A wooden anchor made during the time of King Herod during the first century before the common era has led Hebrew University of Jerusalem (HUJI) and Geological Survey of Israel (GSI) geologists to study the activity of the ancient springs and the restoration of the levels of the Dead Sea over the past thousands of years.
The Dead Sea – the lowest place on Earth (its current level is 435 meters below sea level), absorbs water and alluvial material from a wide drainage basin that extends between the desert and the Mediterranean climate zone. It serves as a “rain gauge” of the Levant. Nurit Weber, a doctoral student at HUJI’s Institute of Earth and the GSI wondered whether the Dead Sea has always been at such a low level and lake’s drainage basin has always been particularly dry or whether today’s climate change and the human impact have contributed to the significant drop in level since the 1950s (when the level was 400 meters below sea level).
She recently published her findings in the prestigious journal Geophysical Research Letters.
During many periods over the past 7,000 years (most of the Holocene period). the level of the Dead Sea was between 420 and 430 meters below sea level, the lake covered only the northern basin and the area of Israel (and the southern Levant) was characterized by a dry and hot climate, wrote Weber.
During periods when the lake stood at its low levels, hot springs abounded, along the west coast from the area of cliff springs to Ein Gedi. Unique bodies of gypsum – a soft sulfate mineral composed of calcium sulfate dihydrate that is today commonly mined and used as a fertilizer and as the main constituent in many forms of plaster blackboard chalk and drywall – were formed near the springs.
Weber’s study of gypsum bodies on the shores of Einot Kedem (north of Ein Gedi) began almost by accident after a particularly intriguing archeological discovery. In December 2003, Dr. Gideon Hadas, an archaeologist from Kibbutz Ein Gedi, called Prof. Moti Stein of HUJI and asked him to visit them at the Einot Kedem beach. There, in the rock outcrop below the path that passed several dozen meters above the lake shore (then stood 419 meters below sea level), a large block of rock appeared to be stuck inside the sediment layers.
When they took a close look, it seemed like an elongated piece of thick gypsum membranes hugging a large tree stump. Stein recalled the incident: “We dug around the gypsum block and extracted some from the beach sediments. “With a lot of effort and with the help of ropes and a pulley, we pulled it up and took it by van to Kibbutz Ein Gedi.
Hadas said with excitement that that a large boat anchor made of wood and containing crumbled lumps of lead was hidden inside the plaster block. It later turned out to be a boat from the time of King Herod. A test using the radioactive carbon 14 dating showed that the wood that comprised the anchor and the rope that attached to it were indeed from the Herodian era.
The anchor apparently got stuck among the coastal rocks as Herod tried to reach the hot springs that originated at Kedem Springs Beach. Hadas and Stein investigated various aspects of the anchor, using isotopes of lead on materials found in the bottom of the anchor, they determined that the lead ingots came from a mine in Italy.
For Weber, the finding was significant since it revealed the importance of the area for marine research. During the 17 years since the anchor was found, the level of the Dead Sea has receded by 25 meters, a retreat that led to the exposure of unique gypsum bodies, and this fascinated Weber. The anchor itself, by the way, was donated to the Israel Museum and is exhibited there in the permanent exhibition in the Roman Period of the archaeology wing.
In her doctoral dissertation, Weber described and dated the gypsum bodies in ancient spring and even recreated sedimentary structures, resembling fans that she called “gypsum deltas.” Insulated concentric gypsum structures that were scattered along the shores were also investigated.
The HUJI researcher showed that the gypsum deltas and the isolated gypsum bodies were formed during periods when the levels of the Dead Sea were low. The hot spring water in a composition similar to the pre-modern springs mixed with the Dead Sea water.
Dating of the gypsum structures by the radiocarbon method indicated that the ages of formation of the unique gypsum structures and the activity of the hot-salt springs corresponded to minimum times of solar radiation – for example, the “Oort Solar Minima” event around the year 1000, which took place during the so-called “Medieval Warm Period.”
During this period, the Levant region underwent dehydration and desertification, and the level of the Dead Sea dropped to a minimum.
If the natural conditions in the region return in the near future to the pattern that characterized most of the Holocene period, she said, they will further strengthen the expected dehydration effects in parallel with global warming.
Her study proved that the Dead Sea level gradually decreased during the Holocene period, except for certain periods (such as the Upper Bronze Age and the Roman-Byzantine period when the level was particularly high and reached heights of 390 to 380 meters below sea level) due to the strengthening of rainfall in the region. The current reality of the lowering of the level reflects a response to human activity – especially the dam of the waters of the Jordan River and its various tributaries. That is, the current decline in the level is something detached from what has happened in the last few thousand years.
On a broader view, Weber showed that the surface of the Dead Sea was at a very low level during most of the Holocene period, indicating extreme and persistent regional aridity in the Dead Sea drainage basin and the Levant as a whole.
In addition, she said, the “historical memory” of most of us from childhood trips to the Dead Sea and from the lake map in school atlases is of “one lake” that stretches from the square from the south of the Dead Sea to Kibbutz Kalia in the north of the Dead Sea. This “one lake” is related to the relatively short period in which the lake level rose above 400 meters below sea level in the 18th and 19th centuries and early 20th century and does not characterize the typical natural state of the Dead Sea during most of the Holocene period.
According to global warming models, the eastern Mediterranean region is expected to undergo significant dehydration in the near future, a level change that entails severe water shortages for the region’s residents. Therefore, further research is expected to continue to examine the dehydration and desertification processes that have occurred in the Dead Sea over the past millennia, she concluded.