Lanyu Island in Taiwan Province belongs to volcanic island and is formed by volcanic eruption. Lanyu Island is located in the western Pacific Ocean southeast of Taiwan Island, with an area of about 45 square kilometers and is home to Dawu people from the alpine tribe. The island is undulating hills and strange rocks on the seaside, with various shapes and covered with lush tropical jungles.
Generally speaking, marine islands are mainly divided into continental islands, coral islands and volcanic islands. The islands in the heart of the river in the inland river are mainly composed of sediment and sediment alluvial deposits, which are extremely rare in the ocean. However, in the Yellow Sea Sand Ridge Group in the eastern waters of Jiangsu, some exposed islands belong to alluvial sedimentary islands.
Continental island is an extension of the continental land, formed by some low-lying areas being submerged by seawater, showing geographical continuity with the mainland. This type of island extends into the sea through mountains. The largest area of my country's Zhoushan Islands is formed by partially submerged by seawater.
Coral Island is formed by coral polyps reproduction and survival, and the lime matter remains left after death. This type of island is generally developed in the shallow waters along the coast of the mainland and islands, as well as some of the undersea mountains in the sea that are closer to the water surface and on the tops of high platforms. There is usually a reef below the coral island, and the islands are distributed in an circular shape, and there are often lakes in the middle. This type of island has a low terrain, with limestone on the bedrock, and some islands are covered with rock phosphate on the surface. In addition, coral polyps are thermophilic organisms, so coral islands are mainly distributed in the tropical areas and some subtropical sea areas with lower latitudes. Our country's South China Sea islands is a typical coral island.
Volcanic island is formed by the eruption of undersea volcanoes and the accumulation of magma. It mainly appears in volcanic earthquake zone , and its bedrock is mainly igneous rocks and the mountain is steep. Volcanic islands are often distributed continuously along the volcanic seismic zone or exist in isolation in the distant sea. Volcanic islands are divided into active volcanic islands and extinct volcanic islands. The terrain of active volcanic islands is steep and there is still volcanic activity on the islands. The extinct volcanic islands are no longer volcanic activity, and the islands are eroded by nature and the terrain is relatively mild. The world-famous Hawaiian Islands and Galapagos are both typical volcanic islands.
Specifically for Lanyu Island, why does it belong to a volcanic island? After all, there are no volcanic activities on the island now! We can use the exclusion method to judge this. First of all, Lanyu Island is located in the western Pacific Ocean southeast of Taiwan Island. The ocean depths around it are more than kilometers, which is not geographically continuous with Taiwan Island, so the possibility of a mainland island can be ruled out. Secondly, Lanyu Island has undulating mountains and its bedrock is not limestone, so the possibility of coral islands can also be ruled out. Lanyu Island is full of hills and strange rocks on the coast. The entire island is composed of andesite and clumping rocks or tuff clumping rocks, which are typical igneous rocks. Moreover, Lanyu Island is surrounded by volcanic clastic rocks, and we can determine from this that Lanyu Island is a volcanic island.
