Camouflet

A camouflet, in military science, is an artificial cavern created by an explosion. If the explosion reaches the surface then it is called a crater.

The term was originally defined as a countermine dug by defenders to prevent the undermining of a fortress's walls during a siege. The defenders would dig a tunnel under the attackers' tunnel. An explosive charge would be detonated to create a camouflet that would collapse the attackers' tunnel.