The YouTube video Skating Lake Baikal, the world's deepest lake - BBC News shows a very heavily cracked lake. It doesn't just appear to be a fault line. It appears to be an actual crack that started that goes all the way to the surface. I believe it's natural. I have two questions. My first question is
When an ice layer on a frozen lake is cracked the way I described, is it plausible that it happened completely naturally with no human intervention such as having walked on it when it was thin?
My second question is
If the answer to my first question is yes, then what is one plausible cause of it?
If the answer to the first question is yes, I really only need the answer of one plausible cause of ice being cracked in that way without human intervention. However, it would be nice if you could give me as many plausible causes from fundamentally different categories as you can find.