Deluge (prehistoric)
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In the relatively recent geological past, several great floods are widely suspected to have occurred, with varying amounts of supporting evidence. The ocean could fill vast basins in matters of weeks or months, in catastrophes that are unimaginable in today's world. Some people argue that these events may have sparked the flood myths found in many cultures.
At the most recent glacial maximum, so much of the planet's water was locked up in the vast ice-sheets that formed ice domes kilometers thick that the sea level dropped by about 120 to 130 meters. As the sheets melted starting around 18,000 years ago sea levels rose. Most of the glacial melt had occurred by around 8,000 years ago, but the changes have not been as regular as a constant drip at the edges of the world's glaciers might suggest.
Sea levels have changed significantly since Late Paleolithic time, and shorelines have migrated. The sea has not always steadily encroached upon the land, for the immense weight of the ice-sheets depressed the continental plates under them and caused isostatic rebound around their edges, which are still adjusting today. Averaged rates of sea-level-rise are misleading. Where sills formed dikes that protected low-lying areas, a winter storm or a sudden spurt of meltwater thousands of miles away could raise ocean levels, and the natural dike could be catastrophically eroded like a dike in the Netherlands. Several examples where such rapid encroachment of the sea occurred are provoking geologists' and archaeological investigations.
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The lower Tigris-Euphrates Valley
When sea levels were low, the combined Tigris-Euphrates river flowed through a wide flat marshy landscape. At a certain time, the sill at the modern Strait of Hormuz and the entire lower Tigris-Euphrates basin from horizon to horizon was flooded, to form the Persian Gulf. This is an interesting, less-publicized possible source for the myths of a universal deluge.
In a 1981 Journal of Cuneiform Studies article, "The Earliest Tangible Evidence for Dilmun," Theresa Howard-Carter espoused her theory identifying Dilmun with Qurna, an island at the Strait of Hormuz. Her scenario put the original mouths of the Tigris-Euphrates rivers, which she thought should be the site of the primeval Dilmun, at or even beyond the Straits of Hormuz. Mainstream archaeologists have avoided mentioning her article, for fear of its apparent catastrophism, an awkward subject in geology.
The Black Sea (around 7,600 years ago)
For more detail, see the main article at Black Sea deluge theory.
The recently disclosed and much-discussed refilling of the freshwater glacial Black Sea with water from the Aegean, was described as "a violent rush of salt water into a depressed fresh-water lake in a single catastrophe that has been the inspiration for the flood mythology" (Ryan and Pitman, 1998). The marine incursion, which was caused by the rising level of the Mediterranean, occurred around 7,600 years ago. It remains an active subject of debate among archaeologists, with subsequent evidence discovered to both support and discredit the existence of the flood, while the theory that it formed the basis for later flood myths is subjective and unprovable.
Reflooding the Persian Gulf (12,000 years ago)
The Persian Gulf today has an average depth of only 35 metres. During the most recent glaciation, which ended 12,000 years ago, worldwide sea levels dropped 120 to 130 metres, leaving the bed of the Persian Gulf well above sea level during the glacial maximum. It had to have been a swampy freshwater floodplain, where water was retained in all the hollows. High in the Taurus Mountains glaciation will have been extensive.
The drainage of the combined glacial era Tigris-Euphrates made its way down the marshes of this proto-Shatt-al-Arab to the sill at Hormuz and disgorged far beyond, into the Arabian Sea. Reports of the exploration ship "Meteor" have confirmed that the Gulf was an entirely dry basin about 15,000 BC. Close to the steeper Iranian side a deep channel apparently marks the course of the ancient extended Shatt al-Arab. A continuous shallow shelf across the top (north) of the Gulf and down the west side (at 20 m.) suggests that this section was the last to be inundated. At the Straits of Hormuz the bathymetric profile indicates a division into two main channels which continue across the Bieban Shelf before dropping to a depth of c 400m. in the Gulf of Oman.
- "It is more likely that the original Gulf inhabitants lived along the banks of the lower or extended Shatt al-Arab, ranging some 800 km. across the dry Gulf bed. We can thus postulate that the pre-Sumerian cultures had more than ample time to be born and flourish in a riverine setting, encouraged by the agricultural potential and the blessings of a temperate climate. The fact that the body of proof for the existence of these societies must now lie at the bottom of the Gulf furnishes at least a temporary excuse for the archaeologist's failure to produce evidence for their material culture." (Theresa Howard-Carter)
In our time, mangrove edge habitat and coral reefs characterize the Persian Gulf. Mangroves recolonize easily from established mangrove fringe colonies elsewhere in the Arabian Sea. Artificial reefs are being established today along the coast of Iran. But if the Persian Gulf filled so recently, then how have the reefs re-established? The present-day natural reef developments in the Persian Gulf, corals grow on hardground substrates but have not yet formed the massive calcium carbonate structures familiar from, say, Australia's Great Barrier Reef.
Dive conditions described in 1999 (see links below) in Dubai found coral-encrusted sand barrier islands situated 32 km off the coast of the Saudi city of Jubail. There lies a chain of five coral cays, barely above the tide. They appear to be formations called diapirs in which a mobile core containing minerals of low density such as salt, deforms under pressure. The core pushes upwards, deforming overlying rock to form a dome. An ancient diapir at Enorama formed an island in shallow seas, buoyed up by salt. There are similar examples today in the Persian Gulf.
- "Protecting the Persian Gulf" (http://sdnp.delhi.nic.in/sustainabledevelopment/subresources/protecting-gulf.html): gives average depth 35 meters.
- Dive conditions described by Eric Bjornstrom, (http://www.divernet.com/travel/arabia699.htm)Diver Magazine June 1999
Reference: G.F. Camoin, ed, Reefs and Carbonate Platforms in the Pacific and Indian Oceans (IAS International Workshop on reefs) held at Sydney 1995
Great Sunda wetlands, Indonesia
During glacial times a huge peaty swampland joined Malaya, Sumatra, Java and southwestern Borneo to the Asian mainland. The present landmasses were highlands framing a vast wetlands ecosystem larger than any on earth today which is now covered by the southern part of the South China Sea. Though the area never lost its tropical to subtropical vegetation, the monsoon weather system, which is powered by the continental mass, is likely to have been more intense than it is today. At one of the "pulses" of sea level rise, the combination of violent monsoons over a single drainage basin, in a landscape that dwarfed modern Bangladesh, provide a scenario for some of the most devastating flooding humans have ever witnessed anywhere.
The Carpenteria plain (12,000 to 10,000 years ago)
During glacial times, a stretch of level plain joined Australia with New Guinea and enabled humans to walk into Australia. That plain flooded to form the Gulf of Carpentaria around 12,000 to 10,000 years ago. It is significant that aboriginal Australian myth of the "dream time" includes a Great Flood which is not ordinarily a recognizable feature of the Australian climate and geography, except for infrequent filling of ordinarily dry lake basins (e.g. Lake Eyre).
The Aegean Basin
Areas that have not been as widely discussed include the refilling of the Aegean basin. A look at a modern chart shows that it must have been a marshy low-lying plain dotted with lakes, where the combined waters of all the glacial-age rivers emptying from the Black Sea passed through the Sea of Marmara which was a fresh-water lake. There is a sill depth about 70 m. at the Dardanelles Strait, where the great river continued to its mouth at the edge of the Sea of Crete. Rising seas reached their present level in the Aegean around 6,000 years ago.
Doggerland
In 1998, the archaeologist B.J. Coles identified as "Doggerland" the now-drowned habitable and huntable lands in the coastal plain that was formed in the North Sea when sea level dropped. Doggerland has not caught the popular imagination, but the terrain was available for settlement. Its gentle swells remain as the Dogger Banks. Paleolithic reindeer hunters roamed the land; some traces of their encampments have been identified, but the timing of the submergence has not been fixed.
- Doggerland website (http://doggerland.dk/PUBLIKATIONER/artikelnyt.html) (Danish), but the map redrawn from official Geological Surveys shows the landscape around 14,000-15,000 years ago in the first warm (interstadial) period after the glacial maximum.
North America
In North America, during glacial maximum, there were no Great Lakes as we know them, but "proglacial" (ice-frontage) lakes formed and shifted. They lay in the areas of the modern lakes, but their drainage sometimes passed south, into the Mississippi system, sometimes into the Arctic, or east into the Atlantic. The most famous of these proglacial lakes was Lake Agassiz. A series of floods, as ice-dam configurations failed created a series of great floods from Lake Agassiz, resulting in massive pulses of freshwater added to the world's oceans. The Missoula Floods of Washington were also caused by breaking ice dams, resulting in the Channeled Scablands.
The last of the North American proglacial lakes, north of the present Great Lakes, has been designated Lake Ojibway by geologists. It reached its largest volume around 8,500 years ago, when joined with Lake Agassiz. But its outlet was blocked by the great wall of the glaciers and it drained by tributaries, into the St. Lawrence far to the south. About 8,300 to 7,700 years ago, the melting ice dam over Hudson Bay's southernmost extension narrowed to the point where pressure and its buoyancy lifted it free, and the ice-dam failed catastrophically. Lake Ojibway's beach terraces show that it was 250 meters above sea level. The volume of Lake Ojibway is commonly estimated to have been about 163,000 cubic kilometres, more than enough water to cover a flattened-out Antarctica with a sheet of water ten metres deep. That volume was added to the world's oceans in a matter of months.
The detailed timing and rates of change after the onset of melting of the great ice-sheets are subjects of continuing study.
There is also a strong possibility that a global climatic change in recent geological time brought about some large deluge. Another theory, although one not widely supported, suggests some of the major floods may have been caused by plate tectonics, the drifting apart of continents. Evidence is mounting from ice-cores in Greenland that the switch from a glacial to an inter-glacial period can occur over just a few months, rather than over the centuries that earlier research suggested.
The refilling of the Mediterranean
An earlier catastrophe, too far back to be within human memory, occurred at the most recent re-flooding of the Mediterranean Sea's dry basin, dated by general consensus about 5 million years ago, before the emergence of modern humans. It is an example of the catastrophic events that punctuate the serenely incremental changes to climate and geography as we think we have experienced them in the last couple of millennia. The basin had previously become a desert once again, the most recent desiccation in a series, as deep cores in the seabed have revealed a series of several layers of salt, separated by loess deposits, after continental movement had closed the Strait of Gibraltar, an event variously placed at 8 million or 5.5 million years ago. The Mediterranean did not dry out during the most recent glacial maximum.
Tollmann's hypothetical bolide
Compare Alexander Tollmann's hypothetical bolide, a hypothesis that one or several bolides (meteors or comets) struck the Earth in 7640 BC (+/-200), with a much smaller one at 3150 BC (+/-20) causing the flooding of myth.
External links
- Kurt Lambeck, "Sea-level change and shore-line evolution in Aegean Greece since Upper Palaeolithic time" (http://intarch.ac.uk/antiquity/lambeck.html) abstract