An explosion occurs when a large amount of energy is released into a small volume of area in a very short time. The energy released comes in many forms, including chemical (artificial explosives), nuclear and hydrothermal.
Burning very rapidly, explosive material releases concentrated gas that expands quickly to fill the surrounding air space and apply pressure to everything in it. That is, it explodes in a blast powerful enough to blow away nearby trees, cars, buildings and anything else in its path.
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