It has long been believed that centuries of erosion destroyed the land bridge between France and Britain, but a new study suggests that a single, catastrophic event was likely the cause. Scientists using high-resolution sonar data now claim that 400,000 years ago, in one of the largest floods on Earth, the land bridge connecting the two masses was broken apart. A 2nd "megaflood," occurring more than 160,000 years ago, deepened the gap and created the characteristic valley system found in the English Channel.