Caves and Stacks on the Bruce Peninsula


Published 10/21/2021

by Andrew Zajch

Recently, member of the lab set out to conduct some field work along Georgian Bay. One of the stops was the Nottawasaga Lookout Trail just south of Collingwood. This site boasts a thick forest littered with dolostone blocks that are fractured and jointed (Figure 1-2). This reflects the site’s proximity to the Niagara Escarpment whose caprock is the notably resistant dolostone. If you have ever travelled across Central Ontario you have undoubtedly noticed the escarpment darting out up and above the relatively flat topography. The escarpment extends all the way from Lake Ontario to the tip of Bruce Peninsula boasting some of the most interesting sites that Ontario has to offer such as Niagara Falls or the Bruce Peninsula National Park. Stradling the escarpment is the renown Bruce Trail. The Nottawasaga Lookout Trail is one of the many segments of the Bruce Trail which extends across the entire extent of the Niagara Escarpment.


Figure 1- Exploring the trails at Nottawasaga Lookout


Figure 2- Large Dolostone blocks along the trail


Venturing down these trails the group stumbled upon the Standing Rocks and Caves, a series of fissure caves caused due the gravitational pull on one side o these ‘standing’ blocks falling away from the edge of the escarpment as the underlying material is eroded. The erosion of the underlying material leads to the toppling of the relatively stronger dolostone caprock. This is the same process that is leading to the retreat of Niagara Falls which, unsurprisingly, also lies on the Niagara Escarpment. As the water flows over the falls, the erosive ability of the plunging water eats away at its weaker foundation. This dynamic has led to the historical retreat of Niagara Falls which persists to this day. Within the caves (Figure 3) the lab members noted clear laminations, thin layers (< 1 cm) observed in sedimentary rocks, within the dolostone blocks. So keep an eye out if you do visit this site to see if you can notice the laminations as well!


Figure 3- Standing Rocks and Caves


This looks like a fantastic site to explore some geology, what should I know?

The trails are only a 1.5 to 2 hour drive from the Toronto area or a short 20-30 minute drive from Collingwood. The Nottawasaga Lookout is a nature reserve which is tasked with protecting rare species, in this case some plant species including uncommon ferns (Ontario Parks, 2021). Therefore, if you do visit come prepared as there will be no facilities. Also, as this is a nature reserve, please do not leave an imprint on the environment. Help in upholding the natural beauty and pristine surroundings for future visitors by being respectful of the environment by staying on the marked paths.

If you are interested in learning more about the geology at this site check out the virtual field trip Limestone Surfaces of Southern Ontario to find more sites like the Nottawasaga Trail and learn about the imprint of the Niagara Escarpment on Central Ontario's geology.

Acknowledgments

Special thanks to Kirsten Kennedy, Alan Yu, and Patrick Peng for pictures and their help.

References

Ontario Parks. (2021). Nottawasaga Lookout. Retrieved from Ontario Parks: https://www.ontarioparks.com/park/nottawasagalookout