Rising SO2 gas output, volcanic tremor at White Island could suggest eruptive activity more likely

Thursday, 31 October 2019

Rising sulphur dioxide (SO2) gas output and volcanic tremor at Whakaari/White Island could suggest the volcano may be entering a period where eruptive activity is more likely than normal.

Sulpur dioxide gas output and volcanic tremor levels at Whakaari/White Island are at the highest levels since 2016, possibly suggesting the volcano is entering a period where an eruption is more likely.

SO2 gas at volcanoes originates from magma (molten rocks), and is measured by scientists as a way to try to get an indication of what is happening to a volcano's magma system.

The level of the White Island crater lake - shown here in a picture from earlier this year - has been rising since early-August.

The changes at White Island could also be explained by increased gas flux - the rate at which gas is coming through the system. The link between gas flux and future activity was not well understood, GNS Science duty volcanologist Yannik Behr said.

There was a 'level of uncertainty' about the meaning of the changes. The volcanic alert for White Island remains at level one, indicating minor volcanic unrest.

Images from Geonet's timelapse cameras of White Island show the start of a small eruption on September 13, 2016.

* Earthquake swarm on White Island could heighten landslide risk**

*** Hot ash surged fast across White Island crater floor

* White Island: Would you dare walk New Zealand's most-active volcano?**

Both SO2 output and volcanic tremor - a continuous vibration - showed an increasing trend in the past several months.

'The SO2 gas originates from magma at depth and the data suggests a possible increase in gas passing through the volcano from depth,' Behr said.

'Volcanic tremor can occur for many reasons, including the movement of gas through the volcano, changes in the geothermal system, and even surface activity (geysering or ash emissions).'

The changes could be explained by a range of processes, including an increased level of unrest, but also variations in background and surface activity. 'Slight uncertainty about the exact meaning of these changes arises from these possible processes.'

None of the monitored parameters at White Island were outside the expected range for minor volcanic unrest and associated hazards.

'While the pattern of signals shows similarities with the 2011-2016 period and could suggest that Whakaari/White Island may be entering a period where eruptive activity is more likely than normal, recent observations can also be explained by the increased gas flux which leads to geysering and lake level changes,' Behr said.

Research was underway to try to better understand the link between gas flux and future activity at the volcano.

'This is the second time in the past decade the volcano has been like this,' GNS Science volcano information specialist Brad Scott said. The unrest started in 2011 and there were eruptions in 2012, 2013 and 2016.

'Some of the things we're seeing now are similar but others aren't,' Scott said.

Volcanoes were like other volcanoes in some ways but in some respects were 'very much individuals'. 'How the hydrothermal system and magma hot rock system works in each volcano is individualistic.'

Around 200-300 tonnes of SO2 per day was being measured at White Island. In the past it had gone over the 1000 tonnes per day level.

The level of the White Island crater lake has also been rising since early-August, affecting surface activity around active vents on the west side of the crater floor, with geysering activity seen in the area.

Other recent measurements made on the island (soil gas, fumarole and water chemistry, ground deformation, magnetics, visual images from the web cameras, and earthquake activity) show no significant changes.

Whakaari/White Island, 48km offshore from Bay of Plenty, is our most active cone volcano, built up by continuous volcanic activity during the past 150,000 years. With 70 per cent of the volcano under the sea, it is also the country's largest volcanic structure.

GeoNet said the longest historic eruption episode was from 1975-2000. During that time, many collapse and explosion craters developed. For long periods active vents in the craters emitted volcanic ash.