Reading Rocks - Chaudiere Falls
Today is the start of a new series of episodes as we take a look at some of the striking geology of Canada’s east coast. We’re starting in Quebec, just on the other side of the St Lawrence from Quebec City, where a beautiful waterfall in the town of Levis has revealed more than 500 million years of history.
EPISODE NOTES
So begins a foolhardy dive into geology, one for which I was completely unprepared. Rocks are nice. You can rely on them. When the wildlife doesn’t show up on the one day you have at a location, the rocks are still there. So finding stories in them is a real pragmatic approach. Until you actually have to research those stories. Then you discover exactly how little you know about geology, and how much there is to know. This episode was the first one I started researching when I got back from my east coast trip, but it’s being released (checks notes) tenth. That’s how long it took me to reckon with how little I know about geology. Publishing still terrified me. I fact checked til my eyes crossed but I will forever live in fear of an actual geologist stumbling across this and calling me out on some overlooked date or mispronounced name.
This was shot while the wildfires of 2023 were raging in New York State, blanketing Levis in a thick haze which gives everything a certain atypical atmosphere.
In the shot where I mention the hiking trails in the park, I pan over some rocks. Later on in the trip I saw those exact rocks from basically that exact angle in a doorstop tome about Canadian geology.
This was the inaugural flight (minus a 2 minute test at home) of the drone that has been doing all the aerial work in the east coast series.
No joke about Chaudierre being hard to research. People write about the Ottawa Chaudierre Falls without making a distinction so you can read a geological summary and it will almost break your brain before you see some casual reference to parliament hill and realize it’s been the wrong one this whole time.
The Iapetus Ocean is sort of, geographically, the precursor to the Atlantic. It was named in keeping with the Greek familial line: Iapetus gave birth to Atlas.
TRANSCRIPT
Just on the other side of the St Lawrence from Quebec City, you’ll find the mouth of a river. Follow it a kilometre south through the town of Levis, and it quite abruptly becomes this.
A gargantuan 35-meter waterfall spilling up to 1240 cubic meters per second into a roiling basin below.
Because of the cauldron-like shape of that basin and the constant misty spray of the falls, French colonists called them the chutes de la chaudiere, ‘chaudiere’ meaning ‘kettle’ or ‘boiler’. They gave that name to the whole river. In fact they liked it so much they gave it to another, much better-known set of falls more than 400 kilometres away on the Ottawa River, which among other things makes these falls… really annoying to research. Thanks Champlain.
Today, these ‘chutes de la chaudiere’ in Levis sit in the centre of a sprawling park with hiking trails, a hydroelectric power station and a 113-metre long suspension bridge dangling and swaying 23 metres over the river.
In their cauldron, the falls have carved the rock away to reveal these striking geological formations: a layer cake of reds and greys and greens, sharply defined strata jutting up and folding over themselves.
The falls now sit on a pretty solid base. But what they’ve revealed here, if you know the language of rocks, is two stories that take us back more than 500 million years.
We’ll start with the supercontinent Rodinia. We’re so far back in time that it’s entirely barren: complex life hasn’t even reached dry land yet. And it’s about to experience a titanic tectonic shift, as 5 million square kilometres of the Laurentia craton begin to separate. Water floods into the newly opened rift and becomes the Iapetus Ocean.
As with any self-respecting ocean, the Iapetus collects sedimentary layers, deposited on the seabed, built up and compacted over millions of years into sedimentary rock.
At the same time, vast geological processes continue to shape geography on a planetary scale. The split that gave birth to the Iapetus is reversing, and the Laurentia craton is now on a slow-motion collision course with the continental assemblage of Gondwana.
In between, at the edges of that collision, are a series of orogenies. That’s the geological term for mountain-building events. When two land masses meet, one is forced down which forces the other up. Or, that’s the clean and tidy version, in reality there’s a whole mess of compression and thrust faulting shoving all those rock layers around.
And the edge of Laurentia is going to have three of these messy orogenies: Taconic, Acadian and Allegheny - before the Iapetus completely disappears and the supercontinent Pangea is formed, along with a new mountain range along the line of collision: the Appalachians. They’ll be a recurring theme as we explore the geology of the East Coast.
But zooming way, way back in on those layer cake rocks at Chaudierre Falls, we now know enough to appreciate the two stories they’re telling.
The individual layers you’re seeing here are the sediments that were laid down at the bottom of the Iapetus Ocean hundreds of millions of years ago. And the sharp delineation of those layers can give us all kinds of clues about what the world was like back then and how it changed. Like pages in a book, they’re a temporal, linear record of tectonic activity, ocean chemistry, sediment sources and sea level change, just to name a few.
And then, stepping back to look at the angles and folds of those individual layers tells the story of the climactic orogenies that gave birth to the Appalachians. All those thrusts and folds are chapters of enormous land masses crashing into each other on a time scale where rock acts almost like a liquid.
Knowing what to look for as you’re picking around the edge of the river, or braving the view from atop the suspension bridge, turns this gorgeous spot into a window half a billion years into the past. And over the next few weeks we’ll be giving the same treatment to a few more spots along the east coast, seeing how changes in the overlooked rocks underfoot gives us clues to the vast stories of earth’s history.