September 5, 2018 by The Canadian Press
OXFORD, N.S. – A large sinkhole that has swallowed trees and picnic tables in a Nova Scotia park has now taken a bite out of a parking lot, as the natural phenomenon continues to capture the attention of geological experts and curious onlookers alike.
The Town of Oxford said Friday the unpredictable sinkhole had remained relatively inactive Thursday.
But it said the muddy hole has been “undercutting” the pavement of the nearby Lions Club parking lot, and pieces of pavement are now falling in.
Amy Tizzard, a geologist with the Nova Scotia Department of Energy and Mines, said the sinkhole was 37 metres by 29.8 metres on Friday, up from 34 metres by 29 metres on Tuesday.
She said the sinkhole’s growth has slowed.
“However, it’s still unpredictable,” said Tizzard. “So we’ll continue to monitor the area.”
Tizzard has said the likeliest cause is an underground cavern caving in the soft gypsum rock that’s common in the region.
Todd Ventura, a professor in the geology department at Saint Mary’s University in Halifax, said sinkholes usually form over limestone, and it’s less common to have a sinkhole formed from gypsum, which is an evaporite – a mineral resulting from the evaporation of water.
“We’re quite intrigued by this, because these are much more rare events,” said Ventura. “It’s going to be really interesting to see what happens here. How much more it will grow? Are there others around?”
Ventura said gypsum is not hard like limestone, and behaves almost like a wax under pressure.
“It can move. And so as you’re dissolving the gypsum, instead of the gypsum then creating typically a cave, it just sort of creates a slump,” said Ventura, a geochemist.
“Imagine that you had a matchbox but there were no matches in it, and you cut a small circle on either side of the matchbox, and you stuck on either side a tube of toothpaste and started squeezing – you’re filling in the empty space with toothpaste.
“That’s more or less, when you think in terms of geology, how that gypsum would behave as a rock under pressure if part of it had been erased by groundwater or other types of events.”
Venutra said sinkholes happen when the roof of an underground cave becomes so unstable it essentially collapses. All the rock, soil and sediment above will also collapse and fall down to fill the void below, he said.
He added that there’s not much one can do to stop a sinkhole from growing: “This is nature.”
“The one thing about sinkholes is no one knows when they will happen or where they will happen,” he said.
“You might get some clues – cracks in the ground – but more often than not, they just surprise people and hopefully there isn’t too much property damage or loss of life.”
A nearby playground was removed after officials found hairline cracks on the pavement near the equipment.
Tizzard said she has been measuring the hole daily, as well as surveying reference points across the parking lot to look for “subtle changes” in the surface.
She has also been recording and measuring cracks in the pavement and surrounding forest to see if the cracks are growing.
The spectacle has been drawing curious onlookers to the small town, located roughly 30 minutes from the New Brunswick border.
Officials said the influx of visitors has caused a few fender-benders, and even a collision in which someone was injured.
Linda Cloney, a deputy clerk with the town, said the sinkhole is not visible from the road because of the perimeter that has been set up, so people should refrain from slowing down when driving by.
Tizzard added: “The public has to stay their distance and stay safe.”
Police are asking people to use caution when travelling near the sinkhole, situated near a giant statue of a blueberry with cartoonish eyes and a smile – a mascot for a town that promotes itself as the “blueberry capital of Canada.”
– By Aly Thomson in Halifax