that Mt Ruapehu's level of heightened volcanic unrest is now judged to have ended. Photo / File

Mount Ruapehu's volcanic alert level has been lowered to level one as volcanic gas emissions return to normal levels and volcanic tremor declines.

The alert level was lowered from level 2 on Monday after GNS scientists followed a gradual reduction in the level of unrest over the last few days.

The aviation colour code, which indicates the risk of potential ash in the atmosphere, has also been lowered from yellow to green.

The active volcano had its alert level raised on December 21 after GNS scientists discovered a significant rise in the crater lake temperature and the level of volcanic gas emissions.

Crater lake temperatures reached a high of 43 degrees on December 21, rising markedly from the 22 degrees recorded in November.

At the time, GNS volcanologist Michael Rosenberg said that there was heightened unrest at the volcano.

However, today's alert level change comes as the volcano begins to settle down.

"On 29 December, volcanic tremor, which had previously been slightly elevated following a volcanic earthquake on 26 December 2020, declined to a low level, and has remained low," volcanologist Steven Sherburn said in the level change decision.

"While the temperature of the water in Crater Lake Te Wai ā-moe remains high at 40 degrees, taking all of the observations into consideration, the period of moderate to heightened volcanic unrest is now judged to have ended."

GNS says that while the alert level system should not be used to forecast future activity, at alert level one, eruptions are less likely than at level two.

Meanwhile, the summit area of the mountain, which the Department of Conservation closed on December 21, has reopened.

The area 2km from the centre of Te Wai ā-moe/Crater Lake was closed in response to the alert level being raised to level 2.

The 2km exclusion zone has now been lifted and there are no longer any restrictions in place.

The volcano last erupted in September 2007 without warning, with two lahars travelling down the mountain, with a seven-minute-long earthquake recorded nearby.