We get the ice problem a lot where I live. It usually snows a moderate amount (and has snowed more in recent years than usual), so there's pretty often at least a foot or so of snow on the ground. But in the middle of the day, it's just warm enough to melt a little bit of it, and then it refreezes afterwards. So over time, you get a layer of ice over the snow, and over any surface you've cleared. The year before last, the ice was one and a half inches thick (just shy of four centimeters). There was a foot and a half of snow underneath, and I could jump up and down on top of it without breaking through. One day, I was trying to get into my house through the back door, and I just started sliding away down the hill, and I couldn't stop myself because I simply couldn't break through the ice.