Gow Lake crater in Saskatchewan a rarity on Earth

Landmark holds one-of-a-kind rocks, rock formations: international expert

Geological research spanning more than a decade found Saskatchewan has one of the rarest kinds of impact craters on Earth.

The only other crater in the world like the one at Gow Lake is in Australia, and is hardly as pristine as the massive hole blown in the northern Saskatchewan landscape by space debris roughly 200 million years ago.

Through the lens of a satellite, Gow Lake is a large body of water with a jagged shoreline and a sizable island in the middle.

At its geological core, the lake — located in remote wilderness about 400 kilometres north of the town of Nipawin — holds unique features that are unparalleled on Earth, according to research led by Gordon Osinski at Western University in London, Ont. Osinski is an international expert on impact cratering.

What makes the Gow Lake crater unique, Osinski said in an interview, is that despite its age, the crater holds remarkably well-preserved rocks and rock formations that are extraordinary.

Whatever hit the Earth at that spot, whether asteroid or comet, generated so much energy that it liquefied the Earth's crust and created rock of a different kind.

“Gow Lake has a lot of these very interesting rocks we call impactites,” Osinski said. “Because of the nature of the impact process, the melt-rock, or breccia, we find at Gow Lake make it unique in the world. You will not find another rock that looks like it anywhere else on Earth.”

Since the 1970s, it has been known that the water in Gow Lake fills an impact crater measuring roughly five km across. It was assumed to be a central peak impact structure — a common form of crater, circular in shape, with terraced walls and a peak in the middle.

In 2011, a team of researchers lead by Osinski, a planetary geologist at Western, conducted a field study at Gow Lake. The unusual characteristics of the crater prompted long-term study, mostly carried out in the lab.

A dozen years later — the blink of an eye in geological time — the team's findings were published this week in the journal Meteoritics & Planetary Science. They show that the Gow Lake crater is far from typical and is actually a transitional impact structure, of which there are only two on Earth.

“Being rare on Earth is one of the significant things about this crater,” Osinski said. “I would say it is the only actual example we have of this type of crater. The only other crater of its kind, in Australia, is quite eroded and there's very little information left.”

A transitional crater is characterized by fairly smooth walls and a floor partially or entirely covered by debris fallen from the crater walls. It is a transitional form between a simple bowl-shaped crater and a complex crater with a central uplift.

Osinski said the 2011 expedition to Gow Lake, enabled by a float plane and the use of canoes, turned up exceptional rocks that held evidence of a cataclysmic event.

“That projectile hits the surface of the Earth, penetrates somewhat and is essentially vaporized,” he said. “It's all about kinetic energy. That thing is coming in staggeringly fast, 15 to 20 km per second, with a huge amount of energy. That energy is left over as heat that can literally melt cubic kilometres of the Earth's crust, instantly. The surrounding rock looks like volcanic rock.”