This is a brief summary of the geology of Indonesia. Indonesia is located between two major tectonic plates namely, the Australian Plate and the newly-separated Sunda Plate.

Tectonics

The

tectonics Tectonics ( via Latin ) are the processes that result in the structure and properties of the Earth's crust and its evolution through time. The field of ''planetary tectonics'' extends the concept to other planets and moons. These processes ...

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania, between the Indian Ocean, Indian and Pacific Ocean, Pacific oceans. Comprising over List of islands of Indonesia, 17,000 islands, including Sumatra, ...

are very complex, as it is a meeting point of several tectonic plates. Indonesia is located between two continental plates: the

Sahul Shelf Geology, Geologically, the Sahul Shelf () is a part of the continental shelf of the Australia (continent), Australian continent, lying off the northwest coast of mainland Australia. Etymology The name "Sahull" or "Sahoel" appeared on 17th c ...

and the Sunda Plate; and between two oceanic plates: the Pacific Plate and the

Philippine Sea Plate The Philippine Sea plate or the Philippine plate is a tectonic plate comprising oceanic lithosphere that lies beneath the Philippine Sea, to the east of the Philippines. Most segments of the Philippines, including northern Luzon, are part of ...

. The subduction of the Indian Plate beneath the Sunda Plate formed the

volcanic arc A volcanic arc (also known as a magmatic arc) is a belt of volcanoes formed above a subducting oceanic tectonic plate, with the belt arranged in an arc shape as seen from above. Volcanic arcs typically parallel an oceanic trench, with the arc ...

in western Indonesia, one of the most seismically active areas on the planet with a long history of powerful eruptions and earthquakes. This chain of active volcanoes formed

Sumatra Sumatra () is one of the Sunda Islands of western Indonesia. It is the largest island that is fully within Indonesian territory, as well as the list of islands by area, sixth-largest island in the world at 482,286.55 km2 (182,812 mi. ...

Java Java is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, proje ...

Bali Bali (English:; Balinese language, Balinese: ) is a Provinces of Indonesia, province of Indonesia and the westernmost of the Lesser Sunda Islands. East of Java and west of Lombok, the province includes the island of Bali and a few smaller o ...

, and the

Lesser Sunda Islands The Lesser Sunda Islands (, , ), now known as Nusa Tenggara Islands (, or "Southeast Islands"), are an archipelago in the Indonesian archipelago. Most of the Lesser Sunda Islands are located within the Wallacea region, except for the Bali pro ...

, most of which, particularly Java and Bali, emerged within the last 2–3 million years. The Pacific and Sahul plate movements controlled the tectonics of the eastern portion of Indonesia. Subduction occurs along Southeastern Sumatra and West Java. Sumatra is more active in recent years despite being in the same subduction margin. The reason for the lack of frequent seismic activity over West Java is a problem of time frame and not of tectonic activity. While it may only take a hundred years for a large-scale earthquake to occur off the coast of Sumatra, it may take roughly 500 years off the coast of western Java. Off the coast of western Java there is potentially a backthrust fault. The existence of the backthrust could increase the height of tsunamis off the coast. There are two megathrust segments, one off of Southeastern Sumatra and the other off of Western Java. These segments contribute to tsunamis that average at in size but that can reach . The combination of megathrusts and backthrusts are reasons for such massive tsunamis.

Structural geology

The tectonics processes in Indonesia formed major structures in Indonesia. The most prominent fault in the west of Indonesia is the Semangko Fault or the Great Sumatran Fault, a dextral strike-slip fault along Sumatra Island (about 1,900 km). The formation of this fault zone is related to the subduction zone in the west of Sumatra. Palu-Koro fault is another major structural feature formed in the central part of Indonesia. This fault runs across the central part of Sulawesi Island and extends offshore to the west across Makassar Strait, and ends in the Mangkalihat Peninsula in Borneo. The fault is named after the capital city of Central Sulawesi, Palu, on the west coast of Sulawesi and the Koro River, which is formed by the fault zone. Sorong fault is a significant left lateral fault in the eastern part of Indonesia, named after Sorong City. It has east-west orientation and extends from the northern part of West Papua to East Sulawesi for about 2000 km.

Indonesian Seaway

The various formations in the Indonesian Archipelago and

New Guinea New Guinea (; Hiri Motu: ''Niu Gini''; , fossilized , also known as Papua or historically ) is the List of islands by area, world's second-largest island, with an area of . Located in Melanesia in the southwestern Pacific Ocean, the island is ...

Torres Strait The Torres Strait (), also known as Zenadh Kes ( Kalaw Lagaw Ya#Phonology 2, �zen̪ad̪ kes, is a strait between Australia and the Melanesian island of New Guinea. It is wide at its narrowest extent. To the south is Cape York Peninsula, ...

form geologic

choke point In military strategy, a choke point (or chokepoint), or sometimes bottleneck, is a geographical feature on land such as a valley, defile or bridge, or maritime passage through a critical waterway such as a strait, which an armed force is for ...

s to

shipping Freight transport, also referred to as freight forwarding, is the physical process of transporting commodities and merchandise goods and cargo. The term shipping originally referred to transport by sea but in American English, it has been ...

and aqueous transport, particularly at depths below 100m (where said aqueous transport is largely closed); such routes, whether closed or still extant, collectively comprise the Indonesian Seaway between the

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is bounded by the cont ...

and Indian oceans.

Tectonic uplift Tectonic uplift is the orogeny, geologic uplift of Earth#Surface, Earth's surface that is attributed to plate tectonics. While Isostasy, isostatic response is important, an increase in the mean elevation of a region can only occur in response to ...

of the region, exacerbated by lowered sea levels during recent glaciation, is hypothesized to have altered the regional climate, especially with respect to

monsoon A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in Atmosphere of Earth, atmospheric circulation and precipitation associated with annu ...

s, beginning ~4 million years ago.

Stratigraphy

Distribution of key Paleozoic and Mesozoic outcrops in Indonesia

The

stratigraphy Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithost ...

of the western part of Indonesia is dominated by Cenozoic age formations, ranging from

Paleogene The Paleogene Period ( ; also spelled Palaeogene or Palæogene) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period Ma (million years ago) to the beginning of the Neogene Period Ma. It is the fir ...

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS), as well as the current and most recent of the twelve periods of the ...

. Minor

Mesozoic The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...

and

Paleozoic The Paleozoic ( , , ; or Palaeozoic) Era is the first of three Era (geology), geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic (the last era of the Proterozoic Eon) and ends 251.9 Ma a ...

formations were found in places.

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

s were found in Telen River,

East Kalimantan East Kalimantan (Indonesian language, Indonesian: ) is a Provinces of Indonesia, province of Indonesia. Its territory comprises the eastern portion of Borneo/Kalimantan. It had a population of about 3.03 million at the 2010 census (within the cu ...

, as fragments within

clastic sediments. Eastern Indonesia has generally older stratigraphy compared to the western part. The stratigraphy ranges from

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...

Tertiary Tertiary (from Latin, meaning 'third' or 'of the third degree/order..') may refer to: * Tertiary period, an obsolete geologic period spanning from 66 to 2.6 million years ago * Tertiary (chemistry), a term describing bonding patterns in organic ch ...

Ichthyosaur Ichthyosauria is an order of large extinct marine reptiles sometimes referred to as "ichthyosaurs", although the term is also used for wider clades in which the order resides. Ichthyosaurians thrived during much of the Mesozoic era; based on fo ...

fossils were found in the

mud volcano A mud volcano or mud dome is a landform created by the eruption of mud or Slurry, slurries, water and gases. Several geological processes may cause the formation of mud volcanoes. Mud volcanoes are not true Igneous rock, igneous volcanoes as th ...

es in Kai Island, indicating Mesozoic deposition in the sub-surface (Charlton, 1992). Mesozoic macrofossils were studied in Misool Island by Fauzie Hasibuan (1996).

References

Sources

* Bemmelen, R. W. van (Reinout Willem van) The Geology of Indonesia The Hague : Govt. Printing Office, 1949. 2 volumes. * Charlton, T., 2004, The petroleum potential of inversion anticlines in the Banda Arc, AAPG Bulletin, V. 88, No. 5 (May 2004), P. 565-585. * Darman, H. & Sidi, H. (eds.), 2000, An Outline of the Geology of Indonesia, Indonesian Geologists Association publication. * Hasibuan F., 2012, Mesozoic Geology and Paleontology of Misool Archipelago, Eastern Indonesia, Geological Agency, Ministry of Energy and Mineral Resources, Republic of Indonesia.

External links

Seismic Atlas of SE Asia Basins
* The Geology of Indonesia: Wikibook Edition (online)
IAGI, Ikatan Ahli Geologi Indonesia (the Indonesian Association of Geologists)

FOSI, Forum Sedimentologiwan Indonesia (the Indonesian Sedimentologists Forum)

Geology of Indonesia Blog

Badan Geologi (Geological Survey) Indonesia

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