debacle
Meaning: a disastrous failure, disruption
Usage: The elaborately designed fireworks show turned into a debacle when the fireworks started firing in random directions.
maelstrom
Meaning: a destructive whirlpool which rapidly sucks in objects
Usage: Little did the explorers know that as they turned the next bend of the calm river a vicious maelstrom would catch their boat.
calamity
Meaning: an event with disastrous consequences
Usage: The earthquake in San Francisco was a calamity worse than any other natural disaster in history.