indonesia Geology

 Technically, Much of Indonesia's area is highly unstable, making it a place prone to volcanoes and frequent earthquakes. The Indo-Australian plate and the Pacific plate lie on the Pacific Ring of Fire, subducting under the Eurasian plate and melting about 100 km (62 mi). Sumatra Java Volcanoes running through Bali and Nusa Tenggara; It then travels northeast from Sulawesi to the Banda Islands. About 130 of the 400 volcanoes are active. Between 1972 and 1991, the volcano erupted 29 times, mostly in Java. Volcanic ash can make agricultural conditions unpredictable in some areas. However, It also resulted in fertile soils, a factor that sustained Java and Bali's historically high population density.

Around 70,000 BC, a massive supervolcano erupted at present-day Lake Toba. This is believed to have caused a global volcanic winter and climate cooling, which later caused genetic bottlenecks in human evolution, although this is still debated. The 1815 eruption of Mount Tambora and the 1883 eruption of Krakatoa were the largest on record. The former killed 92,000 people and created volcanic ash that spread and blanketed parts of the archipelago, leaving the Northern Hemisphere largely without a summer in 1816. It then produced the loudest sound in recorded history, with the eruption and resulting tsunami killing up to 36,000 people, with significant after-effects around the world for years after the event. Recent natural disasters caused by earthquakes include the 2004 Indian Ocean earthquake and the 2006 Yogyakarta earthquake.

Indonesia's size, tropical climate, and archipelagic geography support one of the highest levels of biodiversity in the world and it is among 17 megadiverse countries identified by Conservation International. Its flora and fauna is a mix of Asian and Australasian species.[100] The Sunda Shelf Islands (Sumatra, Java, Borneo, and Bali) were once attached to mainland Asia and have a wealth of Asian fauna. Large species such as the Sumatran tiger, rhinoceros, orangutan, Asian elephant, and leopard were once abundant as far east as Bali, but numbers and distribution have declined dramatically. Having long been separated from the landmasses, Sulawesi, Nusa Tenggara, and Maluku have developed their unique flora and fauna.[101][102] Papua was part of the Australian land mass and is home to unique fauna and flora closely related to those of Australia, including more than 600 species of birds.[103]

Indonesia ranks second only to Australia in terms of total endemic species, with 36% of its 1,531 bird species and 39% of its 515 mammal species being endemic.[104] Tropical seas surround Indonesia's 80,000 kilometers (50,000 miles) of coastline. The country has a variety of marine and coastal ecosystems, including beaches, dunes, estuaries, mangroves, coral reefs, seagrass beds, coastal marshes, tidal flats, kelp beds, and small island ecosystems.[14] Indonesia is one of the Coral Triangle countries with the highest diversity of coral reef fish in the world, with more than 1,650 species in eastern Indonesia alone.[105]

British naturalist Alfred Russel Wallace described a dividing line (Wallace's Line) between the distribution of Asian and Australasian species from Indonesia.[106] It runs roughly north-south along the edge of the Sunda Shelf, between Kalimantan and Sulawesi, and along the deep Lombok Strait, between Lombok and Bali. The flora and fauna to the west of the line are generally Asian, while to the east of Lombok, they are increasingly Australian until the turning point at the Weber Line. In his 1869 book, The Malay Archipelago, Wallace described numerous species unique to the area.[107] The region of islands between the line of him and New Guinea is now called Wallacea.[106]