An Island Built by Volcanoes
Every aspect of Bali's geography and ecology is influenced by the towering range of volcanic peaks that dominate the island. They have created its landforms, periodically regenerated its soils,and helped to produce the dramatic downpours which provide the island with life-giving water. The Balinese recognize these geophysical facts of life, and the island's many volcanoes, lakes and springs are considered by them to be sacred.
Bali is continually being formed by volcanic action. The island lies over a major subduction zone where the Indo-Australian plate collides with the rigid Sunda plate with explosive results. A violent eruption of Mt. Agung (3,142 m before the eruption; 3,014 in now) in 1963 showered the mountain's upper slopes with ash and debris that slid off as mudflows, killing thousands of people and laying waste to irrigation networks and rice fields that had been built up over many years. Mt Batur (1,717 in) to the west is also active, with greater frequency but less violence.
A mild, equatorial climate
Lying between 8 and 9 degrees south of the equator, Bali has a short, hot wet season and a longer, cooler dry season. The mountains are wet year round, averaging 2,500 to 3,000 mm (100 to 120 inches) of rain annually, with warm days and cool nights. The lowlands are hotter and drier, but fresh and persistent winds make the climate less oppressive here than elsewhere in the equatorial zone.
The wet season lasts from November to March, and though there are only five or six hours of sunshine a day, this is also the hottest time of year (30-31" C by day, 24-25o C at night). The dry season is from April to October, when southeasterly winds blow up from the cool Australian interior (28-29o C by day, and a pleasant 23" C at night), with seven or eight hours of sunshine daily.
By itself, the rainfall in the lowlands is not enough for wet rice cultivation. In other parts of Indonesia, particularly Java, flood waters following heavy rains can be collected behind dams, but the steep, narrow valleys of Bali offer no good dam sites. Over the centuries, the Balinese have instead devised many sophisticated irrigation systems which optimize the water available from rain and rivers.
Bali's volcanic soils are in fact not naturally well-suited to wet rice cultivation. They are deep, finely textured and well-drained, so water soaks through them rapidly. While this reduces the risk of floods, it wastes precious water. Paradoxically, the solution is vigorous and repeated plugging, which actually renders the soils less permeable. Irrigated areas, moreover, receive a supply of nutrients from river water enriched by domestic effluents.
Man has extensively modified the natural vegetation of Bali. The moist primary forest which is its natural vegetation now covers only 1,010 sq km or 19 percent of Bali's total area, mainly in the western mountains and along the arc of volcanic peaks from Agung to Batukau. About a quarter of the forest is protected in four nature reserves, the largest of which is Bali Barat National Park (763 sq km. Further reserves are planned to protect another quarter of the island's forests.
An island of great contrasts
Bali may be small, but its physical geography is complex, creating an island of great contrasts. In simple outline, three major areas emerge - the mountains, the coastal lowlands and the limestone fringes. The mountains are lofty and spectacular, dominated by Mt Agung and its neighbors, Abang and Batur. Dramatic lava flows on the northeastern flanks of Agung are Bali's newest landforms, showing what the entire island probably looked like a million years ago.
The western mountains provide the last major wildlife sanctuary. Cultivation is here limited to coastal areas that are very dry in the north, but more prosperous and fertile in the south. Coconut groves, cattle pastures and rain fed fields line the foothills while rice fields are found along the coast. Unique canals vanish into foothill tunnels excavated as protection from landslides. In the extreme southwest, the new Palasari Dam forms the island's only manmade lake. On Bali's western tip, the coral reefs and clear waters around Menjangan Island provide fantastic scuba diving.
The southern lowlands formed the cradle of Balinese civilization. Here it is possible to grow two or more irrigated rice crops per year. Based on this agricultural surplus, eight small but powerful kingdoms arose, symmetrically lining the parallel north-south river valleys that shaped their early growth.
In contrast to the south, the north coast hosted only a single kingdom, centered on the less extensive but equally productive rice lands around Singaraja. Terracing here continues well into the hills, on slopes which elsewhere would be regarded as a severe erosion hazard. In Bali, these terraces stand as firm as masonry because of peculiar clay minerals within the soil. Further east, the dry coast is relieved by several major springs which emerge from fissures in the lava flows. The spring water is used for irrigating table grapes, a crop that thrives here.
southern limestone fringes stand in complete contrast to the rest of
Bali. These are dry and difficult to cultivate. The Bukit Peninsula
south of the airport has impressive southern cliffs and many large caves.
Across the sea to the east, Nusa Ceningan, Nusa Lembongan and Nusa Penida
are dry limestone islands with scrubby vegetation and shallow soils.
Villagers on Penida have built ingenious catchments to collect rainwater.
Springs also emerge from the base of its high southern cliffs, and villagers
scramble down precarious scaffolds to collect water. just as water is
the measure of richness in the interior, so is it the measure of survival
around the periphery. In Bali, water is truly sacred.
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