LONDON (AP) -- One of Earth's largest-ever floods broke apart a strip of land connecting what is now Britain and France, permanently separating them, researchers say.

The flood unleashed about 35 million cubic feet of water per second, 100 times greater than the water discharge of the Mississippi River.

The natural disaster, which occurred about 400,000 years ago during a glacial period, was later followed by rising sea levels that created what is now the English Channel, the study says.

The theory that Britain became an island during a catastrophic flood - rather than through the course of normal erosion - was first proposed in the 1980s. The new study, outlined in the journal Nature, used high-resolution sonar data that were previously unavailable to produce three-dimensional, high-quality imagery of the region.