Complex sentence: They learn from Mikhail that since the implosion at the hatch an electromagnetic pulse wiped out an underwater beacon, making it impossible for the island to be accurately located and, therefore, for anyone to return to the island.
Split into simpler sentences: They learn from Mikhail that the implosion at the hatch sent an electromagnetic pulse which wiped out an underwater beacon. This made it impossible for the island to be accurately located for anyone to return to the island.