by Boris GOLUBOV, Cand. Sc. (Geol. & Mineral.), Institute of Dynamics of Geospheres, Russian Academy of Sciences

Baron Münchhausen, the famous German adventurer and liar of the 18th century immortalized in the fiction of the day, once said he had got into the Caspian Sea through an "underground passage".

Was it really a wild yarn and figment of imagination?

Perhaps not. The Caspian Sea (inland lake) and its awesome phenomena fired people's imagination and begot many a legend in the dim and hazy past. The sudden sea changes with outbursts of flames, oil and gas gushers bursting forth to the accompaniment of the rumble and tumble deep under... Its abrupt water rises and falls, with new islands coming and going... striking temperature differentials with ice floes in the heat of summer... All that was mind-boggling indeed. Add the tsunami-like tidal waves, severe storms, the ebbs and

Articles in this rubric reflect the author's opinion. - Ed.

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The map of Rus. Amsterdam, 1613. On the right below - the Caspian Sea in the works of 17th century Dutch geographers.

flows at one and the same point without any change of wind as well as the fata morganas and other optical illusions; the dark sandstorms carried from the deserts of Central Asia in the east, the reddish mist hanging over Kara Bogaz Gol, a large shallow gulf...

The ancient maps pictured the mysterious Caspian this way and that-extended now along the latitude, now along the meridian; connected to the ocean or else-less often, though-closed, without any outlet to the ocean. But could those maps depict real physical changes? For a clue we should turn to the Caspian's geologic past. By tradition it is regarded as a relict body of water that about 7 million years ago lost a seaway connecting it to the ancient ocean Tethys and that has experienced repeated fluctuation in its water level ever since (as indicated by the succession of shoreline benches and scarps of different age). Such transmutations are still the subject of longtime discussions continuing to this day.*

It would not be amiss if we mention another version of the Caspian's birth. Back in 1694 the English astronomer and geophysicist Edmund Halley suggested that similar large structures could have appeared on the Earth under the impact of comets hitting the terrestrial surface. Such surmises also came from other savants: from the German philosopher Immanuel Kant (1755), the author of the cosmogonic theory of the origin of the solar system (Kant was elected to the St. Petersburg Academy of Sciences honoris causa in 1794); and Pierre Laplace (1796), a French mathematician, astronomer and physicist (like-wise elected to the St. Petersburg Academy of Sciences, 1802). Two centuries after, in 1980, the American physicist Luis Walter Alvarez (Nobel Prize, 1968) related the mass extinction of all living beings, dinosaurs** among them, to the fall of a giant asteroid 65 million years ago, thus giving a new dimension to the postulates of the great minds of the past. Our research center is exploring this possibility; meanwhile our colleagues from the Dubna-based Joint Institute for Nuclear Research*** have detected a hitherto unknown superheavy nuclide characterized by spontaneous fissionability (it was found in the geothermal salt brines of the Cheleken peninsula in the Caspian's east).

Since time immemorial people have been trying to explain the Caspian's transgressions (advances on dry land) by its resumed connection with the World Ocean through a hypothetic seaway. However, the stubborn searchings since the 19th century for any vestiges of that waterway have produced no results. Such searchings may be futile in principle because the mechanism regulating the level of this giant marine lake could be connected with its "underworld". Why not? Such ideas were uttered by Aristotle (384 - 322 B. C.), a Hellene thinker who impersonated the wisdom of the ancient world; by savants of Western Europe in the 17th century, and by Russian scientists of the 18th century. One of them was Ivan Lepekhin - a traveler, naturalist and in fact the first Russian researcher studying the formation of

* See: Ye. Mukhina, Ye. Ignatov, P. Kaplin, "The Caspian: Catastrophe. Hypotheses, and Strategy", Science in Russia, No. 4, 1994. - Ed.

** See: Yu. Avsyuket al., "Did Dinosaurs Die Out Suddenly?", Science in Russia. No. 3. 2002. - Ed.

*** See: A. Sisakian. "Dubna's Worldwide Glory". Science in Russia, No. 2, 2006. - Ed.

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karst* caves and the regime of subterranean waters. We should also mention Vassily Tatishchev and Pyotr Rychkov, the authors of fundamental works on history and geography; and Samuel Gmelin, a scientist who, in 1768 to 1774, was exploring the Don river basin, the lower reaches of the Volga, Caucasia and the Caspian shores.

Up until the 18th century the Caspian, "the lake at the foot of the Caucasus" had been thought to be connected with the World Ocean. The idea was kept alive by the testimonies of the Hellene historian Polybius(ca. 200 - 120 B. C.) about the waterfalls at the mouth of the Amu Darya flowing into the eastern Caspian, by the maps drawn by Eratosthenes, the founder of mathematical geography (ca. 276 - 194 B. C.), and also by the pieces of evidence on the Uzboi, an erstwhile river. The present maps of Quaternary deposits and space photos show traces of its dry bed going from Lake Sarykamysh (where part of the Amu Darya's water was emptied) to the western stretch of the Kara Kum desert towards Lake Kelkor (salt bottom today) and farther to the Caspian. The idea that the Caspian could be linked with the World Ocean was also on the mind of the Russian emperor Peter I the Great, who sought to "cut the window" both to Europe and to India, too.

In November 1714 Prince Bekovich-Cherkasskyset out to explore the Caspian with a crew of seamen and, the following year he handed the first true map of the sea to the emperor. Six years later a more accurate map ("Flat Map of the Caspian Sea") came out, the joint work of Caspian explorers, with Feodor Soimonov, en eminent hydrographer and statesman, among them. This map became a European sensation.

In 1726 Soimonov made another journey to the southern parts to take a closer look at Kara Bogaz Gol. But he would rather not take chances and enter the gulf on hearing the local legend about the abyssal depths engulfing ships and boats; his men "were struck with mortal fear, and each deemed death was inevitable." Turkmen called the gulf a Black Belly because of its ill fame, inaccessibility, high salinity, turbulence and the pervading, choking odor of sulphur. And still Kara Bogaz Gol had a "romantic" setting, with pink flamingo birds wading in reddish foamy waters filled with dead salt fish, and gaggles of countless geese and pelicans, all that against a backdrop of somber ruins of tombs and mosques, and sublime silence reigning supreme...

Acad. Pyotr Pallas, another eminent naturalist, explored the Caspian in 1769 to 1773. He did not agree with Lepekhin and Gmelin on the point of "underground canals" and maintained that sea level ups and downs could be put to the climatic factor. Yet he contended: disastrous volcanic eruptions, which during our planet's long life had caused many uplifts of islands, continents and mountain ranges, were also responsible for the formation of subterranean caves where water kept draining, and that naturally caused a fall in the level of the World Ocean. Acad. Pallas was the first to see some similarity of the Caspian animal kingdom with that of the Sea of Azov, which allowed him to hypothesize on the possible con-

* Karst (cockpit) - sunken structures occurring in soluble rock (gypsum, rock salt, etc.) comprising underground (caves, hollows) and surface relief features, and characterized by a peculiar regime of subterranean waters, rivers and lakes. - Ed.

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junction of the two bodies of water in the geologic past.

Acad. Emil Lenz pioneered in the instrumental climatologic observations on the shores and in the basin of the Caspian (in 1830 to 1832 he made the very first measurements, the reference points of such studies). He analyzed water level marks on the fortress walls of Baku and Derbent, compared testimonies of old eyewitnesses and travel notes of the early 19th century, and even described a fire column and the Bozdag mud volcano.

Like P. Pallas, E. Lenz agreed that the now closed Caspian Sea was once linked to the Sea of Azov and the Aral Sea (and broached the matter of how their water levels correlated); it might have been separated from the Black Sea with the uplift of the floor of what was once a solid sea. He explained the fluctuations of the Caspian's level by the cumulative effect of the tectonic and climatic factors related to floor movements. This set the tone for years and years of debates between geologists and climatologists, with still no victors in this controversy.

From 1849 on the network of hydrometeorological stations in the Caspian basin kept expanding to furnish important information on river runoff, atmospheric precipitation and air temperature. Between 1900 and 1921 a large number of observation posts were set up to monitor the water level. Thus climatologists could rely on rather extensive datasets over many years, convenient for statistical and analytical data management. But geologists, out to prove that tectonic movements of the sea floor were important for the water level and yet unable to "brandish the arms" of mathematical calculations (on account of sporadic observations and the low accuracy of instrumental measurements), looked lackluster on this background.

Meanwhile in 1924 to 1928 came the first pieces of evidence on subterranean springs gushing forth onto the Caspian bottom and adding significantly to the sea's water pool. Broad hydrogeological studies in the Caspian and adjacent areas showed that the amount of subterranean water fed from eastern Ciscaucasia alone could be as high as 50 cu. km/yr, or about 1/6 of the annual runoff of the Volga. Still and all, the Caspian was growing shallow, while calculated data on the level of evaporation differed a good deal.

Turning to the results of instrumental observations begun by Acad. Lenz, we can single out three major stages

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Fluctuations of the sea level.

of the Caspian's regressions (falls of water level): in 1830 to 1928, 1929 to 1941 and 1942 to 1977. During the first and third stages regression proceeded moderately, while in the second stage the water level fell from the benchmark -25.96 to -27.84 m. In 1978, after an all-time low (-29.04 m), there came a rise continuing nonstop up until 1995 at an annual rate of increase 16 to 18 centimeters (ca. 40 inches). This transgression concurred with the filling of the Nizhne-Kama and Cheboksary artificial reservoirs (where part of the Volga water was channeled), and hence the overall amount of water drained by the Volga into the Caspian went down. These events had taken place long before the building of a high dam closing the shallow gulf of Kara Bogaz Gol (1980). In 1993 the dam was pulled down, and the Caspian water rushed into the gulf at an annual rate of 20 to 23 cu. km. Nonetheless the Caspian's level remained the highest even two years after (-26.6 m), then gradually dropped by 54 cm (135 inches) but, as of the year 2002, started going up again.

All these events got scientists to look into the geology of the Caspian basin. In the 18th and 19th centuries fragmentary data were collected by Samuel Gmelin, Karl Baer (elected to the St. Petersburg Academy of Sciences) and Grigory Karelin. Toward the close of the 19th century Nikolai Andrusov, one of the pioneers of paleoecology, began systematic studies of the basin. Such eminent scientists as Vladimir Baturin, Ivan Gubkin (the founder of petrogeology in this country), Leonid Pustovalov and other researchers carried on this work in the 20th century.

Using electrical surveying techniques, our explorers identified certain peculiar features of the tectonic fracture of sedimentary rock off the Daghestani coast of the Caspian, a phenomenon compounding the folded structure of this rock. Surveys of the bottom ground were begun. In 1935 to 1939, Vsevolod Fedynsky, employing gravimetric survey, discovered the cores of salt domes (plugs) underlying the floor of the northern area of the sea (such structures are circular rises of the earth crust). In 1950 the Laboratory of Aeromethods of the USSR Academy of Sciences joined in this work.

Today Caspian is covered with a dense network of gravimetric, magnetometric, electrosounding and seismic prospecting profiles. A large amount of work has been carried out in the past 20 years by the method of back (reflected) waves with a resolution of up to several meters. Seismic surveying (prospecting) has performed just as well: complemented by drilling, such techniques have allowed to pry into the structure of the sedimentary "cover" (mantle) of rock under the sea floor and reconstruct the position of the rock during the last 5 to 7 million years. What is especially important is that such work is being done without chemical explosions, lethal to organic life.

From a geologist's standpoint the Caspian Sea is the world's largest land-locked body of water fabulously rich in natural resources. Its depth averages 208 meters (with 1,025 m, a maximum), surface area - 378,400 sq. km, and the water volume - 78,100 cu. km. This vast marine lake lying in the heart of Eurasia is divided by the Mangyshlak and Apsheron sills (bars) into three segments - the northern, middle and southern ones; extending meridianally, it crosses the climatic zones of temperate and subtropical belts and has more than 130 rivers flowing in.

The Caspian has a well-developed shelf zone. The earth crust of its basin, about 2 mln km large, is of continental

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Geology of the Caspian basin. I: 1 - its contour; 2, 3,4, 5 - deposits on land, shelf, deep-sea troughs, and salt domes, respectively; II: 1, 2, 3 - the ancient East-European platform, the recent Scythian-Turan plate and the region of Alpine folding; III: 1 - deep-sea faults; 2 - tubular bodies under the sea floor; 3 - mud volcanoes; 4, 5 - oil-bearing strata; 6, 7, 8, 9 - oil, gas, gas-condensate and oil-and-gas deposits; 10 - underground nuclear deposits (number).

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Caspian water temperature in 2001 (by space survey data).

Vertical cross-section showing the Caspian's interior with tubular bodies discovered by seismic surveying.

Vertical section of the Caspian, with mud volcanoes and oil slicks on the water surface above.

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type for the most part, and is about 35 km thick. Its structure includes the ancient East European platform, the young (recent) Scythian-Turan plate and the Mediterranean Alpine moving belt. Standing out within these tectonic elements are structural "floors" of different ages, with the uppermost built effractions accumulated in the past 5 to 6 million years and lining the bottom of the basin. The makeup of this layer and its bedding bear vestiges of tectonic movements that have caused an abrupt restructuring of the earth crust. This process is still on, as confirmed by enhanced seismicity of the region, shifts of rock in different directions, mud volcanicity, hydrothermal activity, and shows of volcanism in the mountains of Elbrus (northern Iran), the Greater Caucasus, Ciscaucasia and in other areas. The unstable, not-equilibrated state of the recent Caspian basin is also conditioned by the local dynamics of fluids, such as oils, gases and underground waters. These waters are concentrated under the Caspian in amounts exceeding the sea's sheer volume dozens of times over. Although we are dealing but with tentative estimates only, they are illustrative of the mighty potential of the plutonic depths. We cannot tell how and where this underground pool communicates with the sea. But drawing upon structural geology data (obtained through marine seismic surveys and by other geophysical methods) and evidence supplied by orbital satellites, we can suggest the possible location of "hydrogeological windows" serving as communication channels.

In the 1950s, 1960s and 1970s the Laboratory of Aero-methods registered instances of intensive gas bubbling on the sea surface in the form of linear bands parallel to the Daghestani shoreline, a phenomenon attributed to the degassing of the lake's interior. In 1973 research teams of the Daghestan Branch of the USSR Academy of Sciences, studying heat transfer in the Caspian hydrosphere, could spot upward flows rising from beneath. It became possible ten years later to provide a detailed description of the motion of thermal metalliferous waters in the fault-angle Cheleken structure (a fold of rock compounded by a fault) situated near the gulf of Krasnovodsk and, up until 1925, partly submerged in the Caspian.

Simultaneously research teams of Leningrad State University called attention to the inverse nature of the chemical composition of water at the Apsheron sill. In their opinion, this indicated the draining of underground "rivers" into the sea. The data on the distribution of uranium isotopes in the Caspian basin obtained subsequently showed that the filling of the Caspian could not be explained by the surface runoff alone.

Quite recently researchers in the Republic of Daghestan, using high-precision seismic survey methods, detected numerous tubular bodies 10 to 100 m across under the bottom of the northern Caspian permeating structures of different ages and piercing in places the benthic deposits, a picture suggestive of the present activity of such bodies. But it is still a puzzle as to how this activity manifests itself.

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Yet another proof of the Caspian's "underground life" is in the large number of oil slicks of natural origin spotted in 2003 and 2004 by the international orbital satellite Envisat, which sent radar images of the Caspian's southwestern district. Upon computer processing these images, collated with seismic survey and seismological data, have shown that such phenomena occur largely over local rises of the sedimentary "cover" and craters of mud volcanoes, and they are particularly frequent in periods of heightened seismicity. Space radar sounding indicates that the natural blowout of oil is up to 2.5 - 16 thousand tons a year.

And last, shows of hydrovolcanism are characteristic of brines "buried" under the forceful pressure of gases in domes of the Caspian Depression. There were cases when their natural or artificial tapping caused sudden outbursts of such solutions. Occasionally they flowed out sluggishly, depending on pressure differentials, and then the process dragged on for years.

Zoologists have done their bit, too. Working in the Kara Kum desert in the late 1920s, they discovered 10 varieties of foraminifera-protozoa, typical marine inhabitants, in brackish subsoil waters there. These and similar organisms were subsequently detected in subterranean lakes of Central Asia. All such bits of evidence were summed up in due course. This and a genetic analysis made in 1966 go to show that the Caspian fauna is mostly of marine origin, ancient and relict in its form.

At the same time Niphargus, a cerriped barnacle, usually living in subsoil waters, was found in Kenderly, a gulf off the Caspian eastern shore. This points to a direct link between the sea and abyssal water bodies of contiguous territories. This communication channel may run through porous rocks to fairly great lengths. That explains the "amicable" relations between the denizens of the sea and underground waters. These phenomena may help unlock the mystery of asylums (refuges) that have ensured the survival of the relict Caspian fauna in the geologic past.

The Caspian is obviously linked to the underground hydrosphere. It is the world's unique basin-actually neither sea nor lake-which has received huge volumes of underground waters with their extraordinary salinity and chemical composition. So we come to deal with an essentially novel genetic type of water bodies. While formally the Caspian was perceived as a deep depression with a tight, impermeable bottom getting water from rivers and atmospheric precipitation, it now emerges in a different dimension as a layer of surface waters interacting in a variety of ways with mountain rock deep under, many kilometers thick and saturated with all kinds of fluids.

Photo, A. Oleinikov