lake, Asia

Dead Sea, landlocked salt lake between Israel and Jordan in southwestern Asia. Its eastern shore belongs to Jordan, and the southern half of its western shore belongs to Israel. The northern half of the western shore lies within the Palestinian West Bank and has been under Israeli occupation since the 1967 Arab-Israeli war. The Jordan River, from which the Dead Sea receives nearly all its water, flows from the north into the lake.

Physical features

Physiography and Geology

The Dead Sea is situated between the hills of Judaea to the west and the Transjordanian plateaus to the east. Before the water level began dropping, the lake was some 50 miles (80 km) long, attained a maximum width of 11 miles (18 km), and had a surface area of about 394 square miles (1,020 square km).

The peninsula of Al-Lisān (Arabic: “The Tongue”) divided the lake on its eastern side into two unequal basins: the northern basin encompassed about three-fourths of the lake’s total surface area and reached a depth of 1,300 feet (400 metres), and the southern basin was smaller and considerably shallower, less than 10 feet (3 metres) deep on average. During biblical times and until the 8th century CE, only the area around the northern basin was inhabited, and the lake was slightly lower than its present-day level. It rose to its highest level, 1,275 feet (389 metres) below sea level, in 1896 but receded again after 1935, stabilizing at about 1,300 feet (400 metres) below sea level for several decades.

The drop in the lake level in the late 20th and early 21st centuries changed the physical appearance of the Dead Sea. Most noticeably, the peninsula of Al-Lisān gradually extended eastward, until the lake’s northern and southern basins became separated by a strip of dry land.

In addition, the southern basin was eventually subdivided into dozens of large evaporation pools (for the extraction of salt), so by the 21st century it had essentially ceased to be a natural body of water. The northern basin—effectively now the actual Dead Sea—largely retained its overall dimensions despite its great loss of water, mainly because its shoreline plunged downward so steeply from the surrounding landscape.

The Dead Sea region occupies part of a graben (a downfaulted block of Earth’s crust) between transform faults along a tectonic plate boundary that runs northward from the Red Sea–Gulf of Suez spreading centre to a convergent plate boundary in the Taurus Mountains of southern Turkey. The eastern fault, along the edge of the Moab Plateau, is more readily visible from the lake than is the western fault, which marks the gentler Judaean upfold.

In the Jurassic and Cretaceous periods (about 201 million to 66 million years ago), before the creation of the graben, an extended Mediterranean Sea covered Syria and Palestine. During the Miocene Epoch (23 million to 5.3 million years ago), as the Arabian Plate collided with the Eurasian Plate to the north, upheaval of the seabed produced the upfolded structures of the Transjordanian highlands and the central range of Palestine, causing the fractures that allowed the Dead Sea graben to drop. At that time the Dead Sea was probably about the size that it is today. During the Pleistocene Epoch (2,588,000 to 11,700 years ago), it rose to an elevation of about 700 feet (200 metres) above its modern level, forming a vast inland sea that stretched some 200 miles (320 km) from the H̱ula Valley area in the north to 40 miles (64 km) beyond its present southern limits. The Dead Sea did not spill over into the Gulf of Aqaba because it was blocked by a 100-foot (30-metre) rise in the highest part of Wadi Al-ʿArabah, a seasonal watercourse that flows in a valley to the east of the central Negev highlands.

Beginning about 2.5 million years ago, heavy streamflow into the lake deposited thick sediments of shale, clay, sandstone, rock salt, and gypsum. Later, strata of clay, marl, soft chalk, and gypsum were dropped onto layers of sand and gravel. Because the water in the lake evaporated faster than it was replenished by precipitation during the past 10,000 years, the lake gradually shrank to its present form. In so doing, it exposed deposits that now cover the Dead Sea valley to thicknesses of between about 1 and 4 miles (1.6 and 6.4 km).

The Al-Lisān region and Mount Sedom (historically Mount Sodom) resulted from movements of Earth’s crust. Mount Sedom’s steep cliffs rise up from the southwestern shore. Al-Lisān is formed of strata of clay, marl, soft chalk, and gypsum interbedded with sand and gravel. Both Al-Lisān and beds made of similar material on the western side of the Dead Sea valley dip to the east. It is assumed that the uplifting of Mount Sedom and Al-Lisān formed a southern escarpment for the Dead Sea. Later the sea broke through the western half of that escarpment to flood what is now the shallow southern remnant of the Dead Sea.

Another consequence resulting from the Dead Sea’s lower water level has been the appearance of sinkholes, especially in the southwestern part of the region. As the water in the lake dropped, it became possible for groundwater to rise up and dissolve large subterranean caverns in the overlying salt layer until the surface finally collapses. Several hundred sinkholes have formed, some of them in areas popular with tourists.

Climate and hydrology

The Dead Sea lies in a desert. Rainfall is scanty and irregular. Al-Lisān averages about 2.5 inches (65 mm) of rain a year, the industrial site of Sedom (near historical Sodom) only about 2 inches (50 mm). Because of the lake’s extremely low elevation and sheltered location, winter temperatures are mild, averaging 63 °F (17 °C) in January at the southern end at Sedom and 58 °F (14 °C) at the northern end; freezing temperatures do not occur. Summer is oppressively hot, averaging 93 °F (34 °C) in August at Sedom, with a recorded maximum of 124 °F (51 °C). Evaporation of the lake’s waters—estimated at about 55 inches (1,400 mm) per year—often creates a thick mist above the lake. On the rivers the atmospheric humidity varies from 45 percent in May to 62 percent in October. Lake and land breezes, which are relatively common, blow off the lake in all directions in the daytime and then reverse direction to blow toward the centre of the lake at night.

The inflow from the Jordan River, whose high waters occur in winter and spring, once averaged some 45.5 billion cubic feet (1.3 billion cubic metres) per year. However, the subsequent diversions of the Jordan’s waters reduced the river’s flow to a small fraction of the previous amount and became the principal cause for the drop in the Dead Sea’s water level. Four modest streams descend to the lake from Jordan to the east through deep gorges: the wadis (intermittent streams) Al-ʿUẓaymī, Zarqāʾ Māʿīn, Al-Mawjib, and Al-Ḥasā. Down numerous other wadis, streams flow spasmodically and briefly from the neighbouring heights as well as from the depression of Wadi Al-ʿArabah. Thermal sulfur springs also feed the rivers. Evaporation in summer and the inflow of water, especially in winter and spring, once caused noticeable seasonal variations of 12 to 24 inches (30 to 60 cm) in the level of the lake, but those fluctuations have been overshadowed by the more-dramatic annual drops in the Dead Sea’s surface level.

Salinity

The waters of the Dead Sea are extremely saline, and, generally, the concentration of salt increases toward the lake’s bottom. That phenomenon can create two different masses of water in the lake for extended periods of time. Such a situation existed for some three centuries, lasting until the late 1970s.

Down to a depth of about 130 feet (40 metres), the temperature varied from 66 to 98 °F (19 to 37 °C), the salinity was slightly less than 300 parts per thousand, and the water was especially rich in sulfates and bicarbonates. Beneath a zone of transition located at depths between 130 and 330 feet (40 and 100 metres), the water had a uniform temperature of about 72 °F (22 °C) and a higher degree of salinity (approximately 332 parts per thousand); it contained hydrogen sulfide and strong concentrations of magnesium, potassium, chlorine, and bromine. The deep water was saturated with sodium chloride, which precipitated to the bottom. The deep water thus became fossilized (i.e., because it was highly salty and dense, it remained permanently on the bottom).

The dramatic reduction in inflow from the Jordan River that began in the 1960s gradually increased the salinity of the upper-layer waters of the Dead Sea. By the late 1970s that water mass had become more saline (and denser) than the lower layers, but, because it remained warmer than the layers beneath it, it did not sink. By the winter of 1978–79, however, the upper-level layer had become cool and saturated enough to sink, setting off an event known as an overturn (a mixing of the water layers). Since then the trend has been toward restoring the formerly stratified water layers, but with more instances of overturning.

The saline water has a high density that keeps bathers buoyant. The fresh water of the Jordan stays on the surface, and in the spring its muddy colour can be traced as it spreads southward from the point where the river empties into the Dead Sea. The lake’s extreme salinity excludes all forms of life except bacteria. Fish carried in by the Jordan or by smaller streams when in flood die quickly. Apart from the vegetation along the rivers, plant life along the shores is discontinuous and consists mainly of halophytes (plants that grow in salty or alkaline soil).

Human imprint

The name Dead Sea can be traced at least to the Hellenistic Age (323 to 30 BCE). The Dead Sea figures in biblical accounts dating to the time of Abraham (first of the Hebrew patriarchs) and the destruction of Sodom and Gomorrah (the two cities along the lake, according to the Hebrew Bible, that were destroyed by fire from heaven because of their wickedness).

The desolate wilderness beside the lake offered refuge to David (king of ancient Israel) and later to Herod I (the Great; king of Judaea), who at the time of the siege of Jerusalem by the Parthians in 40 BCE barricaded himself in a fortress at Masada, Israel, just west of Al-Lisān. Masada was the scene of a two-year siege that culminated in the mass suicide of its Jewish Zealot defenders and the occupation of the fortress by the Romans in 73 CE. The Jewish sect that left the biblical manuscripts known as the Dead Sea Scrolls took shelter in caves at Qumrān, just northwest of the lake.

The Dead Sea constitutes an enormous salt reserve. Rock salt deposits also occur in Mount Sedom along the southwestern shore. The salt has been exploited on a small scale since antiquity. In 1929 a potash factory was opened near the mouth of the Jordan. Subsidiary installations were later built in the south at Sedom, but the original factory was destroyed during the 1948–49 Arab-Israeli war. A factory producing potash, magnesium, and calcium chloride was opened in Sedom in 1955. Another plant produces bromine and other chemical products. There are also chemical-processing facilities on the Jordanian side of the southern basin. Water for the extensive array of evaporation pools in the south, from which those minerals are extracted, is supplied by artificial canals from the northern basin.

Because of its location on the contested Jordanian-Israeli frontier, navigation on the Dead Sea is negligible. Its shores are nearly deserted, and permanent establishments are rare. Exceptions are the factory at Sedom, a few hotels and spas in the north, and, in the west, a kibbutz (an Israeli agricultural community) in the region of the ʿEn Gedi oasis. Small cultivated plots are also occasionally found on the lakeshore.

Concern mounted quickly over the continued drop in the Dead Sea’s water level, prompting studies and calls for greater conservation of the Jordan River’s water resources. In addition to proposals for reducing the amount of river water diverted by Israel and Jordan, those two countries discussed proposals for canals that would bring additional water to the Dead Sea. One such project, which received approval from both sides in 2015, would involve constructing a canal northward from the Red Sea. The plan, which would include desalinization and hydroelectric plants along the course of the canal, would deliver large quantities of brine (a by-product of the desalinization process) to the lake. However, the project met with skepticism and opposition from environmentalists and others who questioned the potentially harmful effects of mixing water from the two sources.

Climate

The Dead Sea has a hot desert climate (Köppen climate classification BWh), with year-round sunny skies and dry air. It has less than 50 millimetres (2 in) mean annual rainfall and a summer average temperature between 32 and 39 °C (90 and 102 °F). Winter average temperatures range between 20 and 23 °C (68 and 73 °F). The region has weaker ultraviolet radiation, particularly the UVB (erythrogenic rays). Given the higher atmospheric pressure, the air has a slightly higher oxygen content (3.3% in summer to 4.8% in winter) as compared to oxygen concentration at sea level. Barometric pressures at the Dead Sea were measured between 1061 and 1065 hPa and clinically compared with health effects at higher altitude. (This barometric measure is about 5% higher than sea level standard atmospheric pressure of 1013.25 hPa, which is the global ocean mean or ATM.) The Dead Sea affects temperatures nearby because of the moderating effect a large body of water has on climate. During the winter, sea temperatures tend to be higher than land temperatures, and vice versa during the summer months. This is the result of the water’s mass and specific heat capacity. On average, there are 192 days above 30 °C (86 °F) annually.

Salt mounts formation

In prehistoric times,^{[dubious – discuss]} 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).

Israel

The Dead Sea Works was founded in 1952 as a state-owned enterprise based on the remnants of the Palestine Potash Company. In 1995, the company was privatized and it is now owned by Israel Chemicals. From the Dead Sea brine, Israel produces (2001) 1.77 million tons potash, 206,000 tons elemental bromine, 44,900 tons caustic soda, 25,000 tons magnesium metal, and sodium chloride. Israeli companies generate around US$3 billion annually from the sale of Dead Sea minerals (primarily potash and bromine), and from other products that are derived from Dead Sea Minerals.

Extraction

Both companies, Dead Sea Works Ltd. and Arab Potash, use extensive salt evaporation pans that have essentially diked the entire southern end of the Dead Sea for the purpose of producing carnallite, potassium magnesium chloride, which is then processed further to produce potassium chloride. The ponds are separated by a central dike that runs roughly north–south along the international border. The power plant on the Israeli side allows production of magnesium metal (by a subsidiary, Dead Sea Magnesium Ltd.).

Due to the popularity of the sea’s therapeutic and healing properties, several companies have also shown interest in the manufacturing and supplying of Dead Sea salts as raw materials for body and skin care products.

Life forms

The sea is called “dead” because its high salinity prevents macroscopic aquatic organisms, such as fish and aquatic plants, from living in it, though minuscule quantities of bacteria and microbial fungi are present.

In times of flood, the salt content of the Dead Sea can drop from its usual 35% to 30% or lower. The Dead Sea temporarily comes to life in the wake of rainy winters. In 1980, after one such rainy winter, the normally dark blue Dead Sea turned red. Researchers from Hebrew University of Jerusalem found the Dead Sea to be teeming with an alga called Dunaliella. Dunaliella in turn nourished carotenoid-containing (red-pigmented) halobacteria, whose presence caused the color change. Since 1980, the Dead Sea basin has been dry and the algae and the bacteria have not returned in measurable numbers.

In 2011 a group of scientists from Be’er Sheva, Israel and Germany discovered fissures in the floor of the Dead Sea by scuba diving and observing the surface. These fissures allow fresh and brackish water to enter the Dead Sea. They sampled biofilms surrounding the fissures and discovered numerous species of bacteria and archaea.