Mount Erciyes

Mount Erciyes (Erciyes Dağı), also known as Argaeus (Greek: Ἀργαῖος), its etymon, is an inactive volcano in Kayseri Province, Turkey. It is a large stratovolcano surrounded by many monogenetic vents and lava domes, and one maar. The bulk of the volcano is formed by lava flows of andesitic and dacitic composition. At some time in the past, part of the summit collapsed towards the east.

The volcano began to form in the Miocene. At first, a volcano farther east named formed from lava flows. Then, again to the east, large explosive eruptions formed a caldera. During the Pleistocene, Mount Erciyes proper grew inside the caldera together with a group of lava domes. Lateral eruptions of Erciyes may have generated ash layers in the Black Sea and the Mediterranean during the early Holocene.

The last eruptions occurred during the early Holocene and may have deposited ash as far away as Palestine; the occurrence of historical volcanism is uncertain. Future eruptions of Erciyes may endanger the nearby cities to the north. The volcano was glaciated during the Pleistocene. One regular glacier still exists, but is receding.

Etymology
Erciyes is the adoption into Turkish of the Greek name Argaios (Greek: Ἀργαῖος). The latinized form is Argaeus (a rarely encountered alternative latinization was Argaeas mons, Argeas mons ). The Greek name has the meaning of "bright" or "white"; as applied to the mountain, it may have been eponymous of Argaeus I (678 – 640BC), king of Macedon and founder of the Argead dynasty.

The Turkish name was historically spelled Erciyas, and it was changed to Erciyes to conform with vowel harmony in the 1940s–1960s.

Mons Argaeus on the Moon was named for Argaeus.

Geology and geomorphology
Erciyes lies in the Kayseri Province of Turkey. The city of Kayseri lies 15 km-25 km north of Erciyes volcano; some lava domes generated by the volcano are within the urban limits. Other towns in the region are Talas and Hacilar, also north of Erciyes but closer to the volcano (19 km and 12 km, respectively), Develi, located south, and İncesu, located west and southwest of the volcano. Access to the summit area is difficult. Climbers in antiquity reported that both the Black Sea and the Mediterranean could be seen from the summit.

Regional
Erciyes Dagi and Hasan Dagi are both large stratovolcanoes that lie in Central Anatolia, on the Anatolian Plate. This microplate is part of the collision zone between the Eurasian Plate, the African Plate, and the Arabian Plate that forms the Alpide Belt. This convergence commenced in the Miocene and formed the Anatolian block, with two oceans that existed between these three plates in the Eocene disappearing through subduction. During the late Miocene, the Neo-Tethys ocean disappeared, and Africa and Eurasia collided. Later, the Red Sea and the Gulf of Suez separated the Arabian Plate from the African Plate, causing the former to collide with Eurasia and forming the Bitlis–Zagros Belt. The Anatolian block was pushed westward between the North Anatolian and East Anatolian faults, and it is still moving today.

In central Anatolia, volcanism commenced in the Miocene. After an effusive phase and the eruption of large ignimbrite sheets, volcanoes developed, including stratovolcanoes such as Erciyes Dagi and Hasan Dagi on the one hand and monogenetic volcanoes and maars on the other hand. The tectonic environment has been compared with the Basin and Range Province. The Central Anatolian Volcanic Province, of which Erciyes is a part, covers a surface area of 32500 km2. The Cappadocian volcanic plateau comprises ignimbrites that are up to 2 km thick. The youngest K–Ar dates obtained on these centres are 60,000 ± 20,000 years ago for the Kizirtepe monogenetic centres and 20,000 ± 10,000 for Hasan. Volcanic activity in the Acıgöl-Nevşehir system has been fission track dated at 15,500 ± 2,500 years ago.

Major faults such as the North Anatolian Fault, which were generated by the convergence, are also active. Some of these faults form the edges of the Erciyes pull-apart basin, a tectonic depression up to 1.2 km deep that is split by this volcano into the and  basins, both of which nevertheless are part of the same system. These margin faults have been the source of earthquakes during historical times, resulting in damage to cities in the region, and ongoing extension of this crustal domain is the probable reason for volcanism at Erciyes.

Local
Erciyes Dagi is a large stratovolcano, reaching a height of 3864 m, 3918 m or 3917 m, making it the highest mountain and most voluminous volcano of Central Anatolia. It rises about 900 m above the basin and 2842 m above the floor of the Erciyes pull-apart basin.

The volcano is large, it covers a surface area of 1300 km2 or 3300 km2. It developed over a broad shield, and dacitic domes and flows form the bulk of the volcano's exposed units, including the summit area, where several lava flows have been identified. Lava flows of Erciyes extend both from the summit and from lateral vents. A debris avalanche extending east-northeast from Erciyes was formed by the collapse of the summit, creating a 2 km wide horseshoe-shaped scar that forms the upper segment of the valley. The debris avalanche deposit reaches a distance of 7 km from the summit and has a hummocky appearance. The volcano overall has an eroded appearance.

Two major valleys extend to the summit, the northwesterly Aksu Valley and the easterly valley. The minor valleys of lie north,  south, and  southwest of the summit. The Aksu valley contains sizable moraines left by the Pleistocene glaciation that are up to 60 m high, 60 – wide and 1 - 2.5 km long. A glacial outwash plain formed at the valley foot and was partly buried by lavas. Moraines and outwash plains are heavily eroded.

Andesite and basaltic andesites are exposed on the western, southern, and eastern sides of the volcano; on the eastern side they form the centre with a height of 2628 m. This centre is mostly formed by lava flows. On the western side, andesitic lava flows reach the basin. The huge middle Pleistocene Aliboran lava flow descended the western slopes and blocked the Incesu valley, forming Aliboran Lake in the basin. The lake was fed by glacial meltwater from Erciyes and later overflowed the lava flow at several sites, the most important of which is. This overflow was not continuous; phases of lower lake levels caused it to dry up. Today, the basin contains wetlands that are protected under the Ramsar Convention and are a major nesting site for migratory birds.

Endogenous domes extend from Erciyes, and 184, 210, or 64 individual centres dot its flanks. The domes have diameters of 1 –, and formed along radial dykes. A number of such domes and centres formed on the rim of the 14 by wide caldera in which Erciyes sits and which formed during the Valibaba Tepe eruption. This caldera may originally have had a volume of 110 km3. Clockwise from north, these volcanic centres are, Kızıl Tepe, , , , , , , , , , and. About half of these centres are at distances of about 10 km from Erciyes, and most of them can be found on the northern slopes. Of these centres, 1200 m wide and 100 m deep lies 20 km northwest of Erciyes. It formed within Quaternary andesite lava flows; its formation was probably favoured by a shallow aquifer and was accompanied by strong phreatomagmatic explosions. The formation of this maar was accompanied by the release of tephra, which reached a distance of 3.5 km. Additional basaltic vents are, , , and.

From the more recent volcanic phases, and  lava domes lie on the southern and northern slope of Erciyes, respectively. Both domes are formed of rhyodacite and accompanied by pyroclastic deposits. covers a surface area of 11.7 km2 and reaches a height of 2760 m. The blocky dome flowed down the slopes southwards over 5 km. on the north-northwestern flank stratigraphically belongs to the same unit as. This dome flowed for a distance of about 5 km.

The volcano lies in a tectonic depression. It is cut by the fault, which together with the Tuz Gölü fault border this basin. Other faults converge on the volcano or pass through its outer slopes. Aeromagnetic investigation of the region has evidenced the existence of a magnetic anomaly associated with Erciyes, which is probably caused by the volcanism.

Petrology
Erciyes Dagi has erupted basalt, basaltic andesite, andesite, dacite, rhyodacite, and rhyolite. The rocks are chiefly andesite with smaller amounts of dacite; dacites appear to dominate in the summit region, however. The volcano is dominated by calc-alkaline rocks; one basalt with tholeiitic to intermediary affinity was erupted 1.7million years ago; volcanic activity at first was tholeiitic and later became calc-alkaline. Monogenetic volcanoes in the region also erupted basalt, but this basalt is clearly different from the Erciyes basalt.

Minerals contained in Erciyes rocks include clinopyroxene, ilmenite, orthopyroxene, plagioclase, and titanomagnetite. Samples taken from the summit also contain amphibole, apatite, biotite, feldspar, quartz, and zircon. The mineral was first described from samples obtained on Mount Erciyes, and its chemical formula is ·.

The dacites taken from the summit display a noticeable variability in their composition and texture, with their temperatures at formation varying between 734 –.

The andesites and dacites may have formed from basaltic magma by fractional crystallization involving amphibole, based on elemental composition data. Further, crustal materials were included into the magma. Tholeiitic and calc-alkaline magmas have different elemental compositions and probably formed from separate sources; tholeiitic magmas may have formed from partial melting of the mantle, while the calc-alkaline magmas formed from crustal assimilation in these magmas. Overall, the magma originated in the asthenospheric mantle; lithospheric components may have contributed, however.

Volcanism appears to be associated with crustal extension at Erciyes. Mantle metasomatism from a subducting slab, on the other hand, may or may not have played a major role, and the slab itself did not reach down below Central Anatolia, meaning that subduction probably is not responsible for Central Anatolian volcanism.

Climate and biology
The climate of the region is influenced by topography, with the Taurus and Kaçkar Mountains blocking the entry of moisture into Anatolia. Summers are dry and hot and winters snowy and cold; in Kayseri, summer temperatures are about 19 C and winter temperature about 0 C. Precipitation at Kayseri falls mostly in autumn, winter, and spring and amounts to 383 mm per year. In Develi, south of Erciyes, maximum temperatures are about 29.5 C and minimum temperatures -5.6 C. Estimated temperatures at 2700 m altitude are about -0.4 C, and precipitation 722 mm per year. During the last glacial maximum, precipitation may have been double that of present-day.

Four vegetation belts surround the mountain: a boreal belt, a subalpine, an alpine, and a subnival belt. The boreal belt extends between 1100 – while the subalpine belt goes from 2100 - 2800 m elevation and the alpine from 2800 - 3400 m. Species found in the vegetation belts are different from these found in the equivalent areas of Western European mountains.

The flora of Erciyes is diverse. A number of endemic plant species have been identified, including Astragalus argaeus, Astragalus stenosemioides, Asyneuma trichostegium, Bellardiochloa argaea, Dianthus crinitus argaeus, Festuca cratericola, Festuca woronowii argaea, Hieracium argaeum, Onobrychis argaea, and Vicia canescens argaea. The plant Silene erciyesdaghensis was discovered on Erciyes and named after it. The geographer Strabo claimed that, in antiquity, the volcano was forested. A number of endemic and relic animal species can also be found at Erciyes, as well as a rich lichen flora. Grazing, settlements, and tourism have altered the natural vegetation of the mountain.

Glaciation
The volcano was glaciated during the Pleistocene, during which about three stages of glaciation occurred. Aretes, cirques, horns, and moraines from these glaciations can be found on the volcano, with each of the five valleys that extend from the summit hosting glaciers. In the Aksu valley, these extended down to an altitude of 2150 m. Glaciers reached lengths of 6 km; with the Aksu valley glacier reaching a length of 5.8 km and the glacier of 4.5 km. The snowline was 950 m lower during the last glacial maximum, probably due to a wetter climate. Chlorine-36 dating has yielded ages corresponding to the last glacial maximum and late glacial for the principal moraines in Aksu valley. A late Holocene glacial advance extended down to 3850 m; dating of these moraines has yielded ages of 1,200 ± 300 years ago. In the valley, the lowermost moraines are found at an altitude of 2200 m, with the late Holocene advance forming moraines at an altitude of 3250 m. The maximum extent of glaciers on Erciyes occurred 21,300 ± 900 years ago, when glaciers reached lengths of 6 km. Glacier retreat occurred 20,700 ± 2,200 - 20,400 ± 1,800 years ago in the two catchments. Smaller advances and retreats occurred 14,600 ± 1,200 and 9,300 ± 1,500 years ago. The glaciers expanded last 3,800 ± 400 years ago; there is no clear evidence of a Little Ice Age glacier expansion. Later glacial advances mostly correspond to these estimated for other Mediterranean glaciers. Meltwater from these glaciers nourished a now-gone lake in the basin.

During antiquity, the summit was always covered with snow. Glacial ice is still found on the northwestern slope of Erciyes, in the Aksu Valley at altitudes of 2900 –. It has a volume of about 1,000,000 m3 at a minimum. A report from 1905 says that the glacier was 700 m long. In 2009 the glacier was 260 m long and in 2011 an area of 0.05 km2 was reported; it is actively retreating and, assuming that the pace of retreat does not change, it will be gone by 2070. This is the westernmost glacier in Turkey today; other glaciers are found in the Kaçkar Mountains at the Black Sea, Mount Cilo in southeastern Turkey, and on Ararat. Block streams and rock glaciers developed during the Holocene, the valley hosts a rock glacier with a surface area of 1 km2.

Eruptive history
A number of potassium–argon dates have been obtained for Erciyes Dagi, ranging from 2.59 ± 0.1 million years ago to 80,000 ± 10,000 years ago. Some stratigraphic units from Erciyes have been dated. Early volcanic activity occurred at the same time as the initial formation of the Erciyes basin. Since about 88,000 - 85,000 years ago, the average magma production rate has been about 0.1 km3/kyr, with a long-term flux about four times larger.

The oldest volcanic activity at Erciyes is known as, which forms the eastern slope of Erciyes. This complex erupted pyroxene andesite, 15 km long lava flows from cone and 0.2 km3 dense rock equivalent of fall deposits and scoria from Kızıl Tepe. One date obtained on is 4.39 ± 0.28 million years ago. Overall, was active between 4.4 and 2.9 million years ago.

Caldera-forming activity occurred in several eruption phases, accompanied by pumice flows and ash fall. A first phase of activity formed Plinian deposits that reach thicknesses of 22 m as far as 21 km from the volcano, covering at least 3000 km of surface. At least fifteen individual layers have been found. A second phase of activity formed pumice flows east-northeast of, covering 2100 km2 to a thickness of 8 m.

Eastern Cappadocia features the famous Cappadocian ignimbrites; one of these ignimbrites, the Valibaba Tepe ignimbrite (also known as İncesu Ignimbrite), was linked to Erciyes volcano and is the last Cappadocian ignimbrite. This eruption 2.8million years ago has a total volume of 52 km3 and was preceded by a smaller Plinian eruption that covered a surface of 1500 km2 with pumice falls. The Valibaba Tepe ignimbrite extends east of the Erciyes volcano; it originated there and filled in the previous topography. Its total volume has been estimated at 146 km3, and it contains a large proportion of fiammes. Changes in magma composition from the first phase of caldera-forming activity to the Valibaba Tepe pumice may reflect the emptying of a magma chamber with vertical composition gradient. The Valibaba Tepe ignimbrite was considered part of the famous Cappadocian ignimbrites, but is distinct from them insofar as the other ones (with the possible exception of the Taspinar-Dikmen ignimbrites of Hasan Dagi) are not associated with stratovolcanoes.

Erciyes volcano proper started developing 900,000 years ago. It was formed during two phases, starting with a basaltic andesite lava flow on the southern slope 1.7million years ago. It was followed by the andesitic lava flows on the western flank and then by many of the dacitic lava domes. Another phase of basaltic andesite activity followed, reaching lengths of 15 km. Effusive activity ended with small lava flows of varying composition.

The next phase of activity was explosive, with eruptions at the summit of Erciyes generating block-and-ash flows, pumice flows, and lava domes that formed blocks of 1.5 – in diameter. The deposits of this activity are found north and south of the summit of Erciyes and reach thicknesses of 18 m. is not precisely dated, but probably formed less than 100,000 years ago. The last dacitic eruption occurred 80,000 ± 10,000 years ago at although later research has discovered later lavic eruptions. Activity in the summit region probably ended before the Holocene.

Radiometric dating has yielded evidence of a major pulse of volcanic activity in the early Holocene. ,, and belong to the youngest stages of volcanic activity at Erciyes and formed on the rim of the former caldera. Radiocarbon and chlorine-36 dating of the deposits has yielded ages of 10,200 – 9,700 years before present for, while potassium–argon dating yielded ages of 140,000 ± 20,000 – 110,000 ± 30,000 years ago at first for all three. Radiocarbon dates of 9,971 – 9,594 and 9,984 – 9,596 years before present have been obtained for and, respectively. The three eruptions appear to have occurred within a short timeframe from each other. , a lava dome in Kayseri, is also of Holocene age, having been erupted 8,900 ± 400 years ago.

Before extrusion of, a Plinian fall deposit with base surges and pumice flows covered a surface of 800 km2 at a minimum. This was followed by a phreatomagmatic phase that deposited material up to 3 m thick, followed by another Plinian phase. The eruption was the strongest of the three lava dome forming eruptions and formed an eruption column 25 km high, but it left the smallest crater of the three. This eruption at first formed a tuff ring, within which the lava dome was emplaced. Lava flows extend to lengths of 5 km. The dome and flow have a total volume of 0.82 km3, and the eruption which had a Volcano Explosivity Index of 5 has been compared to that of Mount St. Helens in North America. was extruded later on the northern flank. Another explosive phase, this time dominated by 20 km long pumice flows that contain charcoal followed and generated the lava dome which is compositionally related to.

The last event was the collapse of the eastern flank of Ercyies. This collapse was probably triggered by an earthquake, considering that no evidence for a concomitant eruption exists. Considering the ages of the oldest moraines contained within the collapse scar, it probably happened more than 25,000 years ago. This collapse generated a debris avalanche 16 km long which dammed a lake and presently forms a hummocky deposit. The volume of rock removed by the collapse is about 1.2 - 1.5 km3.

A 1 mm thick ash layer found in a drilling core off the coast of Israel (32.74778°N, 34.65056°W) was dated at 8,365 ± 65 years ago in uncalibrated radiocarbon years. This tephra layer is known as the "S1 tephra" appears to be linked to one of these three eruptions on the basis of its composition, most likely the eruption, over 600 km away from the drilling core. A tephra layer named Tyam-1, found in in Lebanon and dated at 8,600 ± 850 years before present, is probably equivalent to this ash layer. Likewise, a thin tephra layer in the Sodmein Cave of the Red Sea Hills, 1300 km south of Erciyes, has been linked to the eruption, as was a layer in the former lake at Tayma in Saudi Arabia, 1240 km away from Erciyes. Other tephras identified in the Levantine Sea and erupted between 10,000 and 8,000 years ago may also come from Erciyes. The eruptions that formed all these layers probably had profound effects on the affected Mediterranean cultures. Another tephra layer found in the Black Sea appears to come from either the or the  eruptions. The tephra from these eruptions thus was probably spread northeastward, in contrast to the eruption, which spread tephra southeastward and thus is not found in the Black Sea. The unusual southward transport of the tephra may have occurred through low altitude winds.

Andesites of less than 1,000 years of age have been identified. The occurrence of volcanic activity in historical times is not clear; Strabo (63 BC–21 AD) and Claudius Claudianus (370–410 AD) report volcanic activity, and Roman coins found in Cappadocia show the mountain smoking, but these reports may instead refer to swamp gas release in the basin and Strabo's reports appear to refer to fires in swamps. If volcanic activity occurred during historical times, it probably occurred on a parasitic vent, as the principal cone is heavily eroded.

Threats and human interaction
Erciyes Dagi volcano has manifested explosive eruptions preceding the formation of lava domes. Such eruptions may endanger the cities of Kayseri, Hacilar, and Talas. Melting of the remnant ice on the volcano may generate dangerous lahars; in 1985 an eruption of Nevado del Ruiz volcano in Colombia claimed 20,000 fatalities after such a mudflow. Even without an eruption, strong rainfall could form mudflows on the densely populated steep slopes of the volcano. The volcano is monitored with seismometers and its deformation has been measured.

The ancient Hittites left rock carvings and even an artificial tunnel on Mount Erciyes. Strabo mentions the view from its summit. According to a vita of Saint Lazaros of Mount Galesios (11th century CE) written by his disciple Gregory the Cellarer, Lazaros climbed and descended Mount Erciyes in the depths of winter while singing the Psalms, as he encountered harsh weather and even a bear and attacking dogs.

At present, about five hotels exist at the mountain, which is a major winter sports site. In 2010, 324,221 tourists visited the mountain and Kayseri, most of them domestic tourists. A ski centre, Erciyes Ski Resort, exists on Erciyes. The resort lies at an altitude of 2200 m at the valley.