Which of the following would not be classified as a natural event?

An explosion is classified as a man-made event rather than a natural event. Natural events are typically characterized by their origin in natural processes within the Earth's systems, such as meteorological or geological phenomena. Floods, lightning, and tornadoes all arise from natural processes—floods can occur from excessive rainfall or melting snow, lightning is a discharge of electricity during storms, and tornadoes are violent windstorms that form from severe thunderstorms. In contrast, explosions are usually caused by human activity or interventions, such as the ignition of chemicals or gases in a controlled or uncontrolled manner. Thus, the distinction lies in the source of the event, with the other listed phenomena being entirely attributable to natural conditions and processes.