Heat, light, sound and electric energy are all forms produced in a lightning strike. The bottoms of clouds typically become negatively charged, while the earth beneath them becomes positively charged. When the potential difference between the two becomes sufficient to break down the electrical resistance of air, lightning strikes occur.
The energy density of a lightning strike is high. A single bolt can release between 1 billion and 10 billion joules with a current intensity of 30,000 to 50,000 amps. Objects that are struck are exposed to high-intensity electrical and magnetic fields. Lightning passing through a tree may cause its sap to heat up to sufficient temperatures for instantaneous vaporization, causing the tree to explode. These high temperatures may cause the sand or soil beneath the lightning strike to fuse, forming tubular structures called "fulgurites."
Humans and animals that are struck by lightning usually survive, but may suffer traumatic injury to their nervous systems and internal organs. The high temperature electrostatic discharge along the path of the lightning causes surrounding air to superheat and expand explosively, causing thunder. Lightning can sometimes produce high-energy radiation, such as X-rays. There is even ongoing research, as of 2015, investigating the possibility of lightning leading to the creation of antimatter.