Clearwater Lakes
Key facts
- Country
- Canada
- Diameter
- 36 km
- Age
- about 286 million years (West) and about 460 million years (East)
- Location
- 56.15° N, 74.30° W
Two large, round lakes side by side in the forests of northern Quebec: the western lake, about 36 km across, with a ring of islands, and the eastern lake, about 26 km across.
The Clearwater Lakes, in northern Quebec near Hudson Bay, are one of the most famous sights in impact geology. Seen from orbit, two round lakes sit side by side, like a pair of eyes looking up from the forest. For decades they were thought to be twin craters, formed at the same moment by a pair of asteroids. Today we know that their story is rather different.
Two lakes, two craters. Clearwater West is the larger, about 36 km across, and it has a striking ring of islands inside it. These islands are made of the crater's central uplift and of impact melt rock, which once formed a sheet over the crater floor. Clearwater East is about 26 km across and has no islands, but a central uplift lies hidden beneath its waters. Both lakes are surrounded by ancient rock of the Canadian Shield.
The local Cree name for the lakes is often given as Wiyâshâkimî. In French they are called Lac à l'Eau Claire.
Twins no more. For many years the two craters were thought to have formed at the same time, around 290 million years ago. A pair of craters like this could have been made by a binary asteroid, two asteroids orbiting each other, a common type in the Solar System. Clearwater became the textbook example of a double impact.
In 2015 a team of scientists published new, more precise dates for both craters. They found that Clearwater West formed about 286 million years ago, but Clearwater East is much older, around 460 to 470 million years, in the Ordovician period. In other words, the two impacts happened nearly 200 million years apart, and their close placement is a coincidence.
Why it matters. The Clearwater Lakes show why careful dating is so important. Some other proposed double craters have also turned out to have different ages. Genuine pairs of craters formed at the same time do exist, but each must be tested with precise measurements. The Clearwater story also shows how science corrects itself: a long-held idea was overturned by better evidence.
The landscape. Ice-age glaciers scoured the region, removing much of the crater rims and leaving the lakes to fill the eroded basins. The surrounding area is roadless boreal forest and tundra, part of the traditional territory of the Cree and Inuit, and it is reached mainly by floatplane. The lakes are known for fishing, and a few lodges operate in summer.
Seeing it. Astronauts often photograph the Clearwater Lakes, especially in winter, when the frozen lakes stand out clearly against the darker forest.
Did you know?
The two lakes were long thought to be twin craters, but their impacts happened nearly 200 million years apart.
Clearwater West has a ring of islands formed from its central uplift and impact melt.
The lakes are easiest to spot from orbit in winter, when the ice stands out against the forest.