The lack of groundwater, high overnight temperatures and increased storm activity has led to a dangerous build-up of carbon dioxide in one of Wellington's heritage-listed caves.
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The Gaden Cave was closed two months ago and remains off-limits to the public as unsafe levels of carbon dioxide continue to persist.
Wellington Caves manager Michelle Tonkins says staff are unable to predict when conditions may change, so a reopening date is uncertain.
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The caves were discovered in 1902 by James Sibbald, who became their caretaker. It's said he was at first hesitant to open them up to visitors due to the "foul air".
It took seven years for the public to be given access.
While the cave has the potential to vent naturally, Ms Tonkins says that a number of factors can prevent this process occurring, thereby making it too dangerous for visitors.
"When we have nights that are warmer than 17 to 18 degrees, the air down in the cave can't naturally vent, and so it gets trapped."
The water table within the caves is also sinking, creating larger air pockets for the carbon dioxide to occupy.
...the water level has been getting lower and lower and lower...
- Andy Baker
The effects of the heat and drought have been noticeable to a team of scientists who have been working to uncover the secrets of groundwater recharge at the Wellington Caves complex.
University of NSW caves and karst researcher Professor Andy Baker has been working at Wellington Caves and in the surrounding areas since 2010.
"The last time there was major recharge at the cave was about 2016, and we have had one or two events since then where the water has come through from the surface," he said.
"But in general the water level has been getting lower and lower and lower overtime.
"I think at the bottom of the cave if you look down into the well there is no water in there".
Many previous cave managers have tried to increase circulation by creating artificial vents, including even relocating the caves entrance.
However Ms Tonkins explains that unfortunately, "the cave is the cave".
"The climate will have an impact, as I said - we have warmer days and warmer nights and that air can't vent and that's when it's going to become an ongoing issue," she said.
Open seven days a week, Wellington Caves is located approximately 9 kilometres south of the town.
