Simeulue waters are adjacent to the northern part of Sumatra Island, which is undergoing massive land-use transformations; moreover, the waters are located in an active tectonic region. Land changes ...and tectonic activity might affect the metal pollution profile in this deep sea area. Thus, this study aimed to investigate the vertical profile and assess the sediment quality from the deep-sea marine sediment around Simeulue Island based on metal concentration. Seventy-six bottom sediment samples were collected from eight cores at a water depth of up to 2800 m in the Simeulue waters, Indonesia, in November 2017. Metals Cd, Cu, Fe, Ni, Pb, and Zn were quantified from the cores and multivariate analyses were carried out to understand the process. Metals distributions are analogous to the grain size parameters and LOI550 distribution pattern, while Sumatra and Simeulue islands influenced grain size and LOI550 spatial distribution. The vertical grain size profile exhibited no extreme oscillation in the investigated cores. Thus, sediment transport from the Island was the main suspect for these metals' profiles in the deep water, and the tectonic activity had a minor impact. Cu, Ni, Pb, and Zn tend to rise in the collected cores, suggesting that the accumulation of the metals is growing. While Fe tended to be stable and Cd oscillated in the cores. Indices were computed to assess the metal contamination profile. The cores were dominated by EF class 1 (none to slight enrichment) status and Igeo class 1 (unpolluted). Cd was the metal of concern in the study since a high Cd was observed in some layers (maximum EF = 26.45 and maximum Igeo = 3.81). Thus, this study can be used as a database to improve the regulation formulation for improved environmental managerial efforts in the region.
•The Simeulue basin has higher Cd, Cu, Pb, Ni, and Zn levels in sediment than the deeper waters.•The vertical profile of metals fluctuated in the cores, with Cu, Pb, Ni, and Zn inclining.•The land sediment supply was the main suspect in the metal distribution pattern.•The distribution of metals was less affected by tectonic activity.•Cd was the metal of concern in this study, leading to degrading environmental condition.
The 2011 Tohoku-oki tsunami caused severe damage to the coastal regions of eastern Japan and left a sediment veneer over affected areas. We discuss differences in depositional characteristics of the ...2011 Tohoku-oki tsunami from the viewpoint of the sediment source, coastal topography and flow height. The study area on the Misawa coast, northern Tohoku, includes a 20km long coastline with sandy beaches, coastal dunes and a gently sloping lowland. This landscape assemblage provides an opportunity to examine the effects of topography on the characteristics of the tsunami deposit. During field surveys conducted from April 10 to May 2, 2011, we described the thickness, facies, and structure of the tsunami deposit. We also collected sand samples at approximately 20m intervals along 13 shore-perpendicular transects extending up to 550m inland, for grain size and mineral assemblage analysis. The tsunami flow height was estimated by measuring the elevation of debris found in trees, broken tree limbs, or water marks on buildings.
The nature of the coastal lowland affected the flow height and inundation distance. In the southern part of the study area, where there is a narrow, 100m wide low-lying coastal strip, the run-up height reached 10m on the landward terrace slopes. To the north, the maximum inundation reached 550m with a run-up height of 3.2m on the wider, low-lying coastal topography. The average flow height was 4–5m.
The tsunami eroded coastal dunes and formed small scarps along the coast. Immediately landward of the coastal dunes the tsunami deposit was more than 20cm thick, but thinned markedly inland from this point. Close to the dunes the deposit was composed largely of medium sand (1–2 Φ) with planar and parallel bedding, but with no apparent upward fining or coarsening. The grain size was similar to that of the coastal dune and we infer that the dunes were the local source material for the tsunami deposit at this point. The mineral assemblage of the tsunami deposit was dominated by orthopyroxene and clinopyroxene and was also similar to the dune and beach sand. At sites more than half the inundation distance inland, the thinner tsunami deposit consisted mainly of fine sand (2.375 Φ) with some upward fining. The difference in grain size and sedimentary characteristics was probably caused by differences in sediment transportation and depositional processes. We infer that the well-sorted, finer sediments were deposited out of suspension, whereas the relatively coarse sands were laid down from traction flows. The depositional characteristics of the 2011 Tohoku-oki tsunami deposit appeared to have been affected mainly by the coastal topography and the extent of erosion at any one point, as opposed to flow height.
► The tsunami run-up height and depositional features are affected by local topography. ► The tsunami deposit is thick only behind eroded dunes and decreases rapidly inland. ► The tsunami deposit originated from the coastal dunes. ► At coastal sites the sediment was deposited out of traction flow. ► At inland sites it was deposited out of suspension.
On 28 September 2018, a Mw 7.5 earthquake struck Sulawesi Island, soon followed by a destructive tsunami. This study provides a case history of tsunami deposition where submarine landslides or ...coastal collapses have contributed to and intensified tsunami generation. The sedimentary features resulting from this complex tsunami mechanism are not yet well understood. We surveyed tsunami deposits at six locations along the coastline of Palu Bay, in addition to measuring tsunami flow depth, run-up height, and inundation distance at each site. In general, the tsunami height was less than 8 m with a maximum inundation distance of 310 m. The tsunami deposits are thin with simple sedimentary structures such as fining upward sequences. These sedimentary characteristics are typical of tsunami deposits elsewhere around the world. This work is a preliminary study, in that numerical modeling including sediment transport has not been performed. Further work is needed to distinguish tsunamis with different source mechanisms.
The 22 December 2018 Anak Karakatau tsunami in Indonesia was a rare event in that few instrumental records existed of tsunamis generated by volcanic sources before this event. The tsunami, which left ...a death toll of 437, is of global importance as it provides opportunities to develop knowledge on generation, propagation and coastal effects of volcanic tsunamis. Here, we report results of field surveys along the coast of the Sunda Strait, Indonesia to study tsunami wave heights and coastal damage. We surveyed 29 locations and measured ranges of tsunami runup from 0.9 to 5.2 m, tsunami heights from 1.4 to 6.3 m, flow depths from 0.2 m to 3.0 m and inundation distances from 18 to 212 m. The largest tsunami heights and concentration of damage and fatalities occurred on the western shore of Java from Tanjung Lesung to Sumur. The largest cluster of fatalities occurred at Tanjung Lesung, where more than 50 people died while attending an outdoor music being held at the shoreline. The tsunami runup and tsunami height in Tanjung Lesung were 4.0 and 2.9–3.8 m, respectively. We believe this tragedy could have been avoided if the event organizers were more aware of the hazard posed by the Anak Krakatau volcano, as it had been actively erupting for several months prior to the tsunami, and simply moved the concert stage 100 m inland. Many of the locations surveyed demonstrated a similar pattern where the majority of casualties and destruction occurred within 100 m of the coast; in several locations, lives were saved where buildings were located at least this distance inland. The significant damage and numerous deaths which occurred in Sumur, despite the moderate tsunami height of 2.3–2.5 m, can be attributed to the extremely low-lying coastal land there. Flow depth in Sumur was 0.9–2.0 m. During our field surveys, nearly one year after the event, we noted that some of the damaged buildings were being rebuilt in the same locations just 10–30 m from the shoreline. We question this practice since the new buildings could be at the same tsunami risk as those damaged in the 2018 event.
The 220-km-long Palu–Koro Fault, Central Sulawesi, is a major fault with prominent expression in Eastern Indonesia. Many studies about the Palu–Koro Fault have shown its capability of generating ...large earthquakes, but how the Palu–Koro Fault has evolved remains enigmatic. This study is to investigate the geomorphology of NW Palu Valley based on DEMNAS (Digital Elevation Model of Indonesia) and field observations to understand the development of the Palu–Koro Fault. The study area comprises a high mountain in the west and a valley in the east. There are two major normal faults and a strike–slip fault observed in NW Palu Valley. The western normal fault is a basin-bounding fault, which marks the topographic break between mountain and valley. To the east, another normal fault is observed cutting the old alluvial fans and expressed by planar fault scarps. The strike–slip fault is observed within the basin and crosses the distal part alluvial fans. It is expressed by intra-basin ridges in places which are slightly uplifted from the adjacent surface. The surface rupture of the 2018 Mw 7.5 Palu earthquake in NW Palu Valley also shows left-lateral movement up to 4 m. We consider that the development of the Palu–Koro Fault in NW Palu Valley is characterized by toward-central-basin migration of faulting activity from basin-bounding fault to intra-basin fault.
The presence of foraminifera is one of the main criteria for identifying paleotsunami. However, many paleotsunami studies reported the absence of foraminifera, even in the very young paleotsunami ...layers. One possible contributing factor for such absence is the dissolution of the test after deposition (taphonomical process). To identify the type of environment in which the dissolution process is more susceptible and the type of foraminifera that is the most resistant to dissolution, this study mapped the distribution of foraminifera in paleotsunami layers of different ages deposited in different environments. This study shows that the dissolution process might have occurred in all environments, although dissolution in the peat environment is more effective than others. Many foraminifera are identified in the younger paleotsunami layers, while others can be found in the oldest paleotsunami layers. This indicates that some foraminifera are extremely prone to dissolution while others are very resistant. The results of this study are crucial in reducing the bias in using foraminifera for paleotsunami identification.
The 2010 Mentawai earthquake (magnitude 7.7) generated a destructive tsunami that caused more than 500 casualties in the Mentawai Islands, west of Sumatra, Indonesia. Seismological analyses indicate ...that this earthquake was an unusual “tsunami earthquake,” which produces much larger tsunamis than expected from the seismic magnitude. We carried out a field survey to measure tsunami heights and inundation distances, an inversion of tsunami waveforms to estimate the slip distribution on the fault, and inundation modeling to compare the measured and simulated tsunami heights. The measured tsunami heights at eight locations on the west coasts of North and South Pagai Island ranged from 2.5 to 9.3 m, but were mostly in the 4–7 m range. At three villages, the tsunami inundation extended more than 300 m. Interviews of local residents indicated that the earthquake ground shaking was less intense than during previous large earthquakes and did not cause any damage. Inversion of tsunami waveforms recorded at nine coastal tide gauges, a nearby GPS buoy, and a DART station indicated a large slip (maximum 6.1 m) on a shallower part of the fault near the trench axis, a distribution similar to other tsunami earthquakes. The total seismic moment estimated from tsunami waveform inversion was 1.0 × 10
21
Nm, which corresponded to M
w
7.9. Computed coastal tsunami heights from this tsunami source model using linear equations are similar to the measured tsunami heights. The inundation heights computed by using detailed bathymetry and topography data and nonlinear equations including inundation were smaller than the measured ones. This may have been partly due to the limited resolution and accuracy of publically available bathymetry and topography data. One-dimensional run-up computations using our surveyed topography profiles showed that the computed heights were roughly similar to the measured ones.
The Simeulue sub-basin is situated off north-western Sumatra between the outer arc and the mainlands. The sediment and geochemical element characteristics of basins are the important sedimentology ...variables to recognize the process of sediment deposition. However, the characteristics of the sediment and the geochemical elements in the Simeulue subbasin have not been well explained. This study aims to investigate the textural and geochemical elements characteristics of marine sediments and the distribution of these two variables to determine the sedimentary facies in the Simeulue sub-basin. Samples were taken from various depths in the sub-basin and collected during the 2017 Expedition of “Widya Nusantara” by using the “Baruna Jaya VIII” Research Vessel. The grain size trend analysis showed that the middle part of the basin was dominated by mud, while the edge of the basin near the island (mainland) was mostly dominated by coarser sediments. A geochemical element analysis was performed on each sample to observe the origin of the sediments. The results of these two analyses were subjected to multivariate statistics. This approach was selected because it is appropriate for determining the sedimentary facies and the depositional environments. Based on the multivariate analysis, the sedimentary facies in the Simeulue sub-basin was divided into five facies with similar sediment characteristics and depositional environments. These facies were deposited in the environment with low to medium energy.
We evaluated sediment sources of the 2011 Tohoku-Oki tsunami deposits along a 4500m inland transect from the central east Japan coast, using grain size, mineralogy and foraminifera analyses. The ...tsunami run-up height in our study area was 13 to 20m near the coastline, 1.4 to 2.8m in the middle of the valley and 1.3m around the inundation limit. The inundation distance was around 4800m. The deposits are composed of sand and mud and show a fining and thinning trend. Mineral composition of the tsunami deposits was similar to that of coastal dune and beach deposits, indicating that most of the tsunami sediment originated from there. A minor foraminifera population in the deposit (≤15 specimens per 5g of sample compared with ≥100 specimens per 1g for typical marine sediment) indicates that marine sediment source was not dominant. Topography played an important role in sediment transport process and deposit distribution. The run-up wave accelerated faster in concave topography, became more erosive, and resulted in a thin deposit in topographic lows. We infer that the deposits up to 2300m from the coastline were deposited by bedload and suspension, whereas suspension was responsible for deposits farther inland.
Previous studies suggested the multi-millennial scale changes of Australian-Indonesian monsoon (AIM) rainfall, but little is known about their mechanism. Here, AIM rainfall changes since the Last ...Deglaciation (~18 ka BP) are inferred from geochemical elemental ratios (terrigenous input) and palynological proxies (pollen and spores). Pollen and spores indicate drier Last Deglaciation (before ~11 ka BP) and wetter Holocene climates (after ~11 ka BP). Terrigenous input proxies infer three drier periods (i.e., before ~17, ~15–13.5, and 7–3 ka BP) and three wetter periods (i.e., ~17–15, ~13.5–7, and after ~3 ka BP) which represent the Australian-Indonesian summer monsoon (AISM) rainfall changes. Pollen and spores were highly responsive to temperature changes and showed less sensitivity to rainfall changes due to their wider source area, indicating their incompatibility as rainfall proxy. During the Last Deglaciation, AISM rainfall responded to high latitude climatic events related to the latitudinal shifts of the austral summer ITCZ. Sea level rise, solar activity, and orbitally-induced insolation were most likely the primary driver of AISM rainfall changes during the Holocene, but the driving mechanisms behind the latitudinal shifts of the austral summer ITCZ during this period are not yet understood.
PDF
