Remote sensing-based tectonic geomorphology is widely applied to study neotectonic processes. This technique is relatively cheap and easy to apply, and it allows investigating large areas for ...tectonic activity. Existing literature comprises a variety of indices and techniques, seemingly able to work in almost all tectonic settings. In this paper we study a particularly challenging region in W Slovenia and NE Italy, characterised by slow deformation rates, high precipitation, dense vegetation, and intense modification of the landscape and drainage system due to karst processes. We apply a suite of well-established geomorphic indices including terrain ruggedness, surface roughness, hypsometric integral and analyses of drainage parameters, as well as several less commonly applied analyses, such as the assessment of doline density and doline geometry. The aim was to test the capabilities of the applied techniques at various spatial scales and to extract information about the active tectonics. We begin with broad, regional analyses to detect the morphological imprint of active faults in the landscape. Then, we perform detailed studies of selected sites and single faults. Finally, we analyse a polje located on the trace of an active fault in the highest detail. We then compare the different techniques and different digital elevation models regarding their usefulness for detecting tectonic influences on the karstic landscape. The results show that most of the well-established methods we tested are not suitable to detect even the largest, clearly active faults in the area. The resolution of the used DEMs also has a notable impact on the analyses. We conclude that it is almost impossible to identify active faults solely based on the used techniques. This is mainly due to the low deformation rates and to the intense karstification of the study area that leads to a disconnected surface drainage system. Additional problems arise from the strike-slip mechanism of active faulting. Lithological contrasts and inactive dip-slip faults can lead to false-positive signals of tectonic activity. However, some of our results also show a tectonic signal, indicating neotectonic strike-slip deformation with a notable dip-slip component. Remote sensing studies have demonstrated to be powerful tools for tectonic geomorphology studies, but low tectonic rate karstic landscape conditions as in W Slovenia/NE Italy push even the most trusted methods to their limits and highlight the importance of validation and ground-checks of the results.
•Tests quantitative geomorphologic metrics to a challenging karstic study area•Investigates different spatial scales: regional, local fault traces, single polje•Lithology and karst control landscape, with metrics failing to detect active faults•Metrics less sensitive to fault activity than faulting mechanism•Using metrics to inform on active tectonics can fail in slow deforming karst areas
The paper presents a study of the anisotropic properties of the karst surface through the use of semivariograms. Karst is formed by hydrogeological and tectonic deformations that determine the ...surface and subsurface characteristics of the area. Among the most prominent surface features are dolines, which generally form in a linear direction. Semivariograms can be used to determine both the preferred direction of anisotropy and the degree of anisotropy. The surface exhibits the greatest elevation variability in the direction of the most diverse terrain, corresponding to dolines. The results, based on the eight karst areas studied, show that it is possible to detect and, more importantly, quantify anisotropy in all karst areas, although in some cases it is impossible or difficult to detect visually. The directions of the semivariograms agree very well with those obtained from the visual inspection of the maps, as well as with the orientations of the main faults. The method is therefore very useful for quantitative determination of anisotropy and its interpretation could be greatly improved by using the detailed structural geological maps of the karst.
Surface meltwater accumulating on Antarctic ice shelves can drive fractures through to the ocean and potentially cause their collapse, leading to increased ice discharge from the continent. ...Implications of increasing surface melt for future ice shelf stability are inadequately understood. The southern Amery Ice Shelf has an extensive surface hydrological system, and we present data from satellite imagery and ICESat‐2 showing a rapid surface disruption there in winter 2019, covering ∼60 km2. We interpret this as an ice‐covered lake draining through the ice shelf, forming an ice doline with a central depression reaching 80 m depth amidst over 36 m uplift. Flexural rebound modeling suggests 0.75 km3 of water was lost. We observed transient refilling of the doline the following summer with rapid incision of a narrow meltwater channel (20 m wide and 6 m deep). This study demonstrates how high‐resolution geodetic measurements can explore critical fine‐scale ice shelf processes.
Plain Language Summary
Surface melting over Antarctica's floating ice shelves is predicted to increase significantly during coming decades, but the implications for their stability are unknown. The Antarctic Peninsula has already seen meltwater driven ice shelf collapses. We are still learning how meltwater forms, flows and alters the surface, and that rapid water‐driven changes are not limited to summer. We present high‐resolution satellite data (imagery and altimetry) showing an abrupt change on East Antarctica's Amery Ice Shelf in June 2019 (midwinter). Meltwater stored in a deep, ice‐covered lake drained through to the ocean below, leaving a deep, uneven 11 km2 depression of fractured ice (a “doline”) in the ice shelf surface. The reduced load on the floating ice shelf resulted in flexure, with over 36 m of uplift centered on the former lake. Simple flexure modeling showed that this corresponds to about 0.75 km3 of water being lost to the ocean. ICESat‐2 observations in summer 2020 profiled a new narrow channel inside the doline as meltwater started refilling it from a new lake created by the flexure. ICESat‐2's capacity to observe surface processes at small spatial scales greatly improves our ability to model them, ultimately improving the accuracy of our projections.
Key Points
Satellite images showed an 11 km2 depression on Amery Ice Shelf as an ice‐covered lake drained abruptly in winter 2019 forming an ice doline
ICESat‐2 and WorldView data show elevation fell as much as 80 m in the depression, amidst 60 km2 of hydrostatic rebound and uplift over 36 m
ICESat‐2 photon data profiled a new meltwater channel, incised when a lake formed by the flexural uplift overflowed into the doline in 2020
At the Buchan karst in southeastern Australia, Early Devonian carbonates contain >700 caves and karst-related features. The Potholes, in the northern part of the karst, is a densely cavernous area ...with >100 caves and 60 dolines over only ~0.8 km2. The caves here are predominantly vertical and the roofs commonly show smooth upward steps, indicative of having formed by rising groundwater. Because of sea level fluctuations during the Early Devonian, the limestone at The Potholes forms a tongue that lenses out to the south and is overlain and underlain by relatively insoluble marl. Mapping of fluvial sands and gravels and valley-filling basalt shows that in the Paleogene, the limestone lay beneath a broad, southwards-flowing river valley. Cave development occurred along phreatic loops within the limestone underneath the riverbed, and the upwards limbs of these phreatic loops were focussed into a small area where the limestone lensed out. The concentrated upwards groundwater flow, which connected to springs in the riverbed, resulted in intense cave development within a restricted area, where the groundwater exploited many different pathways within the limestone. The Potholes caves developed entirely beneath the riverbed, and are notable in that numerous caves fed multiple resurgences rather the more common situation world-wide of a single passage connecting to a resurgence. Both these characteristics reflect the unique geological configuration of the site, and show how karst development is determined by the particular arrangement of soluble limestone beds.
Dissolution of The Potholes caves could have begun in the mid-Cretaceous, when uplift increased the gradient of the ancestral river flowing over the limestone, driving groundwater flow through phreatic loops beneath the river, and terminated when the caves were drained following a second uplift in the mid-Pliocene. This demonstrates the antiquity of cave formation in this part of Australia.
On Kranjsko polje in central Slovenia, carbonate conglomerates have been dated to several Pleistocene glacial phases by relative dating based on the morphostratigrafic mapping and borehole data, and ...by paleomagnetic and 10Be analyses. To define how the age of conglomerates determines the geomorphological characteristics of karst surface features, morphometrical and distributive spatial analyses of dolines were performed on three test sites including old, middle, and young Pleistocene conglomerates. As dolines on conglomerates are covered by a thick soil cover and show a strong human influence, the ground penetrating radar (GPR) method was first applied to select dolines appropriate for further morphometrical and distributive analyses. A considerable modification of natural morphology was revealed for cultivated dolines, excluding this type of depression from spatial analyses. Input parameters for spatial analyses (doline rim and deepest point) were manually extracted from the 1 × 1 m grid digital elevation model (DEM) originating from the high-resolution LiDAR (Light Detection and Ranging) data. Basic geomorphological characteristics, namely circularity index, planar size, depth, and density index of dolines were calculated for each relative age of conglomerates, and common characteristics were determined from these data to establish a general surface typology for a particular conglomerate. The obtained surface typologies were spatially extrapolated to the wider conglomerate area in central Slovenia to test the existent geological dating. Spatial analyses generally confirmed previous dating, while in four areas the geomorphological characteristics of dolines did not correspond to the existing dating and require further revision and modification. Doline populations exhibit specific and common morphometrical and distributive characteristics on conglomerates of a particular age and can be a reliable and fast indicator for their dating.
This study examines how centimeter- to meter-long fracture sets propagate, link and form m-long structures, which are then karstified in the vadose (aerated) zone in the upper parts of exposed ...layered carbonate units. We characterize the fracture patterns, including both mesoscale extensional joints, veins, stylolites and macroscale faults, within the Rosario pavement, which is a 1100-m-long, 340-m-wide outcrop in the Jandaíra Formation, Potiguar Basin in semiarid Brazil. The work compares the directions of the mesoscale structures with the strikes of surface collapse dolines and cave conduits at depths of 10–20 m. The main results indicate that the background (diffuse) deformation consists mostly of bed-perpendicular, stratabound N-S-striking veins and extensional (opening mode-I) fractures and E-W- to ENE-WSW-striking stylolites, which are consistent with the same stress field. Both sets of structures are laterally continuous and are commonly traceable across the pavement. Linkage of stylolites and stratabound fractures formed via throughgoing fractures that affected several layers, as deep as 15 m. The throughgoing fractures were favorable structures for fluid pathway formation and karstification in the epigenetic environment. We conclude that sets of mesoscale structures fit with the orientations of the collapse dolines and subhorizontal cave passages, and induced hydraulic anisotropy within the vadose level. These findings indicate that the fractures, veins and stylolites grow, link and form localized vertical conduits for water percolation and karst development. These findings can constrain future models and numerical simulations of karst conduits in investigations of groundwater and oil reservoirs.
•Mesoscale fractures and stylolites propagate and form major fractures and faults•Meso- and major-scale structure control karst porosity in carbonate units•Cave passages form conduits along faults and throughgoing fractures•Fluid flow is controlled by fracture orientation, aperture, length and connectivity
•A conceptual model was proposed based on karst aquifer structure.•A physical model was reproduced on laboratory to simulate hydrological process.•The flow process curve can be divided into three ...stages.•The role of influencing factors to hydrological process are analyzed.
A similar physical simulation experiment is a kind of generalization and reduction of real objects by similarity principle, which achieves the simulation of the actual situation. In order to reveal the influencing factors and mechanisms of the groundwater flow process in the karst aquifer system. In this paper, the hydrological cycle process of the karst aquifer system is comprehensively considered, and a conceptual model is established including hydrological factors such as rainfall recharge, epikarst zone, doline, fissure, conduit, and spring. Also, a three-dimensional physical model of karst fissure-conduit for experiments is designed and fabricated from the similarity with the groundwater channel structure based on the hydrological conceptual model. Moreover, karst aquifer under different rainfall conditions and aquifer structures is designed to simulate the process of seepage and recession. The experiments were divided into 24 groups, three times for each group. The experiment results show that: (1) the rainfall intensity has a significant impact on the maximum peak flow, confluence time and flow duration of the spring flow process; (2) the epikarst zone has a vital influence on the confluence time, flow duration and curve shape of the spring flow process, and has little effect on the peak flow; and (3) the aquifer structure is the main factor affecting the initial flow, the slope of the recession curve and the recession coefficient of the spring recession process. Finally, this study indicates that the concept model is reasonable. The physical model for simulating the hydrological process can be applied to a wide range in karst aquifers, taking into account more geological factors.
The most recent major earthquake series struck near Petrinja (December 29th 2020 M 6.2), and triggered extensive ground failures in the wider area of Petrinja, Sisak and Glina. Coseismic ground ...failures including subsidence dolines, liquefaction and landslides have been documented over a large area by various experts and teams. These data are stored in the newly created inventory, which is openly presented in this paper. This inventory is administered and updated by the Croatian Geological Survey, and will be available online via a Web Map Service (WMS) (www.hgi-cgs.hr). The aim of the inventory is to not only provide data for the development of susceptibility maps and more detailed exploration for possible remediation measures, but also to define the priorities for immediate action. The earthquake triggered the rapid development of dropout dolines which endanger the local populations of the villages of Mečenčani and Borojevići. This is still an ongoing process in the vicinity of the houses and therefore in-situ exploration started immediately. Liquefaction related to alluvial sediments of the Sava, Kupa and Glina rivers occurred almost exclusively in loose and pure sands, and was accompanied by sand boils, subsidence and lateral spreading. Liquefaction also presents a greater hazard because settlement of houses and river embankments occurred. Lateral spreading caused failures of river flood embankments and natural river banks. According to the data known to date, the majority of the coseismic landslides were reactivated with minor displacements. Despite that, it has been recognised that houses at the edge, or in landslide colluvium suffered greater damage than other houses located outside the landslide impact zone.
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