Physical geography of Başkale basin (Van)

Başkale Basin is located in the eastern of Southeast Taurus Mountains, in the south-eastern of Lake Van and in Turkey-Iran country border. Başkale Basin located on the Taurus orogenic belt stretches SE-NW direction. The basin surrounded high mountain ranges in the same direction restricts with Başkale and Mengene Mountains in the west and Doğanlı and Yiğit Mountains in the east. Within these borders, Başkale Basin corresponds to morphological basin. Başkale Basin has an area of 2082,79 km2 and an average elevation of 2500 m. With this average elevation value, Başkale Basin is the highest basin of Turkey. Başkale Basin was intermontane basin in the Upper Miocene, after Upper Miocene, it has a pull-apart basin character which develops in the control of strike-slip Başkale Fault Zone. The research area is a Pliocene aged basin which formed depending on depression occurred in Pliocene. Moreover, the conglomeration of high mountainous region which surrounds basin from old formations and of basin base from young units has given geological basin property to this area. In the research area, five different erosion and accumulation periods, which were established to have formed in the Pre-Miocene, Lower-Middle Miocene, Upper Miocene, Pliocene and Lowermost Pleistocene periods, are determined. In the basin which formed depending on compressive tectonic among highlands in its eastern and western, contorted, faulted and overthrust structures have developed. While the structures developed under the effect of compressive regime S-N direction have constituted Paleo-Tectonic structures until Upper Miocene, after this period, the structures formed depending on strike-slip tectonic regime have constituted Neo-Tectonic structures. The old units overthrust by contorting due to compressive effect. Therefore, the units till the Pliocene were contorted in various degrees. After the Upper Miocene, overlaps give place to strike-slip faults. In this period that vertical movement came forward, highlands rose. The alkaline volcanism which developed in this period formed Plio-Quaternary aged Yiğit Volcanic Mountain in the north of basin. Depending on strike-slip faults, deferred valleys and crests, fault sharps, geysers and travertine crest cracks, warped alluvial fan and cones formed in the basin. The materials transported from the highlands formed Plio-Quaternary aged units which has horizontal structure and thickness of 150-200 m in the basin. In the Quaternary, the basin was opened to outside drainage by catchment passage in the basin's south; basin fillings were eroded by Zap River and obtained structural plateau appearance. As a result of tectonically lift, in the valleys opened by Zap River and its tributaries, the antecedent valleys had formed. The terraces found in the valleys of Zap River and its tributaries indicated that the basin rose in periods. The climate of Başkale Basin is influenced by geographic factors as well as planetary factors. Features as elevation, distance from the sea and orographic extent have a great role in basin's climate. In a large part of the year, especially in a winter months, masses of cold air with north direction maintain their efficiency in the basin. Depending on research area's elevation, presence of heavy continentality compared to its surrounding is another geographic factor. Başkale Basin is in the position the north basin of Big Zap River. The basin has drained by Zap River and its tributaries and has been connected to Big Zap River by Karasu Passage in the basin's south. The Zap River has a regular regime. In this regime, character of nival reception is effective. The basin consist of high mountain-meadow soils above 2800 m, chestnut soils in a lower meters, brown soils in the basin base and its surroundings and non-calcareous brown soils in volcanic area in the basin's north. The colluvial, alluvial and hydromorphic soils have been found in the valley bases. The vegetation is deforest and in herb formation. The basin base and its surrounding are anthropogenic steppe areas, while mounted positions are natural steppe areas. Keywords: Başkale Basin, Physical Geography, Geomorphology, Başkale, Pull-Apart Basin, Zap River, Başkale Fault Zone.