and in the Kirshehir and Nigde massifs. The surface however consists mainly of Tertiary volcanic rocks, which are formed both by volcaniclastic material and individual volcanoes. Central Anatolia has undergone uplift, for which several mechanisms have been proposed. Composition Mount Hasan has produced volcanic rocks with compositions ranging from basalt to rhyolite but the dominant components are andesite and dacite which define an older tholeiitic and a younger calc-alkaline or alkaline suite. These rocks in turn include amphibole, apatite, biotite, clinopyroxene, garnet, ilmenite, mica, olivine, orthopyroxene, plagioclase, pyroxene in the form of augite, bronzite, diopside, hypersthene and salite, and quartz. The older volcanic stages have produced basaltic andesite while dacite appears only in the most recent stage. Obsidian also occurs in the most recent stage although it is not an important component while most of the rocks are porphyritic. The basaltic family includes both basaltic andesite and alkali basalts with augite, clinopyroxene, garnet, hornblende, hypersthene, olivine, orthopyroxene, oxides and plagioclase. Magma mixing processes appear to be the most important mechanisms involved in the genesis of Mount Hasan magmas, which are derived from the mantle with participation of crustal components. Evidence of fractional crystallization has been encountered in the most recent stage rocks and more generally plays a role in the genesis of Hasan magmas although it does not explain all of the compositional traits. Older volcanic stages also show evidence of subduction influence while the more recent magmas are more indicative of intraplate processes, the effects of crustal extension and of the presence of water. In general, various sources have been proposed for the magmas of the Central Anatolian province. Ecology and hydrology Oak forests occur on Mount Hasan. Annual precipitation is about . Between October/November and May, the mountain is frequently covered by snow due to the common precipitation at that time and when it melts the water mostly infiltrates into the permeable rocks, making the volcano a principal groundwater recharge area in the region. Additionally, volcanics of Mount Hasan form a major aquifer and the Melendiz River passes north and northeast of the volcano. Eruption history Mount Hasan has been active for the last 13 million years, with the , Paleo-Hasan, Mesovolcano and Neovolcano stages during the Miocene, Miocene-Pliocene and Quaternary; the older two stages might actually not be part of Mount Hasan at all. Aside from the felsic central vent volcanism, basaltic volcanism also took place at