Have you ever been driving through Alberta and suddenly spotted a huge boulder and thought: “How the heck did that get there?”
This question arose recently while I was walking the Legacy Conservation Easement at Jackson Lake. One of these boulders, known as glacial erratics, was noted on the map, but exploring further we discovered three more around the lake. There are probably a few more buried beneath the layers of muck and sediment surrounding the wetland area.
These rocks are members of the so-called Foothills Erratics Train, which follows a rather straight path along Alberta's eastern slopes south into Montana—930 km. These erratics are remarkable for their sheer size—most are in the size range of a refrigerator to a small house. They sit nicely arranged on top of the prairie, usually level and unbroken.
So how did they get here?
Based on their composition of light grey and pink quartzite, the origin of these rocks has been matched to an area near Jasper, close to the headwaters of the Athabasca River. The rocks themselves were formed over 500 million years ago.
Analysis of the most recent fractured sides of the rocks indicates they broke off some fifteen thousand years ago—most likely in a landslide which dropped them on top of a massive ice sheet that covered most of the continent at that time. These giant rocks then “flowed” on top of the glacier from their source, and travelled hundreds of kilometres before reaching their resting places.
Keep your eyes peeled for glacial erratics throughout Mountain View County, especially along Highway 766.
P.S. The largest erratic in the Foothills Erratics Train is Big Rock, south of Okotoks.
Article & Photo by Jordan Collin
Summer Junior Environmental Conservationist