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Bandung, Indonesia

Vidal C.M.,University Paris Diderot | Komorowski J.-C.,University Paris Diderot | Metrich N.,University Paris Diderot | Pratomo I.,Museum of Geology | And 8 more authors.
Bulletin of Volcanology | Year: 2015

The 1257 A.D. caldera-forming eruption of Samalas (Lombok, Indonesia) was recently associated with the largest sulphate spike of the last 2 ky recorded in polar ice cores. It is suspected to have impacted climate both locally and at a global scale. Extensive fieldwork coupled with sedimentological, geochemical and physical analyses of eruptive products enabled us to provide new constraints on the stratigraphy and eruptive dynamics. This four-phase continuous eruption produced a total of 33–40 km3 dense rock equivalent (DRE) of deposits, consisting of (i) 7–9 km3 DRE of pumiceous plinian fall products, (ii) 16 km3 DRE of pyroclastic density current deposits (PDC) and (iii) 8–9 km3 DRE of co-PDC ash that settled over the surrounding islands and was identified as far as 660 km from the source on the flanks of Merapi volcano (Central Java). Widespread accretionary lapilli-rich deposits provide evidence of the occurrence of a violent phreatomagmatic phase during the eruption. With a peak mass eruption rate of 4.6 × 108 kg/s, a maximum plume height of 43 km and a dispersal index of 110,500 km2, the 1257 A.D. eruption stands as the most powerful eruption of the last millennium. Eruption dynamics are consistent with an efficient dispersal of sulphur-rich aerosols across the globe. Remarkable reproducibility of trace element analysis on a few milligrammes of pumiceous tephra provides unequivocal evidence for the geochemical correlation of 1257 A.D. proximal reference products with distal tephra identified on surrounding islands. Hence, we identify and characterise a new prominent inter-regional chronostratigraphic tephra marker. © 2015, Springer-Verlag Berlin Heidelberg. Source

Renema W.,Naturalis Biodiversity Center | Warter V.,Royal Holloway, University of London | Novak V.,Naturalis Biodiversity Center | Young J.R.,University College London | And 2 more authors.
Palaios | Year: 2015

We discuss the ages of twelve (clusters of) localities along the northeastern margin of the Kutai Basin (East Kalimantan, Indonesia). These localities form the basis for a large-scale study to improve our documentation of the fossil record of shallow marine environments in the center of maximum biodiversity. We integrated the results of investigations of occurrences of calcareous nannoplankton, (rare) planktonic foraminifera, larger benthic foraminifera, strontium isotope stratigraphy, and magnetostratigraphy. In addition to previously well-documented middle Miocene carbonates, new surface outcrops of early Tortonian- and Messinian-age carbonates are reported. Source

Marshall N.,University Utrecht | Novak V.,Naturalis Biodiversity Center | Cibaj I.,32 Avenue des Platanes | Krijgsman W.,University Utrecht | And 7 more authors.
Palaios | Year: 2015

Borneo's geologic and paleontological history remains poorly understood because of the lack of outcrops and difficulties with dating. Urban development around the city of Samarinda has produced over four kilometers of well-exposed stratigraphy depicting the progradation of the ancient Mahakam river delta across the Samarinda area, which includes slope, shelf, and deltaic deposits (clastic and carbonate). Previous studies have preliminarily dated the succession as middle Miocene, but reworking and the scarcity of diagnostic fossils make dating difficult. In this paper, an integrated stratigraphic age model has been constructed for the middle Miocene of the Samarinda region with a combination of magnetostratigraphy, sequence stratigraphy, and biostratigraphy (nannofossil, planktonic foraminifera, and larger benthic foraminifera). This age model provides improved temporal constraints for part of the Mahakam Delta succession. It also helps to place the pattern of biodiversity changes seen in Indonesian reef communities into a better time perspective, and permits more accurate sedimentation rates to be determined. It may also serve as a reference point to compare other Neogene sections in Southeast Asia. The two reef complexes at Samarinda, the Batu Putih and the Stadion section, are magnetostratigraphically dated at ∼ 15 Ma and 11.6 Ma, respectively. The new chronology for the Samarinda succession shows that the Mahakam Delta went through a major phase of buildout and progradation during the middle and earliest late Miocene, during which time progradation across the former shelf break took place in the Samarinda area. Source

Budi-Santoso A.,Badan Geologi | Budi-Santoso A.,University of Savoy | Lesage P.,University of Savoy | Dwiyono S.,Badan Geologi | And 6 more authors.
Journal of Volcanology and Geothermal Research | Year: 2013

The 2010 eruption of Merapi is the first large explosive eruption of the volcano that has been instrumentally observed. The main characteristics of the seismic activity during the pre-eruptive period and the crisis are presented and interpreted in this paper. The first seismic precursors were a series of four shallow swarms during the period between 12 and 4months before the eruption. These swarms are interpreted as the result of perturbations of the hydrothermal system by increasing heat flow. Shorter-term and more continuous precursory seismic activity started about 6weeks before the initial explosion on 26 October 2010. During this period, the rate of seismicity increased almost constantly yielding a cumulative seismic energy release for volcano-tectonic (VT) and multiphase events (MP) of 7.5×1010J. This value is 3 times the maximum energy release preceding previous effusive eruptions of Merapi. The high level reached and the accelerated behavior of both the deformation of the summit and the seismic activity are distinct features of the 2010 eruption.The hypocenters of VT events in 2010 occur in two clusters at of 2.5 to 5. km and less than 1.5. km depths below the summit. An aseismic zone was detected at 1.5-2.5. km depth, consistent with studies of previous eruptions, and indicating that this is a robust feature of Merapi's subsurface structure. Our analysis suggests that the aseismic zone is a poorly consolidated layer of altered material within the volcano. Deep VT events occurred mainly before 17 October 2010; subsequent to that time shallow activity strongly increased. The deep seismic activity is interpreted as associated with the enlargement of a narrow conduit by an unusually large volume of rapidly ascending magma. The shallow seismicity is interpreted as recording the final magma ascent and the rupture of a summit-dome plug, which triggered the eruption on 26 October 2010.Hindsight forecasting of the occurrence time of the eruption is performed by applying the Material Failure Forecast Method (FFM) using cumulative Real-time Seismic Amplitude (RSAM) calculated both from raw records and on signals classified according to their dominant frequency. Stable estimates of eruption time with errors as small as ±. 4. h are obtained within a 6. day lapse time before the eruption. This approach could therefore be useful to support decision making in the case of future large explosive episodes at Merapi. © 2013 Elsevier B.V. Source

Budi-Santoso A.,Badan Geologi | Budi-Santoso A.,University of Savoy | Lesage P.,University of Savoy
Geophysical Journal International | Year: 2016

We present a study of the seismic velocity variations that occurred in the structure before the large 2010 eruption of Merapi volcano. For the first time to our knowledge, the technique of coda wave interferometry is applied to both families of similar events (multiplets) and to correlation functions of seismic noise. About half of the seismic events recorded at the summit stations belong to one of the ten multiplets identified, including 120 similar events that occurred in the last 20 hr preceding the eruption onset. Daily noise cross-correlation functions (NCF) were calculated for the six pairs of short-period stations available. Using the stretching method, we estimate time-series of apparent velocity variation (AVV) for each multiplet and each pair of stations. No significant velocity change is detected until September 2010. From 10 October to the beginning of the eruption on 26 October, a complex pattern of AVV is observed with amplitude of up to ±1.5 per cent. Velocity decrease is first observed from families of deep events and then from shallow earthquakes. In the same period, AVV with different signs and chronologies are estimated from NCF calculated for various station pairs. The location in the horizontal plane of the velocity perturbations related with the AVV obtained from NCF is estimated by using an approach based on the radiative transfer approximation. Although their spatial resolution is limited, the resulting maps display velocity decrease in the upper part of the edifice in the period 12-25 October. After the eruption onset, the pattern of velocity perturbations is significantly modified with respect to the previous one. We interpret these velocity variations in the framework of a scenario of magmatic intrusion that integrates most observations. The perturbation of the stress field associated with the magma migration can induce both decrease and increase of the seismic velocity of rocks. Thus the detected AVVs can be considered as precursors of volcanic eruptions in andesitic volcanoes, without taking their sign into account. © The Authors 2016. Source

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