Travels in Geology: Ever-Changing Turkey

by Callan Bentley
Thursday, June 7, 2018

Left: The Hagia Sophia was built as a cathedral in A.D. 532 during the Byzantine Empire. In 1453, the Ottomans turned it into a mosque. Today it is a museum. Right: The Basilica Cistern is a subterranean reservoir that dates to the sixth century A.D. It is supported by more than 300 marble columns, including this one carved into the shape of Medusa's head. Credit: right: © Tuncer; left: © karadayi

The Greek philosopher Heraclitus famously quipped that “change is the only constant.” Few places on Earth are as emblematic of change, both geological and historical, as the Republic of Turkey.

The bedrock of Turkey is a tectonic mishmash of blocks smashed together during the closure of the Tethys Ocean in the Jurassic and Cretaceous. Microcontinents abut deep-ocean sediments that have been metamorphosed in the high-pressure, low-temperature regime of multiple subduction zones. Anatolia, which composes the bulk of Turkey, squishes out to the west, escaping the collision of the Eurasian and Arabian plates. Like the succession of empires that have fought over this dry land, Turkey’s rocks reveal a geological pageant that spans time and circumstance.


I began my trip to Turkey in Istanbul. As both an ancient and modern city, Istanbul has a capacity to juxtapose structures from wildly discontinuous periods of time. At the Valens Aqueduct, for instance, you can see the latest models of cars driving through the narrow arches supporting the multistory fourth century A.D. Roman aqueduct.

If you have only a few hours to spend in Istanbul, I suggest spending them all in the Hagia Sophia, an ancient cathedral turned mosque turned museum. Through all of its incarnations, the Hagia Sophia has retained some of its original features even as new ones have been added on: It is an amalgamation of architecture, symbology and history. Walking through its soaring main chamber, or its side passages and alcoves, visitors experience awe as they peel back the layers of time.

Credit: AGI/NASA

Built in A.D. 532 by Emperor Justinian, the cathedral was erected on the same spot where two earlier churches had stood since A.D. 360. For more than a thousand years, the Hagia Sophia, Greek for “holy wisdom,” served as the principal church of the Byzantine Empire and was the world’s largest cathedral. The shuffling of feet over the floor for almost 1,500 years has worn down the sills of the doorways, some by as much as 20 centimeters. Elsewhere, the traffic of the faithful and the curious has smoothed the stone walkways to a high polish.

The Hagia Sophia also has geological intrigue. It was constructed out of a huge variety of marble and other building stones from across the region. Serpentine breccias, for example, known in the stone trade as “verde antique,” were used as wall decorations. Granites of various hues, white marble and a gaudy red, white and black marble gneiss with layers folded up into intestine-like contortions adorn alcoves and doorways. Often the stone was slabbed and then opened up, with the two halves faced side by side, reminiscent of a Rorschach inkblot. Elsewhere the walls are covered in geometric mosaics or exquisite mosaic renderings of Jesus, Mary and other Christian figures.

Another highlight of Istanbul is the dark interior of the Basilica Cistern, which dates to the same century as the Hagia Sophia. This extraordinary subterranean reservoir, built to serve as a reliable source of water in the event of a siege on the city, is capable of holding almost 21 million gallons of water. It is supported by more than 300 marble columns, mostly utilitarian, but some of which have been carved into interesting shapes, such as Medusa’s head. Today, only a token amount of water is kept in the cave-like cistern, and tourists stay dry by walking on boardwalks. Walking among the gloom, pillars and statues, I felt like I was in an Indiana Jones film.

Boating the Bosporus

One thing that every geographile must do while in Istanbul is take a trip down the Bosporus Strait. This is easy to arrange: Walk down to the narrow Golden Horn inlet, and right next to the Galata Bridge are half a dozen ferries. One leaves every half an hour or so. The hour-and-a-half cruise is sublime. Though the boat is not luxurious, the surrounding landscape is astonishing. As you head north, steep hills rise both east and west of the Bosporus: Europe on the left, Asia on the right.

Connecting the Sea of Marmara (and the Mediterranean beyond) to the Black Sea, the Bosporus Strait may have formed about 5600 B.C. when post-glacial sea-level rise caused Mediterranean waters to breach a narrow landmass and flow down into the freshwater Lake Euxine. The sudden influx of seawater inundated Bronze Age settlements on the shores of the lake, and possibly gave rise to the flood myths of several cultures, including the Epic of Gilgamesh and Noah’s flood in the Bible.

Like the Hagia Sophia, the shoreline of the Bosporus is a compilation of human history. In his memoir “Istanbul: Memories and the City,” Nobel Prize-winning author Orhan Pamuk, who grew up in post-Ottoman Istanbul in the 1950s and 1960s, calls attention to the area’s old wooden mansions, the summer houses of the Ottoman elite. These large waterfront structures burned down with such regularity during Pamuk’s youth that it was a regular social gathering for the people of Istanbul to go down to the shore and gaze across at the spontaneous fireworks display on the Asian side of the strait. Relative to Pamuk’s childhood, few of these structures remain today, but there are enough to give the flavor of what this place must have looked like a century ago.

The Bosporus also offers a tantalizing glimpse into the pre-Ottoman control of Istanbul … but only just. The Rumelihisarı fortress, located on the European side of the strait, is an astonishing structure, winding over the hillside like a Scottish castle, featuring cylindrical towers nine stories tall connected by medieval-looking turreted walls. It was built by the Ottoman Sultan Mehmet II in 1451-1452 as a base of operations, part of his winning strategy for conquering Constantinople (officially renamed Istanbul in 1930, after the fall of the Ottoman Empire).

Alongside these ancient structures are gleaming office towers, soaring bridges and metastatic housing developments that wouldn’t look out of place in the hills of Southern California. Turkey is modernizing, and a cruise along the Bosporus demonstrates that more effectively than any time-lapse movie. Change is the only constant.

Ephesus: A Dry Port

With the rest of Turkey waiting to be explored, head south toward Ephesus, one of the best-preserved ancient cities in the world.

On the bus trip south, you’ll cross over the North Anatolian Fault, a major rupture in Earth’s crust. On the south side of this strike-slip fault, the Anatolian block is slipping west relative to the Eurasian block. Movement along the fault has been responsible for many of Turkey’s destructive earthquakes, including the 1999 Izmit earthquake, a magnitude-7.6 event that killed approximately 17,000 people. The Izmit event was only the most recent in a long chain of major quakes that have accompanied stresses propagating westward along the fault. Each time the fault slips, the stresses are locally relieved, but then new stresses form farther down the line. Like a row of dominoes falling, the chain of earthquakes began in 1939 in Erzincan in eastern Turkey, south of the Black Sea, with a magnitude-8.2 event. Next in line, unfortunately, is the section of the fault immediately adjacent to Istanbul. I’m glad I got to see the city before the next major quake strikes.

Ephesus, once home to Heraclitus, was a port town when it was founded in the 14th or 13th century B.C. Visiting today, especially during the heat of the midday sun, I was struck by the lack of water. Not only has the climate dried since the port’s heyday, but the deposition of sediment by the Small Menderes River has built out the shoreline over time. Today, the sea lies almost three kilometers to the east.

Throughout its history, Ephesus was conquered by a succession of empires, concluding with the Turks. The town was finally abandoned in the 1500s. Today, the regal ancient civilization that once dwelled here is evoked through ruins of its gymnasium, library, baths, roads and dwellings. In some areas, the streets are paved with gleaming slabs of white marble. At its peak in the first century A.D., this was the second-largest city in the world after Rome, home to 250,000 people. The amphitheater is particularly striking, as it conveys just how many people once gathered in Ephesus.

Pamukkale: City on a Hill

The geologically inclined traveler will definitely want to head east from Ephesus for a stop at Pamukkale, an enormous travertine deposit just north of the town of Denizli. Rising above the valley of the Menderes River (where the term “meander” comes from) is a gleaming white hillside. Pamukkale is Turkish for “cotton castle,” a reference to this white color. The white is the mineral calcite, laid down in an infinite number of laminations from mineral-laden hot springs. This layered freshwater limestone is known as travertine.

Visitors pay an admission fee at the bottom of the formation, then hike up a long travertine footpath. To keep it as white as possible, shoes are forbidden. At several points, water trickles down from above, making pools rimmed by fresh calcite. Hiking up is a great exercise in perspective; the half-hour you spend climbing gives scale to the immensity of Pamukkale. If you have ever visited Mammoth Hot Springs in Yellowstone National Park, you have an idea of what a huge pile of travertine looks like. The difference between the two is that Pamukkale is about 10 times the size of Mammoth, and you can swim in Pamukkale’s waters.

When you finally summit the trail, you find that Pamukkale has one more bonus feature: an entire Greek city on top. This is Hierapolis. You are not the first to enjoy the waters here: The location has been used as a spa since about 100 B.C., and it remains very popular today.

If you plan to visit Pamukkale, start your walk up the trail early. Buses begin disgorging tourists at the site at about 10:00 a.m., and it’s magical before the crowds arrive. Also, walk around Hierapolis. In several hours of exploring the ruins, we saw only a handful of other people. It’s easier to imagine life in the ancient spa city if you aren’t distracted by fellow tourists.

A Tuff Time in Cappadocia

My final destination in Turkey was in many ways my favorite. The region of Cappadocia is a wild landscape of eroded rock in central Turkey. (Turks write it as “Kapadokya,” if that gives you a better sense of how to pronounce it.) Over the past several million years of geologic history, nearby Mount Erciyes has erupted layer after layer of ash, which stuck together to form a relatively soft volcanic rock called tuff.

This dry landscape reminded me of the American West — Utah perhaps. The tuff has been sculpted by nature into a series of giant turrets, fins and blobs. Guidebooks use the rather confectionery name “fairy chimneys.” In Utah, similar tall, thin spires would be called “hoodoos.” Think of Bryce Canyon magnified a hundred times to get a sense of what the area looks like: enormous hoodoos spread farther than the eye can see. Their appeal goes far beyond the mere geological — people have been living in these hoodoos for thousands of years. Just as it is easy for nature to carve into volcanic tuff, so too can humans excavate cave-like dwellings.

The joy of going to Cappadocia is that as you wander the hills, you can spot these dwellings, climb up to them, and check them out for yourself. The experience is akin to discovering Native American petroglyphs in Utah’s canyon lands, only with a different cultural heritage. Many of the Cappadocia structures hewn into the tuff are churches and chapels, decorated with Byzantine religious paintings. The iconography of these images is distinctive and charming. It is sad to see how many of the figures' faces have been defaced by later vandalism, most of it no doubt motivated by Muslim iconoclasm, which forbids the depiction of living creatures, particularly religious figures, in images. However, the pocked faces of the Christian saints seem to be yet one more layer of the Turkish palimpsest.

The tuff landscape appears austere and forbidding, but I found Cappadocia to be a hiking paradise. Little Edens are tucked among the towers of tuff, as the valleys are intensely cultivated for grapes, melons and other fruit. One of the best products of this agriculture is the local wine: After a day of hiking and a dip in the hotel pool, a glass of Cappadocian Cabernet is the perfect way to salute the sunset as, one by one, the fairy towers wink out in shadow.

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