Central Crater Research Articles

Three‐dimensional joint inversion of traveltime and gravity data across the Chicxulub impact crater

In 2005 an extensive new seismic refraction data set was acquired over the central part of the Chicxulub impact crater, allowing us to image its structure with much better resolution than before. However, models derived from traveltime data are limited by the available ray coverage and the nonuniqueness that is inherent to all geophysical methods. Therefore, many different models can fit the data equally well. To address these issues, we have developed a new method to simultaneously invert traveltime and gravity data to obtain an integrated model. To convert velocity to density, we use a linear relationship derived from measurements on core from the Chicxulub impact basin, thus providing a reliable conversion equation that is typical for lithologies of the central part of this crater. Prior to utilizing the inversion on the observed data, we have run a suite of tests to establish the optimum weighting between traveltime and gravity constraints, using a synthetic model of central crater structure and the real experimental geometry. These synthetic tests indicate which inversion parameters lead to the best recovery of subsurface structure, as well as which parts of the model are well resolved. We applied the method to all existing gravity data and to seismic refraction data acquired in 1996 and the new, higher‐resolution seismic refraction data acquired in 2005. We favor the traveltime model wherever we have sufficient ray coverage and the joint model where we have no ray coverage.

The effect of target properties on crater morphology: Comparison of central peak craters on the Moon and Ganymede

Abstract— We examine the morphology of central peak craters on the Moon and Ganymede in order to investigate differences in the near‐surface properties of these bodies. We have extracted topographic profiles across craters on Ganymede using Galileo images, and use these data to compile scaling trends. Comparisons between lunar and Ganymede craters show that crater depth, wall slope and amount of central uplift are all affected by material properties. We observe no major differences between similar‐sized craters in the dark and bright terrain of Ganymede, suggesting that dark terrain does not contain enough silicate material to significantly increase the strength of the surface ice. Below crater diameters of ˜12 km, central peak craters on Ganymede and simple craters on the Moon have similar rim heights, indicating comparable amounts of rim collapse. This suggests that the formation of central peaks at smaller crater diameters on Ganymede than the Moon is dominated by enhanced central floor uplift rather than rim collapse. Crater wall slope trends are similar on the Moon and Ganymede, indicating that there is a similar trend in material weakening with increasing crater size, and possibly that the mechanism of weakening during impact is analogous in icy and rocky targets. We have run a suite of numerical models to simulate the formation of central peak craters on Ganymede and the Moon. Our modeling shows that the same styles of strength model can be applied to ice and rock, and that the strength model parameters do not differ significantly between materials.

Volcano Ulcers in Stomach – an Unusual Presentation of Metastatic Non Pigmented Melanoma

Purpose: Malignant melanoma is one of the most common malignancies to metastasize to the gastrointestinal (GI) tract. Metastases to GI tract can present at time of primary diagnosis or decades later as first sign of recurrence. Metastatic melanoma to GI tract is found during diagnostic workup in 1%-4% of patients with cutaneous primary and up to 60% of melanoma patients in autopsy. Methods: Our patient is a 45 year old white male with history of primary non-pigmented urinary bladder melanoma who presented with complaint of dyspepsia for 2 months. Patient had received full course of chemotherapy with Tamodar for 5 months with good response. He denied any nausea, vomiting, dysphagia or bleeding. He had no primary skin lesion found on extensive detailed physical exam. Whole body PET scan showed markedly thickened stomach walls with multiple omental lesions in the perigastric region. Upper endoscopy revealed two large, non-pigmented ulcerating masses in body of stomach on the greater curvature. These masses had “volcano appearance” with heaped up edges and central crater. Multiple biopsies were taken which were consistent with non pigmented metastatic melanoma confirmed by immunohistochemical stains. Patient was subsequently started on carboplatin and has had mild improvement in symptoms. Results: Conclusion: Gastrointestinal invasion by melanoma is a rare condition and is often associated with invasion of other visceral organs. The endoscopic classification of the gastric metastases comprises three main types: (a) melanotic nodules, often ulcerated at the tip; most common (b) submucosal mass, melanotic or not, elevated and ulcerated at apex; typical aspect of “bull's eye” lesion and (c) mass lesions with varying incidence of necrosis and melanosis. Gastric metastases may appear even as a simple ulcer. Majority of gastric metastases are reported to occur in body and fundus, most often on the greater curvature. Most frequent sites of melanoma metastases include small bowel, stomach, colon, and anorectum in decreasing order. Symptoms may include abdominal pain, dysphagia, small bowel obstruction and GI bleed. Diagnosis requires careful inspection of mucosa and biopsy with special immunohistochemical stains. Management may include surgical resection, chemotherapy, immunotherapy, observation, or enrollment in clinical trials. Surgery seems to be of limited value and should be performed in carefully selected patients and in patients with complications. Prognosis is poor, with median survival time in patients presenting with GI invasion being less than 1 year. Endoscopic “Volcano ulcers” in the stomach have been reported in many secondary neoplasms of the stomach and their presence should always raise suspicion for an underlying malignancy.

Hazard map of El Chichón volcano, Chiapas, México: Constraints posed by eruptive history and computer simulations

El Chichón volcano consists of a 2-km wide Somma crater compound cone 0.2 Ma old with peripheral domes with a central crater reactivated several times during the Holocene. The most recent eruption at El Chichón occurred from March 28 to April 4, 1982, resulting in the worst volcanic disaster during historical times in Mexico, killing more than 2000 people and destroying nine towns and small communities. The volcanic hazard map of El Chichón is based on detailed field work that documented twelve eruptions during the last 8000 years, and computer simulations. To validate the results, computer simulations were first performed over pre-1982 topography mimicking the extent of the actual deposits produced and afterwards run over post-1982 topography. These eruptions have produced pyroclastic fall, surge, flow and lahar deposits. Pyroclastic flows have different volumes and Heim coefficients varying from 0.2 (pumice flows), to 0.15 (block-and-ash flows) and 0.10 (ash flows). Simulations using FLOW3D and TITAN2D indicate that pumice flows and block-and-ash flows can fill the moat area and follow main ravines up to distances of ca. 3 km from the crater, with no effect on populations around the volcano. On the other hand, more mobile ash flows related to column-collapse events can reach up to 4 km from the vent, but will always follow the same paths and still not affect surrounding populations. The energy-cone model was used to simulate the outflow of pyroclastic surges based on the 1982 event ( H/ L = 0.1 and 0.2), and shows that surges may reach some towns around the volcano. Explosive activity also produced Plinian columns higher than 27 km that were dispersed towards the NE by prevailing winds. Future fallout will seriously disturb the lives of more than 70,000 inhabitants of cities and towns located in a radius of 35 km from the volcano. Lahar events in the past originated from unconsolidated pyroclastic deposits with volumes varying from 1 to 4 × 10 6 m 3 for single pulses, to a large one from dam-breakout with a volume of 40 × 10 6 m 3. We used the LAHARZ code to model future events with volumes of 1, 2, and 3 × 10 6 m 3 that will reach as far as 10, 14, and 16 km from the crater, posing some danger to the communities of Nicapa, Volcán, and Ostuacán, even some time after the climax of the eruption.

Performance and scientific objectives of the SELENE (KAGUYA) Multiband Imager

Abstract The Multiband Imager (MI) is one of the 14 instruments for the Japanese SELENE (KAGUYA) mission. Goal of the SELENE (KAGUYA) mission is to understand origin and evolution of the Moon by obtaining global element and mineral compositions, topological structure, gravity field of the whole Moon, and electromagnetic and particle environment of the Moon. MI is designed to be a high-resolution multiband imaging camera with a spatial resolution in visible bands of 20 m and a spatial resolution in near-infrared bands of 62 m from the 100 km SELENE (KAGUYA) orbit altitude. The MI flight model has been manufactured and integrated. MTF, viewing vector, over-all sensibility, sensor linearity and electrical noise level (S/N estimation test) were measured, and the results indicate that the MI will provide sufficient MTF and low-noise data, just as estimated in the MI design phase. Operation and data analyses plans have been established, and related tools and algorithms have been developed and checked. One of MI scientific objectives is to investigate small but scientifically very important areas such as crater central peaks and crater walls and to investigate magnesian anorthosites.

Keratoacanthoma centrifugum marginatum: a rare atypical variant of keratoacanthoma

Keratoacanthoma centrifugum marginatum (KCM) is an extremely rare variant of keratoacanthoma (KA), with about 30 cases reported since it was first described in 1962. Clinically, KA is an exoendophytic lesion of 10-25 mm with a horn-filled crater that resolves spontaneously within 6 months. In contrast, KCM is characterized by a larger diameter continuous centrifugal spread, concurrent central atrophy and lack of spontaneous remission. Histologically, KCM is similar to KA, with a central keratin-filled crater, overhanging lips of epithelium, a sharp outline between the tumour nests and stroma, and lack of anaplasia and stroma desmoplasia. We describe a 63-year-old agricultural worker with a 9-month history of a multinodular tumour, 70-75 mm in size, on his right hand. The clinical diagnosis of KCM was confirmed by histological examination. Local radiotherapy proved effective, with no recurrence during a 4-year follow-up.

Spatial mapping of the b value at Mount Etna, Italy, using earthquake data recorded from 1999 to 2005

The spatial pattern of the b value of the frequency‐magnitude relation has been analyzed using gridding techniques beneath Mount Etna, Italy. A regional data set of 2900 events with Md (duration magnitude) ≥1.5 up to 15 km depth occurring between August 1999 and December 2005 has been used. Two regions with an abnormally high b value have been found, one centered beneath the southern part of the Valle del Bove, above the 6 km below sea level (bsl) deep basement, and the other beneath the summit region 2 km bsl east of the Central Craters. We can infer that these high b value anomalies are regions of increased crack density, and/or high pore pressure, related to the presence of nearby magma storage. This interpretation is supported by all the available geophysical evidence, such as tomographic studies and geodetic deformation measurements. The data set has also been subdivided into five periods, corresponding to different phases of volcanic activity: 2001 preeruption, 2001 eruptive, 2002–2003 preeruption, 2002–2003 eruptive, and 2002–2003 posteruption. The minimum magnitude of completeness, Mc, and the b value were computed for each period. A volume of anomalously high b values can be observed in each of these periods (except for the 2002–2003 preeruption interval). This approach has allowed the detection of the transient presence of magmatic intrusions during the various periods evaluated.

Coupled effects of impact and orogeny: Is the marine Lockne crater, Sweden, pristine?

Abstract— Our current understanding of marine‐impact cratering processes is partly inferred from the geological structure of the Lockne crater. We present results of a mapping campaign and structural data indicating that this crater is not pristine. In the western part of the crater, pre‐impact, impact, and post‐impact rocks are incorporated in Caledonian thrust slices and are subjected to folding and faulting. A nappe outlier in the central crater depression is a relic of the Caledonian nappe cover that reached a thickness of more than 5 km. The overthrusted crater is gently deformed. Strike of strata and trend of fold axes deviate from standard Caledonian directions (northeast‐southwest). Radially oriented crater depressions, which were previously regarded as marine resurge gullies formed when resurging seawater erosively cut through the crater brim, are interpreted to be open synclines in which resurge deposits were better preserved.The presence of the impact structure influenced orogenesis due to morphological and lithological anomalies of the crater: i) a raised crater brim zone acted as an obstacle during nappe propagation, (ii) the occurrence of a central crater depression caused downward sagging of nappes, and (iii) the lack of an appropriate detachment horizon (alum shale) within the crater led to an enhanced mechanical coupling and internal deformation of the nappe and the overthrusted foreland. Preliminary results of 3‐D‐analogue experiments suggest that a circular high‐friction zone representing the crater locally hinders nappe propagation and initiates a circumferentially striking ramp fault that delineates the crater. Crustal shortening is also partitioned into the crater basement and decreases laterally outward. Deformation of the foreland affected the geometry of the detachment and could be associated with the activation of a deeper detachment horizon beneath the crater. Strain gradients both vertically and horizontally result in non‐plane strain deformation in the vicinity of the crater. The strain tensors in the hanging and foot walls may deviate up to 90° from each other and rotated by up to 45° with respect to the standard regional orientation. The observed deflection of strata and fold axes within the Lockne crater area as revealed by field mapping is in agreement with the pattern of strain partitioning shown in the analogue models.

January 2002 volcano‐tectonic eruption of Nyiragongo volcano, Democratic Republic of Congo

In January 2002, Nyiragongo volcano erupted 14–34 × 106 m3 of lava from fractures on its southern flanks. The nearby city of Goma was inundated by two lava flows, which caused substantial socioeconomic disruption and forced the mass exodus of the population, leaving nearly 120,000 people homeless. Field observations showed marked differences between the lava erupted from the northern portion of the fracture system and that later erupted from the southern part. These observations are confirmed by new 238U and 232Th series radioactive disequilibria data, which show the presence of three different phases during the eruption. The lavas first erupted (T1) were probably supplied by a residual magma batch from the lava lake activity during 1994–1995. These lavas were followed by a fresh batch erupted from fissure vents as well as later (May–June 2002) from the central crater (T2). Both lava batches reached the surface via the volcano's central plumbing system, even though a separate flank reservoir may also have been involved in addition to the main reservoir. The final phase (T3) is related to an independent magmatic reservoir located much closer (or even beneath) the city of Goma. Data from the January 2002 eruption, and for similar activity in January 1977, suggest that the eruptive style of the volcano is likely to change in the future, trending toward more common occurrence of flank eruptions. If so, this would pose a significant escalation of volcanic hazards facing Goma and environs, thus requiring the implementation of different volcano‐monitoring strategies to better anticipate where and when future eruptions might take place.

The topography of Iapetus' leading side

We have used Cassini stereo images to study the topography of Iapetus' leading side. A terrain model derived at resolutions of 4–8 km reveals that Iapetus has substantial topography with heights in the range of −10 km to +13 km, much more than observed on the other middle-sized satellites of Saturn so far. Most of the topography is older than 4 Ga [Neukum, G., Wagner, R., Denk, T., Porco, C.C., 2005. Lunar Planet. Sci. XXXVI. Abstract 2034] which implies that Iapetus must have had a thick lithosphere early in its history to support this topography. Models of lithospheric deflection by topographic loads provide an estimate of the required elastic thickness in the range of 50–100 km. Iapetus' prominent equatorial ridge [Porco, C.C., and 34 colleagues, 2005. Science 307, 1237–1242] reaches widths of 70 km and heights of up to 13 km from their base within the modeled area. The morphology of the ridge suggests an endogenous origin rather than a formation by collisional accretion of a ring remnant [Ip, W.-H., 2006. Geophys. Res. Lett. 33, doi: 10.1029/2005GL025386. L16203]. The transition from simple to complex central peak craters on Iapetus occurs at diameters of 11 ± 3 km . The central peaks have pronounced conical shapes with flanking slopes of typically 11° and heights that can rise above the surrounding plains. Crater depths seem to be systematically lower on Iapetus than on similarly sized Rhea, which if true, may be related to more pronounced crater-wall slumping (which widens the craters) on Iapetus than on Rhea. There are seven large impact basins with complex morphologies including central peak massifs and terraced walls, the largest one reaches 800 km in diameter and has rim topography of up to 10 km. Generally, no rings are observed with the basins consistent with a thick lithosphere but still thin enough to allow for viscous relaxation of the basin floors, which is inferred from crater depth-to-diameter measurements. In particular, a 400-km basin shows up-domed floor topography which is suggestive of viscous relaxation. A model of complex crater formation with a viscoplastic (Bingham) rheology [Melosh, H.J., 1989. Impact Cratering. Oxford Univ. Press, New York] of the impact-shocked icy material provides an estimate of the effective cohesion/viscosity at 0.04 ± 0.01 MPa/ 0.6 ± 0.2 GPa s . The local distribution of bright and dark material on the surface of Iapetus is largely controlled by topography and consistent with the dark material being a sublimation lag deposit originating from a bright icy substrate mixed with the dark components, but frost deposits are possible as well.

Scientific objectives and specification of the SELENE Multiband Imager

The Lunar Imager/SpectroMeter (LISM) is an instrument being developed for onboarding the SELENE satellite that will be launched in 2007. The LISM consists of the three subsystems: Terrain Camera (TC), Multiband Imager (MI), and Spectral Profiler (SP). The MI is a high-resolution multiband imaging camera consisting of two visible and near infrared sensors. It takes push-broom imaging data by using selected lines of area arrays. The spectral band assignments are 415, 750, 900, 950 and 1000 nm for visible and 1000, 1050, 1250 and 1550 nm for near infrared. The spatial resolution of visible bands is 20 m, and that of near infrared bands is 62 m from the 100 km SELENE orbital altitude. We will observe globally the mineral distribution of the lunar surface in nine band images of MI. Its high spatial resolution will also enable us to investigate small but scientifically very important areas such as crater central peaks and crater walls. The advantage of MI for this aspect is that we can remove topographic effect, which causes false reflectance values seen in the crater wall and crater central peak, by photometric correction with detailed topography. Measurements of MTF, viewing vector, sensor linearity, and stray light and electrical noise level were carried out after the MI integration. Measured data indicate that MI will provide sufficient MTF, low noise and low stray light of spectral imaging data just as estimated in the MI designing phase.

Keratoacanthoma developing on nevus sebaceous in a child

To the Editor: A 12-year-old Japanese boy had a 1-month history of a dome-shaped nodule on his left cheek. Several brown papules had been present on his cheek since birth (Fig 1, A). Physical examination revealed a well-demarcated, pink, dome-shaped nodule with a central keratinous crater on his left cheek sized 12 × 11 mm, and several brown papules distributed on his left cheek with a linear configuration adjacent to the dome-shaped nodule (Fig 1, B).

Multiple keratoacanthomas in a young woman: report of a case emphasizing medical management and a review of the spectrum of multiple keratoacanthomas

A 27-year-old white woman was referred for consultation with regard to the presence of extensive multiple keratotic lesions. She began to develop these lesions at the age of 9 years, with healing of the lesions resulting in scar formation. A biopsy was performed at the age of 16 years, but the patient was unsure of the results. Since then, she had not had any treatment or biopsies, and stated that she had not suffered from any health problems during the intervening period. She was most concerned about the tumors on her heels and soles, which caused difficulty with ambulation. The family history was negative for skin diseases, including melanoma, nonmelanoma skin cancer, psoriasis, and eczema, and positive for Type II diabetes mellitus. A relative reported that the patient's grandfather had similar lesions, but the patient's parents and siblings were healthy. She was married and had one child, a 9-year-old daughter. Her child had no skin lesions. The patient's only medication was Ortho-Tricyclene birth control pills. She had no known drug allergies. Physical examination revealed the presence of multiple lesions on her body (Fig. 1). Her left superior helix contained a well-demarcated, dome-shaped nodule with a rolled, mildly erythematous border with a central hyperkeratotic plug. A similar lesion was present in the scaphoid fossa of the left ear and smaller lesions were scattered on her face. Numerous lesions were present on the arms and legs bilaterally, with the majority of lesions being located on the anterior lower legs. There were also lesions present on the palms and soles. The lesions ranged in size from 5 mm to 3 cm, the largest being a verrucous exophytic nodule on the anterior aspect of her left leg. Overall, there appeared to be two distinct types of lesion. One type appeared round, oval, and symmetric with a central keratotic plug, similar to that on the ear. The other type was larger, more exophytic, and verrucous, including the lesions on the volar surfaces. Also present were numerous, irregularly shaped atrophic scars where previous lesions had healed spontaneously. There were no oral lesions or lesions on her fingernails or toenails, and her teeth and hair were normal. A biopsy was obtained from an early lesion on the right dorsal forearm. Histology revealed an exo-/endophytic growth having a central crater containing keratinous material (Fig. 2). The crater was surrounded by markedly hyperplastic squamous epithelium with large squamous epithelial cells having abundant glassy cytoplasm. Some cells were dyskeratotic. Within the dermis was a dense, chiefly mononuclear inflammatory infiltrate. A buttress of epidermis surrounded the crater. The clinical and pathologic data were consistent with keratoacanthomas. Initial laboratory screenings revealed elevated triglycerides and total cholesterol, 537 mg/dL (normal, < 150 mg/dL) and 225 mg/dL (normal, < 200 mg/dL), respectively, with all other laboratory results within normal limits. In anticipation of starting oral retinoid therapy for her multiple keratoacanthomas, she was referred to her primary care physician for control of hyperlipidemia. After her lipids had been controlled, she was placed on isotretinoin (Accutane) 40 mg/day. There was some interval improvement with regression of some lesions leaving atrophic scars. She was also started on topical application of tazarotene (Tazorac) for all nonresolving lesions. Possible side-effects from the isotretinoin occurred, including dry mouth and eyes. After 8 months of isotretinoin, the patient was switched to acitretin (Soriatane) 25 mg to determine whether it might have a more beneficial effect on the resistant lesions. Many of the larger lesions regressed leaving atrophic scars. The dose of acitretin was subsequently increased to 35 mg because the lesions on her heel and the ball of her foot persisted. Almost all of the lesions resolved, except those on her feet, which are slowly regressing. Currently, the patient is on a regimen of acitretin 25 mg once a day with tazarotene 0.1% gel applied directly to the few residual keratoacanthomas on her feet, which are slowly improving.

Keratoacanthomas associated with sorafenib therapy

Sorafenib inhibits several tyrosine and serine/threonine kinases (vascular endothelial growth factor (VEGF) receptor 2 and 3, platelet derived growth factor (PDGF) receptor B-Raf, Raf-1, Flt3, c-kit, β, and RET).2,3 Common sorafenib toxicities include diarrhea, hypertension, fatigue, and cutaneous lesions (facial and scalp erythema, focal acral erythema/acral erythrodysesthesia/hand-foot syndrome, alopecia, and splinter hemorrhages).

Volcanic processes as alternative mechanisms of landform development at a candidate crater‐lake site near Tyrrhena Patera, Mars

Palos crater, a prominent candidate crater‐lake site in the Hesperia region of Mars, is located at the mouth of a sinuous inlet channel that extends from the northern flanks of Tyrrhena Patera. Previous studies of this site have concluded that channels and basin‐infill units likely formed through aqueous processes that partly involved karst‐like removal of materials in the subsurface by the flow of groundwater. As with many locales on Mars, the aqueous processes hypothesized to have been involved in the formation and evolution of terrain features are compelling. However, the characteristics of this site suggest that an alternative set of mechanisms for landform development should be considered alongside aqueous hypotheses. The main attributes of channels and infill of the central crater include: (1) an association with a very large volcanic rise to the south; (2) the existence of roofed segments of the main inlet channel; and (3) infill of the central crater and outlet channel by materials that have characteristics consistent with those expected of volcanic plains. These general attributes are consistent with formation through or in association with processes that involved the flow of lava. Although a volcanic model may account for the presence and basic nature of landforms previously considered supportive of a paleolake interpretation of the site, an overprint of dendritic valley networks on parts of the inlet system suggests that aqueous processes may have also acted in the evolution of the site. A complex interrelation between past igneous and aqueous processes at this site is possible.

Chesapeake Bay impact structure: Morphology, crater fill, and relevance for impact structures on Mars

Abstract— The late Eocene Chesapeake Bay impact structure (CBIS) on the Atlantic margin of Virginia is one of the largest and best‐preserved “wet‐target” craters on Earth. It provides an accessible analog for studying impact processes in layered and wet targets on volatile‐rich planets. The CBIS formed in a layered target of water, weak clastic sediments, and hard crystalline rock. The buried structure consists of a deep, filled central crater, 38 km in width, surrounded by a shallower brim known as the annular trough. The annular trough formed partly by collapse of weak sediments, which expanded the structure to ˜85 km in diameter. Such extensive collapse, in addition to excavation processes, can explain the “inverted sombrero” morphology observed at some craters in layered targets.The distribution of crater‐fill materials in the CBIS is related to the morphology. Suevitic breccia, including pre‐resurge fallback deposits, is found in the central crater. Impact‐modified sediments, formed by fluidization and collapse of water‐saturated sand and silt‐clay, occur in the annular trough. Allogenic sediment‐clast breccia, interpreted as ocean‐resurge deposits, overlies the other impactites and covers the entire crater beneath a blanket of postimpact sediments.The formation of chaotic terrains on Mars is attributed to collapse due to the release of volatiles from thick layered deposits. Some flat‐floored rimless depressions with chaotic infill in these terrains are impact craters that expanded by collapse farther than expected for similar‐sized complex craters in solid targets. Studies of crater materials in the CBIS provide insights into processes of crater expansion on Mars and their links to volatiles.

Interferon-α Treatment of Molluscum Contagiosum in a Patient With Hyperimmunoglobulin E Syndrome

We report widely disseminated molluscum contagiosum that occurred in a 9-year-old boy secondary to hyperimmunoglobulin E syndrome, a primary immunodeficiency disorder. Cutaneous examination revealed numerous,widespread, skin-colored to translucent, firm, umbilicated papules of varying sizes. They were distributed throughout the perineal and gluteal areas and bilaterally over his lower limbs. A biopsy specimen from his skin lesion demonstrated lobulated epidermal growth that consisted of keratinocytes with large intracytoplasmic eosinophilic inclusion bodies and a central crater. These findings were consistent with the diagnosis of molluscum contagiosum. Many treatments for his skin lesions were ineffective, including physical destruction or manual extrusion of the lesions; cryotherapy; curettage; and topical therapies with phenol, trichloroacetic acid, and imiquimod. The patient was treated successfully with subcutaneous interferon-α for 6 months without any adverse effect.

Silicic lava dome growth in the 1934–1935 Showa Iwo-jima eruption, Kikai caldera, south of Kyushu, Japan

The 1934–1935 Showa Iwo-jima eruption started with a silicic lava extrusion onto the floor of the submarine Kikai caldera and ceased with the emergence of a lava dome. The central part of the emergent dome consists of lower microcrystalline rhyolite, grading upward into finely vesicular lava, overlain by coarsely vesicular lava with pumice breccia at the top. The lava surface is folded, and folds become tighter toward the marginal part of the dome. The dome margin is characterized by two zones: a fracture zone and a breccia zone. The fracture zone is composed of alternating layers of massive lava and welded oxidized breccia. The breccia zone is the outermost part of the dome, and consists of glassy breccia interpreted to be hyaloclastite. The lava dome contains lava with two slightly different chemical compositions; the marginal part being more dacitic and the central part more rhyolitic. The fold geometry and chemical compositions indicate that the marginal dacite had a slightly higher temperature, lower viscosity, and lower yield stress than the central rhyolite. The high-temperature dacite lava began to effuse in the earlier stage from the central crater. The front of the dome came in contact with seawater and formed hyaloclastite. During the later stage, low-temperature rhyolite lava effused subaerially. As lava was injected into the growing dome, the fracture zone was produced by successive fracturing, ramping, and brecciation of the moving dome front. In the marginal part, hyaloclastite was ramped above the sea surface by progressive increments of the new lava. The central part was folded, forming pumice breccia and wrinkles. Subaerial emplacement of lava was the dominant process during the growth of the Showa Iwo-jima dome.

Collapse of large complex impact craters: Implications from the Araguainha impact structure, central Brazil

The 40-km-wide Araguainha impact structure in central Brazil provides extensive outcrops to study the structural evolution of all parts of a complex crater, including the central uplift, annular trough, and crater rim. While most craters of comparable size are buried by impact-related or postimpact sedimentary deposits, Araguainha is deeply eroded and it exposes in detail outcrop-scale structural features that can be used to understand the structural evolution of large impact craters. This study explores evidence from structural features across the entire impact structure in order to provide constraints on the target rock movement during the crater collapse. Most of the structural features described here are consistent with folding and bedding-parallel shearing during several kilometers of lateral inward movement of the target rocks. Vertical movement was, in contrast, restricted to distances of less than a few hundred meters along radial and concentric fault zones around the crater rim.

Subungual Squamous Cell Carcinoma of the Finger

5Department of Surgery, Orthopedic Service, Brooke Army Medical Center, San Antonio, TX 78234. 53-year-old woman presented to a dermatologist with a subungual mass in the right index finger. Radiographs revealed a subungual soft-tissue mass that had eroded into the distal phalanx of the index finger. The dermatologist performed a biopsy, revealing the diagnosis of squamous cell carcinoma. The index finger was amputated. The differential diagnosis of an erosive lesion in the distal phalanx includes implantation dermoid cyst, subungual fibroma, glomus tumor, giant cell tumor of tendon sheath, subungual squamous cell carcinoma, subungual keratoacanthoma, and mucous cyst [1]. Radiologically, subungual squamous cell carcinoma is almost indistinguishable from subungual keratoacanthoma. Keratoacanthoma is a localized endoexophytic growth of squamous epithelium with a characteristic central keratin-filled crater. Keratoacanthomas may be locally destructive and sometimes are associated with transformation to squamous cell carcinoma with subsequent invasion. Some authors consider keratoacanthoma a subset of squamous cell carcinoma [2]; however, keratoacanthomas more frequently undergo spontaneous involution, and the larger consensus is that they are separate lesions with distinctive behavior. The treatment of subungual keratoacanthoma is conservative, while that of subungual squamous cell carcinoma is amputation. Both subungual keratoacanthoma and squamous cell carcinoma may present with pain, localized swelling, and inflammation. Patients with subungual squamous cell carcinoma tend to be older (seventh decade peak) than those with keratoacanthoma (fifth decade peak) [1–4]. Squamous cell carcinoma grows slowly and often is mistaken for chronic inflammation. In contrast, subungual keratoacanthoma grows rapidly, proliferating to an obvious 1to 2-cm mass within several weeks to months; then generally stabilizes and later spontaneously involutes, leaving a small pitted scar [1]. Eighty-four percent of subungual squamous cell carcinomas occur in the fingers, the remaining in the toes. The majority of subungual squamous cell carcinoma in the fingers occurs in the thumb (44%); and those in the toes affect the great toe predominately (64%) [3, 4]. Predisposing factors for subungual squamous cell carcinoma include chronic paronychia, trauma, congenital ectodermal dysplasia, radiation exposure, and previous human papillomavirus (HPV) infection [3, 4]. In A