Gog Group and Lake Louise Geology

The geology of Lake Louise and its surrounding peaks is a story of ancient tropical seas, the Laramide Orogeny, and glacial sculpting. The mountains (Mount Victoria, Mount Temple, Mount Whyte, Mount St. Piran) are primarily composed of the Gog Group, Early Cambrian rock (541–513 million years old) deposited on the western edge of Laurentia when the area was a shallow marine shelf.

The four formations. The Gog Group in this area comprises: (1) Fort Mountain Formation; dark, massive quartzites at the base; (2) Lake Louise Formation; a thin 15–20 m band of grey-green shale that forms the benches where trails (e.g. to Lake Agnes) sit; (3) St. Piran Formation; the dominant cliff-maker, ~500 m of pinkish-white quartzite forming the vertical walls; (4) Peyto Formation; limestone capping the group, marking the transition to carbonate-heavy seas. Charles Doolittle Walcott formally named the Lake Louise and St. Piran formations in 1908.

Laramide orogeny. Approximately 80–60 million years ago, the Laramide Orogeny thrust these sedimentary layers eastward. The mountains were not “grown” but “pushed”; layers snapped along thrust faults and slid like a rug against a wall, creating the “shingle” appearance with layers dipping steeply west. Richard George McConnell first documented this at Castle Mountain (1886), where Middle Cambrian limestone sat atop Cretaceous coal-bearing shales; proof that older rock had been thrust over younger. The Castle Mountain Thrust elevated the Lake Louise peaks to over 3,000 m. McConnell’s Great Overthrust (later named the McConnell Thrust) explained how the mountains were hoisted into the sky; Raymond A. Price and Eric Mountjoy would later map the full thin-skinned fold-and-thrust architecture.

Rock flour and turquoise. Lake Louise sits in a glacial cirque carved during the last glacial maximum. The Victoria Glacier grinds St. Piran quartzite into rock flour; fine silt that remains suspended in summer. Sunlight scattering off these particles (blues and greens reflected, reds absorbed) produces the iconic turquoise hue. W.A. Johnston explained this mechanism in 1922. As glaciers retreat, the rock flour source diminishes; the lake may eventually lose its colour and become a clear alpine blue.