Mt Ruapehu crater lake temperature lowers after reaching 40C

Mt Ruapehu's crater lake temperature has again cooled after a period of heightened temperatures earlier this year.

Geonet duty volcanologist Agnes Mazot said the temperature was now sitting at a cooler 26C after the crater lake temperature rose to 43C in December last year and to 40C later in April.

"Following the period of heightened unrest activity in December 2020, volcanic activity at Mt Ruapehu has remained at a low level over the past six months, with gas emissions, lake chemistry, and volcanic tremor all within typical ranges," Mazot said.

"After the December period of high temperatures, the crater lake cooled then reheated in early April before cooling again now to around 26C."

In December, Geonet raised the Volcanic Alert Level of the mountain to two, indicating a heightened risk of volcanic eruption.

Mt Ruapehu's crater lake has again cooled to 26C after rising to a height of 40C in April. Photo / File

In January, the Alert Level for the volcano was lowered to 1, where it remained despite the crater lake reheating to 40C later in April.

"Since the December 2020 period of elevated unrest, we have conducted routine monitoring gas measurement flights and crater lake water samplings," Mazot said.

"The results from these visits and of our continuous monitoring of volcanic earthquake activity, tremor levels, and crater lake temperature and water level indicate that key monitoring parameters remain within normal ranges."

The Volcanic Alert Level remains at 1, indicating minor volcanic unrest.

"The volcanic alert level should not be used to forecast future activity; however, at volcanic alert level 1, eruptions are less likely than at volcanic alert level 2."

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