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Journal : Indonesian Journal on Geoscience

Dinamika pengendapan lahar permukaan pada alur-alur lembah di bagian selatan Gunung Api Merapi, Yogyakarta Mulyaningsih, Sri; Sampurno, Sampurno; Zaim, Yahdi; Puradimaja, Deny Juanda; Bronto, Sutikno
Indonesian Journal on Geoscience Vol 1, No 3 (2006)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.1.3.129-142

Abstract

http://dx.doi.org/10.17014/ijog.vol1no3.20062Endapan aliran rombakan Gunung Api Merapi, yang lebih dikenal sebagai lahar, terbentuk dari hasil longsoran endapan awan panas yang dipicu oleh curah hujan yang sangat tinggi. Pada saat ini, endapan awan panas tersebut berasal dari guguran kubah lava. Material suspensi tersebut selanjutnya menuruni lereng dengan kecepatan yang tinggi, menghasilkan aliran turbulen. Aliran tersebut biasanya berkembang pada daerah dengan perbedaan morfologi berkemiringan lereng tinggi ke landai, atau yang sering dikenal sebagai daerah tekuk lereng. Studi ini didasarkan pada pengamatan dan pengukuran fragmen lahar yang berukuran besar di permukaan. Analisis meliputi arah penyirapan, bentuk, dan besar butir fragmen. Hasil penelitian mendapatkan model arah aliran fragmen besar lahar dari bagian atas aliran rombakan, yang membentuk “model punggung katak” atau “model punggung gajah”. Bagian depan katak atau gajah (kepala) yaitu arah aliran atau bagian depan aliran. Hasil penelitian juga menunjukkan bahwa model tersebut berlaku pada fragmen dengan diameter 90 cm atau lebih besar. Di daerah penelitian, fragmen dengan diameter 90 cm mencapai jarak hingga 22 km dari sumbernya. Hasil penelitian ini dapat digunakan sebagai model untuk menentukan arah aliran lahar (aliran rombakan) purba yang sumbernya belum diketahui.  
Gunung api maar di Semenanjung Muria Bronto, Sutikno; Mulyaningsih, Sri
Indonesian Journal on Geoscience Vol 2, No 1 (2007)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.2.1.43-54

Abstract

http://dx.doi.org/10.17014/ijog.vol2no1.20074Three maars are well identifi ed in the Muria Peninsula, i.e. Bambang Maar, Gunungrowo Maar, and Gembong Maar. The maars were formed by monogenetic volcanic eruptions due to the interaction between heat source (magma), groundwater and calcareous basement rocks. This interaction is able to produce very high pressure of gas and steam causing phreatic explosions, followed by phreatomagmatic- or even magmatic explosions and ended by a lava extrusion. Satellite image analyses have recognized twelve circular features, comprising Bambang Maar, Gunungrowo Maar, and Gembaong Maar. Phisiographically, these maars are characterized by circular depressions which are surrounded by hills that are gently sloping down away from the crater or having a radier pattern morphology. Outcrops and drilling core in the circular areas that are considered as volcanic maars are lava fl ows, pyroclastic breccias, lapillistones, and tuffs, located far away from the eruption centres of Muria and Genuk Volcanoes. One of the circular features, i.e. Jepara Circular Feature, is also supported by negative anomaly (<30 mgal) showing a circular pattern. In the future, a maar volcano could possibly erupt depending on the tectonic reactivity in the region.  
Vulkanisme kompleks Gunung Patiayam di Kecamatan Jekulo, Kabupaten Kudus, Provinsi Jawa Tengah Mulyaningsih, Sri; Bronto, Sutikno; Kusnaedi, Ari; Simon, I.; Prasetyanto, I. W.
Indonesian Journal on Geoscience Vol 3, No 2 (2008)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.3.2.75-88

Abstract

http://dx.doi.org/10.17014/ijog.vol3no2.20082The Mount Patiayam Complex was interpreted by previous researchers as “Patiayam Dome”. That was reasoned by dips following its slope directions. Field data record that lithology of the complex of Mount Patiayam is dominated by volcanic rocks. The summit of the complex is composed of igneous rocks of pyroxene basalt rich in leucite minerals, associated with autoclastic breccia and beds of volcanic breccia rich in pyroxene basalt and pumice, pumiceous breccia, and tuff. Its flanks are composed of epiclastic rocks of lahar and fluvial deposits. Some river valleys, such as Pontang River, locally consist of pyroclastic breccia, autoclastic breccia and pumiceous breccia, that are overlain by marly limestone and black clay of swampy deposits. Based on the rock composition, the volcanism had more dominated geological processes compared with sedimentary. Mineral composition of volcanic deposits of the Mount Patiayam is closer to Mount Lasem volcanic rocks than Mount Muria, i.e. absarockites, shoshonites and trachyandesite. But, based on the long distance between Patiayam and Lasem, about 60 km, those volcanic rocks could not be produced by Mount Lasem. The Patiayam volcanic deposits were produced by its own volcanic activities. Therefore, the complex of Mount Patiayam is a paleo-volcano. The interpretation is also supported by the landsat imagery, showing depression-shapes in a caldera ring-like. There are four caldera features called as Rim 1,Rim 2,Rim 3, and Rim 4, which crosses each others.  
Waduk Parangjoho dan Songputri: Alternatif Sumber Erupsi Formasi Semilir di daerah Eromoko, Kabupaten Wonogiri, Jawa Tengah Bronto, Sutikno; Mulyaningsih, Sri; Hartono, G.; Astuti, B.
Indonesian Journal on Geoscience Vol 4, No 2 (2009)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.4.2.77-92

Abstract

http://dx.doi.org/10.17014/ijog.vol4no2.20091The Semilir Formation was typically originated from products of a very explosive volcanic activity, i.e. breccias, lapillistones, and tuffs containing abundant pumice. It has a light grey to white colour and high silica andesite to dacite in composition, mainly rich in volcanic glass and quartz. Sedimentary structures of these volcanic rocks are massive, grading, planar bedding, and cross-bedding to antidunes, with grain size varies from ash (≤ 2 mm) to lapilli (2 – 64 mm) to bomb and block (> 64 mm). The formation is widely distributed from the west side (Pleret and Piyungan areas, Bantul Regency, Special Province of Yogyakarta) until Eromoko area in the east (Wonogiri Regency, Jawa Tengah Province). Stratigraphically, the Semilir Formation underlies the Nglanggeran Formation, and overlies the Mandalika Formation in the eastern part and Kebo-Butak Formation in the western part. Geomorphological- and lithological analyses of the Semilir Formation in areas of Parangjoho and Song- putri Dams, Eromoko Sub-regency, Wonogiri Regency indicate that the two depressions were alternatively volcanic sources of the Semilir Formation in the Eromoko area. This is proved by the presence of co-ignimbrite breccias(co-ignimbrite lag fall deposits), that descriptively they are polymict breccias. This rock is characterized by a mixing of pumice and various hard rock fragments that primarily are juvenile materials (volcanic blocks, bombs), accessory-, and accidental rock fragments set in pumice-rich volcanic ash and lapilli sizes. The accessory materials came from older volcanic rocks, whereas the accidental ones were originated from basement rocks. During a caldera forming event or a destruction period of an older composite volcanic cone(s), all older rocks resting above the magma chamber were ejected to the surface by a very high magmatic pressure. Since they were heavier than the juvenile material, most accessory and accidental rock fragments were left (lag fall) in caldera rim behind the ash and pumice flow. In the dam areas of Parangjoho and Songputri, the lag fall fragments consisting of andesite, pyroxene andesite, dacite, and pumice, being 10 – 150 cm in diameter are set in pumice-rich lapilli tuffs. Some of the rock fragments are volcanic blocks and bombs, while the older rocks are angular to very angular shape, having prismatic jointing or jigsaw-crack structures. The eruptions in the Parangjoho and Songputri craters were controlled by north-south trending fractures, and they resemble to the Katmaian caldera explosion type.  
Geochemistry of Basaltic Merbabu Volcanic Rocks, Central Java, Indonesia Mulyaningsih, Sri; Shaban, Godang
Indonesian Journal on Geoscience Vol 7, No 2 (2020)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.7.2.161-178

Abstract

DOI: 10.17014/ijog.7.2.161-178The studied area is located along the hiking track of Kajor - Selo, the south flank of Merbabu Volcano, Central Java, Indonesia. Olivine basalt and augite-rich basalt compose the volcanic rocks. A geochemical study recognizes these basalts which tend to originate from the product of tholeiitic magma, in terms of transitional enriched mantle source. It is interpreted to have been formed as primary magma that mixed later with higher degrees of partial melting with a mantle wedge. Both fl uid and melt were derived from the mixing of lower active continental margin and subducting oceanic slab. This study also shows general trends of increasing incompatible elements, i.e. Rb, Ba, Pb2+, and Sr as LIL trace elements and Th, U, Nb, Ce, Zr, Hf, Nb, and Ta as HFS element comparing to basaltic andesites exposed at Thekelan, they show decreasing compatible of MgO, Fe2O3*, Al2O3, CaO, TiO2, Ni, Sr, and Ba in line with increasing SiO2. It was fractional crystallization process, shown by the slightly wide variation of Rb/Zr and La/Sm that indicates random crustal contamination.
Co-Authors Abdul Faisal Baba Alansa, Frando Ryan Ari Kusnaedi Ari Kusnaedi Arie Kusniadi Ariel l Afrandi Tatawu Arif Wardana, Muhammad Arifin, Muhammad Nur Arisandy, Rydo Faisal Astuti, B. Astuti, B. B. Astuti Bronto, Sutikno Bronto, Sutikno Bronto, Sutikno Bronto, Sutikno Bronto, Sutikno Darwin Alijasa Siregar Deny Juanda Puradimaja Deny Juanda Puradimaja Desi Kiswiranti Dina Tania Dina Tania Dina Tania Dina Tania Dwi Indah Purnamawati, Dwi Indah Emilliana Natalia Trisakti Susanti, Maria Frando Ryan Alansa G. Hartono Godang Shaban Hartono, G. Hartono, G. Heriyadi, Nur Widi Astanto Agus Tri Hidayah, Radhitya Adzan Hidayah, Radhtya Adzan Hidayati, Fika Husadani, Y T I. Simon I. Simon I. W. Prasetyanto I. W. Prasetyanto Iva Mindayani Jayawarsa, A.A. Ketut Kusnaedi, Ari L. Budiyanto Lilis Apriyanti Marausna, Gaguk Mohamad Faizal Mohamad Faizal, Mohamad Muhammad Luqman Bukhori Muhammad Nur Arifin N.A.A.T Heriyadi Nur Rahmawati Prasetyanto, I. W. Prima, Anka Puradimaja, Deny Juanda Puradimaja, Deny Juanda Putong, Rahel Putra, Ikbal Rizki Rachmawati, Desiana Rydo Faisal Arisandy Sampurno Sampurno Sampurno Sampurno Sampurno, Sampurno Sampurno, Sampurno Sanjoto, Siwi Shaban, Godang Shandi Hargian Wijaksono Simon, I. Siregar, Darwin Alijasa Suhartono Suhartono - Suhartono Suhartono Suhartono Suhartono Suhartono Suhartono Suhartono Suparni Setyowati Rahayu Susastriawan, Anak Agung Putu Sutikno Bronto Sutikno Bronto Sutikno Bronto Sutikno Bronto Tatawu, Ariel l Afrandi Umboro, P A Vienastra, Septian Wijaksono, Shandi Hargian Wiloso, Danis Agoes Yahdi Zaim Yahdi Zaim Yoyok Ragowo Siswomijoyo Sukisman Zaim, Yahdi Zaim, Yahdi