Atsumi Bay

The eastern sea area of ​​Mikawa Bay in the southern part of Aichi Prefecture. The western part is called Chita Bay. Surrounded by the Atsumi Peninsula, the important port of Mikawa Port (designated in 1964) is located in the inner part of the bay, and an industrial area was created by reclaiming shallow waters less than 5 meters deep, with about half of the sea area being port land.

The topography is a shallow ocean basin, and the Median Tectonic Line, which continues from the Toyokawa River system, runs east to west through the center. The geology is granite north of the Median Tectonic Line, and Paleozoic to the south, with Himejima in Tahara City made of serpentine rock, and Takeshima and Oshima in Gamagori City made of gneiss-like granite. The mouth of Mikawa Bay is an undersea valley extending from the Irago Strait, and the tip of the Atsumi Peninsula once had a vast Nishiyama sand dune. At high tide, the coastal current flows from the Irago Strait northeast along the Atsumi Peninsula side and toward the Osaki coast, and at low tide it flows in the opposite direction, and the ports of Fukue and Tahara are shallow due to drifting sand. As an inland bay, the waves are calm, and the scenery is rich in variety, with islands floating on the sea, sandy beaches, and rocky coasts, and it is part of the Mikawa Bay Quasi-National Park. High-speed ferries also operate between each port on the Chita Peninsula and Irago, and between Irago and Toba, making it a popular maritime tourist destination.

[Gohei Ito]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

愛知県南部、三河湾の東部海域。西部は知多湾という。渥美半島に囲まれ、湾奥部に重要港湾三河港（1964年指定）と、5メートル以下の浅海を埋め立ててつくった工業地帯があり、海域の約半分が港域になっている。

　地形は浅い海盆状をなし、中央を豊川(とよがわ)水系から続く中央構造線が東西に走り、地質は中央構造線以北は花崗(かこう)岩系、以南は古生代で田原市の姫(ひめ)島は蛇紋(じゃもん)岩、蒲郡(がまごおり)市の竹島、大島などは片麻(へんま)状花崗岩からなっている。三河湾口は伊良湖水道(いらごすいどう)から延びた海底谷で、渥美半島先端部にはかつて広大な西山砂丘があった。沿岸潮流は、満潮時は伊良湖水道から渥美半島側を北東へ、大崎沖へ向かい、干潮時は逆の潮流となり、福江、田原両港は漂砂のため浅海となっている。また、内湾のため波静かで、海上に浮かぶ諸島、砂浜、岩石海岸など景観の変化に富み、三河湾国定公園の一部となっている。知多半島の各港と伊良湖、伊良湖と鳥羽(とば)間には高速船も就航し、海上観光地帯として親しまれている。

［伊藤郷平］

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