White Island's crater lake now less likely to overflow

The latest monitoring shows the famous sulphur-green, highly acidic lake in New Zealand's most active volcano is sitting at around 13m below the point of overflow. Photo / GNS Science

After scientists warned White Island's Crater Lake could overflow by June, the risk at the offshore Bay of Plenty volcano appears to have cooled.

The latest monitoring shows the famous sulphur-green, highly acidic lake in New Zealand's most active volcano is sitting at around 13m below the point of overflow.

That is two metres below a peak level that was reached in January, following months of steady filling.

Late last year, GNS Science had indicated an overflow could happen by mid-2019, but scientists are now confident that is now unlikely to play out, given the falling levels.

The current lake is a relatively new one, and replaced a previous one that was blasted from the crater floor during a 2016 eruption.

Scientists have recorded four of these lakes forming in the last 16 years – but none have ever reached overflow.

"In February-March of 2006, the lake got to within about 1 metre of overflow, before receding as the lake heated and was evaporated away," GNS duty volcanologist Yannik Behr said.

"An overflowing lake would impact the crater floor and potentially the dynamics of the hydrothermal system."

Monitoring data recorded over the past few months and observations made during recent visits to the island confirm volcanic activity remains at a steady and generally low level.

The lake temperature has risen to over 60C, which was not surprising, considering the number of drowned fumaroles which were contributing heat and steam to the lake.

While seismic activity near the lake had been at elevated levels, tremor within the volcano itself remained minimal.

Another key indicator of magma movement - SO2 gas flux – had also been within the normal range.

Meanwhile, there had also been little change at Mt Ruapehu's Crater Lake, which had recently heated to temperatures not seen in years.

That lake tended to cycle between a range of 15C and 45C over year-long periods, and, over the past weeks, the temperature had climbed steadily to 42C.

GNS volcanologist Brad Scott said the lake remained at 42C – although a recent rainfall event may have helped in keeping it in a steady state.