Volcanic gases from Whakaari/White Island have combined with particular weather conditions and sea fog in the Bay of Plenty to create a “very rare” phenomenon known as VOG – volcanic fog.

As the fog rolled over, some in the Whakatāne area described a strong smell of sulphur and an “ominous” grey hazy sky.

GeoNet – which monitors geological hazards in New Zealand such as earthquakes, volcanoes, tsunami, and landslides – this week put out a warning about “VOG” in the Bay of Plenty.

“VOG is created when the sulphur-based volcanic gases mix with atmospheric moisture to form an aerosol.”

The warning comes as volcanic unrest continues on Whakaari, which is located off the coast of Whakatāne in the eastern Bay of Plenty.

Last week, GNS scientists undertook a visual observation flight and a gas emission measurement flight over the active volcano and noted increases in gas emissions.

 Emissions of sulphur dioxide (SO2), carbon dioxide (CO2), and hydrogen sulphide (H2S) had all increased since the last measurements in mid-October.

“The volcano occasionally emits traces of volcanic ash and remains in a state of moderate to heightened unrest.”

GeoNet said on Tuesday afternoon that light northerly winds were driving VOG onshore; “there has not been an eruption to produce this”.

It said VOG could be unpleasant, producing watery eyes and a stinging sensation, and those with respiratory health issues should be cautious.

VOG could also reduce visibility, creating a hazard for road, air and ocean traffic, “so please take care”.

One member of the public took to social media on Tuesday afternoon to say “the sky in Whakatāne right now is out the gate like some kind of ominous horror movie with thick grey hazy something and a strong whiff of sulphur”.

Another woman on Twitter said there was a “weird sulphuric smell and thick haze covering Whakatāne”.

Others also spoke of hazy, foggy conditions and a strong smell.

GNS Science volcanologist Brad Scott told Stuff that VOG in New Zealand “is very rare, may be noted once every 10 years or so”.

 “It is difficult to quantify as no detailed records are kept.”

He said no VOG was noted post the 1995/1996 eruptions of Mt Ruapehu and the 2012 Te Maari eruption.

“The density and spread is not well documented. For example, gas odour was noted in Nelson/Blenheim from Ruapehu.”

 Scott said on Wednesday afternoon that publicly available satellite images suggested VOG was not still present in the Bay of Plenty but a Whakatāne web camera indicated it was still hazy.

He said it was possible the Bay of Plenty would experience VOG again.

“The two key parameters are gas flux from the volcano and atmospheric conditions. While elevated unrest continues we can tick off the gas box,” he said.

“The weather conditions are much less common but can occur maybe yearly or every few years.”

The Volcanic Alert Level remains at level 2 for Whakaari.

 Associate Professor Carol Stewart, from the school of health sciences at Massey University, is a co-director of the International Volcanic Health Hazard Network.

She said VOG was a mixture of acidic sulphur dioxide (SO2) gas and small particles (sulphate aerosol).

 “Most of what we know about VOG health impacts comes from Hawaii, where there is long-term degassing of sulphur dioxide from Kīlauea volcano,” she said.

“Typical health impacts of VOG can include: irritation of the nose, eyes, throat and sometimes skin; aggravation of asthma (wheezing), chest tightness, shortness of breath, headache, nausea and fatigue.”

Stewart said people with asthma were particularly sensitive to the effects of SO2 gas and VOG.

Other sensitive groups are: older adults, babies and young children, and people with pre-existing heart or lung problems.

If there is VOG present, people should try to limit their exposure by staying indoors, closing doors and windows and not using heat pumps or air con units that draw in air from outdoors, she said.

Source: Stuff.co.nz