Hole in lawn
I have a round impression in my lawn, about 8 inches across, that keeps sinking. I fill it with dirt, reseed it, and then it sinks again. Today I pushed a thin rod through it and met little resistance for 18 inches after which I then hit a hard bottom. This happens anywhere inside the 8-inch circle. Outside the circle the rod can't pierce the ground. It's like there's an 8-inch tube of loose soil that goes down 18 inches and then stops. This is the only spot in a large lawn where this occurs. Any ideas?