Geography of Indonesia

Indonesia encompasses a larger part of the South Asian islands that stretch between the Asian mainland and Australia, forming the divide between the Indian Ocean and the Pacific. The country is the world’s largest island kingdom. In addition to a total land area of ​​1.8 million square kilometers, the country, under the motto “Our Land and Water”, also requires sovereignty over a marine area of ​​3.3 million square kilometers.

Officially, the archipelago counts 13,677 islands, of which about 6,000 are named and 992 are permanently populated. The two islands of Java (with Madura ) and Bali comprise only 7.6 percent of the area, but have 58.3 percent of the population (2019). These are often considered the inner islands, while the remaining islands are considered the outer ones.

Bali has many beautiful beaches

Geology and landforms

East Indies are protruding peaks of a ridge formed by the clash between the Eurasian and Indo-Australian plate during the tertiary period (see plate tectonics ). The geological structure of the islands is characterized by long mountain ranges, folded in late geological times and still not settled. The longest chain can be followed along the southwest coast of Sumatra, along the whole of Java and Nusa Tenggara, interrupted only by shallow sea areas. It continues in an arc around Lake Bandas to the Moluccas.

Earthquakes occur frequently in the fold zones, and several of the islands, especially along the southern edge (Sumatra, Java), are strongly volcanic with long rows of beautiful volcanic cones, of which 220 are still active. The most famous volcano is Krakatau (Krakatoa) in the Sunda Strait (Selat Sunda) between Sumatra and Java, which exploded in 1883 in one of history’s most powerful volcanic eruptions. The mountain ranges are in part under continuous rise. Deep ocean pits are formed as part of the folding process, including the Sunda pit (7455 meters deep) in the Indian Ocean off Sumatra and Java. Similar pits are also found north of Nusa Tenggara, in the eastern part of Bandas Lake and in Lake Celeba. The shallow sea between the islands (including Lake Java ) is geologically much more stable.


The most famous volcano in Indonesia is Krakatau (Krakatoa) in the Sunda Strait (Selat Sunda) between Sumatra and Java.

Mountain ranges

Large sediments have been deposited at the foot of the mountain ranges, both in the Tertiary and Quaternary periods, and extensive lowland areas are found on the east coast of Sumatra, on the southern coast of Borneo ( Kalimantan ) and on southern New Guinea ( Papua, formerly Irian Jaya).


Java is one of Indonesia’s largest islands. Here are a number of volcanoes that are still active. The picture shows the Lamongan volcano. The ash from the eruptions provides very fertile soil. In the foreground there is work on the rice field.

The lowland areas are lined with heavy stretches of tidal sumps, which on Sumatra have a width of about 20 kilometers. Otherwise, the islands consist mostly of large mountain areas with high volcanic peaks, including Kerinci (3800 meters above sea level) on Sumatra, Rinjani (3726 meters above sea level) on Lombok, Semeru (3676 meters above sea level) on southeast Java and Agung (3142 meters above sea level). in Bali.

Also at Sulawesi, the mountains reach over 3000 meters above sea level, while only some peaks in the Indonesian part of Borneo (Kalimantan) reach over 2000 meters above sea level. The non-volcanic Maoke Mountains of New Guinea (Papua) form the country’s highest mountain range, with several peaks above the snow border, located here at approximately 4300 meters above sea level. The highest are Puncak Jaya (5030 meters above sea level) and Mandala (4760 meters above sea level).

Volcano Tambora

Volcano Tambora is located on the island of Sumbawa. Between 7 and 12 April 1815, Tambora had the largest known volcanic eruption of historical time.

Rivers and lakes

There are no major rivers except at Borneo (Kalimantan), where Kapuas (1,150 kilometers), Barito (900 kilometers) and Mahakam (770 kilometers) are all navigable in their lower races. In the highlands of Sumatra, there are a number of mountain lakes, including Lake Toba (1774 square kilometers), located at an altitude of about 1000 meters.