Orchid Island in Taiwan Province is a volcanic island formed by volcanic eruptive activity. Located in the western Pacific Ocean southeast of Taiwan Island, Orchid Island covers an area of about 45 square kilometers and is inhabited by the Dawu people of the Alpine tribe. The island is hilly and rocky, with its rocky shores and different shapes, covered in lush tropical jungle.
Generally speaking, marine islands are mainly divided into mainland islands, coral islands and volcanic islands. The core islands in the inland river are mainly sediment deposited by sediment and are extremely rare in the ocean. However, in the sand ridge group of the Yellow Sea in the eastern waters of Jiangsu, some of the outcrops are alluvial sedimentary islands.
Mainland islands are an extension of the mainland's landmass, formed by the submerged submerged seawater in part of the low-lying areas, exhibiting geographical continuity with the mainland. It is more common for such islands to extend into the sea with mountain ranges, and the largest Zhoushan archipelago in China is formed by the remnants of Yandang Mountain being partially submerged by seawater.
Coral islands are formed by the accumulation of calcareous remnants left behind by the multiplication of coral insects and the accumulation of them after death. This type of island generally develops in shallow waters along the coast of the mainland and islands, as well as on top of some submarine mountains and high platforms in the sea that are closer to the surface of the water. Coral islands generally have a reef disc underneath, and the islands are arranged in a circular shape, often with a lagoon in the middle. The terrain of this type of island is low and flat, with the bedrock of the island dominated by limestone and part of the island surface covered with phosphate rock. In addition, polyps are thermophilic organisms, so coral islands are mainly distributed in the tropics, as well as some subtropical seas with lower latitudes. China's South China Sea islands are typical coral islands.
Volcanic islands are formed by the eruption of submarine volcanoes and the cooling of magma. It is mainly found in volcanic seismic zones, whose bedrock is dominated by igneous rocks and steep mountains. Volcanic islands tend to be continuously distributed along volcanic seismic bands or exist in isolation in the open sea. Volcanic islands are divided into active volcanic islands and extinct volcanic islands, active volcanic islands are steep and there is still volcanic activity on the island, and extinct volcanic islands have no volcanic activity, and the islands are relatively mildly affected by natural erosion. The world-famous Hawaiian Islands and galapagos islands are typical volcanic islands.
Specific to Lanyu Island, why does it belong to the volcanic island? After all, there is no volcanic activity on the island now! We can judge this by exclusion. First of all, Orchid Island is located in the western Pacific Ocean southeast of Taiwan Island, and the ocean depth around it is more than one kilometer, which is not geographically continuous with Taiwan Island, so the possibility of mainland islands can be ruled out. Secondly, Lanyu Island has undulating mountains and its bedrock is not limestone, so the possibility of coral island can also be ruled out. Lanyu Island is full of hills and coastal rocks, and the whole island is composed of andes rocks and block rocks or tuff rocks, which are typical igneous rocks. Moreover, Orchid Island is surrounded by volcanic clastic rocks, and we can be sure that Orchid Island is a volcanic island.