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Swirling Sediments in the Great Slave Lake

The Great Slave Lake in Canada's Northwest Territories matched its highest water levels on record in 2020, sitting at 515 above sea level in late June.

At 10,500 square miles, the lake near the provincial capital of Yellowknife is the world's 10th largest. For comparison purposes, Utah's Great Salt Lake is a mere 1,700 square miles.

Landsat satellites don’t measure the depth of water bodies, but they do capture new imagery of lake surfaces every eight days that can help us understand the changes wrought by wet seasonal conditions. The differences between 2019 and 2020 are especially stark.

The Landsat image on the right shows a swirling muddy discharge in the Great Slave Lake on June 29, 2020, appearing in a thick, sandy tan color where the Slave River meets the lake. The image was collected after a wet spring and snowmelt that flowed into the lake both more rapidly and later in the year than usual. The image on the left shows the area in 2019, a notably dry year. Tan runoff is visible but less widespread and less uniform in color near the shoreline.

Viewing the same scenes through the prism of Landsat’ shortwave infrared, near infrared and red bands (7-5-4) reveals even more stark differences.

In the 2020 image on the right, shades of bright emerald swirl in the water, signaling sediment and dissolved organic material in the lake’s swelling waters. The same band combination for 2019, even obscured by cloud cover, paints the surface waters in a near-uniform black.

Landsat imagery is available for download at no charge through EarthExplorer.usgs.gov. Learn more about Landsat bands and how they’re used to study change by following this link.