Natural and human-induced dissolution and subsidence processes in the salt outcrop of the Cardona Diapir (NE Spain)

Identifying the recharge and salinization mechanisms of the Shekastian saline spring in southern Iran

To identify the recharge, and the salinization mechanisms of Shekastian saline spring, appearing via thin limestone layers on the Shekastian stream bed, southern Iran, a comprehensive study was conducted using multi-tracing approach. Hydrochemical tracing indicated that the halite dissolution is the main salinity source for Shekastian spring. Similar to surface waters, spring salinity is amplified by evaporation during dry season, indicating that recharge comes from surface waters. The temperature of the spring water varies hourly, which is another sign that surface waters recharge the spring. Applying the discharge tracing method at two low-discharge times in two consecutive years by precise longitudinal discharge monitoring of the Shekastian stream above and below the spring site revealed that the main source of recharge for the Shekastian saline spring is water escape via thin limestone layers, located on a stream bed above the spring site. Results of isotope tracing indicated that Shekastian saline spring is recharged from evaporated surface water, subjecting to CO₂ gas along subsurface flow path of recharging water. Geologic/geomorphologic evidences, supported by results of hydrochemical tracing, revealed that halite dissolution of Gachsaran evaporite formation by spring recharging water is the main salinization source for the Shekastian saline spring. To avoid salinization of Shekastian stream by Shekastian saline spring, draining the spring recharging water at downstream vicinity of spring recharging stream by building an underground interceptor drainage system is suggested, in which resulted in flow stopping the spring.

Effect of grain dissolution on sloping ground

The static and dynamic stability of natural or constructed slopes can be affected by dissolution or dissolution-like phenomena. Their underlying mechanisms, however, remain unclear. New experimental results and discrete element simulations provide particle-level and macroscale information on the consequences of mineral dissolution on slope behavior. At the microscale, load-carrying grain arches develop around dissolving particles, the porosity increases, and contact force chains evolve to form a honeycomb topology. At the macroscale, while vertical settlements are the prevailing deformation pattern, lateral granular movements that create mass wasting are prominent in sloping ground, even under the quasi-static granular loss. Horizontal grain displacement is maximum at the surface and decreases linearly with the distance from the slope surface to become zero at the bottom boundaries, much like vertical granular displacement along the depth. Sediments with smaller friction angles and steeper slopes experience greater displacement, both vertically and horizontally. Slopes become flatter after dissolution, with the reduction in slope angle directly related to the loss in ground elevation, ΔH/H_o. Yet, because of the porous fabric that results from dissolution, vertical shortening is less than the upper bound, estimated from the loss in the solid mass fraction, ΔH/H_o≈SF. Under water-saturated conditions, the post-dissolution fabric may lead to sudden undrained shear and slope slide.

A decade-long silent ground subsidence hazard culminating in a metropolitan disaster in Maceió, Brazil

Ground subsidence caused by natural or anthropogenic processes affects major urban areas worldwide. Sinkhole formation and infrastructure fractures have intensified in the federal capital of Maceió (Alagoas, Brazil) since early 2018, forcing authorities to relocate affected residents and place buildings under demolition. In this study, we present a 16-year history (2004-2020) of surface displacement, which shows precursory deformations in 2004-2005, reaching a maximum cumulative subsidence of approximately 200 cm near the Mundaú Lagoon coast in November 2020. By integrating the displacement observations with numerical source modelling, we suggest that extensive subsidence can be primarily associated with the removal of localized, deep-seated material at the location and depth where salt is mined. We discuss the accelerating subsidence rates, influence of severe precipitation events on the aforementioned geological instability, and related hazards. This study suggests that feedback destabilization mechanisms may arise in evaporite systems due to anthropogenic activities, fostering enhanced and complex superficial ground deformation.

Factors Governing the Impact of Emerged Salt Diapirs on Water Resources

Salt diapirs in southern Iran are typically in contact with karstic and alluvial aquifers and consequently they are the most likely sources of groundwater salinization in this arid region. However, there are some salt diapirs that have no significant degradation effect on adjacent aquifers. Assessments of 62 of 122 Iranian-emerged salt diapirs based on geological, geomorphological, hydrogeological, and hydrochemical investigations indicated that 45% of the studied salt diapirs did not have a negative impact on surrounding water resources, whereas 55% of the salt diapirs have degraded water quality of adjacent aquifers. The impacts ranged from low- to high-grade salinization. We characterize here four major factors that control the impact of salt diapirs on surrounding water resources: (1) the evolutionary stage of the diapir, (2) the geological and (3) hydrogeological setting of the diapir, and (4) human activities. Identification of the major factors governing the influence of salt diapirs on the adjacent aquifers is necessary to understand the mechanism of salt diapir impact on adjacent aquifers, and subsequently to decide how to mitigate the deteriorating effect of the diapirs on the surrounding water resources.