Imagine that you drive your children to school and suddenly something frightening appears.
You feel like the ground bends under the load of something very heavy. And suddenly, some holes in the ground open.
The hole may appear suddenly and it can swallow cars, roads, houses and other buildings.
They appear very quickly and with no warning. They open regardless of what is above them.
Regardless of the substratum, suddenly it may break and become soft.
Water may disband rocks forming empty pockets that become frightening holes.