I always wanted to hear a detailed explanation for the cause of thunder. I knew that the broad answer was “lightning”, but only now did I get a concise, scientific answer:
The air around a lightning bolt is superheated to about five times the temperature of the Sun. This sudden heating causes the air to expand faster than the speed of sound, which compresses the air and forms a shock wave; we hear it as thunder.
Thank you, livescience.com!