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The Archipelago Sea (Finnish: ''Saaristomeri'', Swedish: ''Skärgårdshavet'') is a part of the Baltic Sea between the Gulf of Bothnia, the Gulf of Finland and the Sea of Åland, within Finnish territorial waters. By some definitions it contains the largest archipelago (island group) in the world by the number of islands, although many of the islands are very small and tightly clustered. The larger islands are inhabited and connected by ferries and bridges. The Åland Islands, including the largest islands of the region, form an autonomous region within Finland. The rest of the islands are part of province of Southwest Finland. The Archipelago Sea is a significant tourist destination. == Geography and geology == The Archipelago Sea covers a roughly triangular area with the cities of Mariehamn (), Uusikaupunki (), and Hanko (), at the corners. The archipelago can be divided into inner and outer archipelagos, with the outer archipelago consisting mainly of smaller, uninhabited islands. The total surface area is 8300 square kilometers, of which 2000 square kilometers is land. The archipelago has a very large number of islands. The exact number depends on the definition of the term "island", as the size of the patches of dry land in the area varies from small rocks peeking out of the water to large islands with several villages or even small towns. The number of the larger islands of over 1 km2 within the Archipelago Sea (in provinces of Åland Isles and Southwest Finland) is 257, whilst the number of smaller isles of over 0.5 ha is about 17,700.〔(Saarten ja vetten maa )〕 If the number of smallest uninhabitable rocks and skerries is accounted, 50,000 is probably a good estimate. In comparison, the number of islands in Canadian Arctic Archipelago is 36,563. Indonesia has 17,508 islands, according to the Indonesian Naval Hydro-Oceanographic Office.〔(【引用サイトリンク】title=Geography of Indonesia )〕 The Philippines have 7,107 islands. The islands began emerging from the sea shortly after the last ice age. Due to the post-glacial rebound the process is still going on, with new skerries and islands being slowly created and old ones enlarged or merged. The current rate of rebound is between 4 and 10 millimetres a year. Because the islands are made of mainly granite and gneiss, two very hard types of rock, erosion is significantly slower than rebound. Hower, due to its southern location, the effect of postglacial rebound is smaller than for example than in Kvarken (Finnish: ''Merenkurkku'') further north. The sea area is shallow, with a mean depth of 23 m. Most of the channels are not navigable for large ships. There are three crater-like formations in the archipelago. One of them, Lumparn in Åland, is a genuine impact crater. () The two other formations are intrusions. The more prominent of these is the Åva Intrusion in the municipality of Brändö, which is easily notable in satellite photos and high-resolution maps. () The other similar formation is in Fjälskär, between the main islands of Houtskär and Iniö. () 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「Archipelago Sea」の詳細全文を読む スポンサード リンク
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