Underwater volcanic eruptions happen every day, but because of the vastness of the ocean and the great depth of water blocking the view, catching an active eruption is a game of chance. In fact, the largest-known underwater eruption of the past century was something of a fluke discovery. In July 2012, an airline passenger spotted a huge pumice raft floating in the South Pacific during a flight to Auckland, New Zealand. Upon landing, she alerted researchers, and scientists confirmed the 400-square-kilometer pumice raft near the Havre Seamount using NASA satellite imagery.