Lava Flow Surfaces Research Articles

Complex lava tube networks developed within the 1792–93 lava flow field on Mount Etna (Italy): insights for hazard assessment

Lava tubes are powerful heat insulators, allowing lava to practically keep the initial temperature and travel longer distances than when freely flowing on the ground surface. It is thus extremely important to recognize how, when and where these structures form within a lava flow field for hazard assessment purposes, in order to plan possible interventions should a lava flow approach inhabited areas. Often being formed within thick and complex lava flow fields, lava tubes are difficult to detect, study and explore. In this study, we analyse the 1792–93 Etna lava flow field emplaced on a steep slope (>4°) which comprises several lava tubes located at different distances from the eruptive fissure, at different levels within the lava flow field, and showing various inner morphologies, with peculiar inner features related to their maturity and eruptive history. Our aim is to verify whether it is possible to connect the underground features with features observed on the lava flow surface in order to reconstruct the extension of the tube network and unravel the genetic processes. Our results show that, in the studied lava flow field, a clear correspondence is possible between shallow tubes emplaced late during the lava flow field growth and surface textures. In addition, vertical and horizontal tube capture is very widespread, and might be the primary process for lava tube persistence and long life. Our results might be applicable to other lava tubes on Earth and other rocky planets.

Dyke positioning according to sedimentary basins markers by processing airborne magnetic data at basalt covered areas

SUMMARY Airborne magnetics have found few applications in investigating basalt-trapped areas because anomaly interferences from deep and shallow sources prevent clear identification of subjacent dyke systems. The structural positioning of dykes is of major importance in basin studies due to their role as a heat source for maturing organic matter and plumbing capacity to feed intrusive bodies and surface lava flows. Aeromagnetic data in such a scenario can outline faults and the basin framework but faces difficulties in identifying the distribution of dykes seated at different depth levels. We present a procedure that sequentially combines conventional processing techniques to identify and retrieve the magnetic anomaly content with 2-D properties, as expected from tabular dykes with contrasting magnetic properties with respect to the background medium. The mean direction of 2-D anomalies is quantitatively evaluated by tracking the directions in which the horizontal component of the transformed anomaly mostly vanishes. The observed field is then cosine-direction filtered to retain the anomaly content along this mean direction. Once isolated, the filtered 2-D content of the anomaly is interpreted with multiple thin-sheet models to determine the dyke distribution and their respective depths to the top. The inferred depths are interpreted concerning basin stratigraphic markers to recognize dykes possibly serving as a heat source for geothermal or petroleum and gas maturation, acting as compartments to aquifer systems, or determining the location of former conduits once feeding the lava flow volcanism. The developed procedure is applied to the Ponta Grossa Dyke Swarm, along its northwestern continuation beneath the basalt-capped sedimentary sequences of the Palaeozoic Paraná Basin. The distribution of the dykes recognizes a sequence confined to the bottom Palaeozoic formations with petroleum and gas potential, a sequence intercepting the upper layers forming the Guarani aquifer system (GAS) and dykes at different depth levels within the basalt Serra Geral traps, indicative of at least two feeding events supplying the Mesozoic surface lava flows.

Glass, crystallinity, and VNIR reflectance from vent to margin at Jordan Craters, OR USA

We present an in-situ analysis of the reflectance of Visible Near Infrared (VNIR) and the petrologic texture of the surface of a relatively young lava flow at Jordan Craters, OR. Jordan Craters is a small young basaltic lava field in Oregon, USA which terminates in a lake, providing a wide variety of petrographic textures related to cooling rates and prolonged seasonal exposure to water, post-emplacement. Field VNIR measurements of 191 in-situ spots were used to calculate the overall reflectance between the bands 500–1000 nm (R500–1000) which serves as a proxy for glass abundance. Analyses were conducted on the surfaces of lava, spatter, and scoria from the vent, mid-portion, and margin of the flow. We assigned the 15 collected hand samples to five cooling environments based on their location and modal mineralogy. Crystal content was measured microscopically and compared with the spectra classification for 15 hand samples. Slower cooling environments had more crystals (30–60%) of plagioclase, olivine, Fe-oxides, and devitrified glass (15–30%) whereas faster cooling environments have higher proportions of vitreous glass (∼70%). In order from slowest cooling to fastest cooling the groups were lava interior, oxidized vent, flow margin, glassy vent, and mid-flow surface. Mid-flow indicates surfaces where inflation or breakouts of the top flows occurred at least five meters from the margin. Additionally, locations that were exposed to prolonged heat or environmental water had higher proportions of devitrification and Fe-oxide crystals. The values of R500–1000 mirrored the cooling histories of the hand samples with interior analyses having the highest values and vent samples having the lowest, though there was much scatter in the vent category due to lumping of oxidized and glassy together in the in-situ dataset. Our findings indicate that VNIR may be used to identify variations in petrologic texture across basaltic lava flows due to eruptive and emplacement conditions such as vent vs mid-flow surface or quickly cooled vs slowly cooled with careful sampling and sufficient number of analyses. This has implications for understanding the cooling dynamics of lava flow surfaces as well as furthering the study of lava flows as paleoenvironmental indicators.

Cheakamus basalt lavas, British Columbia: a Pleistocene record of rapid, continuous eruption within a mountainous drainage system

The Cheakamus basalts are a voluminous (1.65 km3) set of Late Pleistocene, valley-filling lavas erupted from a vent situated near present-day Conflict Lake, in the alpine Callaghan Valley near Whistler, British Columbia. Geochemical and petrographic properties suggest these olivine–plagioclase porphyritic basalt lavas derive from a single batch of magma affected by minor sorting of phenocrysts and xenocrystic plagioclase. Thirty-four sites sampled for paleomagnetic directions record a mean pole direction of 345.2°/73.0° (α95 = 1.3°) and show no statistical variation nor drift with stratigraphic position. These data suggest that the Cheakamus basalt lavas were emplaced in a single paleomagnetic moment—a period of time significantly less than 2000 years. 40Ar/39Ar geochronometry on three lava samples returns a weighted mean age estimate of 15.95 ± 7.9 ka (2σ) and field evidence, including well-glaciated lava flow surfaces overlain by till, indicate the eruption coincided with the early stages of the Fraser glaciation (∼20–18 ka). The lavas preserve features indicative of a landscape hosting diverse and dynamic paleoenvironments. Subaerial eruption of basalt lava filled an ice-free Callaghan Creek drainage system before inundating and damming of the paleo-Cheakamus River creating an upstream rising body of water. Periodic overtopping of the lava dam resulted in syn-eruptive intermittent flooding and overtopping of lavas expressed by discontinuous lenses of interflow sediment. Rare instances of enigmatic cooling columns may also indicate localized ice contact with glaciers that partially filled the Cheakamus Valley. The displacement of the modern Cheakamus River and the long-term damming and formation of Callaghan and Conflict lakes remain direct indicators of the control and impact these basaltic eruptions have had on the geomorphology of the present-day Callaghan and Cheakamus valleys.

Lava Flow Hazard and Its Implication in Geopark Development for the Active Harrat Khaybar Intracontinental Monogenetic Volcanic Field, Saudi Arabia

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.

Emplacement and impacts of lava flows and intrusions on the sediment-buried Escanaba Segment of the Gorda mid-ocean ridge

The Escanaba Segment, the southernmost of the Gorda mid-ocean ridge segments, contains thick sandy to silty turbidite deposits that are Pleistocene to Recent in age. Dozens of deep laccoliths and shallower sills intrude into these sediments. The intrusions uplifted hills of the unconsolidated turbidites and some fed surface lava flows supplied along steeply dipping reverse faults that surround some of the tallest uplifted hills. Multibeam bathymetric mapping at 1-m resolution and chirp subbottom profile (SBP) lines at ~150 m spacing show that the uplifted sediment hills have complex patterns of surface deformation and experienced debris avalanche landslides on over-steepened slopes formed by uplift along reverse faults. The uplifted hills are spatially associated with 262 hydrothermal chimneys that are several-m-tall and abundant at two main areas named NESCA and SESCA (for northern and southern Escanaba). Chimneys are more abundant and widespread than previously mapped. The uplifted hills are also spatially associated with over 600 previously unrecognized pockmarks that range from a few to over 100 m in diameter and are up to 24 m deep. The hydrothermal deposits and pockmarks are associated with oily sediment, oily sulfide deposits, and tar mounds on the seafloor. The intrusions provide the heat to mature hydrocarbons from organic carbon in the sediment and to drive hydrothermal circulation that deposits sulfides and sulfates on the seafloor, mostly surrounding the tallest hills overlying thick laccoliths. The frequency sweep (chirp) subbottom profiles show that most sills and all the laccoliths are deeper than the ~60 m penetration of the system. However, the thicknesses and depths of numerous shallow sills are mapped from the bathymetry and SBP data. The deepest intrusions are all domed or punched laccoliths, those of intermediate depth are thick inflated sills, and the shallowest are the thinnest sills, as determined from the height of the uplifted hills. For most intrusions, depth to the top of the intrusion is roughly 3 times the thickness of the intrusion. The dome laccolith under Central Hill, in the NESCA vent field, is the only laccolith with well-constrained thickness (from the height of the uplifted Central Hill) and depth (from ODP drill 1038H through the hill that bottomed in the upper part of the laccolith. Sediment thicknesses on top of lava flows that pre- and postdate emplacement of the laccolith that uplifted Central Hill, coupled with an average sediment accumulation rate of 17.8 cm/kyr over the past almost 8800 years indicated that active hydrothermal venting on Central Hill began before ~225 years ago (the inferred age of the NESCA Young lava flow) but after ~1685 years ago (the average inferred age of NESCA #1 lava flow).

Isotopic constraints on selenium degassing from basaltic magma and near-surface capture by fumarolic deposits: Implications for Se redistribution onto the Earth's surface

Volcanic emanations from cooling basaltic lava represent a diffuse and relatively poorly constrained source of metallic and non-metallic compounds to the Earth's surface. These compounds become incorporated in fumarolic minerals and redeposit at the surface of lava flows before entering the environmental cycle. The semi-volatile and chalcophile element selenium (Se) can be either vital or toxic to animals and humans. Thus, understanding the pathways of Se capture and relative concentrations in fumaroles is imperative for estimating their contributions to soils and aquifers in volcanically active regions, with implications for animal and human health. In this study, we report Se concentrations and Se stable isotope composition in a sample suite comprising degassed and undegassed basaltic rocks and various fumarolic deposits (thenardite, Na-K sulfate, gypsum, fluoride, and native sulfur) fed from degassing lava flows at Piton de la Fournaise volcano, Réunion Island. Erupted basaltic lavas (136–58 ng·g−1 Se) lost up to more than half of their pre-eruptive Se due to subaerial degassing and retained a heavier isotope composition (δ82/76Se = 0.11 ± 0.17‰, 2 s.d.) compared to less undegassed volcanic glass (138 ng·g−1 Se and δ82/76Se = −0.19 ± 0.04‰, 2 s.e.). Fumarolic deposits that formed over a temperature range of ~800–100 °C and captured Se from the degassing lava show higher to very high Se concentrations ranging from 0.54 μg·g−1 to 1578 μg·g−1 and significant Se isotope fractionation (δ82/76Se = +0.6 to −2.08‰). We propose two separate models that can explain the relative concentration and Se isotope composition of the deposits: 1) A compound oxidation state-dependent Se incorporation into the various fumarolic minerals, or 2) Temperature-dependent Rayleigh condensation from a cooling gas triggered by compound saturation. The Rayleigh condensation model can entirely explain the Se concentration and isotope composition of the fumaroles and predicts that up to 80% of the Se released from the lava is likely to be captured by precipitation to form solid phases within the lava pile, most dramatically in the coldest deposits below the sublimation temperature of SeO2 (< 315 °C). In contrast, mineral-dependent isotope pathways cannot fully explain our data, including the lighter Se isotope compositions in the more oxidized compounds compared to more reduced ones. Such a mineralogical effect cannot be excluded but further investigations and experimental studies are required in order to scrutinize and invoke its role. Finally, the environmental impact of these degassing-induced secondary products will be dependent on the relative compound water solubilities resulting in either Se mobilization towards aquifers or accumulation onto developing soils and plants. Such studies could prove useful for developing risk assessments in volcanically active regions on our planet, and for reaching a better understanding of the global continent-ocean Se isotope budget and signature.

Upper crustal shear wave velocity and radial anisotropy beneath Jeju Island volcanoes from ambient noise tomography

SUMMARYJeju Island offshore of the southern Korean Peninsula is an isolated intraplate volcano formed by multiple basaltic eruptions from the Pleistocene (∼1.8 Ma) to the Holocene (∼3.7 ka). Due to the lack of available seismic data, magma structures at upper crustal depths of the island have not been clearly revealed. In this study, we imaged upper crustal isotropic and radial anisotropic structures beneath the island using ambient noise data from a temporary seismic network. A series of transdimensional hierarchical Bayesian inversions were performed to construct upper crustal (1–10 km) isotropic and anisotropic structures. Surface wave (Rayleigh and Love wave) group and phase velocity dispersion data were jointly inverted for 2–15 s. The results show that layers of negative anisotropy (VSH &amp;lt; VSV) are predominant at shallower (&amp;lt;2 km) and deeper (&amp;gt;5 km) depths, which was interpreted as reflecting dyke swarms responsible for the more than 400 cinder cones at the surface and the vertical plumbing systems supplying magma from deeper sources, respectively. Additionally, a layer with significantly positive radial anisotropy (VSH &amp;gt; VSV, up to 5 per cent) was found at middle depths (2–5 km), and was interpreted as horizontally aligned magma plumbing systems (e.g. sills) through comparisons with several other volcanoes worldwide. In comparison with the isotropic structure, the positive anisotropic layer was separated into upper and lower layers with locally neutral to slightly fast and slower shear wave velocities, respectively, beneath the largest central crater (Mt Halla). Such a structure indicates that the cooled upper part of the magma plumbing systems formed within the horizontally developed sill complex, and is underlain by still-warm sill structures, potentially with a small fraction of melting. With dykes predominant above and below, the island-wide sill layer and locally high-temperature body at the centre explain the evolution of the Jeju Island volcanoes by island-forming surface lava flows and central volcanic eruptions before and after the eruptions of cinder cones.

Surface expressions of morphostructural features at Hasandağ stratovolcano on DEM datasets

Although the young pyroclastic cover tends to hide the structural features, derivatives of Digital Elevation Models (DEM) help reveal the morphological elements exposing the structure of the volcanoes. While the shaded relief maps improve the visuality of the DEM data, they are not the best derivatives to express the detailed morphological characteristics of the terrain. Advanced morphometric DEM derivatives, such as Red Relief Image Maps and Openness images, provide improved terrain legibility especially on volcanic landforms. Satellite-derived mid-resolution DEM and very-high-resolution aerial stereo-photogrammetric summit model of Hasandag was used to investigate the structural features of the volcano. The mid-resolution topographic derivatives evidently mapped structural features which have had important role in the evolution of the volcano. Effect of fault systems on the development of the volcano, evident and probable topographic rims of collapse structures, avalanche and lava flow surface morphologies and characteristics revealed by the advanced derivatives of DEMs were evaluated. Summit of Greater Hasandag volcano was modeled using Structure-from-Motion/Multiview stereo-photogrammetry using acquired drone imagery; the model presents the summit geology in high-resolution and precision.

Geochemical studies on rock varnish and petroglyphs in the Owens and Rose Valleys, California.

We investigated rock varnish, a thin, manganese- and iron-rich, dark surface crust, on basaltic lava flows and petroglyphs in the Owens and Rose Valleys (California) by portable X-ray fluorescence (pXRF) and femtosecond laser-ablation inductively-coupled-plasma mass spectrometry (fs-LA-ICPMS). The major element composition of the varnish was consistent with a mixture of Mn-Fe oxyhydroxides and clay minerals. As expected, it contained elevated concentrations of elements that are typically enriched in rock varnish, e.g., Mn, Pb, Ba, Ce, and Co, but also showed unusually high enrichments in U, Cu, and Th. The rare earth and yttrium (REY) enrichment pattern revealed a very strong positive cerium (Ce) anomaly and distinct negative europium (Eu) and Y anomalies. The light rare earth elements (REE) were much more strongly enriched than the heavy REY. These enrichment patterns are consistent with a formation mechanism by leaching of Mn and trace elements from aeolian dust, reprecipitation of Mn and Fe as oxyhydroxides, and scavenging of trace elements by these oxyhydroxides. We inferred accumulation rates of Mn and Fe in the varnish from their areal densities measured by pXRF and the known ages of some of the lava flow surfaces. The areal densities of Mn and Fe, as well as their accumulation rates, were comparable to our previous results from the desert of Saudi Arabia. There was a moderate dependence of the Mn areal density on the inclination of the rock surfaces, but no relationship to its cardinal orientation. We attempted to use the degree of varnish regrowth on the rock art surfaces as an estimate of their age. While an absolute dating of the petroglyphs was not possible because of the lack of suitable calibration surfaces and a considerable amount of variability, the measured degree of varnish regrowth on the various petroglyphs was consistent with chronologies based on archeological and other archaeometric techniques. In particular, our results suggest that rock art creation in the study area continued over an extended period of time, possibly starting around the Pleistocene/Holocene transition and extending into the last few centuries.

Characteristics of rootless cone tephra emplaced by high-energy lava–water explosions

The effects of external water during hydrovolcanic eruptions are difficult to quantify; however, research investigating the explosive interactions between surface lava flows and water has provided new insights into explosion dynamics. Previous work has focused on relatively low-energy lava–water explosions from a 100-m-diameter cone in the Rauðholar cone group in Iceland. For comparison, we study ejecta derived from higher-energy explosions at the 400-m-diameter Pu‘u Kīholo rootless cone in Hawai‘i, one of the largest rootless cones on Earth. This comparative approach elucidates the effect of lava–water mixing conditions and range of explosivity on ejecta characteristics. Utilizing grain size analysis, we found that Pu‘u Kīholo beds typically have median grain sizes at the cone rim that are smaller than − 3 ϕ (8 mm) and are on average finer-grained than those of the Rauðholar cone. Ash-sized grains, the most energetically significant ejecta size fraction, typically make up > 20% of bed ejecta, with a maximum of 90%, both greater proportions than found in beds of the Rauðholar cone. Utilizing grain morphology, crystal texture, and surface feature analysis, we found that the abundance of ash-sized grains associated with high heat transfer rates (i.e., active particles) increases at Pu‘u Kīholo as explosivity increases, which is an important consideration for energy modeling. This dataset also includes ejecta from the finest-grained beds, and therefore highest-energy lava–water explosions, studied to date.

MMT-Cam: A New Miniature Multispectral Thermal Infrared Camera System for Capturing Dynamic Earth Processes

We have developed a new portable, ground-based imaging system primarily to investigate the thermal properties of volcanic processes during lava propagation and cooling, although it is potentially applicable to any dynamic geologic process. The miniature multispectral thermal camera (MMT-Cam) is an imaging system that acquires six wavelength bands of thermal infrared (TIR) data between 8 and $12~\mu \text{m}$ nearly simultaneously. The spatial and temporal resolutions of the camera system are high, $640 \times 512$ pixels, and 1 s, respectively. The imaging system is calibrated using full-aperture blackbody experiments at a range of temperatures from 283 to 1023 K to account for all instrumental, optical, and transmission effects. In addition, the baseline drift due to changing internal camera temperature is measured and removed. As a result, the accurate multispectral TIR image data are acquired of dynamic surfaces such as propagating and cooling lava flow surfaces captured at the critical temporal (seconds) and thermal (initial rapid cooling) scales. These improved acquisition parameters provide valuable data for both compositional and textural spatiotemporal variability analyses of these volcanic surfaces. Furthermore, the MMT-Cam specifications are designed to be comparable to current and proposed Earth-orbiting TIR instruments to better evaluate the potential for future TIR data sets to deliver similar data sets.

Investigation of target property effects on crater populations in long lava flows: A study in the Cerberus region, Mars, with implications for magma source identification

Young volcanism on Mars is exemplified within the Cerberus region, which enables examination of relatively pristine lava flow surfaces. In this investigation, we derived model ages within the circum-Cerberus channelized lavas for sites proximal, medial, and distal to the lava flow sources, finding that these ages decrease with increasing distance from the inferred source. Investigating multiple possible explanations for this downstream decrease in model ages, we conclude that the most likely cause is changes in the rheological properties of the lava during emplacement. Analogous terrestrial lava flows exhibit rheological changes along their length during emplacement, supporting the hypothesis that target properties affect crater size frequency distributions (CSFDs) on extraterrestrial bodies. Using scaling methods, we investigated how possible material property changes in the Cerberus channelized lavas affected CSFDs. To derive a single model age for each channel, we arithmetically size-scaled the distal and proximal crater sizes. We also used pi-group scaling to estimate the effect of material strength and porosity on the final CSFDs. We infer that the Athabasca, Grjótá, and Marte Valles lavas underwent minor, moderate, and major rheological changes, respectively, to account for the progressively larger age discrepancies along their respective flow lengths. The arithmetic size-scaling yields relative lava emplacement ages, from oldest to youngest, respectively, as Grjótá, Marte, and Athabasca. This lack of a consistent progressive directional emplacement (east-to-west or west-to-east) of lava model ages implies that the magma source was spatially distributed beneath the Cerberus region, although magma contributions from the two bordering volcanic provinces cannot be ruled out. The results of this study support the findings of previous lunar and martian studies that inferred target property changes affected CSFDs, which may have some bearing on age dating of young lava surfaces across the inner Solar System.

Understanding Lava Flow Morphologies and Structures for Hazard Assessment

Lava flow surface morphologies are like pages of a book. If we are able to read the writing of that book, we can understand its content, and learn, act, and react accordingly. In the same way, if we understand lava surface morphology, recognise how it formed and the hazard it poses while flowing, we can adopt actions to protect from lava flow invasion our villages, infrastructures and local population. The surface of lava is a function of intrinsic and extrinsic qualities, and their combination results in different shapes, sizes, and complexities, as well as in different hazards. Initial sheet flows spreading at high speed have great potential for devastating land, as happened in Hawaii in August 2018. However, their destructive potential significantly decreases with time and distance from the vent. Conversely, lava oozing from the far exit of lava tubes moves slowly but allows the tubes to expand, increasing gradually and slowly the potential hazard for invasion of more remote lands. In this paper, I present an overview of diverse lava flow surfaces, morphologies and structures in a framework of their generating eruptive parameters, in order to suggest preliminary but prompt hazard evaluations that could be applied during the initial phases of effusive volcanic crises at basaltic volcanoes worldwide.

The Volume of Lava Erupted During the 2014 to 2015 Eruption at Holuhraun, Iceland: A Comparison Between Satellite‐ and Ground‐Based Measurements

AbstractThe 31 August 2014 to 27 February 2015 eruption at Holuhraun created the largest lava flow field in Iceland since the 1783–1784 Laki eruption. Emplacement of a basaltic flow field of this magnitude onto an effectively flat surface (&lt;0.1°) is a rare occurrence. Lava discharge rate, a fundamental variable that controls flow field emplacement, allows us to estimate the total volume of lava erupted when integrated over time. Thus, discharge rate data are important for volcano monitoring and lava flow modeling. Here we compare discharge rates estimated using data from National Aeronautics and Space Administration's MODerate Resolution Imaging Spectroradiometer (MODIS) and the method of Harris et al. (1997a, https://doi.org/10.1029/96JB03388; 1997b, https://doi.org/10.1007/s004450050174; 2007, https://doi.org/10.1007/s00445‐007‐0120‐y), with estimates of discharge rates derived from comparing intermittent ground‐based measurements of flow field volume. The time‐averaged discharge rates (TADR) reveal a pulsed increase in the first few days of the eruption. Although the trends of the satellite‐ and ground‐based discharge rates are similar, the ground‐based estimates are systematically higher than the satellite‐derived estimates (about 2 to 3 times higher) in the first 30 days of the eruption, and relatively close (within 30%) for the next 20 days. Conversely, during the final 130 days, the satellite‐based estimates are systematically higher than the ground‐based estimates (about 2 times higher). This difference likely arises from the assumption of the lava flow surface temperature used in the space‐based calculation, which may not be entirely representative of this uniquely large and intense basaltic eruption. However, the satellite‐based technique yields a total erupted volume of about 1.21 km3 in good agreement with the 1.2 km3 (84 km2) derived from field observations and mapping.

Dating lava flows of tropical volcanoes by means of spatial modeling of vegetation recovery

AbstractThe age of past lava flows is crucial information for evaluating the hazards and risks posed by effusive volcanoes, but traditional dating methods are expensive and time‐consuming. This study proposes an alternative statistical dating method based on remote sensing observations of tropical volcanoes by exploiting the relationship between lava flow age and vegetation cover. First, the factors controlling vegetation density on lava flows, represented by the normalized difference vegetation index (NDVI), were investigated. These factors were then integrated into pixel‐based multi‐variable regression models of lava flow age to derive lava flow age maps. The method was tested at a pixel scale on three tropical African volcanoes with considerable recent effusive activity: Nyamuragira (Democratic Republic of Congo), Mt Cameroon (Cameroon) and Karthala (the Comoros). Due to different climatic and topographic conditions, the parameters of the spatial modeling are volcano‐specific. Validation suggests that the obtained statistical models are robust and can thus be applied for estimating the age of unmodified undated lava flow surfaces for these volcanoes. When the models are applied to fully vegetated lava flows, the results should be interpreted with caution due to the saturation of NDVI. In order to improve the accuracy of the models, when available, spatial data on temperature and precipitation should be included to directly represent climatic variation. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Newly Discovered Ring‐Moat Dome Structures in the Lunar Maria: Possible Origins and Implications

AbstractWe report on a newly discovered morphological feature on the lunar surface, here named Ring‐Moat Dome Structure (RMDS). These low domes (a few meters to ~20 m height with slopes &lt;5°) are typically surrounded by narrow annular depressions or moats. We mapped about 2,600 RMDSs in the lunar maria with diameters ranging from tens to hundreds of meters. Four candidate hypotheses for their origin involving volcanism are considered. We currently favor a mechanism for the formation of the RMDS related to modification of the initial lava flows through inflated flow squeeze‐ups and/or extrusion of magmatic foams below a cooling lava flow surface. These newly discovered features provide new insights into the nature of emplacement of lunar lava flows, suggesting that in the waning stages of a dike emplacement event, magmatic foams can be produced, extrude to the surface as the dike closes, and break through the upper lava flow thermal boundary layer (crust) to form foam mounds and surrounding moats.

The Northwest Africa 8159 martian meteorite: Expanding the martian sample suite to the early Amazonian

Northwest Africa (NWA) 8159 is an augite-rich shergottite, with a mineralogy dominated by Ca-, Fe-rich pyroxene, plagioclase, olivine, and magnetite. NWA 8159 crystallized from an evolved melt of basaltic composition under relatively rapid conditions of cooling, likely in a surface lava flow or shallow sill. Redox conditions experienced by the melt shifted from relatively oxidizing (with respect to known Martian lithologies, ∼QFM) on the liquidus to higher oxygen fugacity (∼QFM+2) during crystallization of the groundmass, and under subsolidus conditions. This shift resulted in the production of orthopyroxene and magnetite replacing olivine phenocryst rims. NWA 8159 contains both crystalline and shock-amorphized plagioclase (An50–62), often observed within a single grain; based on known calibrations we bracket the peak shock pressure experienced by NWA 8159 to between 15 and 23GPa. The bulk composition of NWA 8159 is depleted in LREE, as observed for Tissint and other depleted shergottites; however, NWA 8159 is distinct from all other martian lithologies in its bulk composition and oxygen fugacity. We obtain a Sm-Nd formation age of 2.37±0.25Ga for NWA 8159, which represents an interval in Mars geologic time which, until recently, was not represented in the other martian meteorite types. The bulk rock 147Sm/144Nd value of 0.37±0.02 is consistent with it being derived directly from its source and the high initial ε143Nd value indicates this source was geochemically highly depleted. Cr, Nd, and W isotopic compositions further support a unique mantle source. While the rock shares similarities with the 2.4-Ga NWA 7635 meteorite, there are notable distinctions between the two meteorites that suggest differences in mantle source compositions and conditions of crystallization. Nevertheless, the two samples may be launch-paired. NWA 8159 expands the known basalt types, ages and mantle sources within the Mars sample suite to include a second igneous unit from the early Amazonian.

A review of mass and energy flow through a lava flow system: insights provided from a non-equilibrium perspective

A simple formula relates lava discharge rate to the heat radiated per unit time from the surface of active lava flows (the “thermal proxy”). Although widely used, the physical basis of this proxy is still debated. In the present contribution, lava flows are approached as open, dissipative systems that, under favorable conditions, can attain a non-equilibrium stationary state. In this system framework, the onset, growth, and demise of lava flow units can be explained as a self-organization phenomenon characterized by a given temporal frequency defined by the average life span of active lava flow units. Here, I review empirical, physical, and experimental models designed to understand and link the flow of mass and energy through a lava flow system, as well as measurements and observations that support a “real-world” view. I set up two systems: active lava flow system (or ALFS) for flowing, fluid lava and a lava deposit system for solidified, cooling lava. The review highlights surprising similarities between lava flows and electric currents, which typically work under stationary conditions. An electric current propagates almost instantaneously through an existing circuit, following the Kirchhoff law (a least dissipation principle). Flowing lavas, in contrast, build up a slow-motion “lava circuit” over days, weeks, or months by following a gravity-driven path down the steepest slopes. Attainment of a steady-state condition is hampered (and the classic thermal proxy does not hold) if the supply stops before completion of the “lava circuit.” Although gravity determines initial flow path and extension, the least dissipation principle means that subsequent evolution of mature portions of the active lava flow system is controlled by increasingly insulated conditions.

Update on the Volcanic Geoheritage Values of the Pliocene to Quaternary Arxan–Chaihe Volcanic Field, Inner Mongolia, China

The Pliocene to Quaternary small-volume monogenetic volcanic field of the Arxan–Chaihe Volcanic Field (ACVF) hosts some typical volcanic landforms associated with continental basaltic volcanism. The volcanic field volcanic geoheritage values were used to establish two geoparks in 2004 and 2010 based on the volcanic geoheritage values of this region. The geoeducational program was quickly designed but shows signs of some lack of full understanding of the volcanic architecture of the region. This manifests in some misinterpretation of volcanic features that are relatively well-established and known elsewhere, and hence it hinders the effectiveness of the correct scientific information transition via geoeducational programs and geotourism. The geoparks established an excellent logistical network to promote volcanic geoscience, funded new educational centres and the local area economic growth created a situation that geotourism can be the main sector in economic growth in this part of Inner Mongolia. On the basis of these positive signs, we revisited some of the key volcanic geotopes of the region and cross-checked the already identified and established geosites mostly located in volcanologically important areas. There have been four major geotope groups identified such as (1) the scoria and spatter cones, (2) the lava flows and their surface morphological features, (3) the maar volcanism and its pyroclastic deposits and (4) the landscape and sedimentary evidence to demonstrate landscape evolution in a volcanically influenced continental region. Here, we provide new field observation-based evidence to demonstrate the volcanic geoheritage values of these geotopes. This information can be transmitted easily to the general public on the significance and formation of (1) scoria and spatter cones; (2) tumuli, pressure ridges, hornitos and various pahoehoe and transitional lava flow surface textures that are well-preserved on Quaternary lava flow surfaces; (3) base surge dominated tephra ring successions and large maars; and (4) landscape that evolved through the interplay of terrestrial sedimentation and monogenetic volcanic eruption influenced volcanic activity. The complex processes that can be seen at the ACVF make this field a high volcanic geodiversity one that can be used for a near-future application for UNESCO Global Geopark status.