Debris is the word used for the rubble or wreckage of material left after some major event. So, for example, the ruined houses after a hurricane or tornado will be unusable and called debris.

But debris is caused by natural events, too. For example, the material left behind after a flood may be made of stones. This is debris. So is the material at the bottom of a cliff after a great storm, or the material left scattered around after a volcanic eruption.

Debris is connected to rare events.

If it is caused by people, then it is usually after a riot or some other uncontrollable event.