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Geosciences, Volume 11, Issue 3 (March 2021) – 41 articles

Cover Story (view full-size image): A large rockslide fell on 21 July 2014 in the Askja Caldera in the northeastern highlands of Iceland. This is a central volcano of international fame and a popular tourist site. This rockslide is one of the largest rockslides that have occurred in Iceland since the settlement of the island more than 1100 years ago. The slide was initiated in the Suðurbotnar area in the southeastern rim of the caldera and fell into the Öskjuvatn Lake. As the rockslide entered the lake, a 20–30 m high tsunami inundated the shore with a vertical runup of 60–80 m. View this paper
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Article
Intermittent but Rapid Changes to Coastal Landscapes: The Tsunami and El Niño Wave-Formed Sea Arch at Laie Point, Oahu, Hawaii, U.S.A.
Geosciences 2021, 11(3), 147; https://doi.org/10.3390/geosciences11030147 - 23 Mar 2021
Viewed by 665
Abstract
Kukuiho’olua Island is an islet that lies 164 m due north of Laie Point, a peninsula of cemented, coastal, Pleistocene and Holocene sand dunes. Kukuiho’olua Island consists of the same dune deposits as Laie Point and is cut by a sea arch, which, [...] Read more.
Kukuiho’olua Island is an islet that lies 164 m due north of Laie Point, a peninsula of cemented, coastal, Pleistocene and Holocene sand dunes. Kukuiho’olua Island consists of the same dune deposits as Laie Point and is cut by a sea arch, which, documented here for first time, may have formed during the 1 April 1946 “April Fools’s Day Tsunami.” The tsunami-source of formation is supported by previous modeling by other authors, which indicated that the geometry of overhanging sea cliffs can greatly strengthen and focus the force of tsunami waves. Additional changes occurred to the island and arch during the 2015–2016 El Niño event, which was one of the strongest on record. During the event, anomalous wave heights and reversed wind directions occurred across the Pacific. On the night of 24–25 February 2016, large storm waves, resulting from the unique El Niño conditions washed out a large boulder that had lain within the arch since its initial formation, significantly increasing the open area beneath the arch. Large waves also rose high enough for seawater to flow over the peninsula at Laie Point, causing significant erosion of its upper surface. These changes at Laie Point and Kukuio’olua Island serve as examples of long-term, intermittent change to a coastline—changes that, although infrequent, can occur quickly and dramatically, potentially making them geologic hazards. Full article
(This article belongs to the Special Issue Natural and Environmental Hazards of Cultural Heritage)
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Editorial
Editorial for Special Issue “Interdisciplinary Geosciences Perspectives of Tsunami Volume 3”
Geosciences 2021, 11(3), 146; https://doi.org/10.3390/geosciences11030146 - 23 Mar 2021
Viewed by 548
Abstract
Disaster-related research has its own interdisciplinary perspectives connected to the disaster cycle (response, recovery, prevention, and preparedness) [...] Full article
(This article belongs to the Special Issue Interdisciplinary Geosciences Perspectives of Tsunami Volume 3)
Article
Hydrogen Emanations in Intracratonic Areas: New Guide Lines for Early Exploration Basin Screening
Geosciences 2021, 11(3), 145; https://doi.org/10.3390/geosciences11030145 - 22 Mar 2021
Cited by 12 | Viewed by 1802
Abstract
Offshore the emissions of dihydrogen are highlighted by the smokers along the oceanic ridges. Onshore in situ measurements in ophiolitic contexts and in old cratons have also proven the existence of numerous H2 emissive areas. When H2 emanations affect the soils, [...] Read more.
Offshore the emissions of dihydrogen are highlighted by the smokers along the oceanic ridges. Onshore in situ measurements in ophiolitic contexts and in old cratons have also proven the existence of numerous H2 emissive areas. When H2 emanations affect the soils, small depressions and vegetation gaps are observed. These depressions, called fairy circles, have similarities with the pockmark and vent structures recognized for long time in the sea floor when natural gas escapes but also differences. In this paper we present a statistic approach of the density, size, and shape of the fairy circles in various basins. New data from Brazil and Australia are compared to the existing database already gathered in Russia, USA, and again Brazil. The comparison suggests that Australia could be one of the most promising areas for H2 exploration, de facto a couple of wells already found H2, whereas they were drilled to look for hydrocarbons. The sum of areas from where H2 is seeping overpasses 45 km2 in Kangaroo Island as in the Yorke Peninsula. The size of the emitting structures, expressed in average diameter, varies from few meters to kilometers and the footprint expressed in % of the ground within the structures varies from 1 to 17%. However, globally the sets of fairy circles in the various basins are rather similar and one may consider that their characteristics are homogeneous and may help to characterize these H2 emitting zones. Two kinds of size repartitions are observed, one with two maxima (25 m and between 220 m ± 25%) one with a simple Gaussian shape with a single maximum around 175 m ± 20%. Various geomorphological characteristics allow us to differentiate depressions of the ground due to gas emissions from karstic dolines. The more relevant ones are their slope and the ratio diameter vs. depth. At the opposite of the pockmark structures observed on the seafloor for which exclusion zones have been described, the H2 emitting structures may intersect and they often growth by coalescence. These H2 emitting structures are always observed, up to now, above Archean or Neoproterozoic cratons; it suggests that anoxia at the time the sedimentation and iron content play a key role in the H2 sourcing. Full article
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Article
Recent Shoreline Changes Due to High-Angle Wave Instability along the East Coast of Lingayen Gulf in the Philippines
Geosciences 2021, 11(3), 144; https://doi.org/10.3390/geosciences11030144 - 22 Mar 2021
Viewed by 1236
Abstract
A small perturbation on the shoreline may develop under high-angle wave conditions, resulting in the formation of sand spits along the shoreline. Serizawa et al. explained the development of sand spits caused by the instability mechanism using the BG model (a model for [...] Read more.
A small perturbation on the shoreline may develop under high-angle wave conditions, resulting in the formation of sand spits along the shoreline. Serizawa et al. explained the development of sand spits caused by the instability mechanism using the BG model (a model for predicting 3-D beach changes based on Bagnold’s concept). However, examples of the development of sand spits caused by this mechanism in the field are limited in number. Lingayen Gulf in the Philippines has a large aspect ratio, so shoreline instability occurs along the coastline, significantly affecting the shore protection along the coast. In this study, the shoreline instability along the river delta coasts around the Balili and Aringay Rivers flowing into Lingayen Gulf and a sand spit were investigated using satellite images together with field observation. The shoreline changes observed south of the Aringay River mouth were compared with those observed in a previous study on the development of a sand spit by San-nami et al. The rate of longshore sand transport to form a sand spit at Santo Tomas in Lingayen Gulf was estimated to be approximately 1.3 × 105 m3/yr, which is in good agreement with the value measured on the Shimizu coast in Suruga Bay, with a comparable aspect ratio of 1.2 relative to 1.3 in Lingayen Gulf. It was concluded that shoreline undulations have evolved downcoast of two river deltas owing to high-angle wave instability along the east coast of Lingayen Gulf and the formation of a sand spit has occurred. A soft measure, such as sand bypassing, would be better to be adopted along the coasts in Lingayen Gulf instead of hard measures against erosion, to prevent rapid expansion of an artificial, protected coastline. Full article
(This article belongs to the Special Issue Shoreline Dynamics and Beach Erosion)
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Communication
Introducing Uncertainty in Risk Calculation along Roads Using a Simple Stochastic Approach
Geosciences 2021, 11(3), 143; https://doi.org/10.3390/geosciences11030143 - 22 Mar 2021
Viewed by 743
Abstract
Based on a previous risk calculation study conducted along a road corridor, risk is recalculated using a stochastic simulation by introducing variability into most of the parameters in the risk equation. This leads to an exceedance curve comparable to those of catastrophe models. [...] Read more.
Based on a previous risk calculation study conducted along a road corridor, risk is recalculated using a stochastic simulation by introducing variability into most of the parameters in the risk equation. This leads to an exceedance curve comparable to those of catastrophe models. This approach introduces uncertainty into the risk calculation in a simple way, and it can be used for poorly documented cases to compensate for a lack of data. This approach tends to minimize risk or question risk calculations. Full article
(This article belongs to the Special Issue Rock Fall Hazard and Risk Assessment)
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Article
Enhancing Paleoreef Reservoir Characterization through Machine Learning and Multi-Attribute Seismic Analysis: Silurian Reef Examples from the Michigan Basin
Geosciences 2021, 11(3), 142; https://doi.org/10.3390/geosciences11030142 - 19 Mar 2021
Cited by 1 | Viewed by 734
Abstract
Historically, Silurian pinnacle reef complexes in the Michigan Basin have been largely identified using 2D seismic with very little research on the reservoir characterization of these reefs using 3D seismic data. By incorporating a high-resolution 3D dataset constrained by a well-studied and data-rich [...] Read more.
Historically, Silurian pinnacle reef complexes in the Michigan Basin have been largely identified using 2D seismic with very little research on the reservoir characterization of these reefs using 3D seismic data. By incorporating a high-resolution 3D dataset constrained by a well-studied and data-rich paleoreef reservoir, the Puttygut reef, seismic attributes were correlated to petrophysical properties through machine learning and self-organizing maps (SOMs). A suite of structural and frequency-based attributes was calculated from pre-stack time migrated (PSTM) seismic data, with only a subset of them selected as SOM inputs. Structural attributes enhanced details in the reef but frequency attributes were overall more useful for correlating with reservoir quality. A strong relationship between certain combination percentages of attributes and certain sections of the reef with porosity and permeability was found after the SOM results were compared to wireline log and core analysis data. Areas with high permeability and porosity correlated with the average frequency and spectral decomposition at 29 and 81 Hz. Areas with high porosity and varying permeability correlated with the average frequency and spectral decomposition at 29, 57, and 81 Hz. Areas with intermediate porosity correlated with the average frequency and spectral decomposition at 29 and 57 Hz. The efficacy of the procedure was then demonstrated on two nearby reefs with very similar results. Full article
(This article belongs to the Special Issue Integrated Stratigraphy of Carbonate Platforms)
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Article
Lifecycle of an Intermontane Plio-Pleistocene Fluvial Valley of the Northern Apennines: From Marine-Driven Incision to Tectonic Segmentation and Infill
Geosciences 2021, 11(3), 141; https://doi.org/10.3390/geosciences11030141 - 18 Mar 2021
Viewed by 911
Abstract
Downcutting and infill of incised valley systems is mostly controlled by relative sea-level changes, and studies on valley-fill successions accumulated independently from relative sea-level or lake-level oscillations are limited. This study focuses on the Plio-Pleistocene evolution of a fluvial drainage system developed in [...] Read more.
Downcutting and infill of incised valley systems is mostly controlled by relative sea-level changes, and studies on valley-fill successions accumulated independently from relative sea-level or lake-level oscillations are limited. This study focuses on the Plio-Pleistocene evolution of a fluvial drainage system developed in Southern Tuscany (Italy) following a regional marine forced regression at the end of Piacentian. Subsequent in-valley aggradation was not influenced by any relative sea-level rise, and valley morphological and depositional history mainly resulted from interaction between sediment supply and tectonic activity, which caused segmentation of the major valley trunk into localized subsiding depocenters separated by upwarping blocks. Fluvial sedimentation occurred until late Calabrian time, when the major river abandoned that valley, where minor fluvio-lacustrine depocenters allowed accumulation of siliciclastic and carbonate deposits. The present study demonstrates that the infill of the valley was not controlled by the forcing that caused its incision. Accumulation of the fluvial succession is discussed here in relation with localized, tectonic-controlled base levels, which commonly prevent from establishing of a clear downdip stratigraphic correlations. Chronological reconstruction of the study depositional dynamics provides solid constrains to frame them in the tectono-sedimentary evolution of the Northern Apennines. Full article
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Article
Exploring Best Practices in Geoscience Education: Adapting a Video/Animation on Continental Rifting for Upper-Division Students to a Lower-Division Audience
Geosciences 2021, 11(3), 140; https://doi.org/10.3390/geosciences11030140 - 18 Mar 2021
Cited by 3 | Viewed by 729
Abstract
Well-crafted and scientifically accurate videos and animations can be effective ways to teach dynamic Earth processes such as continental rifting, both in live course offerings as well as in online settings. However, a quick search of the internet reveals too few high-quality videos/animations [...] Read more.
Well-crafted and scientifically accurate videos and animations can be effective ways to teach dynamic Earth processes such as continental rifting, both in live course offerings as well as in online settings. However, a quick search of the internet reveals too few high-quality videos/animations describing deep Earth processes. We have modified a hybrid 10.5 min video/animation about continental rifting and the formation of new oceans and passive continental margins created for an upper-division geology audience, retailoring it for a lower-division geology audience. A key challenge in successfully modifying such resources is aligning the cognitive load that the video/animation imposes on students, in part related to the technical geoscientific jargon used in explaining such phenomena, with that which they encounter on these topics in their textbooks and classrooms. We used expert feedback obtained at a 2019 GeoPRISMS (Geodynamic Processes at Rifting and Subducting Margins) workshop in San Antonio to ensure the accuracy of the science content of the upper-division video. We followed this with a review of the terminology and language used in the video/animation, seeking to align the video narrative with the technical language used in introductory geology offerings, which we based on examining five current introductory geology textbooks and feedback from students in introductory geoscience courses. The revised introductory-level video/animation was piloted in an online introductory course, where it provided an improved conceptual understanding of the related processes of continental rifting, opening new oceans, and formation of passive continental margins. Full article
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Review
Active Fault Systems in the Inner Northwest Apennines, Italy: A Reappraisal One Century after the 1920 Mw ~6.5 Fivizzano Earthquake
Geosciences 2021, 11(3), 139; https://doi.org/10.3390/geosciences11030139 - 18 Mar 2021
Cited by 4 | Viewed by 1193
Abstract
Based on the review of the available stratigraphic, tectonic, morphological, geodetic, and seismological data, along with new structural observations, we present a reappraisal of the potential seismogenic faults and fault systems in the inner northwest Apennines, Italy, which was the site, one century [...] Read more.
Based on the review of the available stratigraphic, tectonic, morphological, geodetic, and seismological data, along with new structural observations, we present a reappraisal of the potential seismogenic faults and fault systems in the inner northwest Apennines, Italy, which was the site, one century ago, of the devastating Mw ~6.5, 1920 Fivizzano earthquake. Our updated fault catalog provides the fault locations, as well as the description of their architecture, large-scale segmentation, cumulative displacements, evidence for recent to present activity, and long-term slip rates. Our work documents that a dense network of active faults, and thus potential earthquake fault sources, exists in the region. We discuss the seismogenic potential of these faults, and propose a general tectonic scenario that might account for their development. Full article
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Article
Geological Heritage of Syros Island, Cyclades Complex, Greece: An Assessment and Geotourism Perspectives
Geosciences 2021, 11(3), 138; https://doi.org/10.3390/geosciences11030138 - 16 Mar 2021
Cited by 8 | Viewed by 998
Abstract
Syros Island, Cyclades complex, central Aegean Sea, Greece, is a prime locality for the study of processes active in deep levels of orogens and is world famous for its exceptionally well preserved glaucophane schist-to eclogite-facies lithologies. Glaucophane schists and eclogites are witnesses of [...] Read more.
Syros Island, Cyclades complex, central Aegean Sea, Greece, is a prime locality for the study of processes active in deep levels of orogens and is world famous for its exceptionally well preserved glaucophane schist-to eclogite-facies lithologies. Glaucophane schists and eclogites are witnesses of one of the fundamental tectonic processes operating on planet Earth. Results of geological research on Syros have contributed a lot to our present understanding of why and how these processes work that make oceans disappear, how mountain ranges can start to form, how magma chambers form to feed volcanoes, how subduction mechanisms can trigger earthquakes and lead to tsunamis, and a series of other spectacular or very impressive phenomena which have been observed and studied throughout the earth’s window offered in that particular place of the world. The description, interpretation, and evaluation of the important geological heritage of Syros, in combination with a SWOT analysis, showed the geotourism potential of the region. The results of this paper are intended to constitute a valuable tool for enhancing and raising awareness of the geological heritage of the island of Syros, regarding to the added value activities to be developed on a sustainable basis. Full article
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Article
Proposed Model for Shale Compaction Kinetics
Geosciences 2021, 11(3), 137; https://doi.org/10.3390/geosciences11030137 - 15 Mar 2021
Viewed by 734
Abstract
Shales are the most abundant class of sedimentary rocks, distinguished by being very fine-grained, clayey, and compressible. Their physical and chemical properties are important in widely different enterprises such as civil engineering, ceramics, and petroleum exploration. One characteristic, which is studied here, is [...] Read more.
Shales are the most abundant class of sedimentary rocks, distinguished by being very fine-grained, clayey, and compressible. Their physical and chemical properties are important in widely different enterprises such as civil engineering, ceramics, and petroleum exploration. One characteristic, which is studied here, is a systematic reduction of porosity with depth of burial. This is due increases in grain-to-grain stress and temperature. Vertical stress in sediments is given by the overburden less the pore fluid pressure, σ, divided by the fraction of the horizontal area which is the supporting matrix, (1φ), where φ is the porosity. It is proposed that the fractional reduction of this ratio, Λ, with time is given by the product of φ4m/3, (1φ)4n/3, and one or more Arrhenius functions Aexp(E/RT) with m and n close to 1. This proposal is tested for shale sections in six wells from around the world for which porosity-depth data are available. Good agreement is obtained above 30–40 °C and fractional porosities less than 0.5. Single activation energies for each well are obtained in the range 15–33 kJ/mole, close to the approximate pressure solution of quartz, 24 kJ/mol. Values of m and n are in the range 1 to 0.8, indicating nearly fractal water-wet pore-to-matrix interfaces at pressure solution locations. Results are independent of over- or under-pressure of pore water. This model attempts to explain shale compaction quantitatively. For the petoleum industry, given porosity-depth data for uneroded sections and accurate activation energy, E, paleo-geothermal-gradient can be inferred and from that organic maturity, indicating better drilling prospects. Full article
(This article belongs to the Special Issue Recent Advances and Applications of Digital Rock Physics)
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Article
Effects of Stem Density and Reynolds Number on Fine Sediment Interception by Emergent Vegetation
Geosciences 2021, 11(3), 136; https://doi.org/10.3390/geosciences11030136 - 14 Mar 2021
Cited by 3 | Viewed by 1086
Abstract
Suspended sediment collected by vegetation in marshes and wetlands contributes to vertical accretion, which can buffer against rising sea levels. Effective capture efficiency (ECE), a parameter quantifying the fraction of incoming suspended particles directly captured by underwater vegetation surfaces, plays a key role [...] Read more.
Suspended sediment collected by vegetation in marshes and wetlands contributes to vertical accretion, which can buffer against rising sea levels. Effective capture efficiency (ECE), a parameter quantifying the fraction of incoming suspended particles directly captured by underwater vegetation surfaces, plays a key role in determining the significance of direct interception in morphodynamic models. The ways in which physical characteristics of collectors and transitionally turbulent flows affect ECE are not yet thoroughly understood. We conducted a set of 12 experiments at three flow velocities and three stem densities (plus equivalent zero-collector control experiments), plus four experiments where biofilm was allowed to accumulate. We determined that ECE decreases with increasing collector Reynolds number (study range: 66 to 200; p < 0.05 for two of three treatments) and increasing collector density (solid volume fraction: 0.22% to 1.17%; p < 0.05 for two of three treatments). Adding biofilm increased ECE in all cases, by a multiplicative factor ranging from 1.53 to 7.15 at different collector densities and biofilm growth durations. In some cases, the impact of biofilm on ECE far outweighed that of collector Reynolds number and density. By combining our data with those of one similar study, we present a preliminary model quantitatively assessing the effect of collector density on ECE. Full article
(This article belongs to the Special Issue Ecohydraulics and Ecomorphodynamics)
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Article
Burial-Deformation History of Folded Rocks Unraveled by Fracture Analysis, Stylolite Paleopiezometry and Vein Cement Geochemistry: A Case Study in the Cingoli Anticline (Umbria-Marche, Northern Apennines)
Geosciences 2021, 11(3), 135; https://doi.org/10.3390/geosciences11030135 - 13 Mar 2021
Cited by 5 | Viewed by 1077
Abstract
Unravelling the burial-deformation history of sedimentary rocks is prerequisite information to understand the regional tectonic, sedimentary, thermal, and fluid-flow evolution of foreland basins. We use a combination of microstructural analysis, stylolites paleopiezometry, and paleofluid geochemistry to reconstruct the burial-deformation history of the Meso-Cenozoic [...] Read more.
Unravelling the burial-deformation history of sedimentary rocks is prerequisite information to understand the regional tectonic, sedimentary, thermal, and fluid-flow evolution of foreland basins. We use a combination of microstructural analysis, stylolites paleopiezometry, and paleofluid geochemistry to reconstruct the burial-deformation history of the Meso-Cenozoic carbonate sequence of the Cingoli Anticline (Northern Apennines, central Italy). Four major sets of mesostructures were linked to the regional deformation sequence: (i) pre-folding foreland flexure/forebulge; (ii) fold-scale layer-parallel shortening under a N045 σ1; (iii) syn-folding curvature of which the variable trend between the north and the south of the anticline is consistent with the arcuate shape of the anticline; (iv) the late stage of fold tightening. The maximum depth experienced by the strata prior to contraction, up to 1850 m, was quantified by sedimentary stylolite paleopiezometry and projected on the reconstructed burial curve to assess the timing of the contraction. As isotope geochemistry points towards fluid precipitation at thermal equilibrium, the carbonate clumped isotope thermometry (Δ47) considered for each fracture set yields the absolute timing of the development and exhumation of the Cingoli Anticline: layer-parallel shortening occurred from ~6.3 to 5.8 Ma, followed by fold growth that lasted from ~5.8 to 3.9 Ma. Full article
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Article
Monitoring the Organic Matter Quality Highlights the Ways in Which Organic Matter Is Removed from Wetland Soil
Geosciences 2021, 11(3), 134; https://doi.org/10.3390/geosciences11030134 - 13 Mar 2021
Viewed by 702
Abstract
It has long been considered that ferric phases stabilize organic matter (OM) in soils. Temporarily waterlogged soils, in which Fe is submitted to regular reductive solubilization and oxidizing precipitation, have often been used to study these processes. However, few studies have been interested [...] Read more.
It has long been considered that ferric phases stabilize organic matter (OM) in soils. Temporarily waterlogged soils, in which Fe is submitted to regular reductive solubilization and oxidizing precipitation, have often been used to study these processes. However, few studies have been interested in the evolution of the OM quality under such conditions. We therefore experimentally investigated the impact of a redox cycle on the quality of the dissolved organic matter (DOM) from wetland soil. The DOM quality was monitored using a combination of analyses run on the elements (%C, %N, C/N), isotopes (δ15N, δ13C), optical index (specific UV absorbance at 254 nm), and fluorescence indexes (FI, HIX, BIX). In addition, the cation and anion concentrations were also determined in the soil solutions throughout the experiment. As classically demonstrated, OM is solubilized as terrestrial aromatic molecules in the first stage of the reducing period, and then as nonaromatic molecules until the end of the reduction, in response to the dissimilatory reductive dissolution of Fe-oxyhydroxides in the soil. More interestingly, we demonstrate that the reintroduction of O2 involves significant lysis of reducing bacterial cells involving the production of small labile organic carbon which represents a significant pathway for OM degradation. Moreover, in response to the physical constraints, the newly formed Fe-OM precipitates produce small aggregates rich in aromatic OM that are expected to disseminate in the environment, representing a second significant way to remove OM. Full article
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Review
The 2011 Tohoku Tsunami from the Sky: A Review on the Evolution of Artificial Intelligence Methods for Damage Assessment
Geosciences 2021, 11(3), 133; https://doi.org/10.3390/geosciences11030133 - 13 Mar 2021
Cited by 1 | Viewed by 878
Abstract
The Tohoku tsunami was a devastating event that struck North-East Japan in 2011 and remained in the memory of people worldwide. The amount of devastation was so great that it took years to achieve a proper assessment of the economical and structural damage, [...] Read more.
The Tohoku tsunami was a devastating event that struck North-East Japan in 2011 and remained in the memory of people worldwide. The amount of devastation was so great that it took years to achieve a proper assessment of the economical and structural damage, with the consequences still being felt today. However, this tsunami was also one of the first observed from the sky by modern satellites and aircrafts, thus providing a unique opportunity to exploit these data and train artificial intelligence methods that could help to better handle the aftermath of similar disasters in the future. This paper provides a review of how artificial intelligence methods applied to case studies about the Tohoku tsunami have evolved since 2011. We focus on more than 15 studies that are compared and evaluated in terms of the data they require, the methods used, their degree of automation, their metric performances, and their strengths and weaknesses. Full article
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Article
Nisyros Volcanic Island: A Geosite through a Tailored GIS Story
Geosciences 2021, 11(3), 132; https://doi.org/10.3390/geosciences11030132 - 13 Mar 2021
Cited by 2 | Viewed by 1902
Abstract
The volcanic island of Nisyros (Greece) is here presented as it presents unique characteristics being a Quaternary volcano in the eastern Aegean Sea, composed of volcanic rocks, and featuring a central caldera that is surrounded by volcanic domes and thick lavas. Its history [...] Read more.
The volcanic island of Nisyros (Greece) is here presented as it presents unique characteristics being a Quaternary volcano in the eastern Aegean Sea, composed of volcanic rocks, and featuring a central caldera that is surrounded by volcanic domes and thick lavas. Its history is strongly connected to the volcano impressing the visitors with steaming hydrothermal craters, intensive smell of sulfur and fumarolic gases, and hot springs. Due to its morphology and geographical position, its cultural and historical heritage has been unchanged in time, bequeath to the island plenty of churches, monasteries with hagiographic frescoes, castles, caves, and spas. To present the geodiversity, the cultural environment, and the biodiversity of this geosite, a relatively new geographic approach was used, ESRI Story Maps. Being web-based applications, they are widespread as an interactive responsive tool used for spatial data communication and dissemination, by combining thematic 2D and 3D webmaps, narrative text, and multimedia content. Such applications can be an ideal way for presenting the available information of places characterized as geosites or protected areas worldwide, providing quick access to the available information to a broader, non-technical audience, developing the interest, and possibly motivating the public to learn more or visit them. Full article
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Article
Performance Analysis of Multi-Task Deep Learning Models for Flux Regression in Discrete Fracture Networks
Geosciences 2021, 11(3), 131; https://doi.org/10.3390/geosciences11030131 - 12 Mar 2021
Cited by 2 | Viewed by 954
Abstract
In this work, we investigate the sensitivity of a family of multi-task Deep Neural Networks (DNN) trained to predict fluxes through given Discrete Fracture Networks (DFNs), stochastically varying the fracture transmissivities. In particular, detailed performance and reliability analyses of more than two hundred [...] Read more.
In this work, we investigate the sensitivity of a family of multi-task Deep Neural Networks (DNN) trained to predict fluxes through given Discrete Fracture Networks (DFNs), stochastically varying the fracture transmissivities. In particular, detailed performance and reliability analyses of more than two hundred Neural Networks (NN) are performed, training the models on sets of an increasing number of numerical simulations made on several DFNs with two fixed geometries (158 fractures and 385 fractures) and different transmissibility configurations. A quantitative evaluation of the trained NN predictions is proposed, and rules fitting the observed behavior are provided to predict the number of training simulations that are required for a given accuracy with respect to the variability in the stochastic distribution of the fracture transmissivities. A rule for estimating the cardinality of the training dataset for different configurations is proposed. From the analysis performed, an interesting regularity of the NN behaviors is observed, despite the stochasticity that imbues the whole training process. The proposed approach can be relevant for the use of deep learning models as model reduction methods in the framework of uncertainty quantification analysis for fracture networks and can be extended to similar geological problems (for example, to the more complex discrete fracture matrix models). The results of this study have the potential to grant concrete advantages to real underground flow characterization problems, making computational costs less expensive through the use of NNs. Full article
(This article belongs to the Special Issue Quantitative Fractured Rock Hydrology)
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Article
Remote Sensing of Snow Cover Variability and Its Influence on the Runoff of Sápmi’s Rivers
Geosciences 2021, 11(3), 130; https://doi.org/10.3390/geosciences11030130 - 12 Mar 2021
Cited by 5 | Viewed by 1174
Abstract
The boreal winter 2019/2020 was very irregular in Europe. While there was very little snow in Central Europe, the opposite was the case in northern Fenno-Scandia, particularly in the Arctic. The snow cover was more persistent here and its rapid melting led to [...] Read more.
The boreal winter 2019/2020 was very irregular in Europe. While there was very little snow in Central Europe, the opposite was the case in northern Fenno-Scandia, particularly in the Arctic. The snow cover was more persistent here and its rapid melting led to flooding in many places. Since the last severe spring floods occurred in the region in 2018, this raises the question of whether more frequent occurrences can be expected in the future. To assess the variability of snowmelt related flooding we used snow cover maps (derived from the DLR’s Global SnowPack MODIS snow product) and freely available data on runoff, precipitation, and air temperature in eight unregulated river catchment areas. A trend analysis (Mann-Kendall test) was carried out to assess the development of the parameters, and the interdependencies of the parameters were examined with a correlation analysis. Finally, a simple snowmelt runoff model was tested for its applicability to this region. We noticed an extraordinary variability in the duration of snow cover. If this extends well into spring, rapid air temperature increases leads to enhanced thawing. According to the last flood years 2005, 2010, 2018, and 2020, we were able to differentiate between four synoptic flood types based on their special hydrometeorological and snow situation and simulate them with the snowmelt runoff model (SRM). Full article
(This article belongs to the Special Issue Monitoring of the Seasonal Snow Cover)
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Communication
New Evidence of Megaclasts from the Russian South: The First Report of Three Localities
Geosciences 2021, 11(3), 129; https://doi.org/10.3390/geosciences11030129 - 11 Mar 2021
Cited by 1 | Viewed by 576
Abstract
Megaclast research has intensified recently, and its further development needs new factual information from various places of the world. Three new megaclast localities are reported from the Russian South, namely, Shum, Merzhanovo, and the Red Stones. These localities host blocks of all grades, [...] Read more.
Megaclast research has intensified recently, and its further development needs new factual information from various places of the world. Three new megaclast localities are reported from the Russian South, namely, Shum, Merzhanovo, and the Red Stones. These localities host blocks of all grades, sometimes with certain flatness and angle roundness. Megaclasts from Shum and Merzhanovo result from poly-phase slope processes. At the Red Stones locality, a group of residual megaclasts will appear in the future due to weathering processes. This evidence together with the examples brought by the virtual journeys and the literature interpretations prove the genetic diversity of megaclasts and stress the urgency of their further investigations in various depositional environments. Full article
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Article
Climate Variability Indices—A Guided Tour
Geosciences 2021, 11(3), 128; https://doi.org/10.3390/geosciences11030128 - 10 Mar 2021
Cited by 1 | Viewed by 1031
Abstract
The objective of this study is to provide a comprehensive review and characterization of selected climate variability indices. While we discuss many major climate variability mechanisms, we focus on four principal modes of climate variability related to the dynamics of Earth’s oceans and [...] Read more.
The objective of this study is to provide a comprehensive review and characterization of selected climate variability indices. While we discuss many major climate variability mechanisms, we focus on four principal modes of climate variability related to the dynamics of Earth’s oceans and their interactions with the atmosphere: the El Niño–Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), Pacific Decadal Oscillation (PDO), and Atlantic Multi-decadal Oscillation (AMO). All these oscillation modes are of broad interest and considerable relevance, also in climate impact studies related to teleconnections, i.e., relationships between climate variations at distant locations. We try to decipher temporal patterns present in time series of different oscillation modes in the ocean–atmosphere system using exploratory analysis of the raw data, their structure, and properties, as well as illustrating the quasi-periodic behavior via wavelet analysis. With this contribution, we hope to help researchers in identifying and selecting data sources and climate variability indices that match their needs. Full article
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Article
Basement Structure and Styles of Active Tectonic Deformation in Central Interior Alaska
Geosciences 2021, 11(3), 127; https://doi.org/10.3390/geosciences11030127 - 10 Mar 2021
Viewed by 1023
Abstract
Central Interior Alaska is one of the most seismically active regions in North America, exhibiting a high concentration of intraplate earthquakes approximately 700 km away from the southern Alaska subduction zone. Seismological evidence suggests that intraplate seismicity in the region is not uniformly [...] Read more.
Central Interior Alaska is one of the most seismically active regions in North America, exhibiting a high concentration of intraplate earthquakes approximately 700 km away from the southern Alaska subduction zone. Seismological evidence suggests that intraplate seismicity in the region is not uniformly distributed, but concentrated in several discrete seismic zones, including the Nenana basin and the adjacent Tanana basin. Although the location and magnitude of the seismic activity in both basins are well defined by a network of seismic stations in the region, the tectonic controls on these intraplate earthquakes and the heterogeneous nature of Alaska’s continental interior remain poorly understood. We investigated the crustal structure of the Nenana and Tanana basins using available seismic reflection, aeromagnetic and gravity anomaly data, supplemented by geophysical well logs and outcrop data. We developed nine new two-dimensional forward models to delineate internal geometries and the crustal structure of Alaska’s interior. The results of our study demonstrates a strong crustal heterogeneity beneath both basins. The Tanana basin is a relatively shallow (up to 2 km) asymmetrical foreland basin with its southern, deeper side controlled by the northern foothills of the Central Alaska Range. Northeast-trending left lateral strike-slip faults within the Tanana basin are interpreted as a zone of clockwise crustal block rotation. The Nenana basin has a fundamentally different geometry. It is a deep (up to 8 km), narrow transtensional pull-apart basin that is deforming along the left-lateral Minto Fault. This study identifies two distinct modes of current tectonic deformation in Central Interior Alaska and provides a basis for modeling the interplay between intraplate stress fields and major structural features that potentially influence the generation of intraplate earthquakes in the region. Full article
(This article belongs to the Special Issue Satellite/Airborne Gravity and Magnetic Investigations)
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Article
Modifying Effect of Soil Properties on Bio-Accessibility of As and Pb from Human Ingestion of Contaminated Soil
Geosciences 2021, 11(3), 126; https://doi.org/10.3390/geosciences11030126 - 10 Mar 2021
Cited by 3 | Viewed by 691
Abstract
Exposure to soils contaminated with heavy metals can pose human health risk to children through ingestion of contaminated soil. Soil properties such as soil pH, reactive Fe and Al oxide content, clay content, soil organic matter (SOM), and cation exchange capacity (CEC) can [...] Read more.
Exposure to soils contaminated with heavy metals can pose human health risk to children through ingestion of contaminated soil. Soil properties such as soil pH, reactive Fe and Al oxide content, clay content, soil organic matter (SOM), and cation exchange capacity (CEC) can reduce contaminant bio-accessibility and exposure. In vitro bio-accessibility (%IVBA) of As and Pb in 19 soils was determined using U.S. EPA Method 1340. Soil properties reduced the bio-accessibility of As by 17–96.5% and 1.3–38.9% for Pb. For both As and Pb, bio-accessibility decreased with increasing Al and Fe oxide content. Al oxides were found to be the primary driver of As and Pb bio-accessibility. Multiple regressions with AlOx, soil pH, %clay and/or FeOx predicted %IVBA As (p < 0.001). The multiple regression including log (FeOx + AlOx) and %clay explained 63% of the variability in %IVBA Pb (p < 0.01). Fe and Al oxides were found to be important drivers of As and Pb bio-accessibility, regardless of in vitro method. These findings suggested soil pH should be used in addition to reactive oxides to predict bio-accessible As. Risk-based adjustments using soil properties for exposure via incidental ingestion should be considered for soils contaminated with As and/or Pb. Full article
(This article belongs to the Special Issue Medical Geology in the Urban Environment)
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Article
Stratigraphic and Tectonic Setting of the Liguride Units Cropping Out along the Southeastern Side of the Agri Valley (Southern Apennines, Italy)
Geosciences 2021, 11(3), 125; https://doi.org/10.3390/geosciences11030125 - 09 Mar 2021
Cited by 2 | Viewed by 704
Abstract
This paper shows the main results of a multidisciplinary study performed along the southeastern sector of the Agri Valley in Basilicata (Southern Italy), where Cenozoic units, crucial for constraining the progressive evolution of the Southern Apennine thrust and fold belt and, more in [...] Read more.
This paper shows the main results of a multidisciplinary study performed along the southeastern sector of the Agri Valley in Basilicata (Southern Italy), where Cenozoic units, crucial for constraining the progressive evolution of the Southern Apennine thrust and fold belt and, more in general, the geodynamic evolution of the Mediterranean area are widely exposed. In particular, we aimed at understanding the stratigraphic and tectonic setting of deep-sea, thrust-top Cenozoic units exposed immediately to north of Montemurro, between Costa Molina and Monte dell’Agresto. In the previous works different units, showing similar sedimentological characteristics but uncertain age attribution, have been reported in the study area. In our study, we focussed on the Albidona Formation, pertaining to the Liguride realm, which shows most significant uncertainties regarding the age and the stratigraphic setting. The study was based on a detailed field survey which led to a new geological map of the area. This was supported by new stratigraphic, biostratigraphic and structural analyses. Biostratigraphic analysis provided an age not older than the upper Ypresian and not younger than the early Priabonian. Recognition of marker stratigraphic horizons strongly helped in the understanding of the stratigraphy of the area. The study allowed a complete revision of the stratigraphy of the outcropping Cenozoic units, the recognition of until now unknown tectonic structures and the correlation between surface and subsurface geology. Full article
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Article
The Gavorrano Monzogranite (Northern Apennines): An Updated Review of Host Rock Protoliths, Thermal Metamorphism and Tectonic Setting
Geosciences 2021, 11(3), 124; https://doi.org/10.3390/geosciences11030124 - 08 Mar 2021
Cited by 4 | Viewed by 1962
Abstract
We review and refine the geological setting of an area located nearby the Tyrrhenian seacoast, in the inner zone of the Northern Apennines (southern Tuscany), where a Neogene monzogranite body (estimated in about 3 km long, 1.5 km wide, and 0.7 km thick) [...] Read more.
We review and refine the geological setting of an area located nearby the Tyrrhenian seacoast, in the inner zone of the Northern Apennines (southern Tuscany), where a Neogene monzogranite body (estimated in about 3 km long, 1.5 km wide, and 0.7 km thick) emplaced during early Pliocene. This magmatic intrusion, known as the Gavorrano pluton, is partially exposed in a ridge bounded by regional faults delimiting broad structural depressions. A widespread circulation of geothermal fluids accompanied the cooling of the magmatic body and gave rise to an extensive Fe-ore deposit (mainly pyrite) exploited during the past century. The tectonic setting which favoured the emplacement and exhumation of the Gavorrano pluton is strongly debated with fallouts on the comprehension of the Neogene evolution of this sector of the inner Northern Apennines. Data from a new fieldwork dataset, integrated with information from the mining activity, have been integrated to refine the geological setting of the whole crustal sector where the Gavorrano monzogranite was emplaced and exhumed. Our review, implemented by new palynological, petrological and structural data pointed out that: (i) the age of the Palaeozoic phyllite (hosting rocks) is middle-late Permian, thus resulting younger than previously described (i.e., pre-Carboniferous); (ii) the conditions at which the metamorphic aureole developed are estimated at a temperature of c. 660 °C and at a depth lower than c. 6 km; (iii) the tectonic evolution which determined the emplacement and exhumation of the monzogranite is constrained in a transfer zone, in the frame of the extensional tectonics affecting the area continuously since Miocene. Full article
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Article
Carbon Storage Potential of North American Oil & Gas Produced Water Injection with Surface Dissolution
Geosciences 2021, 11(3), 123; https://doi.org/10.3390/geosciences11030123 - 08 Mar 2021
Cited by 3 | Viewed by 1112
Abstract
Carbon dioxide (CO2) geological storage traditionally involves capturing a CO2 stream from a point source such as a power station or from cement, steel, or natural gas processing plant, transporting it and compressing it, prior to injection as a supercritical [...] Read more.
Carbon dioxide (CO2) geological storage traditionally involves capturing a CO2 stream from a point source such as a power station or from cement, steel, or natural gas processing plant, transporting it and compressing it, prior to injection as a supercritical phase into a suitable geological reservoir overlain by a cap-rock or seal. One of the main perceived risks in CO2 geological storage is migration or leakage of the buoyant CO2 stream through the seal, via faults or fractures, or other migration out of the storage complex. Injection of CO2 dissolved in water may be one solution to mitigate the leakage risk. This approach could take advantage of large volumes of wastewater already being reinjected into saline aquifers worldwide but particularly in North America, thus reducing costs. This study examines the potential to “piggyback” off the existing wastewater injection industry as a novel carbon storage option. Full article
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Article
Studying the Depth Structure of the Kyrgyz Tien Shan by Using the Seismic Tomography and Magnetotelluric Sounding Methods
Geosciences 2021, 11(3), 122; https://doi.org/10.3390/geosciences11030122 - 08 Mar 2021
Cited by 5 | Viewed by 682
Abstract
This paper presents new results of detailed seismic tomography (ST) on the deep structure beneath the Middle Tien Shan to a depth of 60 km. For a better understanding of the detected heterogeneities, the obtained velocity models were compared with the results of [...] Read more.
This paper presents new results of detailed seismic tomography (ST) on the deep structure beneath the Middle Tien Shan to a depth of 60 km. For a better understanding of the detected heterogeneities, the obtained velocity models were compared with the results of magnetotelluric sounding (MTS) along the Kekemeren and Naryn profiles, running parallel to the 74 and 76 meridians, respectively. We found that in the study region the velocity characteristics and geoelectric properties correlate with each other. The high-velocity high-resistivity anomalies correspond to the parts of the Tarim and Kazakhstan-Junggar plates submerged under the Tien Shan. We revealed that the structure of the Middle Tien Shan crust is conditioned by the presence of the Central Tien Shan microcontinent. It manifests itself as two anomalies lying one below the other: the lower low-velocity low-resistivity anomaly, and the upper high-velocity high-resistivity anomaly. The fault zones, limiting the Central Tien Shan microcontinent, appear as low-velocity low-resistivity anomalies. The obtained features indicate the fluid saturation of the fault zones. According to the revealed features of the Central Tien Shan geological structure, it is assumed that the lower-crustal low-velocity layer can play a significant role in the delamination of the mantle part of the submerged plates. Full article
(This article belongs to the Section Geophysics)
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Article
Geochemical, Geological and Groundwater Quality Characterization of a Complex Geological Framework: The Case Study of the Coreca Area (Calabria, South Italy)
Geosciences 2021, 11(3), 121; https://doi.org/10.3390/geosciences11030121 - 08 Mar 2021
Cited by 5 | Viewed by 749
Abstract
Hydrogeochemical characterization and statistical methods were used to investigate the groundwater quality and the origin of constituents (anthropic or natural) in groundwater of the Coreca area (Calabria, South Italy). Coreca is characterized by an articulated geological setting where the three main geological complexes [...] Read more.
Hydrogeochemical characterization and statistical methods were used to investigate the groundwater quality and the origin of constituents (anthropic or natural) in groundwater of the Coreca area (Calabria, South Italy). Coreca is characterized by an articulated geological setting where the three main geological complexes that distinguish the Northern Calabria Peloritan Orogen (CPO) outcrop. This complex asset affects the quality of groundwater mainly exploited for irrigation use. In particular, the presence of ultramafic rocks (e.g., serpentinite and metabasite) promotes the release of harmful elements such as Cr and Ni. In the studied area, two groups of waters were identified: Ca-HCO3 waters strongly controlled by the interaction with Ca-rich phases (e.g., limestone), and Mg-HCO3 waters related to the interaction of meteoric water with the metamorphic units. Statistical elaboration allowed to detect, in the Mg-HCO3 group, a good correlation between Cr and Ni (not observed in Ca waters) and a negative correlation between Cr, Ca and Al, in agreement with direct interaction with ultramafic rocks characterized by low concentrations of CaO and Al2O3. The concentration of major and trace elements has been compared with the Italian law limit values and the drinking water guidelines provided by the World Health Organization (WHO). Only three samples showed Mn and Ni concentration higher than the Italian law threshold. Furthermore, the assessment of groundwater quality was carried out using salinity and metal indexes. The groundwater quality assessment for irrigation allowed to classify the resource as “excellent to good” and “good to permissible”; nevertheless, a salinity problem and a magnesium hazard were found. Lastly, a metal index (MI) calculation revealed values <1 for almost all samples, pointing to good overall quality. Only a few samples showed a value extremely higher than 1, attributable to prolonged interaction with ultramafic rocks and/or localized anthropogenic pollution. From a general point of view, groundwater showed a generally good quality except for limited areas (and limited to the set of constituents analyzed) and a mild exceedance of the maximum salinity thresholds that must be monitored over time. Through a multidisciplinary approach, it was possible to ascertain the main anomalies attributable to the interaction with the hosting rocks and not (with few exceptions) to anthropic processes. Full article
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Article
Relationship between the Geotourism Potential and Function in the Polish Part of the Roztocze Transboundary Biosphere Reserve
Geosciences 2021, 11(3), 120; https://doi.org/10.3390/geosciences11030120 - 07 Mar 2021
Cited by 1 | Viewed by 673
Abstract
The Polish part of the Roztocze Transboundary Biosphere Reserve area is characterized by diversified geotourism resources with relatively high value. However, their potential seems not to be fully used in the current product offer. The aim of the study was therefore to assess [...] Read more.
The Polish part of the Roztocze Transboundary Biosphere Reserve area is characterized by diversified geotourism resources with relatively high value. However, their potential seems not to be fully used in the current product offer. The aim of the study was therefore to assess the spatial variability of the geotourism potential and function and to determine their interrelations in view of further development of geotourism in the Roztocze TBR and the perspective of creation of the “Kamienny Las na Roztoczu” geopark. The study was carried out with the use of the taxonomic method of multidimensional comparative analysis consisting of calculation and analysis of general, total, and partial indices of the geotourism potential and function in 22 communes. The results showed the highest total indicator of geotourism potential in two communes, i.e. Józefów and Krasnobród, and the highest value of the total geotourism function index in Krasnobród. The results of the analysis of the relationships between the geotourism potential and function indicate that the geotourism resources and products are fully used in terms of the development of the function only in Krasnobród commune. In turn, the value of the total geotourism function index in the Zwierzyniec commune exceeds the geotourism potential indicator, which implies that this area is overloaded by tourist movement. The total indicators of geotourism potential in the other communes, especially Józefów, Krasnobród, Lubycza Królewska, and Susiec, indicate the possibility of more intensive exploitation of geotourism resources in preparation of interesting products in compliance with the principles of sustainable development and, consequently, the development of the geotourism function. Full article
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Review
Theory of Effective Stress in Soil and Rock and Implications for Fracturing Processes: A Review
Geosciences 2021, 11(3), 119; https://doi.org/10.3390/geosciences11030119 - 05 Mar 2021
Cited by 1 | Viewed by 3074
Abstract
The effective stress principle (ESP) plays a basic role in geology and engineering problems as it is involved in fundamental issues concerning strain and failure of rock and soil, as well as of other porous materials such as concrete, metal powders, biological tissues, [...] Read more.
The effective stress principle (ESP) plays a basic role in geology and engineering problems as it is involved in fundamental issues concerning strain and failure of rock and soil, as well as of other porous materials such as concrete, metal powders, biological tissues, etc. Although since its introduction in the 1920s the main ESP aspects have been unravelled and theoretically derived, these do not appear to have been always entirely perceived by many in the science community dealing with ESP-related topics but having little familiarity with the complex theories of porous media and poroelasticity. The purpose of this review is to provide a guidance for the reader who needs an updated overview of the different theoretical and experimental approaches to the ESP and related topics over the past century, with particular reference to geological fracturing processes. We begin by illustrating, after some introductive historical remarks, the basic theory underlying the ESP, based on theory of elasticity methods. Then the different ESP-related theories and experimental results, as well as main interpretations of rock jointing and fracturing phenomena, are discussed. Two main classical works are then revisited, and a rigorous ESP proof is derived. Such a proof is aimed at geologists, engineers and geophysicists to become more familiar with theories of porous media and poroelasticity, being based on the classical theory of elasticity. The final part of this review illustrates some still open issues about faulting and hydraulic fracturing in rocks. Full article
(This article belongs to the Special Issue Seismotectonics, Active Deformation, and Structure of the Crust)
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Article
Micromorphological Characteristic of Different-Aged Cryosols from the East Part of Lena River Delta, Siberia, Russia
Geosciences 2021, 11(3), 118; https://doi.org/10.3390/geosciences11030118 - 05 Mar 2021
Cited by 1 | Viewed by 659
Abstract
Micromorphological investigation of soils is a powerful tool for studying the transformation of soils under the influence of various weathering mechanisms. In the Arctic region, under the influence of seasonal freezing/thawing processes, cryohydration is the leading type of weathering. Soils of different-aged islands [...] Read more.
Micromorphological investigation of soils is a powerful tool for studying the transformation of soils under the influence of various weathering mechanisms. In the Arctic region, under the influence of seasonal freezing/thawing processes, cryohydration is the leading type of weathering. Soils of different-aged islands of the Lena River Delta were investigated. Thin sections of soils were analyzed using a polarizing microscope Leica DM750P (Leica Camera AG, Wetzlar, Germany). X-ray fluorescence analysis was used to determine the chemical composition of the soils. As a result of the work, the rate of weathering of soil minerals was estimated, soil fabric was considered, as well as the chemical composition of the soil. The accumulation of poorly sorted circular striated sand due to active influence of the Lena River was noted on young soil from Samoylov isl. The formation of biogenic sand-silt crumb aggregates was noted at more ancient sites. Physical weathering of soil minerals under the influence of cryogenic processes has been noted. Full article
(This article belongs to the Section Biogeosciences)
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