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article imageNew network of caves found in Montreal's St. Léonard cave system

By Karen Graham     Dec 5, 2017 in Science
Montreal - Pie-XII Park is a small suburban park in the heart of Montreal, Quebec. But, just 20 feet below the streets of the busy city is a cave system discovered in 1812. A new recently discovered cave system now makes the caverns bigger than anyone expected.
The Saint-Léonard cavern underneath Parc Pie-XII was first discovered in 1812 by a local farmer who owned the land. According to Canada's Capital Gems, during the Rebellion of 1837, the caverns were used to store ammunition and weapons and even served as a secure hiding place for soldiers.
The cavern was largely forgotten for almost 112 years until a story in the journal La Patrie in 1949 revived the public's interest in them. People started visiting the caves in ever-increasing groups, forcing the city to close the caverns to the public for fear someone would get hurt.
So from 1968 until 1978, the entrance to the caverns was sealed. In 1978, the Quebec Speleology Society had the caverns reopened, citing the need for further study. Since that time, the Society has offered tours during the summer months. These main caverns are about 50 meters (160 feet) long and dip down about 5.0 meters (16.5 feet).
Entrance to Cavernicole Cave in Pius XII Park.
Entrance to Cavernicole Cave in Pius XII Park.
Alain Beaudoin, Nathalie Vachon
Caverns left over from the last Ice Age
"Two years ago," François Gélinas, of the Quebec Speleology Society told Atlas Obscura, "we were making some tests outside one of the Saint-Leonard Cave walls and found a crack. We used an endoscopic camera, which showed that beneath the crack lied a room."
At the time, the society members were unable to break through the limestone around the crack. But on October 12, this year, two members of the Quebec Speleology Society, Luc Le Blanc, and Daniel Caron found a softer spot in the limestone and were able to break through.
It took three hours of steady drilling, but once they were through they found an "incredible" chamber. After climbing down a large drop, the men found themselves in a tall, narrow hallway. "The walls are perfectly smooth and the ceiling is perfectly horizontal," said Le Blanc.
Working on entering the new cavern
Working on entering the new cavern
Société québécoise de spéléologie
The ceiling appeared to be about 6 meters high (60 feet), with smooth limestone walls and stalagmites and stalactites throughout the passage. According to the Quebec Speleological Society, a centimeter (0.4 inches) of stalagmite takes about a thousand years to grow.
Caves can be different, depending on where they are found
Finding caves at higher latitudes is far less common than finding caves nearer to the equator. Most caves are formed over time when water dissolves the underlying rock, but keep in mind that Quebec has colder temperatures than those found closer to the equator. This temperature difference makes the water less acidic and slows the cave-making process.
The St. Léonard caverns were instead formed largely by receding glaciers. According to the City of Montreal, the cave itself is "young," somewhere around 10,000 years old, although Caron and Le Blanc believe 15,000 years-old is a more accurate guess.
The Canadian ice age: being notes on the pleistocene geology of Canada  with especial reference to t...
The Canadian ice age: being notes on the pleistocene geology of Canada, with especial reference to the life of the period and its climatal conditions.
Dawson, John William
Regardless, the last Ice Age ended about 10,000 years ago, and it took tens of thousands of years for the ice that covered much of North America to retreat. And those retreating glaciers changed the landscape, creating great fissures above and below ground.
"You have evidence of where you have knobs on one side that fits perfectly into a hole on the [opposite] wall," said Le Blanc, describing the walls' parallel faces, like puzzle pieces. Caron says the farthest reaches of the new cave system reach the Montreal water table and the aquifer that lies beneath.
More about Mornteal Canada, St Lonard cave system, spelunkers, Iceage, 1812