The Niagara Escarpment is falling, naturally. And it's costing Hamilton money.

Two major road and trail closures resulting from the natural erosion of the Niagara Escarpment through Hamillton are the latest incidents related to costly rock slides the city spends tens of thousands of dollars to cleanup and prevent.

Over the past couple of years Hamilton has responded to at least eight of these major events, costing anywhere from $25,000 to $500,000 each to clean up the mess.

Given the number of rock slides already this year, road crews have increased visual inspections at escarpment crossings.

"We know it’s an inconvenience when we have to shut these roadways so we try and get in there and do the work as quickly as possible,” said Darrell Smith, manager of roads in the City’s Public Works Department.

The City said that starting Friday all lanes of the Kenilworth Access will be closed for the next week after a rock slide on May 15.

A minor rock slide in late March caused one lane to be closed on Sydenham Road in Dundas.

Trails closed for 8 weeks

Starting Monday, the Ministry of Transportation is closing the Scenic Iroquois Walk and the Chedoke Radial Trail for approximately eight weeks as crews complete preventative maintenance work near the eastbound lanes of Hwy. 403.

“It’s certainly not ideal that this work is being completed during peak trail season but unfortunately it cannot be delayed due to potential risks to health and safety,” said Tennessee Propedo, manager of parks and cemeteries.

In some cases like the above trails closures, and at Kenilworth, the city will perform scaling - a controlled fall to ensure any loose rocks are removed.

“We control when and how it comes down and then we take the material away,” Smith said. “The only thing we can do is be proactive in our inspection and deal with anything that comes up as quickly as possible."

Hamilton boasts 16 escarpment crossings, each of which is inspected daily by a city employee who reports back on any incidents, or potential problems.

David Webster, a geologist with in the Ministry of Natural Resources Parks and Protected Areas Policy Section, said water is the main force behind rock tumbling off the Escarpment.

The only thing we can do is be proactive in our inspection and deal with anything that comes up as quickly as possible. - Darrell Smith, City of Hamilton manager of roads

"Running water can erode out of less durable rock along the escarpment edge, making any overlying rock unstable and contribute to rock slides," Webster said.

Erosion can also be caused by what's known as karstic dissolution, the movement of mildly acidic water through the escarpment bedrock.

"Since the escarpment is comprised mainly of limestone and dolostone, it is susceptible to karstic processes," Webster said.

The Escarpment's 'tipping point'

Webster noted that because ice doesn't expand, the deep freeze experienced this winter likely has little affect on a potential increase in rock slides this year.

Instead, precipitation from Lake Ontario coupled with the "huge vertical face of the Niagara Escarpment will continue to be a source of rock falls for the next millennium."

Webster said the erosion of these large chunks of rock, or what's called "mass wasting" will continue incrementally up until a more damaging event occurs.

"Mass wasting usually happens incrementally up until a certain 'tipping point,' then can be catastrophic when the supporting structure cannot support an overlying or adjacent rock mass," he said.