27 May 2010
The deltas of large , old rivers on the Mediterranean shore has huge , waterfilled caverns under them . A relatively thin and unstable layer of compacted silt overlies them . This liquefies easily in tremors , and is sensitive to the Med level , salinity and riverflows .(ie climate)
Recent archaeological of sunken Egyptian constructions and statues in Alexandria have once again highlighted the essential soil-instability in the Nile Delta .
What gives ?
This is old knowledge , but worth a revision .
The Med has at least three episodes of drying up in the last 10 million years . The last as recent as 1 million years ago . The Straights of Gibraltar close due to earthquakes .
The evaporation rate is higher than river-inflow rate . So the Med dries up .
But look at the rivers . They keep flowing , but now they have to fall at least about 1500 feet to the new level . In the process , they carve out huge canyons . The silt gets deposited around the delta of the river , as the drying-out is a relatively slow process
(Think Grand Canyon in USA) . The Nile and Rhone , for example , were not little streams , but drained large parts of continents .
Spectacular waterfalls .
Then another earthquake opened the Straights of Gibraltar again . Even more spectacular waterfall as the Atlantic surges into the Med to fill it in a relatively short time .
Notice what happens in the canyons :
The warmer , fresh riverwater slides over the heavier , colder saline seawater . The silt in the riverwater compacts in arches , forming huge caverns in the old canyons . Remember , this happen much more rapidly than the drying-out episodes .
Repeat this three times .
What can we see today ?
The old , large rivers like the Nile and the Rhone has extensive deltas and a large underwater shallow sediment field . There are extensive and very large underwater caverns , in what used to be the old canyons .
The surface soil liquefies easily in earthquakes . Entire cities can and have disappeared overnight . Some are known in the Nile delta . Not much search has been done in the Rhone delta (Marseille) .
Where Else ?
The last 10 million years had a number of episodes when Northern Africa was well-watered with large rivers draining half a continent .
Keeping the above in mind , a cursory look at a topographical map suggests the following (or use GoogleMaps) :
1.Gabes (Tunisia) (10 Degrees East , 34 Degrees North) . Large silt plains in the Med and very large drainage hinterland , with remnants of rivers and lakes .
Note that Carthage was on the edge of this system . Deep soil and steady water .
2.Marsa-al-Burayab (Libya) (19 Degrees East , 31 Degrees North)
Large silt plains in the Med and very large drainage hinterland , with remnants of rivers and lakes . Very wide delta .
3.Ebro (Spain) :
An extensive flood plain , both on land and underwater) . The main outlet seems to have switched often . Notice the similarity with North Africa .
Intriguing . There should be deep caverns connecting Southern Sicily and Malta .
Also between Western Sicily and the Island of Pantalleria . Note effect of strong currents .
5.Po river .
Look between Venice and Comacchio . The Po with its raised banks would wander over a large delta . But look at the peninsula around Ca Tiepolo .
Black Sea Event .
About 8000 years ago a series of earthquakes on the Anatolian Faults opened the Black Sea to the Med (Straights of Dardanelles) . Salt water flooded in and changed a lake into a Sea . Plenty of archeological evidence .
If this has been a frequent geological occurrence , as seems likely , we can also expect very large caverns at the old mouths of the Danube , Dnepr , Bug , etc .
Note that this event would have lowered the Med level , leading to large-scale instability on all Med deltas . Maybe some old Egyptian records indicate this . It will show up as lowering of the Nile flooding in the delta , especially .
Shallow harbours unusable all over the Med . This should have left some traces .
Adjustments to changes in sea-depths around sensitive tectonic areas would probably lead to some strong earthquakes , maybe even swarms of quakes .
Even a moderate quake can shut the Dardanelles again . What will be present consequences ? Note the ecological results and possible human intervention (canals , even using nuclear devices to redig the Dardanelles)
Note that cities are built on the site of maximum instability . This is to be expected .
Remember , this where maximum rewards in short term can be obtained . Skating on the edge of strong attractors . Humans are suckers for this .(Cf Vesuvius)
So , if you are looking for caverns , look to Cairo , Marseille , Carthage , Venice , Valencia , Odessa , etc .
This is where the soil is deepest , most well-watered and fertile . Where the most fishes are . Also the least pollution .
Fishing in the Med and Black Sea should have been wiped out long ago . But the fishes have a refuge cycle in the caverns .
The cost of getting them out of there exceeds value .
If the fishers go in aggressively , they risk collapsing or poisoning the cities on top of them .
The caverns are very large , and in many cases the volume exceeds the productive land capacity of the country above them (eg Libya) .
Energy is provided by "pollutants" , (eg nitrogen fertilizers , detergents , etc,etc . This is filtered through the cavern's compacted many-pocketed silt walls .
And they all need carbon , being carbon-based life-forms . A huge carbon-sink .
The combination of filters and life-forms create a huge garbage disposal in the basement .
Humans can expedite this process by processing their garbage directly into the basement caverns . With a modicum of care , this would create a bio-reactor that would easily feed and water the top-side population .
The ultimate sub-urbanites .