Yossi Mart. The Broadcasting University, published by the Ministry of Defense, 192 pages, NIS 42
Akiva Flekser
The Israeli reader has a great interest in the Mediterranean Sea, the Exiles and the north of it. Herodotus defined Egypt as the gift of the Nile, and paraphrasing this sentence it can be said that Israel is the gift of the sea. Most of Israel's rocks are a gift from the sea: they were created in the sea, and then lifted and transported to the top of the mountain, as Prof. Yossi Mert called it in the title of his fascinating book "The Sea at the Top of the Mountain".
The book is not just another book about the geology of the Mediterranean. Its uniqueness and contribution are mainly in two aspects: the mutual relationship and interrelationships between the geological processes and the climatic processes, and the geographical changes in the geological time tunnel and the subsequent climatic changes.
The book opens with a chapter on ocean and climate, and tells about the chemical and physical properties of sea water. The radiation of the sun, the winds and the currents of the sea that shape the climate on the surface of the earth have a close relationship, and these factors are closely related to the geological structure of the earth and its geographical shape, to the sea-land division, the location of the continents and the relationship between them, and the presence or absence of obstructions to the free flow of sea water . The loss of heat energy due to radiation also depends quite a bit on the sea-land relationship and the amount of glaciers.
Sea-land relations in a geological perspective along the timeline is an interesting problem with many implications. The continents, or more precisely the plates on the Earth, are in an endless and complex dance. The continents move, approach each other, move away from each other or slide side to side, like rafts in a raging lake.
The author briefly explains in chapters B and C the mechanism of the dance, and tells about the internal dynamo of the earth that generates it. In our generation we often talk about the circulation of materials and the fragmentation of superpowers (the Soviet Union for example). Nature preceded man in these actions. Prof. Mert provides a short but clear description of the circulation processes that exist on Earth: oceans open, a new rocky crust is formed in this opening and in other places. "Battles" are taking place on the margins between a land plate and a sea plate. In such an encounter, the sea plate falls down, undergoes melting, loses its identity and later emerges with a new identity to the earth.
Basically, there is a phenomenon of "cannibalism" on Earth: it "eats" itself, or more precisely it eats and digests parts of its own membrane. These cyclical processes have occurred since his birth, but the last cycles are relevant to the birth of the father of the Mediterranean Sea, aka the Tethys Ocean.
The birth of Tethys is associated with a huge landmass (supercontinent) or supercontinent, Pangea, which has undergone strong fragmentation. Figure 15 in the book describes this in a tangible way. The landmasses are divided into a northern continent (Eurasia) and a southern continent (Gondabana), between which a huge equatorial ocean was born, which is the Tethys Ocean. The "life course" of this ocean is intertwined with many vicissitudes and it left its mark on the structure and landscape of Israel, the sea at the top of the mountain.
The innovation in this book is, as mentioned, the emphasis on the climatic aspect: the mutual effects between the development of the Tethys and the earth's climate, and at the same time the fingerprint of the climate cycles on the rocks that were "born" from this ocean.
Ra is interesting about the catastrophic extinction of life that occurred in the process of shrinking and closing Tethys. This extinction is better known by its name "the extinction of the dinosaurs". In fact, many types and species of animals and plants became extinct at that time, but the dinosaurs, being large and eye-catching creatures, deserved to have their name imprinted on this extinction.
The author brings the two views related to the explanation of the phenomenon: the impact of a massive celestial body or a particularly stormy volcanic eruption. Both things happened at the end of the Cretaceous period (65 million years ago), but the event of the asteroid hitting the Earth is considered the main responsible.
Prof. Mert raises the question of whether there were no mitigating circumstances: that is, whether there was not a sort of advance preparation of the geological and biological array for the event. The question is complicated and has no clear solution, but the example of the bag of sugar that fills up slowly and gradually, and suddenly tilts the scales, is a beautiful and instructive example (p. 52).
The geological development of the Eastern Mediterranean is a complex and interesting affair. The number of explanations is more or less the same as the number of researchers. In chapter 180, the Syrian arc and the Cyprus basin, the reader learns about the processes of hatching, opening and creation of a new sea basin about 17 million years ago. The bottom of the basin is studded with volcanic rocks, similar to what is formed today in the mid-oceanic ridges. However, a look at Figure 72, on page XNUMX, is puzzling, since the same rocks that build the infrastructure of the new basin (the basalt layer) already exist under the granite layer in both Israel and Cyprus. The figure illustrates a stretching process (although the arrows showing this are missing) and the tearing of the granite layer, but does not emphasize the formation of a new oceanic crust, which may not have really been formed and developed enough. And maybe the "basalt layer" marked in the diagram is not made of one piece?
A chapter of extraordinary interest is the chapter dealing with the drying up of the Mediterranean Sea. The Strait of Gibraltar closed about 5 million years ago and the water supply from the Atlantic Ocean stopped. The amount of fresh water spilling from the rivers into the Mediterranean Sea is smaller than the rate of evaporation which may reach 1-2 m per year.
And so, in a relatively short time, the waters of the Mediterranean Sea evaporated and left a very thick layer of salt. The reader should close his eyes for a moment, and imagine the landscape of the dry Mediterranean Sea. A huge dry pit, with massive mountain ranges at its edge. The Alps or the Taurus Mountains rose thousands of meters (twice their height today) above deep chasms, and mighty canyons spill into the bottom of the pit. So are the Rhone River, the Po River, and especially the Nile River, which was several times larger than the Grand Canyon of Arizona. The geological and geophysical studies prove that our Kishon and Bashur streams also created amazing and impressive canyons.
The return of the sea with the opening of the Strait of Gibraltar also calls for imagination: the faucet is turned on and the bathtub is filled with mighty waterfalls and a roaring sound. Amazingly, such a description is repeated a second time in the story of the flood, when the Bosphorus strait opens and the Black Sea, which was a relatively small fresh water lake in area and volume, is filled with the waters of the Mediterranean Sea. This is a dramatic description of the bursting of many springs (the "bosphorus taps"), which raised the level of the Black Sea and flooded the Neolithic man's dwellings on its edge. The waters increased, rose and rose as described in a wonderful way in the story of the flood in the Bible and in the Gilgamesh stories.
This theme is reflected in the book in a special chapter on the Black Sea, the neighbor of the Mediterranean Sea. Rises and falls in the level of the Mediterranean Sea and the world's oceans occurred during climatic upheavals that occurred in a young geological period, the Quaternary, two million years ago to the present day. When the sea level dropped by 120 m, the coastal strip west of Tel Aviv spread to a distance of about 15 km. It seems that today one should miss such a time, especially in a densely populated country like ours. The possibilities of expansion and construction are really skyrocketing.
The author devotes a special chapter to the geological situation of the Mediterranean coast in Israel today: sand transportation, construction of marinas and the dangers lurking in their construction. Herod's port in Caesarea is the subject of many studies. Is there damage from an earthquake here or failed planning?
The author did well when he chose the Mediterranean Sea as the subject of his book. Although it is only a remnant of a huge ocean, the Tethys Ocean, it is undoubtedly a magnificent remnant, rich in geological upheavals and rich in historical and cultural heritage.
Prof. Akiva Flechsar teaches in the Department of Geophysics at Tel Aviv University
