Dead Sea hypothesis is that the Dead Sea lies in a true rift zone, an extension of the Red Sea Rift, or even of the Great Rift Valley of eastern Africa. A more recent hypothesis is that the Dead Sea basin is a consequence of a "step-over" discontinuity along the Dead Sea Transform, creating an extension of the crust with consequent subsidence. Around 3.7 million years ago, what is now the valley of the Jordan River, Dead Sea, and the northern Wadi Arabah was repeatedly inundated by waters from the Mediterranean Sea. The waters formed in a narrow, crooked bay that is
Northern Dvina River the west-flowing Vychegda River ( long). The combined river flows northwest into the White Sea, which it joins near the city of Archangelsk. Looking more closely, the Sukhona flows east and meets the north-flowing Yug River at Veliky Ustyug. The combined stream, now called the Northern Dvina, flows north about 60 km and receives the west-flowing Vychegda at Kotlas and then turns northwest to flow into the White Sea. The Sukhona-Vychegda was an important east–west transportation route while the Northern Dvina-Yug was a north–south route. The upper Sukhona is now connected by the Northern Dvina Canal to the Volga–Baltic Waterway,