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The Tsiolkovsky crater is located on the farside of the Moon. It formed in the late Imbrian epoch and was filled with a large area of mare basalts. Multisource remote sensing data are used to interpret the geological features of the Tsiolkovsky area. Compared with previous studies, new remote sensing data and a chronological model based on crater size–frequency distribution are used to further refine the stratigraphic units and determine the absolute ages of the mare basalt units. The evolution of volcanic activity in this crater is discussed. The results are as follows: Abundances of major elements, Th, and silicate minerals suggest that the mare basalt in the crater floor is not a uniform unit but rather nine units with different compositions. The nine basalt units are divided into two episodes of volcanic activity: The first occurred at 3.5–3.7 Ga, when highly evolved lava erupted at the crater floor at a large scale; the second occurred at ~3.4 Ga, when a small area of more primitive lava extended to the northern portion of the crater floor. [ABSTRACT FROM AUTHOR]

Spatial approaches, based on the deformation measurement of volcanic domes and crater rims, is key in evaluating the activity of a volcano, such as Merapi Volcano, where associated disaster risk regularly takes lives. Within this framework, this study aims to detect localized topographic change in the summit area that has occurred concomitantly with the dome growth and explosion reported. The methodology was focused on two sets of data, one LiDAR-based dataset from 2012 and one UAV dataset from 2014. The results show that during the period 2012–2014, the crater walls were 100–120 m above the crater floor at its maximum (from the north to the east–southeast sector), while the west and north sectors present a topographic range of 40–80 m. During the period 2012–2014, the evolution of the crater rim around the dome was generally stable (no large collapse). The opening of a new vent on the surface of the dome has displaced an equivalent volume of 2.04 × 104 m3, corresponding to a maximum −9 m (+/−0.9 m) vertically. The exploded material has partly fallen within the crater, increasing the accumulated loose material while leaving "hollows" where the vents are located, although the potential presence of debris inside these vents made it difficult to determine the exact size of these openings. Despite a measure of the error from the two DEMs, adding a previously published dataset shows further discrepancies, suggesting that there is also a technical need to develop point-cloud technologies for active volcanic craters. [ABSTRACT FROM AUTHOR]

Blasting experiments were performed that investigate multiple explosions that occur in quick succession in unconsolidated ground and their effects on host material and atmosphere. Such processes are known to occur during phreatomagmatic eruptions at various depths, lateral locations, and energies. The experiments follow a multi‐instrument approach in order to observe phenomena in the atmosphere and in the ground, and measure the respective energy partitioning. The experiments show significant coupling of atmospheric (acoustic)‐ and ground (seismic) signal over a large range of (scaled) distances (30–330 m, 1–10 m J−1/3). The distribution of ejected material strongly depends on the sequence of how the explosions occur. The overall crater sizes are in the expected range of a maximum size for many explosions and a minimum for one explosion at a given lateral location. As previous research showed before, peak atmospheric over‐pressure decays exponentially with scaled depth. An exponential decay rate of d¯0=6.47×10−4mJ−1/3 ${\bar{d}}_{0}=6.47\times 1{0}^{-4}\,\mathrm{m}\,{\mathrm{J}}^{-1/3}$ was measured. At a scaled explosion depth of 4 × 10−3 m J−1/3 ca. 1% of the blast energy is responsible for the formation of the atmospheric pressure pulse; at a more shallow scaled depth of 2.75 × 10−3 m J−1/3 this ratio lies at ca. 5.5%–7.5%. A first order consideration of seismic energy estimates the sum of radiated airborne and seismic energy to be up to 20% of blast energy. Finally, the transient cavity formation during a blast leads to an effectively reduced explosion depth that was determined. Depth reductions of up to 65% were measured. Plain Language Summary: Blasting experiments using six successive explosions were performed. Explosives were detonated in unconsolidated ground material in four different geometric setups (linear and triangular). We monitored the experiments using geophysical instruments. The instruments measured explosive energy, and how much of that energy escapes the crater. The experiments help to understand volcanic (phreatomagmatic) and other subsurface explosive processes. Exact measurements of the resulting craters, together with known explosive energies allow the interpretation of real volcanic craters. The experimental results show initial time developments of crater sizes, which occurs on the order of 1 s for crater sizes of the order of 1 m. Up to 8% of an explosion's energy was detected as airborne signal. Up to 20% of the explosion's energy was detected as seismic (elastic) energy in the ground. Key Points: Airborne energy of an underground blast decays exponentially with scaled depth and is in agreement with previous measurementsTransient crater unloading leads to eruption at the surface from depths that were thought to be deep enough to be contained in the groundCrater sizes correlate with measured seismo‐acoustic and high‐frequency atmospheric signals [ABSTRACT FROM AUTHOR]

Topography of a volcano crater can change due to endogenic processes such as deformation or eruption, or surface processes. Erosion and deposition are surface processes that may occur and gradually change the slope of the inner volcano crater. Here, we investigated erosion and deposition processes that occurred in the Kelud crater after the 2014 plinian eruption. We used high-resolution Digital Elevation Models (DEMs) and orthomosaic images derived by drone photogrammetry that acquired between September 2018 and July 2019. We obtained hundreds of aerial images which were reconstructed to obtain 3D models of Kelud’s crater by using Structure from Motion (SfM) technique. Results show erosions at alluvial fans that dominantly located at the east valleys of Kelud crater. The erosion removed the volcanic materials up to -5 m which transported and deposited close to the vicinity of the Kelud crater. The deposition process causes the increase of the Kelud crater lake up to 3 m. Moreover, we also mapped the thermal distribution of the Kelud crater lake by using low cost thermal camera. Our thermal investigation is able to identify some hotspots at the vicinity of the Kelud crater lake with range temperature of 43.7°C – 55.3°C, while the average apparent temperature of the Kelud crater lake is ~ 29°C. This high temperature area may indicate underwater active fractures that continuously release volcanic gasses which leads to convection heat transfer through Kelud’s water lake. [ABSTRACT FROM AUTHOR]

In December 2018, Mount Etna (Italy) experienced a period of increased eruptive activity that culminated in a fissure eruption on the southeast flank. After the onset of the flank eruption, the peak frequency of the summit infrasound signals decreased while resonance increased. We invert infrasound observations for crater geometry and show that crater depth and radius increased during the eruption, which suggests that the flank eruption drained magma from the summit and that eruptive activity led to erosion of the crater wall. By inverting the entire infrasound amplitude spectra rather than just the peak frequency, we are able to place additional constraints on the crater geometry and invert for, rather than assume, the crater shape. This work illustrates how harmonic infrasound observations can be used to obtain high‐temporal‐resolution information about crater geometry and can place constraints on complex processes occurring in the inaccessible crater region during eruptive activity. Plain Language Summary: Volcanoes generate low‐frequency sound waves in the atmosphere (infrasound) that can be recorded by specialized microphones. Much like giant musical instruments, the character of the sound can depend upon the shape and size of the crater. Mount Etna erupted in December 2018 with lava flowing out a fissure on the flank of the volcano. The character of the sound changed after the flank eruption. We study the change in the character of the sound in order to estimate how the shape of the volcanic crater at the summit of Mount Etna changed. Our results show that the crater got deeper and wider, which suggests that the eruption of lava on the flank of the volcano drained magma from the summit area. This work shows how infrasound observations can track changes in crater geometry and provide insight about the magma plumbing systems beneath volcanoes. Key Points: Eruptive activity at Mount Etna's summit generated harmonic infrasound signals due to crater resonancePeak frequency of infrasound signal decreased and resonance increased after fissure eruption on flankInfrasound amplitude spectra can be inverted for crater shape and used to track changes in morphology [ABSTRACT FROM AUTHOR]

The first definitive evidence for continental vents on Mars is the in situ detection of amorphous silicarich outcrops by the Mars Exploration Rover Spirit. These outcrops have been tentatively interpreted as the result of either acid sulfate leaching in fumarolic environments or direct precipitation from hot springs. Such environments represent prime targets for upcoming astrobiology missions but remain difficult to identify with certainty, especially from orbit. To contribute to the identification of fumaroles and hot spring deposits on Mars, we surveyed their characteristics at the analog site of the Solfatara volcanic crater in central Italy. Several techniques of mineral identification (VNIR spectroscopy, Raman spectroscopy, XRD) were used both in the field and in the laboratory on selected samples. The faulted crater walls showed evidence of acid leaching and alteration into the advanced argillic-alunitic facies, with colorful deposits containing alunite, jarosite, and/or hematite. Sublimates containing various Al and Fe hydroxyl-sulfates were observed around the active fumarole vents at 90 °C. One vent at 160 °C was characterized by different sublimates enriched in As and Hb sulfide species. Amorphous silica and alunite assemblages that are diagnostic of silicic alteration were also observed at the Fangaia mud pots inside the crater. A wide range of minerals was identified at the 665 m diameter Solfatara crater that is diagnostic of acid-steam heated alteration of a trachytic, porous bedrock. Importantly, this mineral diversity was captured at each site investigated with at least one of the techniques used, which lends confidence for the recognition of similar environments with the next-generation Mars rovers. [ABSTRACT FROM AUTHOR]

Sakurajima Muography Observatory captured the formation of a volcanic plug beneath the Showa crater with a spatial resolution of ∼60 m in accordance with the end of the eruption episode of Showa crater and the reactivation of Minamidake crater. The increase of average density was observed with above 3 σ standard deviation for both above the floor of Minamidake crater and beneath the floor of Showa crater, respectively, being interpreted as volcanic ejecta deposition and the formation of a volcanic plug laterally extended within a few hundreds of meters. Plain Language Summary: Muography is an imaging technique that provides information about the amount of material across kilometer‐thick geological structures by the measurement of the yield of cosmic rays, similarly to X‐raying of human body. We applied muography to capture two muon images of Minamidake and Showa craters of Sakurajima volcano before and after the shift of eruption activities occurred between the two craters at the end of 2017. The comparison of the images revealed the presence of increased material across the activated Minamidake and beneath the deactivated Showa crater. Muography detected the formation of a magma plug in the conduit of Showa crater that was not detected earlier by any other geophysical technique. These results demonstrate the applicability of cosmic muon imaging for monitoring of magma movements inside active volcanoes. Key Points: Two muographic images were taken across the erupting Sakurajima volcano with a spatial resolution of 60 mIncreased average densities were observed beneath the deactivated crater after the shift of eruption sequenceMuography data suggest that uprising magma formed a plug in the conduit of Showa crater [ABSTRACT FROM AUTHOR]

Lunar volcanism play an important role on studying the thermal and compositional evolution of the Moon. However, the studies on the relationships among composition, location and age of Lunar volcanos are still limit. The high-quality and multi-source remote sensing data offer the opportunity to obtain significant features of the Lunar volcanism and the evolution of the Moon. Specifically, the high-quality gravitational features of volcanic landforms of the Moon are observed by the Gravity Recovery and Interior Laboratory. Besides, the lunar reconnaissance orbiter camera provides detail morphologic features of Lunar volcanos based on high-resolution optical images. This paper aims to find the characteristic of lunar volcanos by observing the gravitational and morphologic features in the center of craters. The final results show that most of the craters with central peaks have gravity anomalies except the Mendeleev crater (5.7 °N and 140.9 °E) whose central area contains significant gravity anomalies but no central peaks. The area of gravity anomaly may indicate heat source under the ground. [ABSTRACT FROM AUTHOR]

Volcanic activity excites low frequency acoustic waves, termed infrasound, in the atmosphere. Infrasound observations can be used to provide constraints on eruption properties, such as crater geometry and volume flux. At open-vent volcanoes, such as Erebus (Antarctica) and Villarrica (Chile), the infrasound signal is modulated by the crater properties. Eruptive activity at the bottom of the crater, such as unsteady degassing or explosions, can excite the air mass within the crater into resonance leading to infrasound generation with signals possessing clear spectral peaks, termed harmonics. Therefore, the effect of the crater on the infrasound signal, or crater acoustic response, must be accounted for when inverting harmonic infrasound observations for eruption properties at open-vent volcanoes. Here we develop a linearized model of quasi-one-dimensional (1D) wave propagation inside volcanic crater coupled with 3D axisymmetric radiation into the atmosphere from the crater, with waves generated by a volumetric flow rate source at the bottom of the crater. We perform simulations for a range of volcanic crater geometries, temperature profiles, gas compositions, and source descriptions to explore the influence of these properties on the infrasound signal. The observed infrasound signal depends on the flow rate source-time function, but interference of up- and down-going waves within the crater selectively amplifies the signal at the resonant frequencies of the crater. The crater resonance model presented here is verified by comparison with an established three-dimensional (3D) infrasound code and is shown to be appropriate for realistic crater geometries when the crater radius is less than approximately one quarter of the acoustic wavelength. The model presented here is more computationally efficient and can be used to invert infrasound observations for a range of properties, such as crater geometry or volumetric flow rate associated with eruptions. We demonstrate the utility of our efficient modeling framework by inverting harmonic infrasound observations for the crater geometry and position of the lava lake at Villarrica volcano. This technique may be used at other open-vent volcanoes to constrain dynamic crater geometry and provide insights about lava lake motions and infrasound producing eruption sources. • Harmonic infrasound from open-vent volcanoes is explained by resonance of crater. • We develop an efficient quasi-1D crater model that describes crater acoustic resonance. • Can invert harmonic infrasound signals for volcano properties, such as crater geometry [ABSTRACT FROM AUTHOR]

• First detailed mapping of the hidden active crater of Lascar volcano by UAS. • Topographical changes of the active crater quantified by DEM of difference analysis. • Thermal orthomosaic helps to determine thermal anomalies and fumaroles. • Nested ring structures have been identified on the crater floor. • Ring structures imply a narrow conduit top less than 40 m in diameter. Details of ongoing changes in geomorphology and structure of nested volcanic craters are lacking due to the difficult and hazardous access. In this study, we present a novel unoccupied aircraft system (UAS) dataset collected at Lascar, northern Chile, one of the most active volcanoes in the Central Volcanic Zone of the Andes. Lascar features nested craters, the deepest crater of which has experienced repeated lava dome emplacement and numerous violent explosions in recent decades. We performed UAS surveys in 2017 and 2020 to collect the optical and thermal imaging data of the active crater. By applying the Structure-from-Motion (SfM) method, we obtained centimeter-scale optical and thermal orthomosaics as well as digital terrain models. We quantify the spatial and volumetric changes that occurred during the observation period. The results show material removal from the crater wall and a significant accumulation of volcanic material on the crater floor. The thermal orthomosaic helps identify thermal anomalies and the spatial distribution of fumaroles. The highest thermal anomaly was found on the crater floor and delimited by ring structures. Both the optical orthomosaics and DEMs from 2017 and 2020 showed a consistent ring structure, which remained stable following two explosive events. Possible localized subsidence was observed within the ring structure. Consequently, we hypothesize that the ring structure represents the surface expression of underlying concentric fracture systems and constrains a narrow conduit top. Our results provide important insights into an active crater's morphological, structural, and thermal features, with implications for understanding the formation mechanism and evolution of volcanic craters. [ABSTRACT FROM AUTHOR]

Pit craters are circular to subcircular depressions that lack a rim and ejecta layer and typically have a conical shape. There are several mechanisms that can explain the formation of such depressions and they are associated with collapse due to the removal of subsurface material. Possible origins of pit craters include: volcanic processes (collapse of lava tubes, magmatic chambers, intrusion of dikes), karstic dissolution, extensional faulting or volatile processes. In this work, we study pit craters in the north-estern external slope of Hale Crater. We identified >40 pit craters that present unique morphological features in association with different landforms associated with volatile activity in the area. We identified moraine like ridges, gullies and aprons together with pits that represent an interesting suite of landforms. After producing a detailed geomorphic map, we classified the pits into: i) single pit craters, ii) chain pit craters, iii) complex pit craters and iv) elongated pit craters. We used DTMs to determine orientation and slopes of the pit craters-hosting terrains and to analyze elevation profiles of the different types of pits and their relation with the gullies and other features. In addition, we performed a spectral analysis using CRISM multispectral dataset in order to characterize the mineralogy of the sediments in the region and to identify any distinctive properties that could promote the formation of these depressions. Here, we propose that pit craters are stratigraphically on top of the ice-related landforms and present complex relationships with the gullies. The spatial relationship between the pits and these structures, along with the absence of evidence of present or past volcanic activity and the lack of evidence of any extensional faulting allows us to propose that the origin of the pit craters in the study area might be related to some volatile process. We propose here that these particular pit craters at Hale crater, are morphologically similar to Icelandic depressions located in a glacial environment. We conclude that the landforms found in the area are in close relation with glacial or periglacial conditions and pit craters might be formed by sublimation/melting of ground ice. • Identification and morphological description of pit craters in Hale Crater. • Association of pit craters with rock glaciers, moraines and gullies. • Iceland as a potential analogue of sublimation pit craters. • Evolution history from single to complex pits. • Sublimation processes leading to collapse and pit crater formation. [ABSTRACT FROM AUTHOR]

Abstract: Lunar irregular mare patches (IMPs) comprise dozens of small, distinctive, and enigmatic lunar mare features. Characterized by their irregular shapes, well‐preserved state of relief, apparent optical immaturity, and few superposed impact craters, IMPs are interpreted to have been formed or modified geologically very recently (<~100 Ma; Braden et al. ). However, their apparent relatively recent formation/modification dates and emplacement mechanisms are debated. We focus in detail on one of the major IMPs, Sosigenes, located in western Mare Tranquillitatis, and dated by Braden et al. ( ) at ~18 Ma. The Sosigenes IMP occurs on the floor of an elongate pit crater interpreted to represent the surface manifestation of magmatic dike propagation from the lunar mantle during the mare basalt emplacement era billions of years ago. The floor of the pit crater is characterized by three morphologic units typical of several other IMPs, i.e., (1) bulbous mounds 5–10 m higher than the adjacent floor units, with unusually young crater retention ages, meters thick regolith, and slightly smaller subresolution roughness than typical mature lunar regolith; (2) a lower hummocky unit mantled by a very thin regolith and significantly smaller subresolution roughness; and (3) a lower blocky unit composed of fresh boulder fields with individual meter‐scale boulders and rough subresolution surface texture. Using new volcanological interpretations for the ascent and eruption of magma in dikes, and dike degassing and extrusion behavior in the final stages of dike closure, we interpret the three units to be related to the late‐stage behavior of an ancient dike emplacement event. Following the initial dike emplacement and collapse of the pit crater, the floor of the pit crater was flooded by the latest‐stage magma. The low rise rate of the magma in the terminal stages of the dike emplacement event favored flooding of the pit crater floor to form a lava lake, and CO gas bubble coalescence initiated a strombolian phase disrupting the cooling lava lake surface. This phase produced a very rough and highly porous (with both vesicularity and macroporosity) lava lake surface as the lake surface cooled. In the terminal stage of the eruption, dike closure with no addition of magma from depth caused the last magma reaching shallow levels to produce viscous magmatic foam due to H2O gas exsolution. This magmatic foam was extruded through cracks in the lava lake crust to produce the bulbous mounds. We interpret all of these activities to have taken place in the terminal stages of the dike emplacement event billions of years ago. We attribute the unusual physical properties of the mounds and floor units (anomalously young ages, unusual morphology, relative immaturity, and blockiness) to be due to the unusual physical properties of the substrate produced during the waning stages of a dike emplacement event in a pit crater. The unique physical properties of the mounds (magmatic foams) and hummocky units (small vesicles and large void space) altered the nature of subsequent impact cratering, regolith development, and landscape evolution, inhibiting the typical formation and evolution of superposed impact craters, and maintaining the morphologic crispness and optical immaturity. Accounting for the effects of the reduced diameter of craters formed in magmatic foams results in a shift of the crater size–frequency distribution age from <100 Myr to billions of years, contemporaneous with the surrounding ancient mare basalts. We conclude that extremely young mare basalt eruptions, and resulting modification of lunar thermal evolution models to account for the apparent young ages of the IMPs, are not required. We suggest that other IMP occurrences, both those associated with pit craters atop dikes and those linked to fissure eruptions in the lunar maria, may have had similar ancient origins. [ABSTRACT FROM AUTHOR]

Abstract: Determining the ages of young planetary surfaces relies on using populations of small, often sub‐km diameter impact craters due to the higher frequency at which they form. Smaller craters however can be less reliable for estimating ages as their size‐frequency distribution is more susceptible to alteration with debate as to whether they should be used at all. With the current plethora of meter‐scale resolution images acquired of the lunar and Martian surfaces, small craters have been widely used to derive model ages to establish the temporal relation of recent geologic events. In this review paper, we discuss the many factors that make smaller craters particularly challenging to use and should be taken into consideration when crater counts are confined to small crater diameters. Establishing confidence in a model age ultimately requires an understanding of the geologic context of the surface being dated as reliability can vary considerably and limitations of the dating technique should be considered in applying ages to any geologic interpretation. [ABSTRACT FROM AUTHOR]

There are many buried craters on Mars invisible in imaging or topographic data; however, the residual gravity anomaly separated from the Mars Bouguer gravity anomaly by minimum curvature separation method can reveal these buried craters. In our research, gravity separation results exposed 39 residual gravity anomaly highs (RGAHs), which may represent deeply buried impact craters with 300–500 ​km diameter. The RGAHs are widely distributed across the surface of Mars, but are especially concentrated in volcanic areas like Tharsis and Elysium, which indicates that there might be more craters buried in these regions. Older craters in volcanic regions were likely buried by subsequent volcanism coming from surrounding volcanoes, so the retention age of craters in all areas where RGAHs are located will be older than reported in the existing research based on topographic data alone. This study will help improve the chronological model of Mars. • The impact craters of Mars with diameter of 300–500 km appear central positive residual gravity anomalies. • The gravity separation results exposed 39 anomaly highs, that is inferred to be buried impact craters. • The most RGAHs are concentrated in volcanic areas just like Tharsis and Elysium. [ABSTRACT FROM AUTHOR]

The morphologies of craters on planetary surfaces reveal clues about the geologic mechanisms by which they originate and subsequently evolve, as well as the materials and physical variables inherent to the environment in which they formed. We carried out a quantitative multivariate analysis of shape descriptors derived from the outlines of craters formed by volcanic processes on Mars, Io, and Earth and by impact cratering on the Moon using elliptic Fourier analysis (EFA) and the Zahn-Roskies (Z -R) shape function. Canonical variate analysis (CVA) was used to construct a statistical model of differences between the crater groups to classify craters produced by various volcanic and impact processes. The classification model from canonical variate analysis of EFA shape descriptors yielded a 90% rate of success for the assignment of group membership among 406 examined craters. It correctly classified 138 of 154 (90%) ionian paterae,154 of 155 (99%) lunar impact craters, 31 of 35 (89%) terrestrial basaltic shield calderas, 32 of 38 (84%) terrestrial ash-flow calderas, and 12 of 24 (50%) martian basaltic shield calderas. The classification model from canonical variate analysis of Z -R shape function descriptors classified 84% of the total population of the examined craters correctly. The analysis correctly classified 96% of ionian paterae, 100% lunar impact craters, 51% terrestrial basaltic shield calderas, and 63% martian calderas, but only 16% of the terrestrial ash-flow calderas were correctly classified. Canonical variate analysis of EFA and Z -R results shows that the shapes of ash-flow calderas and paterae on Io differ the least of all groups included in this study, and basaltic shield calderas and martian calderas analyzed together also have few differences. The Z -R model successfully classifies more ionian patera and impact craters than the EFA classification model but performs poorly at classifying the other crater groups. This result shows that the descriptors convey different shape information. The Z -R model is robust in its ability to classify end-member differences in complexity while the EFA model is robust in its ability to reliably classify among more groups. These differences and similarities in shape confirm previously understood commonalities related to the origin and evolution of various types of craters. In general, basalt shield calderas on Earth and Mars are morphologically similar and are thought to have similar origins; this study confirms that the 2-D shapes of their craters are quantitatively correlated. Similarities have been noted between terrestrial ash-flow calderas and paterae on Io, principally in their large sizes, shallow magma chambers and complex evolution; this study confirms their shapes are also similar. Impact craters and ionian paterae are most dissimilar, as are their evolutions. This study demonstrates rigorous landform shape analysis can greatly increase our understanding of the diversity in craters and the processes involved in their formation. • Adopts methods of outline-based shape analysis from paleontology and evolutionary biology to planetary craters. • Methods can successfully distinguish planetary craters formed by different processes. • Patera on Io most similar in shape to terrestrial ash-flow calderas. • Potential evidence for impact craters on Io. [ABSTRACT FROM AUTHOR]

• The 2.1 kyr Blue Dragon lava flow is one of the largest Holocene basaltic flows in the contiguous U.S. (280 km2/3.4 km3). • Satellite imagery shows the flow is divided into five large sub-areas deposited at different times during the eruption. • Major and trace elements and Pb isotopes show the lava composition changed over the course of the eruption. • The compositional data are consistent eruption of the Blue Dragon flow from a zoned magma chamber. • The changes in composition are consistent with changing magnitudes of fractional crystallization and crustal assimilation. The Blue Dragon lava flow in southern Idaho is one of the largest Holocene basaltic flows in the contiguous U.S. Multispectral remote sensing and field mapping of the flow have revealed its 280 km2 surface is divided into five large sub-areas with different spectral reflectance and morphology that correspond with distinct periods of the eruption. The flow grew outward from its source fissures primarily via a complex system of lava tubes, and stratigraphic relations at the boundaries of the mapped sub-areas provide temporal information about their order of emplacement. This offers a unique opportunity to reconstruct chemical and mineralogical changes in the source magmas as the eruption progressed. In this first comprehensive study of the compositional diversity of the Blue Dragon flow, geochemical data from 28 rock samples show that over the course of the eruption the lavas became progressively more primitive and depleted in incompatible trace elements, and Pb isotopes show subtle increases. These observations are best explained by eruption from a zoned magma source due to variable assimilation-fractional crystallization (AFC), with the initial eruption of more evolved and enriched magmas that may have been residual from the previous eruption, followed by progressively higher proportions of a more primitive and depleted component from deeper in the system. Differences in lava surface color and morphology among the five mapped eruptive phases may indicate changes in eruptive temperature, flow rate, or both as the Blue Dragon eruption progressed. The results support a growing body of evidence that systematic studies of geochemical variations in monogenetic and short-duration lava flows can reveal the relative influence of processes that affect single batches of magma. [ABSTRACT FROM AUTHOR]

Lava emplacement at monogenetic volcanoes has been seldom documented when compared to persistently active volcanoes such as Mt. Etna or Kilauea. To expand the scientific understanding of lava emplacement, and to help assess the hazards posed by monogenetic systems and of lava flows in general, we present an investigation of the lava field at Marcath volcano (~ 35 ka; Lunar Crater volcanic field, central Nevada, USA). Key data include lava surface characteristics as well as size and abundance data of rafted pyroclastic material derived from the source cone. Upon exiting the source crater, lava initially ponded in an upland saddle between Marcath and an older cone before breaking out to feed three lava lobes that spread out onto a flat valley floor below. Quantitative estimates based upon morphological parameters suggest time-averaged discharge rates of 40–100 m3 s−1, emplacement duration of 5–20 days, and bulk lava viscosities on the order of 106 to 107 Pa s in the main lobes. Sizes and distributions of 1021 mapped pyroclastic rafts suggest that the early stages of the eruption produced much of the total raft volume. The source of most of the raft material was likely the now-missing western portion of an early Marcath cone. After the initial breaching of the cone, the raft production rate likely kept pace with cone building over the eruption's duration such that once the cone was breached on one side, it did not heal. Rafts were not always passive passengers on the lava: they had an important impact on lava morphology in specific locations, as they caused bifurcation of entire flow lobes and produced other flow features. The common occurrence of rafts in monogenetic lava fields suggests that incorporation of raft-lava interactions may be important in lava propagation models. [ABSTRACT FROM AUTHOR]