THE MAGNIFICENT MEDITERRANEAN
AN INTRODUCTION TO CULTURAL GEOLOGY
FOR TRAVELERS
Note: I recommend here that the reader, open apps such as Google Earth ( recommended) or Maps and familiarize oneself with the geography of the area —the magnificent Mediterranean. I will also give references for Google Earth in the text. Simply copy and past the reference to Google Earth “search”. (For example to follow a text reference for a longitute and latitude reference in the text or a name place, such as: “Strait of Gibraltar: Copy “Strait of Gibraltar”, Go to Google Maps, elect “Search”, paste in “Strait of Gibraltar” and hit return. Google Maps will take you to the Straits of Gibraltar, or to that particular latitude and longitude reference)
The Roman Republic and later the Empire eventually spread over three continents, Europe, Asia and Africa and incorporated all the shores of a near one million square mile inland sea, the Mediterranean. (See Google Earth, “Mediterranean Sea” ). Rome existed as a political entity for 1,000 years (@ 500 BC-@ 500 AD) and left an incomparable impact on all the nations and cultures that followed. The Romans gave us, their alphabet, art, literature, poetry, language, architecture, calendar, traditions, religion, and impressed us with their sophistication, organizational skills, political flexibility, military prowess, engineering, road building, as well as their their sheer ingenuity and unique ability to absorb elements of foreign cultures into their own. All of these did not disappear in late-Fifth Century AD collapse of the West, but were absorbed and redefined and redeveloped, to appear again, and again in the Middle Ages as the Holy Roman Empire, and to be reborn during the Italian Renaissance. Roman culture with its roots in Britain, Italy, France, Spain and the wider shores of the Mediterranean— spread from this area to eastern Europe and around the world as it morphed into other cultural and political entities which we can see and identify today as of Roman origin, almost two millennia later. We are all inheritors and of the Romans…
But what was the physical world, the geography, and particularly the geology which nourished, stimulated, and supported Rome and the culture which it generated? I hope to elucidate in some small way, aspects of the geological and physical world of the Romans and the connection and realtionships between culture and the geology of the Mediterranean that made the Republic and the Empire so successful and able to lat for so long.
THE ENCLOSED MEDITERRANEAN WORLD
See Google Earth Link https://earth.app.goo.gl/rcRDN5
#googleearth
The Mediterranean Sea is, as its name states is: a “middle of land” sea. The northern shore of this inland sea is almost fully bordered by mountain ranges and rugged highlands, and its southern shore courses along desert lands, even today, mostly uninhabited and uninhabitable. To the west, the narrow 9 mile-wide sea way, or “Pillars of Hercules” we know as the “Straits of Gibraltar” limit access to the wider Atlantic. To the east, the narrow and difficult Dardanelles slow traffic from the Black Sea and the nations and people to the east. In early history Mediterraneans lived in an enclosed world veery much separated from those beyond its shores.
Mediterranean’s “enclosed” geography protected the Roman state from overwhelming invasions by foreign elements, while its open “one million square mile inland sea” permitted and encouraged wide-ranging economic and cultural interaction, and stimulating exposure to new cultures, new technology and new ideas. The Mediterranean shores acted as a “semipermeable, osmotic-like” barrier which protected the Roman culture and state from radical change, yet nourished it.
The Mediterranean region has a pleasant moderate climate with a mean annual temperature above 50 degrees F, with dry summers, and cool, humid winters. These factors are in good part the result of its mid-latitude location where prevailing west winds of marine origin tend to temper the climate. Less frequently, the region it is swept by dry, desert winds from Africa, and at others by cool humid air from the North Atlantic Ocean. The moderate climate of mild winters and hot sunny summer permits farmers to grow two crops per year. Then too the food crops they grow: wheat, rice, olives, grapes, dates, citrus and fresh vegetables are well adapted to the climate. The hilly topography encourages specific land use strategies and planting a variety of crops in one area. Almost every patch of arable land, even on steep slopes, is used by these farmers. In some areas of Puglia, in Italy and in Spain, wheat and other grains are successfully planted and harvested as a crop grown between wide spaced rows of olive trees. Two main crops, olives and wheat are harvested from the same field. In many areas soils in this region are very fertile, the result of their marine limestones or of volcanic origin
But most important is the almost one million square miles of Mediterranean sea surface which moderates the climate of the entire Mediterranean basin. The amazingly clear, deep-blue water* absorbs solar radiation in summer, to cool the air. In winter, the warm seawater re-radiates that absorbed heat to warm the air and the surrounding land. The Mediterranean people living in this temperate, marine climate were not burdened with the need to expend large amounts of energy to overcome the chill of winter or the excessive heat of summer. The Mediterranean’s moderate climate reduced climate stress and modulated pressures for survival. It permitted its inhabitants the time and energy needed to devote to pursuits other than mere survival.
(*Sea water in the Mediterranean is saltier than the Atlantic due to high evaporation and limited interchange with the world ocean. It is so blue because it is very low suspended particulates and in dissolved nutrients. Low levels of nutrients restrict growth of plankton ( algae), and since few rivers enter the basin it also has very little sediment in suspension…both of these factors permit most of the longer wavelengths of sun light to penetrate to depth, reflecting back only the shorter of wavelengths—the blue portion).
The geography and geology of this “one-million-square-mile-ocean in the middle of land” offered many other economic and physical assets. The Mediterranean is a small ocean, with insignificant tidal ranges (only a few feet), and its areal extent tends to limit the “ fetch” of sea wind driven waves, and thus wave heights. Hurricanes and tropical cyclones do not occur here. Although, calms and tempests are not uncommon, sailing this inland sea was relatively safe. Navigation was often by simple “line of sight” means, and was facilitated by to the many visible and recognizable headlands, islands and volcanic peaks. Sailors could follow the shoreline and seek safe anchorages among the many islands and excellent naturally protected harbors and ports, which provided safe harbor and respite from storms or danger.
The character of this inland sea facilitated both travel and trade at a very early time in history. As early as 1500 BC the Phoenicians, from Tyre in modern Lebanon were actively trading all across the Mediterranean. Sea trade permitted and encouraged exchange and spread of technology, language, ideas, mineral wealth, and unique natural products all across Europe of that time. Phoenicians are claimed to travel to have regularly traveld to Cornwall in Britain a near 6,000 mile sea journey where they traded for tin, (See: Google Earth Link https://earth.app.goo.gl/2Avu6K #googleearth) Then they sailed back to their home port in Tyre (Lebanon). But it is more likely that they traded from tin mines in Brittany, France. From there the tin traders would travel overland to their colony in Marsailles (@ 500 miles) and then on to Tyre in Lebanon by sea (@ 2,000 miles). That is still quite an impressive voyage,.
Tin was an essential, though relatively rare metal. In the Mediterranean basin tin was found in Spain, Brittany in France and in Cornwall and Devon in Britain, there were minor deposits in Italy. Tin was an essential minor alloy used with copper in a ten to one ratio to produce the metal bronze, which was harder and more rigid than copper and could be melted and cast into tools, weapons, and cooking implements. Bronze was harder than iron and did not rust. The Bronze Age began around 3300BC and lasted to about 1300 BC when in many places iron came into greater demand for tools and weapons than bronze. Iron was a very common ore, easily smelted with widely available charcoal—but could not be cast. It had to be forged into tools, implements and weapons. The end of the Bronze Age may have simply been the result of the scarcity of tin, and the collapse or disruption of the trade routes that supplied this metal. Later, in the 9th century BC, when iron was in great demand, the Etruscans on Elba Island became wealthy mining and smelting iron, and other minerals, and trading these products all throughout western Mediterranean and northern Europe.
Travel by sea in the Mediterranean was relatively safe, and swift, and a great advantage over overland travel. A Roman trader during the Empire could sail from Rome to Alexandria, Egypt, in about ten days to two weeks, a trip of about 1220 nautical miles. (Roman sailing vessels’ average rate of speed was @ 5 knots or—5 nautical miles/hour. (1220 nm/5 =244 hours/24 hours= @10 days.). While overland travel from Rome to the Alexandria a trip of well over 2000 land miles would take many months of arduous and dangerous travel.
Another` major advantage of maritime travel was the ability to transport bulk products, such as food grains (in wooden barrels), olive oil and wine (in ceramic jars), as well as bulk commodities such as lumber, stone and metal ingots or building materials. Safe and reasonably rapid Mediterranean-based marine-travel and trade made Rome’s wide-flung Empire not only possible, but highly efficient.
In a testament to the massive amount of maritime trade that occurred over the centuries entering the Roman port of Ostia, one can still inspect today a small mountain of ceramic shards—the result of discarded olive oil and wine ceramic amphorae (jugs) at Monte Testaccio in modern day Ostia. (Use Google Search to view “Testaccio” and “Monte Testaccio” mountain peak). See Monte Testaccio:https://www.atlasobscura.com/places/monte-testaccio. See: Google Earth Link https://earth.app.goo.gl/pscNaW
#googleearth
THE GEOLOGIC UNDERPINNINGS OF THE MEDITERRANEAN
To understand the Romans we must begin with their natural and geological environment and physical resources. Students of this part of the world, and its historic period, would be better armed to understand what they see, and develop a deeper understanding if they come informed by a more detailed knowledge of the physical world of the Romans.
GEOLOGY
The geological story of Italy is fascinating, complex and intriguing. It is essentially a story of drifting continents and crustal plate collisions or “tectonics”…i.e. that the Earth’s continents are—like every thing else in nature—not static..stationary or stable…but always in flux. Even the Earth’s continental plates migrate over the Earth’s surface. But their movement is imperceptibly slow, (most often) moving at the rate at which your fingernails grow (a few centimeters annually). Armed with that idea, and that the Earth is very, very old…4.5 billion years…readers may come to understand how so much continental movement and landform change can occur and yet be unperceived. Then too, with crustal movements comes extensive volcanism…the Mediterranean is a virtual textbook of volcanic activity, where super-volcanoes, stratocones, cinder cones, and shield volcanoes like Etna in Sicily and calderas the extinct shells of earlier volcanoes are common elements of the natural world
But to understand Italy’s geology you will have to realize that our Earth-with its evenly-spaced out continents and wide Atlantic and Pacific oceans is only the most recent pattern in which continents are positioned on the Earth’s surface. Not so long ago, in terms of earthEarth history, all the continents were stitched together to form one massive supercontinent. (Note: the Earth’s oceanic crust = 5 km thick, continental crust = 30 km thick, asthenosphere from 30 km to 440 km, Mantle to 2900 km. Earth diameter =12,756 km )
Continental crustal plates move about on the Earth’s surface in an orderly cycle, taking about 500 million years to complete. There are seven (7)major “continental plates”—(North America, South America, Eurasia, Africa, India, Australia, Antarctica) https://en.wikipedia.org/wiki/Plate_tectonics#/media/File:Tectonic_plates_(2022).svg
Crustal plates are thicker (on average about 30km thick) than oceanic plates (5km) and are composed of less dense, more buoyant rocks which tend to “float” higher—in a much more dense, hot and fluid, earth-layer called the mantle.
The Earth’s interior is composed of an outer crust, a middle mantle and an inner core. The mantle’s hot “squishy” upper layer or “asthenosphere”, is the upper part of the mantle. The outer crust is comprised of ocean crust of a more dense composition (SG = @ 3.2) than the lighter colored and less common (only 40%) continental rocks. Ocean crust is also thinner only @ 5km thick, vs @ 30km thick continental crust. As a result, ocean crust settles more deeply into the mantle than the more buoyant continental rocks. That is one reason why the oceans are “basins” and continents rise distinctly higher. Both ocean crust and continental crust “float” on the much more dense mantle which in its upper asthenosphere is able to act as both a rigid solid, as well as a liquid. (“A-stheno-sphere” Gr origin, α “alpa privitive” = “not” “ rigid— layer”)
It is sufficient to know that the seven major continental blocks go through a regular 500 million year cycle, of combining together to form a “supercontinent” and then breaking apart again to repeat that cycle. At present, we are a bit more than about half-way through one cycle..the continents are in some places still separating apart and in others still crunching together. In another 200 million years the continents will complete this cycle and will have rejoined each other and formed one single, huge “world-continent”.
We might consider the Mediterranean to be a part of the crust which is experiencing the last stages of supercontinent formation—while entering the beginning stages of supercontinent breakup.
THE PERMIAN PERIOD 300MYA
The story of the Mediterranean Basin begins about 300 million years ago during the Permian Period of the Paleozoic Era. It was a time when tetrapods such as amphibians and primitive reptiles lived on land among forests, and swamps comprised of the first seed bearing (conifer) trees.
In the Permian, 300MYA the Earth’s continents were aggregated into one “world continent”, termed “Pangaea”. The seven crustal plates of Pangaea were arranged in an elongate north to south supercontinent form, with its center located close to the equator.
By about 250 million years ago (250 MYA) this north-south elongated Pangaea “supercontinent ” began to break apart into two—one north the other south. The southern half of Pangaea, called Gondwana, comprised of crustal plates of Africa, South America, Antarctica, and Australian, these split away from the northern half called Laurasia (comprised of North America and Eurasia). During the separation, the northern part Laurasia, rotated clockwise. This rotation formed a somewhat more enclosed sea— called the Tethys Sea—which approximated the shape of the modern day Mediterranean Sea. https://en.wikipedia.org/wiki/Tethys_Ocean#/media/File:Laurasia-Gondwana.svg
In the Tethys Sea, warm water currents supported abundant sea life within a near tropical, shallow sea basin. The warm upper levels of the ocean harbored simple/celled organisms (like Amoeba), but these marine forms (Foraminifera) had the ability to build a perforated protective shell of calcium carbonate (CaCO3). See: https://www.bgs.ac.uk/discovering-geology/fossils-and-geological-time/foraminifera/
When these organisms died, their shells settled to the bottom of the Tethys to form a thick calcium rich, limey sediment that would in time eventually form thick beds of limestone, and later in time, these beds would be altered by pressure and heat in some places of Italy’s Apennines into pure white marble. See: Carrara: https://lovefromtuscany.com/where-to-go/cities-in-tuscany/carrara/
Pangea continued to undergo further disaggregation. As South America split apart from Africa an ocean took form, between these two continents—-the new Atlantic Ocean. (The present day “seam” of that early break -up can be seen at: “Mid-Atlantic Ridge”, on Google Earth search. PS Look at this image from far-off Earth’s surface.) See:https://en.m.wikipedia.org/wiki/Tethys_Ocean
As these events were progressing, Antarctica, moved to the south to take a position close to the pole. India began to move northward. And Australia spread out into the South Pacific. These processes continued on into modern times, and will be seen to have a major impact on the future of the Mediterranean.
Note : See Google Earth, and with the Google Earth globe in this present position, roll the globe around to see how closely the continents actually do seem to “fit” together. (Alfred Wegener (1880-1930) German climatologist and polar researcher noticed this “fit” of the continents. In 1912 he proposed a theory in his book: ”The Origins of Continents and Oceans” in which he suggested that the continents “drift” on the Earth’s surface. They do! He was correct. But it took another 50 years to prove he was correct. )
This closing up of the Tethys Sea, which began 250 million years ago eventually resolved into simple compression between two great tectonic crustal plates…that of Africa in the south—being driven toward the north, and Eurasia resisting that pressure, with a force directed to the south.
The ancient Tethys Sea, and later the modern Mediterranean, were (and remain) situated in a “continental-vice” between the two major crustal plates. Almost all of the geologic processes, the major mountain chains, earthquakes, volcanoes, mineral deposits, fertile soils and landforms of this part of the world can be related back into the major force of continental convergence or compression between these two crustal plates. *
*Go back to Google Earth (GE) “Mediterranean Sea” and take note of the string of mountainous terrane from the Pyrenees in Spain all the way across Europe to the Himalayas in India. These mountains are all the result of convergent plate activity between Africa and Eurasia referred to as the Alpine Mountain building event —or Alpine Orogeny.
THE ALPS FORM 65 MYA
As Africa continued its push north into Eurasia, the eastern end of the “vise” which trapped Tethys Sea and the sediments on its sea bed were compressed together. By about 65 million years, ago as the Africa Plate collided with the European Plate at a convergent plate boundary, these seabed sediments, deposited millions of years earlier in the Tethys Sea, were thrust and folded up into a 6,000 mile long Alpine mountain chain ranging from Spain all across southern Europe.
The convergent activity or collision began in the west, as Africa drove the “Spain Microplate” into France, pushing up continental rocks to form the Pyrenees. https://www.worldatlas.com/mountains/pyrenees-mountains.html. The European Plate was forced under the African Plate—and raised and deformed the African rocks, altering sedimentary beds into metamorphic rock by heat and pressure. Africa’s continental crust rocks were deformed as they were pushed up 15,000 feet into the magnificent Alps, a mountain chain which forms Italy’s snowy northern border. (See: Google Earth Link https://earth.app.goo.gl/sTLPL4 #googleearth
The famous, almost 15,000 foot, Matterhorn, https://matterhornmountainproject.weebly.com/on the Swiss-Italian border is composed of metamorphic rock termed “gneiss”. (See Google Earth: Search: paste in: “Matterhorn”). A close-up image of the Matterhorn, clearly shows the contorted pattern of gneiss at the summit. That rock began as a sedimentary mud deposited on the bed of ocean crust at the bottom of the Tethys Sea. These mud deposits were hardened into mudstone and shales by pressure. Then they were altered by heat, pressure or “metamorphosed” at the convergent plate boundary into the metamorphic rock known as “gneiss” (pronounced: “nice”). See: https://en.wikipedia.org/wiki/Gneiss . Thus the rocks of the Alps are a mixture of African plate and Tethys Sea bed rocks which were altered and driven upward 15,000 feet by the collision.
HIMALAYA MTS, 50MYA
Fifty (50) million years ago and fifteen (15) million years after the Alpine mountain-building event the great mountain chain of the Himalayas https://kids.britannica.com/kids/article/Himalayas/346140. were formed when India, breaking away from the southern part of Pangaea, moved north to collide with the eastern part of Eurasia.
The Himalayas are younger and almost twice as tall as the Alps ( close to 30,000 feet vs about 15,000 feet for Alps). The reason for this is that in the India-Eurasia-collision the colliding plates were both comprised of thicker continental crust, unlike that of the Alpine collision…which involved thinner Tethys Ocean crust colliding with African continental crust. See: Ocean vs continental crust:
Also go back to Google Earth “search” and enter: 21°54'06"S 80°52'03"E. Observe sea-bed “tracks” of the Indian plate’s rapid northern motion (at about 9 cm per year! ) ending in the convergent zone which produced the Himalayas .
THE RED SEA AND OCEAN SPREADING CENTERS
“Principles of Geology” 1830, by Charles Lyell, “The present is the key to the past”
Ocean spreading-ridges form at plate boundaries where magma in mantle currents rise to the surface, cool and crystallizes into solid rock to create new ocean crust which spread out laterally. An excellent place to see evidences of an active ocean spreading center is the Red Sea. A new spreading center has formed in the Red Sea and is widening by crustal divergence in that seaway. (See: Google Earth Link: https://earth.app.goo.gl/HDTmdd #googleearth
Or go to: Google Earth at: 16°46'38"N 40°58'38"E.)
In this Red Sea Image (above) one can see a linear feature which runs the length of the Red Sea. This is new ocean crust formed in the center of the Red Sea. As magma cools and hardens in the fissure it widens the fissure. The accumulation of new ocean crust within the linear feature it generates forces which are directed perpendicular to the linear feature. As a result, the Red Sea is widening. Note also the geologic impact of this ocean spreading center on the surrounding parts of Africa and Saudi Arabia where evidences of folding and faulting of bedrocks produce landform distortions, which occur to accommodate the new and wider sea way.
THE APENNINE MOUNTAINS FORM 23 MYA (https://en.wikipedia.org/wiki/Apennine_Mountains)
The Apennines are distinct from the Alps and much younger mountains. They formed about about 23 million years ago or 40 million years after the initial Alpine uplift. But by this time the western Tethys Sea had completely disappeared.
During the earlier Alpine mountain building ( or “orogeny”) when the African plate collided with the sea bed of the old Tethys Sea it forced much of the Tethys Sea northward into the Alps. As a result at that time there no peninsula Italy, no Balearic Islands off of Spain, no Corsica or Sardinia, no Sicily or Calabria.
But after the Alpine mountain building, remnants of the old Tethys Sea basins survived in the east— as the deep eastern basin of the Mediterranean, and as the Black Sea, the Caspian Sea and the Aral Sea. But in what would become the western Mediterranean, only the African crustal rocks and remnant Tethys Sea bed occupied this area.
See Google Earth search: “Aral Sea”. The Aral Sea is the most easterly remnant basin of the Tethys Sea, now mostly a salt encrusted dry sea bed. To the west see the Caspian Sea and further west the Black Sea. Google Maps will take you to the Straits of Gibraltar) See https://simple.wikipedia.org/wiki/Strait_of_Gibraltar
It is within this African-Tethys Sea convergence zone that new ocean spreading centers (similar to those today in the Red Sea) begin to develop about 23 MYA. Thus the Mediterranean— is the result of both convergent and divergent tectonic processes.
APENNINE MOUNTAINS BEGIN TO FORM 23MYA
After the end of the Alpine orogeny after the African Plate collied with the Eurasian Plate, the Mediterranean was essentially compressed out of existence. African continental crustal rocks and Tethys Sea bed deposits covered over much of what had been the Tethys Sea. These sediments must have laid dormant for tens of millions of years. But by 23 MYA a new spreading center formed in the west Mediterranean near Spain that would create a new sea basin…to partly replace the old Tethys Sea bed.
CORSICA AND SARDINIA “PUSHED AROUND” BY OCEAN SPREADING
The formation of the modern Mediterranean begins about 23 MYA in what is known as the Balearic Basin the western Mesiterranean basin, near modern day Spain. A new spreading center formed in a part of modern day France that would split off a microplate that would become he Islands of Corsica and Sardinia. . (See: Google Earth Link https://earth.app.goo.gl/pXcpJq #googleearth. See also Google Earth at: 42°30'38"N 4°30'07"E).
The large bay region formed between Marsailles France and Girona France appearss to be the source area of this microplate. A new spreading center and rift zone formed in western Eurasia ( France). This rift would eventually produce new ocean crust that would spread continental fragments of modern day France to the east, to become the islands of Corsica and Sardinia (termed here: “CorSinia” or “CS Microplate”).
As new ocean crust formed northwest of CorSinia—- the CS microplate moved southeast— as ocean crust extension occrred “behind” southwest of it . The Cor-Sinia microplate continue to drift southeast deforming and folding up Tethys Sea-bed sediments and African crustal rocks into low mountains—the beginnings of the Apennines. .
Over a period of about 5 million years, the “CorSinia” microplate moved @ 500 miles into the center of the western basin reaching this position at about 18MYA. The geological process described above for the Balearic Basin is analogous to the modern day process of crustal plate divergence presently taking place in the Red Sea. ( As C.Lyell, 1830, states: “The present is key to the past”).
Thus: expanding ocean crust growing at about 2.5 cm per year “swept” the Corsica-Sardinian-micro plate from its continental origins and moved it almost 500 miles to the southeast to its approximate present day position. (In like manner, new ocean crust also carried the Balearic Islands —Ibiza, Minorca and Majorca— , See: 39°37'30"N 2°59'41"E, away from the coast of Spain.).
The creation and movement of the Corsica-Sardinia micro-plate had far reaching effects. It began the process of reopening the old closed up Tethys sea basin and to the formation of the Apennine mountain chain.
SECOND OCEAN SPREADING CENTER — 10MYA,
OR PUSHING SICILY AND CALABRIA ACROSS THE MEDITERRANEAN
By about 10 MYA , expansion eastward of the CorSinia microplate stalled. But ocean expansion in the Mediterranean was not over. At about this time, a new ocean spreading (or divergent) center developed just `to the east of the CorSinia microplate. This new spreading center would have great impact on the Mediterranean. It opened a low-lying basin which eventually filled with sea water to form the Tyrrhenian Sea and as it expanded it led to the rise of the Apennine Mountain chain, as well as the intrusive and extrusive (volcanoes) which are so characteristic of this area. See: https://www.worldatlas.com/seas/tyrrhenian-sea.html
The new ocean crust southeast of CorSinia generated formation of two small microplates that would become a part of the island of Sicily, and the “toe” of the Italian “boot” or Calabria . The orientation of the spreading center also tended to drive the southern tip of the Apennines into a clockwise rotation toward the southeast (which continues today).
This ocean spreading center “pushed” a section of Calabria (the toe of the Italian “boot”) and the eastern tip of Sicily (near the City of Messina) toward the southeast. As these continental fragments of crust or microplates arrived, about 7 or 8 million years ago, they “pasted” in place, to create the present geographic outline of Italy.
Thus, similar to the way the Corsica and Sardinia micro-plates were driven across the Mediterranean basin,in like manner, did Sicily, and the Calabrian “toe” of the Italian peninsula move into place by ocean spreading.
These processes of new ocean crust formation and movement of micro plates generated new deposits of sediment, on top of earlier calcareous deposits. During this movement sediment deposits derived from the erosion of continental microplates such as clay and sand, were washed into the sea and accumulated on the top of the old, now deformed, fine grained white calcareous sediments of the early Tethys Sea bed. These sandy deposits as well as the calcareous, marine-derived deposits later show up high in the mountains of Florence and central Italy as sandstones, shales and clay-stones which lie above or on top of marine limestones.
The Many of the city of Florence’s buildings are constructed using a common local sandstone — a gray or bluish sandstone called Pietra serena. Pietra serena was formed during the process of new ocean crust formation in divergence zones, as muddy terriginous deposits were washed down into new ocean basins. When these deposits were folded and raised into the Apennine mountains these coarse sandy deposits became sandstones. The fine grained limey marine sediments of the early Tethys Sea bed were also deformed and metamorphosed during this process. The Pietra serena ended up on local buildings, but the marine limestone was metamorphosed into the fine, white marble mined at Carrara…and used by Michelangelo to craft the incomparable Pieta’ and other magnificent sculptures.
SUBDUCTION AND VOLCANIC ARCS
Ocean crust is denser and thinner than continental crust, and when the two meet at a convergent plate boundary the more dense oceanic crust tends to subduct, or slide under the continental crust. As the heavy dense slab of ocean crust sinks down deeper into the hot (1300 C), mushy asthenosphere —mostly under the influence of gravity— the descending rock slab and the sediments it drags down with it, heat up and melt. The molten sediments form magma which, being less dense (and hotter than its surroundings ) tends to rise to the surface with currents generated by the sub-ducting slab.
In some places magma may rise upward, yet not reach the surface. It may remain buried just below the surface to form a magma intrusion. In other places it may work its way upward —erupting onto the surface to form extrusive volcanic landforms or volcanoes.
Wherever plate boundaries converge and subduction takes place, a volcanically active zone —or “volcanic arc“ may form. In these places rising magma generates volcanoes— which appear all along the zone of subduction, creating on the surface a volcanic chain or a volcanic arc. A volcanic arc and numerous volcanoes occur in profusion west of the Apennine, chain all along the western coast of Italy. In these volcanic arcs, volcanoes form and erupt violently. During the eruption process the magma chamber which feeds the colcano empties—sometimes almost completely. This process often causes the upper part of the volcano, no longer supported by a full magma chamber, to collapse into the empty chamber itself and produce at the surface a circular depression or calderas of great depth which eventually fill with water to form a circular lake.
North of Rome, the volcanic arc is older and dominated by formerly active volcanoes now collapsed into their magma chambers. The evidence of volcanism there is in the form calderas—cauldron shaped features often 8-10 miles in diameter. Naples, underlain by a huge super-volcano, is on the boundary zone, and has both active volcanoes and many former active volcanoes now collapsed into calderas. The circular Bay of Naples is an example of an enormous caldera. South of Rome where subduction is presently active, there—active volcanoes dominate all along this arc, where explosively active volcanoes abound such as Vesuvius, Volcano, Stromboli, the Aeolian Islands, and Etna on Sicily.
Thus travelers north of Rome can observe a number of now dormant volcanoes, which have collapsed into their magma chambers and filled with rain water—called calderas. See Rome with one caldera to south and two to north. Google Earth Link https://earth.app.goo.gl/7j4wJA
#googleearth. Also See north of Rome at (42°35'20"N 11°59'33"E and at 42°06'11"N 12°15'56"E, and 41°45'28"N 12°44'58"E ).
Active volcanoes occur to the south of Rome, along the convergent zone, where subduction is occurring. See: active volcano Vesuvius and to north Naples and Phlegrean Fields: See: Google Earth Link https://earth.app.goo.gl/bZySVY #googleearth.
Also Vesuvius at: (40°49'17"N 14°25'40"E ). And active volcano Stromboli (38°47'34"N 15°12'48"E ) also called the “lighthouse” of the Mediterranean, and active volcano Mt Volcano (38°24'01"N 14°57'49"E) in the south Tyrrhenian Sea, and active volcano Mt. Etna on Sicily (37°45'02"N 14°59'41"E ). (Copy and paste these locations on Google Earth to see each feature indicated).
Magmas have different chemical compositions dependent upon their history and source. Some magmas are fluid and low in gas content, others are more viscous and full of gas. These chemical and physical-properties determine what landforms the molten magma will take when it rises to the the surface. Low gas fluid magma may may simply spread out and cool as a surface lava flow. While a gassy viscous magma which reaches the surface by exiting from a point source such as through a single vent, may produce a volcanic cone-like volcano like that of Vesuvius or Etna. If the magma was the result of melting of crustal rocks high in silica content it tends to produce a viscous and gassy lava. Such volcanoes may erupt violently like that of Vesuvius or Stromboli.
As noted above, along the front of the subduction zone in the Mediterranean’s volcanic arc, many volcanoes have formed. These appear as remnants of ancient eruptions north of Rome, where today only the inactive volcanoes occur. These end their lives when their magma chambers empty and the upper cone collapses into the magma chamber to produce a rainwater-filled volcanic “caldera” or “cauldron” like feature.. To the south of Rome, subduction persists with an active volcanic arc. Eruptions there occur regularly, such as at Vesuvius,near Naples, on Stromboli off the southern coast, in the Aeolian Islands, Mt Volcano (“Vulcan’s” forge) and on Mount Etna in Sicily where volcanic derived sulfur was mined in early history.
Wherever volcanoes occur they leave behind rich soils from the weathering of mineral rich magma (high in iron, calcium, and magnesium). Such soils occur widely in Italy and contributed to the health and welfare of the ancient Romans and to the present residents as well.
The volcanic history of Italy brought danger and destruction from occasional violent eruptions and earthquakes, but also created wealth in the form of agriculturally rich, volcanic soils, as on the slopes of Etna in Sicily and in areas around Naples.
Vulcanism also created unique volcanic rocks, such as tuff, (Italian: tuffa), scoria, pumice, volcanic ash, and others which were used in architecture, industry, and specialized construction. A vesicular volcanic rock called Scoria was used as “fill” in concrete, and in the manufacture of the mill stone for grist mills to grind grain. Pumice, a frothy volcanic glass (which so light it will float on water) was used as a fine abrasive, and when finely ground up was used an additive to concrete to reduce the weight of concrete. The fine finish on marble sculptures like Michelangelo’s “Pieta” was likely the result of abrasion and polish with fine volcanic pumice stone. Pumice was added to concrete and mortar used in specialized construction projects such as the dome of the Pantheon in Rome (See: GE search: “Pantheon, Rome Italy” ) Volcanic ash from Pozzuoli near Naples, called “Pozzolana” was used in the preparation of poured concrete which would harden underwater for construction of marine ship-docks.
Perhaps one of the most important advances of the Romans was their use of their vast limestone deposits to make concrete and mortar for construction. To make mortar and concrete they burnt limestone to form CaO or quick lime, and mixed this with volcanic ash, and water. Then they added aggregate such as crushed volcanic rock such as tuffa, (a volcanic rock composed of volcanic ash, lapilli and larger particles welded together) to make long lasting concrete structures.
Roman concrete and mortar structures were capable of “self healing” fissures and cracks which formed in these structures— often caused by the very common Mediterranean earthquakes, or “terremoto”. Modern analysis of these ancient structures with “self healing properties” were recently analyzed and found to be the result of the presence of two elements: volcanic ash or “pozzolana” and coarse clasts of quick lime (CaO). When concrete prepared from this mix formed a crack..the quick lime clasts reacted with silica from the volcanic to fill in the cracks and reestablish competency of the structure.
A seaside city near Naples, known as Pozzuoli, in Roman times known as Puteoli, is the site of ancient volcanism.(Use google Search to See: 40°50'41"N 14°06'24"E ) The aerial view of this city reveals a host of volcanic landforms including volcanic stratocones, cinder cones, calderas, and ancient eroded calderas. The area is famous for its volcanic features such as hot springs, sulfur vents, and the slow rising and falling of the earth due to changes in the size, and fill-level of a local subsurface magma chamber. There are also vast deposits of fine volcanic ash called “pozzolana”. This ash has been used since 200BC as a binder in Roman concrete mixtures.
This part of Naples is underlain by a super-volcano…similar to that which occurs in Yellowstone National Park in the.USA. During the Apennine mountain building event beginning 23 MYA
Pozzuoli in Campania vicinity of Naples, is well known for evidences which indicate that is undergoing the slow rise and fall of its earth surface. The cause has been determined to be the gradual filling and emptying of a semi-dormant magma chamber located just below the city. When the magma chamber fills, the land rises slowly and imperceptibly, then over time it empties and sinks just as imperceptibly.
The slow movement of the earth in response to filling and emptying a deep seated magma chamber s demonstrated in scars and burrows in ancient marble columns—still standing in the former Roman market in Pozzuoli ( See: 40°49'34"N 14°07'14"E ). The proof lies in a ring of marine bivalve borings into the marble columns —which are signs of being submerged underwater. But these columns are now several meters above sea level. The area is said to be affected by byradyseismic movements—or “slow” up and down (and unnoticed) motions of the earth.
Also in Pozzuoli is the well preserved Flavian Amphitheater, only about 1/4 mile to the east of the Roman forum or market place. The 79AD, 50,000 seat, Flavian Amphitheater at Pozzuoli rivals the Colosseum in Rome and its interior is better preserved and is much less crowded and touristed. It was covered by ash from the near by Solfatara volcano and later abandoned for hundreds of years.
About three miles to the southwest of Pozzuoli one can visit the Phlegrean Fields —Campi Flegrei is a “supervolcano” site with hot springs, and beds of white travertine (see below) sulfur vents, and other indications of subterranean volcanism. Supervolcanoes occur where magma rises toward the surface but is unable to break through to the surface. Yellowstone in western USA is a much larger supervolcano with hot springs, travertine beds…etc.
In early 79 AD, a long quiescent volcano, known at that time as “Mount Soma” (Sleeping Mountain) located near the Roman resort village of Pompeii, seemed to come to life, with a series of earthquakes. (See: 40°49'11"N 14°25'29"E ). In 79 AD Mount Soma was a well-formed typical pyramidal or conical volcanic peak known as a strato volcano, which had erupted in the distant past, In Roman times it was thought to be dormant. In 79 AD Mount Soma generated several weeks of minor earthquakes, probably caused as its magma chamber began to fill…and unlike at Pozzuoli, in Naples, the filling magma chamber generated well detected earthquakes, which frightened the Pompeians.
After several more warning earthquakes, and without further warming on August 24, 79AD Mount Soma exploded violently. Gases such as carbon dioxide and steam or water vapor gases built up in the magma chamber below the volcano. As pressure builds builds the volcanic cone swells. Swelling of the cone on steep slopes can cause slippage or slumping of portions of the steep slope of the volcano. When a mass of overriding rock rapidly slips downslope..the confining pressure on the magma chamber is reduced instantly and the trapped gasses escape violently. It is analogous of popping the cork on a warm bottle of champagne. Gas mixed with liquid magma (pryrocastics) escapes explosively. Mt Soma’s lava was viscous and heavily charged with gas. The violent eruption spewed massive amounts of pyroclastics such as volcanic ash, lapilli, lava- blocks, and volcanic bombs high into the air.
Gases released during such eruptions are primarily carbon dioxide and water vapor.
These gases reach temperatures closely approximating that of the lava itself or @ 800-1200C (1,470F -2,190 F). When these hot gases mix with the similarly hot pyroclasts such as ash, it can form a very dense, very hot, ash-cloud termed a nuee ardente ( lit. “hot cloud”)
The mix of carbon dioxide gas, and hot ash create a fluid much heavier than air, which under the influence of gravity, rushes down the steep slopes of the volcano at high speed, incinerating, smothering, driving all in its way down slope where it covers all it encounters.
Later, in these violent eruptions, escaping water vapor at the volcano’s vent condenses above the crater to form clouds. Thunder heads (nimbocumulous clouds) accompanied by lightning flashes form directly above the volcano as a result of the large amount o water vapor in the escaping gas. Heavy rain follows the eruptions. As it pours down the slopes it can form a slurry or loose mud pyroclastic mud, much heavier than water. Pyroclastic mud flows surge down hill at high speed, sweeping up man-made structures, trees, large rocks and all before them.
Pompeii at the foot of Vesuvius (See: 40°45'04"N 14°29'16"E ) may have suffered between 1,500- 3,500 deaths as a consequence of this mix of ash fall, nuee ardente, and pyroclastic mud flows which covered over the entire city. Not far away from Pompeii, the ancient village of Herculaneum (See:40°48'21"N 14°20'52"E ) was buried in ash and later covered by mud flows resulting from the heavy rains that followed the actual eruption.
As the eruption progressed, Mt Soma’s magma chamber emptied. Unsupported from below, about one third of the top of Mt Soma collapsed into its magma chamber, changing the formerly conical volcano into a “caldera”, like an “open pot” or “cauldron like” feature (See: 40°49'55"N 14°26'28"E ridge crest of old Mount Soma). There are many such calderas north of Rome along the Tyrrhenian volcanic arc. (One most famous caldera in the Agean basin is the Greek island of Santorini. See: 36°24'11"N 25°24'32"E )
Modern day “Mount Vesuvius” ( Italian “ Vesuvio”) is a name probably derived from the ancient local Oscan tribe’s word for “steam or smoke”( i.e. “Vesf”or” fesf”) perhaps relating to its continual eruption of gases from its peak vent. In fact, after the 79AD eruption Vesuvius erupted at least 15 times in the first millennium AD, and two dozen more eruptions in the second millennium. A massive eruption in 1631 killed nearly 4000 people, an Epuption in 1873 was photographed for the first time, and most recently a series of eruptions continued from 1913 to 1944.
See: Mexican Popocatepetl volcano, an active stratovolcano much like Vesuvius, presently erupting at:19°01'19"N 98°37'21"W.
BATHOLITHS AND MINERALS
In a convergent zone, as the subducting slab is “pulled down” by gravity into the asthenosphere, these forces may encourage adjacent ocean crust thinning, bulging up of the asthenosphere and permit magma to rise and intrude into existing ocntinetal crust. The magma may collect in chambers deep underground. When such features — are very large they are known as “hot spots” or supervolcanoes—are relatively close to the surface, heat from the depths is manifested at the surface in the form of hot springs, sulfur and steam vent, travertine deposits, geysers, and mud pots. Yellowstone in the USA, and the Phlegrean Fields near Naples are examples. (These “deep molten rock” features are known as “plutons” (after Pluto the god of the underworld.) However, when these magma chambers or plutons are buried at deeper depths, little evidence, is noted at the surface. There, magma cools slowly. These deep-buried magma masses slowly crystalize into varieties of coarse grained igneous rocks—one of which is granite. When they cool to rock and are very large: are called “batholiths” when tens of miles in diameter —or “laccoliths” when of smaller size.
Plutons or intrusive volcanics occur in several parts of the Mediterranean. One is the series of islands of the Tuscan Archipelago. The largest is the Island of Elba just off the coast of northern Italy and just east of French island of Corsica. Elba is a fine example of a laccolith. (See 42°46'18"N 10°10'07"E where a magma intrusion which cooled and crystallized at depth and which is composed of coarse grained igneous rock which is now exposed at the surface as a result of uplift and erosion.)
In this slow-cooling environment the dark, heavy minerals, rich in magnesium and iron (mafic ma = magnesium, fi = ferric or iron) ) such as olivine, augite, hornblende, sodium/calcium feldspars, and biotite, form crystallize out of the hot solution first and grow quickly into large crystals. Gravity causes these heavy, early crystals to sink down in the liquid melt, leaving behind a molten magma that is deficient in mafic minerals. While conversely leaving behind a magma relatively enriched in the potassium/sodium feldspars, quartz and muscovite mica (i.e. felsic minerals i.e. feldspar and silica). These minerals crystallize at lower temperatures. As this process proceeds, the remaining melt becomes a concentrated slush of minerals which crystalize at the lowest tempertatures: such as quartz and a concentrate of very rare low temperature minerals and elements and metal ores such as Pyrite ( Iron sulfide) Chalcopyrite ( Copper iron sulfide) ) Magnetite (Iron oxide), Sphalerite (Zinc sulfide) and the elements silver (Ag) and (Au) gold.
Over long periods of cooling these felsic “concentrates” ultimately force their way into existing fractures in the now mostly solid rock where they rapidly cool and crystallize—into rock veins. . They form very coarse grained, highly concentrated rich deposits of rare mineralsband ore “veins” in the solidified rock. (See. 42°46'18"N 10°10'07"E a prominent, coarse crystalline “vein” in a granite batholith exposed at the top of Monte Cappane on Elba. Another view of granite rock formed deep underground in a batholith can be seen at Punta della Madonna on Elba (See: 42°48'38"N 10°10'56"E ). )
On Elba ( See: 42°47'02"N 10°18'57"E) igneous rocks containing rich veins of ores and native elements such as iron, zinc, sulfur, copper, gold and silver were discovered early in human history. (See prominent quartz vein at :42°46'17"N 10°10'07"E ). The Etruscans of the 8th and 9th centuries BC exploited these minerals extensively and mined many sites on the Island, and the near-by shore..
Greek traders called the island of Elba, “Aetalia” (smokey island) a name derived from the many .Etruscan smelting operations on the island. The Etruscans grew wealthy from mining, smelting and trading, probably copper first, then later iron and other metals mined from Elba. They appear to have operated a trade network in northern and Eastern Europe, where they may have traded iron ingots, and later bronze objects for copper and other ores. The famous “Piombino Apollo” bronze was recovered off Piombino in the 19th Century. It proved to be a 1st C BC copy of an archaic Greek kuros (boy). Copper from Elba may have been used for the bronze statue now in the Louvre.
SUPERVOLCANO AT PHLEGRAEAN FIELDS NEAR NAPLES
A supervolcano is defined as an active volcano which has generated an eruption having ejected more than 1000Km2 of volcanic debris. Yellowstone and Long Lake California are also super volcanoes. See: Google earth Search: 40°48'57"N 14°06'45"E and https://en.wikipedia.org/wiki/Phlegraean_Fields. Cumae a now submeredd ancient resort city for elite Romans such as Julius Caesar and Emperor Hadrain is near by. In the images above try to identify the circular paters of the great suupervolcano which erpted last in 1538.
MARBLE QUARRIES
During the formation of the Apennine mountains thousands of feet of marine limestone were deposited by microscopic marine organisms. When magma intrudes into the earth, or deep seated magma chambers fill with hot magma, the intense heat of the magma can alter surrounding sedimentary rock by heat and chemical action. The heat from the magma chamber, and the fluids from crystallization of the magma can cause both physical and chemical changes to surrounding rocks in a process termed “contact metamorphism”. At these sites, sedimentary rock in contact with the chamber can be metamorphosed into marble, and claystone into slate or gneiss. The deep seated magma chamber which formed the west portion of the Island of Elba (or similar magma chambers near it) could have been responsible for the hugely important marble quarries in and around the city of Carrara. (See: 44°05'25"N 10°08'59"E). Also regional metamorphic processes, such as mountain building events at convergent zones, and burial at depth are also likely to be responsible. These can also alter such limestone deposits into metamorphic rock such as marble. (See : 44°05'39"N 10°08'23"E— a marble quarry at Carrara.).
The Carrara marble quarries are famous for a fine-grained marble, of nearly pure white or white with a bluish tinge, that when polished takes on a fine finish and luster. Romans in antiquity called this marble “Lunar Marble”. The Pantheon, Trajans Column, and the Column of Marcus Aurelius were all constructed of this fine white Carrara marble. In the Renaissance, Michelangelo sculpted the monumental David from a huge block of “ statuario” grade Carrara marble he pickedd out himself from the quarry. (See, Pantheon : 41°53'54"N 12°28'36"E, and Column of Marcus Aurelius 41°54'03"N 12°28'48"E, and “David of Michelangelo”) . Michelangelo carved the magnificent Pieta out of a single block of Carrara marble the artist claimed was the most perfect he had ever worked with.
Carrara marble was and remains in high demand for statuary, columns, and for architectural purposes. These quarries were important during the early history of Tuscany, and of Rome, and during the Renaissance— and into modern times.
TRAVERTINE
Subduction zones produce molten magma, volcanic arcs, and subterranean magma chambers. The heat from volcanic sources and magma chambers can heat ground water to produce “hot springs”. Romans often made use of these hot water sources to site their “Roman baths”. Hot springs occur all along the Italian Volcanic Arc, from north of Rome to the Calabria region. In many places where hot springs bubble up through limestone, the hot slightly acidic water rises to the surface carrying high concentrations of dissolved calcite (CaCO3) mineral. When this solution breaks to the surface it cools and the dissolved calcite precipitates to form a limestone rock type known as “Travertine”..Since the hot waters often contain other dissolved or suspended minerals such as iron oxides, travertine can have a variety of colors and appears as white, gray, tan or red-brown-colored. Since it precipitates from flowing water, it often precipitates into appealing flow patterns which reflect this fact. It is widely used all throughout the Roman world for columns and architectural effects. For those going to Ephesus in Turkey, the small town of Pamukkale, just about nine miles north of Denizli, in Turkey has large, near mile long exposures of hot pools and white and buff flowing travertine deposits. See 37°55'21"N 29°07'22"E .
DEHYDRATION OF THE TETHYS SEA, 6MYA
The fascinating history of the Mediterranean takes on the surreal about 6 million years ago.
At that time (6 MYA) the continued compression of the African plate in the western end of the Mediterranean basin increased. Earth movement there closed off the Straits of Gibraltar, the only access to the Atlantic.
The climate of the ancient Mediterranean tended to high rates of evaporation, as is the case in the modern Mediterranean. As noted earlier, the old Tethys Sea had few rivers emptying into the Tethys to replenish water lost through evaporation. Its only main source of water to replenish water lost though evaporation was the western opening to the Atlantic. The result of closing of the Straits of Gibraltar, was slow dehydration and concentration of salts in a near tropical climate, with high rates of surface evaporation and no access to the Atlantic. In only several hundred thousand years, like the Great Salt Lake in Utah (See Great Salt Lake) and the Dead Sea in Israel/Palestine, sea water evaporated from the Tethys and left behind layers of minerals such as halite (NaCl), and sulfates like gypsum (CaSO4.H2O) and anhydrite (CaSO4) which all form as deposits or layers of whitish crystals on the dry sea bed. These salty deposits accumulated as a new layer of “evaporite sediment” on top of the older Tethys Sea limestones and fine grained clay and shales. (See: 40°24'10"N 113°28'28"W salt deposits at Great Salt Lake Utah…the Mediterranean looked like this 6 million years ago. )
DEEP DRY BASIN
At the end of this dehydration period, the old Tethys Sea was almost completely gone. The dry, thousands-of- feet-deep basin remained, with only a few scattered briny bodies of water as remnants of the old Tethys Sea. In this dry hot basin, the folded up Apennines appeared as a series of dry hills in the eastern end of the dry basin. In the center, two isolated dry and rocky mountainous peaks of Corsica and Sardinia rose up above the dusty arid surface.
The basin was dry enough for land animals to pass freely from Africa to Europe, and on to Asia and the Indian continent. Some did make the passage, like the African elephant to Asia, and the dromedary and camel from Asia to Africa and Europe. Primates of Africa were able to cross the dry basin and populate areas in Asia and India.
THE GREAT FLOOD. 5MYA
The culmination of this geologic history of Italy occurs about a million years later ( 5.3 million years ago) when alterations or faults at the Straits of Gibraltar reopened the Strait of Gibraltar to the Atlantic. The opening must have produced a monumental flood, a torrent of water greater than that of the Niagara Falls. Both Canadian and NY waterfalls are jjst less than a mile wide…while the present day Strait of Gibraltar is nine times (9x) than distance. ( See: 36°12'54"N 1°50'10"W) into the deep basin of the Mediterranean for perhaps a thousand years, filling the basin, flooding the area and establishing the geography of the present day.
The western basins filled up first, creating islands out of the Balearics, as well as Corsica and Sardinia, and Elba too. As the Tyrrhenian Sea basin filled up, the Italian Peninsula took on the modern form of a ‘boot’, with its toe nearly touching Sicily. The sea way between Sicily and Africa must have created another 90 mile wide waterfall as seawater from the western basin poured over the Sicilian-African ledge into the 3.3 mile deep eastern basin called the Calypso Deep. Sea water also filled the shallow Adriatic on the east side of Italy, to create the Adriatic Sea. (The Adriatic is actually not a formal sea bed, but a low-lying part of the Po basin, a depressed area of continental crust related to the formation of the Alps.)
The massive flooding must have spread a great deal of coarse grained sediment across the entire basin. In some places conglomerate which is a mixture of fine and coarse grained sediments lie atop layers of gypsum and anhydrite deposits suggesting these were deposited at the time of the great flood.
One of the largest lakes in Italy, Lake Trasimeno, (See: 43°09'01"N 12°06'47"E ) and which is not a caldera, may be a result of this flooding period.
GREECE
Greek Geology
In the Cyclades and in southern Greece geology is controlled by many of the same forces that operate in the western Mediterranean basin near Italy. The main forces at work are as in the west, related to those of the African Plate moving north to collide with the Eurasian Plate.
At the Hellenic Arc, See (35°06'26"N 24°41'04"E ) islands of Crete, and Rhodes form a bulge which trends to the south toward Africa. The Hellenic Arc is formed by the subduction of the African Plate under the Aegean Sea Plate (a part of the Eurasian Plate). As the African plate descends in the hot asthenosphere it tends to create drag currents in the upper asthenosphere, which draw the Aegean Sea Plate toward the fold in the sub ducting slab of the African Plate (or to the south) opposite to the direction of the African Plate. These circumstances —spreading of the Aegean Sea Plate and thinning of the ocean crust are the causes of the bulge to the Hellenic Arc to the south.
The thinned Aegean Sea Plate also eases the penetration of magma plumes from deep in the asthenosphere arising from the melting African Plate . These plumes reach the surface to feed the magma chamber of the ancient volcano of Thera which continues to be active and in modern times known as Santorini. (See: 36°23'09"N 25°26'43"E ).
THE ETRUSCANS
WHAT TRAVELERS SHOULD KNOW ABOUT THE EARLY INHABITANTS OF THE MEDITERRANEAN.
.svg){kind=link}
