Bandung Basin

Abstract
Environmental problems occurring in the Bandung Basin are resulted from improper management pertaining to land and spatial planning, including landuse policy and control. Arising environmental problems are covering disturbance of watershed hydrological function, surface and groundwater quality and quantity, solid waste, and air quality. Environmental studies in the Bandung Basin have been implemented by landuse change interpretation, surface water regime measurements, water quality, solid waste management, and air quality. Landuse change has occurred where some vegetation areas, such as forests and paddy fields, have decreased for 54% in one hand, and developed area has increased into 223% in the other hand. Watershed degradation is indicated by run off coefficient increasing from 0.3 in 1950 to 0.55 in 1998. Flow regime has also changed by presence of a maximum extreme discharge increasing tendency from 217.9 m3/sec in 1951 to 285.8 m3/sec in 1998, and minimum extreme discharge decreasing tendency from 6.35 m3/sec in 1951 to 5.7 m3/sec in 1998. Groundwater productivity index continued decreasing from 0.1 million m3/unit in 1900 to 0.0188 million m3/unit in 2002. Environmental problem has also occurred in a solid waste management sector where an average level of service is only 43.7%, and air pollution by motor vehicle and industrial emission, such as PM10, NOx, CO2, SO2, Pb, and acid rain phenomena have also occurred. Fresh water supply level of service in the Bandung Basin only covers 43% of the total needs. Watershed degradation occurring in the Basin needs a management system recovery, administrative based-management that shifted to ecological based integrated watershed management.
Effort and strategy required include the policy and institutional reassembling, pollution control, land rehabilitation and conservation, and community empowerment.Keywords: land use, watershed, run off coefficient, environmental strategy

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Hidrotermal Taran Area

Abstract
Taran area is occupied predominantly by piroclastic rocks and locally intercalations of lenticular claystones and sandstones. The pyroclastic rocks are intruded by diorite, dacite and andesite, leading alteration and mineralization within the host rocks. Mineralization occurs as a vein type and is associated with a number of pervasive alteration types named respectively: quartz-illite-montmorillonite-kaolinite ± pyrite, quartz-illite ± pyrite, quartz-illite-chlorite ± pyrite and quartz-kaolinite-illite ± pyrite. On the other hand, a propylitic alteration also occurs within the andesite intrusion composed of calcite-epidote-chlorite-sericite-quartz ± pyrite. The mineralization is characterized by several zones of quartz stockwork containing gold and associated ore minerals of chalcopyrite, sphalerite, galena, pyrite and argentite. The quartz veins occurs as fillings of structural openings in the form of milky quartz and amethyst with textures of sugary, comb, and dogteeth.
Evaluation work on results of microscopic (petrography and mineragraphy), X-Ray Diffraction (XRD), and fluid inclusion studies, and chemical analysis of entirely altered rock/quartz vein samples shows that the alteration and mineralization process were closely related to a change of hydrothermal fluids, from near neutral into acid conditions at a temperature range of >290o – 100oC. The appearances of quartz variation indicate a relationship with repeated episodes of boiling in an epithermal system, as ground water mixed with hot vapor originated from a remained post-magmatic solution. Corresponding to a salinity of average 1,388 equiv.wt.% NaCl, it indicates that the ore minerals bearing quartz veins were deposited at a depth range of 640 – 1020 m beneath paleosurface.
Keywords: Hydrothermal alteration, gold mineralization, epithermal

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Anak Krakatau Volcano

Abstract
Since its appearance in 1929, Anak Krakatau Volcano has been growing fastly. The elevation of Anak Krakatau Volcano from 1930 to 2005, within 75 years, has reached 315 m high. The growth rate is approximated to be four meters per year in average. Based on calculation, the volume of the body from the sea floor since 1927 until 1981 was 2.35 km3, and then in 1983 was 2.87 km3 and then in 1990 it reached 3.25 km3. The latest volume measurement in 2000, was 5.52 km3. Between 1992 up to 2001, within nine years, the eruption of Anak Krakatau took place almost every day, and it had caused its elevation to increase more than 100 m, and its area extent to become 378,527 m2. If the increase in height and the increase in volume are consistent, it is expected that in 2020, the volume of Anak Krakatau’s edifice will proceed the volume of Rakata Volcano, Danan Volcano, and Perbuwatan Volcano (11.01 km3) shortly before catastrophic eruption in 1883. Since this volcano appeared above the sea level, the succession of vegetation never came up to a climax, except some of the species, such as Saccharum sp. and Casuarina sp. those are growing faster after the eruption stopped. The growth of coral reef on the lava flows that entered the sea about ten years ago, was much slower than those which are growing around the Rakata, Panjang and Sertung Islands. This case is probably due to the slow rate of cooling process of the lava flows, although the lava surfaces are blocky.

Keywords: growth of volcano, succession of vegetation

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volcanic merapi

Abstract
The Merapi Volcanic debris flow, which is familiarly known as lahar, is formed from pyroclastic deposits that is slided by high rain water. Now, the pyroclastic deposits are produced from a collapsing lava dome. The suspension flows downhill in a high speed, to produce a turbulent flow. That flow are usually developed within areas of a different morphology having high to lower slope gradient, known as a slope fold of a foot hill. The study is based on the measurement and identification of large fragments of the surface deposits. Analysis includes imbrication direction, grain shape, and grain size of the fragments. The result of the study shows the model of a flow direction of large fragments of upper part of debris that form “frog back model” or “elephant back model”. The head of the frog or elephant explains the flow direction. The result of the research confirms that the model is valid for fragments having a range size of diameter of 90 cm or larger. In the studied area, the fragment of 90 cm in diameter has reached a distance up to 22 km from the source. Therefore the result of this research is able to be used as a model in determining the paleo-debris flows of unknown source.
Keywords: lahar, fragment, imbrication, model, flow

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Geology of Jakarta Basin

Abstract
Geologically the Batuceper and Benda Sub-Regencies belongs to the western part of the Jakarta Basin. The area is covered by coastal alluvial and delta deposits, and volcanic product. Understanding the distribution and groundwater pattern, either in the shallow part or the deep part, are of the basic thing for a geometric model and its groundwater flow in identifying the groundwater conservation.
The result of the aquifer distribution, either in the shallow or the depth parts, was approached by the geoelectrical and hydrogeological surveys in the field and well data that has resulted in aquifer distribution, either in the shallow or the deep parts. In general, the shallow aquifer developed downward becomes semi confined and confined aquifers. Groundwater flow pattern indicated local cones depression of groundwater level, especially around the city. Depression of groundwater level is considered to be related to the natural shape of aquifer as lences. However, it was possible to be caused by over pumping in this zone.
Keywords: Jakarta Basin, groundwater, flow pattern, aquifer, groundwater conservation

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