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Hydrological and Geological Controls on the Evolution of the Dead Sea Sinkholes
Abstract
The human-induced shrinkage of the Dead Sea (DS) has led to the occurrence of thousands of sinkholes along its shoreline, by triggering the intrusion of fresh groundwater that replaced the brine water. The fresh groundwater dissolved a 10 ky old salt layer that formed subsurface cavities. The present chapter presents a summary of the main factors controlling the propagation rate of the DS sinkholes. These factors are: (1) the rheological properties of the sedimentary cap above the dissolution cavities in the salt layer, (2) variations in rate of fresh groundwater supply from rainfall in the recharge area in the Judea Mountains that control salt dissolution rates, and (3) episodes of floods in some of the stream tributaries, where the floodwater penetrates through pre-existing sinkholes that originally were formed by the groundwater dissolution.
... The subsidence strips with clustered sinkholes were formed in the exposed mudflats as part of the adjustment of the Dead Sea periphery to the lowering of the base level as a result of the retreat of the Dead Sea. The origin of the sinkholes on the shore of the Dead Sea is related to the subsiding of sediments following dissolution and salt karstification within a subareal rock-salt unit (Frumkin and Raz, 2001;Yechieli et al., 2016;Watson et al., 2019;Ezersky et al., 2017;Ezersky & Frumkin, 2020, 2021Abelson, 2021). ...
... The subsidence strips with clustered sinkholes were formed in the exposed mudflats as part of the adjustment of the Dead Sea periphery to the lowering of the base level as a result of the retreat of the Dead Sea. The origin of the sinkholes on the shore of the Dead Sea is related to the subsiding of sediments following dissolution and salt karstification within a subareal rock-salt unit (Frumkin and Raz, 2001;Yechieli et al., 2016;Watson et al., 2019;Ezersky et al., 2017;Ezersky & Frumkin, 2020, 2021Abelson, 2021). ...
The retreat of the Dead Sea and the lowering of the base level in recent decades have led to the exposure of the littoral clay sediments on the shore, the occurrence of exposed mudflats and the development of ground subsidence along strips (‘subsidence strips’) and clustered sinkholes. Based on field observations and laboratory analyses, the present study characterizes the clayey sediments in the environment of the exposed mudflats on the western Dead Sea shore. The clayey sediments of the exposed mudflats (‘mudflat sediments’) consist of fine-grained laminated calcareous clays. The mineral composition of the bulk mudflat sediments consists of clay and carbonate minerals (calcite, aragonite and dolomite) with some quartz and feldspar, and frequently gypsum and halite. The clay mineral composition of these samples is smectitic illite–smectite and kaolinite with some discrete illite and palygorskite. The smectitic illite–smectite is randomly interstratified (1.7 nm illite–smectite type R = 0). Although the detrital smectitic illite–smectite in the mudflat sediments is situated in the saline environment of the Dead Sea shore, no significant illitization is observed in the depositional detrital clay. Subsidence strips with clustered sinkholes were formed in the exposed mudflats as part of the adjustment of the Dead Sea periphery to the lowering of the base level as a result of the retreat. The field observations in the studied area reveal that the subsiding of mudflat sediments in the formation of the subsidence strips usually involves mud sagging of wet clayey sediments in the subsurface and sediment collapse of dry clayey sediments near the surface.
... The first dataset is an airborne laser scan acquired over the Ze'elim alluvial fan, Israel (see Fig. 4(a) and [40, Table I]). This region has been the focus of geomorphological study over the past few years, mostly due to the accelerated landform processes that control the fan (e.g., [41], [42], [43], [44], [45]). Gullies dissect the relatively flat surface of the fan at changing depths and widths (2-6 and 5-9 m, respectively), while sinkholes puncture it with depressions of varying diameters and depths (4-20 and 0.5-4.5 m, respectively). ...
Laser scanning technology is becoming ubiquitous
in studies involving 3-D characterizations of natural scenes, e.g.,
for geomorphological or archeological interpretations. Setting the
point density in such scanning campaigns is usually dictated by
the objects of interest within the site yet is applied to the entire
scene. Such campaigns result in large data volumes, which are
difficult to analyze and where the objects of interest may be
hidden in the redundant data. To reduce these excessive vol-
umes, existing simplification strategies maintain smoothness and
preserve discontinuities in the point cloud but disregard the need
to preserve detail at the regions of interest (ROIs). To address
that, this article proposes a new, context-aware, subsampling
approach that retains the high resolution of objects of interest
while reducing the data load of less important regions. To do
so, we identify the ROI by means of visual saliency measures
and reduce the data volume only at the nonsalient regions.
To facilitate progressive subsampling, the reduction is based on
a hierarchical data structure that is surficial in nature. In this
way, the retained representative points describe the underlying
surface rather than an interpolation of it. We demonstrate our
proposed model on datasets originating from different scanners
that feature a variety of scenes. We compare our results to three
common simplification approaches. Our results show a reduced
point cloud that is similar to the original and allows analysis of
ROI at the required point resolution, regardless of the level of
simplification.
This work is openly available on: https://ieeexplore.ieee.org/document/9896902
The drastic drop in Dead Sea lake levels during the last few decades has caused the formation of over 6000
dangerous sinkholes along its coasts. Concurrently, retreating shorelines have led to the exposure of an underexplored
phenomenon – submarine spring systems. Once exposed on land, these features are labeled as the
more familiar geological hazard – i.e. sinkholes, with no distinction between the two. While visually they may
seem similar, the underlying formation mechanism is different, as may well be their hazard potential. This study
utilizes high-resolution seismic reflection data collected in 1984 when lake levels were some 35 m higher,
together with multibeam bathymetric data from 2014, visual observations and water chemistry data from a
verified spring system in order to assess the underlying formation mechanisms of these features, their stability
and morphology. Results show that the springs are relatively stable and long-lived systems. They “deserve” to be
separated from the sinkholes and studied as a distinct phenomenon. The springs discharge into the lake a significant
amount of freshwater from the adjacent aquifers and are therefore, a largely underestimated part of its
hydrological budget and the connected fresh groundwater resources. The acceptance of submarine springs as a
distinct geological phenomenon and their consideration as a major groundwater outlet into the lake will lead to
more realistic groundwater resource models of the Judea and Samaria Eastern Mountain aquifer than exist today.
This is extremely important given the increase aridification of the area and the increased demand for freshwater
resources.
More than 6000 sinkholes have been formed during the last 30 years along the Dead Sea (DS) coastal areas in Israel (Abelson et al 2006, 2021, Yechieli et al 2016, DS sinkhole database 1998–2016) and Jordan (Closson and Abou Karaki 2009, Abueladas 2016—personal communication, Abou Karaki et al 2019). Sinkholes formed in evaporite areas are associated with the dissolution of buried salt layers. Salt is a very soluble material, even in slightly saline (undersaturated) circulating groundwater. Dissolution rates of salt are one to three orders of magnitude higher compared with limestone (Reuter and Stoyan 1993, Gutiérrez et al 2008). Therefore, the subsurface dissolution of salt by such groundwater and collapse of the overlying material (sinkhole formation) may also be relatively rapid, from days to some weeks (Frumkin 1995, Van Sambeek 1996, Stiller et al
2016). On the other hand, the DS groundwater contains essentially more salt (~265–275 g L−1 NaCl) than normal groundwater. Therefore, DS groundwater slightly slows down the dissolution process (months, years) and allows the observation of changes in the geophysical properties of the subsurface on a human life scale. Sinkholes are surface manifestations of subsurface dissolution, internal erosion, and deformation, commonly hidden from direct observations and most subaerial geomorphological study methods (Gutiérrez et al 2014).
The Dead Sea shore is a unique, young and dynamic salt karst system. Development of the area began in the 1960s, when the main water resources that used to feed the Dead Sea were diverted towards deserts, cities and industries. During the last decade, the water level has fallen by more than 1 m per year, causing a hydrostatic disequilibrium between the underground fresh waters and the base level. Thousands of underground cavities have developed as well as hectometre-sized landslides. Despite these unfavourable environmental conditions, large tourism development projects have flourished along the northern coast of the Jordanian Dead Sea. In this work, which is based on a multi-method approach (analyses of radar and optical satellite data, in situ observations, and public science), we show that a 10 km long strip of coast that encompass several resorts is exposed to subsidence, sinkholes, landslides and flash floods. Geological discontinuities are the weakest points where the system can re-balance and where most of the energy is dissipated through erosional processes. Groundwater is moving rapidly along fractures to reach the dropping base level. The salt that fills the sediments matrix is dissolved along the water flow paths favouring the development of enlarged conduits, cavities and then the proliferation of sinkholes. The front beaches of the hotels, the roads and the bridges are the most affected infrastructure. We point out the importance for the land planners to include in the Dead Sea development schemes the historical records and present knowledge of geological hazards in the area.
During the past three decades, the Dead Sea (DS) water level has dropped at an average rate of ~1 m/year, resulting in the formation of thousands of sinkholes along its coastline that severely affect the economy and infrastructure of the region. The sinkholes are associated with gradual land subsidence, preceding their collapse by periods ranging from a few days to about five years. We present the results of over six years of systematic high temporal and spatial resolution interferometric synthetic aperture radar (InSAR) observations, incorporated with and refined by detailed Light Detection and Ranging (LiDAR) measurements. The combined data enable the utilization of interferometric pairs with a wide range of spatial baselines to detect minute precursory subsidence before the catastrophic collapse of the sinkholes and to map zones susceptible to future sinkhole formation. We present here four case studies that illustrate the timelines and effectiveness of our methodology as well as its limitations and complementary methodologies used for sinkhole monitoring and hazard assessment. Today, InSAR-derived subsidence maps have become fundamental for sinkhole early warning and mitigation along the DS coast in Israel and are incorporated in all sinkhole potential maps which are mandatory for the planning and licensing of new infrastructure.
Mechanical and/or chemical removal of material from the subsurface may generate large subsurface cavities, the destabilisation of which can lead to ground collapse and the formation of sinkholes. Numerical simulation of the interaction of cavity growth, host material deformation and overburden collapse is desirable to better understand the sinkhole hazard but is a challenging task due to the involved high strains and material discontinuities. Here, we present 2-D distinct element method numerical simulations of cavity growth and sinkhole development. Firstly, we simulate cavity formation by quasi-static, stepwise removal of material in a single growing zone of an arbitrary geometry and depth. We benchmark this approach against analytical and boundary element method models of a deep void space in a linear elastic material. Secondly, we explore the effects of properties of different uniform materials on cavity stability and sinkhole development. We perform simulated biaxial tests to calibrate macroscopic geotechnical parameters of three model materials representative of those in which sinkholes develop at the Dead Sea shoreline: mud, alluvium and salt. We show that weak materials do not support large cavities, leading to gradual sagging or suffusion-style subsidence. Strong materials support quasi-stable to stable cavities, the overburdens of which may fail suddenly in a caprock or bedrock collapse style. Thirdly, we examine the consequences of layered arrangements of weak and strong materials. We find that these are more susceptible to sinkhole collapse than uniform materials not only due to a lower integrated strength of the overburden but also due to an inhibition of stabilising stress arching. Finally, we compare our model sinkhole geometries to observations at the Ghor Al-Haditha sinkhole site in Jordan. Sinkhole depth / diameter ratios of 0.15 in mud, 0.37 in alluvium and 0.33 in salt are reproduced successfully in the calibrated model materials. The model results suggest that the observed distribution of sinkhole depth / diameter values in each material type may partly reflect sinkhole growth trends.
Near-surface geophysical imaging of alluvial fan settings is a challenging task but crucial for understating geological processes in such settings. The alluvial fan of Ghor Al-Haditha at the southeast shore of the Dead Sea is strongly affected by localized subsidence and destructive sinkhole collapses, with a significantly increasing sinkhole formation rate since ca. 1983. A similar increase is observed also on the western shore of the Dead Sea, in correlation with an ongoing decline in the Dead Sea level. Since different structural models of the upper 50 m of the alluvial fan and varying hypothetical sinkhole processes have been suggested for the Ghor Al-Haditha area in the past, this study aimed to clarify the subsurface characteristics responsible for sinkhole development.
For this purpose, high-frequency shear wave reflection vibratory seismic surveys were carried out in the Ghor Al-Haditha area along several crossing and parallel profiles with a total length of 1.8 and 2.1 km in 2013 and 2014, respectively. The sedimentary architecture of the alluvial fan at Ghor Al-Haditha is resolved down to a depth of nearly 200 m at a high resolution and is calibrated with the stratigraphic profiles of two boreholes located inside the survey area.
The most surprising result of the survey is the absence of evidence of a thick (> 2–10 m) compacted salt layer formerly suggested to lie at ca. 35–40 m depth. Instead, seismic reflection amplitudes and velocities image with good continuity a complex interlocking of alluvial fan deposits and lacustrine sediments of the Dead Sea between 0 and 200 m depth. Furthermore, the underground section of areas affected by sinkholes is characterized by highly scattering wave fields and reduced seismic interval velocities. We propose that the Dead Sea mud layers, which comprise distributed inclusions or lenses of evaporitic chloride, sulfate, and carbonate minerals as well as clay silicates, become increasingly exposed to unsaturated water as the sea level declines and are consequently destabilized and mobilized by both dissolution and physical erosion in the subsurface. This new interpretation of the underlying cause of sinkhole development is supported by surface observations in nearby channel systems. Overall, this study shows that shear wave seismic reflection technique is a promising method for enhanced near-surface imaging in such challenging alluvial fan settings.
The human-induced desiccation of the Dead Sea (DS) has led to the formation of more than 6000 collapse sinkholes along its western coast during the past 20 years, causing severe infrastructural damage. This desiccation led to intrusion of fresh groundwater from the Judea Mountains to the west, which dissolves a 10–70 m deep salt layer forming subsurface cavities. The coastal sediments overlying these cavities become unstable until their final collapse to develop sinkholes. Here we show results of seismic monitoring which identified subsurface instabilities several years before sinkhole collapse. The survey, which included a network of five borehole geophones buried at depths between 11 and 25 m, detected 82 nanoseismic events, of which 75 were in magnitude range between (2) and (3). The hypocenters depths range upward from the base of the salt layer, and the plan view distribution agrees with salt dissolution propagation front. Therefore, these nanoseismic signals likely owe to deformation that precedes the surface collapse of sinkholes. During the monitoring period, there were no indications of subtle land subsidence at the surface above most of the nanoseismic events, as we show from interferometric synthetic aperture radar (InSAR). The first sinkhole collapse occurred 2.5 years after the nanoseismic events, and 7 additional sinkholes during 2016, suggesting that the zone of nanoseismicity is prone to further collapses in the coming years.
One of the most hazardous results of the human-induced Dead Sea (DS) shrinkage is the formation of more than 6000 sinkholes over the last 25 years. The DS shrinkage caused eastward retreat of underground brine replaced by fresh groundwater, which in turn dissolved a subsurface salt layer, to generate cavities and collapse sinkholes. The areal growth rate of sinkhole clusters is considered the most pertinent proxy for sinkholes development. Analysis of light detection and ranging, digital elevation models, and interferometric synthetic aperture radar allows translation of the areal growth rate to a salt dissolution rate of the salt layer, revealing two peaks in the history of the salt dissolution rate. These peaks cannot be attributed to the decline of the DS level. Instead, we show that they are related to long-term variations of precipitation in the groundwater source region, the Judea Mountains, and the delayed response of the aquifer system between the mountains and the DS rift. This response is documented by groundwater levels and salinity variations. We thus conclude that while the DS level decline is the major trigger for sinkholes formation, the rainfall variations more than 30 km to the west dominate their evolution rate. The influence of increasing rainfall in the Judea Mountains reaches the DS at a typical time lag of 4 years, and the resulting increase in the salt dissolution rate lags by a total time of 5–6 years.
We document and analyze the rapid development of a real-time karst system within the subsurface salt layers of the Ze'elim Fan, Dead Sea, Israel by a multidisciplinary study that combines interferometric synthetic aperture radar and light detection and ranging measurements, sinkhole mapping, time-lapse camera monitoring, groundwater level measurements and chemical and isotopic analyses of surface runoff and groundwater. The >1 m/yr drop of Dead Sea water level and the subsequent change in the adjacent groundwater system since the 1960s resulted in flushing of the coastal aquifer by fresh groundwater, subsurface salt dissolution, gradual land subsidence and formation of sinkholes. Since 2010 this process accelerated dramatically as flash floods at the Ze'elim Fan were drained by newly formed sinkholes. During and immediately after these flood events the dissolution rates of the subsurface salt layer increased dramatically, the overlying ground surface subsided, a large number of sinkholes developed over short time periods (hours to days), and salt-saturated water resurged downstream. Groundwater flow velocities increased by more than 2 orders of magnitudes compared to previously measured velocities along the Dead Sea. The process is self-accelerating as salt dissolution enhances subsidence and sinkhole formation, which in turn increase the ponding areas of flood water and generate additional draining conduits to the subsurface. The rapid terrain response is predominantly due to the highly soluble salt. It is enhanced by the shallow depth of the salt layer, the low competence of the newly exposed unconsolidated overburden and the moderate topographic gradients of the Ze'elim Fan.
Over the past several years, the coastal area around the declining Dead Sea has undergone a catastrophic collapse. One of the major expressions of this process is the sudden appearance of hundreds of collapse sinkholes, causing a severe threat to the future of this region. Here we review results and inferences obtained from a multidis-ciplinary research conducted since 1999. Observations were obtained by geological mapping, aerial photographs, drilling, groundwater geochemistry, seismic refraction and refl ection, and satellite radar interferometry. The suggested model for the forma-tion of the Dead Sea sinkholes is based on the following observations: (1) presence of a thick salt layer (or layers) at depths between 20 and 50 m (depth of layer top), and sandwiched between aquiclude layers of clay and silt; (2) identifi cation of cavi-ties within the salt layer in sinkhole sites; (3) presence of water undersaturated with respect to halite in aquifers confi ned beneath the salt layer; (4) composition of the groundwater in the salt layer that indicates salt dissolution; (5) association between sinkhole sites and land subsidence; and (6) formation of sinkholes along and above buried faults. These observations combine to suggest that the primary cause of sink-hole formation is dissolution of the salt layer by undersaturated groundwater. The interface between the Dead Sea brine and this groundwater migrated eastward due to the Dead Sea decline. Undersaturated water accessed the salt layer via faults that cut through the soft aquiclude layers. The opening of these conduit-faults is likely due to differential compaction of the aquiclude layers, explaining the correlation between the land subsidence and sinkhole sites. It appears that the decline of the Dead Sea level affects the formation of sinkholes in three ways: (1) opening the way to eastward migration of the freshwater-saline interface and thus to undersaturated groundwater, (2) generating differential compaction of fine-grained sediments, and (3) destabiliza-tion of underground cavities, which catalyzes their collapse.
A 34.5 m borehole, which was drilled near the Dead Sea coast (altitude -394 m) in the southern part of the fan delta of Wadi Zeelim, reveals the geological history of that area from the latest Pleistocene to present. The depositional time frame is based on six 14C dates and two U-Th dates. An erosional (or nondepositional) period is implied by the hiatus between 21,100 yr B.P. (U-Th age, depth 33 m) and 11,315 yr B.P. (14C age, depth 32 m). A subsequent arid phase is recorded by a 6.5-m-thick layer of halite; based on 14C dates this phase relates to the abrupt Younger Dryas cold period reported in temperate to polar regions. The fragility of the environment in this region is indicated by the fact that the region experienced such a severe, short aridification phase (less than 1000 yr), evidence of which is found widely in the desert fringes of the Middle East and North Africa. The aragonite found in most of the Holocene section indicates that the well site was covered by the lake for most of the Holocene. Exceptions are the intervals at 0-3 and 10-14 m depths which represent low stands of the lake.
1] The Dead Sea (DS) pull-apart basin is one of the more seismically active segments of the DS Transform plate boundary. In the last decade, hundreds of collapse-sinkholes have been formed along the DS coastlines in Israel and Jordan, causing severe damage to the regional infrastructure. The formation of these sinkholes is attributed to the dissolution of a buried salt layer by fresh groundwater due to the drop of the DS and the associated groundwater levels. Here we show that the sinkhole distribution, combined with gradual land subsidence measured by radar interferometry (InSAR) track young fault systems suspected as active, concealed within the fill of the DS rift. This notion is supported by (1) sinkholes clustering along discrete lineaments with a striking trend similarity to that of the exposed rift-margin faults; (2) prominent discontinuities in seismic reflection profiles offsetting young sediments (several kyrs old) below sinkhole lines, and (3) straight boundaries of gradual subsidence features that coincide with or parallel sinkhole lines. Combined, the sinkhole lineaments and the InSAR measurements reveal a zigzag pattern of buried faults within the DS rift fill., Collapse-sinkholes and radar interferometry reveal neotectonics concealed within the Dead Sea basin, Geophys. Res. Lett., 30(10), 1545, doi:10.1029/ 2003GL017103, 2003.
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 nar-row 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 associ-ated 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 appear-ance 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 west-ern 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. The entire phenomenon can be described as a hydrological chain reaction; it starts by intensive extraction of fresh water upstream of the Dead Sea, continues with the eastward retreat of the lake shoreline, which in turn modifi es the groundwater regime, fi nally triggering the formation of sinkholes.
The formation of sinkholes at the Dead Sea area reflects subsurface cavities formed by salt dissolution. This dissolution is related to the recession of the Dead Sea; the groundwater level and the fresh/saline water interface along the shore decline at a similar rate to the rate of the Dead Sea recession, and brines that used to occupy layers below this interface are flushed out by freshwater. Our finite element modeling shows that dissolution of this salt layer is a plausible mechanism to explain the rapid creation of subsurface holes that collapse and form sinkholes. The positive feedback between the rate of flow, the rate of chemical reaction, and the change in permeability accelerates the dissolution processes and might result in “reactive infiltration instability” which is manifested in “fingers” of cavities, into which fluid is channeled, and salt is dissolved. The spacing between the sinkholes and the rate of their creation is controlled by several factors including properties of lineaments/faults, incoming groundwater flux, the salinity of the incoming groundwater, the rate of dissolution, the effective specific surface area, the permeability of the salt and clay layers, the permeability-porosity relation, the dispersivity, and the thickness of the layers. We show that the creation of sinkholes occurs only under specific conditions. These conditions must cause an unstable dissolution front which then causes formation of cavities and eventually sinkholes. The simulations, which utilized the best estimated parameters of the studied area, yield results that are similar to those exhibited in the field.
This paper investigates the effect of a drainage base level drop on the groundwater system in its vicinity, using theoretical analysis, simulations, and field data. We present a simple and novel method for analyzing the effect of a base level drop by defining two characteristic times that describe the response of the water table and the transition zone between the fresh and saline water. The Dead Sea was chosen as a case study for this process because of the lake's rapid level drop rate. During a continuous lake level drop, the discharge attains a constant value and the hydraulic gradient remains constant. We describe this new dynamic equilibrium and support it by theoretical analysis, simulation, and field data. Using theoretical analysis and sensitivity tests, we demonstrate how different hydrological parameters control the response rate of the transition zone to the base level drop. In some cases, the response of the transition zone may be very rapid and in equilibrium with the water table or, alternatively, it can be much slower than the water table response, as is the case in the study area.
The present study examines the response of groundwater systems to expected changes in the Mediterranean Sea (rise of <1cm/yr) and Dead Sea levels (decline of ∼1 m/yr). A fast response is observed in the Dead Sea coastal aquifer, exhibited both in the drop of the water levels and in the location of the fresh-saline water interface. No such effect is yet observed in the Mediterranean coastal aquifer, as expected. Numerical simulations, using the FeFlow software, show that the effect of global sea level rise depends on the coastal topography next to the shoreline. A slope of 2.5‰ is expected to yield a shift of the interface by 400 m, after a rise of 1m (∼100 years), whereas a vertical slope will yield no shift. Reduced recharge due to climate change or overexploitation of groundwater also enhances the inland shift of the interface.
This work presents a high-resolution lake-level record of the late Holocene Dead Sea, a hypersaline terminal lake whose drainage basin encompasses both Mediterranean and hyperarid climatic zones. The lake-level curve reflects the regional hydrologic variations in the drainage basin, which in turn represent the Levant paleoclimates. The curve is based on 46 radiocarbon ages of organic remains from well-exposed sedimentary sequences along the Dead Sea shores. These sequences record fluvial and lacustrine depositional environments. The paleolakeshores are marked by shore ridges, coarse-sand units, and aragonite crusts; in the modern Dead Sea, such features indicate the exact elevation of the shore. The late Holocene Dead Sea level fluctuated within the range of 390 to 415 m below sea level (mbsl). For most of the time the lake was below the topographic sill (402 mbsl) separating the northern and southern basins of the Dead Sea and was confined to the deep northern basin. Nevertheless, short-term rises in the late Holocene Dead Sea level caused the flooding of the shallow and flat southern basin. Highstands occurred in the second and first centuries B.C. and the fourth century A.D. during the Roman and early Byzantine periods, respectively, in the eleventh and twelfth centuries A.D. during the Crusader period, and at the end of the nineteenth century A.D. The rises mark a significant change in the annual rainfall in the region, which likely exceeded the instrumentally measured modern average. The curve also indicates drastic drops that exposed the sedimentary sequences to erosion. The oldest and probably deepest drop in the lake level culminated during the fifteenth and fourteenth centuries B.C. after a retreat from a higher lake stand. The longest lowstand occurred after the Byzantine period and continued at least until the ninth century A.D. This and period coincided with the invasion of Moslem-Arab tribes into the area during the seventh century A.D. The dramatic fall of the Dead Sea level during the twentieth century is primarily artificial and has been caused by the diversion of runoff water for the drainage basin, but the magnitude is not considered exceptional for the late Holocene. Although the past drops in the lake never exceeded the modern artificial drop rates, they do represent extreme and conditions that occurred frequently over the past several thousand years.
The relation between climatic parameters (relative air humidity) and the water activity of the Dead Sea water determines the possible maximum evaporation of the lake. Using the Pitzer thermodynamic approach, the activity of the Dead Sea water during evaporation was calculated and compared to the present relative air humidity above the water. Long-term (1992–1997) quasi-continuous meteorological data acquired at sea provide detailed information on the patterns and trends of the relative humidity above the lake. Present climatic conditions allow the Dead Sea water to evaporate down to a water activity of 0.50, corresponding to the lowest air humidity measured over the lake. This water activity falls in the range of halite precipitation, while carnallite precipitation starts somewhat lower (aH2O=0.49). Our dynamic model predicts that for air humidity as low as 50% (reflecting present climate conditions), the Dead Sea level may drop to as low as −500 m (i.e., 500 m below mean sea level). At that point, the lake will have a volume of 88 km3 and a surface area of 526 km2. For the sake of comparison, at the beginning of 1977, after the southern basin of the Dead Sea was separated from the northern basin, the level of the lake was −402 m, its volume was 146 km3, and its surface area was 815 km2.
This work deals with the tectonic interpretation of an alignment of more than 300 sinkholes stretching along the Jordanian coast of the Dead Sea, Ghor Al Haditha area. Its dimensions are 6 km long with a width of 600 m. Sinkholes appeared during the last decades as a consequence of the very rapid lowering of the lake level. The linear shape was inferred from ground collapse inventories carried out between 1991 and 2008. The lineament is replaced and analyzed in its structural setting at regional and local scales. Its direction (N 24° E) is sub-parallel to the ones displayed by many focal mechanisms, especially the one associated with the earthquake of the 23 April, 1979 (mb = 5·1; N 20° E ± 5°), which is representative of all focal mechanisms calculated on a fault plane compatible with the general direction of the Jordan-Dead Sea Transform fault system for the east coast of the Dead Sea area.
The alignment of sinkholes is constituted by 13 minor linear segments separated by as many empty spaces. Four minor linear units present an en-echelon arrangement from which one can deduce the presence of a local extensional stress field. In this context, the sinkhole locations provide information of subsurface discontinuities interpreted as hidden fractures. In a close future, such results could support the work of decision-makers and engineers in the projected development of the area. Copyright
A geophysical approach is presented for analyzing processes of subsurface salt dissolution and associated sinkhole hazard along the Dead Sea. The implemented methods include Seismic Refraction (SRFR), Transient Electromagnetic Method (TEM), Electric Resistivity Tomography (ERT), and Ground Penetration Radar (GPR). The combination of these methods allows the delineation of the salt layer boundaries, estimating its porosity distribution, finding cavities within the salt layer, and identifying deformations in the overlying sediments. This approach is shown to be useful for anticipating the occurrence of specific sinkholes, as demonstrated on both shores of the Dead Sea. These sinkholes are observed mainly along the edge of a salt layer deposited during the latest Pleistocene, when Lake Lisan receded to later become the Dead Sea. This salt layer is dissolved by aggressive water flowing from adjacent and underlying aquifers which drain to the Dead Sea. Sinkhole formation is accelerating today due to the rapid fall of the Dead Sea levels during the last 30 years, caused by anthropogenic use of its water.
The Dead Sea area is increasingly facing serious subsidence and sinkhole hazards. On March 22, 2000, the dyke of a two-month old major salt evaporation pond, located along the shore of the Lisan Peninsula (Jordan), collapsed over almost two kilometers. The pond was set up over unstable new lands that have been progressively emerging during the last three decades. In one hour, 56 millions m3 of brine poured out into the northern, natural part of the Sea. Here, we present data suggesting that the drop of the water level, in conjunction with the particular tectonic setting of this area, is at least one of the factors that led to the disaster. We focused our study over the northern part of the Lisan Peninsula and Ghor Al Haditha which are two places undergoing the most intense deformations along the Jordanian Dead Sea coast. We used the results of a static high precision gravimetric survey to detect subsurface cavities in Ghor Al Haditha. We analyzed a interferometric digital terrain model of the recent emerged platform of the Lisan peninsula and interpreted radar differential interferograms contemporary with gravity measurements for the peninsula. We discuss the possibilities to detect, assess and monitor areas prone to collapse on the Jordanian side of the southern Dead Sea coast.
Sinkhole development along the western shore of the Dead Sea became a major concern in 1990 with the appearance of a series of holes 2–15 m diameter and up to 7 m deep in the Newe Zohar area. One of these sinkholes, below the asphalt surface of the main road along the western shore of the Dead Sea, was opened by a passing bus. Repeated infilling and collapse of these holes indicated the extent of this ongoing process and the significance of this developing hazard. Since then sinkholes have developed in other areas including Qalia, Ein Samar, Ein Gedi and Mineral Beach.
Three main types of sinkholes have been recognized. Gravel holes occurring in alluvial fans, mud holes occurring in the intervening bays of clay deposits between fans and a combination of both types at the front of young alluvial fans where they overlap mud flats. Fossil, relict sinkholes have been observed in the channels of some old alluvial fans.
Sinkhole development is directly related to the regression of the Dead Sea and the corresponding lowering of the regional water table. Continuation of this process widens the neritic zone enveloping the sea and increases the sinkhole hazard of the region.
Evaporites, including gypsum (or anhydrite) and salt, are the most soluble of common rocks; they are dissolved readily to
form caves, sinkholes, disappearing streams, and other karst features that typically are found in limestones and dolomites.
The four basic requirements for evaporite karst to develop are: (1) a deposit of gypsum or salt; (2) water, unsaturated with
CaSO4 or NaCl; (3) an outlet for escape of dissolving water; and (4) energy to cause water to flow through the system. Evaporites
are present in 32 of the 48 contiguous states, and they underlie about 35–40% of the land area; they are reported in rocks
of every geologic system from the Precambrian through the Quaternary. Evaporite karst is known at least locally (and sometimes
quite extensively) in almost all areas underlain by evaporites. The most widespread and pronounced examples of both gypsum
and salt karst are in the Permian basin of the southwestern United States, but many other areas are also significant. Human
activities have caused some evaporite-karst development, primarily in salt deposits. Boreholes may enable (either intentionally
or inadvertently) unsaturated water to flow through or against salt deposits, thus allowing development of small to large
dissolution cavities. If the dissolution cavity is large enough and shallow enough, successive roof failures above the cavity
can cause land subsidence or catastrophic collapse.
Lake Lisan, the late Pleistocene precursor of the Dead Sea, existed from ∼70,000 to 15,000 yr B.P. It evolved through frequent water-level fluctuations, which reflected the regional hydrological and climatic conditions. We determined the water level of the lake for the time interval ∼55,000–15,000 cal yr B.P. by mapping offshore, nearshore, and fan-delta sediments; by application of sequence stratigraphy methods; and by dating with radiocarbon and U-series methods. During the studied time interval the lake-level fluctuated between ∼340 and 160 m below mean sea level (msl). Between 55,000 and 30,000 cal yr B.P. the lake evolved through short-term fluctuations around 280–290 m below msl, punctuated (at 48,000–43,000 cal yr B.P.) by a drop event to at least 340 m below msl. At ∼27,000 cal yr B.P. the lake began to rise sharply, reaching its maximum elevation of about 164 m below msl between 26,000 and 23,000 cal yr B.P., then it began dropping and reached 300 m below msl at ∼15,000 cal yr B.P. During the Holocene the lake, corresponding to the present Dead Sea, stabilized at ca. 400 m below msl with minor fluctuations. The hypsometric curve of the basin indicates that large changes in lake area are expected at above 403 and 385 m below msl. At these elevations the lake level is buffered. Lake Lisan was always higher than 380 m below msl, indicating a significantly large water contribution to the basin. The long and repetitious periods of stabilization at 280–290 m below msl during Lake Lisan time indicate hydrological control combined with the existence of a physical sill at this elevation. Crossing this sill could not have been achieved without a dramatic increase in the total water input to the lake, as occurred during the fast and intense lake rise from ∼280 to 160 m below msl at ∼27,000 cal yr B.P.
During the past three decades, thousands of sinkholes were formed along the Dead Sea (DS) shorelines in Israel and Jordan, due to dissolution of subsurface salt by undersaturated groundwater. The sinkholes are associated with gradual subsidence preceding their collapse by periods ranging from a few days to almost 5 years. To determine the factors controlling this precursory subsidence, we examine tens of subsidence-sinkhole sequences along the DS shorelines in Israel. The duration and magnitude of the precursory subsidence are determined by Interferometric Synthetic Aperture Radar (InSAR) measurements and simulated by viscoelastic damage rheology models. Longer periods of precursory subsidence are found in the cemented alluvial fans and in simulations of higher-viscosity sediments. While surface subsidence accelerates during the precursory period, the widths of the subsiding areas remain uniform, suggesting that during this period upward propagation of damage from the subsurface cavity is not accompanied by upward migration of the actual cavity. Our observations and simulations are used to constrain the viscosity of the sediments along the DS and to reduce sinkhole hazards by assessing the precursory times of future sinkholes in the different sedimentary environments.
Sinkhole generation and land subsidence are commonly attributed to dissolution of subsurface layers by under-saturated groundwater and formation of cavities. Along the Dead Sea (DS) shorelines, this process also involves seasonal flash floods that are drained into the subsurface by existing and newly formed sinkholes. We quantify the contribution of flash-floods to salt dissolution and land subsidence using high-resolution interferometric synthetic aperture radar (InSAR). Subsidence rates during a 3-year period (2012–2015) were calculated from 57 COSMO SkyMed X-band interferograms bracketing major flood events and intra-flood periods in 21 sinkhole sites. The sites are located within channels and alluvial fans along the western shores of the Dead Sea, Israel. The observed subsidence reaches maximum rates of ~ 2.5 mm/day, accumulating in specific sites to 500 mm/year. In most of the sinkhole sites a gradual increase in the annual subsidence rate is observed during the 3-year study period. Three different modes of response to floods were observed: (1) sites where floodwater is not directly channeled into sinkholes do not respond to floods; (2) sites adjacent to active channels with sinkholes are unaffected by specific floods but their subsidence rates increase gradually from early winter to mid-summer, and decay gradually until the following winter; and (3) sites in active channels with sinkholes are characterized by an abrupt increase in subsidence rates immediately after each flood (by a factor of up to 20) and by a subsequent quasi-exponential subsidence decay over periods of several months. In these latter sites, subsidence rates after each flood are temporally correlated with alternating groundwater levels in adjacent boreholes. The rapid rise in groundwater head following floods increases the hydraulic gradient of the under-saturated groundwater and hence also the groundwater discharge and the dissolution rate of the subsurface salt layer. A subsequent quasi-exponential water level drop results in similar deceleration in dissolution and subsidence rates, with a similar characteristic decay time of about 150 days. The observed subsidence decay pattern may also be explained by viscoelastic relaxation of the overburden in response to instantaneously-formed dissolution cavities. Utilizing a Kelvin viscoelastic model, we show that the contribution of this process is most probably < 30% of the total observed subsidence and is sensitive to the sediment mechanical properties. On a broader scale, this study demonstrates how high-resolution InSAR measurements can improve our understanding of subsurface dissolution and subsidence processes and provide independent constraints on the mechanical properties of heterogeneous alluvial sediments.
Sinkholes commonly form by subsurface dissolution cavities that collapse after the overlying layers become mechanically unsupported. Sinkholes along the Dead Sea shorelines are preceded by, associated with, and followed by gradual surface subsidence that accompanies the cavities' growth. We exploit satellite radar interferometry (InSAR) to resolve temporal and spatial relationships between gradual subsidence and sinkhole collapse. The geometry of the deflating cavity roof is determined by elastic inverse modeling of the surface displacements. A Coulomb failure stress criterion is applied to calculate the stress field induced by the deflating cavity at the ground surface. We find that the induced stress field favors generation of sinkholes at the perimeters of the subsiding areas rather than at their centers, in agreement with field observations, providing important information for sinkhole hazard assessment. Further, our analysis suggests that short-term deformation in consolidated gravel layers at shallow depths could be approximated by simple elastic modeling.
Endorheic continental basins, also termed as terminal or closed basins, are internal drainage systems. The term is usually related to surface water drainage systems, yet endorheic basins often also serve as groundwater base-levels and discharge zones. The basins are typified by the fact that there is no outflow from the basin to the sea by surface rivers and the rain water over the basin leaves the system naturally only by evaporation or seepage. The bottom or the lower surface area of such basins is often occupied by salt lakes or salt pans.
Problems associated with sinkhole development are causing serious concerns in land-use planning in the Dead Sea area. A case study is presented, that demonstrates that microcavity can predict collapse hazards, for detecting and delineating subsurface cavities and for monitoring their development over time.
The level of the Dead Sea (the lowest surface on Earth) is currently
declining at a rate of 0.8 m/yr, and has dropped about 20 m since the
beginning of the twentieth century; it reached -410 m in 1997. We
address the question of whether the level of the Dead Sea will continue
to decline. A numerical model, developed in this study to determine the
water balance, accounts for the increase in salinity and the concomitant
decrease in the rate of evaporation that accompanies reduction in the
activity of the water. Simulations based on ranges of water withdrawal
scenarios suggest that the Dead Sea will not “die”; rather,
a new equilibrium is likely to be reached in about 400 yr after a
water-level decrease of 100 to 150 m.
The water level in the Dead Sea (Israel and Jordan) has been dropping at an increasing rate since the 1960s, exceeding one meter per year during the last decade. This drop has triggered the formation of sinkholes and widespread land subsidence along the Dead Sea shoreline, resulting in severe economic loss and infrastructural damage. In this study, the spatiotemporal evolution of sinkhole-related subsidence and the effect of human activities and land perturbation on sinkhole development are examined through interferometric synthetic aperture radar measurements and field surveys conducted in Israel during 2012. Interferograms are generated using COSMO-SkyMed satellite images and a high-resolution (0.5 m/pixel) elevation model obtained from LiDAR measurements. As a result of this unique combination of high-resolution data sets, millimeter-scale subsidence has been resolved in both natural and human-disturbed environments. Precursory subsidence over a period of a few months occurred before the collapse of all three sinkhole sites reported in this study. The centers of the subsiding areas migrated, possibly due to progressive dissolution and widening of the underlying cavities. Filling of newly formed sinkholes with gravel, and mud injections into drill holes, seem to enhance land subsidence, enlarge existing sinkholes, and form new sinkholes. Apart from shedding light on the mechanical process, the results of this study may pave the way for the implementation of an operational sinkhole early-warning system.
The sudden failure of near-surface cavities and the resulting sinkholes have constituted a recent hazard affecting the populations, lifelines and the economy of the Dead Sea region. This paper describes how seismic monitoring techniques could detect the extremely low-energy signals produced by cavitation in unconsolidated, layered media. Dozens of such events were recorded within a radius of 200 m during several night-time experiments carried out along the western Dead Sea shores.
The absence of prior knowledge about cavitation-induced events in unconsolidated media required an initial signal characterization, for which a series of source processes were simulated in the field under controlled conditions. The waveform analysis by sonograms recognizes two main groups of seismic events: impacts on dry material and impacts in liquid. Our analysis demonstrates that the discrimination between both types of source functions is robust despite the extreme nature of the scatter media.
In addition to their association with specific source processes, these events can be precisely located by a graphical, error-resistant jackknifing approach. Using an extended ML scale, their source energy can be quantified, and related to standard seismic activity. In summary, it is now possible to monitor subsurface material failures before sinkhole collapse since the discrimination of impact signals on the basis of their frequency content is indicative of the maturity of the cavitation process.
The water level of the Dead Sea, a terminal hypersaline lake (total dissolved solids, approximately 340 g/L) has decreased at an average rate of 0.5 m/yr since 1960 and by 0.8 m/yr between 1981 and 1989. The dramatic long-term water level variation of the Dead Sea and the seasonal short-term fluctuations are accompanied by parallel variations of groundwater levels in an adjacent aquifer. A general methodology based on a simplified yet reliable one-dimensional flow model, together with continuous measurements of groundwater levels in observation wells, enables analysis of aquifer structural and hydraulic properties. Furthermore, this analysis enables prediction of future groundwater levels in unconfined and confined aquifers due to future changes in lake levels.
Important elements in the evolutionary history of saline groundwater might be overlooked when they involve both sulfate removal through reduction and input of sulfate via dissolution. These two simultaneous and apparently contrasting processes can result in a negligible net effect on the sulfate concentration. Isotopic composition of sulfur in sulfate and sulfide can be applied to identify the bacterial sulfate reduction (BSR) though the extent of the process is difficult to quantify. Saturation with respect to gypsum may suggest that gypsum dissolution also occurs. However, a more definite identification of these processes and their quantification can be achieved through the use of ammonium concentration in the anoxic brines. This approach assumes that the ammonium is derived only from the oxidation of organic matter through BSR and it requires that the C:N ratio in the oxidized organic matter be known. A minimum estimate for the sulfate reduction can be obtained when the Redfield C:N ratio (106:16) is assumed. Several calculation methods are presented to identify the extent of sulfate reduction prior to, concomitant with, or following gypsum dissolution that are based on combining sulfur isotopic compositions, Rayleigh distillation equation, and calculated gypsum saturation indices. The required assumptions are presented and their validation is discussed. The subsurface hypersaline Ca-chloride brines in the vicinity of the Dead Sea are taken as a case study. Here sulfur isotope compositions of sulfate and sulfide, and high ammonium concentrations indicate BSR occurs in the subsurface. The sulfur isotopic composition of the sulfate makes it possible to distinguish between two major groups of brine and their recent evolutionary histories: (1) the Qedem–Shalem thermal brines (δ34SSO4=21–24‰) which emerge as springs along the shores and are slightly undersaturated with respect to gypsum; (2) DSIF–Tappuah brines (δ34SSO4=30–60‰) which are found in shallow boreholes and are saturated to oversaturated with respect to gypsum. Calculations based on their ammonium content suggest that both groups of brine require apparent unreasonably high oversaturations with respect to gypsum prior to the onset of the reduction. This implies that the groundwater systems were open with respect to sulfate, and that the sulfate reservoir was replenished continuously or intermittently during the BSR. The DSIF–Tappuah brines continue to dissolve gypsum during their BSR. The dissolving sulfate is derived from relatively isotopically enriched gypsums (δ34SSO4>20‰), such as found in the Lisan Formation. These brines approach the steady-state isotopic composition (δ34Sss) dictated by the combination of the δ34S of the dissolving gypsum and the fractionation factor accompanying BSR. The sulfur isotopic composition of the Qedem–Shalem brines implies that most of their ammonium content is derived from an earlier phase of BSR and that the last phase of BSR takes place during the brines’ rapid ascent to the surface. Prior to this stage they evolved through either: (1) dissolution of gypsum with δ34SSO4≤20‰ which occurred after the main BSR in the subsurface; (2) a previous phase in which the brines were part of a lake and later percolated to the subsurface. As such, their isotopic composition and ammonium content were determined by the combined effect of freshwater sulfate input to the lake and BSR in the stratified lake.
Late Pleistocene lacustrine fan-deltas which developed in an arid, disequilibrated submergent environment along the W. fault scarp of the Rift are characterrized by: 1) alluvial fan deposits of crudely stratified conglomerate beds and horizontal and cross-bedded sandstones. 2) fan-front thick and thin interlayers of ripple cross-laminated sandstones and mudstones which constitute a sedimentary belt a few kilometers wide in front of the fan; 3) fan-influenced detrital laminated chalks. - from Author
The sinkholes along the Dead Sea coast are observed in two main sedimentary environments: alluvial fan sinkholes, which usually form abruptly as deep (∼20 m) and narrow (∼3 m) sinkholes, and mud-flat sinkholes, which usually form as shallow (a few centimeters) and wide (>5 m) sinkholes and deepen later. The mechanical collapse of all sinkholes is triggered by cavities created by the dissolution of an underlying salt layer by relatively fresh groundwater. The processes attributed to the mechanical formation of the sinkholes are viscous flow and brittle fracture failure. We use a two-dimensional viscoelastic damage rheology numerical model to quantitatively explain the brittle and ductile aspects of collapsed sinkholes. Three cases of the rheology of the collapsed sediments are simulated, 1) damage controlled failure, 2) viscoelastic controlled failure, and 3) an intermediate damage-viscoelastic case. Results show that viscoelasticity cannot be the sole process acting on the deformed layer because all sinkholes are characterized by sharp boundaries. The damage accumulation progresses until arched cavities are created in the soil layer. Because of the geometric heterogeneity of the layer (represented by the heterogeneity of the mesh) smaller blocks continue to fall after the first breakup into the cavity, advancing the arched cavity upwards. This propagation finally stops when the cavity is shallow enough to hold the irregular arch. The combination of these two processes creates competition within the stress reduction mechanism that may lead to either magnified or reduced deformation. The deformation is magnified in high shear stress locations, where the dispersion of the viscous flow spreads damage failure, and it is reduced in low shear stress locations where viscous flow disperses shear stress before the onset of damage.
Modern-day synoptic-scale eastern Mediterranean climatology provides a useful context to synthesize the diverse late Pleistocene (60–12 ka) paleohydrologic and paleoenvironmental indicators of past climatic conditions in the Levant and the deserts to its south and east. We first critically evaluate, extract, and summarize paleoenvironmental and paleohydrologic records. Then, we propose a framework of eastern Mediterranean atmospheric circulation features interacting with the morphology and location of the southeast Mediterranean coast. Together they strongly control the spatial distribution of rainfall and wind pattern. This cyclone–physiography interaction enforces the observed rainfall patterns by hampering rainfall generation south and southeast of the latitude of the north Sinai coast, currently at 31°15′.
Natural and anthropogenic caves may represent a potential hazard for the built environment, due to the occurrence of instability within caves, that may propagate upward and eventually reach the ground surface, inducing the occurrence of sinkholes. In particular, when caves are at shallow depth, the effects at the ground surface may be extremely severe. Apulia region (southern Italy) hosts many sites where hazard associated with sinkholes is very serious due to presence of both natural karst caves and anthropogenic cavities, the latter being mostly represented by underground quarries. The Pliocene-Pleistocene calcarenite (a typical soft rock) was extensively quarried underground, by digging long and complex networks of tunnels. With time, these underground activities have progressively been abandoned and their memory lost, so that many Apulian towns are nowadays located just above the caves, due to urban expansion in the last decades. Therefore, a remarkable risk exists for society, which should not be left uninvestigated.
The interface between fresh and saline ground water was studied in the Dead Sea area, using in situ profiles of electrical conductivity (EC) of water. The slope of the interface was found to be 10 times shallower than normally expected near the ocean because of the greater density contrast (the density of the Dead Sea is 1.23 g/cc). Although the Dead Sea system is extremely dynamic, the Ghyben-Herzberg approximation was still found to be relevant. The shallow interface is expected to cause Dead Sea water to intrude much farther inland than does sea water adjacent to oceans. This extremely shallow interface needs to be taken into account when exploiting ground water in this area in order to avoid upconing of brines and salinization.
In recent times, the hydrologic system of the Dead Sea area has changed in water levels and salinity. Simulations using SUTRA code were run for a confined subaquifer to examine the effects of such change on the location of the fresh-saline water interface. Following the changes, the new interface is not parallel to the previous one because the increase in density causes a decrease in the interface's slope.
Since the early 1980s, the Dead Sea coast has undergone a near catastrophic land deterioration as a result of a rapid lake-level
drop. One conspicuous expression of this deterioration is the formation of sinkholes fields that puncture the coastal plains.
The evolution of sinkholes along nearly 70-km strip has brought to a halt the regional development in this well-known and
toured area and destroyed existing infrastructures. Great efforts are being invested in understanding the phenomena and in
development of monitoring techniques. We report in this paper the application of airborne laser scanning for characterization
of sinkholes. We demonstrate first the appropriateness of laser scanning for this task and its ability to provide detailed
3D information on this phenomenon. We describe then an autonomous means for their extraction over large regions and with high
level of accuracy. Extraction is followed by their detailed geometric characterization. Using this high-resolution data, we
show how sinkholes of 0.5m radius and 25cm depth can be detected from airborne platforms as well as the geomorphic features
surrounding them. These sinkhole measures account for their embryonic stage, allowing tracking them at an early phase of their
creation.
KeywordsSinkholes–Airborne laser scanning–Dead Sea–Land degradation
For the last four decades, the level of the Dead Sea has been subjected to continual variation which, among other important
factors, has led to the occurrence of much subsidence and many sinkholes in the southern Dead Sea area. Sinkhole activities
occurred repetitively and were observed in open farms, across roads, near dwellings and near an existing factory, thus causing
a serious threat to the locals and farmers of the area and their properties. This paper presents the main results from detailed
geological and geotechnical studies of this area. Aerial photo interpretation and borehole drilling aided these studies. Parallel
geophysical investigations (vertical electrical sounding and seismic refraction) and hydrological and hydrogeological studies
were made by others in the same area to also investigate this phenomenon. It was found that sinkholes are aligned to and follow
old water channels and are concentrated parallel to the recent shoreline of the Dead Sea. The development of subsurface cavities
is associated mainly with the variation in the level of the Dead Sea over the four past decades, the presence of regional
salt intrusion under the surface of salt beds, the fluctuation of the water table and continuous dissolution and the active
tectonism of the area. Moreover, this work showed that the area is still under active sinkhole hazards and other parts of
the area will be inevitably affected by sinkholes in the future.No practical engineering solution to this problem is feasible.
Calatayud in NE Spain is an historically important city built on recent alluvial deposits underlain by gypsum and other soluble rocks. Since its foundation by the Muslims in 716 A.D., the city development has been strongly influenced by geohazards including flooding, subsidence and slope movements. Most of the flooding problems have been mitigated by diversion of the local drainage. However, dissolution of the evaporite bedrock in the urban areas continually causes subsidence and triggers rock-falls from the gypsum cliffs overlooking the city. Subsidence is also caused by the hydrocollapse of gypsiferous silt in the alluvial fan deposits. Building damage in the city was surveyed using a classification scheme developed originally to record damage in British coal mining areas. The Calatayud damage survey shows that the worst building subsidence is concentrated along the line of a buried channel that runs underneath the gypsiferous silt alluvial fan. Natural subsurface drainage causes the dissolution and subsidence, which is aggravated by leakage from water and sewage pipes. Some building damage has been exacerbated during reconstruction by incomplete piling leaving buildings partially unsupported. Mitigation measures include the control of water leakage by the installation of flexible service pipes. Careful construction techniques are needed for both conservation and new developments, especially when piled and minipiled foundations are used. Geomorphological mapping is cost-effective in helping to locate and avoid the zones of subsidence for future development.
Multiple sinkhole susceptibility models have been generated in three study areas of the Ebro Valley evaporite karst (NE Spain) applying different methods (nearest neighbour distance, sinkhole density, heuristic scoring system and probabilistic analysis) for each sinkhole type separately (cover collapse sinkholes, cover and bedrock collapse sinkholes and cover and bedrock sagging sinkholes). The quantitative and independent evaluation of the predictive capability of the models reveals that: (1) The most reliable susceptibility models are those derived from the nearest neighbour distance and sinkhole density. These models can be generated in a simple and rapid way from detailed geomorphological maps. (2) The reliability of the nearest neighbour distance and density models is conditioned by the degree of clustering of the sinkholes. Consequently, the karst areas in which sinkholes show a higher clustering are a priori more favourable for predicting new occurrences. (3) The predictive capability of the best models obtained in this research is significantly higher (12.5–82.5%) than that of the heuristic sinkhole susceptibility model incorporated into the General Urban Plan for the municipality of Zaragoza. Although the probabilistic approach provides lower quality results than the methods based on sinkhole proximity and density, it helps to identify the most significant factors and select the most effective mitigation strategies and may be applied to model susceptibility in different future scenarios.
The considerable influence of the geological structure on groundwater flow regime is exhibited in the thick carbonate aquifer beneath the Judean Desert, Israel. Groundwater flow is diverted from the general steep hydraulic gradient, creating a subsurface ‘river-like’ meandering flow pattern. The structure of the extensive-folded anticlinorium forces groundwater flow through synclinal axes in the upper aquifer and in places it overflows from one to an adjacent syncline. Groundwater outflows are at Tsukim, Kane, Samar and En-Gedi springs near the Dead Sea shore and by sub-surface flow across the Graben faults towards the Dead Sea.In this study all available data are integrated and processed, first ever, to form a complete representation of the three-dimensional hydrostratigraphy and hydrogeology. Using numerical modeling (MODFLOW), we analyzed quantitatively the flow regime, leakage rates between upper and lower sub-aquifers and between adjacent sub-basins, the groundwater mass balance, and aquifer hydraulic properties.This study has practical implications regarding recent groundwater management, future possibilities of groundwater development for the benefit of both Israelis and Palestinians residing in the area, and conservation of nature reserves located along the Dead Sea.
The Dead Sea is a terminal lake of one of the largest hydrological systems in the Levant and may thus be viewed as a large rain gauge for the region. Variations of its level are indicative of the climate variations in the region. Here, we present the decadal- to centennial-resolution Holocene lake-level curve of the Dead Sea. Then we determine the regional hydroclimatology that affected level variations. To achieve this goal we compare modern natural lake-level variations and instrumental rainfall records and quantify the hydrology relative to lake-level rise, fall, or stability. To quantify that relationship under natural conditions, rainfall data pre-dating the artificial Dead Sea level drop since the 1960s are used. In this respect, Jerusalem station offers the longest uninterrupted pre-1960s rainfall record and Jerusalem rains serve as an adequate proxy for the Dead Sea headwaters rainfall. Principal component analysis indicates that temporal variations of annual precipitation in all stations in Israel north of the current 200 mm yr−1 average isohyet during 1940–1990 are largely synchronous and in phase (∼70% of the total variance explained by PC1). This station also represents well northern Jordan and the area all the way to Beirut, Lebanon, especially during extreme drought and wet spells. We (a) determine the modern, and propose the past regional hydrology and Eastern Mediterranean (EM) climatology that affected the severity and length of droughts/wet spells associated with multiyear episodes of Dead Sea level falls/rises and (b) determine that EM cyclone tracks were different in average number and latitude in wet and dry years in Jerusalem. The mean composite sea level pressure and 500-mb height anomalies indicate that the potential causes for wet and dry episodes span the entire EM and are rooted in the larger-scale northern hemisphere atmospheric circulation. We also identified remarkably close association (within radiocarbon resolution) between climatic changes in the Levant, reflected by level changes, and culture shifts in this region.