Volcanic Cones Research Articles

Actinomadura monticuli sp. nov., isolated from Darangshi Oreum (a volcanic cone), and the reclassification of Actinomadura glauciflava Lu et al. 2003 as a later heterotypic synonym of Actinomadura luteofluorescens (Shinobu 1962) Preobrazhenskaya et al. 1975 (Approved Lists 1980).

Two mycelium-forming actinobacterial strains, designated as DLS-47 and DLS-62T, were isolated from volcanic ash collected from the surface of a rock on the peak of Darangshi Oreum (a volcanic cone) in Jeju, Republic of Korea, and their taxonomic positions were investigated by a polyphasic approach. Both of the isolates showed growth at 20-42 °C, pH 6.0-9.0 and 0-1% (w/v) NaCl. Furthermore, DLS-47 was found to grow at 45 °C, while strain DLS-62T grew at pH 10.0 and 3% (w/v) NaCl. The 16S rRNA gene-based phylogeny showed that both of the isolates belonged to the genus Actinomadura; strain DLS-47 was most closely related to Actinomadura chokoriensis DSM 45346T (100% sequence identity), while strain DLS-62T formed a tight cluster with Actinomadura bangladeshensis DSM 45347T (99.5% sequence similarity). Morphological and chemotaxonomic characteristics supported the affiliation of the two isolates to the genus Actinomadura. Phylogenomic analysis based on 92 core gene sequences showed that both of the isolates were most closely related to A. chokoriensis DSM 45346T. Strain DLS-47 shared 100% of orthologous average nucleotide identity and digital DNA-DNA hybridization values with A. chokoriensis DSM 45346T, while strain DLS-62T showed orthologous average nucleotide identity ≤89.8% and digital DNA-DNA hybridization values ≤39.4% with strain DLS-47 and members of the genus Actinomadura. The results of phenotypic assays and comparison of overall genomic relatedness indices support the conclusion that strain DLS-47 (= KACC 23347=DSM 116423) is a strain of A. chokoriensis, while strain DLS-62T (= KACC 23345T = DSM 116424T) represents a new species of the genus Actinomadura, for which the name Actinomadura monticuli sp. nov. is proposed. Also, Actinomadura glauciflava Lu et al. 2003 is reclassified as a later heterotypic synonym of Actinomadura luteofluorescens (Shinobu 1962) Preobrazhenskaya et al. 1975 (Approved Lists 1980) based on analysis of overall genomic relatedness indices and phenotypic similarity.

Geodiversity Assessment of Widodaren Spring: A Treasure Trove Site for Bromo Tengger Volcano’s Future Geopark

Abstract The Bromo Tengger Volcano in Indonesia, a prominent geotourism spot, features the notable Widodaren Spring within its caldera, originating from the inactive Widodaren Vulcanic Cone. This study evaluated the geodiversity of Widodaren Spring through field and laboratory analyses and identified geodiversity elements by assessing their potential educational utility (PEU), potential touristic utility (PTU), and degradation risk (DR). Widodaren Spring is unique, showcasing rocks, hydrogeology, and landscape elements. This location is composed of pyroclastic fall deposits and pyroclastic surges, which characterize the products of volcanic activity on this volcano and provide a Sea of Sand Caldera landscape. Field and laboratory data indicate that this spring is genetically topographic-stratigraphic and hydrochemically calcium-chloride-type. The high levels of sulfate-chloride in the groundwater samples suggest the influence of volcanic gases from the nearby Bromo Volcanic Cone. Rainwater infiltration at the upper cone (2400-2560 meters) flows through lapilli layers serving as aquifers, with tuff and lapilli tuff layers below being impermeable to semi-permeable. Geodiversity assessments revealed a high educational utility potential (PEU) of 310 points, medium tourist utility potential (PTU) of 260 points, and low degradation risk (DR) of 135 points. The high PEU score was attributed to the site’s unique geological elements, making it valuable for education and science. The medium PTU score reflects its location in a national park, limiting accessibility but protecting it from human-caused damage. Potential natural damage may arise from weathering and volcanic eruptions on Mount Bromo. In conclusion, Widodaren Spring possesses significant geodiversity value with great potential for education and tourism, alongside a minimal risk of degradation. This site is a treasure trove for the future Bromo-Tengger Volcano geopark.

Shallow Magmatic System of Arxan Volcano Revealed by Ambient Noise Tomography with Dense Array

The Arxan Volcanic Field (AVF) is an active volcanic region in Northeast Asia, and its last eruption occurred approximately 2000 years ago. Its eruption mechanism remains unknown. To investigate the shallow magma system beneath the volcanic cones in the AVF, we deployed a dense seismic array consisting of 227 portable seismographs and conducted high-resolution ambient noise tomography (ANT). The results of checkerboard test (CRT) and restoring resolution test (RRT) demonstrate that our imaging results are reliable. These results reveale significant slow-velocity anomalies at depths of 5~9 km below the Tianchi caldera and GD1213 volcano in Arxan, with the highest anomaly reaching up to approximately 15%. These anomalies suggest partial melting in a shallow magma chamber, indicating ongoing volcanic activity in the AVF. The velocity of the magma chamber corresponding to a melt fraction of approximately 7.4~12.9%. Therefore, the presence of the magma chamber poses potential hazards to the Arxan region, including volcanic eruptions and their associated risks.

Pumice cone eruptions at Aluto volcano, Ethiopia

Pumice cones are volcanic landforms that exist worldwide, but whose eruption has never been observed. Interpretations of these eruptions vary significantly in style, intensity, and magnitude, pertinent for volcanic hazard assessment. Aluto volcano (Ethiopia) provides an unprecedented insight into the hazardous nature of these enigmatic eruptions. We investigate nine such pumice cones, and find that they are the product of moderate-intensity explosive eruptions that develop a sustained but unsteady eruption column, deposit lapilli- to block-sized tephra close to the vent forming pumice cones, can deposit distal tephra from an umbrella cloud, produce pyroclastic density currents by repeated partial column-collapse, and end with the emplacement of silicic lava. Like basaltic pyroclastic cones, pumice cones can also undergo collapse by lava flow emplacement. Alongside recent evaluation of distal tephras, we suggest that these eruptions, at least at Aluto, vary in intensity and magnitude from violent-Strombolian to sub-Plinian, and each follow a remarkably similar sequence of eruptive processes.

Preliminary results of the interior features inferred from radargrams, Ulanhada Volcano, Inner Mongolia, China

Abstract The Ulanhada Volcano Group is located in Inner Mongolia, China. It is an important Quaternary volcanic geological relic with different types of volcanic cones, craters, lava platforms, and other structures. Ground penetrating radar (GPR) can play an important role in volcanic exploration. We used pulse EKKO radar combined with 100MHz and 250MHz antennas to detect the No.1 Redhill volcanic. The results indicate that there are significant differences in reflection characteristics in radargrams of different frequencies, which can be used to analyze the material composition, eruption period, and stratigraphic coverage relationship of volcanic eruptions. At the same time, an accurate analysis of the region will also be used as an evaluation basis for the field scientific verification experiments of China’s Asteroid Core Scan Radar (ACSR) and Lunar Penetrating Radar (LPR).

Magnetotelluric evidence for the deep causes of different eruptive styles of Changbaishan Tianchi and Longgang volcanoes

Longgang Volcano (LGV) and Changbaishan Tianchi Volcano (CTV) share a common magmatic source at mantle depths. However, the two volcanoes have produced completely different types of eruptions. By performing 3D inversion of an MT dataset that completely covers the LGV and CTV, we have obtained high-resolution electrical resistivity images. The results reveal that the two volcanoes have distinct magmatic plumbing systems, and this is likely the reason for their different eruptive styles. Results from 3D modeling do not show a magma chamber in the shallow crust beneath LGV, interpreted as the rapid rise of the magma from the mantle is responsible for producing a series of densely distributed volcanic cones in the LGV field. In contrast, there is a magma chamber in the upper crust beneath the CTV, where the fractional crystallization and mixing of magma has occurred. This magma chamber has facilitated multiple centralized eruptions, and thereby has led to the formation of the large CTV volcanic cone. These results indicate that differences in their crustal structures may have controlled the different eruptive activities of the LGV and CTV in CVS, Northeast China.

Miocene Petit-Spot Basanitic Volcanoes on Cretaceous Alba Guyot (Magellan Seamount Trail, Pacific Ocean)

New data obtained from core samples of two boreholes and dredged samples from the Alba Guyot in the Magellan Seamount Trail (MST), Western Pacific, including the 40Ar/39Ar age determinations of basanite, and the mineralogy of basanite, tuff, tuffite, mantle-derived inclusions in basanite and tuff (lherzolite xenolith and Ol, Cpx, and Opx xenocrysts), and calcareous nannofossil biostratigraphy, have implications for the guyot′s development and history. Volcanic units in the upper part of the Alba Guyot main edifice and its Oma Vlinder satellite, at sea depths between 3600 and 2200 m, were deposited during the Cretaceous 112 to 86 Ma interval. In the following ~60 myr, the Alba Guyot became partly submerged and denuded with the formation of a flat summit platform while the respective fragment of the Pacific Plate was moving to the Northern Hemisphere. Volcanic activity in the northeastern part of the guyot summit platform was rejuvenated in the Miocene (24–15 Ma) and produced onshore basanitic volcanoes and layers of tuff in subaerial and tuffite in shallow-water near-shore conditions. In the Middle-Late Miocene (10–6 Ma), after the guyot had submerged, carbonates containing calcareous nannofossils were deposited on the porous surfaces of tuff and tuffite. Precipitation of the Fe-Mn crust (Unit III) recommenced during the Pliocene–Pleistocene (<1.8 Ma) when the guyot summit reached favorable sea depths. The location of the MST guyots in the northwestern segment of the Pacific Plate near the Mariana Trench, along with the Miocene age and alkali-basaltic signatures of basanite, provide first evidence for petit-spot volcanism on the Alba Guyot. This inference agrees with the geochemistry of Cenozoic petit-spot basaltic rocks from the Pacific and Miocene basanite on the Alba Guyot. Petit-spot volcanics presumably originated from alkali-basaltic melts produced by decompression partial melting of carbonatized peridotite in the metasomatized oceanic lithosphere at the Lithosphere–Asthenosphere Boundary level. The numerous volcanic cones with elevations of up to 750 m high and 5.1 km in basal diameter, discovered on the Alba summit platform, provide the first evidence of voluminous Miocene petit-spot basanitic volcanism upon the Cretaceous guyots and seamounts of the Pacific.

Substantiating of oil and gas prospects of Mesozoic sediments based on the geochemical model of mud volcanoes in the Shamakhi-Gobustan structural element of the South Caspian megadepression

There are up to 120 mud volcanoes in the Shamakhi-Gobustan region. During the process of mud volcano eruptions, a large amount of solid, liquid, and gaseous products are thrown to the Earth’s surface, which are widely used for the identification of oil and gas deposits and are considered the main indicator of the productivity of the basin. According to laboratory results from the analysis of solid, liquid, and gas products of mud volcanoes, it is possible to obtain detailed information about the oil-gas content of deep-lying sediments. Therefore, the study of the geochemical composition of the mud volcanoes in the Shamakhi-Gobustan trough plays a major role in the discovery of new oil-gas and gas-condensate deposits. To clarify the changes in the chemical and isotopic composition of gases from mud volcanoes in the Shamakhi-Gobustan trough and to evaluate the oil-bearing and gas-bearing potential of Mesozoic sediments, the characteristics of changes in the isotopic composition of methane gas, heavy hydrocarbons, carbon dioxide, ni- trogen, as well as CH4 and CO2, were studied. The amount of methane in the gas emissions released from mud volcanoes in the Azerbaijan region is more than 90%. The amount of CH4 in the mud volcanoes of the Shamakhi-Gobustan trough ranges from 78.5% to 97.56%. The minimum amount of methane is found in North Gobustan (Gizmeydan 86.8%, Malikchobanli 78.5%), while relatively high amounts are mainly noted in Central (Kushchu 97.55%) and South Gobustan (including Dashgil 97.57%, Goturdag 96.55%, Bahar 96.78%). Mud vol- canoes are less developed in the North Gobustan region and are small in size. In the Central zone, both the size and the number of volcanic cones increase significantly compared to North Gobustan. The largest and most active volcanoes have developed in the southern zone of the trough. Huge mud volcanoes such as Dashmerdan, Solakhay, Ayrantoken, Goturdag, Kirdag, and other volcanoes have developed along the Alat range. The mud volcanoes of North and Central Gobustan are mainly confined to Cretaceous and Paleogene sediments, and due to the low occurrence of plastic clay rocks in these sediment sections, mud volcanoes are rare and weakly active. On the contrary, to the south of these zones, that is, in South Gobustan, they are located in Pliocene sediments, and due to the presence of very thick plastic rocks in their section, mud volcanoes are widespread, and they are active volcanoes that are morphologically sharply reflected. It should be noted that in areas where plastic clay rocks with significant thickness and rheologically active properties are developed, large cones of mud volcanoes that erupt frequently are observed. The calculated gas production of mud volcanoes increases from the northern zone towards South Gobustan. Thus, while the calculated gas production of the Nabur volcano located in the Northern zone is 1500 m3/day, the calculated gas production of the Dashgil mud volcano located in South-Eastern Gobustan is 40,000 m3/day. In the central and south- ern zones of the Shamakhi-Gobustan trough, the presence of ancient rock fragments from the Oligocene-Miocene (Maykop) age rocks forming their roots in the solid waste of mud volcanoes (Cretaceous, Paleocene, Eocene), a large percentage of methane gas (97.57%), transverse elevations, and the presence of an intersection zone of longitudinal faults suggests that there is a tectonic rupture zone rich in natural gas below the base of the volcano. This is proven once again by the occurrence of gas flows in Anart (110,000 m3/day), Utalgi (50,000 m3/day), and the Touragay field (20,000 m3/day). The presence of oil films in the eruption products of mud volcanoes indicates the accumulation of oil alongside gas.

Characterization of microbial structure and function in the rhizosphere of Boehmeria nivea L.: A comparative study of volcanic cone and crater

Characterization of microbial structure and function in the rhizosphere of Boehmeria nivea L.: A comparative study of volcanic cone and crater

Submarine morphology of Pantelleria volcano: The interplay between volcanic and erosive-depositional processes modulated by sea-level fluctuations.

High-resolution multibeam data integrated with seismic reflection profiles are used to identify and characterize the main primary volcanic and erosive-depositional features along the submarine part (about the 80%) of the active Pantelleria volcano located in the Sicily Channel. Volcanic features include lava flows, cones and elongated ridges. Lava flows are mainly recognized over the insular shelf, while volcanic cones and ridges are mostly concentrated along the steep submarine flanks, especially along the wider SE and NW ones. A strong volcano-tectonic interaction is envisaged for their formation, as indicated by their preferential elongation or alignment along the (main) SE-NW and (secondary) SW-NE directions that have controlled the evolution of the whole volcanic edifice. Erosive-depositional features mainly include small-scale landslide scars and narrow gullies affecting the edge of the insular shelf and overlying submarine depositional terraces. Gullies sometimes merge downslope in larger channels, whose formation is primarily controlled by the distribution of volcanic features and/or shelf sectors characterized by different age or lithologies. Based on the marked morphological differences between the different flanks of the Pantelleria volcano, we infer an overall migration of the volcanic activity from SE to NW over time. This migration is apparently in contrast with the presence of a much wider but shallower NW insular shelf with respect to the SE one. This anomaly can be explained through a two-stage model, with the formation, in the NW sector, of a polygenic shelf rejuvenated by volcanic progradation during the last eustatic hemicycle. The different depths of the insular shelf edge around the island also provide insights on vertical deformations that affected the Pantelleria volcano during the Late-Quaternary.

Seaway restriction, sea level drop and erosion in the Alboran Basin from a paleotopographic reconstruction for the Messinian Salinity Crisis

The Messinian Salinity Crisis (MSC) resulted from changes in the Atlantic-Mediterranean connectivity in the Alboran Basin, a region with a complex and debated geodynamic configuration. Since the MSC, this basin's topography and its record of the Messinian Erosional Surface have been subject to vertical motions due to sediment accumulation, tectonic deformation, isostasy, and latent effects of thermal cooling after extension and magmatic arc formation. The objective of this work is to restore these contributions to post-Messinian subsidence in order to quantify the original depth of formation of the MSC features. We do this by performing a pseudo-3D planform flexural isostatic reconstruction of the Messinian Erosion Surface mapped from an extensive set of seismic reflection data. We focus on identifying the most likely position of the gateway between Atlantic and Mediterranean, the effect of a drawdown on gateway topography and connectivity, and the depth of proposed erosional features related to the Messinian lowstand. The results indicate that the depth of the Alboran Basin by the end of the Messinian was about 500 m shallower than nowadays, but over 500 m deep on average, reaching depths of >1000 m in most subbasins, even when accounting for the possible ∼300 m isostatic rebound caused by water unloading in a largely desiccated Alboran Sea during the MSC. Although these results are compatible with volcanic cones locally emerging above sea level at the East Alboran Volcanic Arc during the Messinian, several lows remaining in the reconstruction suggest that that region is unlikely to have been the sill between Atlantic and Mediterranean at that time, unless the basin saw unconstrained dynamic topography contributions of over −500 m. Full desiccation of the Alboran Basin implies an uplift of up to 100 m at the Strait of Gibraltar, and uplift rates too high to be counteracted by erosion, suggesting that full disconnection and the main corresponding evaporative drawdown took place only once. The terraces and canyons in the West Alboran are restored to depths between 250 and 550 m (shallowest terrace) and 750–1500 m (deepest terrace), and cannot be clearly linked to a single, stable water level during the MSC, pointing to climate-controlled variations in the water level during the isolation phase.

Characteristics of pyroclastic deposits and evolution of Maar Bethok Lamongan Volcano Tiris Probolinggo East Java Indonesia

The Lamongan Volcano Complex has a very different character from the Bromo and Argopuro Volcano groups. Lamongan Volcano has 37 volcanic cones and 27 maars (ranu). This volcano is quarter-old and occupies part of East Java Province. Maar Bethok is composed of lava and intercalation between pyroclastic deposits from phreatomagmatic and magmatic falls that still need to be firmly consolidated. These pyroclastic deposits characterize a strombolian eruption with more lava dome or crater wall material ejected. The rocks that make up the Bethok maar include olivine-pyroxene basalt lava and pyroclastic fall deposits with fragments of olivine basalt and basalt composition. The evolution of the Bethok maar eruption started from magma with an alkaline composition and ended with a more acidic composition. The magmatism of Bethok maar has an island arc calc-alkaline affinity.

Magnetic response contrast of Oligo-Miocene basaltic magmatism and structural control during its ascent at the northern tip of the Red Sea Rift

Oligo-Miocene volcanic activity has occurred along the northern Egyptian margin of the Red Sea Rift system, leading to the creation of small-volume monogenetic volcanoes. This research delves into the morphology and setting of these rift-related volcanics by combining aeromagnetic data, remote sensing, and field verification. Basaltic exposures in the study area were mapped using False Color Composite (FCC) and band ratios in Landsat 8 OLI data. In a map view, these mappable volcanic rocks appear as discrete semi-circular basaltic bodies and as discontinuous dikes. The basaltic bodies are aligned along ENE and NW-oriented zones, with most dikes orientated NW-SE. Multiple isolated high magnetic zones with NE and NW orientations were identified. Most basaltic outcrops coincide with high magnetic zones except for Gabal Abu Treifiya along the Cairo-Suez Road. The integration and combination of three layers of surface and subsurface structure patterns reveal an array of variance. The dominant trend of surface and deeper structural lineaments is NW-SE and NE-SW respectively. In contrast, shallow structural lineaments have NW-SE, NE-SW, E-W, and N–S trends. Long linear grabens result from the pairing of NW-SE normal faults. The basaltic occurrences such as Qattamiya and Abu Treifiya are located at the intersection of the NW-SE and E-W normal faults along the NW-SE linear grabens. The field investigation at both locations reveals a polyphase magmatic feeding system manifesting in the surface today as coherent and volcaniclastic rock units. This suggests a diverse range of eruptive styles through a complex feeder system that involves more than one volcanic cone. Though the two areas have good basaltic exposures, yet they have different magnetic responses. The severe alteration of Abu Treifiya's volcanic rocks into nonmagnetic minerals assemblage of zeolite, smectite, calcite, and hydrolysis of basaltic glass diminishes the expected high magnetic anomaly. This study contributes to our knowledge of Rift-related volcanism and the factors influencing the distribution of these volcanic materials.

Upper holocene tephro-chronostratigraphy of Irazú Volcano, Costa Rica

Irazú is one of the largest and most active volcanoes in Costa Rica. We present the tephro-chronostratigraphy of the last 2.6 ka of the Irazú volcano based on detailed field work and C14 radiometric dating, as well as a revision of the geological and historical records. In the stratigraphic record we identified at least 30 tephra units. Eight of them corresponding to the historical period (i.e., after 1700 A.D.), separated by repose periods of different durations. The distribution of the deposits, the volcanic morphologies (craters and pyroclastic cones) and the radiometric ages indicate that most of this recent eruptive activity has occurred from the summit of Irazú along an E–W fissure (~ 4 km long). Toward the west of the summit, near the Sapper hill may be the source of the oldest eruptions at 200 A.D., while the La Laguna cone, located to the east of the summit, could have formed around 1540 A.D., and Main Crater to the west could have formed around sixteenth–seventeenth century. Since then, the historical eruptions (i.e., 1723–1724, 1917–1921, 1924, 1928, 1930, 1933, 1939–1940 and 1963–1965) have been sourced from this crater, but not all of them are registered in the stratigraphy. The eruption frequency of Irazú during this period ranges from 23 to 100 years, with a major event about every 80 years. Irazu’s eruptions have been mainly phreatomagmatic and Strombolian, including some phreatic explosions. We present a detailed tephro-chronostratigraphy that will help to building temporal analysis for hazard assessment and risk management plans to face future eruptions at Irazú.

First evidence of Pinaceae and Fagaceae in the fossil wood record of the České středohoří Mts. (Czech Republic): A comprehensive study of fossiliferous sites in pyroclastic rocks surrounding the late Oligocene Milá stratovolcano

A comprehensive anatomical and mineralogical study of fossil wood fragments from fields in the vicinity of Bečov and Břvany villages (NW Bohemia, Czech Republic) indicates that Taxodioxylon gypsaceum (Cupressaceae s.l.) predominates, but also identifies another coniferous wood: Pinuxylon parryoides (Pinaceae) and three angiosperms Quercoxylon böckhianum, Castanoxylon bavaricum and Lithocarpoxylon sp. (all Fagaceae). This paper therefore presents the first occurrence of Pinaceae and Fagaceae fossil wood in the volcanic rocks of the České Středohoří Mts. as well as its youngest palaeobotanical record in general, late Oligocene in age (26.56 ± 0.38 Ma). The samples were buried by alkaline pyroclastic deposits and were mineralized by carbonates. Two distinct depositional processes burying the fossil woods were identified. Closer to the vent, the woods occur in a near-vent pyroclastic fall deposits of the former pyroclastic cone, whereas more distant sites consist of pyroclastic flow deposits. Carbonate mineralization mostly consists of dolomite, but subordinate amounts of magnesite (likely the first time this is documented in fossil wood) as well as calcite and siderite are present. Only one sample collected in the same area, bearing clear signs of riverbed transport (Lithocarpoxylon sp.), was perfectly silicified, but its origin remains unclear.

Overview of Fault Zones Based on Remote Sensing Data as Contribution to the Safety of Infrastructure and Land Use in Southern Egypt

Part of a requisite for natural hazard awareness and damage prevention in Egypt is the detailed monitoring of surface fault zones. The inventory of active faults and their risk assessment is an essential contribution to the safety of settlements, land use and infrastructure (railroads, highways, pipelines) and to damage prevention. Thus, this study aims to contribute to the detection, inventory, and documentation of fault zones. Surface faulting hazard assessment considers any surface consequences caused by surface near faults such as abrupt horizontal and vertical displacements and rotations, or mass movements after stronger earthquakes. Long-term, aseismic, slow-creeping movements along fault zones have to be considered as well. Southern Egypt offers unique and optimal conditions for the research of fault zones and their different structural expressions and conditions because of the dry desert climate conditions and relatively low human influence on the landscape in extended areas, especially for the investigation of different types of faults, their interactions with each other and the outcropping rocks, and fault-related deformation structures. Volcanic activity has been influenced in the geologic past often by larger fault zones as dike intrusions, volcanic cones and plugs or craters occur concentrated along these zones of weakness facilitating the uprise of magma. Larger fault zones are crossing reservoir areas. Surface water intrusions into deep-seated faults have played a role in triggering earthquake swarms in the reservoir areas during the last decades. Mapping of active faults is not only an important but also a cost-intense task when carried out in the field or when using geodetic and geophysical data. In the scope of this study, fault detection was carried out based on different open-source satellite data (Landsat 8 and 9, Sentinel 2 optical data, Sentinel 1 and ALOSPASAR radar data, and Google Earth and Bing Map high-resolution satellite images) from the southern part of Egypt. Faults were digitized using ArcGIS and QGIS software. An inventory of fault-related structural features (depressions, ridges, rotation structures, etc.) and rift zones was elaborated based on remote sensing data. An overview of different types of faults and their related structures as well as their interactions with their host rock conditions could be achieved. By merging the inventory results with infrastructural and land use data, critical areas with potential damage risk were pointed out.

Complex facies architecture of unusual pyroclastic density current deposits at the Rincón de la Vieja Volcano, Costa Rica

Pyroclastic Density Currents (PDCs) constitute a complex, multiphase, and multiscale volcanic process generated in a wide spectrum of eruptive scenarios and being among the most deadly and destructive volcanic hazards. Over the north flank of the Rincón de la Vieja Volcano, Costa Rica, previous works identified PDC deposits related to the plinian Río Blanco eruption, which is the largest Holocene explosive event recorded at this volcano. However, so far, there have been no in-depth studies aimed at understanding the eruptive style, and dynamics of the parental PDCs. This work presents, for the first time, a detailed facies analysis and architecture reconstruction (plus a geochemical characterization and novel C14 age determinations) of these outstanding deposits. The presence of cauliflower bombs, juvenile mega-blocks, scorias, and pumices, coupled with the scarcity of accidental and/or accessory lithics, is interpreted here as evidence of an unusual eruptive style. We propose that the Río Blanco eruption was a single complex eruption consisting of two successive phases, each involving the drainage of distinct magma batches. The PDCs were related to the sudden spill out of a lava-pool (Arenal-type PDC), during the collapse of an ultraproximal pyroclastic cone that was built in an initial plinian phase. The collapse of this ultraproximal cone produced a leading-edge pumice-rich PDC, which increased its mobility through fragmentation-induced fluidization. This leading edge PDC was followed by successive high concentrated, mafic, modified granular flow pulses derived from the lava-pool spill out. These modified granular flows were highly channelized in proximal zones, but when they reached the main break in slope, the basal underflow froze en masse while its upper, more diluted part started to decouple and move in a more unconfined manner. After the decoupling, the material feeding towards the basal zone of the surviving current produced a new underflow by rapid suspension sedimentation (“surge-derived pyroclastic flows”). Finally, our results indicate that the generation of Arenal-type PDCs is an underestimated scenario that should be considered in future short-term hazard and risk assessments at the Rincón de la Vieja Volcano, as well as in many other stratovolcanoes worldwide.

"NOVOSIBIRSK" MUD VOLCANO AND EVIDENCE OF ITS ACTIVATIONS (LAKE BAIKAL)

An integrated study of mud volcanoes in the World Ocean is important for making assessment of potential geological-ecological disasters caused by rapid large-volume gas discharge into the water column and mud volcano eruptions at the bottom. The study of mud-volcanic activity in the past and determination of its periodicity are pioneering for the Baikal. The mud volcanoes and other hydrate-bearing structures are largely concentrated in the Middle Baikal basin along the tectonic faults. The most representative example of these phenomena is the "Gydratny" fault, four of six structures along which are mud volcanoes. An integrated geological-geophysical study (seismoacoustic and hydroacoustic sounding and geological sampling) of the "Novosibirsk" mud volcano, the largest and well-pronounced feature of the lake bottom relief, confirmed its structural identity with classical submarine mud volcanoes. The "Novosibirsk" mud volcano possesses all major elements of other single hydrate-bearing mud volcanoes of the lake which include volcanic cone in the bottom relief, vertical acoustically not transparent feeding channel, mud-volcanic breccia, gas saturation, and gas hydrates. This makes it one of the reference hydrate-bearing mud volcanic-type structures of Lake Baikal.The analysis of the bottom hydroacoustic profiling yielded evidence of the Late Pleistocene mud-volcanic eruptions shaped as two layers-flows at sub-bottom depths of 15 and 26 m (30 and 50 kyr ago, respectively). The presence of mud-volcanic breccia beneath the thin Holocene diatomic silt deposits testifies to the Holocene mud volcano activation due to the warm fluid rising from the depths to the volcano roots along the active segment of the tectonic fault in accordance with the model of the "Baikal-type" mud volcanism. Using the "Novosibirsk" mud volcano and the "Gydratny" fault as an example, it can be shown that the past tectonic activity of the Baikal basin may be determined based on the knowledge of the structure and evolution of the mud volcanoes of the lake.

Postrift buried volcanoes and igneous plumbing systems along a continental ribbon: Insights from the Xisha massif, northwestern margin of the South China Sea

Despite the prevalence of postrift volcanoes and underlying igneous plumbing systems in rifted basins at proximal and hyperextended crustal configurations, well-preserved volcanoes and related intrusions are rare within minimally stretched continental blocks (i.e., continental ribbon). It is now possible to investigate the size, age, and geographical distribution of the buried volcanoes from multibeam, single-, and multichannel seismic data recently collected beneath the South China Sea Xisha massif, which we argue is a continental ribbon. These data made it evident that the Middle Miocene volcanoes frequently generated massive volcanic fields that erupted along the rift fault zones in contrast to the Early Miocene volcanoes, which typically built clusters of small-volume volcanic cones in the rift half-graben. Details include the presence of numerous volcanoes above and to the side of the dome-shaped main edifice that constitutes the middle Miocene volcanic field. Intrusive sills beneath volcanoes are isolated and have a dispersed distribution pattern at different levels, whereas dikes beneath volcanoes are numerous and have vertical zones of disruption that connect to underlying faults or extend through the sediments to the crust. The relationship between the volcanoes and intrusions suggests that shallow igneous plumbing systems within the Xisha massif are most likely dike domains. The Xisha massif has favorable conditions, including a relatively thin sedimentary sequence over a slightly extended continental crust (20–28 km) that might provide sufficient magma pressure for an igneous plumbing system that is primarily fed by dikes. In addition, rifted faults in the upper crust and possibly subvertical foliations in the basement rock mass are thought to be viable routes for magma transport vertically. In conclusion, we emphasize the importance of crustal structure on the continental ribbon in controlling igneous plumbing styles and the distribution of postrift volcanic systems along magma-poor continental margins, including crustal thickness, preexisting faults, heterogeneous basement, and sediments.

Tectono-magmatic coupling at the bends of mid-ocean ridges: Constraints from volcanic cone and fault distributions along the Northwest Indian Ridge

Tectono-magmatic coupling at the bends of mid-ocean ridges: Constraints from volcanic cone and fault distributions along the Northwest Indian Ridge