Stoked on Science: The rocks of Revelstoke colliding, scraping and sliding

Jade Harvey

Special to the Review

When winter arrives on the mountains it has always accentuated to me the grandeur of their presence, the true power of these rock giants.

The Earth’s crust that comprises everything we live on, from the flattest prairie lands to the towering mountain peaks ranges, is between seven and 100 km deep.

This seemingly hard and solid crust is in fact a jigsaw puzzle of pieces or plates that float, moving in relation to each other on the mantle or semi solid layer of molten rock below it.

Plate tectonics (the creation, destruction and movement of these plates) have shaped the creation of every land mass and ocean on our planet.

Around 200 million years ago, when the next key step in the creation of Revelstoke rocks occurred, all of the Earth’s landmasses were congregated in one giant continent, centred over the Equator. It was called Pangea.

As Pangea began to break up around this time, the land masses split apart and began to travel independently.

The Atlantic Ocean opened.

The land mass we now call North America changed direction and began to move northwest, overriding the denser rock making up the floor of the Pacific Ocean.

On the Pacific oceanic there were large floating chains of volcanic islands made of comparatively lighter igneous rocks.

Rather than slipping under the edge of North America like the basement rock did at this subduction zone, these light islands stuck themselves onto the edge of North America.

Much of British Columbia is made up of these terranes.

The force of these collisions—we’re talking about tens of kilometres of rock being smashed together — built the Canadian Corderilla.

The name comes from the old Spanish word for rope or strings, and details a major system of parallel mountain ranges (in our case the Coast, Columbias and Rockies) that look like lines of rope on a map.

The Canadian Corderilla includes the intervening plateaus, valleys and plains that make up all of western Canada.

Some 185 million years ago, the Columbias were the first to rise out of these collisions.

With the land mass of North America to the east and the Pacific plate wedged against it and sucked beneath it to the west, the rocks had nowhere to go but up.

The younger to the East Rockies were fully formed by about 100 million years ago and the Coast ranges were created between the two.

READ MORE: ‘You’re sitting on a jewel, Revelstoke’: Wilderness society proposes new park

If you put your foot on the edge of a rug and push, (signifying the western edge of Canada’s landmass being pressed against the Pacific Ocean crust), the middle of the rug will lift up.

This is the basic premise for how mountain building occurred in our region.

By 60 million years ago, the mountain building phase had calmed down.

By 55 million years, the terrane collisions had all but occurred but the pressure of all this pushing, scraping and sliding caused the Earth’s crust to stretch and huge lateral faults to crack through the rocks.

This main transverse fault (similar to the most famous San Andreas fault in California) is called the Rocky Mountain Trench which divides us in the Columbias from our Albertan neighbours.

Were it not for this trench, we would all still be one continuous mountain range, which it is south of trench in the U.S. in Idaho, Montana and northeast Washington.

So the history of the rocks in Revelstoke is effectively that of a pretty beat up layered cake.

The bottom layer, the tough structural sponge, consisting of two-billion-year-old basement rocks laid down before the Earth looked anything like the mixture of rock and water we see today.

Ancient sediments that in the next few weirdly spotted layers become filled with the detritus of oceanic life that existed 600 million years ago.

READ MORE: U.S. protects already extinct caribou herd

The next light and fluffy frosted layer arriving 200 million years ago, scraped lightly on to those below.

But before the final sprinkles of glacial, wind and water deposits can be shaken on top, over the timespan of 140 million years, somebody repeatedly punches the cake from the side and the layers get all swirled and mashed together.

And so we reach the Cenozoic, from 65 million years on to now.

Next month we’ll discuss the Quaternary, the most recent 2.8 million years of Earth’s history.

Jade Harvey graduated with a 1st Class Honours BSc in Physical Geography from QMUL, a top five university in Europe. She spent the last eight years travelling the mountainous regions of the world, mountain guiding and lecturing on science in schools. She owns and operates Stoked On Science delivering science and sports programs to schools.

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