How Climate Influenced the Dead Sea and History
The Dead Sea, the lowest lake on earth (1368 ft below sea level), figures prominently in the Bible. Near this body of water, Lot settled and the cities of the plain were destroyed. David wandered here, battles were fought nearby, and Herod built a fortress at Masada overlooking the lake. Later, Moslems and Crusaders left marks of their conquests in the region. Did the Dead Sea preserve a record of climactic changes that affected not only the Great Rift Valley in which it resides, but also the whole land of Israel? Students of Biblical history will be interested in two papers about the Dead Sea published in the May Bulletin of the Geological Society of America.
The first paper by R. Bookman (Ken-Tor) et al.1 reconstructs a curve of lake levels during historic times. Currently, the Dead Sea is at a record low due to diversion of Jordan River waters for irrigation. This has exposed historic shorelines for analysis. The team took radiocarbon dates of organic material at three sites around the lake to discern periods when the lake shore rose and fell. They then correlated the lake levels with cultural changes occurring in Palestine at those times:
Highstands occurred in the second and first centuries B.C. and the fourth century A.D. during the Roman and early Byzantine periods, respectively, in the eleventh and twelfth centuries A.D. during the Crusader period, and at the end of the nineteenth century A.D. The rises mark a significant change in the annual rainfall in the region, which likely exceeded the instrumentally measured modern average.
The curve also indicates drastic drops that exposed the sedimentary sequences to erosion. The oldest and probably deepest drop in the lake level culminated during the fifteenth and fourteenth centuries B.C. after a retreat from a higher lake stand. The longest lowstand occurred after the Byzantine period and continued at least until the ninth century A.D. This arid period coincided with the invasion of Moslem-Arab tribes into the area during the seventh century A.D.
The team estimated that high-water levels correspond to annual Jerusalem rainfall rates of 26 inches per year or more, and low-water levels to droughts of 18-20 in/yr or less. Thus Dead Sea lake levels are indicators of overall climate in Palestine. The oldest part of the curve is the least certain, but seems to indicate a high water level during the patriarchal period:
The oldest sediments described (unit I, Fig. 5) correspond to a lake level higher than 411 mbsl dated to 2140�1445 B.C. (3703 � 37 and 3220 � 36 radiocarbon yr B.P., Table 1). At that time the lake level was falling from an earlier highstand (prior to the fifteenth century B.C.), but no indicator for the absolute lake-level elevation was found at our sites. However, unit I may correspond to a distinct shore ridge identified in a western location in the Nahal Darga fan delta (Fig. 1C ) at 370 mbsl, where its age was estimated at 3000�4000 yr B.P.
The second paper by David-Novak et al.2 examined debris flows in the canyons around the Dead Sea. Unusually strong storms in 1995 and 1997 allowed them to calibrate, for the first time, the rainfall conditions necessary to trigger a debris flow in an arid environment. The 1995 storm, in which a convective cell hovered over the area and dumped rain at rates nearly 2 inches per hour, was the most severe and resulted in debris flows in all the canyons under the heaviest rain; the 1997 storm was milder and more localized to the plateau, and only resulted in three debris flows.
Since rainfall measurements were available for these storms, they were able to interpolate an estimate for the rainfall rate necessary to trigger a debris flow, and found the threshold to be approximately 30mm/hr for at least one hour (1.2 inches per hour). Surprisingly, they found evidence for prehistoric debris flows was rare. They estimate only zero to three debris flows occurred during the last 3000 years, but they admit that “it is possible that some deposits, mainly at the larger basins, were formed by multiple flows that are currently indistinguishable.”
Although “Debris flows are major processes of sediment transport in arid regions, particularly in areas of high relief,” their rarity has made it difficult to measure the rainfall necessary to trigger them. Fortunately, at Nahal Arugot and Nahal David on the western slopes of the Dead Sea, rain gauges and a stream flow measurement station were available for the intense storms of 1995 and 1997.
1R. Bookman (Ken-Tor), Y. Enzel, A. Agnon and M. Stein, “Late Holocene lake levels of the Dead Sea,” Geological Society of America Bulletin Vol. 116, No. 5 (May/June 2004), pp. 555�571, doi: 10.1130/B25286.1.
2 Hagit Ben David-Novak, Efrat Morin and Yehouda Enzel, “Modern extreme storms and the rainfall thresholds for initiating debris flows on the hyperarid western escarpment of the Dead Sea, Israel,” Geological Society of America Bulletin Vol. 116, No. 5 (May/June 2004) pp. 718�728, doi: 10.1130/B25403.2.
Bible study is enhanced by considering the environment in which the great sagas of history took place. How did the geology, climate, zoology, botany, mineralogy, topography and hydrology affect culture, or influence decisions of kings and tribal groups? Availability of water, for instance, is a primary deciding factor for settlers, and strongly influences the locations of cities and roads. Of particular interest is the story of Abraham and Lot. Anyone looking at the Dead Sea shores today would wonder why Lot would find the place attractive; today, it is hot, dry and nearly devoid of vegetation. Yet when Lot viewed it, it was “well watered everywhere (before the LORD destroyed Sodom and Gomorrah) like the garden of the LORD, like the land of Egypt as you go toward Zoar” (Gen. 13:10). Was this desert once a garden?
Though scientific investigations of the past depend on assumptions, studies that can be corroborated by eyewitnesses have more credibility. The paper on Dead Sea lake levels lends support to Lot’s description of its environs. Now that probable remains of the wicked cities of Sodom and Gomorrah have been found (along with evidence of their fiery destruction) the historicity of the Biblical account has been strengthened, because these ruins hint at thriving civilizations that must have prospered under a milder, wetter climate than is found there today. Also, from this paper one can see why Herod would have found Jericho and Masada attractive for his palaces, if Palestine were enjoying one of the well-watered periods. Between those times, from after the Exodus through the monarchies, David and the Judean kings would apparently have found the Dead Sea region much like we see it today, since by the patriarchal period the lake level was falling rapidly, such that “The oldest and probably deepest drop in the lake level culminated during the fifteenth and fourteenth centuries B.C. after a retreat from a higher lake stand.” A long era of drought would also shed light on the heroic efforts of Hezekiah to protect the Gihon Spring (see 09/10/2003 headline). Perhaps the “land flowing with milk and honey” was subjected to drought as God’s judgment for Israel’s disobedience, just as prophesied by Moses (see Deuteronomy 28).
The second paper on debris flows is not as pertinent to Bible history, but is important for understanding the conditions necessary for rapid geologic change. Huge alluvial fans are common in deserts of the world. Southern California, particularly Death Valley, has massive alluvial aprons surrounding arid peaks in regions of (currently) low rainfall. The paper shows that a lot can happen in a short time if the rain is concentrated and intense. Combine that fact with the first paper, that rainfall was more plentiful in ancient times in the Dead Sea region. There is no reason to reject the possibility that major geological change took place rapidly under the right conditions. In Red Rock Canyon State Park, California, a usually dry and arid desert, an intense storm under a localized convection cell in 1997 caused a flood that washed out a major highway, deposited mud three feet deep in trailers, and carried objects as big as refrigerators far down the channel. They estimate this was a “once in 300 to 500 year flood” for the area. Extrapolating present erosion rates, say from 1990 to 1996, would have been very misleading. But how do they know these floods are so rare, even at Red Rock? No settlers who kept records inhabited the area as long as 300 years ago. Did the formation of large erosional features like alluvial fans require a little water a lot of time, or a lot of water a little time? Science is limited to make such determinations when they cannot be cross-checked by observations. These scientists estimated “zero to three” Holocene debris flows in the Dead Sea canyons they investigated, but admitted there could have been more that were indistinguishable.
Today, when you drive through the desert, you see landforms that look static, ancient, and unchanging. You can come back year after year and see no difference. All it takes is a flood or earthquake big enough, and you would hardly recognize the place. Geologists have been becoming increasingly aware of the power of catastrophic agents to effect rapid change. Perhaps much of what we observe today is not slowly-evolving landforms, but relicts of intense, concentrated forces in the past.