For sedimental reasons: What the till in the tunnel tells us about the region’s geology

Geologist to discuss the up-and-down history of the Tri-Cities

The light dim and the roar ratchets up as the SkyTrain slips down, down into the Earth below Clarke Road into Port Moody.

Those 2.2 kilometres of tunnel are a transit route. They’re also, as geologist Lionel Jackson explains, a path into the past.

“People might consider when they take the SkyTrain and they enter the tunnel there at Burquitlam that they’re kind of going through a time machine,” he says. “There’s a whole story that they’re passing through.”

This Tuesday, Jackson, an adjunct faculty member at Simon Fraser University and former research scientist with the Geological Survey of Canada, is set to discuss that story during a free talk at the Dogwood Pavilion on Winslow Avenue in Coquitlam.

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When tunneling started there were stops and starts and sinkholes as crews expecting rock grappled with till.

“They discovered it was all glacial sediment,” Jackson explains.

Intrigued, Jackson reached out to the contractors running the project and explained his scientific interest.

Dubbed Alice, this is the machine that bore through the Earth to create the 2.2-kilometre tunnel to facilitate the SkyTrain extension. photo supplied

They were quite supportive, he reports. And, after going over the geotechnical data, Jackson started to understand the story in the tunnel.

“I realized that there was a very extensive record there of different times this area’s been covered by glaciers,” he says.

A fjord was buried beneath the Evergreen Line tunnel and filled sediment. Having studied cores from the drilling, Jackson realized the sediment had been left there during three ice ages.

“We see evidence of the area rising and falling over the last, perhaps, 150,000 years,” Jackson says. “Each time an ice sheet starts building up over the mountains adjacent to us, the weight or the mass of the ice sheet causes the Earth’s crust to be depressed.”

Tuesday’s talk is set to feature a discussion about ice ages, glaciation and the cause of the sinkholes.

The tunnel discovery answers many questions a geologist could have about the region. However, there are still questions to be answered, Jackson notes.

“Anything you do in science, you answer some questions and other questions show up,” he says.

For more information about the event, click here and scroll down to “Evergreen Tunnel Reveals Geological History.”

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