Great Lakes Coloured by Sediment and Algae (Photo of the Day)

The Great Lakes – one of the most amazing geographic sites to see from space – is pictured below in what NASA describes as a ‘contradiction’ of colours.

The blue streaks that can be seen in Lake Michigan and Lake Huron is the result of sediment brought to the surface as a result of strong winds. The green Lake Erie and in Lake Huron’s Saginaw Bay shows algae which, conversely, is brought to the surface as a result of calm winds.


The image was taken using the Moderate Resolution Imaging Spectroradiometer on board NASA’s Aqua satellite on October 9, just after a persistent mid-latitude cyclone had moved out of the region.

Sediment most often colors the Great Lakes in the spring and fall when transitioning weather patterns bring storms and strong winds. The winds stir the water, pulling quartz sand and silt from the lake bottom to the surface, says Richard Stumpf, an oceanographer with the National Oceanic and Atmospheric Administration. The white sand looks milky blue when viewed through the water from space. It is a good tracer, says Stumpf, illustrating how circulation in the lake moves material from the banks to the center.

Some of the pale blue in Lake Erie may be sediment, but the green is an extremely large algal bloom. The algae may have initially spread across the western side of the lake because of windy weather, but calm weather and warm temperatures after the storm allowed green scum to build on the surface, says Colleen Mouw, a researcher at the University of Wisconsin-Madison. The bloom now covers much of the western half of the lake.

“This is considered the worst bloom in decades,” added Stumpf. The green in Saginaw Bay is probably an algal bloom as well.

Source: NASA

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