Central Crater Research Articles

Quantifying the attenuation of structural uplift beneath large lunar craters

Terrestrial crater observations and laboratory experiments demonstrate that target material beneath complex impact craters is uplifted relative to its preimpact position. Current estimates suggest maximum uplift is one tenth of the final crater diameter for terrestrial complex craters and one tenth to one fifth for lunar central peak craters. These latter values are derived from an analytical model constrained by observations from small craters and may not be applicable to larger complex craters and basins. Here, using numerical modeling, we produce a set of relatively simple analytical equations that estimate the maximum amount of structural uplift and quantify the attenuation of uplift with depth beneath large lunar craters.

P-wave velocity and density structure beneath Mt. Vesuvius: a magma body in the upper edifice?

<p>A high-resolution image of the compressional wave velocity and density structure in the shallow edifice of Mount Vesuvius has been derived from simultaneous inversion of travel times and hypocentral parameters of local earthquakes and from gravity inversion. The robustness of the tomography solution has been improved by adding to the earthquake data a set of land based shots, used for constraining the travel time residuals. The results give a high resolution image of the P-wave velocity structure with details down to 300-500 m. The relocated local seismicity appears to extend down to 5 km depth below the central crater, distributed into two clusters, and separated by an anomalously high Vp region positioned at around 1 km depth. A zone with high Vp/Vs ratio in the upper layers is interpreted as produced by the presence of intense fluid circulation alternatively to the interpretation in terms of a small magma chamber inferred by petrologic studies. In this shallower zone the seismicity has the minimum energy, whilst most of the high-energy quakes (up to Magnitude 3.6) occur in the cluster located at greater depth. The seismicity appears to be located along almost vertical cracks, delimited by a high velocity body located along past intrusive body, corresponding to remnants of Mt. Somma. In this framework a gravity data inversion has been performed to study the shallower part of the volcano. Gravity data have been inverted using a method suitable for the application to scattered data in presence of relevant topography based on a discretization of the investigated medium performed by establishing an approximation of the topography by a triangular mesh. The tomography results, the retrieved density distribution, and the pattern of relocated seismicity exclude the presence of significant shallow magma reservoirs close to the central conduit. These should be located at depth higher than that of the base of the hypocenter volume, as evidenced by previous studies.</p>

A global inventory of central pit craters on the Moon: Distribution, morphology, and geometry

The origin of central pit craters on the Moon has long been an enigma, and a primary reason is that their geographic distribution and morphometric characteristics were unknown. We investigated a global inventory of lunar central pit craters using high-resolution image and topography data obtained from the Lunar Reconnaissance Orbiter. 56 certain and 35 probable central pit craters are found on both the lunar maria and highlands. The certain pit craters are ∼9–57km in diameter. The average diameter ratio between the central pits and their parent craters is ∼0.12 and the average depth/diameter ratio for the central pits is ∼0.072. With irregular-shaped rims, the central pits have conical profiles and some have flat floors. The central pits occur on both crater floors and central peaks. The floor pits are generally larger, deeper, and with more irregular shape compared with summit pits. Both the summit and floor pit craters have formed in every lunar stratigraphic epoch from Nectarian to Copernican. Target properties of background terrains affect the morphology and size of central pits, but they do not determine whether or not a central pit forms during a cratering event. The lunar central pits may have formed by deformation of central peaks caused by some mechanical processes during or soon after the cratering process of their parent craters.

A Hemorrhagic-Crusted Papule With a Central Crater on the Heel

A young woman presented with an asymptomatic papule on her right heel that shenoticed2weekspriorwhile traveling inUganda. It initially had a black center that disappeared as the lesion grew. She was able to express purulent material, but the papule failed to resolve.Thepatientdeniedsystemicsymptomsandwasotherwisewell. Physical examination revealed a circular hemorrhagic-crusted papulewith a central crater (Figure, A). The surrounding skin had a slight yellowish discoloration. A shave biopsy was performed with complete excision of the lesion (Figure, B and C). What is your diagnosis?

The geochemistry of thermal waters and fumarolic gases on Shiashkotan I., Kuril Islands

Based on geochemical studies we have updated our knowledge of the generation conditions and discharge of thermal waters on Shiashkotan Island. The thermal springs, which are abundant on the island, are surface expressions of the North Shiashkotan and Kuntomintar hydrothermal systems. The North Shiashkotan hydrothermal system shows the classical hydrochemical zonality. The discharge of the Kuntomintar hydrothermal system is confined within two thermal fields that are situated in the central and northeastern craters of the eponymous volcano. The high temperature of the gases that are issuing from Kuntomintar Volcano to the ground surface and the higher predictive ratios S/Cl, S/C, and CO2/H2 in its composition provide evidence of a possible renewal of its fumarole activity.

Hydrovolcanic tuff rings and cones as indicators for phreatomagmatic explosive eruptions on Mars

AbstractHydrovolcanism is a common natural phenomenon on Earth and should be common on Mars, too, since its surface shows widespread evidence for volcanism and near‐surface water. We investigate fields of pitted cones in the Nephentes/Amenthes region at the southern margin of the ancient impact basin, Utopia, which were previously interpreted as mud volcanoes. The cone fields contain pitted and breached cones with associated outgoing flow‐like landforms. Based on stratigraphic relations, we determined a Hesperian or younger model age. We test the hypothesis of a (hydro)volcanic origin. Based on a detailed morphological and morphometrical analysis and an analysis of the regional context, an igneous volcanic origin of these cones as hydrovolcanic edifices produced by phreatomagmatic eruptions is plausible. Several lines of evidence suggest the existence of subsurface water ice. The pitted cones display well‐developed wide central craters with floor elevations below the preeruptive surface. Their morphometry and the overall appearance are analogous to terrestrial tuff cones and tuff rings. Mounds that are also observed in the same region resemble terrestrial lava domes. The hydrovolcanic interaction between ascending magma and subsurface water and/or water ice may explain the formation of the pitted cones, although other scenarios such as mud volcanism cannot be ruled out. Together with the mounds, the cones might represent effusive and explosive edifices of a monogenetic volcanic field composed of lava domes, tuff rings, tuff cones, and possibly maars.

Reprint of: Impact craters with ejecta flows and central pits on Mercury

Impact craters with ejecta flows and/or central pits have been found on Venus, the Moon, Earth, Mars, and some icy satellites. Using the MESSENGER camera data obtained during the orbital mission, we found craters with ejecta flows and central pits on Mercury. The ejecta flows differ from normal ballistically emplaced ejecta deposits in their long mobilized distances. They all flowed in downslope directions and exhibited a layered morphology. Analog study suggests that the ejecta flows probably have formed by fluidization in the ejecta deposits. Crustal volatiles are not required to form the ejecta flows on Mercury, although they may have helped. The ejecta flows are most likely to be a type of avalanche features in forms of dry granular flows. Central pits in impact craters on Mercury are located on summits of central peaks when viewing in sufficiently high-resolution images, but some of the central pits may occur on crater floors. The central pit craters are all fresh craters located on smooth plains and intercrater plains. The pits are different from the other forms of rimless and irregularly-shaped depressions on Mercury in the size, morphology, and/or occurrence. Crustal volatiles are not required in forming the central pit craters and they may form in a similar way with the central pit craters on the Moon.

3D Digital Terrestrial Model Creation Using Image Assisted Total Station and Rapid Prototyping Technology

This paper presents the integrate procedure for the documentation and fabrication of the 3D Digital Terrestrial Model (DTM) of inaccessible and rough surfaces. The proposed procedure combines the use of modern Image Assisted Total Stations (IATS) with Rapid Prototyping (RP) Technology. The determination of the measurement accuracy, as well as, the a-priori estimation of σo of the surface creation is achieved by using the Monte Carlo technique and the least square method. Also, basic concepts and principles of RP technologies are presented. The application of the procedure was realized at the difficult and inhospitable area of the central crater “Stefanos” on Nisyros Island's Volcano, Greece. The a-priori calculation of the minimum essential scanning step, as well as, the testing use of two IATSs is included. Additionally, the elaboration and the special algorithms used for the actual RP fabrication of the crater's tangible model are illustrated. Finally a scholastic check of the model's reliability is applied.

Chlorine isotope composition of volcanic gases and rocks at Mount Etna (Italy) and inferences on the local mantle source

We present the first chlorine isotope compositional data for gases and lavas from Mount Etna (Italy), and to our knowledge, of active Mediterranean volcanism. We investigated lavas erupted and gases discharged during 2008–2011 from a high-temperature fumarole (HT; >300°C) and plume gases from both North East and Central Craters. Most of the samples vary in a narrow range of chlorine isotope composition (δ37Cl values≈0±0.7‰) with gases partially overlapping with rocks. Only HT gases sampled in 2009 have been clearly affected by secondary processes (δ37Cl values>15.9‰), resulting in partial removal of chlorine and isotopic fractionation producing a 37Cl enrichment in the residual gaseous HCl. These secondary processes also affect, although to a lesser extent, plume gases from North East Crater (NEC). Although post-magmatic processes are able to modify the chlorine isotope composition, δ37Cl values are not affected by magma degassing for residual fractions ≥0.3 in the melt, or any effect is within our data variability. Finally, δ37Cl values and Cl/K ratios of magmatic chlorine constrain the Etnean source to be compatible with depleted mantle (DMM) contaminated by altered oceanic crust (AOC), in agreement with indications from more common isotopic tracers of mantle processes.

Moment tensor inversion for the source location and mechanism of long period (LP) seismic events from 2009 at Turrialba volcano, Costa Rica

Long-period (LP) seismic events were recorded during the temporary installation of a broadband seismic network of 13 stations from March to September 2009 on Turrialba volcano, Costa Rica. Over 6000 LPs were extracted using a modified STA/LTA method and a family consisting of 435 similar LP events has been identified. For the first time at Turrialba volcano, full-waveform moment tensor inversion is performed to jointly determine the location and source mechanism of the events. The LPs in the family are likely to be caused by crack mechanisms dipping towards the southwest at angles of approximately 10 to 20°, located at shallow depths (<800m) below the active Southwest and Central craters. As the locations are so shallow, the most probable causes of crack mechanisms are hydrothermal fluids resonating within or “pulsing” through a crack. The waveforms observed at the summit stations suggest a “pulsing” mechanism, but source resonance with a high degree of damping is also possible.

Impact craters with ejecta flows and central pits on Mercury

Impact craters with ejecta flows and/or central pits have been found on Venus, the Moon, Earth, Mars, and some icy satellites. Using the MESSENGER camera data obtained during the orbital mission, we found craters with ejecta flows and central pits on Mercury. The ejecta flows differ from normal ballistically emplaced ejecta deposits in their long mobilized distances. They all flowed in downslope directions and exhibited a layered morphology. Analog study suggests that the ejecta flows probably have formed by fluidization in the ejecta deposits. Crustal volatiles are not required to form the ejecta flows on Mercury, although they may have helped. The ejecta flows are most likely to be a type of avalanche features in forms of dry granular flows. Central pits in impact craters on Mercury are located on summits of central peaks when viewing in sufficiently high-resolution images, but some of the central pits may occur on crater floors. The central pit craters are all fresh craters located on smooth plains and intercrater plains. The pits are different from the other forms of rimless and irregularly-shaped depressions on Mercury in the size, morphology, and/or occurrence. Crustal volatiles are not required in forming the central pit craters and they may form in a similar way with the central pit craters on the Moon.

Valleys in pit craters on Mars: Characteristics, distribution, and formation mechanisms

New observations of central pit craters on Mars reveal that some craters contain prominent interior valley networks that drain into their central pit. In this study, we catalog the distribution of pit craters with associated valleys, and characterize in detail five diverse, well-preserved examples. In some instances, sedimentary deposits we interpret as either alluvial fans or deltas are found in the central pits, and evidence suggests that at least some of these pits once contained lakes. Fluvial activity within the five pit craters we detail, appears to have occurred relatively late in Mars history, during the Hesperian or Amazonian periods. For this reason, further understanding the formation mechanisms of these valleys has important implications for the history of water on Mars.

English

Abstract Introduction Keratoacanthomas are rapidly growing cutaneous tumours, which usually resolve leaving an atrophic scar. The term ‘giant keratoacan-thoma’ is applied to a lesion greater than 2–3 cm in diameter. This case report discusses squamous cell carci-noma-like giant keratoacanthoma with delayed presentation in a known case of xeroderma pigmentosum. Case report A 50-year-old female patient, a known case of xeroderma pigmen-tosum, presented with a large, dome-shaped, crateriform lesion over her right cheek that had persisted for the last four months. Histological exami-nation showed an exophytic lesion with a large central keratin-filled crater surrounded by deep bulbous nodules of proliferating squamous cells that had abundant keratin with a lip of normal epidermis. The demar-cation was discrete except for tiny foci of deep infiltration at the periphery. However, immunohistochemistry for p53 revealed strong positivity only in the basal layer of the infiltrating islands, weak Ki-67 and desmoglein positivity, along with down regula-tion of Bcl-2 and E-cadherin. Follow-up for 18 months did not reveal any site recurrence or metastasis.

Ries crater and suevite revisited—Observations and modeling Part I: Observations

AbstractWe report results of an interdisciplinary project devoted to the 26 km‐diameter Ries crater and to the genesis of suevite. Recent laboratory analyses of “crater suevite” occurring within the central crater basin and of “outer suevite” on top of the continuous ejecta blanket, as well as data accumulated during the past 50 years, are interpreted within the boundary conditions imposed by a comprehensive new effort to model the crater formation and its ejecta deposits by computer code calculations (Artemieva et al. 2013). The properties of suevite are considered on all scales from megascopic to submicroscopic in the context of its geological setting. In a new approach, we reconstruct the minimum/maximum volumes of all allochthonous impact formations (108/116 km3), of suevite (14/22 km3), and the total volume of impact melt (4.9/8.0 km3) produced by the Ries impact event prior to erosion. These volumes are reasonably compatible with corresponding values obtained by numerical modeling. Taking all data on modal composition, texture, chemistry, and shock metamorphism of suevite, and the results of modeling into account, we arrive at a new empirical model implying five main consecutive phases of crater formation and ejecta emplacement. Numerical modeling indicates that only a very small fraction of suevite can be derived from the “primary ejecta plume,” which is possibly represented by the fine‐grained basal layer of outer suevite. The main mass of suevite was deposited from a “secondary plume” induced by an explosive reaction (“fuel‐coolant interaction”) of impact melt with water and volatile‐rich sedimentary rocks within a clast‐laden temporary melt pool. Both melt pool and plume appear to be heterogeneous in space and time. Outer suevite appears to be derived from an early formed, melt‐rich and clast‐poor plume region rich in strongly shocked components (melt ≫ clasts) and originating from an upper, more marginal zone of the melt pool. Crater suevite is obviously deposited from later formed, clast‐rich and melt‐poor plumes dominated by unshocked and weakly shocked clasts and derived from a deeper, central zone of the melt pool. Genetically, we distinguish between “primary suevite” which includes dike suevite, the lower sublayer of crater suevite, and possibly a basal layer of outer suevite, and “secondary suevite” represented by the massive upper sublayer of crater suevite and the main mass of outer suevite.

Chemical and ecological evolution of the Miocene Ries impact crater lake, Germany: A reinterpretation based on the Enkingen (SUBO 18) drill core

Scientific drilling conducted at the inner slope of the Miocene central Ries impact crater recovered a partial section of crater lake sediments. Four sequences were recovered, composed of suevite-derived sandstones, thin lignite seams, bituminous shales, and marlstones to claystones. These flooding-evaporation sequences reflect the impact of short-term climatic fluctuations on a hydrologically closed basin. The superimposed trend from sequences rich in bituminous shales in the lower parts of the section to sequences dominated by organic-poor claystones and intercalated lignites in the upper parts of the section resembles that of the 300-m-thick central crater basin succession, which has previously been considered to reflect a climate-controlled development from an alkaline saline lake to a freshwater lake with temporary coal swamps. In the sediment core of Enkingen, however, the change from bituminous shales to organic-poor claystones with intercalated lignites is associated with a general increase in salinity, as indicated by (1) palynomorphs, (2) increase in δ13C of the lipid biomarker archaeol (bis-O-phytanylglycerol), and (3) the occurrence of 13C-enriched C20/C25-archaeol (O-phytanyl-O-sesterterpanylglycerol) specific to halophilic Archaea. In addition, the unidirectional trend in 87Sr/86Sr of carbonates, declining from ratios of Variscan basement rocks toward marine ratios, indicates a change from (1) weathering of crystalline rocks and suevite to (2) ejected Jurassic sediments (Bunte Breccia) in the catchment area as the major source of ion influx to the lake. From that trend, a change in lake water composition and a general increase in ion concentrations are inferred. These new results can be applied to a reassessment of major parts of the lacustrine succession of the Ries crater. We use these data to propose a new hypothetical model for the chemical and ecological evolution of the Ries crater lake: (1) After the establishment of a stratified brackish eutrophic soda lake due to silicate weathering and evaporation, the increasing influx of waters from the Bunte Breccia carbonate and authigenic silicate precipitation led to a mesotrophic halite lake with marine-like ion ratios and concentrations. (2) Further increase in ions, among them Mg2+ and Sr2+, resulted in hypersaline conditions with gypsum precipitation, low primary production, and phreatic Sr-rich dolomitization in marginal carbonates. (3) The final, sudden change to oligotrophic freshwater conditions is explained by the formation of an outlet late in the lake history. We conclude that the chemical and ecological evolution of the Ries lake therefore appears to have been mainly controlled by the weathering history of the catchment area, with climate fluctuations causing superimposed cycles. Similarly, changes in terrestrial palynomorph associations may at least partly reflect a change in soil types in the catchment area, from fertile, moist soils on suevite to dry karst soils and soils on Bunte Breccia. These interpretations imply that the initial suevite blanket of the Ries crater was much more continuous and widespread than previously assumed.

Keratoacanthoma and other types of squamous cell carcinoma with crateriform architecture: Classification and identification

The terminology and classification of keratoacanthoma (KA) and other types of squamous cell carcinoma (SCC) with crateriform architecture have not been clarified. The study evaluated the clinicopathological features of 41 nodular (exo-endophytic) SCC lesions with a central keratin-filled crater, including KA (well-developed stage). The lesions were histopathologically classified into six categories: (i) KA (well-developed stage) (27 lesions); (ii) KA-like SCC (three lesions); (iii) KA with malignant transformation (three lesions); (iv) infundibular SCC (crateriform) (four lesions); (v) crateriform SCC arisen from actinic keratosis (three lesions); and (vi) crateriform Bowen's disease (one lesion). The true characteristics of KA-like SCC remain unresolved, but there are three possibilities, namely, that it is one step in the evolution of KA, it is a borderline lesion between KA and invasive SCC, or it is one form of "KA with malignant transformation". KA, KA-like SCC, KA with malignant transformation and infundibular SCC (crater form) are considered to be hair follicle-related neoplasms. In contrast, crateriform SCC arisen from actinic keratosis and crateriform Bowen's disease are SCC, which are not related either to the hair follicles or KA. From an etiological standpoint, the presented lesions in these six categories are considered to be mixed up due to the similarity of crateriform architecture between the various types of lesions. However, the information provided in this report is intended to help physicians to make an accurate differential diagnosis of these conditions in clinical practice. The present study provides an opportunity to standardize the terminology for KA and related neoplasms.

Multiple keratoacanthomas developing in healing plaques of Psoriasis

A 22 year old male psoriatic patient presented with multiple reddish scaly plaques all over body. After hematological and biochemical investigations the patient was started on oral methotrexate 15 mg weekly. PASI score at the start of treatment was 26.2. After 3 months PASI dropped to 11.5, the dose of methotrexate was tapered to 7.5mg weekly and the patient was maintained on this dose and kept under monthly follow up. Four months later, the patient presented with reddish to hyperpigmented raised firm nodules having a central crater over the healing plaques of psoriasis. Few lesions showed self resolution over a period of 6-12 weeks. Histopathology of the lesion confirmed it to be Keratoacanthoma. We believe the most likely etiologic factors for the multiple KAs in our patient could be a genetic susceptibility stimulated by multiple causes.

The theoretical plausibility of central pit crater formation via melt drainage

Central pit craters are seen in large craters on some icy satellites and on Mars. We investigate the hypothesis that central pits form when impact melt drains into fractures beneath the impact crater. For this process to occur, the volume of melt generated during the impact, the volume of void space in fractures beneath the impact crater, and the volume of melt able to drain before the fractures freeze shut all must exceed the volume of the observed central pits. We estimate the volume of melt generated using results from previous numerical modeling studies. The fracture volume is estimated using gravity anomalies over terrestrial craters. To estimate the amount of melt able to drain before freezing, we consider flow through plane parallel fractures. These calculations all suggest that enough liquid water could drain into fractured ice beneath a crater on Ganymede to form a central pit. On Earth and the Moon, silicate impact melt will freeze before a large volume is able to drain, so we do not expect to see central pits in impact craters in targets with no ice. In summary, we find our calculations are consistent with observed central pits in craters on Ganymede and the lack of central pits in craters on Earth and the Moon.

New insights into volcanic processes at Stromboli from Cerberus, a remote-controlled open-path FTIR scanner system

The ordinary, low intensity activity of Stromboli volcano is sporadically interrupted by more energetic events termed, depending on their intensity, “major explosions” and “paroxysms”. These short-lived energetic episodes represent a potential risk to visitors to the highly accessible summit of Stromboli. Observations made at Stromboli over the last decade have shown that the composition of gas emitted from the summit craters may change prior to such explosions, allowing the possibility that such changes may be used to forecast these potentially dangerous events.In 2008 we installed a novel, remote-controlled, open-path FTIR scanning system called Cerberus at the summit of Stromboli, with the objective of measuring gas compositions from individual vents within the summit crater terrace of the volcano with high temporal resolution and for extended periods. In this work we report the first results from the Cerberus system, collected in August–September 2009, November 2009 and May–June 2010.We find significant, fairly consistent intra-crater variability for CO2/SO2 and H2O/CO2 ratios, and relatively homogeneous SO2/HCl ratios. In general, the southwest crater is richest in CO2, and the northeast crater poorest, while the central crater is richest in H2O. It thus appears that during the measurement period the southwest crater had somewhat more direct connection to a primary, deep degassing system while the central and northeast craters reflect a slightly more secondary degassing nature, with a supplementary, shallow H2O source for the central crater, probably related to puffing activity. Such water-rich emissions from the central crater can account for the lower crystal content of its eruption products, and emphasise the role of continual magma supply to the shallowest levels of Stromboli's plumbing system.Our observations of heterogeneous crater gas emissions and high H2O/CO2 ratios do not agree with models of CO2-flushing, and we show that simple depressurisation during magma ascent to the surface is a more likely model for H2O loss at Stromboli. We highlight that alternative explanations other than CO2 flushing are required to explain distributions of H2O and CO2 amounts dissolved in melt inclusions.We detected fairly systematic increases in CO2/SO2 ratio some weeks prior to major explosions, and some evidence of a decrease in this ratio in the days immediately preceding the explosions, with periods of low, stable CO2/SO2 ratios between explosions otherwise. Our measurements, therefore, confirm the medium term (~weeks) precursory increases previously observed with MultiGas instruments, and, in addition, reveal new short-term precursory decreases in CO2/SO2 ratios immediately prior to the major explosions. Such patterns, if shown to be systematic, may be of great utility for hazard management at Stromboli's summit.Our results suggest that intra-crater CO2/SO2 variability may produce short-term peaks and troughs in CO2/SO2 time series measured with in-situ MultiGas instruments, due simply to variations in wind direction.

Crater-and-split technique for phacoemulsification: Modification of the crater-and-chop technique

We describe a modification of the crater-and-chop technique for removing cataracts of all densities. Following creation of a central crater approximately 3.0 mm in diameter at the geometric center of the endonucleus, a nucleus splitter is inserted under the capsule and the phaco tip is inserted in the crater. Simultaneously, the splitter is moved from the nucleus periphery toward the phaco tip horizontally to split the nucleus and both the phaco tip and nucleus splitter are pushed aside as they come very close without vacuum at any point. The nucleus is rotated and splitting is repeated in the same manner until the nucleus is divided into pieces that are small enough to be emulsified easily. With this technique, the soft nucleus is split without vacuum and a very hard nucleus can be split through the posterior plate with minimal stress to zonular fibers.