A GNS scientist samples a volcanic vent on White Island, where a series of eruptions took place last year. Photo / Supplied
A GNS scientist samples a volcanic vent on White Island, where a series of eruptions took place last year. Photo / Supplied
Calmer conditions on White Island, our most active volcano, has allowed scientists to get up close to areas transformed by explosive eruptions last year.
For the first time since late 2015, GNS Science staff have been able to access the rowdy Bay of Plenty submarine volcano's crater lake, which was completely cleared out in a single event last April.
The team was also able to sample gas-firing fumaroles inside the crater - including those on a lava dome that sprouted during an earlier eruptive sequence in 2012.
GNS volcanologist Brad Scott said the April 2016 eruption generated a blast so violent it travelled straight across the island's main crater floor, damaging and burying markers his team uses, and obscuring tourist trails.
White Island's new crater lake, as pictured this month. Photo / Supplied
The blast was followed by mild ash eruptions in September.
"For about a year after the April 2016 eruption, water was sitting ponded in depressions and in small craters on the crater floor, however, only since April this year has there been a stable lake," Scott said.
"While we are now comfortable to call this a 'new' crater lake, it is quite different from past lakes.
The temperature of gases billowing out of fumaroles had dropped from more than 450C during the 2012 episode, to 330C after the 2016 eruptions, and finally to 114C today. Photo / Supplied
"The most noticeable difference is the temperature, which last week was only 20C - in the past, a temperature of 30 to 70C has been typical."
Chemical analysis of one sample collected late last month showed the concentration of most volcanic elements in the lake water was the lowest for 10 or even 15 years.
This was because there were now few volcanic gases and liquids entering the lake, which was mostly formed by rainfall and run-off.
"While the lake is now very dilute, it is still as acidic as battery acid, so you wouldn't want to drink it or swim in it."
A GNS scientist inspects a fumarole that has cooled from 190C to 152C over recent months. Photo / Supplied
The team also found how the temperature of gases billowing out of fumaroles had dropped from more than 450C during the 2012 episode, to 330C after the 2016 eruptions, and finally to 114C today.
"Due to the declining activity we have been able to access and sample these."
One fumarole that was a highlight for tourists had cooled from more than 190C to 152C.
"We have also re-established our survey networks damaged or destroyed by the April 2016 eruption and are now establishing trends in those data."
Overall, the latest observations suggested the level of volcanic unrest was declining.
"This reduction in activity is however creating a new opportunity for us to collect data we couldn't before, especially about the gases in the active crater.
"These data, along with our more traditional data, confirm volcanic unrest is still present and Whakaari remains an active volcano."
White Island, the tip of a submarine volcano in the Bay of Plenty, is our most active volcano. Photo / Supplied
Over past decades, Scott has watched White Island transform from what it was in the mid-1970s to what it is now - a 100-metre deep, 300-metre wide crater that was dug out over a particularly fiery 12-year period now forms the sulphur-stained ampitheatre in which most activity happens today.
On any given day, the island, which rises a staggering 1.6km from the sea floor, spits out 1500 to 2000 tonnes of carbon dioxide and up to 800 tonnes of sulphur dioxide.
