Dark Spots and Patterns on Lake Ice

January 15, 2021

Mm_spots01 (002)a

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Photographer: Mr. Moose 
Summary Author: Mr. Moose 

Patterns on Lake Ice2222222222A few weeks back, ice covered the lake near my home for the first time this season. It was quite thin (less than one-quarter inch or 6 mm) and completely clear and smooth and thus appeared rather dark since lake water was easily visible through it. Not until ice thickens and gets rough does it attain the matte white look that most people think of when they envision ice.

During the early afternoon I noticed that a thin layer of snow covered the ice and also it was now littered with a few leaves (top photo). Later on, there were dark spots on the ice, and at the center of each spot was a leaf (inset photo). Later yet, these spots had grown in size (bottom photo). The leaves were melting the snow and exposing the ice, not because they were warm but rather because dark leaves absorb solar radiation more readily than does snow. This continued in a feedback loop where the dark spot on the ice then absorbed more radiation and continued to get larger and larger, even when the sky was overcast. Notice also the more star-like or spider-like pattern of the smaller spots (bottom photo). It should be mentioned that when the snow or ice is thicker, I never see this phenomenon. Photos taken on November 21, 2020.