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

Characterizing and monitoring a high-risk sinkhole in an urban area underlain by salt through non-invasive methods: Detailed mapping, high-precision leveling and GPR

Two critical aspects for assessing the hazard and managing the risk associated with active sinkholes in developed areas are the precise mapping of the areas affected by ground instability and the quantitative characterization of the ground displacement (kinematic style, spatial-temporal patterns, rates). However, sinkhole site investigations typically provide a static picture of the instability phenomena, and the performance of remediation measures is rarely evaluated using time-series of displacement. This work illustrates the practicality of a non-invasive approach, combining detailed mapping, ground penetrating radar (GPR), and high-precision leveling, for the characterization at different time scales of the ground deformation associated with an active sinkhole in an urban area. The selected highly-active sagging and collapse sinkhole affects four multi-storey buildings in Zaragoza city, Spain, involving direct losses higher than 15 Meuro. GPR data provided information on the internal structure of the sinkhole and the subsidence mechanisms. The boundaries of the ground-deformation zone, established with the GPR data, and especially high-precision leveling, indicate a sinkhole area two times larger than that previously proposed on the basis of airborne imagery and surface deformation features (length from 100 m to 130 m). The leveling profiles reveal an inner rapidly subsiding zone with vertical displacement rates as high as 3 cm/yr, an outer slow settlement ring, and a marginal uplifting bulge with vertical displacement rates that reach 0.6 cm/yr. This phenomenon of marginal bulging is probably a relatively common process in sagging sinkholes, which may have gone unnoticed since its identification requires the use of geodetic methods with utmost accuracy, such as high-precision leveling. Monitoring data indicate that ongoing salt dissolution significantly contributes to the active subsidence and reveal the high impact on the subsidence of water pumping from the evaporitic aquifer and the limited efficiency of a shallow compaction grouting program performed above cavities and karstification zones

Estudio de estructuras gravitacionales asociadas a la karstificación de evaporitas mediante la técnica del trenching

Las formaciones mio-pliocenas en el flanco NO de Los Mansuetos (sección tipo del Turoliense, Fosa de Teruel) están afectadas por subsidencia como consecuencia de la karstificación de las evaporitas triásicas infrayacentes, presentando un monoclinal de 1.7 km de longitud y una sinforma con 130 m de relieve estructural. La cresta del monoclinal está afectada por una fosa que contrarresta el acortamiento causado por la flexión pasiva en el sinclinal adyacente. La fosa está controlada por una falla maestra sintética y un cortejo de fallas sintéticas y antitéticas secundarias con una patente expresión morfológica. Tras la adquisición e interpretación de perfiles de georadar (GPR), se han excavado tres trincheras en depresiones asociadas a escarpes orientados a contra-pendiente. Según nuestro conocimiento, estas son las primeras trincheras excavadas en fallas recientes generadas por karstificación interestratal de evaporitas. Las relaciones geométricas observadas en dos de las trincheras permiten inferir eventos de desplazamiento (hasta 3) ocurridos en el Holoceno reciente. Algunos de los parámetros estimados para las fallas investigadas son claramente diferentes de los esperables para fallas tectónicas en esta zona de intraplaca: Tasas de desplazamiento vertical elevadas (0.6-1 mm/a), baja recurrencia media de los eventos de rotura (1.2-2 ka) y valores de desplazamiento por evento muy elevados (>65 cm) para roturas superficiales de menos de 200 m de longitud. Estos datos sugieren que el considerar las fallas relacionadas con la disolución profunda de evaporitas como estructuras tipo creep no constituye un criterio fiable para diferenciar entre éstas y las fallas tectónicas activas (sismogénicas)

Subsidence mechanisms and sedimentation in alluvial sinkholes inferred from trenching and ground penetrating radar (GPR). Implications for subsidence and flooding hazard assessment

Sinkholes function as small sediment traps that may host valuable stratigraphic records for paleoenvironmental reconstructions and hazard assessments (e.g., subsidence, floods, hurricanes, tsunamis, tephra fall-out). The sedimentological features and completeness of such archives are influenced by the sedimentation and subsidence patterns and rates. However, karst depressions are frequently treated as static basins unaffected by settlement. This work illustrates the practicality of integrated studies combining trenching, numerical dating and shallow geophysical techniques (GPR) for characterizing the subsurface subsidence structure associated with sinkholes and reconstructing their deformational and sedimentary history. The approach is applied in two collapse sinkholes located in contrasting geomorphic settings (relict terrace and floodplain) related to deep-seated interstratal karstification of evaporites. The analysis of the sinkholes, particularly the trenching technique, provides practical information for assessing the associated subsidence hazard, including the presence of larger cavities at depth, the kinematic regime (episodic versus progressive), evidence of catastrophic displacement (fluidization structures) and the magnitude and timing of collapse events, especially the most recent one. The sinkhole located in the floodplain offers the opportunity of analyzing the possibilities and limitations of subsidence sinkholes as recorders of past floods in alluvial environments. This depression shows a largely incomplete record attributable to the high frequency of flood events compared to that of the collapse events, which create the accommodation space for sediment deposition. These limitations could be partially overcome by selecting old sinkholes situated in low terraces and/or affected by rapid subsidence

Cartografía geomorfológica de detalle del tramo del valle del Río Jiloca comprendido entre Villafeliche y Fuentes de Jiloca (Zaragoza)

The villages of Villafeliche, Montón and Fuentes de Jiloca are located in the low sectionof the Jiloca Valley, Calatayud Community, Province of Zaragoza. This area presentsgeomorphological diversity because it is in the union area of Aragonese Branch of the IberianChain with the Neogene Calatayud Basin. This modeling is mainly conditioned by tectonic,fluvial and lithological factors.Geomorpholical analysis is performed by geomorphological mapping and descriptionsof deposits and morphologies. Fort he geomorphological mapping has been done on a detailscale 1:15.000. This project includes a geomorphological mapping of the study area realized ona scale 1:25.000 (Annex II) and a scale 1:70.000 (In this dossier, in 9. Geomorphologicalanalysis) and a characterization of the geomorphological elements according to modelling.As a result of geomorphological mapping and the description of morphologies andmodelling, this proyect includes also an evolutionary geomorphological synthesis. Thegeomorphological evolution of this section of Jiloca Valley is more relevant at the end ofMiocene Period, because the processes that have modelled this area until now started at the endof endorheism of Calatayud Basin.<br /

The application of GPR and ERI in combination with exposure logging and retrodeformation analysis to characterize sinkholes and reconstruct their impact on fluvial sedimentation

This work illustrates the practicality of investigating sinkholes integrating data gathered by ground penetrating radar(GPR), electrical resistivity imaging (ERI) and trenching or direct logging of the subsidence-affected sediments in combination withretrodeformation analysis. This mutidisciplinary approach has been tested in a large paleosinkhole developed during the depositionof a Quaternary terrace on salt-bearing evaporites. The subsidence structure, exposed in an artificial excavation, is located next toPuilatos, a village that was abandoned in the 1970s due to severe subsidence damage. Detailed logging of the exposure revealedthat the subsidence structure corresponds to an asymmetric sagging and collapse paleosinkhole with no clear evidence of recent ac-tivity. The sedimentological and structural relationships together with the retrodeformation analysis indicate that synsedimentary sub-sidence controlled channel location, the development of a palustrine environment and local changes in the channel pattern. GPRprofiles were acquired using an array of systems with different antenna frequencies, including some recently developed shielded an-tennas with improved vertical resolution and penetration depth. Although radargrams imaged the faulted sagging structure and pro-vided valuable data on fault throw, they did not satisfactorily image the complex architecture of the fluvial deposit. ERI showed lowerresolution but higher penetration depth when compared to GPR, roughly capturing the subsidence structure and yielding informationon the thickness of the high-resistivity alluvium and the nature of the underlying low-resistivity karstic residue developed on top ofthe halite-bearing evaporitic bedrock. Data comparison allows the assessment of the advantages and limitations of these comple-mentary techniques, highly useful for site-specific sinkhole risk management

1:5000 landslide map of the Upper Gállego Valley (central Spanish Pyrenees)

[EN] A 1:5000 scale geomorphological landslide inventory map of the glaciated headwaters of the Gállego River in the Spanish Pyrenees is presented. This map, covering an area of 57.6 km2 and mainly produced by direct mapping in the field, provides a more comprehensive and accurate picture of the distribution of slope movements than previous maps. Around 20% of the area is affected by large flow-dominated slope movements developed on Paleozoic slates. Our map shows that some of these post-glacial landslides have blocked the main drainage at several sites creating landslide-dammed lakes. The damage caused by landslides in the mapped area, with an estimated cost of greater 10 million euros, is mostly related to the activity of pre-existing slope movements, some of which have been reactivated or accelerated by adverse human alterations (e.g., excavation at the toe, overloading, higher water infiltration). This study illustrates that the incorporation of detailed cartographic landslide inventories in the planning and development process of alpine areas may contribute to reduce significant landslide-related damage in a cost-effective manner.Peer Reviewe

Paleoflood records from sinkholes using an example from the Ebro River floodplain, northeastern Spain

53 Pags.- 10 Figs. The definitive version is available at: https://www.cambridge.org/core/journals/quaternary-researchThis work introduces for the first time the concept of using sinkholes in fluvial valleys as recorders of past floods. The notion is illustrated through the investigation of a complex sinkhole located in a broad floodplain underlain by salt-bearing Cenozoic evaporites. This active sinkhole comprises a large subsidence depression affecting the floodplain and the edge of a terrace, and a nested collapse sinkhole that used to host a sinkhole pond. A borehole drilled in the buried sinkhole pond revealed an ~7.8-m-thick fill that records around 2700 yr of clayey lacustrine deposition interrupted by three types of detrital facies. Two thick pebble gravel beds have been attributed to major high-competence floods: a paleoflood that occurred in Visigothic times (1537–1311 cal yr BP) and the 1961 Great Ebro River Flood, which is the largest event of the instrumental record. A trench dug in the portion of the terrace affected by subsidence exposed a mid-Holocene slack-water paleoflood deposit. The disadvantages and advantages of sinkholes as archives of past flood histories are discussed.This work has been funded by project CGL2013-40867-P (Ministerio de Economía y Competitividad, Spain). The work conducted by CC has been supported by project PCIN-2014-106.Peer reviewe

Hydrogeochemical characterization of an evaporite karst area affected by sinkholes (Ebro Valley, NE Spain)

The main processes controlling the hydrochemistry of an alluvium-covered evaporite karst area with high sinkhole risk (Ebro Valley, NE Spain) are examined by means of multivariate analyses (Principal Component Analysis and Hierarchical Cluster Analysis), ion correlations and geochemical speciation-solubility calculations. The hydrogeochemistry of the studied system seems to be governed by the interaction between the groundwater from the salt-bearing evaporitic karst aquifer and from the overlying Ebro River alluvial aquifer. The observed hydrochemical features in the alluvial-karst aquifer system are mainly determined by the relative contribution of gypsum/anhydrite and halite dissolution, showing a wide spectrum from relatively fresh recharge waters (mainly irrigation waters) to highly evolved groundwater from the evaporitic aquifer. The variability of these contributions is especially evident at sinkhole ponds which, in some cases, seem to be associated with discharge areas of the karst aquifer in the valley bottom alluvium. Calculated saturation indexes suggest that, in contrast to gypsum, the amounts of halite in the sampled portions of evaporitic aquifer are not large enough to attain equilibrium, which is consistent with the predominance of gypsum/anhydrite reported for these materials. Furthermore, the observed Na:Cl and Ca:SO4 correlations and stoichiometries suggest that other possible processes, such as glauberite dissolution or Na/Ca-exchange, generally play a minor role (compared to halite and gypsum dissolution) in this system. Another important process in the system is the dissolution of carbonate minerals (dolomite and, possibly, calcite) fostered by the input of CO2(g), which is probably produced by pedogenic processes. Dolomite dissolution seems to be particularly relevant in the evaporitic materials probably due to dedolomitisation triggered by gypsum/anhydrite dissolution