Hamilton’s iconic escarpment is constantly crumbling. Researchers are finding the reasons why

While erosion along Hamilton’s escarpment has caused costly clean-ups and headaches for drivers on the city’s Mountain passes, researchers are trying to better understand the phenomenon to help the city respond to it. 

A team at McMaster University has been studying erosion along Hamilton’s portion of the 725-kilometres-long Niagara Escarpment, known for its crumbly, layered rocks, which often curve inward from the top. 

The escarpment is constantly crumbling but the researchers say understanding how and why it erodes can help the city better respond to the falling rocks that litter parts of the city and close roads, like they did on the Claremont Access for eight months last year. 

The team recently released findings from their study, showing that Hamilton’s escarpment walls erode more quickly if they face southeast and that climate change will likely impact the rate of erosion. 

But the study, published in the peer-reviewed journal, Frontiers in Earth Science, also found that vegetation slows that process down.

Henry Gage, who is now pursuing PhD at Princeton University in New Jersey, is one of the study’s authors and a McMaster graduate. Going for runs around the city and spending a lot of time along the escarpment inspired his interest in it. 

“I would always notice these exposures of the escarpment that were crumbling. There’d be chunks of rock everywhere,” said Gage.

His curiosity inspired him to learn more by working at professor and geologist Carolyn Eyles’s lab at the Hamilton university.

Along with researcher Julia Nielsen, the team looked into the formation, part of the steep rock face that stretches between Queenston, Ont., in the Niagara Region, and St. Joseph Island, near Sault Ste Marie in northern Ontario. 

Temperature fluctuations increase rock fractures

Gage researched the escarpment in Hamilton using a network of probes measuring moisture and temperature across its fractures.

The escarpment’s geological make-up explains the iconic way it erodes, Gage said. The undercutting — where the middle and bottom of the rock face erodes more quickly than the top — occurs because across the escarpment, a layer of shale sits below a layer of dolostone. The shale erodes more quickly and recedes faster, cutting beneath the dolostone and leading chunks of the other rock to fall off. 

The researchers found temperature is a significant factor in that process. Heating and cooling causes rock to expand and contract, which can lead to fracturing.

Along the escarpment, a heating-cooling cycle can happen within minutes, such as when a cloud blocks sunlight, Gage said. Water freezing and thawing within the rock face also weathers it.

The study found the potential for temperature-driven weathering is highest during the spring, when warming-cooling cycles range the most, and minute-scale changes can be frequent. 

This spring has provided a good example of those conditions, Gage said. Hamilton has broken heat records and experienced much colder seasonal temperatures, sometimes within the same day. 

Gage said he expects climate change to make temperature and precipitation more irregular. 

“Those two components of climate change can perhaps have a very significant impact on weathering,” he said in an interview with CBC Hamilton.  

“That’s the perfect situation to cause more of this thermal weathering where you’re heating and cooling the rock really quickly.”

Gage’s team also found that southeast-facing escarpment walls experience the highest daily fluctuations in temperature because of how the sun hits them, and that plant cover generally reduces temperature fluctuations.   

Helping to minimize road closures

The hope, Gage says, is that the city can take his team’s learnings and put them to use maintaining sites where there are significant rock falls, such as the roadways that travel along the escarpment.

In November, the city re-opened the Claremont Access after dealing with erosion and stability issues that begin in spring last year. Rockfall-related work has closed other roadways in the last several years, too. 

“If you’re a Hamiltonian, what we care about is how can we make this a little more cost effective … and preventative,” Gage said, adding he has no reason to believe the city is doing anything wrong, but wants to offer another tool.

“We’re trying to minimize the frequency of road closures and the risk of damage.”

‘Part of the character of Hamilton’

While the escarpment runs through much of southwestern Ontario, Hamilton is rare in that the formation effectively cuts the city in half. Locally, the two parts are called the lower city and the Mountain. 

“The escarpment is certainly part of the character of Hamilton,” Jackie Kennedy, Hamilton’s director of engineering services, said.

She oversees the team that takes care of the city’s access routes. “We can’t prevent [erosion],” she said, but city workers monitor and deal with it. 

Recent work along the Claremont Access involved workers removing outdated steel barriers that had failed to hold back debris, and removing loose debris from the escarpment walls. Along the Kenilworth Access, Kennedy said, workers have been installing drapery and rock mesh to catch falling debris.

Kennedy said it can be hard to see changes along the escarpment, and that research out of McMaster offers information the city may be able to use. “We would take that information and then decide how we respond to it on a case-by-case basis,” she said. 

Going forward, Eyles says her lab at McMaster is working on a process to measure erosion across the whole of the escarpment and along access routes specifically. 

She said she wants to use drone photography of the escarpment to measure changes year to year. She said there are also researchers looking at fracture patterns to determine the size of rocks that will eventually fall, and at how rivers crossing the escarpment impact erosion. 

“The escarpment is going to continue to erode. It’s not going to stop,” she said. “We need those data to best predict what’s going to happen.”

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