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Encyclopedia of the indonesia‘s coastal landforms 2010 Document Transcript

  • 1. 19.8 Indonesia Otto Ongkosongo1. Introduction Much of Indonesia has a humid tropical climate, with high temperatures and rainfall, but there are variationsIndonesia consists of about 18,000 islands, with an intri- related to the position of the Intertropical Convergencecate coastline of just over 80,000 km ( Fig. 19.8.1). In Zone of unstable air and heavy rainfall, which migratesterms of global tectonics, the Indonesian archipelago north and south over Indonesia, crossing the Equator inoccupies the collision zone between the Indo-Australian, May and November each year and reaching about 15° S inPacific and Eurasian plates and is a region of continuing January. When this zone is to the south, there are prevail-instability marked by frequent earthquakes and volcanic ing westerly winds and heavier rainfall, although north-eruptions.It includes mountainous areas of Tertiary and easterly trade winds reach some northern coasts; when itQuaternary uplift, augmented by large volcanoes, and in moves north, southeasterly winds bring drier conditions,coastal regions, there is widespread evidence of uplift and especially along the southern coasts. Winds are generallydepression, often accompanied by tilting and faulting, in light to moderate.Pleistocene and Holocene times. Coral reefs are numerous Wave action in Indonesian waters is largely generatedand extensive in Indonesian waters, and in many places, by local winds, gentle in the equatorial zone but strongerthey have been raised out of the sea by tectonic move- on the northern and southern coasts subject to north-ments as in Sumatra, Java and Irian Jaya (West Papua). The east and southeast trade winds, respectively. Ocean swellsouthern part of Indonesia is controlled by an active sub- moves in to the southern coast from the Indian Ocean andduction zone which is marked by deep trenches off to the northern coast from the southwest Pacific. In gen-Sumatra and Java. eral, wave energy is low. Tropical cyclones do not reach Fig. 19.8.1Indonesia: Location Map. (Courtesy Geostudies.) Kota Bharu Str bac Penang Bala MALAYA Kota Kinabalu Sandakan CAROLINE ISLANDS Ipoh WEST MALAYSIA BRUNEI SABAHSIMEULUE Medan St Kuala ra it of Lumpur EAST MALAYSIA Celebes M al Sea PACIFIC OCEAN ac Tarakan NIAS ca SINGAPORE SARAWAK Kuching Manado S UMA TR A HALMAHERA EQUATOR M Padang KALIMANTAN it EN Ka Stra Molucca TA rim Sea W at AI Balikpapan a MOLUCCAS IS BANGKA LA sar Jayapura St ND Palembang CELEBES SULA kas ra S Wewak it BELITUNG Ma Java Sea Bandjarmasin CERAM IRIAN JAYA PAPUA it BURU a StrDjakarta I N D O N E S I A NEW Udjung Pandang BUTUNG GUINEA a nd Banda Sea Su Bandung RU ISLANDS MADURA Surakarta Flores Sea Surabaja WETAR INSET MAP Jogjakarta J A V A g BALI LOMBOK ALOR JAMDENA lan FLORES N Ma Torres Strait Denpasar Dili Arafura Sea SUMBAWA Christmas I. TIMOR SUMBA Kupang (Australia) Cocos Is. (Australia) INDIAN Timor Sea Weipa OCEAN Darwin Gulf of Carpentaria 0 500 1000 km AUSTRALIAEric C.F. Bird (ed.), Encyclopedia of the World’s Coastal Landforms, DOI 10.1007/ 978-1-4020-8639-7_19.8, © Springer Science+Business Media B.V. 2010 (Dordrecht)
  • 2. 1158 19.8 Indonesia Indonesia, but waves generated by such disturbances are platforms and coral reefs. These are seen along the south- occasionally transmitted into Indonesian waters, espe- ern shores of Sumatra and Java, in western and northern cially along the southern coasts. Sulawesi (including Gorontalo Province), on the south Tidal movements result from impulses that arrive coasts of the eastern islands and in the north of Irian Jaya. from the Pacific Ocean by way of the South China Sea and Limestone cliffs, in particular, show the effects of intense the Philippine Sea and from the Indian Ocean through the physical, chemical and biological weathering, with notches Straits of Molucca and along the southern coasts to the and caves. Timor and Arafura seas. Mean maximum tide ranges Beaches are extensive in Indonesia, some derived from ( Fig. 19.8.2) are generally less than 2 m and only exceed fluvial sands and gravels, others from cliff erosion and still 6 m locally on the southwest coast of Irian Jaya. Tides are others from the erosion of calcareous material from fring- complicated by wind action, especially in the trade wind ing coral reefs. Beach sediment derived from volcanic zones, and by the effects of tectonic and volcanic distur- rocks are typically black or grey; those of coralline origin bances that generate tsunamis. The explosive eruption of are white or yellow. In the granitic zone of the Riau, Krakatau in Sunda Strait in 1883 generated a tsunami up Bangka and Belitung Islands, white quartz sands domi- to 30 m high on adjacent coasts and lesser surges all nate beaches. Sandy backshores are colonised by coastal around the Indonesian coastline. Tectonic tsunamis some- vegetation, notably Ipomoea pes-caprae and Spinifex lit- times res-hape the coasts in the subduction zones and may toreus, then coconut and casuarina trees. Coastal dunes also near faults in the internal waters of Indonesia, as on are poorly developed in the humid tropics, but on the Maumere and the surrounding islands, notably Babi southern shores of Java and Sumatra, prograded beaches Island. The Boxing Day 2004 earthquake south of Sumatra are backed by dunes, some of which carry woodland generated a large tsunami that caused extensive damage vegetation. and sea flooding, particularly in Aceh province, and Some parts of the Indonesian coast have prograded another earthquake in March 2005 caused uplift and sub- by the deposition of lava and ash from volcanic eruptions, sidence on Nias and nearby islands south of Sumatra. as in the Krakatau Islands. Large quantities of pyroclas- High parts of the coast are generally steep and forested tic sediment have been transported down to the coast rather than cliffed, but where there is relatively strong from active volcanoes, such as Merapi in southern Java or wave action (including swell) from the Indian Ocean or Agung in Bali, and from the erosion of dormant or extinct the Philippine Sea, there are bold cliffs, fronted by shore volcanoes as on Manado Tua Island north of Menado. Fig. 19.8.2 Variations in tide range around the Indonesian archipelago. (Courtesy Geostudies.) 1.2 0 500 1000km 1.4 1.9 N 0.4 2.0 0.4 3.8 2.5 CELEBES 0.4 0.6 2.2 2.8 SEA 2.2 S 0.6 1.7 1.8 U 1.1 M 0.8 0.9 1.5 1.7 A 1.0 T 1.9 0.7 0.8 0.6 1.2 1.3 1.4 R KALIMANTAN 0.9 A 1.0 2.2 0.9 1.2 1.0 1.5 2.4 MOLUCCAS 0.7 0.9 1.6 2.1 0.7 0.9 0.8 0.6 1.5 SULAWESI0.4 1.0 0.8 1.7 0.6 1.0 IRIAN 0.8 1.0 1.4 1.4 JAYA 0.7 1.5 1.0 1.7 0.5 0.6J A V A SEA 0.5 0.5 1.9 1.0 0.8 0.9 BANDA SEA 0.4 1.4 1.5 2.6 IN 0.9 0.4 0.6 0.5 DO 1.2 4.2 1.1 JAVA 5.4 NE 1.7 1.1 FLORES SEA SI 1.5 0.6 1.0 1.5 1.6 1.4 3.4 AN 1.8 1.5 1.0 1.2 2.4 2.6 O R 2.0 ARAFURA SEA TIM 0.7 2.1 OC 2.0 EAN 2.8 2.0 TIMOR SEA 5.5 MEAN SPRING TIDE RANGE 1.7 1.9 (metres) 6.4 5.7 AUSTRALIA 6.6 10.5 1.1
  • 3. Indonesia 19.8 1159Apart from volcanic sources, rivers draining mountainous the opinion that the higher Holocene stillstand, welluplands of conglomerate, sandstone and shale have car- documented on the east coast of peninsular Malaysia,ried gravel, sand, silt and clay to the coast to form deltas could also be traced through much of Indonesia. Duringand coastal plains as in East Sumatra, North Java, the Last Glacial low sea level phase, Java, Sumatra andKalimantan and Irian Jaya. Kalimantan occupied an enlarged Malaysian peninsula, Prograded coasts are commonly marked by multiple separated by deep straits from Sulawesi and the easternbeach ridges alternating with swales, as on the central islands, Australia then being linked to New Guinea. Onsouth coast of Java. Many features of coastal topography Timor and Atauro, stairways of emerged coral terracesare related to the effects of deep weathering under humid have been dated and related to land uplift at rates of up totropical conditions: there are steep vegetated coastal slopes 0.5 m per thousand years during the Late Quaternary seawith recurrent slumping on deeply weathered rock out- level oscillations, and there are emerged reefs on Sumbawacrops, with cliffs confined to occasional bedrock head- Islands.lands, and extensive deltas have been built by rivers thatbring down an abundance of fine-grained sediment fromsloping hinterlands, as in eastern Sumatra, northern Java, 2. The Coasts of IndonesiaKalimantan and the south of Irian Jaya. At least 50 mangrove species are found in Indonesia, 2.1. Sumatraand mangrove-fringed coasts are extensive, especially inthe northeast of Sumatra, alongside the estuaries of south- The western and southern coasts of Sumatra are mostlyern Kalimantan, and in southern Irian Jaya. Mangrove steep and cliffed, with intervening lowlands dominatedswamps develop on mud rich in organic matter, which by beach ridge plains, as at Tapak Tuan, Sibolga, Padangdarkens the sediment. In densely populated areas, as in (Verstappen 1973), Padang Bai (Bengkulu) and Teluknorthern Java, the mangrove fringe has been largely Lampung. There are many pocket beaches that werecleared to make way for brackish-water fishpond (tambak) formed and nourished with sediment from eroding cliffs,construction. Coastal features have also been modified by rivers and fringing coral reefs, with some local shell con-human activities where the sediment yield from rivers has tributions. Rivers are generally short compared with thoseincreased as the result of accelerated erosion in their flowing to the east (Malacca Strait) coast, and somedeforested and cultivated catchments. Some parts of descend over waterfalls on or inland from coastal cliffs.Indonesia, however, have a semi-arid climate that results An anticlinorial mountain chain with associated volca-in thin soils and exposed rock outcrops, as in Nusa noes runs NW–SE through the island, dissected by theTenggara Timur and Nusa Tenggara Barat. active Semangko fault system. It is bordered to the south Coral reefs are widespread, except off the mouths of of Sunda Strait by the Java trench and other roughly paral-rivers where the sea is freshened and made turbid by water lel submarine fault systems between the mainland ofand sediment discharge and where active volcanic activity Sumatra and the island arc of Sinabang, Nias and Mentawai,has inhibited coral establishment. There are many reef- which have most of the cliff and bluffs along the southwestfringed islands and reefs that enclose lagoons with central coast. There was local uplift and depression on theseislands, and true atolls, especially in the Flores and Banda islands, as well as tsunami submergence, during the MarchSeas. The major barrier reefs and atoll reefs are the Great 2005 earthquake.Sunda Reef, rising from the submerged shelf margin The rivers that flow northeast and east coasts to thesoutheast of Kalimantan, the Takabonerate reef south of shallow Straits of Malacca have formed a broad deposi-Sulawesi and the reefs that curve out toward the islands of tional lowland with extensive wetlands bearing freshBatu and Banyak off Sumatra. Algal rims are better devel- water forest in the upper coastal plain and mangroveoped on reefs along the oceanic southern shores than in swamps in the lower coastal plain. Beach ridges havethe inner seas. Many small islands are formed by coral been found up to 150 km inland, and the coastline of thereefs such as the Seribu Islands north of Jakarta or as reef- Jambi area has prograded by up to 75 km in the past cen-fringed islands such as Karimunjawa Islands north of tury, narrowing to the southeastern tip of Sumatra toSemarang. form lineaments. In Lampung Bay, mining of a coastal The record of changing sea levels in Indonesia has hill has exposed the inner part of a volcanic neck as anbeen complicated by uplift and subsidence of the land by artificial bluff.Quaternary tectonic movements. There are terraces and The Peusangan Delta in northern Sumatra showsformer coastlines at various levels, and Tjia (1975) was of stages in growth and decay related to river capture. The
  • 4. 1160 19.8 Indonesia beheading of Djuli River by river capture was followed Growth of a longshore spit has partly enclosed a coastal by erosion of its delta, while the pirate stream, the lagoon in Padang Bay. Sediment from an inflowing river Peusangan River, built a new delta to the east in two has been deposited in the lagoon, and there has been stages. Beach ridges enable the sequence of delta growth shoaling of the lagoon mouth, narrowed by the growth of and decay to be traced ( Fig. 19.8.3). When the Batang the spit. The lagoon had been used as a port, and a long Arau river in Padang was diverted to the south, the for- jetty was built to maintain the lagoon mouth, but this has mer delta to the north was eroded, and the coastline had led to updrift accretion and downdrift erosion. to be maintained by building revetments and sea walls. Emerged fringing reefs up to 3 m above sea level are Erosion has also occurred on the Tapak Tuan coastal found on the Aceh coast and nearby islands south of plain in Aceh Province. The Boxing Day 2004 tsunami Lampung Bay, and the shores of Semangka and Lampung caused extensive sea flooding and structural damage in Bays, and along the coast of Sunda Strait, are strewn with Aceh Province. wave-deposited coral boulders. Farther south rivers such as the Rokan, Kampar, Parts of the mangrove coast are still prograding, but Indragir and Musi-Banyuasin open to broad tidal estuar- some have been retreated, even on relatively protected ies fringed with mangroves and occupied by low-lying coasts as in the Dumai area. In the large Rokan, Kampar islands. Ports which were close to the sea in the fifteenth and Musi-Banyuasin estuaries, mangroves occupy low century, such as Palembang and the more recent depositional islands, especially where there is protection Bagansiapi-api, are now far upstream, indicating that there by offshore hilly islands. Within mangrove swamps, there has been rapid coastal progradation. However, rapid clear- are crab mounds that rise several centimetres above the ing and exploitation of the mangroves have led to erosion mud surface. Many mangrove swamps have been con- on many parts of the coast, as at Musi-Banyuasin, and verted into intensive fish or shrimp ponds (tambak) that deforestation has caused severe shore erosion in East no longer receive river-borne silt because the enclosing Lampung. banks exclude flood waters. Fig. 19.8.3 Changes near the mouth of the Peusangan River, northern Sumatra, following a river capture. Beach ridge patterns indicate the trend of an old delta north of Bireuen and two stages in the development of a new delta to the east: At A, a lobe that has been truncated by erosion. At B, a developing modern delta. (Courtesy Geostudies.)
  • 5. Indonesia 19.8 1161 Rias are common in the Riau Islands, produced by the 2.2. KrakatauLate Quaternary marine transgression invading the lowerparts of river valleys. They are generally mangrove fringed. Krakatau, an island volcano in Sunda Strait, erupted explo-On Batam Island, Duriangkang Bay is one of several bays sively in 1883, leaving residual steep-sided islandsthat have been enclosed by artificial dykes to form fresh ( Fig. 19.8.4), Panjang, Sertung and Rakata ( Fig. 19.8.5).water reservoirs. Subsequently, a new volcano, Anak Krakatau, has formed There has been tin mining in granitic areas on some of within the caldera ( Fig. 19.8.6).the Riau islands, together with Singkep, Bangka and Beli- Sunda Strait is bordered by steep volcanic coasts, andtung Islands, and quartzose waste has formed beaches, the effects of the 1883 eruption of Krakatau (Symons 1888)spits and barriers and a small artificial island east of are still evident. The eruption left a caldera of irregularBangka. There has also been sand quarrying on these outline, 7 km in diametre and up to 250 m deep, which hasislands for export to Singapore and Malaysia as reclamation been modified by rapid recession of cliffs cut into softmaterial. As a result, some of the small islands have disap- pumice on the residual islands, which are now forested.peared, others have been intensively eroded, and many The 1883 tsunami destroyed reefs and mangrovefringing coral reefs have been destroyed. The granitic swamps, and the large coral boulders that were thrown upcoasts are dominated by quartz sand beaches, while coasts on the shore have since been undercut by up to 35 cm byon metasedimentary rocks have rocky cliffs and muddy shore weathering processes. By 1927 the new volcanicshores. The island of Karimun, west of Singapore, has island, Anak Krakatau, had formed in the caldera, and wasgranite-weathering features, including tors and rillenkar- expanding in area and growing in height. It reached aren, rising from deeply weathered mantles on coastal height of 198 m by 1983, and in 2000 it was about 230 mslopes. high. It is dissected by deep gravelly gullies, and has coasts Fig. 19.8.4 spitThe Krakatau Islands. ng g(Courtesy Geostudies.) e ro d in ti accre Panjang Sertung sandy cusp Anak Krakatau cliff cliff cliff iff cl lav sandy cusp af cliff low Karang Serang ff cli s . 0m . 20 250 m N ll wa cli caldera ff Rakata cli ff 0 1 2 3 4 5 km.
  • 6. 1162 19.8 Indonesia Fig. 19.8.5 The steep cliff on Rakata is the wall of the crater formed by the 1883 explosion. (Courtesy Geostudies.) Fig. 19.8.6 Anak Krakatau, the new volcano developing in the Krakatau caldera. (Courtesy Geostudies.) with promontories of lava ( Fig. 19.8.7) and cliffs cut in 200 km wide. The higher parts of the island are formed by volcanic ash ( Fig. 19.8.8). Some plants and animals have a chain of active and dormant volcanoes that run along its colonised the new island. length, and have supplied large quantities of sediment as a result of frequent eruptions (as from the Merapi volcano), or erosion of the volcanic mountains. The drainage divide 2.3. Java follows the chain of volcanic peaks. Other sedimentary or volcanic mountains and hills also contribute large quanti- Java is the most densely populated island of Indonesia. ties of sediment, aided by intensive humid tropical weath- It extends about 1,000 km from west to east and is up to ering processes. Rainfall of up to 7,000 mm/year produces
  • 7. Indonesia 19.8 1163 Fig. 19.8.7Lava promontory of AnakKrakatau. (CourtesyGeostudies.) Fig. 19.8.8Cliffs cut into pyroclasticdeposits on the southcoast of Anak Krakatau.(Courtesy Geostudies.)continuous flow in many rivers that have deposited sedi- from fringing coral reefs by the 1883 tsunami and depos-ment to form wide coastal plains and growing deltas. ited on the shore platform ( Fig. 19.8.9) and the coastalRapid deforestation, especially in mountainous areas, has plain. There are erratic boulders of volcanic agglomerateintensified erosion of the land surface and increased the and breccia in addition to the coral blocks.yield of sediment to rivers, some of which show channel On the north coast of Java, deltaic plains have beenand river mouth shoaling. built out into the relatively low wave-energy microtidal The west coast of Java, between Anyer and Labu-han, Java Sea by sand and silt-laden rivers. During the past cen-is mainly formed by an emerged fringing coral reef, the tury sectors around the mouths of rivers and canals haveseaward margin of which is being eroded in many places. prograded, while sectors no longer receiving fluvial sedi-Coral boulders are widespread along the shore, swept in ment have been subject to erosion. In several cases, river
  • 8. 1164 19.8 Indonesia Fig. 19.8.9 Coral reef blocks deposited on the shore at Anyer, Java, by the 1883 tsunami. (Courtesy Geostudies.) Fig. 19.8.10 eroding 0 6 12 Km N The Citarum delta, northern Java, formerly former river courses built a delta northward, but this is eroding away beach ridge following a swing to the northwest, where the modern delta is develop- C it ing. Dam construction arum upstream has reduced the sediment yield here and slowed delta growth. (Courtesy Geostudies.) mouths have been diverted either naturally like the following the completion of the Jatiluhur Dam upstream Cimanuk in 1947 or as the result of the cutting of canals, in 1970 (Bird and Ongkosongo 1980). Erosion has dam- as on Ciujung and Ciwandan deltas, initiating new delta aged shrimp ponds (tambak) that has been constructed growth. near the delta margin. The coastline of Jakarta Bay shows stages in delta pro- Northwest of Jakarta Bay are the coral reefs and cays gradation, especially on the eastern shores around the of the Thousand Islands, many of which have changed mouths of Citarum River distributaries. Earlier coastlines in outline during the past century. Some have enlarged are traceable from patterns of beach ridges in the Jakarta by the accretion of sand on cays and shingle on north- region and also in the deltaic plains to the east. In re- eastern (windward) ramparts; others show erosion or cent years, the Citarum Delta has grown northwestward lateral displacements related to variations in the local ( Fig. 19.8.10) and erosion has become extensive on its wind regime. Some are subsiding, others are rising and northern flank, partly because river outlets have migrated some have been eroded as the result of removal of shin- westward and partly because sediment yield has diminished gle and coral.
  • 9. Indonesia 19.8 1165 To the east of Jakarta, the Citarum, Cipunegara and The south coast of Java has cliffed promontories andCimanuk, with smaller intervening rivers, have built up a limestone cliffs, often fronted by shore platforms and fring-major confluent deltaic plain. The Cimanuk has built a ing reefs. The limestone cliffs have basal notches and visorsnew delta following its diversion northeastward during a behind the shore platforms ( Fig. 19.8.11), and as theseflood in 1947. There has been subsequent growth along are as well developed on the lee shores of stacks and islandsthree distributaries, with further branching developing as that have been shaped largely by solution processes.the result of median shoal formation in the river mouths. Sand supplied by rivers has been deposited to formThe older delta to the west is eroding away, as is the east- extensive beaches, with local cuspate forelands, as behindern flank, which curves out to a low-lying promontory, Nusa Barung Island and tombolos, as at Pangandaran. TheCape Ujung. This was thought to be a relic of an earlier wide coastal plain near Yogyakarta is related to an abun-subdelta, but there are no relics of former channels leading dant fluvial sediment yield from the steep hinterland,in this direction. Another suggestion has been that it is including sand and gravel brought down by rivers fromrelated to a buried or nearshore reef structure, but no the Merapi volcano, particularly after eruptions, whenevidence exists for this either. The promontory occurs lahars flow down slopes and river discharge is torrential.where an earlier beach ridge system was truncated by the Dark grey sand is delivered to river mouths and spreadpresent coastline. along the shore. Formation of protruding deltas of the On the smaller deltas to the east (Bangkaderas, Bosok, kind seen in northern Java is prevented by relatively strongPemali, Comal and Bodri), Hollerwöger (1964) traced the wave action, the shoreline being almost straight past thestages in historical evolution and noted an acceleration of mouths of several rivers, each of which shows westwardgrowth after 1920, related to increased sediment yield due deflection by longshore drifting produced by waves gener-to clearance of forests on steep hinterlands and the intro- ated by southeasterly winds. To the west of Parangtritis,duction of farming to these areas. In detail, there have the seaward margin consists of beach ridges and activebeen sectors of advance and retreat related to the changing dunes up to 30 m high, driven inland by the southeasterlylocations of river mouths. Near Jepara a new delta formed winds. These dunes were evidently mobilised when theirat the mouth of a canal cut in 1892 to divert the outflow scrub and woodland cover were destroyed by sheep andfrom the Kedung River, and the Solo delta has grown rap- goat grazing and the harvesting of firewood. They are quiteidly. There has been substantial progradation of the coastal anomalous in a humid tropical environment.plains around Surabaya in recent centuries, narrowing On the south coast of Central Java the westwardSurabaya Strait, which shows tidal scour features indica- growth of longshore spits due to the oblique arrival oftive of strong current action. waves generated by southeasterly winds may block river Fig. 19.8.11Notched coastal slope atBaron, southern Java,behind a shore platformthat has a veneer of blackvolcanic sand. (CourtesyGeostudies.)
  • 10. 1166 19.8 Indonesia Fig. 19.8.12 Beach ridges on the coastal plain east of Cilacap. (Courtesy Geostudies.) SOUTH SERAYU RANGE SOUTH SERAYU RANGE 1 N Segara Anakan 2 INDIAN OCEAN Cilacap NUSA KAMBANGAN Uplands Beach ridges Alluvium 1 Heavily silt-laden water 0 5 10km. Wetlands 2 Slightly silt-laden water Fig. 19.8.13 Segara Anakan, a mangrove-fringed lagoon. (Courtesy Geostudies.) SEGARA ANAKAN W E T L y A ndu N D m S Cita m m m m m m m m Segara m m m m m m m Anakan m m m m m m m m m m m m m m m m m m m m m m m m m Kali Kem m bangkuni ng C. Cimangga Uplands CILACAP Beach ridges C. Karang - N m Mangroves Nusa Kambangan bolong Mangrove encroachment 1943 - 1976 0 5 10 km.
  • 11. Indonesia 19.8 1167mouths for some weeks or months during the dry season, where the tide range is more than 2 m, but the Mahakamforming temporary coastal lagoons. The spits are usually has built a major delta ( Fig. 19.8.14) formed largely ofbreached when river outflow increases in the wet season. coarse, sandy sediment derived from fluvial erosion of The coast west to Cilacap has prograded intermittently, sandstone ridges near Samarinda, with swampy areas be-with the addition of successive beach ridges which are tween the distributaries. On the west coast, only the Pawaninterrupted by alluvial tracts where rivers such as the Serayu and Kapuas rivers have carried sufficient sediment fromflow across them ( Fig. 19.8.12). At Cilacap the coastal their extensive catchments to build protruding deltas.plain extends behind a high limestone ridge, and extensivemangrove swamps, intersected by tidal channels and creeks,border the broad, shallow estuarine lagoon of Segara 2.5. SulawesiAnakan. Inflow of large quantities of silt, especially fromthe Citanduy River, is reducing the depth and extent of this Sulawesi has generally steep coasts, with terraces (includ-lagoon system and promoting mangrove encroachment ing emerged, tilted, and warped coral reefs) up to 600 m( Fig. 19.8.13). Farther west, sectors of steep coast alter- above sea level indicating tectonic uplift. Rivers are shortnate with beach-ridge plains along and towards Java Head, and steep, with waterfalls and incised gorges and onlyat the southern entrance to Sunda Strait. minor depositional plains at their mouths. Volcanoes are active locally, notably on Menadotua off the north of the island.2.4. KalimantanGeomorphologists have given very little attention to the 2.6. Maduracoasts of Kalimantan. Swampy plains are extensive, butrates of progradation have not been documented. Many The island of Madura is notable for its straight northernriver mouths are estuarine, especially on the east coast coast which may follow a fault line. Fig. 19.8.14Morphological M A H A K A M D ELTAfeatures of the 0 5 10 15 20 km. 0°20 SMahakam delta Swamp Hilly ridges Mud, sand 20 Fathom lineson the east coast i elof Kalimantan. Ka a 20 r 10 uaThe high-tide Mshoreline is Soeintricate and Muara llu nga Samarinda 0°30 Sdynamic, but the idelta really Ma hak amextends seawardas a submerged Muara Pantuansedimentary lobewith a steep outer 0°40 Sslope, hereindicated by the Muara Bajor10- and 20-fathomlines. (CourtesyGeostudies.) M ua ra IT 10 20 Bu A 0°50 S dj R it T S Mu ara R Muara Djaw A SS Ul A K u A M 117°00 E 117°10 E 117°20 E 10 117°30 E 117°40 E a 20
  • 12. 1168 19.8 Indonesia Fig. 19.8.15 The limestone cliff at Uluwatu on the southeast coast of Bali. (Courtesy Geostudies.) Fig. 19.8.16 Fringing reef on the east coast of Bali, backed by a beach of coralline sand derived from the reef. (Courtesy Geostudies.) 2.7. Bali and partly of coralline limestone formations, which are cliffed on the Bukit Peninsula to the southeast Bali consists partly of volcanic terrain, with active volca- ( Fig. 19.8.15). Beaches border much of the island, with noes such as Agung periodically generating lava and coral sands behind fringing reefs ( Fig. 19.8.16) con- ash deposits that are washed down to the sea by rivers, trasting with dark grey sand derived from cliff outcrops
  • 13. Indonesia 19.8 1169of volcanic ash, or carried down to the sea by rivers 2.9. Lesser Sunda Islandsdraining the volcanic terrain. The spit at Gilimanukshows evidence of alternating growth and truncation, Many of the features seen on Bali and Lombok are repeatedand in the Sanur area spits and barrier islands enclose a on the Lesser Sunda Islands to the east. High cliffs ofbroad, mangrove-fringed tidal embayment north of the limestone and volcanic rock fringe the southern coasts ofsandy isthmus at Denpasar. Sumbawa, and Sumba, and active volcanoes have depos- ited material on the coasts of Flores and Halmahera. Uplift is indicated by emerged coral reefs, attaining 700 m on2.8. Lombok Sumbawa and over 1,200 m on Timor, where the sequence dated by Chappell and Veeh (1978) indicated uplift ratesThe north coast of the island of Lombok has cliffs cut of up to 0.5 m per thousand years. Many of the smallerin lava and ash from the Mount Rinjani volcano, and islands of eastern Indonesia are either high volcanicoff the east coast coral reefs are extensive in coastal islands or uplifted coralline structures of various kinds.waters. Beaches are generally of dark grey volcanic sand,often with coralline gravel, and backed by progradedbeach ridge plains. Off the northeast coast Gili Petangan, 2.10. Irian JayaGili Sulat and Gili Lawang are sand cays on coral reefs,the sandy beaches containing layers of beach rock The north coast of Irian Jaya is generally steep, but rivers( Fig. 19.8.17), the cays having grassy and shrubby vege- have built deltas and beach-ridge plains. Evidence of con-tation. On the south coast headlands of sandstone exposed tinuing tectonic activity is common: earthquakes causeto ocean swell from the southwest are cliffed and fronted landslides on coastal slopes, and the Mamberamo Deltaby subhorizontal shore platforms produced by weathering has been modified by subsidence ( Fig. 19.8.18). Thedown to the water table ( Fig. 19.8.18). There are broad south coast borders the broad, swampy lowlands traversedprograded sandy beaches, especially behind coral reefs as by rivers that open into widening muddy estuaries withat Kuta on the central south coast. strong tidal currents; tide ranges here are up to 6 m. The Fig. 19.8.17Beach rock on the shoreof Gili Petangan, Lombok.(Courtesy Geostudies.)
  • 14. 1170 19.8 Indonesia Fig. 19.8.18 Zone of subsidence across the Mamberamo Delta in northern Irian Jaya, showing the Rombebai Lake formed as the land subsided and the spread of mangroves back into the lowered area. (Courtesy Geostudies.) Hollerwöger F (1964) The progress of the river deltas in Java. Scientific rivers have not built protruding deltas, but deposition is problems of humid tropical zone deltas and their implications, locally advancing the swampy shorelines. UNESCO, Paris, pp 347–355 Symons GJ (ed) (1888) The eruption of Krakatoa, and subsequent phe- nomena. Royal Society, London References Tjia HD (1975) Holocene eustatic sea levels and glacioeustatic rebound. Z Geomorpholo Suppl.(Bd) 22:57–71 Bird ECF, Ongkosongo OSR (1980) Environmental changes on the coasts Verstappen H (1973) A geomorphological reconnaissance of Sumatra and of Indonesia. United Nations University Press, Tokyo, Japan adjacent Islands. Wolters-Noordhoff, Groningen Chappell J, Veeh HH (1978) Tectonic movements and sea level changes at Timor and Atauro Island. Bull Geol Soc Amer 89:356–368