What is the sound that thunder makes caused by?

The dramatic sound we know as thunder is a direct consequence of the immense energy released by a lightning bolt. When lightning streaks across the sky, it creates an incredibly narrow channel of superheated air. This electrical discharge can reach temperatures as high as 30,000 degrees Celsius (54,000 degrees Fahrenheit), which is five times hotter than the surface of the sun itself.

This extreme and instantaneous heating causes the air within the lightning channel to expand outward with explosive force. This rapid expansion generates a powerful shockwave, much like a sonic boom created by a supersonic aircraft. As this shockwave travels through the atmosphere, it gradually dissipates and slows to the speed of sound, reaching our ears as the rumbling or cracking sound of thunder. The reason we see the flash (Review) of lightning before hearing its accompanying thunder is due to the vast difference in speed between light and sound; light travels significantly faster.

The specific sound of thunder can vary widely, from a sharp, sudden crack to a long, low rumble. A loud crack or snap often indicates that the lightning strike was very close, while a prolonged rumble suggests the lightning occurred further away. This variation is also influenced by the length and shape of the lightning channel, as sound waves from different parts of the extensive bolt reach our ears at slightly different times, creating a drawn-out effect. Additionally, atmospheric conditions like temperature inversions can affect how far and how loudly thunder can be heard.