Dissolution Subsidence Research Articles

The episodic rise, net growing rate and kinematics of radial faults of the Salinas de Oro diapir using paleoseismological techniques (NE Spain). Salt upwelling versus karstic subsidence

This paper explores the use of trenching and paleoseismological techniques to determine salt flow rates into a salt diapir for the first time in the literature. The Salinas de Oro diapir, located in the northern Spanish Pyrenees, is an oval-shaped Triassic-salt stock that extends vertically for ≫7 km down to the Paleozoic basement. Salt dissolution subsidence and diapir growth are coeval active processes. Karstification is responsible for the development of large sinkholes, a thick caprock and the monocline folding and ring faulting of the Cretaceous and Early Tertiary limestone rim. The evaporite karstic aquifer discharges high-concentration water of up to 137 g/l of total dissolved solids and a conductivity over 200 mS/cm into the Salado Creek, which drains the diapir top. The salinity monitoring of this drainage provides a maximum karstic surface lowering rate of around 2.8 mm/yr. Salt upwelling has caused the 150 m uplift of the annular limestone escarpment and the development of ≫3000 m long radial grabens with up to 90 m of vertical offset that disrupt drainages, displace Quaternary deposits and overprint concentric faults. The 260 cm drag folding of lacustrine facies exposed in a 42 m long and 6.5 m deep trench due to the creep motion of the western radial fault of Azanza Graben yielded a minimum short-term uplift slip rate of 1.75 mm/yr for the last 1485 years and provides a minimum salt supply rate of over 5 mm/yr considering karstification lowering. This value that is several hundred times higher than average, evidence the discontinuous growth of Salinas de Oro diapir.

Dissolution collapse of a growing diapir from radial, concentric, and salt-withdrawal faults overprinting in the Salinas de Oro salt diapir, northern Spain

AbstractA geomorphic investigation of the Salinas de Oro salt diapir in the Pyrenees reveals that the ring fracture pattern related to the karstic collapse of the diapir crest may vary significantly depending on the rates of dissolution and salt flow, and the rheology of the overburden. The salt diapir has well-developed concentric faults related to salt dissolution subsidence throughout the Quaternary. Roof strata accommodate subsidence by a combination of downward sagging and brittle collapse leading to the development of a ring monocline that is broken by 5 to 20 m throw conjugated normal faults and a 40 m throw, 9.5-km-long and 200-m-wide keystone graben. The salt diapir top has >100-m-long sinkholes that coalesce to form hollows >70 m deep. Up to 3-km-long radial grabens with a 70 to 90 m vertical throw overprint concentric-ring faulting and displace Quaternary deposits demonstrating active salt flow and diapir rise. Radial faults are linked with salt-withdrawal faults of the Andia Fault Zone (AFZ). Salt flow from the AFZ into the Salinas de Oro salt diapir causes brittle gravitational extension of limestone strata leading to a sequence of grabens and Quaternary faults >10 km long and several hundred meters deep.

A reactive transport model for the quantification of risks induced by groundwater heat pump systems in urban aquifers

Shallow geothermal resource exploitation through the use of groundwater heat pump systems not only has hydraulic and thermal effects on the environment but also induces physicochemical changes that can compromise the operability of installations. This study focuses on chemical clogging and dissolution subsidence processes observed during the geothermal re-injection of pumped groundwater into an urban aquifer. To explain these phenomena, two transient reactive transport models of a groundwater heat pump installation in an alluvial aquifer were used to reproduce groundwater-solid matrix interactions occurring in a surrounding aquifer environment during system operation. The models couple groundwater flow, heat and solute transport together with chemical reactions. In these models, the permeability distribution in space changes with precipitation-dissolution reactions over time. The simulations allowed us to estimate the calcite precipitation rates and porosity variations over space and time as a function of existent hydraulic gradients in an aquifer as well as the intensity of CO2 exchanges with the atmosphere. The results obtained from the numerical model show how CO2 exolution processes that occur during groundwater reinjection into an aquifer and calcite precipitation are related to hydraulic efficiency losses in exploitation systems. Finally, the performance of reinjection wells was evaluated over time according to different scenarios until the systems were fully obstructed. Our simulations also show a reduction in hydraulic conductivity that forces re-injected water to flow downwards, thereby enhancing the dissolution of evaporitic bedrock and producing subsidence that can ultimately result in a dramatic collapse of the injection well infrastructure.

Radar interferometry techniques for the study of ground subsidence phenomena: a review of practical issues through cases in Spain

Subsidence related to multiple natural and human-induced processes affects an increasing number of areas worldwide. Although this phenomenon may involve surface deformation with 3D displacement components, negative vertical movement, either progressive or episodic, tends to dominate. Over the last decades, differential SAR interferometry (DInSAR) has become a very useful remote sensing tool for accurately measuring the spatial and temporal evolution of surface displacements over broad areas. This work discusses the main advantages and limitations of addressing active subsidence phenomena by means of DInSAR techniques from an end-user point of view. Special attention is paid to the spatial and temporal resolution, the precision of the measurements, and the usefulness of the data. The presented analysis is focused on DInSAR results exploitation of various ground subsidence phenomena (groundwater withdrawal, soil compaction, mining subsidence, evaporite dissolution subsidence, and volcanic deformation) with different displacement patterns in a selection of subsidence areas in Spain. Finally, a cost comparative study is performed for the different techniques applied.

Investigating gravitational grabens related to lateral spreading and evaporite dissolution subsidence by means of detailed mapping, trenching, and electrical resistivity tomography (Spanish Pyrenees)

The active lateral spread of the Peracalc Range (Spanish Pyrenees) has developed on a Cretaceous limestone sequence around 250 m thick, underlain by tectonically thickened (∼2.5 km) Triassic halite-bearing evaporites and clays. Outward expansion of the Triassic sequence by ductile deformation and probably halokinesis toward the debuttressed and unloaded front of the range has been accommodated in the overlying cap rock through the development of a striking horst and graben morphostructure. Fault scarps show anomalously high height to length ratios (aspect ratio; H max / L ) compared to the values reported for tectonic faults. This retrogressive gravitational deformation has aborted a paleodrainage, expressed as wind gaps, hanging valleys, and defeated streams. The significant vertical displacement component in this rock spread is attributed to subsidence caused by interstratal evaporite dissolution, as supported by the dissolution-induced collapse and graben structures mapped at the foot of the range. To our knowledge, the rock spread of Peracalc, covering around 4.5 km 2 and with a minimum volume of 0.9 km 3 , is the largest documented landslide of the Pyrenees. The excavation of trenches and the acquisition of electrical resistivity tomography profiles provided information on the thickness and subsurface structure of the graben fills, the age of the lateral spread (older than 45 ka), an unexpected episodic kinematic behavior of the gravitational faults, and the timing of deformation events, including slumping of lake deposits.

Geomorphic and stratigraphic evidence of incision-induced halokinetic uplift and dissolution subsidence in transverse drainages crossing the evaporite-cored Barbastro–Balaguer Anticline (Ebro Basin, NE Spain)

The evaporite-cored Barbastro–Balaguer Anticline, located in the northeastern sector of the Ebro Tertiary Basin, NE Spain, is traversed perpendicularly by several drainages coming from the Pyrenees, including the Cinca, Noguera-Ribagorzana and Segre rivers. The terraces associated with these discordant fluvial systems, deposited upon evaporitic and detrital formations across the anticline, allow the analysis of geomorphic and stratigraphic anomalies related to the soluble and ductile nature of the halite-bearing rocks in the core of the anticline. Geomorphological mapping reveals that the gravels discontinuously capping the evaporitic core of the anticline, together with some alluvial mantles disconnected from the present-day river valleys, constitute the oldest sediments deposited under exorheic conditions in this sector of the Ebro Tertiary Basin. These alluvial deposits inset into the basin fill record an early post-capture palaeogeographic stage during which the drainage was dominated by unconfined distributary channels developed on extensive alluvial fans fed by perennial rivers coming from the Pyrenees. The terraces associated with the present-day fluvial valleys correspond to a later palaeogeographic stage characterized by a well-integrated drainage confined to fluvial valleys entrenched in the basin fill. These terraces show evidence of both dissolution-induced subsidence and halokinesis restricted to areas underlain by the evaporites of the anticline core. The deposits of the highest terrace levels of the Noguera-Ribagorzana and Segre rivers and its tributaries, Lo Reguer Creek and Farfanya River, are locally thickened filling basins generated by dissolution-induced synsedimentary subsidence up to several kilometers long and more than 100m deep. Subsidence caused by the karstification of the evaporites reached higher magnitude and extent during the early stages of development of the new external drainage network, when the more soluble halite-bearing units were closer to the new incisional base level. Most likely, the development of a thick caprock, rich in less soluble sediments, has hampered dissolution and subsidence processes in subsequent stages. Incision-induced halokinetic deformation is locally recorded by differentially uplifted terraces dipping away from the valley. The increasing differential loading caused by the entrenchment of the fluvial systems has driven the lateral and upward flow of salt-rich evaporites from the valley margins towards the valley bottom. A minimum long-term uplift rate of 0.3mm/yr has been calculated for a titled OSL-dated Upper Pleistocene terrace of the Cinca River valley. The capture of the Ebro Basin and its change to exorheic conditions have played an instrumental role in the development of the Quaternary gravitational deformations associated with the evaporitic bedrock. The new incisional drainage network propitiated the karstification and evacuation of large amounts of evaporites, and its entrenchment has created adequate differential loading conditions for the salt to flow towards the valley floors.

Impact of halite dissolution subsidence on Quaternary fluvial terrace development: Case study of the Huerva River, Ebro Basin, NE Spain

This paper analyses the control of evaporite dissolution subsidence on the evolution of the lower 30 km-long reach of the Huerva River up to its confluence with the Ebro River. In the study area the Huerva River flows across different interfingered lithofacies of the subhorizontally lying Ebro Basin fill: (1) shales and sandstones upstream of Cadrete; (2) evaporites dominated by gypsum between Cadrete and Cuarte; (3) gypsum with glauberite and halite units in the subsurface downstream of Cuarte. The halite shows a marked downvalley increase in thickness. Twelve terrace levels and seven pediment levels correlative to some of the terraces have been mapped in the studied area. Upstream of Cadrete, the terrace deposits, with a relatively constant thickness less than 4 m and overlying unsoluble bedrock, remain undeformed. Between Cadrete and Cuarte the deposits of some terraces show local thickening (< 20 m). Downstream of Cuarte, a markedly asymmetric valley carved in gypsiferous bedrock and flanked by a prominent gypsum escarpment changes into a narrower and symmetric valley excavated in the > 60 m-thick terrace alluvium that fills a 5 km-long trough generated by synsedimentary subsidence phenomena caused primarily by the interstratal dissolution of halite. The older terraces (T1 to T4) show slight thickening (> 18 m) and locally truncate paleocollapse structures ascribed to the interstratal karstification of halite beds. The intermediate terraces (T5 to T7) correspond to degradation surfaces that grade downstream of Cuarte into aggradation flights underlain by the abruptly thickened deposits that fill this 5 km-long dissolution trough. Subsidence migrated episodically downstream during the generation of these terraces and the subsidence/aggradation rate was probably large enough to induce a base-level drop and knickpoint migration upstream generating strath terraces with convergent longitudinal profiles. The sedimentological changes that show the thickened terrace deposits in the subsidence area (high proportion of overbank fines (> 60%) including palustrine facies, gravel channels with lower width/depth ratio, multiple fining-upward cycles, decrease in the calibre of the channel gravels) indicate a change in the channel pattern from braided to meandering due to the lowering of the valley slope in the reach affected by subsidence. Some of the anomalous features of the lower terraces (T8 to T12) attributable to dissolution subsidence include: (1) steepening of the T8 terrace profile; (2) change of the T10 terrace from degradational to aggradational downstream Cuarte; and (3) thickening recorded beneath the T11 terrace surface.

Environmental problems and geological implications derived from evaporite dissolution in the Barbastro salt anticline (NE Spain)

The halite-bearing Barbastro Formation crops out in the core of the Barbastro Anticline (Ebro Tertiary Basin). This anticline is traversed perpendicularly by some of the most important Pyrenean drainages such as the Cinca and Noguera-Ribagorzana Rivers. The terrace sequences of these fluvial systems have been used as markers to identify and assess dissolution-induced subsidence and salt tectonics. In the limbs of the anticline, terrace deposits underlain by detrital bedrock do not show any evidence of deformation and have a consistent thickness of less than 10 m. The deposits of certain terrace levels of the Noguera-Ribagorzana River and its tributary, the Lo Reguer Creek, are locally thickened filling basins generated by dissolution-induced synsedimentary subsidence up to several kilometers long and more than 100 m deep. Conversely, terraces of the Cinca River do not show anomalously high thicknesses, but local uplifts related to differential upward flow of the halite-bearing bedrock. Locally, a minimum uplift rate of 0.3 mm/year has been estimated from a 64-ka terrace tilted away from the valley. The subsidence hazards occur chiefly in areas where the ground receives artificial water recharge. Serviceability of some canals has been notoriously affected by evaporite karstification. The problem has been mitigated to acceptable levels by grouting. Numerous buildings of Ivars de Noguera are severely damaged by dissolution subsidence, and possibly, by hydrocompaction of gypsiferous silts. The pipe network has been replaced to ameliorate the subsidence risk. In the Cinca River valley, cavities with a total volume of about 180,500 m3 have been created by solution mining at depths greater than 500 m. No investigation methods are applied in the brine field to monitor the distribution and evolution of artificial voids. Substantial increase in salinity of the Cinca River is another evidence of subjacent evaporite dissolution.

Origin of the salt valleys in the Canyonlands section of the Colorado Plateau: Evaporite-dissolution collapse versus tectonic subsidence

The salt valleys over the axis of the salt-cored anticlines in the Paradox fold and fault belt (Canyonlands, Utah and Colorado) are created by subsidence of the anticline crests. Traditionally, the collapse of the anticlinal crests was attributed to dissolution of the salt walls (diapirs) forming the anticline cores. Recent studies based on scaled physical models and field observations propose that the salt valleys are a result of regional extension and that salt dissolution had only a minor influence in the development of the axial depressions. This paper presents several arguments and lines of evidence that refute the tectonic model and support the salt dissolution subsidence interpretation. The development of contractional structures in salt dissolution experiments led the advocates of the tectonic interpretation to reject the dissolution-induced subsidence explanation. However, these salt dissolution models do not reproduce the karstification of salt walls in a realistic way, since their analog involves removal of salt from the base of the diapirs during the experiments. Additionally, numerous field examples and laboratory models conducted by other authors indicate that brittle subsidence in karst settings is commonly controlled by subvertical gravity faults. Field evidence against the regional extension model includes (1) a thick cap rock at the top of the salt walls, (2) the concentration of subsidence deformation structures along the crest of the anticlines (salt walls), (3) deformational structures not consistent with the proposed NNE extension, like crestal synforms and NE–SW grabens, (4) dissolution-induced subsidence structures controlled by ring faulting, revealing deep-seated dissolution, (5) large blocks foundered several hundred meters into the salt wall, (6) evidence of recent and active dissolution subsidence, and (7) the aseismic nature of the recently active collapse faults. Although underground salt dissolution seems to be the main cause for the generation of the salt valleys, this phenomenon may have been favored by regional extension tectonics that enhance the circulation of groundwater and salt dissolution.

Evaporite dissolution subsidence in the historical City of Calatayud, Spain: Damage appraisal and prevention

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.

The stratigraphical record and activity of evaporite dissolution subsidence in Spain

The evaporite formations (in outcrop and at shallow depth) cover an extensive area of the Spanish territory. These soluble sediments are found in diverse geological domains and record a wide time span from the Triassic up to the present day. Broadly, the Mesozoic and Paleogene formations (Alpine cycle) are affected by compressional structures, whereas the Neogene (post-orogenic) sediments remain undeformed.

The investigation of dissolution subsidence incorporating microgravity geophysics at Ripon, Yorkshire : D. A. Patterson, J. C. Davey, A. H. Cooper & J. K. Ferris, Quarterly Journal of Engineering Geology, 28(1), 1995, pp 83–94

The investigation of dissolution subsidence incorporating microgravity geophysics at Ripon, Yorkshire : D. A. Patterson, J. C. Davey, A. H. Cooper & J. K. Ferris, Quarterly Journal of Engineering Geology, 28(1), 1995, pp 83–94

The investigation of dissolution subsidence incorporating microgravity geophysics at Ripon, Yorkshire

Abstract Dissolution subsidence affords some of the most difficult ground conditions with which engineering geologists have to deal. Within the UK, areas underlain by gypsiferous Permo-Triassic strata, most notably around Ripon in Yorkshire, are prone to dissolution structures and resultant building failures are well documented. Conventional drilling of such unstable sites is often a ‘hit and miss’ affair and most geophysical techniques do not provide sufficient resolution to offer adequate confidence in the results. Proposals for the redevelopment of a site within the urban area at Ripon could not rely on such frequently inconclusive methods and it was necessary to implement a phased approach to site investigation. Following a desk study, high-resolution microgravity geophysics was carried out both inside and outside the existing building. This indicated a major negative anomaly of peak amplitude -74 μGal. Subsequent static core probing, rotary drilling and trial trenching confirmed the existence of a potentially unstable breccia pipe which could therefore be taken into account in the engineering design.