In the middle of Quebec there is a hundred-kilometre ring of water left by an asteroid

Look at a photograph of Quebec taken from the International Space Station and one thing jumps out before anything else: an almost perfect dark ring in the middle of the forest, about a hundred kilometres across. Astronauts call it the eye of Quebec.

It is not an ordinary lake, or a volcanic caldera, or a chance shape. It is the scar of an impact 214 million years ago, and its present form is the result of three chained events: an asteroid, two hundred million years of wear, and a hydroelectric dam built in the 1960s.

01 A province that is almost all old rock

To understand the ring you have to understand the ground it sits on. More than 95% of Quebec's territory belongs to the Canadian Shield: a platform of extremely ancient rock, scoured by successive glaciations until it was left low, undulating and bare.

That scouring explains the look of the province's north. The ice scraped the rock, left basins everywhere and then withdrew, and those basins filled. The result is more than half a million lakes and some 4,500 rivers, to the point that water occupies 12% of the provincial surface.

And here is the visual key: all those lakes have capricious shapes, dictated by the direction the ice moved and by the fractures in the rock. None is round. A hundred-kilometre circle on that map is an anomaly so obvious it can be seen from orbit.

02 The ribbon where everyone lives

The other half of the map is human. Quebec has around eight million inhabitants spread over nearly three times the area of France, but that figure misleads: almost the whole population is concentrated in the St. Lawrence lowlands, a narrow ribbon with rich soils and a relatively mild climate.

The countryside along that ribbon keeps a very particular pattern: long, narrow rectangular plots that start at the river and run inland. It is the trace of the old seigneurial system, when the river was the only road and every family needed its own access to the water.

Everything else — 92% of the territory is public land — is Shield. Boreal forest first, then taiga, then Arctic tundra in the far north. The further up you go, the fewer roads, the fewer trees and the more water.

03 The impact

Two hundred and fourteen million years ago, in the Late Triassic, an asteroid some five kilometres across struck this platform. Radiometric dating places the melt produced by the impact at 214 ± 1 million years, and a later estimate refines it to 215.4 million.

The crater it opened originally measured about a hundred kilometres side to side, with a structure of several concentric rings. And the blow was no local affair: layers of shocked quartz thrown out by that impact have been found in rocks as far away as England and Japan.

One frequent confusion is worth undoing. This impact happened more than twelve million years before the end of the Triassic, so it cannot have caused the extinction that closes that period. It has been proposed that it contributed to an earlier marine extinction, but there is no direct evidence confirming it.

04 What erosion took away

Two hundred million years of rain, ice and sediment ate away the crater's rim. Of the original hundred kilometres, the visible structure was reduced to about 72, and of the outer relief practically nothing remains: there is no walled crater to look into.

What did survive is the centre. In an impact of this size, the rock at the bottom rebounds upwards and forms a central peak. Here that peak is the plateau occupying the inside of the ring, and its highest point, Mount Babel, rises 952 metres above sea level and 590 above the water.

05 The dam that closed the circle

And now the part almost nobody tells. Until the 1960s, the ring was not a ring: there was a lake on one side of the central plateau and another, smaller one, on the other. The shape was hinted at in the ground, but not drawn.

What completed it was a hydroelectric project. When the Daniel-Johnson dam was built, the water rose, the two lakes joined at their ends and the circle closed. The resulting reservoir covers 1,942 square kilometres and holds 137.9 cubic kilometres of water.

There is a curious consequence of the ring being a working reservoir as well: its level rises and falls with electricity demand. At the peaks of winter cold the water drops, because the turbines run non-stop to cover the province's heating. And it drops again during summer heatwaves, when electricity is exported south.

06 Getting there and what you see from the ground

There is a single road, Route 389, which leaves Baie-Comeau on the north shore of the St. Lawrence and climbs inland. The reservoir lies some 300 kilometres north of that town, and the road runs along its eastern shore.

And it is worth arriving with adjusted expectations, because from the ground no circle is visible. You see a large lake, shores of low forest and a plateau on the far side of the water. A hundred kilometres across is too much for the human eye: the figure exists only on the map and in satellite photographs.

What you do perceive is the scale of the emptiness. Kilometres of road without meeting anyone, no village, no signal, and that low forest repeating to the horizon. It is the best way to understand why eight million people live pressed against a river along the southern edge of an immense province.