induration. 1. the process of hardening or being hardened.
1 They're weak against the Ice and Water types in reference of erosion, which cause this elements to the ground. 2  They're immune against the Electric type because in real life, the ground is a natural sink of electrons.  The Bug type resists them because many bugs like worms live inside the ground and many of them eat it.
The ground originally gave out Saturday and is now threatening two homes in a retirement community of The Villages in Florida. No one will ever know a sinkhole was there, Meredith Tucker, one of the contractors, told the Orlando Sentinel, but three days later, the ground collapsed again.