Terrain shapes and bedrock
According to COUNTRYAAH, Indonesia’s many islands lie in arcuate rows along the continental shelves, often with deep-sea tombs on the convex side. In Indonesia, the Eurasian plate, the Pacific plate and the Indian-Australian plate meet. Along the boundaries between these large plates and a number of smaller ones between them, different types of movements occur, such as collisions, fracturing and rotation. Indonesia, together with the surrounding mainland, forms a moving and fragmented land area. Deep-sea tombs and volcanoes form when one plate dives below another. Thus, Borneo, Sumatra and Java as well as Bali and the other Small Sunda Islands form part of the Eurasian plate. This is bounded by the Java tomb in the south, where the Indian-Australian plate dives. The Sulawesi and the Moluccas with their associated tombs are an extension of the Philippines and the Japanese islands.
Low alluvial plains spread along the coasts. At Borneo, their average height falls below 200 m above sea level.
Sumatra, 1,700 km long, has two mountain ranges between the two coastal plains, of which the western is volcanically active.
Java is 1,050 km long and has several longitudinal zones, including a northern one with some 35 active volcanoes, of which 17 have recently erupted. The many small islands have similar structure and terrain.
Irian Jaya is penetrated by a wide and high mountain range, whose highest peak reaches 5,030 m above sea level. It has a core of gneisses and granites, most overlain by young sediments, and belongs to the alpine mountain range.
Indonesia’s location on both sides of the equator provides a humid tropical climate. The temperature is high and even all year round and varies more with the altitude than with the latitude. The annual average temperature is 23-31 ° C, but varies widely in the mountain areas. Only in Irian Jaya is the height sufficient for snow to fall.
According to BRIDGAT, the rainfall in Indonesia follows the monsoon and varies greatly. Most rain falls in December – March, while June – October is dry season in the area from central Java and east. The annual rainfall in most of Indonesia is 2,000-3,000 mm or more. The western monsoon from Southeast Asia provides high rainfall in southern Sumatra, Java and the Small Sunda Islands, while the eastern monsoon in June – August introduces dry air from Australia. As it passes the equator it becomes southwest monsoon and provides additional rainfall.
Botanically, the area – along with tropical South America – is the richest in the world, with perhaps 45,000 species of vascular plants. It is dominated by tropical rainforests, including species in the families palms (including sago palm), mulberry plants (including figus), dipterocarpus plants, cherimoyas plants and clusia plants. The rainforests are rich in epiphytes, not least orchids (more than 2,000 species in New Guinea). Despite extensive forests, there are still large areas of native forest, mainly on Sumatra, Borneo and western New Guinea. The densely populated Java is dominated by rice crops and has only fragments of natural vegetation. In drier areas, there are sparse, deciduous monsoon forests, which have often been transformed into savannah or grassland dominated by, among other things. the genus Imperata and Andropogon. At sea bays and estuaries, mangrove vegetation occurs, often along with the low-stemmed nipa palm.
Of the approximately 2,200 families in the area, 25% are white, 25% Asian, 40% more or less endemic, 5% Australian, and a few (mainly on mountain peaks) of Holarctic origin. Australian elements include the genus iron trees and eucalyptus. The world’s southernmost pine species, Piʹnus merkuʹsii, grows on Sumatra.
Since colonial times, Leiden in the Netherlands has been the center of exploration of Indonesia’s flora; where coordinated the Flora Malesiana project (started in the 1940s). One of the world’s largest botanical gardens is found in Bogor near Jakarta.
Wildlife is very rich and includes more than 500 species of mammals (of which almost 200 are endemic), about 1,500 species of birds, about 1,000 species of amphibians, about 7,000 species of fish and probably well over 100,000 species of insects. The richness of the species is because rainforest biome dominates, because isolated islands provide a prerequisite for species formation and because Indonesia lies within two different animal geographic regions with different fauna: the oriental region west of Sulawesi and the Australian region (compare animal geography). Within the former region there are a number of large placental mammals, such as Indian elephant, orangutan (Borneo and Sumatra), nose monkey (Borneo), macaques, leaf monkeys, gibbones, tiger (Sumatra) and other cats, Malay bear, deer, scabies, java horn, Sumatran rhino (Sumatra and Borneo) and a variety of Asian bird groups; in the other region there are marsupials, paradise birds, deciduous birds and cashiers.
Many islands have endemic species, on Sulawesi almost all mammals, including anoa and dwarf genoa (two related species of ox animals) and two species of ghost animals, on Borneo 79 species of mammals, on Bawean Kuhl’s deer (Ceʹrvus kuʹhli); silver-colored gibbon (Hyloʹbates moʹloch), on Komodo and Rinca the giant Komodo Waran and on New Guinea, among others. long- billed marsupial pigs (Zagloʹssus bruiʹjni) and a wide variety of bird species.
There are three species of crocodiles in Indonesia: delta crocodile (formerly widespread throughout the area, now rare), New Guinea crocodile (Crocodyʹlus noʹvaeguineʹae; endemic in New Guinea) and false gavial (on Borneo and Sumatra). Among the insects are the large colorful bird butterflies, up to more than 30 cm long wandering sticks, wandering leaves and very large cicadas.
See also Borneo and New Guinea.
In 2010, Indonesia had 50 national parks (including three marinas). Of these, six were World Heritage sites. About 15% of Indonesia’s land area has some form of nature protection.