Deccan Plateau - English spelling: Deccan Plateau

A plateau occupying the southern half of India. The word Deccan is derived from the Sanskrit word Dakshina (meaning south), and although it can refer to the entire Indian peninsula, it originally referred to the plateau south of the Aryan territories, that is, the plateau south of the Narmada River. This is also the basis for the division of India into regions. The foundation of the Deccan Plateau is made up of Precambrian gneiss and crystalline rocks, which were eroded over a long period of time as part of the Gondwana continent and turned into a peneplain. From the Cretaceous period, uplift accompanied by block movements and the eruption of basaltic lava (Deccan Traps) gave it its present-day shape. The uplift was high in the west and low in the east, raising the Western Ghats on the western edge at an elevation of 1,000 to 1,500 meters, and the Eastern Ghats on the eastern edge at an elevation of 500 to 600 meters, and the Godavari, Krishna, and Cauvery rivers that flow over the plateau all flowed eastward. At the same time, an east-west rift line was formed, forming the valley of the Narmada River and the Binja and Satpura mountain ranges on either side of it in the north, and the Palghat graben in the south. The eruption of basalt formed a lava plateau of about 500,000 square kilometers in the northwest, which resulted in a thick distribution of black soil. This soil is fertile and has good water retention, so cotton and various fine grains (jowar, bajra) are cultivated. The entire plateau is downwind of the Western Ghats in the summer southwest monsoon, so the annual rainfall is less than 800 mm and varies greatly from year to year. For this reason, reservoir irrigation has been used since ancient times, and in recent years, river irrigation using irrigation channels and groundwater utilization using lifting pumps have become popular. In addition to old cities such as Hyderabad and Mysore, there are cities such as Bangalore and Nagpur that have undergone remarkable industrialization.

[Kenzo Fujiwara]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

インドの南半分を占める高原。デカンとはサンスクリットのダクシナDakshina（南の意）で、全インド半島をさす場合もあるが、元来はアーリア人の支配地の南方、つまりナルマダ川以南の高原をさす。インドの地域区分もこれによっている。デカン高原の基盤は先カンブリア紀の片麻(へんま)岩、結晶質岩石からなり、それがゴンドワナ大陸の一部として長い間侵食を受けて準平原化したすえ、白亜紀のころから地塊運動を伴う隆起と玄武岩質溶岩（デカン・トラップ）の噴出によって今日の概形ができた。隆起は西高東低であったので、西縁に標高1000～1500メートルの西ガーツ山脈、東縁に500～600メートルの東ガーツ山脈を高め、高原上を流れるゴダバリ、クリシュナ、カーベリの諸河川はいずれも東流した。同時に東西性の地形裂線が生じ、北縁ではナルマダ川の谷とその両側のビンジャ、サトプラ両山脈、南縁ではパルガートの地溝となった。玄武岩の噴出は北西部に約50万平方キロメートルの溶岩台地を形成し、それに由来する黒色土が厚く分布する。この土壌は肥沃(ひよく)なうえ保水力がよいので綿花や各種の細粒穀物（ジョワール、バジラ）が栽培される。高原全体は夏の南西モンスーンに対して西ガーツ山脈の風下になるため、年降水量は800ミリメートル以下、年による変化が激しい。そのため、古くから溜池灌漑(ためいけかんがい)、近年は用水路による河川灌漑や揚水ポンプによる地下水利用が盛んである。ハイデラバード、マイソールなどの古い都市のほか、工業化の目覚ましいバンガロール、ナーグプルなどの都市がある。

［藤原健蔵］

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