Today’s post comes from Mat St-Jules, an interpreter at Samuel de Champlain Provincial Park.
The views of the Mattawa River continue to draw me in.
I find incredible beauty in an unkempt cedar tree clinging to a craggy rock or in the glistening fur of a river otter standing on a sandbar. But, of course, these wonders do not stand on their own.
Beneath the wildlife and beyond the trees lies the foundation of this land: the geology on which everything rests.
The rock at our feet
The course of the Mattawa River runs through the Canadian Shield. Near the beginning of its path, it widens to form Turtle Lake. Dotted with rocky islands, it is typical of a lake in this region.
The stone here is primarily gneiss (pronounced “nice”), a pink rock with black veins. It is a metamorphic rock, meaning it was created from a previously existing rock that was transformed with incredible heat or pressure.
In this case, the pressure came from the collision of continents about 1.2 billion years ago. That’s five times older than even the first dinosaurs, before the evolution of fish and before the evolution of insects.
This collision bent, cracked and thickened pre-existing rocks, forming a new mountain range that rises tens of kilometers into the sky. This era was known as the Grenville orogeny (geologists speak of mountain-building orogeny).
Over the eons since then, the Grenville Mountains have been eroded.
The gneiss formed beneath these peaks is known as Grenville Gneiss.
Its dark, pale bands are caused by minerals such as micas that have aligned and organized against pressure. Some of the rock material reached such temperatures that it melted and flowed through the surrounding stone, eventually cooling to form fringes of granite.
The colliding continents finally separated again 200 million years ago.
The Mattawa River follows one of the faults that developed during this time. A fault is a fracture in the Earth’s crust. This is appropriately called the Mattawa Fault.
Striking evidence of their existence can be seen a little downstream at Talon Chutes.
Here, the stream runs through a narrow gorge flanked by cliffs that extend far above the water and echo the sound of the falls. Along the lower half of the Mattawa River, similar cliffs are common.
The Mattawa fault is not the only one in the region. In fact, it is the northernmost fault in an entire fault system.
Together they form a structure called the Ottawa-Bonnechere Graben. “Graben” may be a new word to most of us, but think of it as a valley.
Due to the separation and stretching of the continent, the Earth’s crust shifted downward. This happened along what would be a valley. The Mattawa River and its fault are a section of the larger and more complex graben.
Geology in action
Geological forces have continued to shape the Mattawa River. The slow erosion of the surrounding hills is probably most noticeable at their base.
Here, small streams flow into the Mattawa River. These have picked up sediment, created erosion, and then dropped it as sandbars and sand deltas into the main Mattawa River valley.
There are such sandbars near Samuel de Champlain Provincial Park at Elm Point, Purdy Creek and Simpson’s Falls.
The sandbars make these areas ideal places to rest during a day of paddling. Visiting these beautiful beaches brings you face to face with the continuing impact of geology on the Mattawa River landscape.
The landscape of the Mattawa River is based on its geology.
Paddling along makes me realize the extent to which our world is shaped by these powerful but invisible forces.
It’s a fact I often forget, but the Mattawa serves as a striking reminder.
And for that I am grateful.