There are two contending hypotheses about the origin of the low elevation of the Dead Sea. The older 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,[citation needed]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 called by geologists the Sedom Lagoon, which was connected to the sea through what is now the Jezreel Valley. The floods of the valley came and went depending on long-scale climate change. The Sedom Lagoon[17] deposited beds of salt that eventually became 2.5 km (1.55 mi) thick.
Approximately two million years ago,[citation needed] the land between the Rift Valley and the Mediterranean Sea rose to such an extent that the ocean could no longer flood the area. Thus, the long lagoon became a landlocked lake. The Sedom Lagoon extended at its maximum from the Sea of Galilee in the north to somewhere around 50 km (30 mi) south of the current southern end of the Dead Sea, and the subsequent lakes obviously never surpassed this expanse. The Hula Depression was never part of any of these water bodies due to its higher elevation and the high threshold of the Korazim blockseparating it from the Sea of Galilee basin.[18]
The first prehistoric lake to follow the Sedom Lagoon is named Lake Amora, followed by Lake Lisan and finally by the Dead Sea.[17] The water levels and salinity of these lakes have either risen or fallen as an effect of the tectonic dropping of the valley bottom, and due to climate variation. As the climate became more arid, Lake Lisan finally shrank and became saltier, leaving the Dead Sea as its last remainder.[17][18]
Pebbles cemented with halite on the western shore of the Dead Sea near Ein Gedi.
In prehistoric times, great amounts of sediment collected on the floor of Lake Amora. The sediment was heavier than the salt deposits and squeezed the salt deposits upwards into what are now the Lisan Peninsula and Mount Sodom (on the southwest side of the lake). Geologists explain the effect in terms of a bucket of mud into which a large flat stone is placed, forcing the mud to creep up the sides of the bucket. When the floor of the Dead Sea dropped further due to tectonic forces, the salt mounts of Lisan and Mount Sodom stayed in place as high cliffs (see salt dome).
From 70,000 to 12,000 years ago, the lake's level was 100 m (330 ft) to 250 m (820 ft) higher than its current level. This lake, Lake Lisan, fluctuated dramatically, rising to its highest level around 26,000 years ago, indicating a very wet climate in the Near East.[19] Around 10,000 years ago, the lake's level dropped dramatically, probably to even lower than today's. During the last several thousand years, the lake has fluctuated approximately 400 m (1,300 ft), with some significant drops and rises. Current theories as to the cause of this dramatic drop in levels rule out volcanic activity; therefore, it may have been a seismic event.
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