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Java island

Java (Jawa) is an island of Indonesia and the site of its capital city, Jakarta. Once the center of powerful Hindu-Buddhist kingdoms, Islamic sultanates, and the core of the colonial Dutch East Indies, Java now plays a dominant role in the economic and political life of Indonesia. Home to a population of 130 million in 2006, it is the most populous island in the world. Java is also one of the most densely populated regions on Earth.

Geography & geology
Densely populated, fertile island

Java is a beautiful island. From the sky it looks like a far stretched quilt of green rice fields disrupted by some villages, palm forests and rubber-, djati-, and sugar plantations. The bright green vegetation is in grave contrast with the fertile, brownish-red soil. The Javanese landscape is dominated by the bold peaks of the blueish-gray volcanoes, which slopes are densely forested with tropical trees. Even so remarkable are the uncountable little dams and canals, which are for irrigation of the fields and paddies. Via a widespread system of waterways are even the smallest canals connected to wide silty rivers, which find a way to the sea in an smooth way.

On this most fertile and most densely populated island on the world live about 130 million people. Java counts for seven per cent of the total land mass of Indonesia, but hoses not less than sixty per cent of the total population of Indonesia. However the islands counts four metropolis and a big number of cities over 100,000 inhabitants, three quarters of the Javanese live on the countryside. The population density averages on 850 people per square km, but shows big regional differences. In some countryside areas the population tops twice the average, and in a half circle around Yogya it tops 2000 per Their most important source of living is tradition wet rice-farming, which doesn't know it's opposite in the world for what labor intensity concerns.

The island also knows areas where the standards of living are remarkably lower. The low hills along the southern coast and some areas along the northern coast were not formed by volcanic activities, and therefore lack the fertility. The limestone plateaus in Central-, and East Java are extraordinary poor, while the lowlands along the northern coast are flooded during the wet monsoon, and in the dry season is heavily cracked. That's why big areas of the mountain areas and the far-away southern coasts have low population density.

Volcanic 'Ring of Fire'

Volcanoes form the spine of Java. They formed the landscape and gave the island it's fertility. The numerous eruptions caused fertile ashes to spread over the island, as well as the lava. This process caused the soil to renew over and over again. Farmers use the water that also washed away the fertile soil for centuries to irrigate their rice fields. Normally they can harvest two or even three times a year.
Picture: Sulfur lake
The irregular chain of volcanoes, which spread over the entire length of the island, forms the most active part is the big 'Ring of Fire', which encloses the big moving plates around the Pacific Ocean. Java is on the south-edge of the huge Sunda-plate, which formed a subcontinent in the last ice-age with Java, Bali, Borneo, Sumatra and Malaysia were a part of. The formation of Java was a process in different steps, which started about 15.000 years ago during the Pleistocene, when the ice melted, and the sea-level rose.

The Java Sea on the northern side of the island is not deeper than 200 meters. The Java-trench, on the other hand, on the south of the island can be as deep as 7400 meters. This trench marks the restless zone where the Indo-Australian plate glides under the Sunda Plate. Two parallel to the line laying faultines form a northern and southern mountain range. In the steep trench between them, volcanoes were pushed up. Built from andesit or basalt, they lay densely packed in West-Java. Eastwards they are less densely packed, and form far less steep slopes, ideal for terraced rice fields.

Mountain peaks which evolved in the Tertiary period have lost their original shape due to erosion. Younger ones, on the other hand, still have perfect shapes. Together, Java and Bali count 37 volcanoes, which of them 23 were active after 1600. The past 25 years 13 erupted, and six are sleeping. Gunung Semeru ('Mount Semeru'), with 3676 metres the highest volcano, emits fumes and smoke on a regular base. The most famous and also most feared volcano is Krakatau, in the Sunda Strait, the strait between Java and Sumatra.

The disastrous eruption of 1883 caused the volcano to explode entirely and caused a 30 meters high tidal wave which killed 36.000 people. Gunung Merapi ('Fire-spitting Mountain'), to the north of Yogyakarta is the most active volcano, but the most powerful is Gunung Kelud, near Blitar, his eruption killed more than 200 in 1966. Due to better warning system the number of casualties of the eruption in 1990 was only 31.

The different behavior of volcanoes was marked by the eruption of Galunggung in 1982, a volcano which hadn't been active for centuries. The surrounding area was completely destroyed, and covered under a thick layer of ashes, in some places over two meters thick. Two airplanes on their way from Singapore to Australia were almost forced to land because of the clouds of ash. Until the city of Bogor cars were forces to drive with their lights on.

In this zone full with subterranean activity, earthquakes are fairly common. Most of them are not very powerful. The most known quakes took place in 1903, 1937, 1943 and 2006. The first one was a 8,1 on the Richter-scale, the heaviest ever reported. The epicenter of this quake was just below the southern coast. Cities in the north are barely hit by heavy quakes. Despite of potential danger the farmers keep settling down on the slopes, because they are the most fertile soil for their sawah's. Eruptions and earthquakes are not the only danger they are facing. More dangerous are the poisonous gasses with have no odor. These gasses regularly escape from the Dieng Plateau. Despite those dangers sometimes the inhabitants themselves visit the crates mouths, like the crater of Ijen, East-Java, where sulfur is being harvested and collected.

Big regional differences

There consist a clear contract between wealthy green hills at the bottom of volcanoes and the limestone formations along the northern- and southern coast. The Rembang Plateau and the island Madura in the east, and the Gunung Sewu mountain range in the south look more like Mediterranian landscapes instead of the tropics. The soil is thin, what causes rainwater to dissapear in the ground below very fast. In the dry season the landscape is very dry, but in the wet season the clay becomes one big heavy, untreatable mass.

The other hills in the southern part of java are formed over older folded volcanic sediments, comparable with the eastern islands of Indonesia. The sour, dried-up soil can't be used without intensive fertilization. But they are good enough to make cultures for tea and rubber, while in west-java a start is made with planting oilpalm trees.

The mountains are nowhere far from the coast. That causes the rivers to be short. The two longest rivers, the Bengawan Solo and the Brantas, got their remarkable stream by volcanic activity. They spring not far from the south-coast and meander through the mountains before they mouth near Surabaya. The same goes for the Citareum in West-Java, which springs in the former lake-plains, streams through several clefts and the Jatiluhur reservoir, and mouths on Cape Krawang, east of Jakarta.

When drainage only helps a little, all low plains at the northern coast are used intensively for producing rice. Towards the sea, those rice fields are regularly replaced by fishing ponds. Here the mangrove forests were recently transformed into shrimp-farms (tambak). In the dry coastal areas around Surabaya, Rembang and the island Madura there are also numerous salt ponds were created.

Hot and humid

Java's climate is hot and humid, and hardly knows seasonal changes. Temperatures vary all year between 22 and 34C. In the lowlands, the record high is 36C. Because the temperature as well as the length of the day and the night are constant, Indonesians calculate the seasons through their harvest of rice and fruit and to the arrival of the yearly monsoon rains.

The mountainous areas are cooler than the lowlands. The temperature drops remarkably when a person get higher, about 1C every 200 meters. In the mountain city of Puncak, south of Jakarta, altitude 900 meters, temperatures fluctuate between 17 and 26C. On the mountain peaks temperatures vary between 4 and 14 degrees. Tourists who undertake a nightly climb to the top of the Mount Bromo volcano in East-Java, have to take into account that it can freeze on an altitude of over 1500 meters. Warm clothing, not what many people instantly think of when visiting a tropical country, are necessary.

In some parts of Java lots of rain falls. The slopes of Gunung Slamet ('Mount Slamet') get over 7,000 mm every year, most other slopes between 3,000 and 4,000 mm. This much rain falls only on a few places on earth. On the other hand, the average rainfall on the northern coasts is about 1500 mm. The driest place is Asembagus (cool name, means good breath), in the northeastern corner of the islands with less than 900 mm, but that's still more than average in more moderate areas on earth. The division of rainfall is extremely irregular. It is not uncommon that rainfall changes 100% on a distance of less than 20 km.

Most rain falls in short, heavy downpours. In one such downpour can 50 to 100 mm be reached. In Bogor a year with 320 thunder-days was reported, a world record. Java luckily doesn't know the destroying force of cyclones and tornadoes, however the thundershowers can be very violent.

The west monsoon (wet monsoon) starts in January and February, when the winds from the northwest bring humid air to a depression above Australia. The northwest coast gets a daily amount of water of about 15 to 20 mm. From July until September is the dry time. The east monsoon brings dry air and somewhat lower temperatures from the Australian desert to Indonesia. The drought is noticeable on the east-, and southern coast of Java, the other parts hardly notice it. Noticeable are the cooler and clear skies above Yogyakarta and Bali.

Last revised on December 27, 2009
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