Dead sea

The Dead Sea (Hebrew: יָם הַ‏‏מֶּ‏‏לַ‏ח, Yām HaMélaḥ, "Sea of Salt", also Hebrew: יָם הַ‏‏מָּוֶת, Yām HaMā́weṯ, "The Sea of Death"; Arabic: البحر الميت‎  al-Baḥr al-Mayyit (help·info),^[4]), also called the Salt Sea, is a salt lake bordering Jordan to the east, and Palestine and Israel to the west. Its surface and shores are 427 metres (1,401 ft) below sea level,^[3] Earth's lowest elevation on land. The Dead Sea is 306 m (1,004 ft) deep, the deepest hypersaline lake in the world. With 34.2% salinity (in 2011), it is also one of the world's saltiest bodies of water, though Lake Vanda in Antarctica (35%), Lake Assal (Djibouti) (34.8%), Lagoon Garabogazköl in the Caspian Sea (up to 35%) and some hypersaline ponds and lakes of the McMurdo Dry Valleys in Antarctica (such as Don Juan Pond (44%)) have reported higher salinities. It is 9.6 times as salty as the ocean.^[5] This salinity makes for a harsh environment in which animals cannot flourish, hence its name. The Dead Sea is 50 kilometres (31 mi) long and 15 kilometres (9 mi) wide at its widest point.^[1] It lies in the Jordan Rift Valley, and its main tributary is the Jordan River.
The Dead Sea has attracted visitors from around the Mediterranean basin for thousands of years. Biblically, it was a place of refuge for King David. It was one of the world's first health resorts (for Herod the Great), and it has been the supplier of a wide variety of products, from balms for Egyptian mummification to potash for fertilizers. People also use the salt and the minerals from the Dead Sea to create cosmetics and herbal sachets.
The Dead Sea seawater has a density of 1.240 kg/L, which makes swimming similar to floating.^[6][7]

Etymology and toponymy

In Hebrew, the Dead Sea is  Yām ha-Melaḥ (help·info) (ים המלח), meaning "sea of salt" (Genesis 14:3). In the Bible, the Dead Sea is called the Salt Sea, the Sea of the Arabah, and the Eastern Sea. The designation "Dead Sea" never appears in the Bible.
In prose sometimes the term Yām ha-Māvet (ים המוות, "sea of death") is used, due to the scarcity of aquatic life there.^[8] In Arabic the Dead Sea is called  al-Bahr al-Mayyit (help·info)^[4] ("the Dead Sea"), or less commonly baḥrᵘ lūṭᵃ (بحر لوط, "the Sea of Lot"). Another historic name in Arabic was the "Sea of Zoʼar", after a nearby town in biblical times. The Greeks called it Lake Asphaltites (Attic Greek ἡ Θάλαττα ἀσφαλτῖτης, hē Thálatta asphaltĩtēs, "the Asphaltite^[9] sea"). The Bible also refers to it as Yām ha-Mizraḥî (ים המזרחי, "the Eastern sea") and Yām ha-‘Ărāvâ (ים הערבה, "Sea of the Arabah").

Geography

Satellite photograph showing the location of the Dead Sea

The Dead Sea is an endorheic lake located in the Jordan Rift Valley, a geographic feature formed by the Dead Sea Transform (DST). This left lateral-moving transform fault lies along the tectonic plate boundary between the African Plate and the Arabian Plate. It runs between the East Anatolian Fault zone in Turkey and the northern end of the Red Sea Rift offshore of the southern tip of Sinai. It is here that the Upper Jordan River/Sea of Galilee/Lower Jordan River water system comes to an end.
The Jordan River is the only major water source flowing into the Dead Sea, although there are small perennial springs under and around the Dead Sea, forming pools and quicksand pits along the edges.^[10] There are no outlet streams.
Rainfall is scarcely 100 mm (4 in) per year in the northern part of the Dead Sea and barely 50 mm (2 in) in the southern part.^[11] The Dead Sea zone's aridity is due to the rainshadow effect of the Judean Hills. The highlands east of the Dead Sea receive more rainfall than the Dead Sea itself.
To the west of the Dead Sea, the Judean Hills rise less steeply and are much lower than the mountains to the east. Along the southwestern side of the lake is a 210 m (700 ft) tall halite formation called "Mount Sodom".

Natural history

There are two contending hypotheses about the origin of the low elevation of the Dead Sea. The older hypothesis is that it 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, 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^[12] 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 Korazin block separating it from the Sea of Galilee basin.
The first prehistoric lake to follow the Sedom Lagoon is named Lake Amora, followed by Lake Lisan and finally by the Dead Sea.^[12] 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.^[12][13]

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.^[14] 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.

Climate

The Dead Sea's climate offers 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 weakened ultraviolet radiation, particularly the UVB (erythrogenic rays). Given the heavier atmospheric pressure, the air has a slightly higher oxygen content (3.3% in summer to 4.8% in winter) as compared to oxygen density at sea level.^[15][16] Barometric pressures at the Dead Sea were measured between 796 and 799 mmHg and clinically compared with health effects at higher altitude.^[17] (This barometric measure is about 5% higher than sea level standard atmospheric pressure of 760 mmHg, 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 30C (86F) annually.^[18]