Volcanic Necks Research Articles

Geoconservation History of a Basalt Quarry – The Case of Mt. Wilkołak, Land of Extinct Volcanoes Geopark, SW Poland

Mt. Wilkołak is one among many hills built of mid-Cenozoic basalts in SW Poland, within the Land of Extinct Volcanoes UNESCO Global Geopark. Appreciated as a recreational ground since the first half of the 19th century, it began to be quarried at the beginning of the 20th century. The quarry located on the western slope was soon abandoned, leaving impressive exposures of variously oriented basaltic columns due to thermal jointing and volcanic breccia. Briefly re-used after World War II, the quarry was definitely closed in 1956 and a small geological reserve was established in 1959. In the meantime, basalt exploitation developed at a much larger scale within the eastern slope, leading to the major conflict between conservation and industry, with frequent voices to delist the reserve and continue quarrying towards complete exhaustion of resources and removal of the entire hilltop. In addition, as a result of poor management of the reserve and uncontrolled vegetation growth its values significantly diminished. In the 21st century various actions initiated by the local community, supported by scientists, concurrent with incoming termination of quarrying, opened the debate about the future of Mt. Wilkołak and its quarries. Stone extraction ended in 2019, after a catastrophic collapse of one quarry wall, and rehabilitation works were executed in 2021–2023, aimed at the conversion of the locality into a place focused on geo-education and recreation. Opened in May 2023, it has various interpretation facilities and offers unprecedented insights into the internal structure of a volcanic plug. However, challenges related to site management, enhancement of educational content, and the future of the nature reserve remain.

Potential fields as a tool to characterize the inaccessible areas of the earth: The case of Pine Island–Ellsworth Mountains area, West Antarctica

We seek to characterize the geophysical properties of the West Antarctic Rift System. While it is recognized as one of the largest rift systems on the earth, the West Antarctic Rift System is poorly understood as it is covered by the thick West Antarctic Ice Sheet, making any geologic evaluation difficult. We used the potential-field data sets acquired by the British Antarctic Survey, which included aeromagnetic surveys, to conduct a multiscale analysis to identify the main structural lineaments, i.e., contacts, dikes, sills, volcanic necks and conduits, and spherical source distributions. Several interesting areas were defined in which contact-type sources were associated with faults bordering major rift systems (Pine Island, Byrd Subglacial Basin, and Bentley Subglacial Trench) or related to the tributaries in the Pine Island Rift. Moreover, we detected magmatic sources close to rifting zones based on their shape and orientation (Bentley Subglacial Basin edges), helping to define the depth of the sub-ice topography. Our results helped improve our knowledge of the structural regional geology of the West Antarctic Rift System. This work opens interesting scenarios about the extent and position of magmatic sources and how they contribute to the topography of this sector of the West Antarctic Rift System.

Mateo Tepe or Devils Tower: Native and Tourist Differences in Geosite Interpretations

Devils Tower is located in Wyoming, USA. It is composed of volcanic elements from the Tertiary Period of geologic time. Geologists are interested in this geosite because it is a unique, upstanding, steep-sided, high-relief exhumed Tertiary-age volcanic plug. As a Native American cultural geosite, however, it is often called Mateo Tepe, and it is a sacred place to over 20 Native American tribes. It was inscribed as America’s first national monument in 1906 by President Theodore Roosevelt, because of its special geology. It is visually dramatic due to its columns, which are understood by earth scientists as a wonder of geology but by Native people as the claw scratches of a spiritual bear. These vertical cracks are the focus of rock climbers and Native people, respectively as opportunities for adventure and self-fulfillment and spiritual paths to another dimension and the achievement of religious balance in the world. Mateo Tepe became a national monument due to it being a unique geologic feature. The geopark concept is used in this analysis to talk about this geologically based monument.

FORMATION OF TRACHYTES FROM WANGTIAN’E VOLCANIC NECK OF THE CHANGBAISHAN AREA (NORTHEAST CHINA) AS A RESULT OF THOLEIITIC MAGMA CRYSTAL FRACTIONATION

Tholeiitic basalts and trachytes of Wangtian’e bimodal association are studied. It is shown that trachytes were formed under the leading role of crystal fractionation of the initial tholeiitic magma. Based on the method of melt and fluid inclusion studies, it was determined that hedenbergite phenocrysts from Wangtian’e volcanic neck crystallized in the temperature range of 1080–1100°С, and plagioclase phenocrysts crystallized at temperatures of 1050–1060°С. After thermometric experiments with melt inclusions in plagioclase from trachytes, in some cases relics of carbonates and carbon dioxide were observed in the inclusions. Trachyte phenocrysts contain hydrous Fe-rich silicate globules and CO2 inclusions containing carbonate phases. Fe-rich silicate globules are often intergrown with titanomagnetite and covered with films of amorphous carbon. A model the appearance of hydrous Fe-rich globules and CO2 inclusions with carbonate relics is proposed. It results due to the silicate-silicate and silicate-carbonate liquid immiscibility processes, that are caused by the evolution of the initial basaltic melt. As the trachyte melt has been risen to the surface, the ferrocarbonate liquid decomposed into magnetite, carbon, and carbon dioxide.

Formation of Trachytes from Wangtian’e Volcanic Neck of the Changbaishan Area (Northeast China) as a Result of Tholeiitic Magma Crystal Fractionation

Tholeiitic basalts and trachytes of the bimodal association of Wangtian’e volcano are studied. It is shown that trachytes formed with the leading role of crystal fractionation of the parental tholeiitic magma. It has been identified from the melt inclusion study that hedenbergite and plagioclase phenocrysts of trachytes from Wangtian'e volcanic neck crystallized in the temperature range of 1080–1100 and 1050–1060°C, respectively. After heating experiments with melt inclusions in plagioclase of trachytes, in some cases relics of carbonates and CO2 were observed in the inclusions. The trachyte phenocrysts host water-bearing Fe-rich globules and CO2 inclusions with carbonate phases. The Fe-rich silicate globules are often intergrown with titanomagnetite and are covered by amorphous carbon films. A model is suggested explaining the formation of water-bearing Fe-rich globules and CO2 inclusions with carbonate relics as a result of silicate–silicate and silicate–carbonate liquid immiscibility, that was caused by the evolution of the parental basaltic melt. Upon the trachytic melt ascending to the surface, the ferrocarbonate liquid was decomposed on magnetite, carbon, and carbon dioxide.

Spatial and temporal control of the volcanic activities over the distribution of sediments in the Magadi basin, Kenya Rift

High-velocity layers in basins with significant sub-basalt coverage, such as the Magadi basin, can impede geophysical imaging of potential subsurface hydrocarbon deposits. Using magnetic and gravity methods, this study examines the influence of volcano-tectonic processes and the basement on the evolution of the Magadi basin. Regional-residual separation analyses identified key structures and signatures. Lineaments and depths of the causative sources were determined using Euler deconvolution. Butterworth low-pass filters on aeromagnetic data isolated depth-varying magnetic layer responses. The study demonstrates a westward displacement of volcanic flows in the Magadi basin, originating from nearly all volcanic plugs. Depocenters near the western boundary fault are more affected by westerly movements of the volcano-tectonic flows than depocenters near the eastern boundary fault. The Rift underwent internal compartmentalization, resulting in depocenters with unique and intermittent tectonic and sedimentary occurrences. Rift segmentation led to modifications in catchment areas, which caused sudden variations in sediment flux, ultimately leading to the isolation of the depocenters. This study identifies the initial compartmentalized depocenters of Nguruman, Koora, and Forty-six. The initial Nguruman depocenter is oriented SW-NE and spans approximately 2512 sq. km with a sediment thickness range of 2000–4000 m. The presence of horsts in the southern and northern parts precludes volcaniclastics from the depocenter. Active tectonics and inversion caused the initial Nguruman depocenter to split into two halves: the northern Musenke depocenter and the southern Pakase. Euler depth analysis indicates sedimentary formations are thicker in compartmentalized depocenters in Magadi's western and southern regions than near the eastern boundary fault. The sediment thickness range in the Koora basin is approximately 1000–3000 m, while Pakase on the western flank has a sediment thickness range of 2000–3800 m.

Vulcanian eruption processes inferred from volcanic glow analysis at Sakurajima volcano, Japan

Volcanic glow, which is often observed at active craters during nighttime, contains information on high-temperature zones deep in the crater that are hidden from view. We analyzed 90 eruption videos capturing volcanic glow before the onset of Vulcanian eruptions at the Showa crater of Sakurajima volcano (Japan), and found that they show clear temporal changes. The red (R)-value and the green-to-red ratio (GR ratio) are used to track glow intensity and temperature change, respectively. We found two types of temporal change in glow intensity: a short-term change approximately 1 s before the onset of explosions, and a long-term change 3 to 330 s before an explosion. Short-term changes were observed for 28 of 90 eruptions, and coincided with an increase in the GR ratio and with a modest precursory infrasound pressure increase. Since an increasing GR ratio means a temperature increase, we consider that the change was associated with the opening of tensile cracks on the crater floor before an explosion. However, the other 62 eruptions did not show short-term changes, suggesting that the opening of cracks is sporadic. Long-term changes were observed for 73 of 90 eruptions, the GR ratio did not exhibit a significant increase. We suggest that long-term changes are caused by gradual gas leakage, which precedes initiation of Vulcanian eruptions. We hypothesize that the long-term gas leakage causes gradual decompression of the conduit, which induces supersaturation of volatile-rich magma beneath the lava plug causing explosive expansion, thereby triggering an eruption.

The anomalous magmatism in the southern part of the Santos basin, and the non-continuous salt layer over Abimael Ridge

The magmatism in the Santos Basin is related to the following main events: (1) the pre-rift volcanic episode; (2) the syn-rift to late syn-rift episode; (3) the late Cretaceous episode; and (4) the Paleogene episode. This works focuses on the characterization of these events using seismic data and borehole interpretation in the southern part of the basin. The late Cretaceous magmatic episode is recorded in the shelf break region by 3D seismic data. A mini-basin with possible turbidite reservoirs was tested by an exploratory borehole that revealed several igneous features, including volcaniclastic sequences, sills, and volcanic plugs. Basinward, the evaporite layers are thicker and form salt walls above a detachment at the base of the salt reflector, which climbs up oceanward. The analysis of strong reflectors within the distal salt wall suggested three alternative interpretations, including igneous sills within the salt mass, anhydrite lenses, carbonate rafts, carbonate stringers, pre-salt microbialite buildups, and pre-salt volcanic rocks. The interpretation of the seismic and potential field data, constrained by the borehole results, indicates that the strong reflector corresponds to the top of the volcanic layers below the pre-salt microbialites.The anomalous magmatism and salt tectonics styles in the southern part of the Santos Basin are related to a swath of embryonic oceanic crust that was emplaced during the late Aptian to early Albian. The interpretation of a regional profile extending from the continental shelf to the oceanic crust provides evidence for the separation of the salt masses by a failed oceanic spreading center, which is corroborated by the gravity and magnetic models.

Tracing the human movements of three thousand years ago by volcanic grinding tools in the Final Bronze Age settlement of Monte Croce Guardia (Arcevia-Marche Region, central Italy)

Volcanic rocks were among the most sought-after materials to produce grinding tools in antiquity because lavas lithologies, either mafic or felsic, ensured good wear resistance and grinding capacity with respect to many other kinds of rocks. The interest in findings made of vesciculated lavas, referable to parts of querns, mortars, and/or pestles of the Final Bronze Age site of Monte Croce Guardia (Arcevia) lies in the fact that this settlement was built upon limestones belonging to the sedimentary sequence of the Marche-Umbria Apennines (central Italy) and far away from potential raw materials of volcanic rocks. A petrologic study of 23 grinding tool fragments clearly indicates a provenance from the volcanic provinces of central Italy: Latium and Tuscany Regions. Few leucite tephrites (5) and one leucite phonolite lavas have a clear magmatic affinity with the high-K series of the Roman Volcanic Province (Latium) whereas the most abundant volcanic lithotype (17 samples) is represented by shoshonites (K-series) whose thin section texture, modal mineralogy and major-trace elements contents closely match with the shoshonite lavas from the Radicofani volcanic centre in the Tuscan Magmatic Province. At Radicofani (a volcanic neck in the eastern sector of Tuscany) a Final Bronze Age site coeval to that of Arcevia is present and a potential pathway corridor from that site towards Arcevia (air-line distance of ca. 115 km) is dotted with many settlements of the same age. Through analytical algorithms based on the slope and the different human-dependent cost-functions which can be applied to determine non-isotropic accumulated cost surface, least-cost paths and least-cost corridors, the best route from Radicofani to Monte Croce Guardia, approximately 140 km long, was simulated, with a walking time of 25–30 h, possibly using pack animals and wheel chariots. Three thousand years ago the Apennine Mountains did not thus constitute a barrier for human movements. This study also shed light on some other possible patterns of interactions between Final Bronze Age communities of central Italy through the present-day regions of Tuscany, Umbria and Marche, aimed towards the best performance of strategic economic activities at that time such as that of the transformation of cereals, and accompanied to cultural and social reasons.

Contrasting thermal histories in the Dom Feliciano Belt triggered by magmatism related to the Paraná-Etendeka LIP and fracture zone proximity

The present-day southern Brazilian continental margin rests on top of the Dom Feliciano Belt (DFB) and adjacent cratons. This belt formed through the collision of the Rio de La Plata, Kalahari, Paranapanema, Congo and Luis Alves paleoplates in the Neoproterozoic. Several low-temperature thermochronology works were executed in the area, although none of them demonstrated how the basement temperature of the entire DFB evolved through time. To this end, this work aims to provide new Apatite Fission Track (AFT) and Apatite (UTh)/He (AHe) ages for samples collected in the Catarinense Shield, in the northern DFB, and to perform inverse modeling in those samples. Besides, the collection of the basement temperature of 128 locations across the entire belt and adjacent cratons provided thermal information to create inverse-distance weighted interpolation maps documenting the progression of the temperature from 360 to 30 Ma. New AFT ages range from 126.6 ± 24.1 to 60.3 ± 6.03 Ma, whereas AHe ages span from 153.0 ± 9.2 to 62.5 ± 3.7 Ma. Mean track lengths are short to medium, suggesting complete thermal annealing of apatite crystals. Apatite single-grain eU concentration range from 4.5 to 96 μg/g and display a sparse correlation with AHe ages. Interpolation maps evidence a contrasting temperature evolution of the northern DFB and bordering cratons relative to the southern segment and surrounding cratons. Near-surface exposure of the basement in the northern segment was possibly much earlier than in the south, followed by partial burial by the sedimentary successions of the Paraná Basin. The emplacement of volcanic rocks of the Paraná-Etendeka Large Igneous Province and associated dyke swarms and alkaline volcanic plugs related to the Florianópolis Fracture Zone raised and sustained higher basement temperatures until 30 Ma, resetting low-temperature thermochronometers in the northern DFB, which was minor to absent in the southern DFB.

The Hornsby Quarry Geosite, NSW, Australia—A Geoheritage Treasure

Quarrying for aggregate material at Hornsby in New South Wales (Australia) exposed a >100 m-deep cross-section of the volcanic neck of a Jurassic diatreme, which extruded through the Sydney Basin deposits. The cross-section reveals volcanic features at many scales. Globally, there are very few instances of such excellent 3D exposure. It is arguable that this exposure alone makes it a geosite of international value. However, evaluation of the Hornsby Diatreme using a geoheritage toolkit shows that it meets various geoheritage conservation criteria, being a reference site, and an historically and culturally important site, as well as hosting important archival material. It has significant features at various scales: at the macroscale, where dish beds are visible on all quarry walls, preserving the structure formed during volcanic accretion and later caldera collapse; at the mesoscale, where breccia and surge layers are visible, providing insight into how magma interacted with various host rock types; and at the microscale, where lapilli, chilled margins on host rock blocks, and carbon-rich xenoliths are visible in hand specimens. As such, the Hornsby Quarry hosts a world-class array of volcanic features and preserves an important period of volcanic and post-volcanic history within the Sydney Basin, fostering geoeducation and geotourism.

A reappraisal of explosive–effusive silicic eruption dynamics: syn-eruptive assembly of lava from the products of cryptic fragmentation

Silicic volcanic eruptions range in style from gently effusive to highly explosive, and may switch style unpredictably during a single eruption. Direct observations of subaerial rhyolitic eruptions (Chaiten 2008, Cordón Caulle 2011–2012, Chile) challenged long-standing paradigms of explosive and effusive eruptive styles and led to the formulation of new models of hybrid activity. However, the processes that govern such hybrid explosive–effusive activity remain poorly understood. Here, we bring together observations of the well-studied 2011–2012 Cordón Caulle eruption with new textural and petrologic data on erupted products, and video and still imagery of the eruption. We infer that all of the activity – explosive, effusive, and hybrid – was fed by explosive fragmentation at depth, and that effusive behaviour arose from sticking and sintering, in the shallow vent region, of the clastic products of deeper, cryptic fragmentation. We use a scaling approach to determine that there is sufficient time available, during emplacement, for diffusive pyroclast degassing and sintering to produce a degassed plug that occludes the shallow conduit, feeding clastogenic, apparently effusive, lava-like deposits. Based on evidence from Cordón Caulle, and from other similar eruptions, we further argue that hybrid explosive–effusive activity is driven by episodic gas-fracking of the occluding lava plug, fed by the underlying pressurized ash- and pyroclast-laden region. The presence of a pressurized pocket of ash-laden gas within the conduit provides a mechanism for generation of harmonic tremor, and for syn-eruptive laccolith intrusion, both of which were features of the Cordón Caulle eruption. We conclude that the cryptic fragmentation models is more consistent with available evidence than the prevailing model for effusion of silicic lava that assume coherent non-fragmental rise of magma from depth to the surface without wholesale explosive fragmentation.

The Discovery and Geochemical Characteristics of an Eocene Peridotite Xenolith-Bearing Mafic Volcanic Neck in Coastal Southeast China

The mantle beneath coastal SE China evolved from enriched to depleted between the Cretaceous and the Neogene, although the precise timing of this change remains unclear. Here, we focus on a newly discovered Eocene mafic volcanic neck that contains peridotite xenoliths in the Fuding area of Fujian Province, and present new whole-rock Ar–Ar data which indicate that flood basalts formed during the Eocene (ages of 38.5 ± 1.2 and 42.3 ± 2 Ma). The basalt, gabbro, and diabase in the Fuding area are geochemically similar to ocean island basalt (OIB) and have SrI values that range from 0.703794 to 0.703911 (average of 0.703865) and εNd(t) values from 3.05 to 4.56 (average of 3.90). These samples yield two-stage Nd model (TDM2) ages of 0.61–0.73 Ga (average of 0.67 Ga). These data indicate that all of these units formed from magmas derived from an OIB-type mantle source, with both the gabbro and diabase units recording minor amounts of crustal contamination. Its OIB type geochemical characteristics may be inherited from crustal materials with similar characteristics. Peridotite xenoliths within the Fuding basalts provide evidence of the nature of the Eocene mantle in this area, especially the post late-Mesozoic evolution of the mantle beneath coastal SE China. The mantle beneath coastal SE China evolved from enriched in the Cretaceous to depleted in the Neogene, with this change occurring during the Eocene.

Audiomagnetotelluric (AMT) studies across Aravali-Tural-Rajawadi geothermal zones, western Maharastra, India

Thermal springs of Aravali, Tural and Rajawadi are located in the Deccan volcanic province (DVP) in the western part of Maharashtra, India and are covered by Deccan basalts. These springs run parallel to the Western Ghats and geochemical studies denote that these hot water springs are of meteoritic origin that emerge from basement rock.To understand the geoelectric structure and possible source zone of hot water springs, a 26-station audiomagnetotelluric (AMT) survey was carried out along E W profiles across Aravali, Tural and Rajawadi geothermal springs with a station spacing of about 1–1.5 km. A 2D inversion was carried out jointly for transverse electric (TE) and transverse magnetic (TM) data after the distortion and decomposition analysis.These geothermal zones appear as high conductive zones at shallow depth and are associated with fault/fracture zones within the sedimentary basin. The basement depth increases from 1 km to 2.5 km moving from Aravali to Rajawadi geothermal zones. Volcanic plugs at a shallow depth beneath Tural and Rajawadi thermal springs act as a source rock for heat. Thus, hot water temperatures are higher for these two thermal springs relative to Aravali thermal spring, which is devoid of magma intrusion and related to circulation of meteoric water over basement.

Alteration Characteristics and Precious Metal Availability in Gunung Gembes & Surroundings, Jeruk Village, Pacitan Regency, East Java Province

The research area is located in the area of Mount Gembes, Jeruk Village in Pacitan (East Java). This study aims to determine the characteristic and temperature in the formation of alteration which refers to petrography with the help of samples taken in the study area. The petrographic observations carried out were thin section observations which were then analyzed for the mineral content contained in the sample rock. After knowing the minerals contained in the sample rock, it is then entered into the mineral formation temperature diagram (White & Hedenquist, 1995). The method used in this study includes primary data in the form of geological observations such as lithology, geological structure geomorphology, environmental geology and alteration observations and combined with secondary data. Alteration observations in this study were carried out descriptively (megascopic) and subjective (microscopic). The geomorphic unit that works is of volcanic origin, with high hilly sub-units of porphyry dacite intrusion (volcanic neck). Geological structures that develop in the study area are faults, namely the left horizontal fault of Jeruk 1, the left horizontal fault of Jeruk 2 and the interpretation of the oranges right horizontal fault. Geological resources or sources found in the research area are mineral potential resources that are economical, and negative sources are in the form of mass movement of debris flow type. The Zonation and the type of alteration that developed in the research area are the clay alteration zone and silicification. The clay zone is formed at a temperature >100⁰C-220⁰C with a pH of 3-5 and a silicification zone is formed at a temperature>100⁰C-300⁰C with a pH <2 which is directly controlled by the faults found in the study site.

End-to-end simulations of the MUon RAdiography of VESuvius experiment

The MUon RAdiography of VESuvius (MURAVES) project aims at the study of the summital cone of Mt. Vesuvius, an active volcano near Naples (Italy), by measuring its density profile through muon flux attenuation. Its data, combined with those from gravimetric and seismic measurement campaigns, will be used for better defining the volcanic plug at the bottom of the crater. We report on the development of an end-to-end simulation framework, in order to perform accurate investigations of the effects of the experimental constraints and to compare simulations, under various model hypotheses, with the actual observations. The detector simulation setup is developed using GEANT4 and a study of cosmic particle generators has been conducted to identify the most suitable one for our simulation framework. To mimic the real data, GEANT4 raw hits are converted to clusters through a simulated digitization: energy deposits are first summed per scintillator bar, and then converted to number of photoelectrons with a data-driven procedure. This is followed by the same clustering algorithm and same tracking code as in real data. We also report on the study of muon transport through rock using PUMAS and GEANT4. In this paper we elaborate on the rationale for our technical choices, including trade-off between speed and accuracy. The developments reported here are of general interest in muon radiography and can be applied in similar cases.

A Preliminary Geothermal Prospectivity Mapping Based on Integrated GIS, Remote-Sensing, and Geophysical Techniques around Northeastern Nigeria

Spatial mapping of potential geothermal areas is an effective tool for a preliminary investigation and the development of a clean and renewable energy source around the globe. Specific locations within the Earth’s crust display some manifestations of sub-surface geothermal occurrences, such as hot springs, a volcanic plug, mud volcanoes, and hydrothermal alterations, that need to be investigated further. The present area of investigations also reveals some of these manifestations. However, no attempt was made to examine the prospectivity of this terrain using the efficient GIS-based multicriteria evaluation (MCE) within the scope of the Analytic hierarchy process (AHP). The integration of remote sensing, Geographic information system (GIS), and other geophysical methods (Magnetic and gravity) was performed to map the promising geothermal areas. Multiple input data sets such as aero-magnetic, aero-gravity, aero-radiometric, digital elevation model (DEM), geological map, and Landsat-8 Operational Land Imager (OLI) data were selected, processed, and use to generate five thematic layers, which include heat flow, temperature gradients, integrated lineaments, residual gravity, and lithology maps. The five thematic layers were standardized and synthesized into a geothermal prospectivity map. The respective ranks and weight of the thematic layers and their classes were assigned based on expert opinion and knowledge of the local geology. This research aims to apply an efficient method to evaluate the factors influencing the geothermal energy prospects, identify and map prospective geothermal regions, and, finally, create a geothermal prospectivity model.

Inventory and Assessment of Geosites for Geotourism Development in the Eastern and Southeastern Lake Tana Region, Ethiopia

Geotourism is a niche form of sustainable tourism that focuses on the geological and geomorphological features of an area, and the associated culture and biodiversity. Geosites are important resources for geotourism development. The eastern and southeastern Lake Tana region in Ethiopia has several geosites with a potential for geotourism development. Despite the diversity of potential geosites and the strategic location of the area in the Northern Tourist Circuit of Ethiopia, only a few attractions such as Lake Tana and the Blue Nile Falls are currently being visited. The objective of this paper is twofold: to inventory geosites in the eastern and southeastern Lake Tana region and assess their potential for geotourism development; and to propose a geosite inventory and assessment methodology for geotourism purposes with adaptations from previous studies. Several studies were reviewed and finally nine of them used as the main references to prepare the criteria, indicators, and sub-indicators for this study. The indicators used for assessing the potential of geosites relate to scientific, educational, scenic, recreational, protection, functional, and ecological values. This research presents the first inventory of geosites in the Lake Tana basin. A first list of 120 geosites has been inventoried. Further screening and clustering resulted in 61 geosites, of which 17 are viewpoints. Among the major geosites are waterfalls, a lake with islands and island monasteries, a flood plain, caves and cave churches, lava tubes, a mountain (shield volcano), volcanic plugs, volcanic cones, rock-hewn churches, and viewpoints. Quantitative assessment of the geotouristic potential of these geosites revealed that clustered (complex area) geosites received higher scientific, scenic, and recreational value scores.

Stochastic sensitivity analysis of volcanic activity

In the present paper, we study the stochastically induced behavior of a nonlinear volcanic model containing three prognostic variables: the plug velocity u, the pressure p under the plug, and the conduit volume V. The nouvelle phenomena of noise‐induced transitions from the equilibrium to the cycle in the bistability parametric zone and noise‐induced excitement with the generation of spike oscillations in the monostability zone are found in the presence of N‐shaped friction force. To study these phenomena numerically, we used the computations of random solutions, the phase trajectories and time series, the statistics of interspike intervals, and the mean square variations. To study these phenomena analytically, we applied the stochastic sensitivity function technique and the confidence domains method. This approach is used to predict the noise‐induced transition from a “dormant volcano” state to the “active volcano” mode. From the physical point of view, the volcano is capable to become active under the influence of external noises in the friction force, which model various compositions and properties of volcanic rocks. What is more, the volcanic plug can pop out when its slipping becomes heavy, and the volcano can erupt.

Structural fabric over the seismically active Kachchh rift basin, India: insight from world gravity model 2012

The Kachchh rift basin (KRB), located in the western continental margin of India, is very important due to repeated large magnitude occurrence of intraplate earthquakes. The present study elucidates the subsurface structural features using wavelength filtering, total horizontal derivative (THD) and 2.5 dimensional (2.5D) density modelling of the gravity data. Power spectrum analysis of the gravity data gives the cut-off wavelength of 100 km that has been used for wavelength filtering for regional-residual separation. The residual gravity anomaly significantly enhances the shallow features (like Allah-Bund fault, Kachchh mainland uplift, Wagad uplift, and Pachham uplift) and gives an NW–SE subsurface structural trend. The predominant direction for major lineaments derived by the THD of gravity data shows the ENE–WSW as well as NE–SW and NW–SE directions. The 2.5D density model of the regional gravity anomaly reveals the presence of high-density magmatic underplating layer and intrusive mafic body in the lower crust that is in accordance with the previous studies. The regional slope of the Moho in the KRB is towards the SW direction. An intrusive mafic body in the lower crust and volcanic plugs in the upper crust act as stress concentrator which is responsible for seismicity in the KRB. Several new lineaments have been identified based on the present study, which may be accountable for seismicity over the different part of KRB.