A subspace implosion is a violently destructive phenomenon that can be produced in a warp core
In an alternate timeline in which Jonathan Archer had been infected by interspatial parasites, he was able to eliminate the parasites with a subspace implosion. He did this by initiating an overload in three of the Enterprise NX-01's plasma injector's, causing a feedback pulse to travel through the reactor, destroying the ship. Since the parasites existed outside normal time, destroying them had the effect of wiping them out in all time periods, changing history in that the infection never occured.