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Gegham mountains
Gegham mountains (or Ghegam Ridge, ISO 9985: Geġam), (アルメニア語:Գեղամա լեռնաշղթա) (''Gyeghama lernasheghta'') are a range of mountains in Armenia. The range is a tableland-type watershed basin of Sevan Lake from east, inflows of rivers Araks and Hrazdan from north and west, Azat and Vedi rivers from south-west and Arpachai river from south. The average elevation of the Geghama mountain range is near 2500m. The range is of volcanic origin including many extinct volcanoes. The range is 70 km length and 48 km width, and stretch between Lake Sevan and the Ararat plain. The highest peak of the Geghama mountains is the Azhdahak, at 3597m. They are formed by a volcanic field, containing Pleistocene-to-Holocene lava domes and cinder cones. The highland reaches a height of 1800–2000m up to 3000m in the dividing ridge.〔
==Geological history==
Volcanism in Armenia and in the Geghama mountains is related to mantle processes accompanying, but not necessarily related to the collision of the Arabian plate with the Eurasian Plate. Unlike in other parts of the Caucasus region, the Geghama mountains have generated primarily small scale volcanoes. The Kaputan Formation (including Mt. Atis and Gtsain Ridge) from the Late Miocene has been dated at 5.7-4.6 Ma by K-Ar and is the oldest sequence in the region. Late Pliocene activity involved various basaltic lavas (including Lchain Volcano) and subsequently, during the Quaternary, rhyolite and obsidian from the Kotayk centre (Gutansar and Atis 700 ka, then associated fissure volcanoes 550–480 ka). The volcanic activity peaked round 200 ka, when most of the Geghama centres formed from trachyandesitic lavas. Aknotsasar and Sevkatar were active less than 100ka ago.
The highest point is the volcano Azhdahak, elevation - 3597.3m above sea level, in the western part of the range. There is a lake in the crater of the volcano Azhdahak that is formed from melting snow.
The volcanoes Spitaksar (3560 m) and Geghasar (3446 m), the former erupted 120ka ago and the latter 80-40ka, are sources of obsidian in Armenia.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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