+972 231 0424
The Geology of the Jordan Rift Valley and the Dead Sea
THE PREHISTORIC LAKE
Three million years ago, when the mountains behind Auja were not so high, the Mediterranean repeatedly flooded the trench that is now the Jordan Rift Valley. You can still find marine fossils in the limestone as you hike the hills around the eco center. Deeper down, below the silt that covers the valley floor, there are deposits of marine salt up to three kilometers thick.
The waters formed a narrow, crooked bay, connected to the Mediterranean through what is now the Jezreel Valley. By about two million years ago, as the mountains rose, this bay became an isolated inland sea that submerged the Rift Valley from Lake Tiberius to the southern reaches of the Wadi Araba.
As the earth cycled through its ages of ice and heat, rain and drought, the shoreline of this lake advanced and retreated. At times, the waters deepened and flooded the rift; at others, they vanished completely. The most recent of these pre-historic lakes, known to geologists as Lake Lisan, formed around 70,000 years ago. At its height, its surface was more than 100 meters above the level of today’s Dead Sea. But towards the end of the last ice age, as the climate grew warmer and drier, Lake Lisan began to evaporate faster than it was replenished.
By about 15,000 years ago the shoreline had retreated to roughly the level we see today, slowly concentrating the salt and killing the plants and animals that lived in the lake. The flat plain that runs along the valley floor is the lakebed, exposed by the retreating waters. And the Dead Sea is all that remains of Lake Lisan.
THE SEA OF SALT AND TAR
This unique geological history has left us with a landscape that is profoundly strange. On the shores of the Dead Sea, more than 400 meters below the level of the Mediterranean, the earth’s atmosphere is so thick that it filters ultraviolet light from the sun and becomes heavy with oxygen. The warmth and density of the air, the glittering blue against the red hills, the shoreline encrusted with salt – all this feels so unfamiliar that it seems, at times, like the surface of a different planet entirely.
The closer you look, the stranger things get. This is a sea in which the human body cannot sink; that disgorges huge globs of asphalt from beneath the waves; and that even, on rare occasions, changes color. That last happened in the winter of 1980, when rainwater pouring in from the River Jordan lifted the level of the lake, diluting the salt and allowing microscopic algae and bacteria to bloom in such abundance that the water was stained red.
You have to go back even further, to the 1930s, to find the last time that islands of bitumen seeped out from faults in the seabed and floated to the surface of the lake. They appeared so often in ancient times that the Dead Sea was known to the Roman geographer Strabo as the Mare Asphaltum.
Even earlier, in 312 BCE, a Greek general called Hieronymus of Cardia witnessed the Nabataean Arabs (the builders of Petra) camped on the eastern shore of the sea, waiting for the bitumen to appear.
‘They make ready large bundles of reeds and cast them into the sea. On these not more than three men take their places, two of whom row with oars, but one carries a bow and repels any who sail against them from the other shore, or who venture to interfere with them. When they come near the floating bitumen they jump upon it with axes and, just as if it were soft stone, they cut pieces and load them onto the raft.’
Back on shore, the bitumen was sprinkled with sand, stuffed into leather bags, loaded onto camels and carried off “like the plunder of war.” Nabataean caravans took the bitumen south across the Sinai, towards Alexandria and the cities of the Nile. The ancient Egyptians used it for embalming the dead, as well as for caulking boats. In the Bronze Age, it was used as mortar in the walls of Jericho. And later, it became a key ingredient in a kind of proto-napalm called ‘Greek Fire’, the most terrifying weapon of the Byzantine navy.
Along with salt and bitumen, a whole range of unusual minerals has been concentrated in this basin by faults in the earth’s crust and the slow evaporation of Lake Lisan. Most of these minerals – magnesium and bromine, phosphate and potash - do not sound like the kind of thing that we come across in our everyday lives. But if you’ve ever applied a face pack or sprayed de-icer onto the windscreen of your car, then the chances are you’ve used some of the chemical compounds that accumulate in the mud of the Dead Sea.
The grinding and stretching of the earth’s crust along the African – Arabian fault has long triggered earthquakes around the Jordan Rift Valley. And because this fault runs through one of the most historically literate regions of the world, we have a record of seismic activity that stretches back as far as 1365 BCE.
Written in Assyrian and Hebrew, Greek and Arabic, some of these accounts remain extraordinarily vivid. The Byzantine monk Theophanes records the quake that struck this valley in the winter of 749. Shocks were felt from the Gulf of Aqaba to the banks of the Euphrates, and from Gaza to Baghdad, and Theophanes’s chronicle still carries the note of superstitious dread that these events would have caused in a pre-scientific age:
‘January 18th, 749. A violent earthquake occurred in Palestine, by the Jordan, and in all of Syria. Numberless multitudes perished, churches and monasteries collapsed, especially those in the desert of Jerusalem. Some cities were completely destroyed, other partially so, while some slid down entire, with their walls and houses, from the mountains to the plains. In Mesopotamia the ground was split along two miles, and out of the chasm was thrown up a different soil, very white and sandy, in the midst of which, they said, there came up an animal like a mule, quite spotless, that spoke in a human voice and announced the incursion of a certain nation from the desert against the Arabs.’
In what may be one of the earliest historical references to Auja, another Byzantine chronicler who lived through this earthquake, Michael the Syrian, wrote “a water source near Ariha [Jericho] was moved six miles.” It also cracked the roof of the great mosque in Damascus, collapsed the Roman temple of Baalbek in Lebanon, destroyed Hisham’s palace in Jericho, and caused a tsunami in the Dead Sea.
THE VANISHING OF THE DEAD SEA
The Dead Sea has no outlet. Over the last 10,000 years or so, the inflow from the Jordan River has more or less matched the evaporation of water from the lake’s surface, and the shoreline has held steady. But over the last 50 years, with the Jordan reduced to a trickle by the pumping of its water and the damming of its tributaries, the Dead Sea has started to retreat. Some of the hotels built on the northern and western shore in the 50s and 60s are now stranded more than a kilometer from the water’s edge.
As the shoreline retreats, deposits of underground salt are coming into contact with fresh water from the aquifers around the edge of the Dead Sea. Pockets of salt dissolve in the flow of sweet water, causing the land above to collapse without warning. Huge sinkholes have opened around the perimeter of the Dead Sea. (The good news, according to Friends of the Earth’s co-director Gidon Bromberg, is that if you get swallowed up by one of these sinkholes, they’ll name it after you J.)
The vanishing of the Dead Sea is now a real possibility. Until recently, most scientists believed that as the surface of the lake gets smaller the rate of evaporation will decrease, causing the shoreline to stabilize around 100 meters lower than its present level. But in 2010, scientists drilled deep into the bed of the Dead Sea, pulling out a core of salt and sediment some 400 meters long and allowing them to read the history of the lake. At the 120,000 year mark, they found a flat layer of beach pebbles covering the salt. The lake, it seems, had vanished completely.
Without urgent and dramatic action to revive the river and replenish the Dead Sea, we may soon see a salt flat in the center of the Jordan Valley.
See FoEME Reports for more information on the threat to the Dead Sea.