The Rotorua District Council is urging locals to be on the lookout for smoke or fires around Sulphur Point and Ngapuna following a number of small sulphur fires in the past two weeks.
Council geothermal inspector Peter Brownbridge said sulphur fires were natural events which could occur as a result of sulphur growing and pushing its way to the surface, forming yellow mounds.
Leaves and twigs from nearby tea trees accumulate on the mounds when there is no rain to wash it away.
A combination of heat in the ground and the sun can ignite the dry material, which in turn ignites the sulphur.
Mr Brownbridge said in the past couple of weeks there had been four sulphur fires in the Sulphur Point area alone.
"So far we've been lucky the fires have been spotted and our fire service has extinguished them before the flames have reached nearby dry scrub.
"The reason we're having fires at this time of year is still a bit of a mystery, although some patterns are starting to emerge.
"We're certain however, that the fires are a naturally occurring phenomenon and are not being deliberately lit."
Mr Brownbridge said that, in daylight the flames were not visible and apart from the smoke, all that could be seen was a black mark spreading along the ground as the sulphur slowly burns.
He urges local people to call the Rotorua Fire Brigade as soon as they see smoke in these areas.
"I'd caution people not to approach the fire because when sulphur burns it produces sulphur dioxide which is a very toxic gas and is an acute irritant.
"The tea tree and debris is tinder dry and people may potentially find themselves in a life-threatening situation if the fire takes hold in the scrub.
"Some of the ground surface in these areas has a very thin crust which people can also fall through, so this is another danger to be aware of," he said.
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