Nuclear weapon effects
EMP (Electromagnetic Pulse)
A burst of electromagnetic energy released by a nuclear detonation, capable of damaging or destroying unhardened electronics over a wide area.
A high-altitude nuclear detonation (above 30 km) produces a particularly strong EMP because gamma rays from the bomb interact with the upper atmosphere to generate a downward-directed electromagnetic wave covering thousands of kilometers. A single high-altitude burst over the central US could disable power grids and unhardened electronics across most of the continent.