When you're done exploring the School of Hard Rocks, try these experiments to see the erosion process for yourself:
450 million years in the making
It's hard to believe that the rocks that you hike across while on the Bruce Trail are as old as 450 million years old. A very large mountain range existed along the eastern edge of North America. This large landform was eventually eroded and weathered by rain, wind and ice. As the eroded material moved west toward a shallow sea known today as the Michigan Basin (a much larger sea containing current Lake Michigan, Lake Huron and Georgian Bay combined).
All of this eroded sediment accumulated and eventually formed new rocks through compression, called sedimentary rocks. Layers of mud turned into red shale while layers of sand turned into sandstone.
Animals turning into stone?
As the basin increased in size, it became a warm, clear ocean where coral reefs developed and a variety of animal life was found. As these animals died, their bones, containing calcium, fell to the bottom of the ocean floor. Eventually, all of this calcium was compressed into layers of limestone.
As landforms continued changing, the vast water body known as the Michigan Basin became shallower and shallower. The concentration of salt and magnesium from the ocean water seeped into the porous limestone and the chemical reaction created dolostone, a hard erosion resistant rock. Today dolostone forms the cap rock of the Niagara Escarpment.
Over the next 100 million years, the Michigan basin dried up considerably. This left an immense plain of eroded material, called sediment. Eventually, rivers cut through this plain and they carved out narrow valleys.
Erosion on the vertical face of rocks is called differential erosion. These surfaces incurred more weathering and as the softer underlying layers were eroded away, huge blocks of dolostone broke off the top of the formations.
Ice sheets 4 to 6 times the height of the CN Tower!
All of this happened long before the Ice Ages. There were actually four periods of time when the escarpment was covered with two or three kilometers of ice. That is 4 to 6 times the height of the CN Tower. The last ice age only ended twelve thousand years ago. As all of this ice was moving, it scraped across the rock layers of the escarpment. Land formations changed. River valleys became broader with steeper sides.
When the glaciers finally retreated, they deposited all the material that had been scraped and pushed as they moved. Those deposits are called glacial till. Since the glaciers moved from north to south, the deposits of this loose material is deeper in the southern regions. After the melt rivers slowly decreased in size.
Water and weather continue to play a role in shaping the escarpment. Waves create caves and sea stacks along the coast of what is now Georgian Bay and Lake Huron. Rainwater and snow melt penetrate the porous dolostone to create karst features like caves and crevices. Water droplets in the porous spaces of the rocks also freeze and expand during colder months. This expansion can further change the face of the escarpment by releasing loose or weakened rocks.