Glacial Lake Invermere EarthCache
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The upper Columbia River Valley as we know it today forms part of the Rocky Mountain Trench, is 3-15 km wide, and bordered by the Rocky Mountains on the east and the Purcells to the west. The drainage divide is at Canal Flats, where the Columbia River flows north and the Kootenay River flows South.
During the last glacial period, the valley was filled with ice. During deglaciation, the ice retreated north. As it reached the upper Columbia Valley, meltwater pooled between the glacier and a sediment dam to the south, creating Glacial Lake Invermere.
At its maximum, Glacial Lake Invermere stretched from Bluewater Creek, north of Donald, to north of Skookumchuck - a distance of 210 km. It was 2.5 km wide (on average), and about 100 m deep. The northern end of the lake was blocked by retreating glacial ice from the Trench and Beaver glaciers. The southern end of the lake was dammed by outwash gravel (gravel deposited by a stream emerging from a glacier), till (unsorted glacial sediment of all sizes deposited by a glacier), and bedrock outcroppings.
Breaching of the dam and retreat of the ice northward marked the end of Glacial Lake Invermere, and the drainage in the valley was established as we see it today.
Glaciolacustrine (glacial lake) deposits form terraces and deposits bordering the floor of the Rocky Mountain Trench. Current ripples in the deposits indicate that lake-bottom currents were directed south.
Where rivers and streams joined the lake, deltas formed. The fast-moving streams that carried sediment slowed and deposited their loads. One such delta is located where the ancient Kicking Horse River flowed into the lake. Coarse-grained glacial deltas such as this one typically have three components: the topset, foreset, and bottomset beds (from top to bottom). The topset beds are typically the coarsest beds, contain a wide range of size fractions, and are horizontal. They are the sediments that were dropped from the stream first as it reached the lake margin. Sediments that were carried to the front of the delta cascaded into deeper water and formed the foreset beds. The foreset beds are generally composed of a mix of sand and gravel, and dip in the direction of the stream's entrance into the lake. The contact between the topset and foreset beds indicates the level of the bottom of the stream. The bottomset beds are the finest layer, formed by the fine sediments that were carried beyond the foreset beds and deposited on the bottom of the lake in front of the delta. As deposition occurred, the delta built outwards into the lake, so a cross-section of the delta now shows all of the beds on top of each other.
At this EarthCache site, the beds of the ancient Kicking Horse delta are visible across the river in the cutbank. The topset beds, in this case 3-5 m thick, form the uppermost layer. Most of what is visible in the cutbank are the dipping foreset beds.
To log this EarthCache, please email the owner the following information:
1. Which direction do the foreset beds in the cutbank dip?
2. Estimate the height of the cutbank.
This EarthCache is located along the Rotary Trail in Golden, behind the municipal campground. Please respect any persons using the campground and don't cut through their campsites.
Sources:
Sawicki, O., Smith, D., Glacial Lake Invermere, upper Columbia River valley, British Columbia: a paleogeographic reconstruction, Can. J. Earth Sci., 29, 687-692 (1992).
Mathews, B., Monger, J., Roadside Geology of Southern British Columbia, Mountain Press Publishing Company, Missoula, Montana, 2005.
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