Walking on Ancient Mountains

Shayne Thiessen

September 1983, lightning flashed across the night sky, striking the ground below. The dry boreal forest was suddenly alive with fire! The drought that had plagued Nopiming Provincial Park had created the perfect conditions for a massive forest fire. By the time the fire stopped burning it covered over 98 square miles of forest.

One of the after-effects of this fire was that it exposed the Canadian Shield rocks. Previously most of the rock faces were hidden by the forest vegetation. These rocks, which come from the Precambrian era, were once part of an ancient mountain chain, which would have resembled the rocky mountains. It is estimated that the highest mountains would have reached 39,000 ft(12,000 m) tall. There is also evidence that this mountain range would have contained a lot of volcanic activity.

Over time the mountains slowly eroded, eventually settling into their present condition. As the mountains eroded, their “roots” were pushed up from the ground. As a result, the rocks that now form the surface of the Canadian Shield were once far below the Earth’s surface.

It is theorized that the Canadian Shield was once part of an ancient continent called Arctica, which was formed about 2.5 billion years ago during the Neoarchean era (estimated 2.8 to 2.5 billion years ago). This ancient continent eventually moved further north and is now situated in the Arctic around the current North Pole. Parts of the continent split into multiple different islands including Greenland, Laurentia, and Scotland while the rest was submerged beneath the Arctic ocean.

Within Manitoba’s Nopiming Provincial Park there is a short hiking trail called Walking on Ancient Mountains (which this blog post was inspired by), that goes through the Boreal Forest and then climbs up the remains of these Ancient Mountains. It provides a fantastic glimpse into the distant past as well as a look at the geology of this area.

Along the trail, you can discover Pegmatite, which is a white igneous rock that’s similar in appearance to granite. Igneous means that the rock was formed from magma. The Pegmatite is mixed with large grey quartz, pale pink feldspar, black tourmaline and brown flakes of mica. Some gemstones, like emeralds, are found almost exclusively in Pegmatite rock.

The rock hill that the trail takes you upon is made almost entirely of pegmatite. At one location there is a 50 cm by 5 cm long pink feldspar crystal that is intertwined with grey quartz, mica flakes and black tourmaline.

Upon reaching the top of the trail, it continues in a small loop around the summit. To the east, you can see what appears to be a never-ending forest, and to the west lies Tooth Lake.

From here you can inspect the size and shape of the distant rock hills. You will notice that this one and the others around it appear smooth on one side, and rough on the other. A keen observer will notice that the rough side always faces the same direction.

Approximately 13,000 years ago, this entire area was covered by a giant glacial sheet of ice, which would have approached 2 kilometres in height. As the glacial ice moved, it slid smoothly up one side of the rock hills and caused the other side to crumble. This information reveals which direction the glacial ice moved. Here, you can see that it moved from northeast to southwest. The name for rock formations formed through this process is roche moutonée which comes from the French term “sheep’s back”.

The forest landscape here has changed a lot over time. One of the places this is most evident is a few miles north of the Ancient Mountains trail on the Fire of ’83 hiking trail. This trail takes trekkers out to Maberly Lake where the wetlands contain an “island” of unburnt trees. There is a stark contrast between the burnt and unburnt areas.

This area is a good example of the changes that have occurred over the past couple of decades. However, the more drastic changes that have taken place over the centuries and millenniums are not visible. The secrets to these changes are hidden beneath the vegetation and within the Precambrian rocks.

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