Summer at Setting Lake…endless sunshine, blue skies and long hours of daylight, the sound of waves lapping softly against sand beaches, and loons calling. Fresh pickerel for supper. Does it ever get any better than that?
Turns out there’s plenty of evidence that summers at Setting Lake weren’t always so pleasant. The clues are all around us – in the lake itself, the landscape, and the river that runs through it. It’s time for some geological detective work!
First the river. From its headwaters near Cranberry Portage, the Grass River flows east across northern Manitoba, emptying into the Nelson River about five kilometers upstream from Split Lake.
The river, at the time unnamed, was first noted in a crudely drawn map Moses Norton, Factor at Prince of Wales’s Fort, obtained from a group of indigenous traders in 1760. The name “Grass River” first appeared on a map drawn by Samuel Hearne in 1776, an explorer and Hudson Bay Company employee.
In 1876, geologist Robert Bell surveyed the lower portions of the river, but it was not until 1896 that geologist, historian and map maker, Joseph Tyrrell, completed the first survey of its entire length. Tyrrell recorded that the Cree name for the river was Muskuskow’ Sipi, meaning “Grassy River”.
Over its 600-kilometer course, the Grass River runs through two vastly different geological regions. The good news is you don’t have to be a geologist or mining engineer to pick them out. They’re easy to spot!
To the west, from Simonhouse to Tramping Lake, the landscape is dominated by a buff limestone called dolomite, which was formed on the floor of an ancient sea. Over time, bits of weathered rock and the remains of living organisms were deposited on the seabed, and under the pressure of their own weight, they turned to stone. A flat sedimentary rock, dolomite is a perfect paving stone that not surprisingly finds its way, on a regular basis, from rocky outcrops south of Ponton to Setting Lake cabins.
A Dolomite Inukshuk Along Highway 6. Credit: Wiki Media Commons
Further downstream, eons of erosion have exposed the much harder rock of the Precambrian or Canadian Shield. These are some of the oldest rocks in the world. The Precambrian Era is the longest and arguably the most important part of Earth’s history. It begins with the formation of the planet and represents a time so vast and long ago that it challenges our comprehension.
The Precambrian is the time for our biggest questions: “How old is the Earth? What was it like then? How old are the oldest rocks? When did life appear and what did it look like?”
Precambrian Outcrop at Wekusko Falls
Between Wekusko and Setting Lake, the Grass River tumbles through a series of picturesque falls, chutes, and rapids. Fault lines in the rock hint at ancient mountain ranges that once covered the region.
Rapids Between Wekusko and Setting Lake
Throughout its length, the Grass River runs through an ancient geological zone, one with a very fancy name – the Trans-Hudson Orogen (THO). Simply put, an orogen is a zone that’s created when the earth’s crust lifts and forms mountains.
Trans-Hudson Orogen Credit: Canadian Plains Research Center Mapping Division
The THO played an especially important role in forging of North American continent. It was the glue that held everything together.
The THO was created almost two billion years ago when three ancient land masses collided with a force so intense that it pushed up mountain ranges that would have rivalled the grandeur of the Himalayas. During this process, the THO or as it is sometimes called the “suture zone” welded the continents together. The roots of these ancient mountains are visible at Pisew Falls, with a 13 m drop of water rushing down through the gorge. Kwasitchewan Falls and Pisew Falls are the highest and second highest known waterfalls in Manitoba. They can be seen from viewing platforms along the short boardwalk, or longer hiking trail for the avid adventurer, and they are right in our backyard!
Pisew Falls Credit: Hugh Fraser
Kwasitchewan Falls Credit: Jenn Thackeray
When the land masses collided, volcanoes formed and rocks that were deeply buried beneath the earth’s crust were “cooked”, transformed by heat and pressure. The resulting folds and bends can be seen in the outcrops all around us. The collision created two regions of deformed volcanic rock that are economically important today – the Flin Flon Greenstone Belt with its valuable deposits of copper, zinc, silver, and gold – and closer to home – the Thompson Nickel Belt.
Folding of Archean Gneiss Credit: Angie Kennedy
But time marched on and winter was coming! An ice age was on its way. The earth’s temperature turned much colder, and snow began falling. In the years that followed, it grew so cold the snow never melted, and storms brought even more precipitation. Snow piled up year after year, century after century, millennium after millennium. Eventually, the compressed snow became a thick blanket of ice, spreading out from Hudson Bay and covering much of North America.
Continental Glacier Credit: Mario Tama – Getty Images
The last ice age began about 115,000 years ago. It lasted tens of thousands of years. At its peak, the Laurentide Ice Sheet covered 97 percent of Canada. At Setting Lake, the ice was about four kilometers thick – almost the length of Road 1!
The glaciers advanced and receded, flowing like a very slow-moving river. They scoured the land like cosmic bulldozers and brought the ancient mountains to their knees.
When Earth’s temperatures began to warm up, the glaciers stopped advancing and the thick blanket of ice began to melt. Ten thousand years ago most of the ice had disappeared. But in its wake, the continental ice sheet left enough meltwater to create one of the largest and deepest lakes the world has ever known, a glacial lake contained on its north side by a wall of ice three kilometers thick.