Q: I discovered a ten inch wide hole in my yard by stepping in it while mowing. I didn’t see it because it was covered by grass. There was no dirt piled up around it. It descends eight inches and in the bottom are fist-sized tunnels.
A: Although limestone sinkholes occur in Tampa, I think your hole formed when a covered tree stump rotted away. In fact, my neighbor nearly broke her leg when she stepped into an unseen hole in her yard while mowing. Upon investigation, it turned out to be the cavity left when an underground pine stump decomposed. We found pine bark on the sides of the hole plus tunnels radiating away from its bottom where roots once grew. I did for her what I recommend for you: fill the hole with broken bricks, cover with soil and plant more grass.