it could be a few things. it might be a small sinkhole warming up the snow above. it could be a depression in the ground from when there used to be a large tree there. it also might be one of those buffalo wallows or something. its a marshy spot in the middle of the prairie where the buffalo used to hang out in. i mean, sure it could be a big ole UFO coming in for a landing, but they are supposed to leave burn marks in the ground where they were.When I was in third grade, there was one time in the middle of winter when everything was covered in about a foot of snow. I went sledding and the next day I went back to the same area just to walk around. There was a nearby field that at this point had probably half a foot of snow or more left, and the snow over there was completely pristine and undisturbed by any kind of footsteps. Well, the second day, there was a huge circle indentation in the snow in the middle of the field. Probably about 12-15 feet across if I had to guess. It was bizarre because there was nothing else leading to it indicating that people had done anything, and the day before, the field had been completely normal. So something left a large circular indentation in that field overnight. I went back there during future snowstorms and didn't see the indentation. Even back then we theorized that maybe a craft had landed there overnight. Though it's also possible that there was a heat source over there (like a giant manhole cover) that was causing the snow to collapse. That'd be a pretty weird thing to find in the middle of a field though. It certainly piqued my interest in the unexplainable, though.