Volcanoes are the very essence of Java. They have molded the landscape and provided the basis for Java’s rich soils. Frequent outpourings of nutrient-rich lava and ash was washed by heavy rains down across the foothills and plains, providing a continuous renewal of the land. For centuries, farmers have diverted these rich waters into their fields, planting two or even three crops a year.
The volcanoes form an irregular line running the entire length of the island – one of the most active segments in the Circum-Pacific “Ring of Fire” that marks the boundary of drifting continental plates. Java lies at the southern extremity of one of these plates, which during the ice Ages formed huge sub-continent encompassing all of Java, Bali, Borneo, Sumatra, Malaya and the intervented area that now lies submerged beneath the shallow Java Sea. Java became an island at several stages in the past, most recently about 15.000 years ago when the seas rose with the last melting of the Pleistocene Ice.
The Java Sea to the north of the island is in fact extremely shallow – less than 200 meters, at its deepest point. The Java Trench to the south, on the other hand, drop precipitously to 7.000 meters. This trench marks as a zone of violent sub-duction where the Indo-Australian plate is sliding northward beneath the Sunda plate.
Two longitudinal folds along the line of impact between these two colliding continental plates form Java’s basic “foundation”, a northerly and a southerly line of hills, whit a trough running in between them . It is trough this trough that the island’s volcanoes are thrust dramatically upward. The volcanoes, which are andesitic or basaltic in composition, are more tightly packed in the west, where they create a tangled complex of upland plateaus and valleys. To the east, they are more widely spaced, creating a series of gradually sloping valleys that are perfectly suited to rice fields terracing.
While many peaks date back to the Tertiary are and have long since weathered and lost recognizable form, other are very young. Java and Bali together have 37 volcanoes officially listed, of which 23 have been active since 1600. There are 13 that have erupted in the last 25 years and another 6 are currently dormant. The most active volcano is Merapi volcano, lies in the north section of Yogyakarta district. The Merapi known with its Piroclastic flows, Javanese call it “Wedhus Gembel” that means the sheep, because it is look like the sheep.
The highest peak is Mt Semeru at 3.676 meters, which sends forth intermittent puffs of smoke. The most famous volcano is Krakatau in the Sunda Strait separating Java from Sumatra, whose cataclysmic eruption in 183 set up tidal waves that reportedly killed 36.000 people.
Mt. Merapi to the north of Yogyakarta erupts most frequently, but Mt. Kelud near Blitar is the most violent. Kelud’s 1996 eruption killed over 200 people, but with improved early warnings systems, an eruption in February 1990 resulted a death toll only 31.
The unpredictability of Java volcanoes is well illustrated by the eruption of Mt. Galunggung in west Java in 1982, which occurred after the volcano had lain dormant for centuries. The surrounding area was devastated – blanketed in grey ash that accumulated locally to over a meter in depth. Two jumbo jets en route from Singapore to Australia were nearly brought down by the dust clouds, while cars as fat away as Bogor had to use headlamps in broad daylight.
In this tectonically active zone there are frequent earthquakes, though usually not very severe. There are major quake in 1903, 1937 and 1943 the first was the largest recorded, measuring 8.1 on the Richter scale. The newest was in May 27, 2006, it’s about 5,9 Richter scale. The epicentrum was in the deep of Bantul, Yogyakarta. The victims of Its quake was about 4.000 people, from Bantul Yogyakarta and Klaten.
With their potential for devastation, volcanoes are a mixed blessing, yet as the dust settles after each eruption, land-hungry farmers move back into the area to redevelop the fertile soils. In some areas, the dangers are more subtle –a as, for example, the clouds of odorless poisonous gas that sometimes waft across the Dieng Plateau. Yet the Javanese often seek a livelihood in the very jaws of volcanic death, as in the quarries of fresh sulphur formed by hissing fumaroles in the crater of Mt. Ijen, Java’s easternmost peak.
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