http://dfair.virtualave.net/bombs/blu82.htm
The BLU-82B/C-130 weapon system, nicknamed Commando Vault, is the high altitude delivery of a 15,000 pound general purpose bomb from a C-130. This system depends upon the accurate positioning of the aircraft by either a fixed ground radar or onboard navigation equipment. The ground radar controller or aircrew navigator as applicable, is responsible for positioning the aircraft prior to final countdown and release. Primary aircrew considerations include accurate ballistic and wind computations provided by the navigator, and precision instrument flying with strict adherence to controller instructions. The minimum altitude for release due to blast effects of the weapon is 6,000 feet AGL.
The BLU-82 is a 15,000 pound GP bomb originally designed to clear helicopter landing zones in Vietnam. The warhead contains 12,600 pounds of GSX slurry and is detonated just above ground level by a 38-inch fuze extender. The weapon produces an overpressure of 1,000 pounds per square inch. Eleven BLU-82s were dropped during Desert Storm, all from Special Operations C-130s. The initial drops were intended to test the ability of the bomb to clear mines; no reliable bomb damage assessment exist on mine clearing effectiveness. Later, bombs were dropped as much for their psychological effect as for their destructive power.
Primarily because the top 12 inches of top soil for a several hundred yard radius were blown into the the next province.