Dynamics of hydrological and geomorphological processes in evaporite karst at the eastern Dead Sea – a multidisciplinary study (original) (raw)
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Solid Earth Discussions
The fall of hydrological base-level is long established as a driver of geomorphological change in both fluvial and karst systems, but few natural occurrences occur on timescales suitable for direct observation. Here we document the spatiotemporal development of fluvial and karstic landforms along 20 the eastern coast of the hypersaline Dead Sea (at Ghor al-Haditha, Jordan) during a 50-year period of regional base-level decline from 1967 to 2017. Combining remote sensing data with close-range photogrammetric surveys, we show that the 35 m base-level fall has caused shoreline retreat of up to 2.5 km, and resulted in: (1) incision of new meandering or straight/braided stream channels and (2) formation of >1100 sinkholes and several salt-karst uvalas. Both alluvial incision and karst-related subsidence 25 represent significant hazards to local infrastructure. The development of groundwater-fed meandering stream channels is in places interlinked with that of the sinkholes and uvalas. Moreover, active areas of channel incision and sinkhole development both migrate seaward in time, broadly in tandem with shoreline retreat. Regarding theoretical effects of base-level fall, our observations show some deviations from those predicted for channel geometry, but are remarkably consistent with those for groundwater-30
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.
Journal of Hydrology, 2009
The effects of base (sea or lake) level changes on the location and elevation of the groundwater divide were examined in the hydrological system between the Mediterranean Sea and the Dead Sea. Steadystate simulations were conducted with a 1-D analytical model and transient conditions were simulated using FEFLOW groundwater modeling software. Two hydrological scenarios were simulated: (a) a transition to a new steady-state, following the expected drop of 150 m of the Dead Sea level; and (b) the time of the precursor of the Dead Sea (Lisan Lake), some 20,000 years ago, when the lake level was about 250 m above the present-day Dead Sea level and the Mediterranean Sea level was 120 m below its present one. The results of the simulations show that the Dead Sea level drop has led to a progressive decline in the groundwater level up to several kilometers inland from the shoreline. The hydraulic gradient increases, and thus the discharge to the lake also increases at the expense of the storage, and also due to a small enlargement of the recharge zone by a $600 m shift of the divide.
Self-accelerated Development of Salt Karst during Flash-floods along the Dead Sea Coast, Israel
Journal of Geophysical Research: Earth Surface, 2015
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.
Lower crustal flow and the role of shear in basin subsidence: an example from the Dead Sea basin
Earth and Planetary Science Letters, 2002
We interpret large-scale subsidence (5^6 km depth) with little attendant brittle deformation in the southern Dead Sea basin, a large pull-apart basin along the Dead Sea transform plate boundary, to indicate lower crustal thinning due to lower crustal flow. Along-axis flow within the lower crust could be induced by the reduction of overburden pressure in the central Dead Sea basin, where brittle extensional deformation is observed. Using a channel flow approximation, we estimate that lower crustal flow would occur within the time frame of basin subsidence if the viscosity is 9 7U10 19^1 U10 21 Pa s, a value compatible with the normal heat flow in the region. Lower crustal viscosity due to the strain rate associated with basin extension is estimated to be similar to or smaller than the viscosity required for a channel flow. However, the viscosity under the basin may be reduced to 5U10 17^5 U10 19 Pa s by the enhanced strain rate due to lateral shear along the transform plate boundary. Thus, lower crustal flow facilitated by shear may be a viable mechanism to enlarge basins and modify other topographic features even in the absence of underlying thermal anomalies. ß
Journal of Hydrology, 2020
Lake-level fluctuations brought on by climatic changes and anthropogenic factors may affect the flow regime in adjacent aquifers that discharge toward those lakes. Such fluctuations may also cause displacement of springs that discharge these aquifers. Using a calibrated numerical model, an extreme example of such phenomenon is observed in the Dead Sea rift valley and the adjacent Eastern Mountain Aquifer of the Judea and Samaria Mountains. Lake levels along the Dead Sea rift have changed dramatically and rapidly by hundreds of meters, followed by changes in the lake areas by hundreds of square kilometers. Simultaneously, the aquifer exhibited spring displacements, both on large and small scales. Currently, 50% of the aquifer water discharge in the Zuqim zone, and 10% north of the Dead Sea. But in the past, only 30% discharged at Zuqim and 40% north of the Dead Sea. There is evidence for such an occurrence in the past, and it is likely to recur in the future, based on the predicted progressive decline of the current Dead Sea level. This may have an impact on wetland habitats along the coast. 1.2. Lakes in the Dead Sea rift valley The Dead Sea (Fig. 1B) is the lowest terrestrial lake on Earth; its present level (2019) is −433 m above sea level (masl) (Israel Water Authority). It is a unique hyper-saline and deep terminal lake with a maximum depth of about 300 m. Its margin slopes are relatively steep, reflected in extreme lake-level fluctuations that follow climate changes or anthropogenic activity. The Dead Sea level currently falls at an average rate of > 1 m per year, mainly due to the damming of its
Collapse and subsidence associated with salt karstification along the Dead Sea
Carbonates and Evaporites, 2001
Two types ofsinkholes are observed along the Dead Sea shore, Israel. The first is associated with vadose dissolution in Mount Sedom salt diapir. The second is associated with dissolution under the watertable along the retreating Dead Sea shore. The Dead Sea level is falling dramatically, mainly because of human activity. Simultaneously, the lake shores suffer tremendous impact since the late 1980s: The ground is collapsing and subsiding in hundreds of points along the lake, with people, roads and property being swallowed in the more catastrophic events. The collapse is believed to result from dissolution of salt by aggressive groundwater, following the retreat of Dead Sea level and the groundwater halocline. Geological evidence suggests that a previous major lake level fall occurred naturally-2000 BCE. This may provide a new explanation for a curious historical-geological phrase in the book of Genesis, suggested to record formation of collapse sinkholes which occurred in response to the historic falling lake level, associated with climatic desiccation. with recent environmental changes within the rift valley. In addition, past and present hazard to society is evaluated. We also combine field evidence of Holocene Dead Sea level
A B S T R A C T Ground subsidence and sinkhole collapse are phenomena affecting regions of karst geology worldwide. The rapid development of such phenomena around the Dead Sea in the last four decades poses a major geological hazard to the local population, agriculture and industry. Nonetheless many aspects of this hazard are still incompletely described and understood, especially on the eastern Dead Sea shore. In this work, we present a first low altitude (< 150 m above ground) aerial photogrammetric survey with a Helikite Balloon at the sinkhole area of Ghor Al-Haditha, Jordan. We provide a detailed qualitative and quantitative analysis of a new, high resolution digital surface model (5 cm px −1) and orthophoto of this area (2.1 km 2). We also outline the factors affecting the quality and accuracy of this approach. Our analysis reveals a kilometer-scale sinuous depression bound partly by flexure and partly by non-tectonic faults. The estimated minimum volume loss of this subsided zone is 1.83 • 10 6 m 3 with an average subsidence rate of 0.21 m yr −1 over the last 25 years. Sinkholes in the surveyed area are localized mainly within this depression. The sinkholes are commonly elliptically shaped (mean eccentricity 1.31) and clustered (nearest neighbor ratio 0.69). Their morphologies and orientations depend on the type of sediment they form in: in mud, sinkholes have a low depth to diameter ratio (0.14) and a long-axis azimuth of NNE–NE. In alluvium, sinkholes have a higher ratio (0.4) and are orientated NNW–N. From field work, we identify actively evolving artesian springs and channelized, sediment-laden groundwater flows that appear locally in the main depression. Consequently, subrosion, i.e. subsurface mechanical erosion, is identified as a key physical process, in addition to dissolution, behind the subsidence and sinkhole hazard. Furthermore, satellite image analysis links the development of the sinuous depression and sinkhole formation at Ghor Al-Haditha to preferential groundwater flow paths along ancient and current wadi riverbeds.
This study aims to locate the zones of groundwater discharge into the eastern shores of the Dead Sea and to estimate its quantity. The evaluation of inflow was accomplished by different ways of approach: the first one to use the electrical conductivity-temperature with a depth, the second to use a chemical tracer (Radon-222), the third to use thermal infrared imagery and the last is to use electromagnetic radiation techniques in addition to the schematic geological and hydrogeological models of the study area. The Dead Sea divides into two layers relating to the electrical conductivity and temperature with depth. The upper layer subdivides into two members. The upper member extends from the sea surface down to a depth of 15-25 m. The lower member extends from a depth of 15-25 m to 40 m and it characterized with high TDS and low EC. The second layer extends from a depth of 40 m to the end of profiles. Laboratory experiments carried out to find a relationship between the EC at a specific T and the TDS. These experiments indicate that the EC reachs its maximal 202 mS/cm at a salinity of about 267 g/l from where it starts decreasing with the increase of the TDS and it reachs about 175 mS/cm at a salinity of 404 g/l. The minimal of TDS was observed at about 460 g/l at EC about 156 mS/cm. The submarine groundwater discharged into the Dead Sea in the upper 16 m in Sweimah area. It is discharged in the upper 25 m in Zarka Ma'in area, in the upper 15 m in Zara and it is discharged in the upper 18 m in Mujeb. The reason why the lower member has the highest TDS was explained. It is due to the very high T at the Dead Sea area in summer and very high evaporation. The density of the upper layer becomes higher than that of the layer underneath. Therefore this denser upper layer sinks beneath the layer which has lower density at the layer where the groundwater discharged into the Dead Sea and this last layer upwelling to the surface. The chemical tracer radon-222 technique shows that the highest radon concentrations were found at the area close to the shoreline. This means that the largest amount of groundwater discharge is close to the shoreline. As well the highest radon-222 concentrations were found at a depth of 12 m in the three stations while it was at a depth of 7 m in the Zarka Ma'in station. It shows also that the groundwater dischargs into the Dead Sea in the upper 20 m. This is coinciding with the finding from the EC and T survey. The submarine groundwater discharge is estimated using Radon-222 as 135.7 million m 3 /y in Sweimah area, about 128.5 million m 3 /y at Zarka Main area, about 33.7 million m 3 /y in Zara area and it is about 90.3 million m 3 /y in Mujeb area. The total quantity of submarine groundwater discharge into the eastern shoreline of the Dead Sea is 388.2 million m 3 /y. The quatity of groundwater discharge is estimated by using mixing of TDS about 181 MCM/y, and it is estimated about 59 MCM/y by using Darcys' law. The results of SGD estimations from different methods compared with the discharge from water balance 480 MCM/y. The results showed that the discharge might be between 200 and 300 MCM/y. The thermal infrared imagery (TIR) was used to identify thermal anomalies along the eastern shoreline of the Dead Sea, thereby to determine the exact locations of submarine groundwater discharge. As well as, the locations of springs onshore surround the area. Many submarine groundwater discharge zones were identified. The main zones were in Zarka Ma'in, Zara and Mujeb areas. The highest differences in temperature between the groundwater discharge and the sea surface water were observed at the Zarka Ma'in and Zara areas, because these areas have a hot springs flow into the Dead Sea. The TIR imagery showed that the extent of the discharge was between 350 m and about 750 m away from the shoreline. The electromagnetic radiation (EMR) identifies the energy anomalies, thereby determining the active faults and fractures as well as the sinkholes along the eastern shoreline of the Dead Sea. These features are considered zones of weakness for the submarine groundwater discharge. The maximum radiation was observed in Sweimah area. Many major faults and non-opened sinkholes were found along this area at different locations. This proves the finding from chemical tracers that showed that the maximum discharge is in this area. As well few major fault and non-opened sinkholes were observed in Zara-Zarka Ma'in and Mujeb areas. The geological and hydrogeological models showed that the direction of the groundwater flow is to the west and northwest directions toward the Dead Sea.