Cinder Cones of Mount Slamet, Central Java, Indonesia

Http://dx.doi.org/10.17014/ijog.vol4no1.20096The Mount Slamet volcanic field in Central Java, Indonesia, contains thirty five cinder cones within an area of 90 sq. km in the east flank of the volcano. The cinder cones occur singly or in small groups, with diameter of the base ranges from 130 - 750 m and the height is around 250 m. Within the volcanic field, the cinder cones are spread over the volcanic area at the distance of 4 to 14 km from the eruption center of the Slamet Volcano. They are concentrated within latitudes 7°11'00” - 7°16'00” S,, and longitudes 109°15'00” - 109°18'00” E. The density of the cinder cones is about 1.5 cones/km2. Most of the cinder cones lie on the Tertiary sedimentary rocks along the NW-trending fault system and on radial fractures. The structural pattern may be related to the radial faults in this region. The cone surfaces are commonly blanketed by Slamet air-falls and lava flows. The deposits consist of poorly bedded, very coarse-grained, occasionally overlain by oxidized scoria, and large-sized of ballistic bombs and blocks. There are various kind of volcanic bombs originating from scoriae ballistic rock fragments. The other kind of volcanic bombs are breadcrust bomb, almond seed or contorted shape. All of the cinder cones have undergone degradation, which can be observed from the characters of gully density and surface morphology. By using Porter parameters, Hco is equal to 0.25 Wco, whilst Wcr is equal to 0.40 Wco. The Hco/Wco ratio is higher than Hco = 0.2 Wco reference line. A radiometric dating using K-Ar method carried out on a scoria bomb yields the age of 0.042 + 0.020 Ma

The Effects of Tropospheric Bias on Deformation Monitoring of MT. Guntur using GPS Survey Method

Pemantauan deformasi gunung api yang andal menuntut ketelitian yang tinggi, yaitu sampai level keteliatian mm untuk kasus gunung api yang tengah 'bangkit' kembali. Konsekuensinya adalah kesalahan dan bias yang dapat mengurangi ketelitian dalam penentuan posisi dengan satelit GPS harus dieliminasi dana tau direduksi, seperti kesalahan yang disebabkan oleh bias troposfer. Pada kasus pemantauan deformasi gunung api dengan metode survei GPS, karena adanya perbedaan tinggi yang cukup besar dan variatif antara titik-titik dalam jaringan, maka efek kesalahan bias troposfer tidak sepenuhnya dapat direduksi dengan proses pengurangan data (differencing). Residu (sisa) bias troposter ini harus dikoreksi agar tingkat keteliatian yang dituntut oleh sistem pemantauan deformasi gunung api dapat tetap tercapai. Pada makalah ini akan dibahas efek bias troposfer pada pemantauan deformasi gunung api. Pembahasan didasarkan pada hasil yang diperoleh dari pemantauan deformasi G. Guntur (Garut, Jawa Barat) dengan metode survei GPS. The Effects of Tropospheric Bias on Deformation Monitoring of MT. Guntur using GPS Survey MethodA reliable volcano deformation monitoring requires a high positioning accuracy, i.e. up to mm level in the case of reawakening volcanoes. As a consequence of this requirement, the errors and biases affecting the GPS positioning accuracy has to be eliminated or reduced, which one of them is the tropospheric bias. In the case of volcano deformation monitoring using the GPS survey method, due to a relatively large altitude variation in the stations altitude, the effects of tropospheric bias could not be effectively reduced by the differencing process. In order to meet the accuracy requirement of volcano deformation monitoring system, this residual tropospheric bias, therefore, has to be somehow corrected or taken into account. In this paper, the effects of tropospheric bias on the volcano deformation monitoring will be discussed. The discussion is based on the results from the deformation monitoring of Guntur volcano in Garut, West Java, by using repeated GPS surveys

Energi panas bumi di Indonesia : kebijakan pengembangan dan keputusan investasi

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Bathymetric and geochemical investigation of Kawah Ijen Crater Lake, East Java, Indonesia

A bathymetric survey of Kawah Ijen crater lake was conducted by acoustic sounding in 1996 to compare the lake morphology with those measured in 1922, 1925 and 1938, and to calculate the present lake volume. Even though the lake experienced several hydrothermal eruptions, the maximum depth became shallower (182 m) than before (200 m), resulting in a reduced lake volume (3.0×107 m3).Fifty-two major and minor constituents including rare earth elements and polythionates (PT) of the lake waters at various depths were determined by ICP-AES, ICP-MS and HPLC, respectively. These ions except for several volatile elements are taken up by lake fringe through congruent dissolution of pyroclastics of Kawah Ijen volcano. Most ions are homogeneously distributed throughout the lake, although PT showed a considerable vertical variation. Rare earth elements (REE) in the Kawah Ijen water as well as those from other hyper-acidic crater lakes show distribution patterns likely due to the three rock dissolution (preferential, congruent and residual) types, and their logarithmic concentrations linearly depend upon the pH values of the lake waters.Using the PT degradation kinetics data, production rates of PT, injection rates of SO2 and H2S into the lake were estimated to be 114, 86 and 30 tons/day, respectively. Also travel time of the spring water at the Banyupahit Riverhead from Kawah Ijen was estimated to be 600-1000 days through the consideration of decreasing rates of PT. Molten sulfur stocks containing Sn, Cu, Bi sulfides and Pb-barite exposed on the inner crater slope were presumed to be extinct molten sulfur pools at the former lake bottom. This was strongly supported by the barite precipitation temperature estimated through the consideration of the temperature dependence of Pb-chlorocomplex formation. © 2004 Elsevier B.V. All rights reserved.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

10,000 Years of explosive eruptions of Merapi Volcano, Central Java: Archaeological and modern implications

Journal of Volcanology and Geothermal Research1001-49-50JVGR