These somewhat interesting ‘mushroom’, like landforms are part of the volcanic landscape of Cappadocia, the ‘Land of Beautiful Horses’. Cappadocia lies in south eastern central Turkey, some 275 km south-east of Ankara.
This article should serve as an introduction to what is an exceedingly complex volcanic province and only ‘scratches the surface’ of what is in the locale.
The volcanism in the area and in southern Turkey in general, is associated with the Alpine front orogenic belt with the Afro-Arabian plate moving northwards and being subducted below, the Anatolian sub-plate of the main Euro-Asian plate; the Taurus mountains being the Alpine equivalent. The volcanism, which here began in the Miocene period about 18m years ago and as with most subduction zones, is predominantly of the calc-alkaline type, with arcuate volcanic features. In Cappadocia, the main volcanoes (out of 19 major and many other satellite monogenetic and maar vents) are Erciyes Dag (3916m), Hasan Dag (3253), Melendiz (2963m), Kegiboydoran and Develi; the former 2, being most recent, have had the most obvious effects on the landscape of the area.
The simplified structural/geological maps of the area, below, indicates the volcanism is related in part to major tectonic lateral displacement or (strike-slip) faults interacting with a second east-west structural trend, being that of the Pontides/Taurus orogenic belts and further with a lithospheric thinning. This thinning and the extensional strike-slip faulting is assumed to be a result of plate post-collisional rebound. Also of note is the SW-NE trending Ecemish fault having the both the same trend and displacement direction as the East Anatolian fault; the latter forming an active transform fault boundary between the Anatolian and Arabian plates.The tectonics are further complicated by the distant rifting associated with the Dead Sea fault involving the separation of the Arabian- from the African plates.
There is a general range of rock types, the majority of the ignimbrites are of rhyolitic to rhyodacitic composition, mixed with basaltic lavas and ash deposits and show a general progression from the older rhyodacite ignimbrites through basaltic andesites to younger pyroxene-hornblende basalt and finally more recent olivine basaltic magmas. In some areas there are thin interbedded limestone horizons.
There are at least 9 major Miocene/Pliocene ignimbrite horizons, covering over 40,000sq km and a volume in excess of 1000cu km; for example, the Inescu ignimbrite, dated at c2.8m years covers 7,750sq km and has an estimated volume of 38cu km. and is associated with the Erciyes/Kocdag complex and along with the Valibaba Tepe ignimbrite, are the most widespread.
The whole volcanic area is superimposed on a crystalline basement of granodiorite, which contains spilitic/ophiolitic inclusions, c/f the Troodos Complex of Cyprus.
Erciyes Dag; from www.panoramio.com/photo/55273967
As can be seen, Erciyes Dag is heavily eroded; the present cone has been developing in the multiple collapse caldera of the Kocdag complex in two phases for about 0.9m years. The Kocdag complex was the first stage of the development of Erciyes Dag, with basalt and andesite lavas emitted from cinder cones; to be followed by the caldera collapse – 14x18km – associated with massive eruption of 110cu km (including 63cu km of tephra) of pyroclastics in two phases, with plinian fall deposits found 50km from the vent. The second phase involves emplacement of several pyroclastic flow deposits, culminating with the major Valibaba Tepe ignimbrite (2.8m years) with a volume of some 40cu km. Later eruptions vented andesite flows, dacite dome production and basic andesite flows, but limited to the immediate vicinity. The last dated eruption was a dacite flow c83000years ago, but minor eruptions have been noted from satellite cones since.
The Hasan Dag is much less eroded than Erciyes Dagi, the present cone being built in a 4km diameter caldera formed approximately 10000years ago, extruded lavas and pyroclastics covering some 750sq km and a volume of around 350cu km. Continued fumarolic activity indicates the possibility or potential for future activity.
The combined products from Erciyes- and Hasan Dag have produced the Cappadocian landscape as indicated in the ‘mushroom’ picture. These structures’ known as ‘fairy chimneys’ are weathering product, where relatively soft, less consolidated airfall ash is capped by resistant welded tuffs or lavas , the ‘cap’ being the latter material that has protected the ash from weathering. A closer inspection of these mushrooms, shows the ‘stem’ to be of fine grained variably stratified ash. Where sufficiently thick, these features have been easily excavated and make for excellent, if different dwellings.
For further reading and with detailed figures and maps that wouldn’t copy (!)