Klasifikasi Gunung Api Aktif Indonesia, Studi Kasus Dari Beberapa Letusan Gunung Api Dalam Sejarah

Http://dx.doi.org/10.17014/ijog.vol1no4.20065Indonesia is well known as a volcanic country, where more than 30% out of all the world volcanoes occupied this region. Volcanic region is generally densely populated, because of their soil fertility and other land use. Based on their historical eruptions noted since and before 1600 A.D., the Indonesian active volcanoes are regrouped in to A type (79 volcanoes), which were defi ned as volcanoes erupted since 1600 A.D., B type (29 volcanoes) erupted before 1600 A.D., and C type (21 volcanoes) are solfatar fi elds (Bemmelen, 1949; van Padang 1951; Kusumadinata, 1979). Studies on parts of the Indonesian active volcanoes, show different eruptive characters, which are generally related to hazard potentials. A new classifi cation of Indonesian active volcanoes was proposed based on the combination of their physical properties, morphology, volcanic structure and eruptive styles to the eight differents types, those are Tambora (caldera formation), Merapi (lava dome), Agung (open crater), Papandayan (sector failure), Batur (post-caldera activities), Sangeangapi (lava fl ows) and Anak Krakatau types (volcano islands and submarine volcano). This classification would be make a better understanding to different characteristics of Indonesian active volcanoes, for the volcanic hazard and mitigation and also for the applied volcanological researches

Karakter Endapan Kuarter di Lepas Pantai Tepian Cekungan Sumatera Tengah - P. Kundur

Studi yang dilakukan pada karakter endapan Kuarter di lepas pantai tepian cekungan Sumatera Tengah-P. Kundur mencakup analisis sedimentologi dan stratigrafi terhadap lima belas hasil pemboran yang dilakukan di sepanjang lintasan yang berarah barat - timur di baratlaut P. Kundur. Kedalaman pemboran berkisar antara 8,00 hingga 27,00 m. Studi ini, menunjukkan terdapatnya enam lingkungan pengendapan. Keenam lingkungan pengendapan itu ialah: endapan-endapan material rombakan (Mr), alur sungai (F), limpah banjir (Fp), cekungan banjir (Fb), pantai (Br), dan dekat pantai sampai lepas pantai. Berdasarkan korelasi Perubahan lingkungan pengendapan secara lateral dan vertikal, diketahui pula bahwa runtunan stratigrafi tersebut dicirikan oleh berubahnya lingkungan pengendapan yang dikendalikan oleh Perubahan iklim dan muka laut, dan mungkin juga oleh tektonik. Selama proses pengendapan, aktifitas Perubahan iklim terekam dalam 4 fasa kejadian ialah: (1) minimum, (2)minimum menuju maksimum, (3)maksimum menuju minimum, dan (4)minimum. Kata kunci: Endapan Kuarter, iklim, muka-laut, tektonik The study of the Quaternary sediment characters on offshore of the Central Sumatera basin margin-Kundur Island was based on the analyses of sedimentology of fiveteen boreholes information obtained along the West to East at the northwest of Kundur Island. The penetration of the bore head varied from 8.00 to 27.00 m. This study revealed six deposition environments. These are: mass flow (Mr), river channel (F), floodplain (Fp), floodbasin (Fb), beach (Br), and nearshore to offshore (M) deposits . Based on the correlation of the lateral and vertical variation of the depositional environments, the stratigraphy successions/characterized by the variation of the depositional environments which is controlled by climatic and sea level changes, and also probably by tectonic. During the deposition processes, the activity of climatic changes were recorded in four stages episodes: (1)minimum, (2)minimum to optimum, (3)optimum to minimum, and (4)minimum. Keywords: Quaternary sediments, climate, sea-level, tectoni

Resurgent Toba—field, chronologic, and model constraints on time scales and mechanisms of resurgence at large calderas

Highlights: New data reveal for the first time a history of the last ∼33.7 ky of uplift of Samosir. Minimum uplift rates were high (4.9 cm/year) for the first 11.2 ky but diminished after that to <1 cm/year for the last 22.5 ky. Numerical modeling suggests that rebound of remnant magma augmented by deep recharge appears to be the most likely driver for uplift. Detumescence makes a negligible contribution to resurgent uplift. The volume of the resurgent dome is isostatically compensated by magma. Average rates of uplift at Toba are much lower than currently restless calderas indicating a distinction between resurgence and “restlessness”. New data reveal details of the post-caldera history at the Earth’s youngest resurgent supervolcano, Toba caldera in Sumatra. Resurgence after the caldera-forming ∼74 ka Youngest Toba Tuff eruption uplifted the caldera floor as a resurgent dome, Samosir Island, capped with 100m of lake sediments. ¹⁴C age data from the uppermost datable sediments reveal that Samosir Island was submerged beneath lake level (∼900 m a.s.l) at 33 ka. Since then, Samosir experienced 700 m of uplift as a tilted block dipping to the west. ¹⁴C ages and elevations of sediment along a transect of Samosir reveal that minimum uplift rates were ∼4.9 cm/year from ∼33.7 to 22.5 ka, but diminished to ∼0.7 cm/year after 22.5 ka. Thermo-mechanical models informed by these rates reveal that detumescence does not produce the uplift nor the uplift rates estimated for Samosir. However, models calculating the effect of volume change of the magma reservoir within a temperature-dependent viscoelastic host rock reveal that a single pulse of ∼475 km³ of magma produces a better fit to the uplift data than a constant flux. The cause of resurgent uplift of the caldera floor is rebound of remnant magma as the system re-established magmastatic and isostatic equilibrium after the caldera collapse. Previous assertions that the caldera floor was apparently at 400 m a.s.l or lower requires that uplift must have initiated between sometime between 33.7 and 74 ka at a minimum average uplift rate of ∼1.1 cm/year. The change in uplift rate from pre-33.7 ka to immediately post-33.7 ka suggests a role for deep recharge augmenting rebound. Average minimum rates of resurgent uplift at Toba are at least an order of magnitude slower than net rates of “restlessness” at currently active calderas. This connotes a distinction between resurgence and “restlessness” controlled by different processes, scales of process, and controlling variables.This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by the Frontiers Research Foundation. The published article can be found at: http://journal.frontiersin.org/journal/earth-science.Keywords: Magmastatic equilibrium, Resurgence, Lake sediments, Magmatic intrusion, Numerical modeling, Toba caldera, Carbon-14 dating, Remnant magm

SOUTHERN TASIKMALAYA ANCIENT SUBMARINE VOLCANO: VESTIGES OF ERUPTIONS AND THEIR DIVERSITY AS GEOLOGICAL HERITAGE

In the southern Tasikmalaya area West Java Province, Indonesia, there are Tertiary volcanic rocks, with an east-west trending distribution pattern.  Physiographically, this area is included in the southern mountain zone of West Java and is generally composed of tuff and polymic breccias with intercalated of lava and limestone which are grouped into the Jampang Formation and Genteng Members Jampang Formation. The existence of these volcanic and sedimentary rocks of Oligocene – Middle Miocene in the area is an indication of submarine volcano. The purpose of this paper to identify traces of eruptions and submarine volcano products found in the southern Tasikmalaya area, for further assessment of the geological diversity potential as a geological heritage. The method used are field data collection and quantitative data analysis, namely identification of geological heritage based on "Technical Guidelines for the Assessment of Geological Heritage Resources". The submarine volcano products which found in this area are peperite, and basaltic andesite lava at Karang Tawulan Beach, traces of alteration, and hydrothermal mineralization like jasper Panca Tengah, and Cipatujah volcanogenic massive sulphide. This shows that volcanic activities in the southern Tasikmalaya took place continuously from Oligocene to Middle Miocene. From the results of the assessment, the geological diversity in this area has a scientific value of "medium-high"

The 21 February 2005, catastrophic waste avalanche at Leuwigajah dumpsite, Bandung, Indonesia

International audienceOn 21 February 2005 the Leuwigajah dumpsite, Bandung (Java, Indonesia) was affected by a largeslide after heavy rainfalls. Second deadliest waste slide in history, it buried 71 houses and killed 143 people.Amongst the contemporary disastrous events of this type, only a few have been documented. We explored failurepreconditions, triggering mechanisms and local context that conducted to this disaster. We carried on four fieldinvestigations on the site. A series of aerial photographs were acquired and completed by topographical measureson the ground. The morphology of the slide and its trajectory were reconstructed. To constrain the movementcondition, we studied the internal structure of the source area and realized surveys among stakeholders of thedumpsite and citizen.Results: 2.7 10 6 m3 of waste materials spread 1000 m from the source in a rice field with an average thickness of10 m. The material displays a preferential fabric parallel to the previous topography. Numerous internal slip surfaces,underlined by plastic bags explain the low friction coefficient. The presence of methane within the waste dumpwas responsible for explosions prior to sliding and for the fire that affects whole sliding mass.Conclusions: Resulting of a combination of heavy rainfall and consecutive explosions due to biogas suddenrelease, this disaster was predictable in reason ofi) a front slope of the dump of about 100% before the failure;ii) a poor dumpsite management;iii) the extreme vulnerability of the marginalized scavengers living at risk at the foot of the instable dump