Setting Lake Rocks!
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!
Credit: Coral Thompson
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.
Area Covered by Lake Agassiz
The ice wall acted as an enormous dam that blocked natural drainage systems. Water from all the rivers and lakes that drained into Hudson Bay had nowhere to go. They pooled at the base of the soaring Laurentide Ice Sheet, expanding from a pond to a lake and finally, to a colossal fresh-water sea.
Ice Sheet Wall Credit: Olaf Otto Becker for The New York Times
Glacial Lake Agassiz was the mother of all lakes. It covered most of Manitoba for four thousand years. Setting Lake was a mere drop in the bucket, part of a massive inland sea, a sea 700 feet deep.
Not only in size, but also in strength, Lake Agassiz was a giant. The force of its waves separated sand and gravel from silt and clay. Setting Lake gardeners will tell you we got more than our fair share of clay! And swimmers know that sand beaches are the exception, not the rule, at Setting Lake.
For the geologically curious, however, there are two notable Agassiz beach ridges nearby. It’s no surprise they’re right along the Hudson Bay Rail Line at Mile 109 and 110 near Ponton. Railway companies, governments and road construction contractors discovered they could save money by building on the elevated, well-drained beach ridges that Agassiz left behind. Many of these sand and gravel beaches were turned into conveniently located borrow pits.
Standing on one of those beaches, our imagination takes hold. It’s easy to envision an expanse of water stretching as far as the eye can see, towering waves pounding on the lake’s rocky shorelines, crashing against the ice wall to the north. Great chunks of ice creak and groan as they break off the ice cliff. We hear cracks of thunder as icebergs collapse into the water, shatter, then drift away and melt.
Calving Iceberg Credit: University of California Davis
Setting Lake fishermen want to know, “Were there fish in Lake Agassiz?” The answer, “Yes!” According to the late Ken Stewart, Professor of Zoology at the University of Manitoba, only four species of fish are represented in fossil remains found in the lakebed, but he estimated that thirty others – including pickerel, jack, sturgeon, and lake trout – entered the province through Agassiz.
“Was Lake Agassiz the ultimate fishing spot?” We’ll never know. But one thing is certain, travelling back in time to explore this amazing lake would be the ultimate adventure!
Lake Agassiz was a tempestuous shape shifter, changing its form and size as it advanced and retreated, taking on a whole new look as its drainage outlets were opened or blocked. At times Agassiz morphed into a serpent, its neck and spine snaking along the curved edge of the melting ice sheet.
As for the massive Laurentide Ice Sheet, it didn’t just block Agassiz’s drainage. It also weighed down the earth’s crust, causing it to sink by up to a kilometre.
Video: From Glaciation to Global Warming – A Story of Sea Level Change
Credit RealSim Movies
At the end of the great lake’s life, a horseshoe-shaped ice dam about 200 kilometres wide curved around the bottom of Hudson Bay. That was all that held Lake Agassiz back.
When the ice dam collapsed, Agassiz released so much water that it raised sea levels and interrupted ocean currents, which lowered the earth’s temperature for the next 150 years.
Plants quickly moved in, establishing themselves on Agassiz’s sandy shores and rich lakebed. Elsewhere, wetlands and marshes formed. Eventually lichens, mosses and grasses were replaced by bushes and trees; forests grew up. And animals and humans moved north into the Setting Lake area.
The prominent beach ridges that Agassiz left behind were elevated, sandy, and well-drained. Migrating animals and hunters that followed them used the ridges as convenient trails. They made good campsites and lookouts, and were rich sources of chert, prized for spear and arrow points that are often found in the Setting Lake area.
First Nations used Agassiz’s beach ridges for religious and ceremonial events. Ridges also served as natural burial grounds for indigenous people and Europeans. It was easier to dig in sandy soil, and rain and meltwater easily drained away. Dozens of cemeteries are located on beach ridges. In fact, that’s one way to spot a beach ridge.
Much later, beach ridges were used by fur traders and European settlers for the same reasons – they were elevated and well-drained. In 1890, the geologist, historian and mapmaker Joseph Tyrrell wrote, “They often form beautiful dry roads through country that would otherwise be an impenetrable forest”.
For all these reasons, beach ridges are important archaeological sites with great cultural significance.
Clues to our rich geological, historical, and cultural heritage are all around us. The beach ridges, the rivers, and the lakes – Setting, Paint, Cedar, Winnipeg, Winnipegosis, and Manitoba – they’re all remnants of the mother lake – Agassiz. We see the land – freed of the weight of glaciers – bouncing back. Here in north, it will keep rising for another 10,000 years. Take some time to explore this amazing landscape. You may be surprised by what you discover!
Setting Lake Beach Credit: Angie Kennedy
The author, Donna Henry, is a former Parks Canada Superintendent for York Factory and Fort Prince of Wales National Historic Parks, a founding Director of the Grass River Corridor Tourism Association and a research associate with Sinora International.
Content editors – Angie Kennedy and Bob Southern.
Angie Kennedy is a Professional Geologist with Vale, Manitoba Operations and a Setting Lake adventurer.
Bob Southern is a rockhound. Retired from a career in mining, his passion is geology.
Bibliography
Gertner, John. “The Secrets in Greenland’s Ice Sheet.” New York Times Magazine. New York Times. 15 November 2015, www.nytimes.com/2015/11/15/magazine/the-secrets-in-greenlands-ice-sheets.html Retrieved 19 April 2021.
Huck, Barbara and Doug Whiteway. In Search of Canada’s Ancient Heartland. Winnipeg, MB: Heartland Associates Inc., 2016.
Lutgens, Frederick K., and Edward J Tarbuck. Essentials of Geology. 11th ed. Boston: Prentice Hall, 2012.
Redekop, Bill. Lake Agassiz: The Rise and Demise of the World’s Greatest Lake. Winnipeg, MB: Heartland Associates Inc., 2017.
University of California Davis. “Science and Climate: What’s the Difference Between a Glacier and an Ice Shelf”. https://climatechange.ucdavis.edu/climate-change-definitions/difference-between-glacier-and-ice-shelf/ Retrieved 19 April 2021.
Stauffer, M. “Trans-Hudson Orogen”. The Encyclopedia of Saskatchewan. esask.uregina.ca/entry/trans-hudson_orogen.jsp. Retrieved 18 April 2021.
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