A human-rock ecosystem

Took a while for the place to snap into focus. Kapadokya is a vast field of petrified volcanic spew. We were lodging literally inside it. Hollowing out rock to provide living space that is comfortable and easy on the eyes … How to sort out the whys and wherefores of this unusual human ecosystem? Turns out there are many such carved-rock “cave” dwelling cultures scattered about in volcanic settings (Santorini, Greece, for example) and sedimentary — here is an absorbing video about some “troglodytes” carved into 90 million year old limestone in the Loire Valley, France.

In Kapadokya it begins with volcanoes. You launch across a frothy sea of touristic rapture in search of scholarly and scientific accounts.  And scholarship sometimes raises more questions than it answers, for example in this:

Throughout the centuries, the hard layer of limestone on Cappadocia’s plateaux has eroded to reveal the soft volcanic tuff underneath. Winds and rains then shaped this tuff into cone-like formations, often leaving a limestone block at the top of the cone.

“Early explorations of Cappadocia and the monastic myth.” Veronica G. Kalas. Byzantine and Modern Greek Studies 28 (2004), p. 103.  Accessed via PDF downloaded July 29, 2014.

The premise is that limestone covers tuff on a desert-like upland plateau ringed by volcanoes.  Wasn’t limestone always formed of the shells of marine critters on seabottoms? Under pressure for millions of years? Always at the bottom? Grade, like, six Science? But — leave no stone unturned — this will have to be investigated.

This is a useful map from Wikimedia showing all the centres and main highways in the context of major geophysical features, with three volcanic peaks, one elevated nearly 4,000 metres above sea level, on the eastern and southwestern edges of Cappadocia.

0 Cappadocia topo map lo(Why are some places identified in white letters, others in black? Doesn’t say.)

Here is is schematic map of geomorphic landforms; the whole area between Ercyes Dagi and Hasan Dagi is within the Central Anatolian Volcanic Province:

0 landform mapMap in “Cappadocia, Turkey: Civilisations in a Volcanic Terrain” by Rasoul Sorkhabi. GEO ExPro magazine, Vol. 8, No. 1 (2011). “A simplified geologic map of Cappadocia. Modified from Toprak and Göncüoglu, Geological Journal, 1993, v. 28, pp. 357-369.” 

Section of a 1:500,000 geology map of the region — (as always, click to enlarge) — with towns and roads superimposed and showing rock formations.

0 geology 500 000 map cropGeological Map of Turkey: Kayseri @ 1:500 000 (detail). Ankara: General Directorate of Mineral Research and Exploration, nd. Published online. Accessed August 3, 2014.

In the upper right quarter, in the triangle of Nevsehir, Urgup and Avanos, five types of rock are identified in the key, herewith heavily reworked, with some names in Turkish:

  1. Piroclasticlel (M3P), Upper Miocene volcanics: south of Urgup; southeast of Derenkuyu; east slope of Melendez Dagi
  2. Piroclasticlel (M2plP), Upper Miocene-Pliocene volcanics: all around Urgup; north of Avenos; northwest to Gulshehir; west of Nevsehir in patches; south to near Hodul Dagi
  3. Aramamis Karasal Kinntihlar(?) (Q1), Pleistocene sedimentaries: patches south and east of Avenos and in the river valley west of Avenos; extensive around Derinkuyu to north and south and further to southeast
  4. Piroclastiklar (QP), Quaternary volcanics: around Nevsehir and in a block to southwest; around Ihlara Valley, alternating with M2plP and
  5. Basalt (Qb), Quaternary volcanics: near Ihlara Valley, in bands running to north and west.

Here’s a blow-up of that corner of the map:

0 geology 500 000 map detail

Another map on a much smaller scale employs a different classification of rock types in the Göreme-Urgup area:

http://www.mta.gov.tr/v2.0/birimler/jeolojik_miras/images/GoremeHarita.jpg

Geological Map of Historical Göreme National Park. Ankara: General Directorate of Mineral Research and Exploration, nd. Published online. Accessed August 3, 2014.

Key:

  1. North and south of Urgup, including Zelve: Urgup formation, Bayramhacili member (T1), Upper Miocene sedimentaries; sandy and clayey, more or less lacustrine
  2. All around Goreme and in most of the map area: Urgup formation, Kavak Ignimbrites member (TUK), Upper Miocene volcanics; Ignimbrites containing “white, yellow coloured, ponza and rock fragments”
  3. Lower slopes of the ridge northwest of Urgup and northeast of Goreme: Urgup formation, Tahar member (TUT), Upper Miocene volcanics: Ignimbrites containing “pinkish coloured, ponza and volcanic rock fragments”
  4. Upper slopes of same, above T1: Kisladag Limestone (TUK2), Upper Pliocene sedimentaries: “yellow, white coloured lacustrine limestone”
  5. South of Uçhisar, running east-west: Kumtepe Ash (QK), Upper Pliocene(?) volcanics: pumice-rich, glassy ash
  6. On lowlands and river valleys: [no name] Ancient alluvial deposits (QE), Quaternary sedimentaries
  7. Ditto, [no name] Modern and recent alluvial deposits (Qal), Quaternary sedimentaries.

One of the submaps has this 3-D representation of the rock types and their topographic relationships:

http://www.mta.gov.tr/v2.0/birimler/jeolojik_miras/images/GoremeHarita.jpg

Of note is the the ridge northwest of Urgup and northeast of Goreme at the top of this map. On the more detailed National Park map the topographic markers are difficult to trace, so it helps to show the L-shaped ridge — although I’m not sure I follow the classification it proposes. The detailed map shows the following zonation from lower to higher, and I’ve reworked the nomenclature in the above keys here:

TUK, Urgup formation, Kavak Ignimbrites member, Upper Miocene volcanics; Ignimbrites containing “white, yellow coloured, ponza and rock fragments;”

TUT, Urgup formation, Tahar member, Upper Miocene volcanics: Ignimbrites containing “pinkish coloured, ponza and volcanic rock fragments;”

T1, Urgup formation, Bayramhacili member, Upper Miocene sedimentaries; sandy and clayey, more or less lacustrine.

TUK2, Kisladag Limestone, Upper Pliocene sedimentaries: “yellow, white coloured lacustrine limestone”

Well I be dog — so there are sedimentary rocks here, including limestone (TUK2) and other sedimentaries (Ti of lacustrine origin, QE, Qal). Hard to believe a lake could generate enough shellfish to create limestone. What am I missing?

And what are these ignimbrites that seem to cover the majority of the national park? From a semi-scholarly website, How Volcanoes Work:

Ignimbrites are pumice-dominated pyroclastic flow deposits with subordinate ash.There are many historic examples, most of which are restricted to valleys emanating from summit craters. One such deposit from the 1980 eruption of Mt. St. Helens … contains abundant pumice blocks at its terminus. … [D]eposits can cover many thousands of square kilometers. They often appear as coherent, well-compacted, often partially welded, layers that in some cases resemble lava flows, as demonstrated by the Miocene Rio Loa sheetflows of northern Chile.

What then is a pyroclastic flow? Wikipedia:

A pyroclastic flow (also known scientifically as a pyroclastic density current[1]) is a fast-moving current of hot gas and rock (collectively known as tephra), which reaches speeds moving away from a volcano of up to 700 km/h (450 mph).[2] The gas can reach temperatures of about 1,000 °C (1,830 °F). Pyroclastic flows normally hug the ground and travel downhill, or spread laterally under gravity. Their speed depends upon the density of the current, the volcanic output rate, and the gradient of the slope. They are a common and devastating result of certain explosive volcanic eruptions.

[1] Branney M.J. & Kokelaar, B.P. 2002, Pyroclastic Density Currents and the Sedimentation of Ignimbrites. Geological Society London Memoir 27, 143pp. ¶ [2] Pyroclastic flows USGS

So: a superhot 450-mile-an-hour avalanche of burning gasses and glass shot out of a volcano — cool! Remember Dante’s Peak (1997), where Pierce Brosnan and Linda Hamilton flee a pyroclastic flow in a pick-up truck? The pyroclastic flow was the real star of the film. This 7-minute documentary about the Mount St. Helens eruption in southern Washington on May 18, 1980 has a fact-based account of the pyroclastic flow unleashed that day (begins at 2:58). And here’s an astounding 1991 video of a deadly pyroclastic flow in Unzen, Kyushu, Japan.

The US Geological Service has this about Mount St. Helens:

Pyroclastic flows commonly are produced either by the fallback and downslope movement of fragments from an eruption column or by the direct frothing over at the vent of magma undergoing rapid gas loss. Volcanic froth so formed is called pumice. Pyroclastic flows originated in both ways at Mount St. Helens on May 18, but flows of mappable volume were of the latter type. The flows were entirely restricted to a small fan-shaped zone that flares northward from the summit crater. (Pyroclastic flows)

From the diversity of volcanics hereabouts, one wonders how active those squirtin spurtin mountains were. The tuff is said to be 400 metres thick in places. Where  the Cappadocian ignimbrites came from:

0 volcanic origins of ignimbrites crop

Map in “Correlation of ignimbrites in the central Anatolian volcanic province using zircon and plagioclase ages and zircon compositions.” Erkan Aydar, Axel K. Schmitt, H. Evren Çubukçu, Lutfiye Akin, Orkun Ersoy, Erdal Sen, Robert A. Duncan, Gokhan Atici. Journal of Volcanology and Geothermal Research 213-214 (2012), p. 85. “Digital elevation model of the study area … showing major eruptive centers for CAVP ignimbrites.”

 The time scales of formation are given in this stratigraphic chart:

0 stratigraphic column ignim succ“Stratigraphy and age of the Cappadocia ignimbrites, ignimbrites, Turkey:
reconciling field constraints with paleontologic, radiochronologic,
geochemical and paleomagnetic data.” J.-L. Le Pennec et al.  Journal of Volcanology and Geothermal Research 141 (2005), p. 49.

Here’s a more recent version of the same chart:

0 stratigraphic column 2011“Correlation of ignimbrites in the central Anatolian volcanic province using zircon and plagioclase ages and zircon compositions,” p. 88.

From these it appears that the volcanic rocks are of differing age, some less than 10 million years old, some a little more than 2.5 million years old. The very extensive Kavak group is dated to nine million years ago, give or take, on the more recent chart above. There are four layers of Kavak; fourteen layers of ignimbrites in all. In between are layers of fluvio-lacustrine sediments.

I’m stumped. Don’t see how there’s enough calcium in that kind of ecosystem to make thick-ish crusts of rock within that timeframe. Maybe mud flows? Altered landscapes as on Mount St. Helens? Heavily alkaline lakes as in the Cariboo (Fraser Plateau, British Columbia)?

In this place of climatic extremes, the volcanic layers’ more recent evolution is erosion by water — penetrating the crust — and wind — sculpting the tuff.

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