Ice covered cobble at the beach.

I have been trying to get my head around the physics of this ice covered cobble, found on our local beach, yesterday. If you look closely you will see that the whole cobble, which was about the size of a grapefruit, is coated in a smooth shell of ice about 3/8 of an inch thick…very uniform…very tight. Though it appears clear at first glance, as though the stone had been dipped in poly-carbonate or liquid glass, looking even closer shows that the shell is made up of a lacework of tiny ice bubbles fused into the tight shell. This was not the only one. The stone had to be within a certain size range…not much bigger or smaller than this…and it had to be pretty much perfectly round and relatively smooth itself. As you see from the photo, other stones near this one were not effected the same way. I still can not imagine the mechanics of the process. It was very cold the night before…but, still, how did the receding tide produce this effect? (If you know the answer, feel free to post it in the comments.)

Sony HX400V at 45mm equivalent field of view and macro. In-camera HDR. Nominal exposure (Program shifted for greater depth of field) ISO 80 @ 1/1000th @ f6.3. For scale, the snow drift at the edge of the sand is at least 5.5 feet tall. 🙂