Search Results (45)

Polymer co-extrusion experiments are described simulating the dynamics of two different magmas (e.g., silicic and mafic having different viscosities) flowing simultaneously in a vertical volcanic pipe or conduit which results in the effusion of composite lava domes on the surface. These experiments, involving geologically realistic conduit length-to-diameter aspect ratios of 130:1 or 380:1, demonstrate that co-extrusion of magmas having different viscosities can explain not only the observed normal zoning observed in planar dikes and the pipelike conduits that evolve from dikes but also the compositional layering of effused lava domes. The new results support earlier predictions, based on observations of induced core-annular flow (CAF), that dike and conduit zoning along with dome layering are found to depend on the viscosity contrast of the non-Newtonian (shear-thinning) magmas. Any magma properties creating viscosity differences, such as crystal content, bubble content, water content and temperature may also give rise to the CAF regime. Additionally, codependent flow behavior involving the silicic and mafic magmas may play a significant role in modifying the nature of volcanic eruptions. For example, lubrication of the flow by an annulus of a more mafic, lower-viscosity component allows a more viscous but more volatile-charged magma to be injected rapidly to greater vertical distances along a dike into a lower pressure regime that initiates exsolving of a gas phase, further assisting ascent to the surface. The rapid ascent of magmas exsolving volatiles in a dike or conduit is associated with explosive silicic eruptions. Full article

The crust and upper mantle structure of Mars is determined in the depth range of 0 to 100 km, by means of dispersion analysis and its inversion, which is performed for the surface waves present in the traces of the seismic event: S1094b. From these traces, Love and Rayleigh waves are measured in the period range of 4 to 40 s. This dispersion was calculated with a combination of digital filtering techniques, and later was inverted to obtain both models: isotropic (from 0 to 100 km depth) and anisotropic (from 0 to 15 km depth), which were calculated considering the hypothesis of the surface wave propagation in slightly anisotropic media. The seismic anisotropy determined from 0 to 5 km depth (7% of S-velocity variation and ξ ~ 1.1) could be associated with the presence of sediments or lava-flow layering, and wide damage zones surrounding the long-term fault networks. For greater depths, the observed anisotropy (17% of S-velocity variation and ξ ~ 1.4) could be due to the possible presence of volcanic materials and/or the layering of lava flows. Another cause for this anisotropy could be the presence of layered intrusions due to a single or multiple impacts, which could cause internal layering within the crust. Finally, the Moho depth is determined at 50 km as a gradual transition from crust to mantle S-velocities, through an intermediate value (3.90 km/s) determined from 50 to 60 km-depth. Full article

Surface unloading due to impact cratering results in lava filling the crater floor. Elevation differences in the crater floor, a common geological phenomenon on the Moon, represent direct evidence of cratering processes. However, few studies have been conducted on mare-filled craters on the Moon. Al-Biruni (81 km) is a farside impact crater with an inclined topographic profile on its floor. We quantitatively measure the morphology of Al-Biruni and model the basaltic lava emplacement to depict the cratering process. Differential subsidence due to melt cooling, wall collapse, impact conditions and structural failure were assessed as potential factors influencing the formation of the elevation differences on the floor. The results suggest that pre-impact topography is a plausible cause of the differences in floor elevation within Al-Biruni. Other factors may also play a role in this process, affecting lava flow by altering the topography of the crater floor after the impact. Thus, regardless of whether the lava inside the crater is impact-generated or comes from outside the crater, altering topography at different stages of the cratering process is an essential factor in creating the sloped terrain on the crater floor. Full article

Characteristic dynamics in lava flows, such as the formation processes of lava levees, toe-like tips, and overlapped structures, were reproduced successfully through numerical simulation using the smoothed particle hydrodynamics (SPH) method. Since these specific phenomena have a great influence on the flow direction of lava flows, it is indispensable to elucidate them for accurate predictions of areas where lava strikes. At the first step of this study, lava was expressed using a molten metal with known physical properties. The computational results showed that levees and toe-like tips formed at the fringe of the molten metal flowing down on a slope, which appeared for actual lava flows as well. The dynamics of an overlapped structure formation were also simulated successfully; therein, molten metal flowed down, solidified, and changed the surface shape of the slope, and the second molten metal flowed over the changed surface shape. It was concluded that the computational model developed in this study using the SPH method is applicable for simulating and clarifying lava flow phenomena. Full article

Numerous analytical radar-scattering laws have been published through the past decades to interpret planetary radar observations, such as Hagfors’ law, which has been commonly used for the Moon, and the cosine law, which is commonly used in the shape modeling of asteroids. Many of the laws have not been numerically validated in terms of their interpretation and limitations. This paper evaluates radar-scattering laws for self-affine fractal surfaces using a numerical approach. Traditionally, the autocorrelation function and, more recently, the Hurst exponent, which describes the self-affinity, have been used to quantify the height correlation. Here, hundreds of three-dimensional synthetic surfaces parameterized using a root-mean-square (rms) height and a Hurst exponent were generated, and their backscattering coefficient functions were computed to evaluate their consistency with selected analytical models. The numerical results were also compared to empirical models for roughness and radar-scattering measurements of Hawaii lava flows and found consistent. The Gaussian law performed best at predicting the rms slope regardless of the Hurst exponent. Consistent with the literature, it was found to be the most reliable radar-scattering law for the inverse modeling of the rms slopes and the Fresnel reflection coefficient from the quasi-specular backscattering peak, when homogeneous statistical properties and a ray-optics approach can be assumed. The contribution of multiple scattering in the backscattered power increases as a function of rms slope up to about 20% of the backscattered power at normal incidence when the rms slope angle is 46°. Full article

As an important part of the lava flow reservoir, vesicles affect reservoir performance to some extent. To explore the distribution, origins and importance of vesicles in different facies belts of basic lava flows. In this study, we selected representative field outcrops and samples from different facies belts of the Laoheishan and Huoshaoshan lava flows in the Wudalianchi volcanics, Heilongjiang Province, identified and examined vesicles, measured their porosity and permeability, and analyzed their surface porosity. Three facies belts of vesicle shape, size, quantity, arrangement, origin, and connectivity between vesicles and fractures were identified. The results showed that the vesicles in the crater–near-crater belt were ellipsoidal and spherical, with many vesicles. The vesicles in the proximal belt were dominated by many ellipsoids with a uniform distribution. The vesicles in the distal belt were dominated by spherical and ellipsoidal vesicles, with a few tubular vesicles and a small number of vesicles. The findings suggest that the crater-near-crater belt and proximal belt have the best reservoir performance, whereas the distal belt has the worst. Full article

Mapping volcanic flow deposits can be achieved by considering backscattering characteristics as a metric of surface roughness. In this study, we developed an approach to extract a measure of surface roughness from dual-band airborne Synthetic Aperture Radar (ASAR) backscattering data to characterize and map various volcanic flow deposits—namely, debris avalanches, lahars, lava flows, and pyroclastic density currents. We employed ASAR and Indian Space Research Organization (ISRO) airborne SAR datasets, from a joint project (ASAR-ISRO), acquired in December 2019 at 2 m spatial resolution, to assess the role and importance of incorporating dual-band data, i.e., L-band and S-band, into surface roughness models. Additionally, we derived and analyzed surface roughness from a digital surface model (DSM) generated from unoccupied aircraft systems (UAS) acquisitions using Structure from Motion (SfM) photogrammetry techniques. These UAS-derived surface roughness outputs served as meter-scale calibration products to validate the radar roughness data over targeted areas. Herein, we applied our method to a region in the United States over the Mount St. Helens volcano in the Cascade Range of Washington state. Our results showed that dual-band systems can be utilized to characterize different types of volcanic deposits and range of terrain roughness. Importantly, we found that a combination of radar wavelengths (i.e., 9 and 24 cm), in tandem with high-spatial-resolution backscatter measurements, yields improved surface roughness maps, compared to single-band, satellite-based approaches at coarser resolution. The L-band (24 cm) can effectively differentiate small, medium, and large-scale structures, namely, blocks/boulders from fine-grained lahar deposits and hummocks from debris avalanche deposits. Additionally, variation in the roughness estimates of lahar and debris avalanche deposits can be identified and quantified individually. In contrast, the S-band (9 cm) can distinguish different soil moisture conditions across variable terrain; for example, identify wet active channels. In principle, this dual-band approach can also be employed with time series of various other SAR data of higher coherence (such as satellite SAR), using different wavelengths and polarizations, encompassing a wider range of surface roughness, and ultimately enabling additional applications at other volcanoes worldwide and even beyond volcanology. Full article

Nitrate is globally the most widespread and widely studied groundwater contaminant. However, few studies have been conducted in sub-Saharan Africa, where the leaching potential is enhanced during the rainy monsoon phase. The few monitoring studies found concentrations over drinking water standards of 10 mg N-NO₃⁻ L⁻¹ in the groundwater, the primary water supply in rural communities. Studies on nitrate movement are limited to the volcanic Ethiopian highlands. Therefore, this study aimed to evaluate the transport and fate of nitrate in groundwater and identify processes that control the concentrations. Water table height, nitrate, chloride, ammonium, reduced iron, and three other groundwater constituents were determined monthly in the groundwater in over 30 wells in two contrasting volcanic watersheds over two years in the Ethiopian highlands. The first watershed was Dangishta, with lava intrusion dikes that blocked the subsurface flow in the valley bottom. The water table remained within 3 m of the surface. The second watershed without volcanic barriers was Robit Bata. The water table dropped rapidly within three months of the end of the rain phase and disappeared except near faults. The average nitrate concentration in both watersheds was between 4 and 5 mg N-NO₃⁻ L⁻¹. Hydrogeology influenced the transport and fate of nitrogen. In Dangishta, water was blocked by volcanic lava intrusion dikes, and residence time in the aquifer was larger than in Robit Bata. Consequently, nitrate remained high (in several wells, 10 mg N-NO₃⁻ L⁻¹) and decreased slowly due to denitrification. In Robit Bata, the water residence time was lower, and peak concentrations were only observed in the month after fertilizer application; otherwise, it was near an average of 4 mg N-NO₃⁻ L⁻¹. Nitrate concentrations were predicted using a multiple linear regression model. Hydrology explained the nitrate concentrations in Robit Bata. In Dangishta, biogeochemistry was also significant. Full article

Harrat Khaybar is an active monogenetic volcanic field in western Saudi Arabia that hosts spectacular monogenetic volcanoes and a Holocene volcanic cone with extensive lava fields. The volcanic region is a subject of intensive land use development, especially along tourism ventures, where the volcanic features are the key elements to utilize for increasing visitation rates to the region. The youngest eruption is suspected to be Holocene and occurred fewer than 5000 years ago based on the cross-cutting relationship between the youngest lava flows and archaeological sites. Lava flows are typical, from pāhoehoe to ‘a‘ā types with great diversity of transitional textural forms. Here, we recorded typical transitional lava flow surface textures from the youngest flows identified by digital-elevation-model-based terrain analysis, satellite imagery, and direct field observations. We performed lava flow simulations using the Q-LavHA plug-in within the QGIS environment. Lava flow simulations yielded satisfactory results if we applied eruptions along fissures, long simulation distances, and ~5 m lava flow thickness. In these simulations, the upper flow regimes were reconstructed well, but long individual lava flows were not possible to simulate, suggesting that morphological steps likely promoted lava ponding, inflation, and sudden deflation by releasing melts further along shallow syneruptive valley networks. Full article

The Echus-Kasei region on Mars has been exposed to different episodic volcanic, fluvial, and glacial events in Amazonian time. The goal of the present work is to demonstrate the usefulness of radar instruments to find preserved late Amazonian subsurface structures that may have been encapsulated underneath recent lava flows on Mars. We have analysed 27 radar observations of the SHAllow RADar (SHARAD) instrument on board the Mars Reconnaissance Orbiter (MRO), over the region of Echus Chasma. We discovered the presence of subsurface reflectors in five consecutive SHARAD radargrams at a depth from 35 to 79 m beneath the structure of a lava fan that formed about 59 ± 4 Ma ago. Some vents are preserved above the surface of this lava flow, which stands at a height of 80 m above the surrounding surface. A few kilometres to the north, we find other subsurface reflectors at a depth of about 30 m and a long pit chain formed by the collapse of a lava tube. These kinds of subsurface late Amazonian structures are of interest for astrobiology because they date from the last period when the planet still experienced intense volcanic activity over regions that were previously extensively covered by water. Full article

Between December 2020 and February 2022, the South East Crater of Etna has been the source of numerous eruptions, mostly characterized by the emission of lava fountains, pyroclastic material and short-lasting lava flows. Here we estimate the volume and distribution of the lava deposits by elaborating multi-source satellite imagery. SEVIRI data have been elaborated using CL-HOTSAT to estimate the lava volume emitted during each event and calculate the cumulative volume; Pléiades and WorldView-1 data have been used to derive Digital Surface Models, whose differences provide thickness distributions and hence volumes of the volcanic deposits. We find a good agreement, with the total average lava volume obtained by SEVIRI reaching 73.2 × 10⁶ m³ and the one from optical data amounting to 67.7 × 10⁶ m³. This proves the robustness of both techniques and the accuracy of the volume estimates, which provide important information on the lava flooding history and evolution of the volcano. Full article

El Mirador de los Túneles is a tube-shaped volcanic cave with a sinuous structure in the Galápagos Islands formed due to cooled near-surface lava flows. Since this natural formation is considered a tourist site, a large number of people frequent it daily; however, its safety conditions have not yet been defined by a comprehensive geotechnical study. In this research, a stability analysis was carried out by combining both empirical methodologies based on geomechanical classifications using Barton’s Q Index and the recently created Cave Geomechanical Index (CGI), and numerical modeling through the finite element method. In addition, three-dimensional modelling was performed using the remote photogrammetric technique Structure from Motion (SfM) to create the numerical calculation sections and dimensions of the different critical parts of the cave. The results of the analysis showed that there is evidence of instability and subsidence along the tunnel. Furthermore, the geotechnical parameters obtained from the different methods complemented each other, resulting in more realistic engineering representation of the subsurface environment. Finally, a graph showing the two empirical methodologies Barton’s Q Index and CGI, with the addition of the Factors of Safety (FoS) obtained from the modeling is presented. Full article

Magma-filled dikes may feed erupting fissures that lead to alignments of craters developing at the surface, yet the details of activity and migrating eruptions at the crater row are difficult to monitor and are hardly understood. The 2021 Tajogaite eruption at the Cumbre Vieja, La Palma (Spain), lasted 85 days and developed a pronounced alignment of craters that may be related to changes within the volcano edifice. Here, we use COSMO-SkyMed satellite radar data and ground-based time-lapse photographs, offering a high-resolution dataset to explore the locations and characteristics of evolving craters. Our results show that the craters evolve both gradually and suddenly and can be divided into three main phases. Phase 1, lasting the first 6 weeks of the eruption, was characterized by a NW–SE linear evolution of up to seven craters emerging on the growing cone. Following two partial collapses of the cone to the northwest and a seismicity increase at depth, Phase 2 started and caused a propagation of the main activity toward the southeastern side, together with the presence of up to 11 craters along this main NW–SE trend. Associated with strong deep and shallow earthquakes, Phase 3 was initiated and continued for the final 2 weeks of the eruption, expressed by the development of up to 18 craters, which became dominant and clustered in the southeastern sector in early December 2021. In Phase 3, a second and oblique alignment and surface fracture was identified. Our findings that crater and eruption changes coincide together with an increase in seismic activity at depth point to a deep driver leading to crater and morphology changes at the surface. These also suggest that crater distributions might allow for improved monitoring of changes occurring at depth, and vice versa, such that strong seismicity changes at depth may herald the migration and new formation of craters, which have major implications for the assessment of tephra and lava flow hazards on volcanoes. Full article

The last volcanic eruption in Western Samoa, which occurred between 1905 and 1911, produced a complex scoria and lava spatter cone and an extensive lava field that destroyed Sale’aula village, near the Pacific coast. This eruption, referred to as the Matavanu eruption, also produced pahoehoe-type lava flows with superbly preserved surface textures, tumuli, and some littoral explosion craters in its distal lava field. The unique nature of the location meant that it was selected as one of the first of the 100 IUGS Geological Heritage Sites, in October 2022. The region has been under an investigation that aims to document the geoheritage elements of the location, estimate its geodiversity, and explore the potential to develop a geopark together with local communities. All this work intends to provide a firm knowledge base to identify effective geoconservation strategies. While the youngest eruptive products after over 100 years of revegetation are restricted to a coastal zone, previous research has demonstrated that other young volcanic eruptions also took place in northern Savai’i in 1760 and 1902. In this study, we provide further data based on a systematic evaluation of SENTINEL satellite imagery, in combination with an ALOS-PALSAR and SRTM 30-m resolution digital terrain model-based calculation of morphometric elements, to demonstrate that the young volcanic landscape in northern Savai’i has great volcanic geodiversity and the entire region should be considered for specific geoconservation strategies. The young volcanic landforms of scoria cones in the high-altitude regions of the island, along with extensive and commonly tube-fed lava flows which have invaded the northern region of Savai’i, pose a volcanic hazard to the region. Hence, volcanic geoheritage can be the core element to enforce strong community volcanic hazard resilience. The newly proposed Samoa Geopark Project is the perfect avenue to achieve this. Full article

Volcanic eruptions pose a great threat to humans. In this context, volcanic hazard and risk assessment constitute crucial issues with respect to mitigating the effects of volcanic activity and ensuring the health and safety of inhabitants. Lava flows directly affect communities living near active volcanoes. Nowadays, remote sensing advances make it possible to effectively monitor eruptive activity, providing immediate and accurate information concerning lava evolution. The current research focuses on the mapping of the surface deformation and the analysis of lava flow evolution occurred on the island of La Palma, during the recent (2021) eruptive phase of the volcano. Sentinel-1 data covering the island were collected throughout the entire eruptive period, i.e., September 2021 until January 2022. The processing was based on amplitude-based and phase-based detection methods, i.e., Synthetic Aperture Radar interferometry (InSAR) and offset tracking. In particular, ground deformation occurred on the island, while Line-Of-Sight (LOS) displacements were derived from Sentinel-1 interferograms. Moreover, the evolution of lava flow velocity was estimated using Sentinel-1 imagery along with offset tracking technique. The maximum lava flow velocity was calculated to be 2 m/day. It was proved that both approaches can provide rapid and useful information in emergencies, especially in inaccessible areas. Although offset tracking seems a quite promising technique for the mapping of lava flows, it still requires improvement. Full article