High temperatures and increased seismic activity has been recorded at Mt Ruapheu's Crater Lake.

GNS Science duty volcanologist Agnes Mazot said the levels of volcanic tremors typically increased when the lake temperature rose and this had been the case in the last two weeks.

The Volcanic Alert Level remained at one.

Mazot said, since 2009, GNS had continuously recorded the temperature of Te Wai ā-moe (Crater Lake) and over this time the temperature had often cycled between 15C and 45C over a period of about 12 months.

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In the six months since September 2018 the lake temperature remained elevated at 30C and over the last two weeks the lake temperature had risen further at a rate of
around 0.5C per day, to 42°C on April 9.

Mazot said to put this in context, only 1 per cent of post-2009 temperatures had exceeded 42C and similar temperature last occurred in May 2016.

The current tremor intensity is moderate. In previous heating cycles, these increased tremors lasted for a few days to several weeks.

In the past, eruptions at Mt Ruapehu had occurred more often when the lake exceeded
45C, however, a temperature of 46C was recorded in 2016 with no eruption.

Mazot said while Volcano Alert Level 1 was minor unrest, eruptions could occur with little or no warning.

GNS Science continues to closely monitor Mt Ruapehu and our other active volcanoes.