Dead whales can explode as a result of gas pressure building up beneath the thick blubber to the point that the blubber ruptures, ejecting the innards with explosive force. This gas is generated naturally through the decomposition process by methane-producing bacteria present in the carcass of the whale.
Whales are protected from the elements by a thick layer of blubber, which is located under the skin of the animal and extends across the body but excludes the flukes and fins. The blubber also serves as a protective shield for the internal organs from the high pressures experienced during deep dives.
However, this high strength means that, once a whale dies and begins to decompose, the gases produced inside the animal during decomposition can continue to build up pressure. As the carcass continues to decay, weak points begin to appear across the animal's body, permitting an often explosive ejection of internal tissues and fluids when the weak points can no longer contain the internal gas pressure.
Whale carcass explosions are not rare in nature, but when they occur close to shores occupied by humans, the event can garner considerable attention. For example, on Jan. 26, 2004 in Tainan City, Taiwan, a decomposing sperm whale carcass exploded en route to a necropsy, spilling blood and entrails with explosive force onto the street in the city center.