Northern part of Lombok island has a unique geological phenomenon of submarine groundwater discharge. Submarine groundwater discharge needs to be conserved for its sustainability. This study asseses ...groundwater vulnerability for SGD conservation in the northern part of Lombok Island Indonesia. The assessment was conducted using aquifer vulnerability index methods. Vulnerability index value in the study area is high vulnerability index. This vulnerability index is getting higher toward the coast. The layer is tuffaceous pumice layer with a hydraulic conductivity value of 5 m/day. This layer makes the aquifer in the study area very vulnerable to contamination, especially for pollution involving vertical percolation and infiltration. Protective management is needed to prevent groundwater hazard in the research location due to groundwater pollution and heavy pumping. Anthropogenic activity at the study area should be anticipated because of the high index of aquifer susceptibility at the study area.
Small islands are often promoted as a tourism destination in spite of the limited fresh water resources availability that they could retain for daily needs. In this context, efforts to provide fresh ...water resources sustainable in the small island are necessary to support the tourism destination purpose. This study aims to estimate the carrying capacity of the fresh water resources in Pari Island. The estimation method is the ratio between the fresh water availability and its demand by calculating the island size, aquifer thickness, annual rainfall, hydraulic conductivity or soil permeability, and the application of rainwater harvesting technology (RHT). The result shows that the carrying capacity of the fresh water resources without technological intervention in Pari Island is 2.05. Even though this score indicates the safe level, the measure has not taken the water quality into consideration yet. Expectedly, it could be improved by applying the RHT technology but it results in the carrying capacity score of 1.37 and 1.47 (conditionally safe) for the current state and 25-year future prediction respectively. This study recommends the improvements in tourism management by limiting the visitor number in order to support their sustainability for the local livelihood and Pari Island’s ecosystem conservation.
Lembang groundwater basin has an area of 209 km
2
. Increased tourism activities in the Lembang Groundwater Basin require sufficient groundwater resources to support the sustainability of these ...tourism activities. The purpose of this study was to analyze the hydrostratigraphy of the groundwater recharge zone of the Lembang groundwater basin in the Cikole-Lembang. Electrical Resistivity Tomography (ERT) with dipole–dipole electrode array and seismic refraction was used to analyze the hydrostratigraphy. The results of ERT and seismic refraction inversion show that Tangkubanparahu Pyroclastic Fall 2 can be characterized as aquifers. This layer consists of low (123–292
Ω
m) and intermediate (293–700
Ω
m) resistivity value and also has low (300–1350 m/s) to medium (2700–1350 m/s) velocity. Tangkubanparahu lava (Tl) layer has a high resistivity value (701–3875
Ω
m) and high (1350–2999 m/s) velocity. The Tangkubanparahu Pyroclastic Fall 1 has a resistivity of 300–700 ohms. Tangkubanparahu (Tl) lava deposits can be characterized as fracture aquifer and impermeable layers in the Tangkubanparahu volcanic hydrogeological system depend on the historical structural geology event.
In recent years, dozen low-intensity earthquakes occurred in southern Garut, West Java Indonesia; two of them were reported destructive. However, those shallow earthquake clusters are hardly ...associated with well-known active faults in the area. Hence, we conducted 3D gravity combined with 2D magnetotellurics (MT) inversions to study the subsurface. Gravity and MT modeling confirm a basin with around 5 km depth consisting of two subbasins separated by a NE-SW trending local-high ridge. The local high coincides with the magmatic intrusion in geothermal fields and aligns with a series of volcanic bodies’ lineament observed on the surface. We interpret this structural high as a preexisting fault that serves as a magma pathway in the tectonomagmatic interaction. Shallow low-magnitude seismicity in the southern Garut area tends to occur in the resistive bodies. We interpret that heat from the cooling magmatic intrusion may decrease the effective fault-normal stress of the rocks, leading to a decrease in fault failure resistance and may initiate rupture. The resistivity structure around the initial rupture may affect whether or not the nucleation will end up as a large-magnitude earthquake. Furthermore, the unconsolidated young volcanic cover in this area could amplify ground shaking when earthquake occurs that might lead to more extensive damage.
DOI: 10.17014/ijog.4.1.39-47The characteristic of Cimandiri Fault Zone has not been completely defined despite plenty of studies had already been accomplished. Therefore, an audio-magnetotelluric ...modeling was carried out. An audiomagnetotelluric survey was conducted at two parallel lines (N166oE) that intersected Cimandiri Fault Zone in Cibeber area, Cianjur. The distance between those two lines was 4.5 km and each line consisted of twenty-one stations with the distance between stations was 500 m. From the acquired forty-two apparent resistivity curves, inversion was executed to obtain two models. The models indicate layers with resistivity value of > 1000 ohm.m at about 500 m depth at both lines, which are associated to the basement layer. Columns of low resistivity zones in about the middle of each model represent fault zones as the weak zones of the area, and both models displayed them slightly dip southward as thrust faults.
A detailed study had been conducted on the sediment of Mount Samalas’ volcanic eruption in 1257 AD. Using the framework of the reconstruction of the ancient eruption of Mount Samalas, the first step ...was to map and analyze the deposits of volcanic sediment. Secondly, we analyzed the effect of geomorphology and the distance function to the isopach thickness. The results show that a combination of methods allowed to provide a high resolution map of the distribution of the thickness of the volcanic deposits, both on the slope and in alluvial areas. Geo-electric survey results (both Vertical Electric Sound (VES) and 2D mapping) show consistent changes in the pattern of contrast resistivity layer interface, for all areas. The pattern changes in a row of the top layer, the high resistivity turned into the low. Furthermore, the second and third layer interface changes from low to the high resistivity. High resistivity on the top layer is interpreted as a layer of unconsolidated volcanic sediment. High resistivity values are range from 736 to 2000 Ohm.m on the top layer in the area of the slopes while in the area of alluvial, the resistivity values range from 20 to 958 Ohm.m. Generally, the volcanic deposits in the area of the slopes have a higher value of isopach (>17 m) than in areas of alluvial (<25 m). The geomorphology seemed to have no significant effect on the isopach value, particularly pyroclastic fallout. Such is the case with distance from the source to the site, which is not linear. The value of isopach increases westward from 21 to 31 km, in contrast to the East, which began to occur at a distance of 14 km to 21 km.
The 1257 CE eruption of Samalas volcano, Indonesia, buried the entire island of Lombok beneath various thicknesses of pyroclastic material during this Volcanic Explosivity Index (VEI) 7 event. This ...study aims to reconstruct the paleo‐topography of western Lombok before the Samalas eruption in 1257 CE and analyse the sedimentation processes that led to its landscape evolution over the last 700 years. Stratigraphic data were collected from various surveys, such as outcrops, coring, drilling, hand auger and wells observation. Electrical resistivity tomography (ERT) measurements were performed to complement the stratigraphic data. A combination of stratigraphy, ERT and topographic data from various sources (topographic map, Digital Elevation Model Nasional DEMNAS and Real Time Kinematic RTK measurement) is employed to determine the depth of the paleo‐surface. Topographic modelling was performed by subtracting the delta‐DEM (DDEM) from the current‐DEM (CDEM). The result of this operation is a paleo‐DEM, which is used to reconstruct the paleo‐hydrographic features such as shoreline positions and river channels. Modelling results demonstrate that the relief has not been significantly modified, except in lowland areas, which is the sediment accumulation zone. River channels have experienced minor changes, except for the location of the river mouth and the degree of meandering. Significant changes occurred at the shoreline that has prograded by approximately 1.6 km during the last 700 years. A schematic model is built to illustrate the evolution processes of the study area, consisting of the pre‐eruption condition, the immediate post‐eruption condition and development of the current condition. This model further develops the previously proposed model with a higher resolution and simultaneously revises the estimated boundary of the pyroclastic density current (PDC) deposit from previous work.
We present an interpretation of newly acquired audio-magnetotelluric data to reveal the subsurface geometry of Cimandiri Fault Zone, one of the major active faults in the western part of Java. The ...line section is 25 km long in a nearly north–south direction across the axes of CFZ with 24 stations of 750–1200 m spacing intervals. The 2D AMT inversion model shows two conductive zones in the southern part that may be associated to the Miocene rocks of the Southern Mountains, and a conductive zone in the northern part that is likely to be associated with Gunung Walat fold-belt. The subsurface structures of the Southern Mountains are dominated by south-dipping thrusts that may uplift the shallow marine sediments. Shallow seismicity occurred around CFZ indicating the activity of these blind thrusts.
Abstract
The morphology of the Karangsambung area shows a unique form, namely the morphology of the amphitheater. This area results from the complexity of tectonic, erosion, and depositional ...processes. The active tectonics in this region greatly influence the drainage system and geomorphic expression. The study area provides evidence of subduction in Java. It is an ideal natural laboratory for studying evidence of tectonic activity due to the subduction of the Indo-Australian plate with the Eurasian plate during the Cretaceous period. We evaluated active tectonics using the DEM to assess the characteristics of the geomorphic index. The results obtained from these indices were combined to produce an index of relative active tectonics (IRAT) using GIS. The average of the seven geomorphic indices measured was used to evaluate the distribution of relative tectonic activity in the study area. We defined four classes to determine the relative level of tectonic activity: class 1: very high (1.0 ≤ IRAT < 1.5); class 2: high (1.5 ≥ IRAT < 2); grade 3: moderate (2 ≥ IRAT < 2.5); and grade 4: low (2.5 ≥ IRAT). The results show that the study area was strongly deformed and was influenced by tectonic activity. Landsat imagery, DEM, and field observations also proved the presence of active tectonics in the form of uplift accompanied by high vertical erosion forming pointed hills with narrow valleys, the exposure of Cretaceous-aged rocks, amphitheater morphology, and the uplift of river terraces. The indicative IRAT values were consistent with the relative uplift levels, landforms, and geology.
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