What causes thunder?
An average lightning strike produces currents of 30,000 amperes, but could approach 30 million volts at 100,000 amperes. The rapid rise in current produces temperatures in the lightning channel of more than 50,000 degrees Fahrenheit which causes the air in the channel to expand. The expanding air cools, then contracts. Rapid expansion and contraction of the air around lightning occurs as molecules move back and forth, making sound waves we hear as thunder.