Subaerial morphology affected by groundwater aggressiveness: Sinkhole susceptibility above karstified salt, Dead Sea (original) (raw)
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The Dead Sea sinkhole hazard - new findings based on a multidisciplinary geophysical study
2010
A geophysical study has been carried out in the Dead Sea (DS) coastal area of Israel and Jordan with the goal of better understanding the development of sinkholes in the area. Th e following surface geophysical methods have been applied: (1) Seismic Refraction method for mapping the buried salt formation; (2) Microgravity and Magnetic Resonance Sounding (MRS) for detecting cavities in the subsurface; (3) Transient Electromagnetic method (TEM) for estimating groundwater salinity. It has been found that: (1) sinkholes have formed within a strip 50-100 m wide along the salt formation edge; (2) a zone with a large density of cavities with a total volume of tens of thousands of cubic meters have been inferred in sinkhole sites; (3) cavities underlying sinkholes are fi lled with unconsolidated sediments locally reducing hydraulic conductivity. Further development of new cavities has not been detected; (4) groundwater salinity variations along the DS shore are insignifi cant and changes in the electrical conductivity of the groundwater obtained using TEM were in most cases related to changes of porosity caused by collapse of subsurface sediments. (5) the applied geophysical methods provide valuable data on the development of sinkholes in the DS coastal areas.
Geomorphology, 2020
The western and eastern Dead Sea (DS) shores are hit by intensive sinkhole collapse during the last 30 years. The first researchers have considered a piping model of sinkhole formation, based on washing out fines by underground flows. Then, it was proved by numerous boreholes and seismic refraction surveys that sinkholes along western shore are caused by dissolution of buried salt layers and collapse of the surface into dissolution caverns. However, signs of piping and subsurface flows were observed in some sinkhole sites. In this paper, we show that robust identification of sinkhole origin can be achieved when proper geophysical methodologies and their application are used. We consider Newe Zohar site located in the southern part of the Dead Sea in order to analyse different signs of sinkhole formation models using various geophysical methods. The Seismic refraction method (SRFR), enables us to discover the salt layer based on longitudinal wave velocity Vp; the Multichannel Analysis of Surface Waves (MASW) method allows to determine the salt layer properties (rigidity) based on shear wave velocity Vs; finally, the Time Electromagnetic (TEM) method allows us to evaluate the degree of aggressiveness of groundwater with respect to salt, based on bulk resistivity values. Here we analyse competitive models of sinkhole formation and suggest geophysical methods to determine the subsurface geomorphology. We show that various geophysical methods should be applied in concert to explore the subsurface for the occurrence of salt, as well as understanding sinkhole formation processes. The underlying voids along the Dead Sea are shown to form primarily by salt dissolution, with some cases of additional piping. Applying the right geophysical parameters for groundwater and salt sediments classification proves to be crucial for understanding the subsurface geomorphology.
SN Applied Sciences , 2020
FOR CITATION: Salem, Hilmi S. (2020). Multi-and Inter-Disciplinary Approaches Towards Understanding the Sinkholes' Phenomenon in the Dead Sea Basin, SN Applied Sciences, (2020) 2:667. https://doi.org/10.1007/s42452-020-2146-0\. Springer URL: https://www.researchgate.net/publication/339044303\_Multi-and\_Inter-Disciplinary\_Approaches\_Towards\_Understanding\_the\_Sinkholes'\_Phenomenon\_in\_the\_Dead\_Sea\_Basin\_SN\_Applied\_Sciences\_Springer\_March\_2020/stats ABSTRACT: Over the last few decades, thousands of sinkholes have developed at an increasing pace, with the majority along the western and eastern shores of the Dead Sea. Recent studies indicate that the number of sinkholes in the Dead Sea Basin (DSB) has reached more than 6000; each of them, on average, 1–10 m deep and up to 25–30 m in diameter. These sinkholes can open-up suddenly and swallow whatever exists above them, resulting in an area that looks like an earthquake zone. Sinkholes in the DSB are formed when a subterranean salt layer that once bordered the Dead Sea is dissolved by underground freshwater that follows the migration of the saltwater–freshwater interface, due to receding water level of the Dead Sea. Consequently, large areas of land are subsiding, causing the formation of sinkholes in the region. Also, based on the fact that the Dead Sea’s region is tectonically and seismically active, as being greatly affected by the Dead Sea transform fault system, sinkholes can also be evolved as a result of tectonic and seismic activities. This paper presents multi- and inter-disciplinary approaches towards understanding the occurrence of sinkholes in the DSB, with respect to geomorphology, geology, geophysics, tectonics, seismology, limnology, climatology, biodiversity, and socioeconomics, as well as the steady decline of the Dead Sea’s water level and the continuous shrinkage of its surface area and its water volume, at alarming rates. The occurrence of sinkholes in this region could be attributed to anthropogenic reasons and/or natural reasons. KEYWORDS: Sinkholes · Dead Sea Basin · Water level’s decline · Surface area’s shrinkage · Anthropogenic causes · Naturally induced · Brine and freshwater · Tectonics and seismicity · Transform fault system
Geophysical prediction and following development sinkholes in two Dead Sea areas, Israel and Jordan
Environmental Earth Sciences, 2013
Geophysical methods - seismic refraction (SRFR), electrical resistivity tomography (ERT), and microgravity were applied to the Dead Sea (DS) sinkhole problem in the Ein Gedi area at the earlier stage of the sinkhole development (1998-2002). They allowed determining the sinkhole formation mechanism and localization of the sinkhole hazardous zones. The SRFR method permitted the delineating of the underground edge of a salt layer at a depth of 50 m. The salt edge was shaped like the sinkhole line on the surface. It was concluded that the sinkhole development is linked to the salt edge. Geoelectrical quasi-3D mapping based on the ERT technique detected significant resistivity anomalies with 250-300 m 2 diameter and 25-35 m deep. The use of the microgravity method has also mapped the Ein Gedi area. The residual Bouguer gravity anomaly map shows negative anomalies arranged along the edge of the salt layer. Those gravity anomalies overall are very similar in plan to the resistivity distribution in this area. The results of forward modeling indicate that high resistivity and residual gravity anomalies are associated with a subsurface decompaction of the soil mass and deep cavity at the sinkhole site. Following monitoring of the sinkhole development carried out by the Geological Survey of Israel confirmed our suggestions. The drilling of numerous boreholes verified the location of the salt edge. The Geographical Information System (GIS) database testifies that during 2003–2009 new sinkholes continued to develop along the salt edge within a narrow 50–100 m wide strip oriented approximately in the north–south direction (slightly parallel to the shoreline). No promotion in west–east direction (perpendicularly to the DS shoreline) was observed in Israel. The collapse of sinkholes and their clustering have occurred within the area of high resistivity anomaly and negative residual gravity anomaly. Similar studies carried out in the Ghor Al-Haditha area (Jordan) have shown that sinkholes are also arranged along the winding line, conforming to the salt edge. In this area, sinkholes are slowly moved to the Dead Sea direction. Results of geophysical studies in numerous DS sites indicate similar sinkhole development. It allowed the sinkhole formation model to be generalized based on an ancient (10,000–11,000-year-old) salt belt girding the Dead Sea along its shores.
Geological Society of America Bulletin, 2006
More than a thousand sinkholes have developed along the western coast of the Dead Sea since the early 1980s, more than 75% of them since 1997, all occurring within a narrow strip 60 km long and <1 km wide. This highly dynamic sinkhole development has accelerated in recent years to a rate of ~150-200 sinkholes per year. The sinkholes cluster mostly over specifi c sites up to 1000 m long and 200 m wide, which spread parallel to the general direction of the fault system associated with the Dead Sea Transform. Research employing borehole and geophysical tools reveals that the sinkhole formation results from the dissolution of an ~10,000-yr-old salt layer buried at a depth of 20-70 m below the surface. The salt dissolution by groundwater is evidenced by direct observations in test boreholes; these observations include large cavities within the salt layer and groundwater within the confi ned subaquifer beneath the salt layer that is undersaturated with respect to halite. Moreover, the groundwater brine within the salt layer exhibits geochemical evidence for actual salt dissolution (Na/Cl = 0.5-0.6 compared to Na/Cl = 0.25 in the Dead Sea brine). The groundwater heads below the salt layer have the potential for upward cross-layer fl ow, and the water is actually invading the salt layer, apparently along cracks and active faults. The abrupt appearance of the sinkholes, and their accelerated expansion thereafter, refl ects a change in the groundwater regime around the shrinking lake and the extreme solubility of halite in water. The eastward retreat of the shoreline and the declining sea level cause an eastward migration of the fresh-saline water interface. As a result the salt layer, which originally was saturated with Dead Sea water over its entire spread, is gradually being invaded by fresh groundwater at its western boundary, which mixes and displaces the original Dead Sea brine. Accordingly, the location of the western boundary of the salt layer, which dates back to the shrinkage of the former Lake Lisan and its transition to the current Dead Sea, constrains the sinkhole distribution to a narrow strip along the Dead Sea coast.
International Journal of Speleology, 2017
Since the early 80s, a progressively increasing number of sinkholes appeared along the Dead Sea coastal line. It has been found that their appearance is strongly correlating with the lowering of the Dead Sea level taking place with the rate of approximately 1 m/yr. Location of areas affected by sinkhole development corresponds to location of the salt formation deposited during the latest Pleistocene, when the Lake Lisan receded to later become the Dead Sea. Water flowing to the Dead Sea from adjacent and underlying aquifers dissolves salt and creates caverns that cause ground subsidence and consequent formation of sinkholes. Before subsidence, these caverns are not visible on the surface but can be investigated with surface geophysical methods. For that, we applied Surface Nuclear Magnetic Resonance (SNMR), Transient Electromagnetic (TEM) Seismic refraction and reflection, Multichannel Analysis of Surface waves (MASW), microgravity and magnetic surveys and their combinations. Our geophysical results allowed us to locate the salt formation and to detect caverns in salt thus contributing to better understanding sinkhole development mechanisms. Comparison of sinkhole appearance along the western DS shore derived from the recent database (2017) shows that predictions made on the base of geophysical data (2005-2008) are now confirmed thus demonstrating efficiency of our study. In this paper, we briefly present a summary of up to date knowledge of the geology and hydrogeology of Dead Sea basin, of the physical properties of the salt rock and the most popular models explaining mechanisms of sinkhole development. We also share our experience gained during geophysical studies carried out in the framework of national and international research projects in this area for the last 20 years.