William Alfred (W.A.) Johnston

William Alfred Johnston was a pioneering Quaternary geologist and limnologist with the Geological Survey of Canada, widely regarded as a founding leader in Canadian Quaternary studies. His 1922 paper “Sedimentation in Lake Louise, Alberta, Canada” (American Journal of Science) remains a classic; one of the first to apply quantitative methods to glacial processes and to link modern glacial dynamics directly to lake sediments.

The Lake Louise study (1921–1922). Johnston conducted fieldwork at Lake Louise in Banff National Park in 1921. He identified that sediment on the lake floor was deposited in distinct annual couplets; varves; each consisting of a coarser, lighter summer layer (meltwater) and a finer, darker winter clay. He calculated an average sedimentation rate of ~4 mm per year and, from total sediment depth (then estimated at ~30 m in places), inferred that the lake had been forming for roughly 4,000–5,000 years; remarkably close to modern paleolimnological estimates. He treated the sediment as a “clock” or calendar of geological history: by counting and measuring varves, he could infer the retreat history of the Victoria Glacier since the last major glaciation.

The turquoise colour. Johnston provided the definitive scientific explanation for Lake Louise’s world-famous hue. He proposed that “rock flour” (glacial milk); fine silt and clay ground from bedrock by the Victoria Glacier; remains suspended in the water column. These particles scatter shorter wavelengths (blues and greens) while the water absorbs longer wavelengths (reds), producing the brilliant turquoise. As glaciers disappear, the source of glacial milk vanishes; Lake Louise may eventually lose its iconic colour and become a clear, deep blue alpine lake.

Legacy. Johnston’s work bridged glaciology and limnology, demonstrating that lake sediments are high-resolution archives of environmental change. His approach to varve chronology remains foundational for reconstructing past climates and glacier fluctuations in the Rockies. The Canadian Quaternary Association (CANQUA) awards the W.A. Johnston Medal; its highest honour; for professional excellence in Quaternary research. His 1922 observations provide a critical baseline for measuring modern climate change and glacial retreat.