Ise Bay

A large bay on the Pacific coast in the center of Honshu. It was also called Ise-no-umi in the old days. It is surrounded by the three peninsulas of Shima, Chita, and Atsumi, and the area between Tsuruga Bay on the Japan Coast is the narrowest part of Honshu. Mikawa Bay is on the east side, and Ise Bay is divided by the Chita Peninsula, Morozaki Channel, and Nakayama Channel. Its maximum width from east to west is about 30 km, its length from north to south is about 60 km, and its marine area is about 1,700 square km, about 1.7 times that of Tokyo Bay and about three times that of Mikawa Bay. At the end of the Tertiary Period (about 3 million years ago), it was a large freshwater lake called Lake Tokai. During the last geological period, the Würm Glacial Period (about 20,000 years ago), the Japanese archipelago was connected to the Asian continent due to sea regression, and Ise Bay was completely converted into land. In the next interglacial period (warm climate), sea levels rose by 5 meters, and the sea level spread to the vicinity of Ogaki and Ichinomiya in the Nobi Plain and to the vicinity of Kariya City in the Okazaki Plain. The Jomon people, who made a living from fishing, settled near the border with the mainland and left behind shell mounds. In front of the sea, sediment carried by various rivers accumulated, causing a slight uplift, forming the alluvial plain around Ise Bay, which is now the alluvial lowlands of the Nobi, Ise, Okazaki, Toyohashi and other plains.

The current land and sea area was created through repeated glacial and interglacial periods and sea level rise and fall, and is not unrelated to Ise Bay and the land around Ise Bay. The average depth of Ise Bay is 19.5 meters (Mikawa Bay is 9.2 meters), the deepest point is 38 meters, and the drainage area of ​​the related rivers is about 13,400 square kilometers. The Irago Channel at the mouth of the bay has strong tidal currents and is locally 100 meters deep. The Kiso River, Nagara River, Ibi River, and Shonai River flow into the inner part of the bay, and large and small rivers such as the Suzuka River, Ano River, Kumozu River, and Miya River flow into the coast of the Ise Plain, and the sediment carried by each river makes the sea shallow. Ports such as Nagoya, Yokkaichi, and Tsu, as well as reclaimed coastal industrial zones have been built there. The ports of Nagoya and Yokkaichi, located at the inner bay, play particularly large roles, making the Ise Bay area an internationally important maritime transport route.

[Gohei Ito]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

本州中央部の太平洋岸にある大湾。古くは伊勢海(いせのうみ)ともいった。志摩(しま)、知多(ちた)、渥美(あつみ)の3半島に囲まれ、日本海岸の敦賀(つるが)湾との間が、本州の一番狭くくびれた地域である。東側には三河(みかわ)湾があり、伊勢湾とは知多半島、師崎(もろざき)水道、中山水道によって区分されている。東西の最大幅約30キロメートル、南北約60キロメートル、海域面積約1700平方キロメートル、東京湾の約1.7倍、三河湾の約3倍である。地質時代の第三紀末（約300万年前）には東海湖とよばれる一大淡水湖であった。地質時代最後のビュルム氷期（約2万年前）には、海退によって日本列島がアジア大陸と陸続きになり、伊勢湾も全面的に陸化した。次の亜間氷期（温暖な気候）には、海水面が5メートルも高まり、海進によって濃尾(のうび)平野では大垣、一宮付近、岡崎平野では刈谷(かりや)市付近まで海面が広がり、陸地との境付近には漁労生活の縄文人が住み着き、貝塚群を残した。その前面の海に、各河川の運搬した土砂が堆積(たいせき)し、わずかに隆起したのが環伊勢湾の沖積平野で、現在、濃尾、伊勢、岡崎、豊橋などの諸平野の沖積低地となっている。

　気候的には氷期と間氷期の繰り返しと海面の海進、海退現象のなかで現在の陸地と海域がつくられたもので、伊勢湾と環伊勢湾周辺の陸地とは無縁な存在ではない。伊勢湾の平均深度は19.5メートル（三河湾は9.2メートル）、最深部は38メートル、関係河川の流域面積約1万3400平方キロメートル。湾口部の伊良湖水道は潮流が激しく、局所的に100メートルの水深となる。湾奥は、木曽(きそ)川、長良(ながら)川、揖斐(いび)川、庄内(しょうない)川が、伊勢平野の沿岸には鈴鹿(すずか)川、安濃(あのう)川、雲出(くもず)川、宮川などの大小河川が流入し、各河川の運ぶ土砂によって遠浅な海となっている。そこに名古屋、四日市、津などの港湾と、埋立て臨海工業地帯がつくられている。とくに湾奥にある名古屋、四日市両港の占める役割は大きく、伊勢湾海域は国際的に重要な海上輸送ルートとなっている。

［伊藤郷平］

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