The Dead Sea: Its Forgotten Resource—Asphalt
Today the Dead Sea is known worldwide as the lowest place on the Earth’s surface. It is also known for its high salt content—virtually saturated with dissolved halite—table salt—making the water very buoyant. The salt deposited on the shore has been a valued commodity throughout human history for preserving foods. But in millennia past the Dead Sea was known just as much for a different resource that today has been nearly forgotten—Bitumen—or Asphalt. One major reason this has been forgotten is that it tends to appear in greater or lesser amounts sporadically over the centuries. The last century has seen lesser amounts. The asphalt exudes from the bottom of the lake through deep-seated faults. It originated from organic rich sediments buried millions of years ago that have been slowly cooked into a very viscous black organic liquid that rises through the faults episodically into the lake. The large masses cool into solid chunks (some the size of small cars) as they float on the surface where the wind can blow them to shore. This resource was well known to the Greeks and the Romans. They built boats to go out and push the floating islands of bitumen to the shore. In fact, the Romans’ official name for this lake was not the Dead Sea, or the Salt Sea, but Lake Asphaltites.
Asphalt in ancient history has had many valuable uses. Josephus wrote of its use by the Romans as medicine for all kinds of ailments, both external and internal. Dead Sea asphalt has been detected in the materials of Egyptian mummies using chemical fingerprints. Its most popular use though was as an adhesive. Because it is solid at room temperature, yet liquifies above 50 degrees Celsius (110 degrees Fahrenheit), it can easily be melted and applied to objects that then become essentially fused when cooled. Digs in Jericho that date from several thousand years ago have produced axes where the head is attached to the shaft using asphalt. It was known in the early biblical accounts as a sealant for boats (Noah’s ark was sealed with pitch). Reed boats sealed with asphalt from thousands of years past have been found in both the Dead Sea area and Mesopotamia. Asphalt could be used not just in boats though, but in mortar for bricks. The account of the Tower of Babel records that bricks and mortar were used, where the word for mortar indicated asphalt. Along the southwestern shores of the Dead Sea there are conglomerate deposits where asphalt is the cement holding the cobbles together. I can imagine ancient men observing these and getting the idea they could use the asphalt to hold their own stones together to build houses. But there is a hidden risk of using asphalt as mortar. Asphalt if heated enough will burn. It will release vapors that will both burn and are toxic. Dead Sea asphalt is known for its high sulfur content. Thus, heating and burning it produces a noxious odor as well. One can now begin to imagine in the story of Sodom and Gomorrah along the Dead Sea that a lightning strike might have ignited asphalt in the buildings, and once burning the heat could melt and spread through the entire town, releasing deadly, noxious, sulfurous gases (brimstone) at the same time.
For further reading:
Nissenbaum A (1993) Utilization of Dead Sea asphalt through history, Reviews in Chemical Engineering, vol. 9, no. 3-4, p. 365-383.
Nissenbaum A (1993) The Dead Sea—An economic resource for 10,000 years, Saline Lakes, vol. 5, p.127-141.
Oron A, Galili E, Hadas G, and Klein M (2015) Early maritime activity on the Dead Sea: Bitumen harvesting and the possible use of reed watercraft, Journal of Maritime Archaeology, vol. 10, p. 65-88.