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Geosciences, Volume 9, Issue 4 (April 2019)

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Cover Story (view full-size image) This paper uses dimensional data from over 700 tafoni in Antarctica to assess how tafoni size and [...] Read more.
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Open AccessArticle
Role of Trapped Air on the Tsunami-Induced Transient Loads and Response of Coastal Bridges
Geosciences 2019, 9(4), 191; https://doi.org/10.3390/geosciences9040191
Received: 9 February 2019 / Revised: 20 April 2019 / Accepted: 23 April 2019 / Published: 25 April 2019
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Abstract
In response to the extensive damage of coastal bridges sustained in recent tsunamis, this paper describes an investigation into tsunami-induced effects on two common bridge types, an open-girder deck with cross-frames and one with solid diaphragms. To this end, large-scale (1:5) physical models [...] Read more.
In response to the extensive damage of coastal bridges sustained in recent tsunamis, this paper describes an investigation into tsunami-induced effects on two common bridge types, an open-girder deck with cross-frames and one with solid diaphragms. To this end, large-scale (1:5) physical models with realistic structural members and elastomeric bearings were constructed and tested under a range of unbroken solitary waves and more realistic tsunami-like transient bores. The flexible bearings allowed the superstructure to rotate and translate vertically, thus simulating the wave–structure interaction during the tsunami inundation. Detailed analysis of the experimental data revealed that for both bridge types the resistance mechanism and transient structural response is characterized by a short-duration phase that introduces the maximum overturning moment, upward movement, and rotation of the deck, and a longer-duration phase that introduces significant uplift forces but small moment and rotation due to the fact that the wave is approaching the point of rotation. In the former phase the uplift is resisted mainly by the elastomeric bearings and columns offshore of the center of gravity of the superstructure (C.G.), maximizing their uplift demand. In the latter phase the total uplift is distributed more equally to all the bearings, which tends to maximize the uplift demand in the structural members close to the C.G. The air-entrapment in the chambers of the bridge with diaphragms modifies the wave–structure interaction, introducing (a) a different pattern and magnitude of wave pressures on the superstructure due to the cushioning effect; (b) a 39% average and 148% maximum increase in the total uplift forces; and (c) a 32% average increase of the overturning moment, which has not been discussed in previous studies. Deciphering the exact effect of the trapped air on the total uplift forces is challenging because, although the air consistently increases the quasi-static component of the force, it has an inconsistent and complex effect on the slamming component, which can either increase or decrease. Interestingly, the air also has a complex effect on the uplift demand in the offshore bearings and columns, which can decrease or increase even more than the total deck uplift, and an inconsistent effect on the uplift force of different structural components introduced by the same wave. These are major findings because they demonstrate that the current approach of investigating the effect of trapped air only on the total uplift is insufficient. Last but not least, the study reveals the existence of significant differences in the effects introduced by solitary waves and transient bores, especially when air is trapped beneath the deck; it also provides practical guidance to engineers, who are advised to design the elastomeric bearings offshore of the C.G. for at least 60% and 50% of the total induced uplift force, respectively, for a bridge with cross-frames and one with diaphragms, instead of distributing the total uplift equally to all bearings. Full article
(This article belongs to the Special Issue River, Urban, and Coastal Flood Risk)
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Open AccessArticle
Character, Rates, and Environmental Significance of Holocene Dust Accumulation in Archaeological Hilltop Ruins in the Southern Levant
Geosciences 2019, 9(4), 190; https://doi.org/10.3390/geosciences9040190
Received: 16 March 2019 / Revised: 6 April 2019 / Accepted: 9 April 2019 / Published: 24 April 2019
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Abstract
Loess accumulated in the Negev desert during the Pleistocene and primary and secondary loess remains cover large parts of the landscape. Holocene loess deposits are however absent. This could be due low accumulation rates, lack of preservation, and higher erosion rates in comparison [...] Read more.
Loess accumulated in the Negev desert during the Pleistocene and primary and secondary loess remains cover large parts of the landscape. Holocene loess deposits are however absent. This could be due low accumulation rates, lack of preservation, and higher erosion rates in comparison to the Pleistocene. This study hypothesized that archaeological ruins preserve Holocene dust. We studied soils developed on archaeological hilltop ruins in the Negev and the Petra region and compared them with local soils, paleosols, geological outcrops, and current dust. Seven statistically modeled grain size end-members were identified and demonstrate that the ruin soils in both regions consist of mixtures of local and remote sediment sources that differ from dust compositions deposited during current storms. This discrepancy is attributed to fixation processes connected with sediment-fixing agents such as vegetation, biocrusts, and/or clast pavements associated with vesicular layers. Average dust accretion rates in the ruins are estimated to be ~0.14 mm/a, suggesting that ~30% of the current dust that can be trapped with dry marble dust collectors has been stored in the ruin soils. Deposition amounts and grain sizes do not significantly correlate with wind intensity. However, precipitation may have contributed to dust accretion. A snowstorm in the Petra region delivered a significantly higher amount of sediment than rain or dry deposition. Snowfall dust had a unique particle size distribution relatively similar to the ruin soils. Wet deposition and snow might catalyze dust deposition and enhance fixation by fostering vegetation and crust formation. More frequent snowfall during the Pleistocene may have been an important mechanism of primary loess deposition in the southern Levant. Full article
(This article belongs to the Special Issue Aeolian Processes and Geomorphology)
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Open AccessArticle
First Identification of Periodic Degassing Rhythms in Three Mineral Springs of the East Eifel Volcanic Field (EEVF, Germany)
Geosciences 2019, 9(4), 189; https://doi.org/10.3390/geosciences9040189
Received: 14 February 2019 / Revised: 5 April 2019 / Accepted: 19 April 2019 / Published: 24 April 2019
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Abstract
We present a geochemical dataset acquired during continual sampling over 7 months (bi-weekly) and 4 weeks (every 8 h) in the Neuwied Basin, a part of the East Eifel Volcanic Field (EEVF, Germany). We used a combination of geochemical, geophysical, and statistical methods [...] Read more.
We present a geochemical dataset acquired during continual sampling over 7 months (bi-weekly) and 4 weeks (every 8 h) in the Neuwied Basin, a part of the East Eifel Volcanic Field (EEVF, Germany). We used a combination of geochemical, geophysical, and statistical methods to describe and identify potential causal processes underlying the correlations of degassing patterns of CO2, He, Rn, and tectonic processes in three investigated mineral springs (Nette, Kärlich and Kobern). We provide for the first time, temporal analyses of periodic degassing patterns (1 day and 2–6 days) in springs. The temporal fluctuations in cyclic behavior of 4–5 days that we recorded had not been observed previously but may be attributed to a fundamental change in either gas source processes, subsequent gas transport to the surface, or the influence of volcano–tectonic earthquakes. Periods observed at 10 and 15 days may be related to discharge pulses of magma in the same periodic rhythm. We report the potential hint that deep low-frequency (DLF) earthquakes might actively modulate degassing. Temporal analyses of the CO2–He and CO2–Rn couples indicate that all springs are interlinked by previously unknown fault systems. The volcanic activity in the EEVF is dormant but not extinct. To understand and monitor its magmatic and degassing systems in relation to new developments in DLF-earthquakes and magmatic recharging processes and to identify seasonal variation in gas flux, we recommend continual monitoring of geogenic gases in all available springs taken at short temporal intervals. Full article
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Open AccessArticle
Role of Salt Migration in Destabilization of Intra Permafrost Hydrates in the Arctic Shelf: Experimental Modeling
Geosciences 2019, 9(4), 188; https://doi.org/10.3390/geosciences9040188
Received: 4 April 2019 / Revised: 18 April 2019 / Accepted: 20 April 2019 / Published: 23 April 2019
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Abstract
Destabilization of intrapermafrost gas hydrate is one possible reason for methane emission on the Arctic shelf. The formation of these intrapermafrost gas hydrates could occur almost simultaneously with the permafrost sediments due to the occurrence of a hydrate stability zone after sea regression [...] Read more.
Destabilization of intrapermafrost gas hydrate is one possible reason for methane emission on the Arctic shelf. The formation of these intrapermafrost gas hydrates could occur almost simultaneously with the permafrost sediments due to the occurrence of a hydrate stability zone after sea regression and the subsequent deep cooling and freezing of sediments. The top of the gas hydrate stability zone could exist not only at depths of 200–250 m, but also higher due to local pressure increase in gas-saturated horizons during freezing. Formed at a shallow depth, intrapermafrost gas hydrates could later be preserved and transform into a metastable (relict) state. Under the conditions of submarine permafrost degradation, exactly relict hydrates located above the modern gas hydrate stability zone will, first of all, be involved in the decomposition process caused by negative temperature rising, permafrost thawing, and sediment salinity increasing. That’s why special experiments were conducted on the interaction of frozen sandy sediments containing relict methane hydrates with salt solutions of different concentrations at negative temperatures to assess the conditions of intrapermafrost gas hydrates dissociation. Experiments showed that the migration of salts into frozen hydrate-containing sediments activates the decomposition of pore gas hydrates and increase the methane emission. These results allowed for an understanding of the mechanism of massive methane release from bottom sediments of the East Siberian Arctic shelf. Full article
(This article belongs to the Special Issue Gas Hydrate: Environmental and Climate Impacts)
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Open AccessArticle
Hydropower Dam State and Its Foundation Soil Survey Using Industrial Seismic Oscillations
Geosciences 2019, 9(4), 187; https://doi.org/10.3390/geosciences9040187
Received: 1 March 2019 / Revised: 15 April 2019 / Accepted: 18 April 2019 / Published: 23 April 2019
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Abstract
In this article, we suggest a new type of seismic source for surveying both structure state and foundation soil conditions regardless of the level of seismic noise. In our opinion, powerful industrial equipment can be treated as seismic sources. We describe the results [...] Read more.
In this article, we suggest a new type of seismic source for surveying both structure state and foundation soil conditions regardless of the level of seismic noise. In our opinion, powerful industrial equipment can be treated as seismic sources. We describe the results of a survey conducted on the Song Tranh-2 hydropower dam located in Central Vietnam. After a М = 4.7 earthquake, the dam visual inspection revealed zones of the excessive durability loss: cracks and areas with an elevated infiltration of water into the dam galleries. Powerful industrial equipment generates continuous quasi-harmonic mechanical oscillations (seismic waves) that travel through layers of rocks. These seismic oscillations are recorded by receivers in different measurement points such as the dam body, abutments, and the foundation soils. Anomalous amplitudes of these oscillations indicate the presence of weakened zones in the structure or in foundation soil. We coupled passive and active seismic methods to more precisely find such zones. In this case, active seismic methods allowed us to investigate dam abutment zones, and passive seismic methods were used to localize weakened zones in the dam-foundation soil system. We assumed that the joint contribution of two factors was the cause of the dam weakening. One of them was caused by increased water infiltration through the rock mass and its contact zones, and the other was reservoir-induced seismicity contributing to the deterioration of the foundation soils, which was possibly the reason for a shift in the dam in the contact zone with the rock mass foundation. It is necessary to perform computer modelling, which was not included in our research. The developed method can be used for the safety control of the hydropower station dams. Full article
(This article belongs to the Special Issue What Is Really New in Seismic Response Analysis of Soil Deposits)
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Open AccessArticle
Estimation of Vs Structure of Krueng Aceh and its Suburb Basin of Aceh Province, Indonesia, Derived from Microtremor Measurements
Geosciences 2019, 9(4), 186; https://doi.org/10.3390/geosciences9040186
Received: 25 February 2019 / Revised: 2 April 2019 / Accepted: 16 April 2019 / Published: 22 April 2019
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Abstract
The Aceh and Seulimeum Faults flank the Krueng Aceh Basin in Indonesia, and the shear-wave velocity (Vs) structure of the basin is not extensively available. Understanding the Vs structure is very important in order to figure out how the basin structures seemingly appear, [...] Read more.
The Aceh and Seulimeum Faults flank the Krueng Aceh Basin in Indonesia, and the shear-wave velocity (Vs) structure of the basin is not extensively available. Understanding the Vs structure is very important in order to figure out how the basin structures seemingly appear, and this can eventually be used to generate a microzonation map for other forthcoming studies. To provide this, Vs was measured over an area approximately covering Banda Aceh City and its surroundings, by setting two lines consisting of eight points projected in the NW–SE and SW–NE orientations. This research aims to facilitate the approximation of the Vs structure characteristics of the Krueng Aceh Basin using the microtremor array method (MAM). Triangular configurations were set by deploying four seismometers following an M-station geometry for three different array sizes (i.e., 3, 10, and 30 m in distance). The data were then processed by utilizing the spatial autocorrelation (SPAC) technique. The result shows that the Vs structure generally dips down from SE to NW, and it gradually declines from SW to NE. The combination of these Vs structures tends to be oblique toward the SW–NE direction. This form may be affected by the Aceh Segment Fault which is more active than the Seulimeum Segment Fault. The average maximum penetration depth and Vs are 603 m and 947.5 m/s in the SE–NW orientation, and 650 m and 958 m/s in the SW–NE direction. Generally, the thickness of the strata is greater in the upstream area compared to the downstream area. Their composition consists of alluvium (A) at the uppermost layer and diluvium (D) at the underlying layers. Then, all of the identified strata are aged from the Pleistocene to Tertiary Pleistocene (Tp). These characteristics of the strata could potentially cause surface damages as a result of site effect responses when an earthquake is occurring. Full article
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Open AccessArticle
Planning Landslide Countermeasure Works through Long Term Monitoring and Grey Box Modelling
Geosciences 2019, 9(4), 185; https://doi.org/10.3390/geosciences9040185
Received: 5 April 2019 / Revised: 18 April 2019 / Accepted: 19 April 2019 / Published: 22 April 2019
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Abstract
The design of countermeasure works to mitigate landslide risk needs to deal with the multiple unknowns that are linked with soil properties, distribution and rheology. Most of the time, the degree of definition of all these elements is low. Through landslide monitoring, it [...] Read more.
The design of countermeasure works to mitigate landslide risk needs to deal with the multiple unknowns that are linked with soil properties, distribution and rheology. Most of the time, the degree of definition of all these elements is low. Through landslide monitoring, it is possible to acquire signals from the landslide that carry synthetic information about its dynamic. Thus, if it is possible to define a model that is able to link the landslide displacements with the triggering factors and to predict them consistently, that model may be used to evaluate the effect of a countermeasure work directly, bypassing the geomechanical uncertainty. In this paper, an example application of this approach is described. The displacements of a landslide located in North East Italy are connected with the water discharge of the small stream the crosses the landslide body. A countermeasure work that intercepts the discharge of the torrent is expected to reduce the landslide displacements of approximately 70%, with lower costs of construction and smaller impacts on the environment and landscape with respect of other types of structural mitigation works such as slope reprofiling and large retaining walls. Full article
(This article belongs to the Special Issue Mountain Landslides: Monitoring, Modeling, and Mitigation)
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Open AccessReview
Associations between Fossil Beetles and Other Organisms
Geosciences 2019, 9(4), 184; https://doi.org/10.3390/geosciences9040184
Received: 26 February 2019 / Revised: 15 April 2019 / Accepted: 18 April 2019 / Published: 21 April 2019
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Abstract
The present work reveals plant and animal associates of 16 families and subfamilies of fossil beetles that have been preserved in amber from Mexico, the Dominican Republic, and Myanmar. The associates include mites, pseudoscorpions, spiders, insect parasites and predators, fungi, angiosperm parts, vertebrates, [...] Read more.
The present work reveals plant and animal associates of 16 families and subfamilies of fossil beetles that have been preserved in amber from Mexico, the Dominican Republic, and Myanmar. The associates include mites, pseudoscorpions, spiders, insect parasites and predators, fungi, angiosperm parts, vertebrates, and nematodes. The presence of these fossil associates can be attributed to the rapid preservation of organisms in resin, thus maintaining natural associations almost “in situ”. Examples of present-day associations similar to those of the fossils show that specific behavioral patterns are often far more ancient than the specific lineages involved. Full article
(This article belongs to the Special Issue The Evolutionary History of the Coleoptera)
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Open AccessArticle
Sources and Impacts of Bottom Slope Uncertainty on Estimation of Seafloor Backscatter from Swath Sonars
Geosciences 2019, 9(4), 183; https://doi.org/10.3390/geosciences9040183
Received: 29 March 2019 / Revised: 14 April 2019 / Accepted: 15 April 2019 / Published: 20 April 2019
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Abstract
Seafloor backscatter data from multibeam echosounders are now widely used in seafloor characterization studies. Accurate and repeatable measurements are essential for advancing the success of these techniques. This paper explores the impact of uncertainty in our knowledge of the local seafloor slope on [...] Read more.
Seafloor backscatter data from multibeam echosounders are now widely used in seafloor characterization studies. Accurate and repeatable measurements are essential for advancing the success of these techniques. This paper explores the impact of uncertainty in our knowledge of the local seafloor slope on the overall accuracy of the backscatter measurement. Amongst the various sources of slope uncertainty studied, the impact of bathymetric uncertainty and scale were identified as the major sources of slope uncertainty. The bottom slope affects two important corrections needed for estimating seafloor backscatter: (1) The insonified area and; (2) the seafloor incidence angle. The impacts of these slope-related uncertainty sources were quantified for a shallow water multibeam survey. The results show that the most significant uncertainty in backscatter data arises when seafloor slope is not accounted for or when low-resolution bathymetry is used to estimate seafloor slope. This effect is enhanced in rough seafloors. A standard method of seafloor slope correction is proposed to achieve repeatable and accurate backscatter results. Additionally, a standard data package, including metadata describing the slope corrections applied, needs to accompany backscatter results and should include details of the slope estimation method and resolution of the bathymetry used. Full article
(This article belongs to the Special Issue Geological Seafloor Mapping)
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Open AccessArticle
Legacy Data: How Decades of Seabed Sampling Can Produce Robust Predictions and Versatile Products
Geosciences 2019, 9(4), 182; https://doi.org/10.3390/geosciences9040182
Received: 22 March 2019 / Revised: 12 April 2019 / Accepted: 15 April 2019 / Published: 19 April 2019
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Abstract
Sediment maps developed from categorical data are widely applied to support marine spatial planning across various fields. However, deriving maps independently of sediment classification potentially improves our understanding of environmental gradients and reduces issues of harmonising data across jurisdictional boundaries. As the groundtruth [...] Read more.
Sediment maps developed from categorical data are widely applied to support marine spatial planning across various fields. However, deriving maps independently of sediment classification potentially improves our understanding of environmental gradients and reduces issues of harmonising data across jurisdictional boundaries. As the groundtruth samples are often measured for the fractions of mud, sand and gravel, this data can be utilised more effectively to produce quantitative maps of sediment composition. Using harmonised data products from a range of sources including the European Marine Observation and Data Network (EMODnet), spatial predictions of these three sediment fractions were generated for the north-west European continental shelf using the random forest algorithm. Once modelled these sediment fraction maps were classified using a range of schemes to show the versatility of such an approach, and spatial accuracy maps were generated to support their interpretation. The maps produced in this study are to date the highest resolution quantitative sediment composition maps that have been produced for a study area of this extent and are likely to be of interest for a wide range of applications such as ecological and biophysical studies. Full article
(This article belongs to the Special Issue Geological Seafloor Mapping)
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Open AccessReview
The Top-Viewed Cryosphere Videos on YouTube: An Overview
Geosciences 2019, 9(4), 181; https://doi.org/10.3390/geosciences9040181
Received: 27 March 2019 / Revised: 10 April 2019 / Accepted: 16 April 2019 / Published: 19 April 2019
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Abstract
Youtube.com has become one of the most popular places to share videos on the Internet, storing a large amount of audiovisual materials. People all over the world can upload their videos and watch videos of others. The research potential of this information source [...] Read more.
Youtube.com has become one of the most popular places to share videos on the Internet, storing a large amount of audiovisual materials. People all over the world can upload their videos and watch videos of others. The research potential of this information source has received increasing popularity across scientific disciplines. In this contribution, we explore the top viewed videos containing selected cryospheric keywords, both general (cryosphere, glacier, ice, permafrost, snow), and specific, focusing on different types of cryospheric hazards (avalanche, blizzard and glacial lake outburst flood/jokulhlaup). Searching 100 top-viewed videos for each keyword, our database consists of 859 videos. Each video is described by several qualitative characteristics (e.g., video type, geographical focus) as well as quantitative characteristics (e.g., views per day, likes). A total of 310 videos in our database (36.1% of all) are classified as videos with factual cryospheric content. We show that the broader audience represented by YouTube users is particularly interested in videos capturing dynamic processes such as calving of glaciers. While videos found for general cryosphere keywords have attracted a generally higher attention of YouTube users (total views), videos found for specific keywords are ranked among the most liked. Further, we analyze where the videos with cryospheric content are filmed, revealing several hotspots for different keywords located in all continents except for Africa. Finally, we discuss the potentials of cryosphere videos for educational and research purposes, pointing out that videos filmed by incidental witnesses of low-frequency processes such as glacial lake outburst floods might contribute to the elucidation of their dynamics, magnitude and behavior as well as the occurrence in space and time. Full article
(This article belongs to the Special Issue Cryosphere II)
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Open AccessArticle
Developing an Optimal Spatial Predictive Model for Seabed Sand Content Using Machine Learning, Geostatistics, and Their Hybrid Methods
Geosciences 2019, 9(4), 180; https://doi.org/10.3390/geosciences9040180
Received: 1 March 2019 / Revised: 15 April 2019 / Accepted: 15 April 2019 / Published: 17 April 2019
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Abstract
Seabed sediment predictions at regional and national scales in Australia are mainly based on bathymetry-related variables due to the lack of backscatter-derived data. In this study, we applied random forests (RFs), hybrid methods of RF and geostatistics, and generalized boosted regression modelling (GBM), [...] Read more.
Seabed sediment predictions at regional and national scales in Australia are mainly based on bathymetry-related variables due to the lack of backscatter-derived data. In this study, we applied random forests (RFs), hybrid methods of RF and geostatistics, and generalized boosted regression modelling (GBM), to seabed sand content point data and acoustic multibeam data and their derived variables, to develop an accurate model to predict seabed sand content at a local scale. We also addressed relevant issues with variable selection. It was found that: (1) backscatter-related variables are more important than bathymetry-related variables for sand predictive modelling; (2) the inclusion of highly correlated predictors can improve predictive accuracy; (3) the rank orders of averaged variable importance (AVI) and accuracy contribution change with input predictors for RF and are not necessarily matched; (4) a knowledge-informed AVI method (KIAVI2) is recommended for RF; (5) the hybrid methods and their averaging can significantly improve predictive accuracy and are recommended; (6) relationships between sand and predictors are non-linear; and (7) variable selection methods for GBM need further study. Accuracy-improved predictions of sand content are generated at high resolution, which provide important baseline information for environmental management and conservation. Full article
(This article belongs to the Special Issue Geological Seafloor Mapping)
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Open AccessArticle
The Impact of Sea Shore Protection on Aeolian Processes Using the Example of the Beach in Rowy, N Poland
Geosciences 2019, 9(4), 179; https://doi.org/10.3390/geosciences9040179
Received: 1 March 2019 / Revised: 26 March 2019 / Accepted: 16 April 2019 / Published: 17 April 2019
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Abstract
The Polish Baltic Sea coast is subject to constant changes as a result of sea erosion on sandy and clayey sections. Sand accumulates only on a few sandy sections of the shore. There are various methods of protection limiting the negative impact of [...] Read more.
The Polish Baltic Sea coast is subject to constant changes as a result of sea erosion on sandy and clayey sections. Sand accumulates only on a few sandy sections of the shore. There are various methods of protection limiting the negative impact of sea waves on the shore. In the city of Rowy, the coast was secured with the use of a comprehensive method (artificial reef, textile tube, spurs, and beach nourishment), which has mitigated the sea’s negative impact. The beach has been widened. The upper part of the beach has been built up to the level of the foredune. Biotechnical protection has not been applied at the border between the beach and the foredune (fascine hurdles from brushwood, sand fences, and branches). This has caused wind blowing of sand from the beach to the forest growing on the foredune. The sand also covered the access road to holiday resorts. This was favored by the strong wind from the sea. Several morphological surveys were carried out, including topographic surveys and sedimentological samplings. The range of sand coverage and types of forms (aeolian shadows and drifts) were determined. Fifty eight samples of sand from various sources were collected for sedimentological analysis. Speed and directions of winds that occurred in 2001–2018 were also analyzed. Three wind speed criteria were distinguished: ≥4 m·s−1, ≥10 m·s−1, and ≥15 m·s−1, responsible for blowing away and transporting material. Results indicate that reconstruction of the beach to the height of the foredune, lack of biotechnical protection, and strong, coastal directions of the wind were the main factors responsible for increased aeolian transport of sand inland. Effects of aeolian processes such as those observed on the beach in Rowy were not observed elsewhere on the Polish coast of the South Baltic Sea, where beach nourishment was also performed. Full article
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Open AccessArticle
Atmospheric Control of Deep Chlorophyll Maximum Development
Geosciences 2019, 9(4), 178; https://doi.org/10.3390/geosciences9040178
Received: 21 January 2019 / Revised: 5 April 2019 / Accepted: 11 April 2019 / Published: 17 April 2019
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Abstract
The evolution of the near-surface phytoplankton bloom towards a Deep Chlorophyll Maximum (DCM) in mid-latitudes and subpolar regions of the global ocean is a well-known biological feature. However, our knowledge about the exact mechanism that determines the end of the bloom and its [...] Read more.
The evolution of the near-surface phytoplankton bloom towards a Deep Chlorophyll Maximum (DCM) in mid-latitudes and subpolar regions of the global ocean is a well-known biological feature. However, our knowledge about the exact mechanism that determines the end of the bloom and its irreversible evolution towards a DCM is still limited. In this work, combining satellite and in-situ oceanographic data together with reanalysis data, we investigate why and when this transition between the near-surface phytoplankton bloom and the development of a DCM occurs. For this aim, we investigate the links between changes in air-sea heat exchanges, the near-surface signature of phytoplankton bloom, and the water column vertical structure by calculating the mixed layer depth (MLD) and depth of the DCM on hydrographic and chlorophyll profiles. We find that the occurrence of the last convective mixing event (heat loss by the ocean surface) at the end of the spring which is able to reach the base of the MLD and inject new nutrients into the mixed layer marks the end of the near-surface bloom and its transition towards a DCM. Identified in this way, the spring bloom duration and the start of the transition towards a DCM can be systematically and objectively determined, providing sensitive indexes of climate and ecosystem variability. Full article
(This article belongs to the Special Issue Ocean-Atmosphere Interaction)
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Open AccessArticle
Tropospheric and Ionospheric Anomalies Induced by Volcanic and Saharan Dust Events as Part of Geosphere Interaction Phenomena
Geosciences 2019, 9(4), 177; https://doi.org/10.3390/geosciences9040177
Received: 8 February 2019 / Revised: 5 April 2019 / Accepted: 10 April 2019 / Published: 17 April 2019
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Abstract
In this work, we assessed the possible relation of ionospheric perturbations observed by Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER), Global Positioning System total electron content (GPS TEC), National Oceanic and Atmospheric Administration (NOAA)-derived outgoing longwave-Earth radiation (OLR), and atmospheric chemical [...] Read more.
In this work, we assessed the possible relation of ionospheric perturbations observed by Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER), Global Positioning System total electron content (GPS TEC), National Oceanic and Atmospheric Administration (NOAA)-derived outgoing longwave-Earth radiation (OLR), and atmospheric chemical potential (ACP) measurements, with volcanic and Saharan dust events identified by ground and satellite-based medium infrared/thermal infrared (MIR/TIR) observations. The results indicated that the Mt. Etna (Italy) volcanic activity of 2006 was probably responsible for the ionospheric perturbations revealed by DEMETER on 4 November and 6 December and by GPS TEC observations on 4 November and 12 December. This activity also affected the OLR (on 26 October; 6 and 23 November; and 2, 6, and 14 December) and ACP (on 31 October–1 November) analyses. Similarly, two massive Saharan dust episodes, detected by Robust Satellite Techniques (RST) using Spinning Enhanced Visible and Infrared Imager (SEVIRI) optical data, probably caused the ionospheric anomalies recorded, based on DEMETER and GPS TEC observations, over the Mediterranean basin in May 2008. The study confirmed the perturbing effects of volcanic and dust events on tropospheric and ionospheric parameters. Further, it demonstrated the advantages of using independent satellite observations to investigate atmospheric phenomena, which may not always be well documented. The impact of this increased detection capacity in reducing false positives, in the framework of a short-term seismic hazard forecast based on the study of ionospheric and tropospheric anomalies, is also addressed. Full article
(This article belongs to the Special Issue Detecting Geospace Perturbations Caused by Earth)
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Open AccessArticle
Increasing Summit Degassing at the Stromboli Volcano and Relationships with Volcanic Activity (2016–2018)
Geosciences 2019, 9(4), 176; https://doi.org/10.3390/geosciences9040176
Received: 26 January 2019 / Revised: 3 April 2019 / Accepted: 15 April 2019 / Published: 17 April 2019
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Abstract
The last increased volcanic activity of the Stromboli volcano, from 2016 to 2018, was characterized by increases in the number and frequency of crater explosions and by episodes of lava overflow. The volcanic activity was monitored utilizing CO2 soil fluxes acquired from [...] Read more.
The last increased volcanic activity of the Stromboli volcano, from 2016 to 2018, was characterized by increases in the number and frequency of crater explosions and by episodes of lava overflow. The volcanic activity was monitored utilizing CO2 soil fluxes acquired from the Stromboli summit area (STR02 station). To better understand the behavior of the shallow plumbing system of the Stromboli volcano in the period of 2016–2018, we utilized a large data set spanning from 2000 to 2018. The data in this last period confirm a long growing trend of CO2 summit degassing, already observed in the years since 2005 (reaching 23,000 g·m−2·d−1). Moreover, within this increasing trend, episodes of sudden and sharp increases in the degassing rate, up to 24.2 g·m−2·d−2 were recorded, which are correlated with the observed paroxysmal activity (increased summit explosions and overflow). Full article
(This article belongs to the Special Issue Volcano Monitoring – Placing the Finger on the Pulse)
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Open AccessArticle
Post-Wildfire Landslide Hazard Assessment: The Case of The 2017 Montagna Del Morrone Fire (Central Apennines, Italy)
Geosciences 2019, 9(4), 175; https://doi.org/10.3390/geosciences9040175
Received: 19 February 2019 / Revised: 11 April 2019 / Accepted: 15 April 2019 / Published: 16 April 2019
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Abstract
This work focused on a post-wildfire landslide hazard assessment, applied to the 2017 Montagna del Morrone fire. This wildfire increased the possibility of landslides triggering, as confirmed by the occurrence of a debris flow, triggered by an intense, short duration rainfall event in [...] Read more.
This work focused on a post-wildfire landslide hazard assessment, applied to the 2017 Montagna del Morrone fire. This wildfire increased the possibility of landslides triggering, as confirmed by the occurrence of a debris flow, triggered by an intense, short duration rainfall event in August 2018. The study area was investigated through a detailed analysis incorporating morphometric analysis of the topography and hydrography and geomorphological field mapping, followed by the landslide hazard assessment. In detail, the analysis was performed following a heuristic or expert-based approach, integrated using GIS technology. This approach led to the identification of five instability factors. These factors were analyzed for the construction of thematic maps. Hence, each factor was evaluated by assigning appropriate expert-based ranks and weights and combined in a geomorphology-based matrix, that defines four landslide hazard classes (low, moderate, high, and very high). Moreover, the morphometric analysis allowed us to recognize basins prone to debris flows, which, in relevant literature, are those that show a Melton ratio of >0.6 and a watershed length of <2.7 km. Finally, all the collected data were mapped through a cartographic and weighted overlay process in order to realize a new zonation of landslide hazard for the study area, which can be used in civil protection warning systems for the occurrence of landslides in mountainous forested environments. Full article
(This article belongs to the Section Natural Hazards)
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Open AccessArticle
Geochemical Processes Controlling Ionic Composition of Water in the Catchments of Lakes Saana and Saanalampi in the Kilpisjärvi Area of North Scandinavia
Geosciences 2019, 9(4), 174; https://doi.org/10.3390/geosciences9040174
Received: 14 March 2019 / Revised: 9 April 2019 / Accepted: 12 April 2019 / Published: 16 April 2019
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Abstract
The study focuses on chemical composition of stream and subsurface water in the catchments of two small arctic alpine lakes in the Kilpisjärvi area (northwest Finland). Differences and changes in chemical components of both water types are followed in order to detect spatial [...] Read more.
The study focuses on chemical composition of stream and subsurface water in the catchments of two small arctic alpine lakes in the Kilpisjärvi area (northwest Finland). Differences and changes in chemical components of both water types are followed in order to detect spatial variability and impact of environmental factors. To achieve this, ion compositions of subsurface water and streams were measured at 12 sites in the catchments of Lakes Saana and Saanalampi during four years (2008–2010, and again in 2017). In the Lake Saanalampi catchment, the salinity of stream water (7.0 to 12.7 μS·cm−1) corresponded to that of snow. In the catchment of Lake Saana, however, the conductivity in stream water was much higher (40 to 220 μS·cm−1), connected mainly to the increase of SO42 and less with Mg2+ and Ca2+ contents, especially in the western part of the Saana catchment. These results demonstrate that arctic conditions do not preclude intense chemical weathering where conditions are favourable. Although chemical composition of the soil fluid does not match the geochemical signal from the local soil, rock composition, especially the presence of pyrite, is the main controller of chemical weathering rates of the rocks on the area. This supports earlier views that the character of precipitation mostly controls water chemistry of local lakes in the Kilpisjärvi area. Full article
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Open AccessArticle
Geological and Structural Control on Localized Ground Effects within the Heunghae Basin during the Pohang Earthquake (MW 5.4, 15th November 2017), South Korea
Geosciences 2019, 9(4), 173; https://doi.org/10.3390/geosciences9040173
Received: 29 January 2019 / Revised: 4 April 2019 / Accepted: 8 April 2019 / Published: 16 April 2019
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Abstract
On 15th November 2017, the Pohang earthquake (Mw 5.4) had strong ground shaking that caused severe liquefaction and lateral spreading across the Heunghae Basin, around Pohang city, South Korea. Such liquefaction is a rare phenomenon during small or moderate earthquakes (MW [...] Read more.
On 15th November 2017, the Pohang earthquake (Mw 5.4) had strong ground shaking that caused severe liquefaction and lateral spreading across the Heunghae Basin, around Pohang city, South Korea. Such liquefaction is a rare phenomenon during small or moderate earthquakes (MW < 5.5). There are only a few examples around the globe, but more so in the Korean Peninsula. In this paper, we present the results of a systematic survey of the secondary ground effects—i.e., soil liquefaction and ground cracks—developed during the earthquake. Most of the liquefaction sites are clustered near the epicenter and close to the Heunghae fault. Based on the geology, tectonic setting, distribution, and clustering of the sand boils along the southern part of the Heunghae Basin, we propose a geological model, suggesting that the Heunghae fault may have acted as a barrier to the propagation of seismic waves. Other factors like the mountain basin effect and/or amplification of seismic waves by a blind thrust fault could play an important role. Liquefaction phenomenon associated with the 2017 Pohang earthquake emphasizes that there is an urgent need of liquefaction potential mapping for the Pohang city and other areas with a similar geological setting. In areas underlain by extensive unconsolidated basin fill sediments—where the records of past earthquakes are exiguous or indistinct and there is poor implementation of building codes—future earthquakes of similar or larger magnitude as the Pohang earthquake are likely to occur again. Therefore, this represents a hazard that may cause significant societal and economic threats in the future. Full article
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Open AccessArticle
Archaeometric Characterisation of Decorated Pottery from the Archaeological Site of Villa dei Quintili (Rome, Italy): Preliminary Study
Geosciences 2019, 9(4), 172; https://doi.org/10.3390/geosciences9040172
Received: 18 February 2019 / Revised: 3 April 2019 / Accepted: 12 April 2019 / Published: 16 April 2019
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Abstract
This work focused on the study of decorated pottery dated back to the 16th century from the Roman archaeological site of Villa dei Quintili, a monumental complex located in the south-eastern part of Rome (Italy). A minero-petrographic and geochemical study was undertaken to [...] Read more.
This work focused on the study of decorated pottery dated back to the 16th century from the Roman archaeological site of Villa dei Quintili, a monumental complex located in the south-eastern part of Rome (Italy). A minero-petrographic and geochemical study was undertaken to analyse five archaeological samples in order to define textural features and raw materials used for their production, along with the chemical and physical composition of the superficial decorative glazed coatings. For this purpose, different analytical methods were used, such as polarising optical microscope (POM), X-ray diffraction (XRD), micro-Raman spectroscopy, X-Ray fluorescence (XRF), and electron microprobe analysis coupled with energy dispersive spectrometry (EMPA-EDS). The results of such a multidisciplinary approach allowed us to achieve important results crucial to recognise the shards as majolica of the Renaissance period, improving knowledge about manufacturing processes of these renowned painted ceramic artefacts. Full article
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Open AccessArticle
Data Acquisition Methodologies Utilizing Ground Penetrating Radar for Cassava (Manihot esculenta Crantz) Root Architecture
Geosciences 2019, 9(4), 171; https://doi.org/10.3390/geosciences9040171
Received: 5 March 2019 / Revised: 8 April 2019 / Accepted: 10 April 2019 / Published: 15 April 2019
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Abstract
Cassava (Manihot esculenta Crantz), a root crop utilized as food and industrial starch product, develops and maintains its marketable product sub-surface. Often, however, it is difficult to determine the potentially marketable goods available at any given time due to the sub-surface nature [...] Read more.
Cassava (Manihot esculenta Crantz), a root crop utilized as food and industrial starch product, develops and maintains its marketable product sub-surface. Often, however, it is difficult to determine the potentially marketable goods available at any given time due to the sub-surface nature of the product and the inability to non-destructively sample. This dilemma has provided an avenue for application of ground penetrating radar. Relatively available designs of this technology, however, are cumbersome and do not provide the efficiencies for field applications. The objective of this research was to determine the functionality of a two Gigahertz frequency IDS GeoRadar C-Thrue antenna for the detection and parameterization of root architecture to be utilized for estimating marketable product. Cassava roots were buried across three horizontal and two vertical orientations to simulate the multi-directional nature of cassava roots. The antenna has dual polarization which also allowed to testing efficacy of polarization for detecting the varying root orientations. This study found that the C-Thrue system, more specifically, the Vertical transmit and Vertical receive polarization, was the most effective at accurately estimating cassava root length and widths at varying angles that simulate root development in true fields. Full article
(This article belongs to the Special Issue Advances in Ground Penetrating Radar Research)
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Open AccessArticle
A Detailed Reconstruction of the Roman Landscape and the Submerged Archaeological Structure at “Castel dell’Ovo islet” (Naples, Southern Italy)
Geosciences 2019, 9(4), 170; https://doi.org/10.3390/geosciences9040170
Received: 12 March 2019 / Revised: 4 April 2019 / Accepted: 10 April 2019 / Published: 13 April 2019
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Abstract
In this paper, we present the results of a multidisciplinary study aimed to reconstruct the Roman coastal landscape between Pizzofalcone hill and Megaris islet—the area of the ancient Parthenope, the first settlement along the Naples coast. This coastal sector was surveyed by a [...] Read more.
In this paper, we present the results of a multidisciplinary study aimed to reconstruct the Roman coastal landscape between Pizzofalcone hill and Megaris islet—the area of the ancient Parthenope, the first settlement along the Naples coast. This coastal sector was surveyed by a team of specialized divers (archaeologists and geomorphologists) and by using an Unmanned Surface Vessel (USV) equipped with acoustic and optical sensors. The indirect surveys provided a high-resolution dataset of morpho-acoustic and optical measurements, useful to obtain the geological, geomorphological and archaeological interpretations necessary to formulate hypotheses on the functionality of the complex submerged archaeological structure detected in the study area. In particular, the integration between the surveyed data, the high-resolution seafloor mapping and the previous knowledge deriving from the 1980s underwater research carried out by Centro Studi Subacquei, led us to interpret the submerged remains as a vivarium related to a 1st century BC Roman villa. Finally, by measuring the submersion of several channels and a well-preserved crepido, a relative sea level during the period of use at −2.2 m ± 0.2 m mean sea level (MSL) was deduced, in agreement with the previous geoarchaeological studies realized in the near coastal sectors. Full article
(This article belongs to the Special Issue Geoarchaeology: A Review of Case Studies in the Mediterranean Sea)
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Open AccessArticle
Bayesian Variable Selection for Pareto Regression Models with Latent Multivariate Log Gamma Process with Applications to Earthquake Magnitudes
Geosciences 2019, 9(4), 169; https://doi.org/10.3390/geosciences9040169
Received: 10 January 2019 / Revised: 3 April 2019 / Accepted: 9 April 2019 / Published: 12 April 2019
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Abstract
Generalized linear models are routinely used in many environment statistics problems such as earthquake magnitudes prediction. Hu et al. proposed Pareto regression with spatial random effects for earthquake magnitudes. In this paper, we propose Bayesian spatial variable selection for Pareto regression based on [...] Read more.
Generalized linear models are routinely used in many environment statistics problems such as earthquake magnitudes prediction. Hu et al. proposed Pareto regression with spatial random effects for earthquake magnitudes. In this paper, we propose Bayesian spatial variable selection for Pareto regression based on Bradley et al. and Hu et al. to tackle variable selection issue in generalized linear regression models with spatial random effects. A Bayesian hierarchical latent multivariate log gamma model framework is applied to account for spatial random effects to capture spatial dependence. We use two Bayesian model assessment criteria for variable selection including Conditional Predictive Ordinate (CPO) and Deviance Information Criterion (DIC). Furthermore, we show that these two Bayesian criteria have analytic connections with conditional AIC under the linear mixed model setting. We examine empirical performance of the proposed method via a simulation study and further demonstrate the applicability of the proposed method in an analysis of the earthquake data obtained from the United States Geological Survey (USGS). Full article
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Open AccessArticle
Dynamics of the Zones of Strong Earthquake Epicenters in the Arctic–Asian Seismic Belt
Geosciences 2019, 9(4), 168; https://doi.org/10.3390/geosciences9040168
Received: 28 February 2019 / Revised: 27 March 2019 / Accepted: 9 April 2019 / Published: 12 April 2019
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Abstract
Our comprehensive study of the Russian Arctic region aims to clarify the features and types of seismotectonic deformation of the crust in the Arctic–Asian Seismic Belt, specifically in the zones of strong earthquakes in the Laptev Sea Segment, the Kharaulakh Segment, and the [...] Read more.
Our comprehensive study of the Russian Arctic region aims to clarify the features and types of seismotectonic deformation of the crust in the Arctic–Asian Seismic Belt, specifically in the zones of strong earthquakes in the Laptev Sea Segment, the Kharaulakh Segment, and the Chersky Seismotectonic Zone. We have analyzed modern tectonic structures and active fault systems, as well as tectonic stress fields reconstructed by tectonophysical analysis of the Late Cenozoic faults and folds. The investigated neotectonic structures are ranked with respect to the regional classification principles. Changes in the crustal stress–strain state in the lithospheric plate boundaries between the Eurasian, North American, and Okhotsk Sea Plates are analyzed, and regularities of such changes are discovered. A set of models has been constructed for the studied segments of plate boundaries with account of the dynamics of the regional geological structures. The models can give a framework for the assessment of potential seismic risks of seismogenerating structures in the Russian Arctic region. Full article
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Open AccessArticle
Time-Lapse 3D Electric Tomography for Short-time Monitoring of an Experimental Heat Storage System
Geosciences 2019, 9(4), 167; https://doi.org/10.3390/geosciences9040167
Received: 21 March 2019 / Revised: 5 April 2019 / Accepted: 9 April 2019 / Published: 11 April 2019
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Abstract
A borehole thermal energy storage living lab was built nearby Torino (Northern Italy). The aim of this living lab is to test the ability of the alluvial deposits of the north-western Po Plain to store the thermal energy collected by solar panels. Monitoring [...] Read more.
A borehole thermal energy storage living lab was built nearby Torino (Northern Italy). The aim of this living lab is to test the ability of the alluvial deposits of the north-western Po Plain to store the thermal energy collected by solar panels. Monitoring the temperature distribution induced in the underground and the effectiveness of the heat storage in this climatic context is not an easy task. For this purpose, different temperature evolution strategies are compared in this paper: Local temperature measurements, numerical simulations and geophysical surveys. These different approaches were compared during a single day of operation of the living lab. The results of this comparison allowed to underline the effectiveness of time-lapse 3D electric resistivity tomography as a non-invasive and cost-effective qualitative heat monitoring tool. This was obtained even in a test site with unfavorable thermo-hydrogeological conditions and high-level anthropic noise. Moreover, the present study demonstrated that, if properly calibrated with local temperature values, time-lapse 3D electric resistivity tomography also provides a quantitative estimation of the underground temperature. Full article
(This article belongs to the Special Issue Subsurface Thermography and the Use of Temperature in Geosciences)
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Open AccessArticle
Stress-Tolerance and Taxonomy of Culturable Bacterial Communities Isolated from a Central Mojave Desert Soil Sample
Geosciences 2019, 9(4), 166; https://doi.org/10.3390/geosciences9040166
Received: 28 February 2019 / Revised: 3 April 2019 / Accepted: 8 April 2019 / Published: 10 April 2019
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Abstract
The arid Mojave Desert is one of the most significant terrestrial analogue objects for astrobiological research due to its genesis, mineralogy, and climate. However, the knowledge of culturable bacterial communities found in this extreme ecotope’s soil is yet insufficient. Therefore, our research has [...] Read more.
The arid Mojave Desert is one of the most significant terrestrial analogue objects for astrobiological research due to its genesis, mineralogy, and climate. However, the knowledge of culturable bacterial communities found in this extreme ecotope’s soil is yet insufficient. Therefore, our research has been aimed to fulfil this lack of knowledge and improve the understanding of functioning of edaphic bacterial communities of the Central Mojave Desert soil. We characterized aerobic heterotrophic soil bacterial communities of the central region of the Mojave Desert. A high total number of prokaryotic cells and a high proportion of culturable forms in the soil studied were observed. Prevalence of Actinobacteria, Proteobacteria, and Firmicutes was discovered. The dominance of pigmented strains in culturable communities and high proportion of thermotolerant and pH-tolerant bacteria were detected. Resistance to a number of salts, including the ones found in Martian regolith, as well as antibiotic resistance, were also estimated. Full article
(This article belongs to the Special Issue Planetary Evolution and Search for Life on Habitable Planets)
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Open AccessArticle
Establishment of a Greek Food Database for Palaeodiet Reconstruction: Case Study of Human and Fauna Remains from Neolithic to Late Bronze Age from Greece
Geosciences 2019, 9(4), 165; https://doi.org/10.3390/geosciences9040165
Received: 10 February 2019 / Revised: 1 April 2019 / Accepted: 8 April 2019 / Published: 10 April 2019
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Abstract
We review the stable isotopic data of recovered Greek bones from the Early Neolithic to the Late Bronze period in order to examine dietary changes over time. As an isotopic baseline we use the published fauna data of the periods. The analysis revealed [...] Read more.
We review the stable isotopic data of recovered Greek bones from the Early Neolithic to the Late Bronze period in order to examine dietary changes over time. As an isotopic baseline we use the published fauna data of the periods. The analysis revealed a diet that included a significant proportion of foods based on C3 plants, and the bulk of the animal protein must have been provided by terrestrial mammals with a small but detectable proportion of marine protein for coastal and island populations. A more significant contribution of marine protein is observed for Bronze Age populations while the enrichment in both C and N isotopes is connected, for some areas, to the introduction of millet during the Bronze Age, and to freshwater consumption. An extensive database of Greek food sources is presented and compared to the fauna from the prehistoric periods (Early Neolithic to Late Bronze Age) of the literature. We propose that this database can be used in palaeodiet reconstruction studies. Full article
(This article belongs to the Special Issue Isotope Geochemistry)
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Open AccessArticle
Investigation of Trace and Critical Elements (Including Actinides) in Flotation Sulphide Concentrates of Kassandra Mines (Chalkidiki, Greece)
Geosciences 2019, 9(4), 164; https://doi.org/10.3390/geosciences9040164
Received: 10 January 2019 / Revised: 2 April 2019 / Accepted: 3 April 2019 / Published: 9 April 2019
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Abstract
Pyrite/arsenopyrite (Py-AsPy), galena (PbS), and sphalerite (ZnS) concentrates from the flotation plants of Olympias and Stratoni (Kassandra mines, Chalkidiki, N. Greece) were investigated for their major, trace, minor, and critical element contents, including actinides associated to natural radioactivity. It is revealed that in [...] Read more.
Pyrite/arsenopyrite (Py-AsPy), galena (PbS), and sphalerite (ZnS) concentrates from the flotation plants of Olympias and Stratoni (Kassandra mines, Chalkidiki, N. Greece) were investigated for their major, trace, minor, and critical element contents, including actinides associated to natural radioactivity. It is revealed that in addition to the Pb, Zn, Ag, and Au being exploited by Hellas Gold S.A., there are also significant concentrations of Sb and Ga (Sb: >0.2 wt.% in PbS concentrate; Ga:25 ppm in ZnS concentrate), but no considerable contents of Bi, Co, V, or REE. Concerning other elements, As was found in elevated concentrations (>1 wt.% in Py-(As)Py-AsPy Olympias concentrate and almost 1 wt.% in Stratoni PbS and ZnS concentrates) together with Cd (specifically in ZnS concentrate). However, actinides occurred in very low concentrations (U < 2 ppm and Th < 0.5 ppm in all examined concentrates), limiting the possibility of natural radioactivity in the Hellas Gold S.A. products. The concentrations of the natural radionuclides (238U, 232Th, and 40K) are much lower than those of commercial granitic rocks, and thus the associated radioactive dose is insignificant. Full article
(This article belongs to the Special Issue Magmatic-Hydrothermal Ore Deposits)
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Open AccessArticle
GIS-Based Rockfall Susceptibility Zoning in Greece
Geosciences 2019, 9(4), 163; https://doi.org/10.3390/geosciences9040163
Received: 19 February 2019 / Revised: 31 March 2019 / Accepted: 2 April 2019 / Published: 8 April 2019
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Abstract
The assessment of rockfall risks on human activities and infrastructure is of great importance. Rock falls pose a significant risk to (a) transportation infrastructure, (b) inhabited areas, and (c) Cultural Heritage sites. The paper presents a method to assess rockfall susceptibility at national [...] Read more.
The assessment of rockfall risks on human activities and infrastructure is of great importance. Rock falls pose a significant risk to (a) transportation infrastructure, (b) inhabited areas, and (c) Cultural Heritage sites. The paper presents a method to assess rockfall susceptibility at national scale in Greece, using a simple rating approach and Geographic Information Systems (GIS) techniques. An extensive inventory of rockfalls for the entire country was compiled for the period between 1935 and 2019. The rockfall events that were recorded are those which have mainly occurred as distinct rockfall episodes in natural slopes and have impacted human activities, such as roads, inhabited areas, and archaeological sites. Through a detailed analysis of the recorded data, it was possible to define the factors which determine the occurrence of rockfalls. Based on this analysis, the susceptibility zoning against rockfalls at the national scale was prepared, using a simple rating approach and GIS techniques. The rockfall susceptibility zoning takes into account the following parameters: (a) the slope gradient, (b) the lithology, (c) the annual rainfall intensity, (d) the earthquake intensity, and (e) the active fault presence. Emphasis was given on the study of the earthquake effect as a triggering mechanism of rockfalls. Finally, the temporal and spatial frequency of the recorded events and the impact of rockfalls on infrastructure assets and human activities in Greece were evaluated. Full article
(This article belongs to the Section Natural Hazards)
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Open AccessArticle
Spatial and Temporal Variations in the Incidence of Dust Storms in Saudi Arabia Revealed from In Situ Observations
Geosciences 2019, 9(4), 162; https://doi.org/10.3390/geosciences9040162
Received: 15 March 2019 / Revised: 2 April 2019 / Accepted: 3 April 2019 / Published: 8 April 2019
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Abstract
Monthly meteorological data from 27 observation stations provided by the Presidency of Meteorology and Environment (PME) of Saudi Arabia were used to analyze the spatial and temporal distribution of atmospheric dust in Saudi Arabia between 2000 and 2016. These data were used to [...] Read more.
Monthly meteorological data from 27 observation stations provided by the Presidency of Meteorology and Environment (PME) of Saudi Arabia were used to analyze the spatial and temporal distribution of atmospheric dust in Saudi Arabia between 2000 and 2016. These data were used to analyze the effects of environmental forcing on the occurrence of dust storms across Saudi Arabia by considering the relationships between dust storm frequency and temperature, precipitation, and wind variables. We reveal a clear seasonality in the reported incidence of dust storms, with the highest frequency of events during the spring. Our results show significant positive relationships (p < 0.005) between dust storm occurrence and wind speed, wind direction, and precipitation. However, we did not detect a significant relationship with temperature. Our results reveal important spatial patterns, as well as seasonal and inter-annual variations, in the occurrence of dust storms in Saudi Arabia. For instance, the eastern part of the study area experienced an increase in dust storm events over time, especially in the region near Al-Ahsa. Similarly, an increasing trend in dust storms was also observed in the west of the study area near Jeddah. However, the occurrence of dust storm events is decreasing over time in the north, in areas such as Hail and Qaisumah. Overall, the eastern part of Saudi Arabia experiences the highest number of dust storms per year (i.e., 10 to 60 events), followed by the northern region, with the south and the west having fewer dust storm events (i.e., five to 15 events per year). In addition, our results showed that the wind speeds during a dust storm are 15–20 m/s and above, while, on a non-dust day, the wind speeds are approximately 10–15 m/s or lower. Findings of this study provide insight into the relationship between environmental conditions and dust storm occurrence across Saudi Arabia, and a basis for future research into the drivers behind these observed spatio-temporal trends. Full article
(This article belongs to the Special Issue Observing Atmospheric Dynamics and Dust Activity)
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