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Usa ((ロシア語:Уса́); (コミ語:Усва, ''Usva'')) is a river in the northeast corner of European Russia that drains the Polar Urals southwest into the Pechora River. The Polar Urals tend to the northeast and the Usa runs parallel to them. It is in the Komi Republic of Russia and the largest tributary of the Pechora River, which it joins from the right. It is long, with a drainage basin of . The Usa has an average discharge of , but this varies from a maximum of in June to a minimum of in April. It freezes over in October or November and is icebound until the spring thaw begins in May or June. Its largest tributaries are, from the left: Yelets, Lemva, Bolshoy Kochmes and Kosyu, and from the right: Vorkuta, Seyda and Kolva. The river has its sources in the northern Ural Mountains, and it flows towards the southwest, roughly parallel to the mountain range. The main river is formed by the confluence of the Bolshaya Usa (''Large Usa'') and the Malaya Usa (''Little Usa'') some 30 km east of Vorkuta. The two tributaries are steep, with many rapids and waterfalls. After the confluence the main river is calm, with only a few rapids in its upper sections. Its banks here are high and cliff-like, but further downriver they become lower, wooded and boggy, except for a section around the settlement of Adak (Russian: Адак), where the river cuts through the Chernyshov Hills. Below the settlement of Sivomaskinsky (Russian: Сивомаскинский) the river gets much wider, and in its lower reaches it is from wide. It also starts forming meanders and sand islands, and it keeps this appearance all the way to its mouth. Some from its mouth lies the town of Usinsk and the river port of Parma. The Usa flows into the Pechora River at the settlement of Ust-Usa. The river is navigable upstream from its mouth, and there are river ports at Abez, Petrun, Makarikha, Parma and Ust-Usa. Within the Usa basin is the large Pechora coalfield, and in its lower parts, by the town of Usinsk, there are several big petroleum and natural gas fields. The Usa valley has been inhabited for 40,000 years, as evidenced by the archaeological site Mamontovaya Kurya (Russian: Мамонтовой Курьи, "the mammoth curve"). With the Russian conquest of Siberia it became one of the main routes into Siberia. The route ran from the Pechora, which connects to other rivers in northern Russia, up the Usa, across the low Kamen Portage and down the Sob River to Ob River where there were customhouses at the Sob barrier and Obdorsk. During the short summer season this route was preferred by west-bound travellers since most of the sailing was down-river. For other Ural crossings see Verkhoturye. ==References== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Usa River (Komi Republic)」の詳細全文を読む スポンサード リンク
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