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Density, temperature, salinity, and hydraulic head are physical scalars governing the dynamics of aquatic systems. In coastal aquifers, lakes, and oceans, salinity is measured with conductivity sensors, temperature is measured with thermistors, and density is calculated. However, in hypersaline brines, the salinity (and density) cannot be determined by conductivity measurements due to its high ionic strength. Here, we resolve density measurements using a hydrostatic densitometer as a function of an array of pressure sensors and hydrostatic relations. This system was tested in the laboratory and was applied in the Dead Sea and adjacent aquifer. In the field, we measured temporal variations of vertical profiles of density and temperature in two cases, where water density varied vertically from 1.0 × 103 kg·m−3 to 1.24 × 103 kg·m−3: (i) a borehole in the coastal aquifer, and (ii) an offshore buoy in a region with a diluted plume. The density profile in the borehole evolved with time, responding to the lowering of groundwater and lake levels, that in the lake demonstrated the dynamics of water-column stratification under the influence of freshwater discharge and atmospheric forcing. This method allowed, for the first time, continuous monitoring of density profiles in hypersaline bodies, and it captured the dynamics of density and temperature stratification.

Co-seismic and post-seismic groundwater response to the Sea of Galilee 2018 seismic swarm, along with other teleseismic earthquakes are analyzed in nine water pressure monitoring wells, with high sampling rates (40 sps). The largest event of the swarm (Mw 4.6) caused significant water level oscillations of 0.216 bar (2.16 m) and sustained water level drop of 0.121 bar (1.21 m). The response of groundwater to this event and two other distant large events include co-seismic oscillations, co-seismic undrained sustained change, and post seismic drained change. In addition, the proximity of the earthquake swarm to high resolution monitoring wells provides an opportunity to analyze the changes in the oscillations’ amplitudes of most events. The ratio of the water level to ground motion acceleration amplitudes increased after the Mw 4.6 event, suggesting that the aquifer poro-elastic properties have changed. These co-seismic amplitude changes are more sensitive measure than the water level response to earth tides that showed no significant change in the phase and amplitude associated with any of the events. The maximum amplitude of the oscillations is correlated to the amount of drained response, suggested to be caused by activation of a nearby fault and drainage of water between aquifers. The undrained behavior is related to poro-elastic properties changes within the aquifer and depends on the duration of the oscillations. Details of the groundwater high sampling rate can shed light on deformation processes that were described previously as step like changes.

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.