This is something we NEVER see in Florida and I really only had the vaguest understating about the frost line. Never had I heard of heave. Well, for all of you warm weather people, here it is. It’s basically a frozen shoot of water as it expands out of the ground.
When it does this is disturbs the soil, creating space. Almost as if it has been scratched by chickens or a light tilling of the soil.
We have been told broadcasting grass or other seed like clover, in late winter takes advantage of heave. It ground will lift up and then as it warms will draw in the seeds and settle back down. Lazy gardening? I’m all for it!