Task: Question Answering
Input (English): Passage: Off the coast of Alaska, oceanographer Emma MacNeil is studying the migration patterns of whales aboard an experimental submarine she took without permission from her employer. Meanwhile, a military helicopter drops experimental sonar transmitters into the water, causing a pod of whales to go out of control and start ramming a nearby glacier. In the chaos, the helicopter crashes into the glacier, and the combined damage breaks the glacier open, thawing two hibernating, prehistoric creatures. MacNeil narrowly avoids destruction as, unknown to her, a giant shark and octopus are freed. Some time later, a drilling platform off the coast of Japan is attacked by the octopus, which has tentacles large enough to wrap around the entire structure. After returning to Point Dume, California, MacNeil investigates the corpse of a beached whale covered with many bloody wounds. Her employer Dick Richie believes them to be from a tanker propeller, but MacNeil insists they appear to be from a creature. Later, she extracts what appears to be a shark's tooth from one of the wounds. Elsewhere, the huge shark leaps tens of thousands of feet into the air from the ocean and attacks a commercial aircraft, forcing it to crash into the water. 
Question: What two forces combine to break open a glacier and free hibernating prehistoric creatures?
Output (English): helicopter crashes.