I came across this interesting weapon by H.G. Wells, from his novel, The World Set Free, about a special type of atomic bomb that will explode indefinitely.
Here is a description on Wikipedia:
Wells's "atomic bombs" have no more force than ordinary high explosive and are rather primitive devices detonated by a "bomb-thrower" biting off "a little celluloid stud." They consist of "lumps of pure Carolinum" that induce "a blazing continual explosion" whose half-life is seventeen days, so that it is "never entirely exhausted," so that "to this day the battle-fields and bomb fields of that frantic time in human history are sprinkled with radiant matter, and so centres of inconvenient rays."
I doubt such a material as presented here would cause such an effect. However, I wonder if there is a possibility of any type of explosive, as long as it is hard in nature, that can cause an effect of "non-stop explosions".
Assume that all resources are present. However, total Unobtainium or Handwavium will not be appreciated.