An Electromagnetic Pulse, or EMP, is a burst of electromagneticradiation (light, magnetism, electricity), and is caused by a huge release of energy. A "common" cause for an electromagnetic pulse is a nuclear explosion. A scientist named Enrique Fermi predicted that electromagnetic pulses would result from a nuclear weapon being launched. An EMP can damage electronic recording equipment and shut off digital clocks, regardless of their electronic shielding.
Further reading
ISBN978-1-59248-389-1 21st Century Complete Guide to Electromagnetic Pulse (EMP) Attack Threats, Report of the Commission to Assess the Threat to the United States from Electromagnetic ... High-Altitude Nuclear Weapon EMP Attacks (CD-ROM)
ISBN978-0-16-056127-6 Threat posed by electromagnetic pulse (EMP) to U.S. military systems and civil infrastructure: Hearing before the Military Research and Development Subcommittee ... first session, hearing held July 16, 1997 (Unknown Binding)