Geoelectrical Resistivity Research Articles

Integrated Very Low Frequency and Geoelectrical Resistivity Methods to Study Possibility Shallow Groundwater Pathway in Bedrock Area

Exploration of groundwater movement has a specific challenge in thick forest area and cover with the shallow hard rock. The use of active and passive geophysical method is needed for groundwater exploration. This study aims to explore the prospect of groundwater zone especially for the groundwater pathway in the area around the hot spring zone. Geoelectrical resistivity and very low frequency (VLF) methods were used with electrode spacing of 2 meter and reading stations of about 5 meter, respectively. The geoelectrical resistivity was carried out using the Wenner configuration in the sites around the hot spring. The results show that the VLF model indicates occurrence of the conductive zones at the depth of about 10 m. The geoelectrical resistivity data show the same pattern with the VLF image. These conductive zones which is appeared in the VLF model are indicating as the zone of groundwater water pathway from the source to the hot spring zones. The geoelectrical resistivity data also showed the same possibility of groundwater pathway.

Groundwater potential zones identification in Purwobinangun, Pakem, Sleman, D.I. Yogyakarta using vertical electrical sounding (VES)

Water is crucial part in tourism development. However, not all locations have good and accessible groundwater resources. Ngepring Vineyard in Purwobinangun Village, Pakem District, Sleman, Yogyakarta face this problem. Ngepring vineyard is a developing tourism area at southern mountainside of Merapi which is one of geotourism destination in Indonesia. In its development, there were obstacles to fulfill the water supply for tourism and locals’ daily use. This research aims to determine groundwater potential zone and recommend a drilling point for a new well. Geoelectric resistivity survey conducted to evaluate subsurface condition by measuring and interpretating rock resistivity properties. Schlumberger Vertical Electrical Soundings (VES) configuration used with a maximum spacing from the center point as far as 250 meters with three VES were measured in study area along two N-S profiles perpendicular to one E-W profile. As the results, there is a sand layer at approximately 80m depth interpreted as aquifer. This result can be used as a preliminary study used to determine potential location for a new water resource in Ngepring vineyard.

Identification of Seawater Intrusion in Kota Lama Semarang and Surrounding Based on Geoelectrical Resistivity Survey

Kota Lama Semarang is a tourism potential that causes a high demand for groundwater, which can cause seawater intrusion. Seawater intrusion can affect groundwater quality and soil conditions. This research aimed to determine the depth and distribution of seawater intrusion in the Kota Lama Semarang and surrounding. The research used electrical resistivity tomography (ERT) and vertical electrical sounding (VES). Geoelectrical resistivity surveyed consist of 4 ERT lines and 3 VES lines with a line length was 100 to 160 m. Lines were scattered north and south of the Kota Lama to determine the distribution of seawater intrusion. Inversion processing used Progress for VES and Res2DInv for ERT. The content of chloride as well in Kota Lama was measured as supporting data. At this location it was estimated that it has 3 layers: top soil, sand and sandy clay. The sand layer at a depth of 3 to 11 m was the layer affected by seawater intrusion. Seawater intrusion on the north side was higher than on the south side. This was indicated by the lower resistivity value of the groundwater layer on the north side. The resistivity value of the groundwater layer on the north side was 0.96 Ωm while the south side was 3.76 Ωm. This result was appropriate to the chloride content which indicates a higher concentration on the north side of the Kota Lama Semarang.

Investigation of Aquifer Zone in Tambakromo Village, Ponjong Subdistrict, Gunung Kidul Regency, Yogyakarta, Indonesia

The presence of surface water is always being a primary issue in Gunung Kidul regency. An aquifer investigation would support groundwater exploration. The research area is located in Tambakromo village, Ponjong subdistrict, Gunung Kidul Regency, Daerah Istimewa Yogyakarta Province. The aim of this research is about geological and subsurface conditions based on geological data and geoelectrical resistivity methods. By resistivity value interpretation, the position, depth, and thickness of aquifer could be determined. The purpose of this research is to identification of geological conditions that supported being aquifer rock. The method in this research is used geological mapping combined with petrographic analysis. The geophysics method is used to identification of aquifer in research area. Three locations were selected to acquisition geoelectrical resistivity survey. In Grogol village, there is no aquifer based on resistivity values of more than 10000 ohmmeters (andesitic breccia). An akuifuge is interpreted there in andesitic breccia instead of the presence of aquifer. The tuffaceous is interpreted as lapillistone that contained the glass with resistivity value of 43.63 and 340.11 ohmmeters. The Garon and Sumberejo village have aquifer at depth of 50 to 80 meters with a thickness of 13 to 70 meters. The type of aquifer in both area is included an unconfined aquifer, specifically located in between the limestone rock layer and andesitic breccia. By regional stratigraphic correlation, tuffaceous lapillistone is interpreted as derived from Semilir Formation. In addition, the presence of aquifer in research area could recommend for local people and government to reduce the drought disaster.

Hydrogeophysical Study of Sub-Basaltic Alluvial Aquifer in the Southern Part of Al-Madinah Al-Munawarah, Saudi Arabia

Groundwater is extremely important in a water-scarce country such as Saudi Arabia, where permanent surface water resources are absent. Sustainable and future developments plans are essentially relying on the clear understanding of water resources. To evaluate the water resources in arid countries, the groundwater should be quantified through either traditional or scientifically advanced techniques. Aquifer characteristics, particularly the hydraulic conductivity and transmissivity, are essential for the evaluation the aquifer properties as well as the management and development of groundwater modelling for specific aquifers. The present study aims to evaluate the sub-basaltic alluvial aquifer in the northern part of Harrat Rahat, south of Al-Madinah city, and then estimates the principal aquifer’s hydraulic parameters based on the interpreted 1D resistivity-depth models along the study area. For that, 49 Vertical Electrical Soundings (VES’s) utilizing a Schlumberger electrode array were performed along the southern part of Al-Madinah city. The resistivity of the water-bearing formation, thickness, porosity, hydraulic conductivity, and transmissivity parameters were calculated along the measured longitudinal profile from the interpreted VES data. The estimated porosity, hydraulic conductivity, and transmissivity were achieved along the whole profile with average values of 0.2, 3.5 m/day, and 369.6 m2/day, respectively. The resulting transmissivity values from the VES models were compared with those of previous pumping test measurements carried out in the area and a reasonable correlation between the two data sets was observed. These results indicate that surface geoelectrical resistivity techniques may provide an alternative, rapid, and cost-effective method of estimating the aquifer hydraulic parameters where pumping data is rare or unavailable.

High-resolution electrical resistivity tomography and seismic refraction for groundwater exploration in fracture hard rocks: A case study in Kanthan, Perak, Malaysia

• High-resolution ERT and seismic results were validated by tube-well drillings. • Sharp vertical boundary between high and low resistivity zones indicates fault zone. • Depression zone in seismic refraction depth profile indicates highly fractured rock. • DLS method of Wenner-Schlumberger + dipole–dipole arrays are the most effective. • Groundwater source is discovered at the intersection of major discontinuities . This research article describes the integration of high-resolution electrical resistivity tomography (ERT) and seismic refraction to explore potential groundwater in fracture carbonate hard rocks. Data Levels Synthesization (DLS) method is developed where the data levels of two different optimized arrays were merged to produce one final subsurface resistivity image to achieve high-resolution ERT. Numerical modeling was initially conducted on three different geoelectrical arrays. The results of before and after applied DLS method were compared to evaluate the effectiveness of each geoelectrical array to delineate fracture and anomalies accurately. Lineament map is constructed beforehand to map the major discontinuities which could possibly be the potential target for water-containing and water-conducting zones in the subsurface. Two geophysical survey lines were conducted where each survey line covered both ERT and seismic refraction methods. Two tube wells were successfully drilled exactly on the fracture zone with a flow rate around 1000 L/h. The potential water-containing zones within the subsurface limestone bedrock were identified as zones of low to moderate geoelectrical resistivity values ranging from 10 to 400 Ωm and V p velocities exceeding 2000 ms −1 . The fault zones were determined by sharp vertical boundary between the high and low resistivities zones in ERT image and lateral decrease in the V p velocities of the limestone bedrock and depressions along the overburden-bedrock interface. The DLS method of Wenner-Schlumberger and dipole–dipole arrays had been proven effective in enhancing the horizontal and vertical resolutions to produce high-resolution ERT image validated with seismic refraction, lineament map, and tube well drillings.

Sea Water Intrusion Monitoring on the Sendangbiru of the Southern Malang Coastal Area based on Geoelectrical Resistivity Data

The study was conducted with the objective to distinguish the presence of seawater intrusion layer or salt-water aquifer distribution along the data acquisition line at the locations. Data acquisition was conducted by using the Wenner-Schumberger configuration of geoelectrical resistivity. From this research, 4 lines and 4 points of vertical electrical sounding (VES) data for every line were obtained with the distance between electrode a as 10m. Based on the data processing, obtained depth up to 120m with the smallest resistivity value is 0.02Ωm and the largest is 6764.52Ωm. To make the distribution of resistivity values along the path line of the study, cross sections were made until a depth of 120m. Based on the cross-section, the low resistivity value (less than 1.5 Ωm) that interpreted as a seawater intrusion layer or salt water aquifer distribution is located at varying depths. There are intrusions for the SB1 cross section, there is an intrusion at a depth of 6m-7m as far as 10m, at a depth of 6m-8m as far as 10m for the SB2 cross section and at a depth of 22m - 26m as far as 25m for the SB3 cross section.

Delineation of shallow groundwater potential zones using integrated hydrogeophysical and topographic analyses, western Saudi Arabia

Groundwater potentiality mapping is currently receiving more attention, particularly in arid regions, where natural freshwater resources are limited and scarce and instead costly unconventional methods such as seawater desalination are widely used to satisfy water demands. Water demand in Makkah city is considered a vital task, which receives millions of visitors every year for religious purposes. The present study evaluates the potential zones of groundwater in the southwest Makkah city applying hydrogeophysical modeling approach that integrates geoelectrical resistivity in form of vertical electrical sounding (VES), ground-penetrating radar (GPR), and topographic analyses. VES results indicate five main geoelectric layers: (1) dry wadi-fill deposits with a true resistivity varying from 73 to 650 Ohm.m and average thickness of 3.14 m, (2) partially saturated sands with a resistivity range between 19 and 43 Ohm.m and average thickness of 13 m, (3) water-bearing layer of saturated sands with a resistivity range between 55 and 110 Ohm.m, and average thickness of 52 m, (4) highly fractured diorite rocks with resistivity values ranging from 750 to 1450 Ohm.m and average thickness of 1.5 m, and (5) fresh diorite basement rocks with a resistivity of more than 4000 Ohm.m. Results of GPR profiles support the gained results of the VES technique, and together they are confirmed by the wells data. The integrated results suggest a structural control on the groundwater accumulation and call for a detailed mapping of alluvium-covered faults to provide a high-resolution mapping of groundwater occurrences and ensure environmental sustainability in southwest Makkah city.

Geoelectrical Exploration of Groundwater by Using Vertical Electrical Sounding Technique at Wadi Morra, South Sinai, Egypt

Wadi Morra area is one of the most important areas targeted by the government for sustainable development. This development depends mainly on groundwater occurrences. This research aims to explore groundwater in this region, which depends on groundwater for its needs. To achieve this aim, the geoelectrical resistivity method was used, represented by Schlumberger Vertical Electrical Soundings (VESs). Seventeen VESs have been carried out with a maximum half current electrode spacing (AB/2) of 700m. The measured VESs are interpreted qualitatively and quantitatively to construct a geoelectrical model. To detect the water-bearing layers and their extensions, three geoelectric cross-sections in addition to a one-panel diagram were constructed using all the available data. Also, both true resistivity and isopach contour maps of waterbearing layers were created based on these data. The interpretation results indicate that there are five geoelectric layers (A, B, C, D, and E), two of them (C and D) are water-bearing layers. The first water-bearing layer is layer C, which represents the Nubian sandstone aquifer, and the second layer is layer D, which represents the fractured basement aquifer. These two aquifers were observed along the northern part of the Saint Catherine - Nuweiba road that dissects the Wadi Morra basin, while it is absent at the southern part of this road. It is due to the presence of a few faults. According to groundwater occurrences, the study area was divided into two zones. The first zone is zone (A) where the groundwater is present, either in the Nubian sandstone aquifer or in the fractured basement aquifer and the second zone is zone (B) where there is no groundwater at all due to the presence of basement rocks at a few depths. This research also recommends that the best places for drilling productive wells be at zone A.

Gravity Analysis for Subsurface Characterization and Depth Estimation of Muda River Basin, Kedah, Peninsular Malaysia

Gravity survey is one of the passive geophysical techniques commonly used to delineate geological formations, especially in determining basement rock and the overlying deposit. Geologically, the study area is made up of thick quaternary alluvium deposited on top of the older basement rock. The Muda River basin constitutes, approximately, of more than 300 m of thick quaternary alluvium overlying the unknown basement rock type. Previous studies, including drilling and geo-electrical resistivity surveys, were conducted in the area but none of them managed to conclusively determine the basement rock type and depth precisely. Hence, a regional gravity survey was conducted to determine the thickness of the quaternary sediments prior to assessing the sustainability of the Muda River basin. Gravity readings were made at 347 gravity stations spaced at 3–5 km intervals using Scintrex CG-3 covering an area and a perimeter of 9000 km2 and 730 km, respectively. The gravity data were then conventionally reduced for drift, free air, latitude, Bouguer, and terrain corrections. These data were then consequently analyzed to generate Bouguer, regional and total horizontal derivative (THD) anomaly maps for qualitative and quantitative interpretations. The Bouguer gravity anomaly map shows low gravity values in the north-eastern part of the study area interpreted as representing the Main Range granitic body, while relatively higher gravity values observed in the south-western part are interpreted as representing sedimentary rocks of Semanggol and Mahang formations. Patterns observed in the THD anomaly and Euler deconvolution maps closely resembled the presence of structural features such as fault lineaments dominantly trending along NW-SE and NE-SW like the trends of topographic lineaments in the study area. Based on power spectral analysis of the gravity data, the average depth of shallow body, representing alluvium, and deep body, representing underlying rock formations, are 0.5 km and 1.2 km, respectively. The thickness of Quaternary sediment and the depth of sedimentary formation can be more precisely estimated by other geophysical techniques such as the seismic reflection survey.

Pendugaan sebaran intrusi air laut melalui sungai di desa Ujungmanik kecamatan Kawunganten kabupaten Cilacap menggunakan metode geolistrik resistivitas konfigurasi Wenner

The estimation of the distribution of the sea water intrusion through the rivers in Ujungmanik Village, Kawunganten District, Cilacap Regency has been carried out using the Wenner configuration resistivity geoelectric. This research aims to estimate the distribution of sea water intrusion through rivers in Ujungmanik Village, Kawunganten District, Cilacap Regency based on geoelectric resistivity and conductivity data of groundwater. The geoelectric data acquisition was carried out on four lines. They were Wen1 Line, Wen2 Line, Wen3 Line, and Wen4 Line. Each line had a range of 200 meters. The results of geoelectric data processing showed that the subsurface rock structure consisted of sand, clay, sandy loam, and sandy clay. The Seawater intrusion shown by the sand layer occurred in all trajectories which had a range of resistivity value of 0.20 - 2.79 Ωm. Groundwater samples was carried out at fifteen points with the conductivity value varies between 1363 - 4145 µS / cm so that they can be classified that the water was fresh and brackish due to the sampling done in the rainy season. From this research it can be implied that the entire Ujungmanik area is evenly intruded by the sea water at the coordinates 7º38ꞌ15.62ꞌꞌLS 108°57ꞌ20.89ꞌꞌBT to 7º39ꞌ22.86ꞌꞌLS 108º56ꞌ35.33ꞌꞌBT.

Integrated survey to identify potential groundwater aquifers in Jabungan Semarang using geoelectric and microtremor methods

The morphology of the Jabungan Village area has relatively steep land conditions. In lithology, this area has a layer of soil composed of sandstone, claystone, and limestone. Based on direct observations in the field, it was found difficult to obtain clean water that could be used for consumption. The water available and used by the majority of residents is shallow well water, which is not of very good quality. There is only one deep well with a depth of 68 meters but according to residents, the water that is channeled to these houses smells unpleasant and feels oily. To detect the potential of ground water in this area, the geoelectric method is integrated using the microtremor method. Geoelectric measurements were made at 3 location points while microtremor measurements were carried out at 9 location points. Based on geoelectric resistivity and microtremor measurements, it can be concluded that the potential of subsurface water sources is below the JAB3 path or near Point 9 microtremor with soil layers composed of sand layers with resistivity values of 0.43-4.64 ohm-meter at depth > 70 meters with Vs value of 840 m/s with a Poisson’s ratio value > 0.3, the more eastward the greater the value.

Geoelectrical and Geotechnical Characterization of Different Types of Soil in Ede, Osun State, Nigeria

Geoelectrical and geotechnical investigations were carried out to characterize soils from different locations in Ede, Osun State, Nigeria for engineering purposes. Wenner electrode configuration technique was deployed in carrying out the geoelectrical survey of about 40m for each profile. The data analysis was approached by plotting the apparent conductivity against electrode spacing (s) and the result was interpreted. The geoelectrical resistivity survey revealed locations 1 and 2 with resistivity values of 25.01-419.22ohm-m (conductivity 0.002 - 0.194 (ohm-m)-1and 5.5-1246.57 ohm-m (conductivity = 0.0002 - 0.001 (ohm-m)-1) respectively could be classified as clay. Sample 3 recorded a resistivity value of 1.00- 22,787.39 ohm-m (conductivity= 0.00004- 1.00 (ohm-m)-1) thus, was classified as silt/sand respectively. Soil from the said different locations in Ede, Nigeria, were tested in the Laboratory for certain properties like Atterberg limits, specific gravities, sieve analysis, compaction test, etc and the results showed that samples 1, 2 and 3 have specific gravity values of 2.50, 2.13 and 2.40 respectively and could therefore be referred to as organic soil. Samples 1, 2 and 3 have maximum dry density (MDD) of 1.45g/cm3­, 1.92g/cm3, 1.95g/cm3 and optimum moisture content (OMC) of 15.40%, 13.36% and 9.61% respectively. The analysis conducted in this study revealed that the soil type found in Ede, Nigeria could be classified as silt-clay, sandy clay, clay and sand.Keywords- Electrical conductivity, Characterization, Compaction, Plasticity, Wenner array.

Application of Vertical Electrical Sounding for Groundwater Investigation in the Premises of the Sabaragamuwa University of Sri Lanka

Growing social, as well as development activities in the premises of Sabaragamuwa University of Sri Lanka (SUSL) and its surroundings, have reformed the natural landscape of the area. Consequently, water demand is increasing. Therefore, an understanding of the subsurface geology and their potential as beneficial aquifers help to overcome the impending water demand because surface water scares in the area. In view of assessing the groundwater potential of the area, an initial study was conducted using topographic and satellite maps followed by a geo-electrical resistivity survey, consisting of vertical electrical sounding (VES) and electrical profiling. Results revealed three subsurface layers in most places. The resistivity of the topsoil layer is ranging between about 50 to 2800 Ωm and the average thickness between 1 m to 15 m. The second layer is characterized by resistivity between about 16 to 9760 Ωm. The resistivity of the third layer ranges from about 2 to 5600 Ωm, and extending to a depth of more than 100 m. Most of the curves were identified as K type. The rest of the curves were H, Q, and A types. Out of 18 VES points, nine locations were identified as possible locations for groundwater abstraction. Groundwater could be located at a depth of between 25 to 60 m. Resistivity data indicate that the regolith mostly forms the aquifers in the area along with some weathered rock aquifers at depth. Most of the points close to or at valleys were found to be deep aquifers. Considering all the geological, structural, and morphological features, nine locations were identified as most convincing and could be recommended for test drilling.

Nature Inspired Bargain Optimization Algorithm for Effective Interpretation of Geoelectrical Data

Geoelectrical resistivity data collected from the ground contain lot of noises and errors. It requires efficient algorithm to reduce the errors to make an actual inversion models. Though different algorithm can be applied, nature inspired algorithm is more potential in inverting geoelectrical data in an elegant and comprehensive way. Bargain Optimization (BO) algorithm is framed on the concept of bargaining things to purchase for needs. In general, effective bargaining results in more profit and leads to loss when it fails. In this research work, Bargain Optimization algorithm is applied to invert geoelectrical data and the effective bargaining will take time to process and to obtain the required model. The input data is AB/2, apparent resistivity data and the inverted model through BO algorithm is successfully matched with the available litholog section of the study area. The output graphs have profit/loss bar graph, which reveals the status of bargaining during a particular number of epochs.

GEOPHYSICAL INVESTIGATION OF GROUNDWATER POTENTIAL OF A SITE IN OBALE AREA OF AKURE, NIGERIA.

Electrical Resistivity method using Vertical Electrical Soundings (VES) were carried out at a site in Aba-Oyo area FUTA Southgate area, Akure, Nigeria, with the aim to access groundwater potential of the site. The study area is underlain by crystalline rocks of the Precambrian basement complex of the Southwestern Nigeria. Twelve (12) VES were carried out using Schlumberger electrode array configuration with AB/2from 1 to 65m. The VES data generated were processed and interpreted using partial curve matching method and computer iteration techniques. The interpreted data revealed three to four geoelectric sections with varied thicknesses and resistivity. The top soil layer ranges from 44 to 181?m, lateritic clay layer ranges from 20 to 174?m, the weathered horizon resistivity ranges from 20.0 to 424.0?m while the competent rock/fresh rock has resistivity values greater than 424.0.3?m. The top soil layer resistivity and thickness ranges from 44 to 181?m and 0.4 to 2m, the lateritic clay layer resistivity and thickness range from 20 to 174?m and 1.7 to 6.0m respectively, the weathered horizon resistivity ranges from 20.0 to 424.0?m and 1.4 to 7.4m respectively while the competent rock has resistivity values greater than 424.0?m and ?m respectively. The third geoelectric layer constitutes the aquiferous zone in the 4-layer geoelectric section while the second geoelectric layer is the aquiferous zone in all the 3- layer geoelectric sections. VES station 2, 7, 9 stations shows good groundwater potential as revealed by the thick overburden and weathered layer with low resistivity values. VES stations 1, 4, 5, 6, 8, 10 and 12 shows moderate groundwater potentials while VES stations 3 and 11 are non-aquifereous in nature.

KAJIAN GEOLOGI UNTUK MENENTUKAN AIR TANAH DAERAH SAMBIREJO, KECAMATAN PRAMBANAN, KABUPATEN SLEMAN, YOGYAKARTA

Daerah Sambirejo, Kecamatan Prambanan, Kabupaten Sleman merupakan salah satu daerah sulit air berdasarkan kenampakan morfologi berupa perbukitan. Berdasarkan kejadian geologi disuatu daerah memiliki produk yang berbeda satu dengan yang lain. Produk geologi tersebut berupa morfologi, litologi dan genesis, sehingga berdampak pada pengaruh air tanah. Bertambahnya jumlah penduduk sangat berpengaruh pada kebutuhan air secara besar perhari. Daerah yang terindentifikasi kekurangan air, sehingga penting diketahui sebagai dasar untuk mengetahui daerah yang perlu dikaji lebih detail sebagai dasar eksploitasi air tanah dalam dan air bawah permukaan. Penelitian ini bertujuan untuk mengidentifikasi potensi air tanah di daerah Sambirejo. Masalah dalam penelitian ini adalah bagaimana menetukan daerah potensi air tanah yang berkwalitas dan bermafaat untuk memenuhi kebutuhan air baku pada masyarakat.Pemanfaatan air bawah permukaan sangat di perlukan untuk mendapatkan potensi yang besar dan dapat segera dimanfaatkan oleh masyarakat. Penelitian ini dilakukan dengan metode berupa pemetaan geologi untuk menentukan sebaran litologi dan pengukuran geofisika berupa pengukuran geolistrik untuk menentukan daerah potensi air tanah yang berada pada morfologi lereng dan pungungan. Berdasarkan dari hasil geolistrik keberadaan air tanah terdapat pada kedalaman 20-40 meter yang dikatagorikan dangkal sedangkan pada kedalaman 98-142 meter yang di katagorikan sebagai akuifer hampir dalam. Jenis akuifer yang berkembang pada daerah Sambirejo yaitu akuifer setengah tertekan (leaky unconfined aquifer) dimana batuan breksi pumice pada bagian bawahnya terdapat lapisan kedap air berupa tuff.
 Kata kunci: Aquifer, litologi, Air bersih, Sambirejo

Identification of seawater intrusion using geoelectrical resistivity method in the Goa Cina Beach Malang Area, Indonesia

Seawater intrusion can cause groundwater that is looked fresh initially but becomes brackish and even salty. It makes decreasing the quality of groundwater in the area. The Goa Cina Beach, Malang has a geological structure of rock in limestone, sand, and gravel. These rocks have greater porosity, so that the potential to pass water or water infiltration is also quite large, both freshwater and saltwater. Starting from these problems, it is needed to identify groundwater distribution that is not affected by the seawater intrusion process. The geoelectric method effectively determines geological parameters such as depth of bedrock, minerals, fluids, and shallow exploration to identify groundwater aquifers. Data acquisition was carried out using the geoelectrical resistivity method with Wenner configuration with three measurement points. Furthermore, the data processing used Res2dinv Software. The results showed that the measured resistivity value between 0.01000-501 Ωm with a maximum depth of 19.9 meters. The seawater intrusion distribution is assumed to be on lines 1 and 2 at an average depth of 10-19.9 meters with a resistivity value of 0.01000-0.230 Ωm. At the same time, the area that is not expected to experience seawater intrusion is on Line 3. The making of wells for coastal areas needs to consider the distance from the shoreline and rock porosity for minimizing the potential for seawater intrusion.

SEBARAN AIR TANAH MENGGUNAKAN METODE GEOLISTRIK RESISTIVITAS KONFIGURASI DIPOLE-DIPOLE

This research has been worked in the Graha Mustamindo Permai 3 Housing area, Rimba Panjang Village, Tambang District. This research been thorough to calculate the value of measured rock resistivity in Graha Mustamindo Permai 3 Housing and analyze rock layer types through rock resistivity values at Sepakat street, Rimba Panjang, Riau. The method using in this research is geoelectric resistivity of the Dipole-dipole configuration, two lanes with the same length of 100 meters are used and spacing between electrodes is 7 meters. The data obtained were processed using Res2Dinv software version 3.54.44. The data result that obtained show two differences trajectories in Rimba Panjang Village has varying resistivity, namely in the first lane around 1.595 Ωm to 2,762 Ωm and in the second lane 1.594 Ωm to 5,879 Ωm. Groundwater potential in the first and second lanes is quite large and is thought to be in a free aquifer so that it is easy to drill.

Buoyant calving and ice-contact lake evolution at Pasterze Glacier (Austria) in the period 1998–2019

Abstract. Rapid growth of proglacial lakes in the current warming climate can pose significant outburst flood hazards, increase rates of ice mass loss, and alter the dynamic state of glaciers. We studied the nature and rate of proglacial lake evolution at Pasterze Glacier (Austria) in the period 1998–2019 using different remote-sensing (photogrammetry, laser scanning) and fieldwork-based (global navigation satellite system – GNSS, time-lapse photography, geoelectrical resistivity tomography – ERT, and bathymetry) data. Glacier thinning below the spillway level and glacier recession caused flooding of the glacier, initially forming a glacier-lateral to supraglacial lake with subaerial and subaquatic debris-covered dead-ice bodies. The observed lake size increase in 1998–2019 followed an exponential curve (1998 – 1900 m2, 2019 – 304 000 m2). ERT data from 2015 to 2019 revealed widespread existence of massive dead-ice bodies exceeding 25 m in thickness near the lake shore. Several large-scale and rapidly occurring buoyant calving events were detected in the 48 m deep basin by time-lapse photography, indicating that buoyant calving is a crucial process for the fast lake expansion. Estimations of the ice volume losses by buoyant calving and by subaerial ablation at a 0.35 km2 large lake-proximal section of the glacier reveal comparable values for both processes (ca. 1×106 m3) for the period August 2018 to August 2019. We identified a sequence of processes: glacier recession into a basin and glacier thinning below the spillway level; glacio-fluvial sedimentation in the glacial–proglacial transition zone covering dead ice; initial formation and accelerating enlargement of a glacier-lateral to supraglacial lake by ablation of glacier ice and debris-covered dead ice forming thermokarst features; increase in hydrostatic disequilibrium leading to destabilization of ice at the lake bottom or at the near-shore causing fracturing, tilting, disintegration, or emergence of new icebergs due to buoyant calving; and gradual melting of icebergs along with iceberg capsizing events. We conclude that buoyant calving, previously not reported from the European Alps, might play an important role at alpine glaciers in the future as many glaciers are expected to recede into valley or cirque overdeepenings.