Dicromantispa interrupta

Dicromantispa interrupta

Friday, January 1, 2010

Chill Mystery at Lake Baikal

I ran across the banner NASA photograph and a very interesting, unexplained occurrence today at http://earthobservatory.nasa.gov/IOTD/view.php?id=38721

Ahem, I have a theory...

Start with a relatively warm upwelling that thaws, thins and cracks the ice, creating a mix of ice floes and open water in a restricted area that remains surrounded by thicker ice. Add a moving air mass, probably a cyclonic system (larger than a tornado, smaller than a typhoon) passing over the lake or close by. Winds caused by the storm and experienced on the lake will "clock around," say starting from the northwest, then becoming northerly then northeasterly then easterly in turn. Sailors know this phenomenon well. Such winds can steadily push ice floes initially to one side of the upwelling, compressing them into a denser mass, slowly rolling the mass around within the hole in a clockwise direction over the course of the storm event. If air temperature drops during the storm, the aggregated floes can refreeze together into a single mass that grows larger by accretion of adjacent floes, rather like rolling a snowball in fresh snow to make it larger.

This theory can explain several things observed in the NASA imagery: (1) the rolling ice mass is off-center in the hole, (2) ice floes are larger and presumably thicker in the center of the rolling mass, (3) there is a nearly complete ring of semi-open water around the perimeter of the hole and (4) there is a concentric ring-like appearance in floes around the hole propagating outward at least a full hole diameter to the north-northwest.

Because the rolling mass is pasted a teensy bit south of west on the west side of the hole, the wind was likely blowing from 85 – 90 degrees east of north when the NASA image was taken, or the wind had ceased to be a controlling factor after those conditions ended and new surface ice formed.

The theory does not need the upwelling to produce circular ice thinning, and indeed this hole is irregular in shape.

As for the upwelling, geothermal inputs may not be needed in this case. Ordinary wind seiche under northeasterly or easterly winds could produce an upwelling in this, the southern tip of Lake Baikal.

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