explosive volcanic eruptions on mercury eruption conditions magma volatile content and implications for interior volatile abundances images obtained by the messenger spacecraft have revealed evidence for pyroclastic volcanism on mercury because of the importance of this inference for understanding the interior volatile inventory of mercury we focus on one of the best examples determined to date a shield volcano like feature just inside the southwestern rim of the caloris impact basin characterized by a near central irregularly shaped depression surrounded by a bright deposit interpreted to have a pyroclastic origin this candidate pyroclastic deposit has a mean radius of 24 km greater in size than the third largest lunar pyroclastic deposit when scaled to lunar gravity conditions from the extent of the candidate pyroclastic deposit we characterize the eruption parameters of the event that emplaced it including vent speed and candidate volatile content the minimum vent speed is 300 m s and the volatile content required to emplace the pyroclasts to this distance is hundreds to several thousands of parts per million ppm of the volatiles typically associated with pyroclastic eruptions on other bodies e g co co2 h2o so2 h2s for comparison measurements of the exsolution of volatiles h2o co2 s from basaltic eruptive episodes at kilauea volcano hawaii indicate values of 1300 6500 ppm for the terrestrial mantle source evidence for the presence of significant amounts of volatiles in partial melts derived from the interior of mercury is an unexpected result and provides a new constraint on models for the planet s formation and early evolution

caloris impact basin exterior geomorphology stratigraphy morphometry radial sculpture and smooth plains deposits the mariner 10 flybys revealed the eastern third of the caloris basin and demonstrated its importance as a chronostratigraphic marker for the geological history of mercury uncertain after that mission were the size of the basin the full distribution of materials deposited or modified during the impact process and the stratigraphic and age relationships between caloris and surrounding terrain images obtained during messenger s january 2008 flyby of mercury revealed that the caloris basin is 15 larger than previously estimated and moderately elliptical 1525 by 1315 km basin related sculpture and secondary craters are dispersed widely in areas surrounding the basin confirming the widespread significance of this event as a stratigraphic marker units mapped around caloris on the basis of mariner 10 data are generally recognized in regions observed for the first time by messenger including most facies of the caloris group the caloris montes odin formation and van eyck formation the only unit without obvious exposures in messenger images is the nervo formation which was originally interpreted as impact melt or fallback ejecta new measurements of the size frequency distribution of impact craters both within the caloris basin and on surrounding units particularly the odin formation support the hypothesis that the vast majority of circum caloris plains postdate the basin and are likely volcanic the messenger observations re emphasize the importance of understanding the exterior stratigraphy of the basin in order to utilize the caloris event as a discrete time horizon in the geological history of mercury

investigating the origin of candidate lava channels on mercury with messenger data theory and observations received 12 april 2012 revised 31 august 2012 accepted 1 november 2012 published 31 march 2013 1 volcanic plains identified on mercury are morphologically similar to lunar mare plains but lack constructional and erosional features that are prevalent on other terrestrial planetary bodies we analyzed images acquired by the messenger spacecraft to identify features on mercury that may have formed by lava erosion we used analytical models to estimate eruption flux erosion rate and eruption duration to characterize the formation of candidate erosional features and we compared results with analyses of similar features observed on earth the moon and mars results suggest that lava erupting at high effusion rates similar to those required to form the teepee butte member of the columbia river flood basalts 0 1 1 2 10 6 m 3 s 1 would have been necessary to form wide valleys 15km wide observed in mercury s northern hemisphere first by mechanical erosion to remove an upper regolith layer then by thermal erosion once a lower rigid layer was encountered alternatively results suggest that lava erupting at lower effusion rates similar to those predicted to have formed rima prinz on the moon 4400 m 3 s 1 would have been required to form via thermal erosion narrower channels 7km wide observed on mercury although these results indicate how erosion might have occurred on mercury the observed features may have formed by other processes including lava flooding terrain sculpted during the formation of the caloris basin in the case of the wide valleys or impact melt carving channels into impact ejecta in the case of the narrower channels citation hurwitz d m j w head p k byrne z xiao s c solomon m t zuber d e smith and g a neumann 2013 investigating the origin of candidate lava channels on mercury with messenger data theory and observations j geophys res planets 118 471 486 doi 10 1029 2012je004103

volcanism on mercury evidence from the first messenger flyby for extrusive and explosive activity and the volcanic origin of plains the first messenger flyby of mercury obtained images of 21 of the surface not seen by mariner 10 including the center and western half of the caloris basin and regions near the terminator that show details of the nature of smooth and intercrater plains these new data have helped to address and resolve a series of longstanding questions on the existence and nature of volcanism on mercury and the distribution of volcanic materials data from the mercury dual imaging system mdis on the messenger spacecraft have shown the following 1 numerous volcanic vents in the form of irregularly shaped rimless depressions are concentrated around the interior edge of the caloris basin 2 these vents appear to be sources for effusive volcanism that in one case built a shield in excess of 100 km in diameter and in some cases formed bright haloes around the vents that are interpreted to represent pyroclastic eruptions 3 lobate margins of plains units seen previously in mariner 10 data are documented in messenger images with more clarity and are often distinctive in morphology and color properties supporting the interpretation that these features are the edges of lava flow units 4 the interior of the caloris basin is filled with plains units spectrally distinctive from the rim deposits and comparison with the lunar imbrium basin and superposed impact crater stratigraphy provide evidence that these units are volcanic in origin detailed differences in the mineralogy of lava flow units so prominent in imbrium are not seen in the caloris interior 5 some of the smooth plains surrounding the exterior of the caloris basin show distinct differences in color and morphological properties supporting a volcanic origin 6 some smooth and intercrater plains units distant from the caloris basin show evidence of flooding and embayment relations unrelated to caloris ejecta emplacement local and regional geological and color relationships support a volcanic origin for these plains 7 large impact craters show a sequence of embayment of interior floor and exterior ejecta deposits that supports a volcanic origin for the embayment and filling processes 8 crater embayment and flooding relationships in selected areas suggest volcanic plains thicknesses of many hundreds of meters and local thicknesses inside impact craters of up to several kilometers 9 impact crater size frequency distributions for caloris exterior deposits including the facies of the caloris group and relatively high and low albedo smooth plains show that they are younger than plains interior to caloris and thus must be dominantly the product of post caloris volcanism these new data provide evidence that supports and confirms earlier hypotheses from mariner 10 data that volcanism was important in shaping the surface of mercury the emerging picture of the volcanic style of mercury is similar to that of the moon the other small one plate planetary body there are no major shield volcanoes e g comparable to tharsis montes on mars shallow magma reservoirs are rare and there is little evidence for surface deformation or long lived volcanic sources related to sites of upwelling mantle the close association of volcanic plains and surface deformation features suggests that future observations and analyses can help document the relation between the volcanic flux and the evolving state and magnitude of stress in the lithosphere of mercury

birth growth and morphologic evolution of the laghetto cinder cone during the 2001 etna eruption we have undertaken detailed observations of the formation of the laghetto cinder cone a new cone that formed during a 2 week period of intense activity in piano del lago on the upper slopes of mount etna in summer 2001 we describe the events leading to the formation of a small graben the formation of pit craters on the base of the graben the onset of phreatomagmatic activity a transition to intense strombolian activity and a return to phreatomagmatic activity as the eruption came to an end we discuss the reasons for these transitions and describe the morphological development of the cone during these events arcuate cracks on the southern part of the cone were related to withdrawal of magma at the end of the eruption other slope instabilities that developed during the eruption include the formation of small radial grain flows on the outer flanks of the cone and the collapse into the crater of part of the crater rim some of the failure planes we observed were first identified using a flir tm 695 thermal infrared camera this is the first time that infrared thermography has been used to detect instability of volcanic structures results obtained during this test case demonstrate that thermal cameras are a very useful tool for studies of volcanic instability

absence of large shield volcanoes and calderas on the moon consequence of magma transport phenomena large shield volcanoes and calderas are not observed on the moon theoretical assessments show that melt ascending from the mantle will stall at rheological traps or at the shallower density trap at the base of the low density lunar crust magma will then only reach the surface along dikes propagated from these deep reservoirs and such events will be infrequent and characterized by very large volume eruptions these conditions favor the formation of sinuous rules single long flows and widespread flow units rather than abundant small eruptions from a central edifice the absence of large shield volcanoes and calderas on the moon is interpreted to be related to the fact that shallow neutral buoyancy zones and magma reservoirs are not favored on the moon

evidence for young volcanism on mercury from the third messenger flyby during its first two flybys of mercury the messenger spacecraft acquired images confirming that pervasive volcanism occurred early in the planet s history messenger s third mercury flyby revealed a 290 kilometer diameter peak ring impact basin among the youngest basins yet seen having an inner floor filled with spectrally distinct smooth plains these plains are sparsely cratered postdate the formation of the basin apparently formed from material that once flowed across the surface and are therefore interpreted to be volcanic in origin an irregular depression surrounded by a halo of bright deposits northeast of the basin marks a candidate explosive volcanic vent larger than any previously identified on mercury volcanism on the planet thus spanned a considerable duration perhaps extending well into the second half of solar system history

late pleistocene glacial events in the central apennines italy the study of glacial evidence in the gran sasso massif of the central apennines italy has allowed the last maximum advance and the subsequent stadial phases to be dated and the mean annual temperature and quantity of precipitation in the form of snow to be assessed for a number of periods the glaciers probably reached their maximum extension campo imperatore stade ca 22 60014c yr b p and started to retreat ca 21 000 yr b p leaving behind three recessional moraines after a first interstade fornaca interstade the fontari stade appears to have taken place shortly after 16 000 yr ago ca 15 000 yr ago the glacier started retreating leaving behind four more recessional moraines an interstade venacquaro interstade preceded the mount aquila stade datable at ca 11 000 yr b p a strong correlation is evident between the glacial phases on land and the isotopic variations in cores from the tyrrhenian sea

the last 40 ka tephrostratigraphic record of lake ohrid albania and macedonia a very distal archive for ash dispersal from italian volcanoes abstract a 1075 cm long core lz1120 was recovered in the south eastern part of the lake ohrid republics of macedonia and albania and sampled for identification of tephra layers magnetic susceptibility investigations show rather high magnetic values throughout the core with peaks unrelated to the occurrence of tephra layers but instead to the relative abundance of detrital magnetic minerals in the sediment naked eye inspection of the core allowed us to identify of two tephra layers at 896 897 cm and 1070 1075 cm laboratory inspection of the grain size fraction 125 m allowed for the identification of a third cryptotephra at 310 315 cm major element analyses on glass shards of the tephra layers at 896 897 cm and 1070 1075 cm show a trachytic composition and indicate a correlation with the regionally dispersed y 3 and y 5 tephra layers dated at ca 30 and 39 cal ka bp the cryptotephra at 310 315 cm has a mugearitic benmoreitic composition and was correlated with the fl eruption of mt etna dated at 3370 70 cal yr bp these ages are in agreement with five 14 c ams measurements carried out on plant remains and macrofossils from the lake sediments at different depths along the core the recognition of distal tephra from italian volcanoes allows us to link the lake ohrid succession to other archives located in the mediterranean area and in eastern europe the benmoreitic mugearitic tephra layer at 310 315 cm is the first recognition in the balkan area of a distal ash deposit from a mid intensity explosive eruption of mt etna as far as 600 km from the source

scaling impact melting and crater dimensions implications for the lunar cratering record abstract the dimensions of large craters formed by impact are controlled to a large extent by gravity whereas the volume of impact melt created during the same event is essentially independent of gravity this differential scaling fosters size dependent changes in the dynamics of impact crater and basin formation as well as in the final morphologies of the resulting structures a variety of such effects can be observed in the lunar cratering record and some predictions can be made on the basis of calculations of impact melting and crater dimensions among them are the following 1 as event magnitude increases the volume of melt created relative to that of the crater will grow and more will be retained inside the rim of the crater or basin 2 the depth of melting will exceed the depth of excavation at diameters that essentially coincide with both the inflection in the depth diameter trend and the simple to complex transition 3 the volume of melt will exceed that of the transient cavity at a cavity diameter on the order of the diameter of the moon this would arguably correspond to a moon melting event 4 small lunar craters only rarely display exterior flows of impact melt because the relatively small volumes of melt created can become choked with clasts increasing the melt s viscosity and chilling it rapidly larger craters and basins should suffer little from such a process 5 deep melting near the projectile s axis of penetration during larger events will yield a progression in cen tral structure morphology with growing event magnitude this sequence should range from single peaks through multiple peaks to peak rings 6 the minimum depth of origin of central peak material should co incide with the maximum depth of melting the main central peak in a crater the size of tycho should have had a preimpact depth of close to 15 km

geology and tectonics of the southwestern boundary of the unstable sector of mt etna italy abstract the etna volcano is known to be unstable and gradually moving downslope toward east and south the study of the local geology and structure of these unstable flanks and of their boundaries is important to understand the evolution of the flank instability and the stress field driving the spreading of the edifice in this paper we present the geological evolution of the lower south western sector of mount etna base on a detailed field survey at 1 10 000 scale this area located at the boundary of the unstable south eastern flank of the volcano is affected by the active ragalna fault and by distinctive eruptive fissures monte calvario formation 18 15 ka the monte calvario formation is made of viscous lavas often associated to breccia and autoclastic lava facies fed by a set of eruptive fissures ne sw oriented their emplacement occurred immediately before the ellitico caldera collapse marking a previously poorly constrained shift in the feeding system of the volcano the orientation of these eruptive fissures and lineaments and the geometry of the sedimentary substratum modeled from subsurface data indicate that the area was dominated by a local stress field consistent with the lateral spreading of mount etna since at least from the final ellittico phase about 18 ka with a nearly constant mean displacement rate these data give new insights into the geology and structure of the flank instability at etna the main geologic hazard of the studied area is not related to the opening of a new eruptive fissures but it is posed by the presence into il calvario quarry of fluoro edenite an asbestiform mineral that caused an high mortality rate for respiratory system cancer in biancavilla town in fact the monte calvario formation groups other eruptive fissures with similar volcanological and geochemical characteristics where hydrothermal alteration occurred with the likely formation of health threatening minerals

geology of mare deposits in south pole aitken basin as seen by clementine uv vis data a multispectral analysis of 21 discrete lunar mare deposits within the south pole aitken basin was undertaken in order to model the general mineralogical composition of farside mare deposits so that the near and farside may be compared in terms of magma generation and emplacement determination of each deposit s mineralogy was based upon albedo the 0 75 0 95 m ratio indicating the presence of a 1 0 m absorption band and the strength and shape of that band a combination of improved spatial resolution and the availability of the general multispectral signature for each pond allowed deposits to be examined for homogeneity in order to assess the nature and number of flows represented feo and tio 2 abundances were also estimated based upon the resultant data 19 out of 21 ponds were determined to be mare deposits of these 19 15 had spectra well defined enough to classify general mineralogy nine having high ca pyroxene signatures indicative of basalt and six showing low ca signatures suggesting a substantial noritic component we believe these noritic signatures can plausibly be attributed to vertical lateral soil mixing processes for the smallest ponds although a unique lithology cannot be ruled out for the largest pond a majority of ponds in this study region have homogeneous spectral signatures interpreted to represent individual eruptive phases this indicates that very large volumes for these regions may be typical also because such volumes are comparable to the largest terrestrial eruptions they may have formed by a similar mechanism of emplacement the vast majority of mature soils are spectrally redder and thus have a lower estimated feo abundance than the mare serenitatis soil standard ms 2 in particular and nearside basalts in general these soils also average low to medium estimated tio 2 abundance similar to apollo 12 and 15 and luna 24 the observations made here are consistent with a scenario in which basalts with low feo and low to medium tio 2 contents were deposited during the lunar peak volcanic period that occurred in the late imbrian 3 80 3 20 ga and because of their small areal extent were more susceptible to mixing processes than nearside basalts

mercury cratering record viewed from messenger s first flyby morphologies and size frequency distributions of impact craters on mercury imaged during messenger s first flyby elucidate the planet s geological history plains interior to the caloris basin displaying color and albedo contrasts have comparable crater densities and therefore similar ages smooth plains exterior to caloris exhibit a crater density 40 less than on interior plains and are thus volcanic and not caloris impact ejecta the size distribution of smooth plains craters matches that of lunar craters postdating the late heavy bombardment implying that the plains formed no earlier than 3 8 billion years ago ga at diameters less than or equal to 8 to 10 kilometers secondary impact craters on mercury are more abundant than primaries this transition diameter is much larger than that on the moon or mars a low density of craters on the peak ring basin raditladi implies that it may be younger than 1 ga

unusual magma storage conditions at mt etna southern italy as evidenced by plagioclase megacryst bearing lavas implications for the plumbing system geometry and summit caldera collapse at mt etna volcano the emission of plagioclase megacryst bearing lavas known locally as cicirara has occurred rarely and generally in association with unusual volcanological phenomena in this work we interpret the magma chamber processes and the structural features of the plumbing system that led to the production of these peculiar volcanic rocks based on a detailed study of plagioclase megacrysts including their oscillatory zoning sieve textures and fluid inclusions patchy zoning suggests limited ascent in the deep levels of the plumbing system based on the plagioclase nucleation threshold and the volatile saturation depth at intermediate water undersaturated levels of the plumbing system ascent is faster as indicated by crystals with coarse sieve textures storage at shallow water saturated levels less than 6 km deep is associated with oscillatory zoning with very small changes in an slightly larger an variations coupled with different wavelengths provide evidence of convection of crystals across distinct zones of the chamber stripes of melt inclusions formed at steps of magma ascent and volatile loss whereas layers of fluid inclusions may be related to episodes of volatile flushing into the magma chamber in contrast strongly sieve textured envelopes with an increase and constant feo may be related to mixing with more volatile rich magmas of similar composition we interpret the repeated occurrence of cicirara lavas as evidence that the shallow portion of the plumbing system underwent a progressive coalescence of a complex network of dykes and sills in response to increasing rates of magma supply from depth major magma withdrawals from this larger reservoir may be linked to episodes of summit instability associated with major caldera collapses

buried stratigraphic relationships along the southwestern shores of oceanus procellarum implications for early lunar volcanism the composition of mare highland boundaries is investigated in the region of southwestern oceanus procellarum using multispectral images from the galileo solid state imaging system the data are analyzed using a linear image based spectral mixture model to map the distribution and abundance of spectral end members representing mare basalt mature highland soils and fresh crater materials the fraction images that result from the mixture modeling are then integrated into a geographic information system database to analyze the relationship between the compositional gradients and regional geologic and geomorphic units within this framework three basic types of mixing gradients are recognized narrow mixing zones broad mixing zones and complex mixing zones the narrow zones appear to be the result of simple postformation lateral mass transport of surface materials due to the time averaged effects of impact cratering and regolith gardening the broad or moderate mixing zones exhibit evidence for significant incorporation of basalt into the distal basin ejecta of orientale and thus are interpreted to indicate that pre orientale volcanism and volcanic deposits were widespread in the procellarum region this is further corroborated by the mare rich ejecta blanket observed for the 100 km diameter impact crater letronne the complex mixing zones show evidence for extensive pre orientale and perhaps pre imbrium cryptomare as well as some volcanism extending into the late imbrian period these results indicate that mare highland boundaries frequently contain a convolved geologic record that allows insight into the geologic events prior to the final one apparently recorded by surface deposits for this region of the moon we now recognize that volcanism was well established and widespread in early imbrian time but had become more focused to a few major volcanic regions humorum procellarum by the late imbrian

volumes of lunar lava ponds in south pole aitken and orientale basins implications for eruption conditions transport mechanisms and magma source regions in an effort to characterize individual eruptive phases and events 86 isolated mare deposits ponds in the lunar south pole aitken and orientale regions were analyzed to obtain information on areas volumes and other characteristics deposits likely to represent single eruptive episodes have area mean values of 2000 km2 in the south pole aitken basin and 1100 km2 in the orientale basin pond volumes range from 35 to 8745 km3 with a mean value of 860 km3 for south pole aitken and 10 to 1280 km3 with a mean value of 240 km3 for the orientale region no evidence was found for shallow crustal magma reservoirs the relatively common occurrence of sinuous rilles in orientale is consistent with very high effusion rates and the large volumes of individual eruptive episodes tens to many hundreds of km3 are comparable to flood basalt eruption volumes on earth pond morphologies are consistent with extrusion from deep probably subcrustal reservoirs distribution of deposits suggests that many ponds may be derived from single reservoirs comparison of ponds in both basins shows a higher areal density and average volume of lava ponds in the south pole aitken basin relative to the orientale area this is plausibly attributed to the extreme depths of the south pole aitken basin and the correspondingly thinner crust there relative to the orientale region these observations are consistent with magma ascent and eruption mechanisms that are strongly dependent on the overpressurization of deep seated source regions the subsequent propagation of dikes and the thickness of the intervening lunar crust through which these dikes must rise

stratigraphic sequence and ages of volcanic units in the gruithuisen region of the moon 1 several domes indicative of non mare volcanism morphologically as well as spectrally distinct from surrounding mare and highland units are located in the gruithuisen region in northern oceanus procellarum the determination of the nature and age of non mare volcanism helps to put constraints on lunar crustal evolution the ages of the domes were previously thought to be mid imbrian or possibly even eratosthenian in order to assess more closely the stratigraphic relationships in this region we carried out geologic mapping and crater size frequency measurements 1 on the gruithuisen volcanic domes 2 on the adjacent mare units and 3 in the highland areas 4 the nearby iridum impact event was also dated by means of crater counts a recently updated and improved version of the lunar production function polynomial was used to fit measured crater size frequency distributions of geologic units and a cratering chronology model was applied in order to assign these units to the periods and epochs of the lunar chronology system oceanus procellarum mare materials in the study area were found to range in age from late imbrian to eratosthenian and show peak cratering model ages at 3 55 gyr 1 gyr 1 billion years 3 2 3 3 gyr and about 2 4 gyr some mare units show evidence for at least two events in their crater size frequency distributions these are most likely due to the superposition of later thin lava flows mare volcanism hence has lasted over a period of several hundred million years in the gruithuisen region the gruithuisen domes show a much more restricted age range they were found to range in age from 3 85 to 3 72 gyr and thus were formed in the early part of the late imbrian an older age than previously thought iridum crater stratigraphically older than the gruithuisen domes was formed about 3 7 3 8 gyr ago the iridum impact event and the formation of the two gruithuisen domes cannot be well separated by means of crater counts a few stratigraphically older highland units and some mare areas show ages of less than 2 0 gyr but these are less reliable due to 1 the crater distributions being close to saturation 2 less effective crater retention on slopes and 3 erosional removal of craters

ages and stratigraphy of mare basalts in oceanus procellarum mare nubium mare cognitum and mare insularum accurate estimates of mare basalt ages are necessary to place constraints on the duration and the flux of lunar volcanism as well as on the petrogenesis of lunar mare basalts and their relationship to the thermal evolution of the moon we performed new crater size frequency distribution measurements in order to investigate the stratigraphy of mare basalts in oceanus procellarum and related regions such as mare nubium mare cognitum and mare insularum we used high resolution clementine color data to define 86 spectrally homogeneous units within these basins which were then dated with crater counts on lunar orbiter iv images our crater size frequency distribution measurements define mineralogical and spectral surface units and offer significant improvements in accuracy over previous analyses our data show that volcanism in the investigated region was active over a long period of time from 3 93 to 1 2 b y a total of 2 7 b y volumetrically most of the basalts erupted in the late imbrian period between 3 3 and 3 7 b y and we see evidence that numerous units have been resurfaced during the eratosthenian period significantly less basalt was erupted depending on the absolute model ages that one can assign to the lunar chronostratigraphic systems five units might be of copernican age younger basalts are generally exposed in the center of the investigated area that is closer to the volcanic centers of the aristarchus plateau and marius hills older basalts occur preferentially along the northwestern margin of oceanus procellarum and in the southeastern regions of the studied area i e in mare cognitum and mare nubium combining the new data with our previously measured ages for basalts in mare imbrium serenitatis tranquillitatis humorum australe and humboldtianum we find that the period of active volcanism on the moon lasted 2 8 b y from 4 b y to 1 2 b y on the basis of the basalts dated so far which do not yet include the potentially young basalts of mare smythii e g schultz and spudis 1983 we conclude that oceanus procellarum not only exhibits the widest range of ages of all investigated basins but probably also is the location of some of the youngest basalts on the lunar surface

fragmental lava versus welded ignimbrite on mount etna arguments inferred from crystal preferred orientation abstract structural and textural similarities of some silicic lavas with strongly welded tuffs often lead to alternative interpretations of silicic rocks with doubtful origin such silicic lavas associated with pyroclastic deposits of benmoreitic composition were described on mount etna in the first part of this paper we discuss the stratigraphic and lithologic arguments that lead to correlate these products with the cratere ellittico caldera in a second part we focus on the emplacement mechanism of these foliated lava like flows and we reinterpret them as the result of welding and local rheomorphism of pyroclastic flow deposits to discriminate between the two processes fragmentation of a flowing lava or flattening of a fragmental deposit we make a finite strain analysis deduced from crystal orientation density distribution functions ddf in selected planes of the samples results of strain ratios show good agreement with previous values obtained by others on welded pyroclastic flow or welded air fall deposits we conclude that the cratere ellittico caldera is a major explosive event in the evolution of etna on the southwestern flank of the volcano the deposits of this eruption arc known as the biancavilla montalto ignimbrite

volcanism on mercury evidence from the first messenger flyby the origin of plains on mercury whether by volcanic flooding or impact ejecta ponding has been controversial since the mariner 10 flybys 1974 75 high resolution images down to 150 meters per pixel obtained during the first messenger flyby show evidence for volcanic vents around the caloris basin inner margin and demonstrate that plains were emplaced sequentially inside and adjacent to numerous large impact craters to thicknesses in excess of several kilometers radial graben and a floor fractured crater may indicate intrusive activity these observations coupled with additional evidence from color images and impact crater size frequency distributions support a volcanic origin for several regions of plains and substantiate the important role of volcanism in the geological history of mercury

new findings of late glacial etna pumice fall deposits in ne sicily and implications for distal tephra correlations in the mediterranean area pumice fall deposits found in the nebrodi mountains and along the alcantara river close to the town of randazzo ne sicily have been studied to derive information about their volcanic source and age the geochemical na alkaline affinity of juvenile products benmoreite to trachyte clearly indicates they originated from etna volcano sicily major empa and trace la icp ms element compositional data on matrix glasses indicate that the investigated deposits have a compositional affinity consistent with the tephra deposits of unit d produced by the ellittico caldera forming eruptions between ca 17 and 19 cal ka bp furthermore their compositions correspond to the distal tephra equivalent found in some lacustrine and marine cores in central italy y 1 tm 11 tyrrhenian sea et 1 md10 and adriatic sea pal94 66 358 pal94 8 353 we applied the principal components analysis pca a statistical tool able to reduce the variability of a complex system to compare the compositions of the proximal samples with the possible distal counterparts found in drill cores of the mediterranean area on the basis of northward dispersal of the studied deposits and their geochemical features we suggest they represent a previously unreported sub plinian plinian eruption of ellittico volcano producing medial distal pumice fall deposits in the nebrodi mountains and close to randazzo named here the d1c layer the discovery of these deposits helps solve the problem of distal correlations of the northerly dispersed tephra from etna related to unit d for which no definitive attribution with proximal units was given in previous studies the results presented here add to the knowledge of the eruptive history of the volcano and contribute to expanding the proximal geochemical glass dataset for distal tephra correlation in the mediterranean region during the late glacial period

soil formation in kettle holes from high altitudes in central apennines italy abstract kettle holes are relatively common features of glaciated landscapes and have been widely reported in the literature the work reported here documents the presence of kettle holes at high altitude and low latitude in the central apennines italy and describes the geomorphic and pedogenic processes that originated the soils infilling these depressions the areas selected for this study were located on three of the main massifs of the central apennines italy gran sasso majella and sibillini the kettle holes on these massifs formed at the end of the wurm glaciation appear smaller and shallower than those reported from elsewhere in the northern hemisphere are roughly circular in form and do not contain bogs or lakes in each area the dimensions of 40 kettle holes were measured and three kettle holes were excavated to examine the soils developed inside them the size of the kettle holes was highest in the sibillini massif where the glaciers reached altitudes as low as 1700 m in the very narrow low lying valleys it is hypothesised that at lower elevations the glacier receded more rapidly generating larger blocks of ice and consequently larger kettle holes once formed the kettle hole depressions were very effective as sediment traps and acted as sink for materials washed in from the surrounding slopes or from more distant wind blown sources in the kettle holes from gran sasso and majella massifs small fragments of woody charcoal were found the material filling the kettle holes accumulated inside them in the form of layers soils formed inside the kettle holes showed horizons whose thickness and properties appeared mostly inherited from the amassed layers the only pedogenic process common to the kettle holes of the three massifs was the incorporation of organic matter that as expected from the rather cold climatic conditions was subjected to slow dynamics in the kettle holes of the majella massif the horizons developed from layers rich of materials of volcanic origin and the formation of short range order minerals occurred we conclude that the soils inside the kettle holes are a repository of geomorphic pedogenic and in reference to the source of the charcoal paleo environmental information

geo volcanological mineralogical and environmental aspects of quarry materials related to pleural neoplasm in the area of biancavilla mount etna eastern sicily italy the town of biancavilla located on the lower flanks of mt etna volcano eastern sicily italy showed high mortality rates owing to malignant pleural neoplasms a cause of death specifically related to exposure to asbestos fibres an environmental survey indicated the stone quarry site of il calvario as a possible source of asbestos fibre exposure while a mineralogical study allowed to identify the new asbestiform mineral fluoro edenite a joint epidemiological and environmental study was conducted to assess the characteristics of the outbreak of malignant mesothelioma and to test the assumption of a causal relation with exposure to fluoro edenite due to the lack of awareness of fluoro edenite releases il calvario may not be the only source of the fibre but is probably the main one the evolution of the volume of material quarried from il calvario was studied on the basis of maps printed from 1896 to 1995 by using a digital elevation model the natural and anthropogenic causes of the territorial spread of the newly discovered amphibole fibres are discussed relatively to a geo volcanological territorial and environmental evolution of the area affected

tephra layers in late quaternary sediments of the central adriatic sea abstract magnetic susceptibility curves of ten cores collected in the western adriatic shelf and in the mid adriatic deep allowed us to recognize thirty tephra layers whose age based on physical and biostratigraphic data encompass a time interval ranging from less than 70 ka to the present chemical features of the tephra defined by sem eds analyses performed on glass shards indicate alkaline affinity mainly with k na 1 and trachytic compositions with two minor benmoreitic and phonolitic groups these characteristics are consistent with campanian and subordinate etnean provenances because of chemical and age constraints the glass shards can be referred to six tephra layers already described in the literature such as c20 c14 citara ischia c10 campanian ignimbrite c2 nyt neapolitan yellow tuff ams pf agnano monte spina phlegrean fields from campanian area and y1 from etna volcano indicating an age ranging from about 70 to 4 ka ams pf and c2 nyt dated 4 4 and 12 3 ka respectively are the most widespread tephra beds in the study cores the occurrence of ams pf never recorded in marine sequences up to now represents a very good marker for holocene adriatic sediments c2 nyt already recorded in the central tyrrhenian sea in lacustrine sediments from southern italy and in the campanian area is a good stratigraphic marker for inter sea and sea land correlations y1 tephra dated 14 2 ka also occurs in on land sediments of central italy and in marine sediments from the tyrrhenian and ionian seas it now represents one of the most widespread stratigraphic markers in the central mediterranean region

lunar mare basalt flow units thicknesses determined from crater size frequency distributions accurate lava flow unit thicknesses estimates are necessary to place constraints on volcanic flux estimates we refine the technique of using the shape of crater size frequency distribution csfd curves to estimate the thickness of individual lunar mare flow units we find that a characteristic knee often observed in csfd curves is reasonably interpreted to represent the presence of two lava flow units separated in time and that the diameter at which this knee occurs is related to the thickness of the overlying flow unit examination of 58 curves with this characteristic knee in several lunar nearside basins oceanus procellarum imbrium tranquillitatis humorum cognitum nubium and insularum allowed us to identify flow units that have not been detected in low sun images we found that the range of flow unit thickness is 20 220 m and the average is 30 60 m this technique expands considerably the ability to assess lava flow unit thicknesses and volumes on the moon and planets

geology of the caloris basin mercury a view from messenger the caloris basin the youngest known large impact basin on mercury is revealed in messenger images to be modified by volcanism and deformation in a manner distinct from that of lunar impact basins the morphology and spatial distribution of basin materials themselves closely match lunar counterparts evidence for a volcanic origin of the basin s interior plains includes embayed craters on the basin floor and diffuse deposits surrounding rimless depressions interpreted to be of pyroclastic origin unlike lunar maria the volcanic plains in caloris are higher in albedo than surrounding basin materials and lack spectral evidence for ferrous iron bearing silicates tectonic landforms contractional wrinkle ridges and extensional troughs have distributions and age relations different from their counterparts in and around lunar basins indicating a different stress history

evidence for intrusive activity on mercury from the first messenger flyby images from messenger s first flyby of mercury have shown convincing evidence for surface volcanism here we report on evidence in the new data for several features that are characterized by fractures and graben rare features on a planet dominated by contractional deformation that may be linked to intrusive activity these features include 1 a floor fractured crater interpreted to have been the site of laccolith like sill intrusions the feature is similar to some floor fractured craters on the moon and shows evidence for individual fractured dome like uplifts on the floor 2 a concentric complex of graben observed inside the peak ring on the floor of the 250 km diameter raditladi basin and associated with dark plains and possibly embayed by them the feature may represent an unusual type of floor fracturing associated with deeper intrusions and related ring dikes or cone sheets or the graben may instead be the product of non magmatic uplift of the basin floor 3 a large radial graben swarm pantheon fossae located near the center of the caloris basin thus far unique on mercury and characterized by hundreds of individual graben segments ranging from 5 km to 110 km in length in the nexus graben crosscut one another and produce a local polygonal pattern others curve away from the center as the nexus is approached two scales of graben length are observed the radius of the dense radially symmetric plexus of graben is 175 km and a few graben extend to greater radial distances to the north and southwest out to distances that intersect with a ring of generally concentric graben around the outer basin floor two width scales of graben are observed a large graben about 8 km wide emerges from the nexus and extends for 100 km most graben are less than half this width some graben walls appear cuspate with convex outward wall segments that resemble crater chain segments one crater chain with distinctive raised rims parallels nearby graben locally some graben appear in en echelon patterns and smaller graben sometimes show cross cutting superposition relationships abundant impact craters the most prominent being apollodorus and secondary crater clusters and chains are superposed on the graben system there is little evidence that craters greater than 5 km in diameter have been cut by a graben this relation implies that the graben swarm formed soon after the emplacement of the caloris floor plains these graben are interpreted to be the surface expression of a radial dike swarm emanating from a subsurface magma reservoir similar features in which the dikes contribute to a near surface stress field that favors radial graben are known on the earth venus and mars the location of pantheon fossae in the center of the caloris basin suggests that formation of the radial graben structure is linked to basin evolution

evolution of the fossa cone vulcano abstract in decreasing order of abundance the principal emplacement mechanisms for deposits of the fossa edifice of vulcano include dry surge wet surge pyroclastic fall lahar lava flow pyroclastic flow and epiclastic processes most samples from pyroclastic beds on fossa contain two grain size populations the coarser mode at 0 5 1 5 resulted from modified ballistic transport whereas the finer mode at 2 5 3 5 is related to surge transport reconstruction of the entire stratigraphy of the cone permits the beds to be grouped into five principal eruptive cycles all of which postdate the lower pilato ash of lipari dated at 11 000 to 8 500 y b p pte nere cycle palizzi cycle commenda cycle pietre cotte cycle and the modern cycle additional cycles may be present but exposures on the cone are insufficient for their adequate definition all cycles follow a similar stochastic pattern starting with surge eruptions and ending with effusion of lava from the crater rim the frequency of pyroclastic fall events increases with time throughout each cycle this progressive decrease in the efficiency of water melt interaction through the duration of each cycle may be due to a gradual rise of each new magma column coupled with an increase in magmatic volatiles tectonism and magma mixing both play a role in triggering eruptions on fossa the present crater lies at the intersection of two prominent tectonic trends a nnw fracture system parallels the main eruptive centers and an ene set aligns with the migration of minor vents the silicic lavas of fossa contain a mixture of two components xenocrysts of plagioclase augite and olivine surrounded by a dark glass are intimately dispersed into an evolved rhyolitic matrix

the redox state feo content and origin of sulfur rich magmas on mercury 1 mercury surface space environment geochemistry and ranging messenger orbital observations of mercury have revealed elevated s abundances ca s and mg s correlations and a low upper limit for ferrous iron in surface silicates these data indicate the presence of ca and or mg sulfides in volcanic rocks and a low oxygen fugacity fo2 in their parental magmas we have evaluated coupled fo2 and fs2 values and feo contents in mercury s magmas from silicate sulfide equilibria and empirical models for silicate melts and metallurgical slags the evaluated fo2 at 1700 1800 k is 4 5 to 7 3 log10 units below the iron wustite buffer these values correspond to 0 028 0 79 wt feo implying that fe must be also present in sulfides and metal and are also consistent with the composition of the partial melt of an enstatite chondrite this derived upper limit for feo is substantially lower than the limits obtained from reflectance measurements of mercury s surface materials the low fo2 and feo values provide new constraints for igneous processes on mercury as well as the formation evolution and internal structure of the innermost planet

hazards from pyroclastic density currents at mt etna italy abstract despite the recent recognition of mount etna as a periodically violently explosive volcano the hazards from various types of pyroclastic density currents pdcs have until now received virtually no attention at this volcano large scale pyroclastic flows last occurred during the caldera forming ellittico eruptions 15 16 ka ago and the risk of them occurring in the near future is negligible however minor pdcs can affect much of the summit area and portions of the upper flanks of the volcano during the past 20 years small pyroclastic flows or base surge like vapor and ash clouds have occurred in at least 8 cases during summit eruptions of etna four different mechanisms of pdc generation have been identified during these events 1 collapse of pyroclastic fountains as in 2000 and possibly in 1986 2 phreatomagmatic explosions resulting from mixing of lava with wet rock 2006 3 phreatomagmatic explosions resulting from mixing of lava with thick snow 2007 4 disintegration of the unstable flanks of a lava dome like structure growing over the rim of one of the summit craters 1999 all of these recent pdcs were of a rather minor extent maximum runout lengths were about 1 5 km in november 2006 and march 2007 and thus they represented no threat for populated areas and human property around the volcano yet events of this type pose a significant threat to the lives of people visiting the summit area of etna and areas in a radius of 2 km from the summit craters should be off limits anytime an event capable of producing similar pdcs occurs the most likely source of further pdcs in the near future is the southeast crater the youngest most active and most unstable of the four summit craters of etna where 6 of the 8 documented recent pdcs originated it is likely that similar hazards exist in a number of volcanic settings elsewhere especially at snow or glacier covered volcanoes and on volcano slopes strongly affected by hydrothermal alteration

emplacement and tectonic deformation of smooth plains in the caloris basin mercury abstract messenger s first flyby of mercury provided the first complete view of the caloris basin and its interior smooth plains multispectral imaging shows that the interior plains are spectrally distinct from surrounding terrain with a reflectance about 15 20 higher and a steeper spectral slope than the global average the caloris basin rim massifs and hummocky material in contrast have lower reflectance and a shallower spectral slope than the global average and extend around the entire basin isolated relatively red patches along the margins of caloris each surround irregularly shaped scalloped edged rimless depressions that are interpreted to be volcanic vents some with associated pyroclastic deposits a nearly continuous annulus of smooth plains exterior to the basin displays spectral characteristics that contrast sharply with those of the basin interior smooth plains the exterior smooth plains are lower in reflectance and spectrally similar to the caloris rim massifs and the hummocky materials the rims and floors of larger impact craters in the interior plains expose low reflectance material there is widespread evidence of contractional and extensional tectonic deformation of the caloris interior smooth plains a set of linear radial graben pantheon fossae radiates outward from a zone near the basin center and some of these graben extend to and intersect a set of generally basin concentric graben distributed along the outer margin of the caloris basin floor the average areal extensional strain expressed by the mapped system of graben is 0 08 wrinkle ridges also deform the interior smooth plains and predate both basin radial and basin concentric graben the average areal contractional strain expressed by the mapped wrinkle ridges is 0 07 the density of wrinkle ridges on the western interior smooth plains is less than on the eastern interior plains in contrast to the more even distribution of graben a similar difference is seen between the density of wrinkle ridges on the western and eastern exterior smooth plains with far fewer wrinkle ridges per unit area on the western annular plains superposition relations spectral contrast and the occurrence of volcanic vents and possible pyroclastic deposits all support a volcanic origin for the caloris interior plains crater counts indicate that the caloris exterior plains and hummocky material are younger than the caloris rim and interior plains and are therefore also likely volcanic in origin the contrast in spectral properties between the interior and exterior plains indicates a difference in the composition of the two expanses of volcanic material models for extensional tectonic deformation of the caloris basin interior inferred from the distribution of graben viewed by mariner 10 must be reevaluated to account for the discovery of pantheon fossae

pyroclastic density currents resulting from the interaction of basaltic magma with hydrothermally altered rock an example from the 2006 summit eruptions of mount etna italy after 16 months of quiescence mount etna began to erupt again in mid july 2006 the activity was concentrated at and around the southeast crater sec one of the four craters on the summit of etna and eruptive activity continued intermittently for 5 months during this period numerous vents displayed a wide range of eruptive styles at different times virtually all explosive activities took place at vents at the summit of the sec and on its flanks eruptive episodes which lasted from 1 day to 2 weeks became shorter and more violent with time volcanic activity at these vents was often accompanied by dramatic mass wasting processes such as collapse of parts of the cone highly unusual flowage processes involving both old rocks and fresh magmatic material and magma water interaction the most dramatic events took place on 16 november when numerous rockfalls and pyroclastic density currents pdcs were generated during the opening of a large fracture on the se flank of the sec cone the largest pdcs were clearly triggered explosively and there is evidence that much of the energy was generated during the interaction of intruding magma with wet rocks on the cone s flanks the most mobile pdcs traveled up to 1 km from their source this previously unknown process on etna may not be unique on this volcano and is likely to have taken place on other volcanoes it represents a newly recognized hazard to those who visit and work in the vicinity of the summit of etna

identification of mercurian volcanism resolution effects and implications for messenger the possibility of volcanism on mercury has been a topic of discussion since mariner 10 returned images of half the planet s surface showing widespread plains material these plains could be volcanic or lobate crater ejecta an assessment of the mechanics of the ascent and eruption of magma shows that it is possible to have widespread volcanism no volcanism on the surface whatsoever or some range in between it is difficult to distinguish between a lava flow and lobate crater ejecta based on morphology and morphometry no definite volcanic features have been identified on mercury however known lunar volcanic features cannot be identified in images with similar resolutions and viewing geometries as the mariner 10 dataset examination of high resolution low sun angle mariner 10 images reveals several features which are interpreted to be flow fronts it is unclear if these are volcanic flows or ejecta flows this analysis implies that a clear assessment of volcanism on mercury must wait for better data messenger will take images with viewing geometries and resolutions appropriate for the identification of such features

the biancavilla montalto ingnimbrite etna sicily stratigraphic granulometric and sem grain texture studies have been carried out on pyroclastic deposits in the biancavilla and montalto areas on the lower sw flank of etna these studies support the interpretation that the deposits were emplaced as pyroclastic flows during the final stage of the ellittico eruptive activity 14 18 26 ka based on the high percentage of juvenile components and granulometric characteristics the deposits are classified as normal ignimbrite four separate flow units have been distinguished based on the presence of fine grained basal layers a multivariate g mode statistical analysis has been used to discriminate particle morphology populations between flow units and infer temporal changes in the nature of the eruptive processes the initial flow i was emplaced at a high temperature and involved a juvenile gas phase exolved from the magma subsequent flows ii iii iv exhibit evidence for the interaction of external water

dark ring in southwestern orientale basin origin as a single pyroclastic eruption 1 a large 154 km diameter dark annular ring located in the southwestern part of the orientale basin along the montes rook ring was first discovered and documented in soviet zond 8 images clementine uv visible multispectral data indicate that the dark ring consists of material similar to the pyroclastic glasses collected by the apollo astronauts with the glasses being more closely related to the orange glass beads that comprise the aristarchus plateau than to the crystallized black beads typical of taurus littrow this implies relatively rapid cooling times for the eruption products we propose that the dark ring is the manifestation of a pyroclastic eruption originating at a fissure vent an elongate 7 5 km by 16 km depression located near the center of the ring the event producing the eruption began with a dike rapidly emplaced from subcrustal depths to within 3 4 km of the surface the dike stabilized and degassed over 1 7 years to form an upper foam layer which then penetrated to the surface to cause an eruption lasting 1 2 weeks the eruption produced a 38 km high symmetrical spray of pyroclasts into the lunar vacuum at velocities of 350 to 420 m s and the pyroclastic material accumulated in a symmetrical ring around the vent the geometry of eruption caused the deposits to accumulate preferentially in a ring representing the material ejected at 45 the paucity of pyroclastic rings of this type on the moon can be attributed to the low probability of a dike stalling at just the right depth 3 4 km to create these eruption conditions the detailed characteristics of this ring provide important new insight into the emplacement of pyroclastics in the more regionally continuous lunar dark mantle deposits suggesting that their sources are dominated by effusive and hawaiian style eruptions the orientale dark ring deposit has similarities to the pyroclastic rings on the galilean satellite io both the orientale dark ring and ionian eruptions involve acceleration of small particles to a high velocity in an expanding gas stream silicate pyroclasts derived from the disrupted foam layer in the lunar case and a mixture of silicate pyroclasts and snowflakes of condensing so2 solids on io in both cases the silicate pyroclasts ejected from the vent are accelerated by the gas until they become decoupled and continue on ballistic trajectories controlled only by gravity differences in mass flux and cloud opacity between the moon and io are the direct result of the origin and mass fraction of the volatile phase the accumulation of a magmatic foam layer on top of a silicate intrusion in the lunar case and the intimate mixing on io of a steadily erupting magma and liquid so2 the interpretation of the orientale dark mantle ring as a pyroclastic eruption provides an alternative to the hypothesis that the dark ring represents the presence of an ancient pre orientale impact structure and that the orientale basin cavity of excavation must therefore lie within the outer rook mountain ring

late glacial explosive activity on mount etna implications for proximal distal tephra correlations and the synchronisation of mediterranean archives abstract plinian and ignimbrite deposits represent explosive activity ca 17 19 cal ka within the predominantly effusive and mildly explosive strombolian volcanic history of mount etna italy proximal glasses from the biancavilla ignimbrites and unit d plinian fall deposits are characterised fall deposits recorded at acireale d1b and d2b and giarre d1a and d2a are geochemically distinct confirming they relate to different eruptions the acireale plinian fall d1b and d2b deposits compositionally overlap with the biancavilla ignimbrite deposits these explosive eruptions from etna are considered responsible for widespread ash dispersals throughout the central mediterranean region producing the marker tephra layers y 1 et 1 recorded in marine and lacustrine sedimentary archives stratigraphically these distal tephras occur at or close to the onset of the last deglaciation termination 1 within their respective palaeoenvironmental records therefore making them potentially crucial tephrostratigraphic markers this study investigates distal tephra deposits thought to be from etna recorded in the ionian sea y 1 lago grande di monticchio lgdm italy tephras tm 11 and tm 12 1 lago di mezzano italy and the haua fteah cave libya the glass chemistry of y 1 tephras recorded in the ionian sea and at haua fteah is consistent with the biancavilla ignimbrites 16 965 17 670 cal yrs bp and the upper acireale plinian fall d2b the lgdm record indicates that explosive activity on etna associated with unit d spans a minimum of 1540 80 varve years tm 12 1 19 200 19 804 cal yrs bp in lgdm appears to represent the oldest distal counterpart of etna unit d explosive activity and is associated with the lower acireale d1b plinian eruption the proximally undefined tm 11 17 640 18 324 cal yrs bp and distal correlatives are geochemically distinct from the ionian sea y 1 tephra such significant compositional differences seen between distal tephra layers are not observed within individual proximal units and are likely to indicate that the distal tephras relate to separate eruptive phases until proximal relationships can be established the tm 11 type y 1 equivalents should be termed tm 11 great care should be exercised when using these distal ash layers to synchronise sedimentary records during a crucial period of environmental change

tephrostratigraphy of the last 170 ka in sedimentary successions from the adriatic sea abstract in this study are discussed new sem eds analyses performed on glass shards from five cores collected in the central adriatic sea and two cores recovered from the south adriatic sea a total of 26 tephra layers have been characterized and compared with the geochemical features of terrestrial deposits and other tephra archives in the area south adriatic sea and lago grande di monticchio vulture volcano the compositions are compatible with either a campanian or a roman provenance the cores located on the central adriatic inner and outer shelf recorded tephra referred to explosive events described in the literature ap3 sub plinian activity of the somma vesuvius 2710 60 14 c years bp avellino eruption somma vesuvius 3548 129 14 c years bp agnano monte spina phlegrean fields 4100 400 years bp mercato eruption somma vesuvius 8010 35 14 c years bp agnano pomici principali eruption phlegrean fields 10 320 50 14 c years bp neapolitan yellow tuff phlegrean fields 12 100 170 14 c years bp some of these layers were also observed in the south adriatic core in68 9 in addition to younger ap2 sub plinian eruption somma vesuvius 3225 140 14 c years bp and older layers pomici di base eruption somma vesuvius 18 300 150 14 c years bp significant is the tephra record of core rf95 7 that for the first time in the adriatic sea reports the occurrence of tephra layers older than 60 ka the well known mediterranean tephra layers x2 ca 70 ka w1 ca 140 ka and v2 roman origin ca 170 ka as well as other tephra layers attributed on the basis of geochemistry and biostratigraphy to explosive eruptions occurred at vico 138 2 and 151 3 ka bp and ischia 147 140 ka bp previous tephra correlations performed on other cores in the central adriatic sea were also critically revised according to new available data and integrated with the results of this study for a correlation at a regional scale the most important key beds for correlation are the agnano monte spina and neapolitan yellow tuff tephra layers which occur in both central and south adriatic sea other tephra layers younger than 15 ka are relatively less frequent the y1 etna 14 180 260 14 c years bp and agnano pomici principali in the more recent record in the shelf cores north of gargano promontory the ap3 tephra layer is also frequent

eruption and emplacement of a basaltic welded ignimbrite during caldera formation on gran canaria the 14 1 ma old composite ignimbrite cooling unit p1 45 km3 on gran canaria comprises a lower mixed rhyolite trachyte tuff a central rhyolite basalt mixed tuff and a slightly rhyolite contaminated basaltic tuff at the top the basaltic tuff is compositionally zoned with a an upward change in basalt composition to higher mgo content 4 3 5 2 wt b variably admixed rhyolite or trachyte commonly 5 wt and c an upward increasing abundance of basaltic and plutonic lithic fragments and cognate cumulate fragments the basaltic tuff is divided into three structural units i the welded basaltic ignimbrite which forms the thickest part c 95 vol and is the main subject of the present paper ii poorly consolidated massive bomb and block rich beds interpreted as phreatomagmatic pyroclastic flow deposits and iii various facies of reworked basaltic tuff tuff unit i is a basaltic ignimbrite rather than a lava flow because of the absence of top and bottom breccias radial sheet like distribution around the central tejeda caldera thickening in valleys but also covering higher ground and local erosion of the underlying p1 ash a gradual transition from dense rock in the interior to ash at the top of the basaltic ignimbrite reflects a decrease in welding the shape of the welding profile is typical for emplacement temperatures well above the minimum welding temperature a similar transition occurs at the base where the ignimbrite was emplaced on cold ground in distal sections in proximal sections the base is dense where it was emplaced on hot felsic p1 tuff the intensity of welding especially at the base and the presence of spherical particles and of mantled and composite particles formed by accretion and coalescence in a viscous state imply that the flow was a suspension of hot magma droplets the flow most likely had to be density stratified and highly turbulent to prevent massive coalescence and collapse model calculations suggest eruption through low pyroclastic fountains 1000 m high with limited cooling during eruption and turbulent flow from an initial temperature of 1160 c the large volume of 26 km3 of erupted basalt compared with only 16 km3 of the evolved p1 magmas and the extremely high discharge rates inferred from model calculations are unusual for a basaltic eruption it is suggested that the basaltic magma was erupted and emplaced in a fashion commonly only attributed to felsic magmas because it utilized the felsic p1 magma chamber and its ring fissure conduits evolution of the entire p1 eruption was controlled by withdrawal dynamics involving magmas differing in viscosity by more than four orders of magnitude the basaltic eruption phase was initially driven by buoyancy of the basaltic magma at chamber depth and continued degassing of felsic magma but most of the large volume of basalt magma was driven out of the reservoir by subsidence of a c 10 km diameter roof block which followed a decrease in magma chamber pressure during low viscosity basaltic outflow

ages of mare basalts on the lunar nearside the chronology of lunar volcanism is based on radiometric ages determined from apollo and luna landing site samples regional stratigraphic relationships and crater degradation and size frequency distribution data for units largely defined prior to the end of the apollo program here we report on new crater size frequency distribution data for 139 spectrally and morphologically defined basalt units which are exposed in six nearside impact basins australe tranquillitatis humboldtianum humorum serenitatis and imbrium crater size frequency distribution measurements are a statistically robust and accurate method to derive absolute model ages of unsampled regions of the moon compared to crater degradation ages crater size frequency ages performed on spectrally defined units offer significant improvements in accuracy our investigation showed that 1 in the investigated basins lunar volcanism was active for at least 1 5 2 0 b y starting at about 3 9 4 0 b y and ceasing at 2 0 b y 2 most basalts erupted during the late imbrian period at about 3 6 3 8 b y 3 significantly fewer basalts were emplaced during the eratosthenian period 4 basalts of copernican age were not found in any of the investigated basins 5 lunar basin filling volcanism probably started within 100 m y after the formation of the individual basins we also assessed the relationship between impact basin age and the history of mare basalt emplacement in these basins we found that 1 in all pre nectarian basins australe and tranquillitatis as well as in the humboldtianum basin which is of nectarian age the distribution of surface ages is clearly dominated by only a single peak in the number of erupted units at 3 6 3 8 b y 2 in the younger basins humorum serenitatis and imbrium a second peak at 3 3 3 5 b y is observed 3 basalt eruptions younger than 2 6 b y occur only intermittently and 4 in the youngest basins serenitatis and imbrium we see an extended period of active basin filling volcanism 1 5 1 6 b y which is 500 m y longer than in the australe and humorum and even 1 0 b y longer than in tranquillitatis and humboldtianum

compositional analyses of lunar pyroclastic deposits abstract the 5 band clementine uvvis data at 100 m pixel were used to examine the compositions of 75 large and small lunar pyroclastic deposits lpds and these were compared to representative lunar maria and highlands deposits results show that the albedo spectral color and inferred composition of most lpds are similar to those of low titanium mature lunar maria these lpds may have consisted largely of fragmented basalt with substantial components of iron bearing mafic minerals pyroxenes olivine and smaller amounts if any of volcanic glass several smaller lpds also show substantial highland components three classes of very large deposits can be distinguished from most lpds and from each other on the basis of crystallinity and possible titanium content of their pyroclastic components one class has spectral properties that are dominated by high titanium crystallized black beads e g taurus littrow a second consists of a mixture of high titanium glasses and beads with a higher glass bead ratio sulpicius gallus than that of taurus littrow and a third has a significant component of quenched iron bearing volcanic glasses aristarchus with possible moderate titanium contents although areally extensive these three classes of very large pyroclastic deposits compose only 20 of the 75 deposits studied 27 and eruption of such materials was thus likely to have been less frequent on the moon

the fractal and multifractal dimension of volcanic ash particles contour a test study on the utility and volcanological relevance abstract image processing analysis is used to check the ability of the fractal dimension for quantitatively describing the shape of volcanic ash particles digitized scanning electron microscopy images of fine pyroclasts from the eruptions of monte pilato rocche rosse lipari italy are investigated to test the efficiency of the fractal dimension to discriminate between particles of different eruptive processes multivariate analysis of multiple fractal components allows distinction between magmatic particles and phreatomagmatic particles which however is less significant than the discrimination obtained in previous studies by the use of simple adimensional shape parameters approximation of the actual particle boundary and the not rotation invariant nature of the fractal data frequently result in a significant scatter of data points in the mandelbrot richardson plot such behavior obscures in some cases the actual information of particle shape and renders the discriminating power of fractal analysis less effective than classical shape descriptors data less affected by scatter reveal that phreatomagmatic particles of the monte pilato rocche rosse eruptions are true mono fractals whereas magmatic particles are multifractals the textural small scale fractal of magmatic particles is similar to the fractal dimension value of phreatomagmatic particles and is attributed to the rheological behavior of melt upon brittle fragmentation the structural large scale fractal of magmatic particles refers to the walls of ruptured vesicles that lay on the particle outline the high difference between the values of the textural and structural fractals of magmatic particles of the monte pilato rocche rosse eruptions suggests two distinct and independent processes in the formation of such pyroclasts at the scales corresponding to the textural fractal the fragmentation process is independent of vesicles magmatic fragmentation is not simply related to growth expansion interference and explosion of vesicles but to a brittle cracking of the highly viscous melt likely related to rapid decompression

volcanism on mercury a new model for the history of magma ascent and eruption 1 we use the identification of volcanism on mercury together with lobate flow front like topography crustal composition information and data on the stress state and history of the lithosphere to derive a new model for the ascent and eruption of magma on mercury we find that extrusion is likely to be dominated by high effusion rate events initial emplacement of dikes in the crust and extrusions to the surface will result in a denser crust favoring even more extrusive volcanism this will be followed by cooling associated with planetary thermal evolution that will rapidly decrease the ability of magma to reach the surface resulting in a decline and termination of volcanism following the emplacement and deformation of regional smooth plains these predictions and the resulting history can be tested with observations from missions to mercury

complex magma dynamics at mount etna revealed by seismic thermal and volcanological data 1 three eruptive episodes during the 2006 summit eruptions of mount etna were exceptionally well documented by visual seismic and thermal monitoring the first 16 november was strongly explosive with vigorous strombolian activity and ash emission from multiple vents lava emission and phreatomagmatic explosions generating pyroclastic density currents pdcs the second episode 19 november had a rather weakly explosive component with mild strombolian activity but more voluminous lava emission the third 24 november was a moderately explosive paroxysm with intermittent lava fountaining and generation of a tephra column as well as lava emission and pdcs data recorded by a thermal monitoring camera clearly document the different phases of each paroxysm weather clouds occasionally hampering thermal monitoring the images show a rapid onset of the volcanic activity which during each of the paroxysms reached a peak in eruptive and thermal intensity and then decreased gradually the stronger phreatomagmatic explosions and pdcs on 16 and 24 november did not yield any seismic signature linked to the opening of new vents nor were they associated with peculiar characteristics of the seismic signal nevertheless eruptive styles strombolian activity lava emission and different levels in the intensity of explosive activity were generally well reflected in the amplitude and frequency content of the seismic signal and in the source location of the volcanic tremor centroid throughout the three eruptive episodes this multidisciplinary study therefore not only provides a key to distinguish between endogenous and exogenous origins of the phenomena observed but also documents the complex magma dynamics within the volcano

lunar mare volcanism stratigraphy eruption conditions and the evolution of secondary crusts abstract lunar mare basalt deposits cover 17 of the lunar surface occur preferentially in topographic lows on the nearside and have a total volume estimated at 1 107 km3 analysis of returned samples and photogeologic and remote sensing studies shows that mare volcanism began prior to the end of heavy bombardment the period of cryptomare formation in pre nectarian times and continued until the copernican period a total duration approaching 3 5 4 ga stratigraphic analyses show that the flux was not constant but peaked in early lunar history during the imbrian period which spans the period 3 85 3 2 ga average volcanic output rate during this peak period was about 10 2 km 3 a very low relative to the present global terrestrial volcanic output rate and comparable to the present local output rates for individual volcanoes such as vesuvius and kilauea hawaii volcanic landforms indicate that many eruptions were of high volume and long duration some eruptions associated with sinuous rules may have lasted of the order of a year and emplaced 103 km3 of lava representing the equivalent in one year of about 70 000 years at the average flux shallow magma chambers were uncommon the nearsidefarside mare deposit asymmetry can be readily explained by differences in crustal thickness magma ascending from the mantle or from a buoyancy trap at the base of the crust should preferentially extrude to the surface on the nearside but should generally stall and cool in dikes in the farside crust extruding only in the deepest basins the occurrence of farside maria within craters whose diameter is generally near to or less than the thickness of the crust may be accounted for by the difference between local and regional compensation dikes that establish pathways to the surface on the nearside should have very high volumes comparable to the volumes associated with many observed flows and sinuous rilles an abundance of dikes should exist in the lower crust of the moon many more than those feeding surface eruptions the upper limit is 37 50 of the crust by volume the presence and abundance of such dike swarms have important implications for the interpretation of the average composition of the lunar crust and the composition of basin and crater ejecta the interplay between thermal contraction and differentiation leads to net cooling and ultimate contraction of the outer portions of the moon resulting in a regional horizontal compressive stress acting on the lunar crust in addition overall cooling and deepening of sources require the production of ever larger volumes of magma in order to reach the surface with time stresses became high enough so that few dikes could open to the surface causing eruptive activity to be severely diminished in the eratosthenian and perhaps to cease in the copernican period lower stress levels are required to terminate eruptive activity on the lunar farside consistent with the imbrian age of the farside maria and the nearside location of the youngest maria lunar mare deposits provide an example of the transition from primary crusts to secondary crusts and illustrate the significance of several factors in the evolution of secondary crusts such as crustal density variations in crustal thickness presence of impact basins state and magnitude of stress in the lithosphere and general thermal evolution these factors are also responsible for the extremely low volcanic flux even during periods of peak extrusion

tephrostratigraphy study for the last 18 000 14 c years in a deep sea sediment sequence for the south adriatic abstract a detailed tephrostratigraphy supported by accelerator mass spectrometry ams 14c dating and isotopic and geochemical analyses has been carried out for a deep sea core collected from the southern adriatic sea which spans the last 18 14c kyr fourteen ash layers have been recognized in the marine core and the origin was determined by comparing their age and geochemistry with tephra detected in terrestrial deposits the geochemical signatures of marine ash layers indicate a prevailing campanian and subordinate etnean and eolian provenances collectively they are attributed to sources in the phlegraean fields lam lagno amendolare ln1 ln2 gm1 c 2 nyt neapolitan yellow tuff c 1 agnano pomici principali ams pf agnano monte spina ast astroni somma vesuvius l9 pomici di base l8 greenish mount etna et1 y1 biancavilla ignimbrite lipari e 1 gabellotto fiumebianco and palinuro seamount pal 1 some of these eruptions have been detected for the first time in marine cores astroni lam l9 l8 and three were detected and dated by marine tephra ln1 ln2 and pal 1 providing new more precise stratigraphic markers for the last 18 kyr in the south adriatic marine record

a sharper view of impact craters from clementine data the ultraviolet visible camera on the clementine spacecraft obtained high spatial resolution images of the moon in five spectral channels impact craters mapped with these multispectral images show a scale of lithologic diversity that varies with crater size and target stratigraphy prominent lithologic variations feldspathic versus basaltic occur within the south wall of copernicus 93 kilometers in diameter on the scale of 1 to 2 kilometers lithologic diversity at tycho 85 kilometers in diameter is less apparent at this scale although the impact melt of these two large craters is remarkably similar in this spectral range the lunar surface within and around the smaller crater giordano bruno 22 kilometers in diameter is largely dominated by the mixing of freshly excavated material with surrounding older soils derived from a generally similar feldspathic lithology

return to mercury a global perspective on messenger s first mercury flyby in january 2008 the mercury surface space environment geochemistry and ranging messenger spacecraft became the first probe to fly past the planet mercury in 33 years the encounter revealed that mercury is a dynamic system its liquid iron rich outer core is coupled through a dominantly dipolar magnetic field to the surface exosphere and magnetosphere all of which interact with the solar wind messenger images confirm that lobate scarps are the dominant tectonic landform and record global contraction associated with cooling of the planet the history of contraction can be related to the history of volcanism and cratering and the total contractional strain is at least one third greater than inferred from mariner 10 images on the basis of measurements of thermal neutrons made during the flyby the average abundance of iron in mercury s surface material is less than 6 by weight

explosive volcanism on mercury analysis of vent and deposit morphology and modes of eruption abstract the messenger mission revealed for the first time conclusive evidence of explosive volcanism on mercury several previous works have cataloged the appearance and location of explosive volcanism on the planet using a variety of identifying characteristics including vent presence and deposit color as seen in multispectral image mosaics we present here a comprehensive catalog of vents of likely volcanic origin our classification scheme emphasizes vent morphology we have analyzed the morphologies of all vents in our catalog and recognize three main morphologies simple vent pit vent and vent with mound the majority of vents we identify are located within impact craters the spatial distribution of vents does not correlate with the locations of volcanic smooth plains deposits in contrast to the moon nor do vents correlate with the locations of large impact basins except for the caloris and tolstoj basins using the degradation state of the vent host crater as a proxy for maximum age we suggest that vent formation has been active through the mansurian and into the kuiperian periods although the majority of vents were likely formed much earlier in mercurian history the morphologies and locations of vents are used to investigate a set of plausible formation geometries we find that the most likely and most prevalent formation geometry is that of a dike stalled at depth which then explosively vents to the surface we compare the vent and deposit size of mercurian pyroclastic deposits with localized and regional lunar pyroclastic deposits and find a range of possible eruption energies and corresponding variations in eruption style localized lunar pyroclastic deposits and the majority of mercurian pyroclastic deposits show evidence for eruption that is consistent with the magmatic foam at the top of a dike reaching a critical gas volume fraction a subset of mercurian vents including the prominent copland rachmaninoff vent to the northeast of the rachmaninoff basin indicates eruption at enhanced gas volume fractions this subset of vents shows a similar eruptive behavior to the lunar orientale dark mantle ring deposit suggesting that the dikes that formed these vents and deposits on mercury underwent some form of additional volatile build up either through crustal volatile incorporation or magma convection within the dike there also exists a population of mercurian vents that no longer retain a visible associated pyroclastic deposit we hypothesize that the visible signature of the pyroclastic deposit has been lost through space weathering and regolith mixing processes together these results provide a comprehensive analysis of explosive volcanism on mercury and inform continued research on the thermal history of mercury and magma composition and evolution

recalibrated mariner 10 color mosaics implications for mercurian volcanism recalibration of mariner 10 color image data allows the identification of distinct color units on the mercurian surface we analyze these data in terms of opaque mineral abundance iron content and soil maturity and find color units consistent with the presence of volcanic deposits on mercury s surface additionally materials associated with some impact craters have been excavated from a layer interpreted to be deficient in opaque minerals within the crust possibly analogous to the lunar anorthosite crust these observations suggest that mercury has undergone complex differentiation like the other terrestrial planets and the earth s moon

copernicus a regional probe of the lunar interior earth based telescopic spectral imaging techniques were used to document the spatial distribution of crater materials within the large lunar crater copernicus at the subkilometer scale on the basis of spectral ultraviolet visible near infrared characteristics the proposed spectral mixing analysis leads to a first order mapping of the impact melt material within the crater olivine was detected not only within the three central peaks but also along a significant portion of the crater rim consideration of an olivine bearing end member in the mixing model emphasizes the overall morphological pattern of the rim and wall terraces in the associated fraction image the identification of widely exposed olivine units supports the idea that the lower crust and possibly the lunar mantle itself are regionally at shallow depth

gruithuisen domes region a candidate for an extended nonmare volcanism unit on the moon small lunar areas known as red spots are thought to represent good candidates for nonmare volcanic units predating or contemporaneous with the period of mare volcanism in this study we present imaging telescopic and orbital clementine multispectral surveys of the gruithuisen region located in the northwestern border of mare imbrium which contains imbrian age domical features of likely viscous volcanic origin with spectral characteristics of red spot areas a rather spectrally homogeneous unit having typical characteristics of red spots is found to coincide with the material within the morphological boundaries of the gruithuisen delta gamma and northwest domes an extended dome like unit is identified spectrally and surrounds and extends to the west and the north of the domes this unit shows spectral characteristics close to those of the domes suggesting the presence of a significant amount of dome material extending many kilometers away from the domes themselves both the spectral characteristics of the dome and the dome like unit are clearly different from those of highlands and the surrounding mare basalts the spectral identification of a widespread dome like unit suggests that the specific style of eruption that is inferred for the formation of the domes i e viscous flows of possible more silicic composition might have occurred on a regional scale in this part of the moon prior to the iridum event about 3 8 gyr ago this volcanic style appears to be more widespread in the early part of lunar history than previously thought

architecture and sedimentary evolution of the southwestern gissar carbonate platform uzbekistan during the middle late jurassic abstract sedimentological investigations have been carried out in the southwestern part of the gissar range uzbekistan in order to document the stratigraphic evolution of a vast middle upper jurassic carbonate platform developed on the northern margin of the amu darya basin two major sequences are distinguished based on their contrasting facies pattern platform configuration and carbon isotope signature 1 a callovian sequence and 2 an upper jurassic sequence potentially oxfordian to kimmeridgian in age a carbonate ramp with a double proximal distal polarity developed during the callovian sequence oo bioclastic grainstones were produced in two permanently agitated shallow water areas developing to the north and to the south patch and pinnacle reefs mainly built up close to the storm wave base passing distally to pellet and foraminiferal oncoid rich mid to outer ramp deposits the top of the callovian sequence is a regional discontinuity that could have formed by subaerial exposure of the platform this probable hiatus could record a major climatic change associated to the middle late jurassic transition the upper jurassic sequence consists of metre thick alternations of pellet algal pack to grainstones microbial oncoid floatstones ooid grainstones and mudstones which have likely accumulated in a vast lagoon protected by a large scale barrier reef observed south of the study area gypsum and anhydrite content gradually increased towards the top of the upper jurassic sequence ending up with a thick chicken wire gypsum accumulation recording the progradation of a large scale sabkha over the lagoon this phenomenon is related to a progressive aridification and restriction of the amu darya basin that could have begun during the middle late oxfordian and reached its climax during the tithonian with massive halite deposition comparable events occurred in jurassic platforms located along the tethyan margins pointing to regional and global controls on sedimentation

late quaternary tephra layers along the cilento coastline southern italy abstract the results of stratigraphic and tephrostratigraphic analyses of several pyroclastic levels collected along the coastal sector of the cilento region southern italy are presented some of these levels are here described for the fist time others already known in literature were reconsidered in order to better understand their stratigraphic position and to point out the possible volcanic sources the main outcrops are located along the southern coast of the campania region cilento coast all pyroclastic layers are interbedded within coastal or continental successions younger than the substage 5e of the last interglacial the results of sem eds analyses on well preserved glass fragments indicate a composition falling between the trachyte and phonolite fields of the tas plot as typical of phlaegrean fields products by comparing their composition with those of the main tephra marker layers recorded in southern italy the correlation of the cilento pyroclastic layers with well known eruptive episodes was hypothesised in summary four different eruptions were recognised the first one is testified by a pyroclastic layer not correlated with a terrestrial counterpart covered by a middle pleistocene alluvial fan the second one is the eruptive event emplacing the x 6 marker tephra layer and dates around 107 ka the third is the campanian ignimbrite eruption 39 ka and the last one is testified by the layers correlated with the y 3 tephra about 30 ka these pyroclastic layers can be useful tools for stratigraphic correlations of late quaternary successions in southern italy

modeling the effects of eruptive and seismic activities on flank instability at mount etna italy 1 the identification and evaluation of trigger mechanisms for volcano flank instabilities and or collapse represent a key issue for risk assessment in densely populated volcanic areas as well as in long distance settings particularly in case of island or coastal volcanoes here we address quantitatively the effects of external seismic and inner magmatic forcing on the stress strain state associated to flank instabilities at mount etna sicily southern italy by means of a 2 d finite difference method numerical modeling modeled seismic actions include strong near field strong far field and low magnitude near field earthquakes magmatic actions consider the inner pressure changes induced by energetic lava fountains in the summit crater area and subvertical and oblique dike ascent below the summit area model results are validated in light of available monitoring data and recent eruptive activity numerical results show that the main strain effects are produced by high magnitude near field earthquakes expected return time of 103 yrs and by vertical uprise of a magma dike below the volcano summit area maximum displacements in the order of tens of centimeters may involve the summit area up to some 106 m3 m over some kilometers laterally stress releases up to 107 pa may affect a limited portion of the magmatic conduit thus favoring major effusive flank eruptions major catastrophic events such as volcano flank collapse should not be expected by applying either individually or combined the aforementioned actions

leaving the city for the suburbs the dominance of ordinary decision making over volcanic risk perception in the production of volcanic risk on mt etna sicily abstract the belief that perception plays a central role in the production of risk has tended to dominate research on natural hazards critics have commented on its lack of explanatory power in situations where individuals are heavily constrained in their actions but less has been said about how it might also be a weak form of explanation in contexts where individuals have more choices albeit ultimately bounded on etna italy in the last fifty years the expansion of towns to accommodate the city of catania s population has taken place despite very obvious threats from volcanic activity and alternative safer sites for building being available people are moving into these towns for the same reasons people across the world are moving out of cities to improve their quality of life individuals living in one of these expanded towns trecastagni appear to cognitively diminish their perceptions of volcanic threat within a context of social representations of low risk this is especially true of those who have moved into the town it is concluded that the production of risk within society on etna is strongly related to the socio economic nature of the region and wider european and global contexts that create opportunities and constraints across socio physical space encouraging behaviour and forms of life that are higher risk risk perception appears to play little or no role in this process

an exceptional case of endogenous lava dome growth spawning pyroclastic avalanches the 1999 bocca nuova eruption of mt etna italy abstract during an eruption at the bocca nuova one of the summit craters of mt etna in october november 1999 a part of the crater floor near its wnw rim was uplifted to form a dome shaped feature that consisted of older lava and pyroclastics filling the crater this endogenous dome grew rapidly over the crater rim thus being perched precariously over the steep outer slope of the bocca nuova and near continuous collapse of its steep flanks generated swiftly moving pyroclastic avalanches over a period of several hours these avalanches advanced at speeds of 10 20 m s and extended up to 0 7 km from their source on top of lavas emplaced immediately before their deposits were subsequently covered by lava flows that issued from vents below the front of the dome and from the bocca nuova itself growth of the dome was caused by the vertical intrusion of magma in the marginal western part of the crater which deformed and uplifted previously emplaced still hot and plastically deformable eruptive products filling the crater the resulting avalanches had all the characteristics of pyroclastic flows spawned by collapse of unstable flanks of lava domes but in this case the magma involved was of mafic hawaiitic composition and would under normal circumstances have produced fluid lava flows the formation of the dome and the generation of the pyroclastic avalanches owe their occurrence to the rheological properties of the eruptive products filling the crater which were transformed into the dome and to the morphological configuration of the bocca nuova and its surroundings the density contrast between successive erupted products may also have played a role although events of this type are to be considered exceptional at etna their recurrence might represent a serious hazard to visitors to the summit area

reflectance and color variations on mercury regolith processes and compositional heterogeneity multispectral images of mercury obtained by the messenger spacecraft reveal that its surface has an overall relatively low reflectance with three large scale units identified on the basis of reflectance and slope 0 4 to 1 0 micrometer a higher reflectance relatively red material occurs as a distinct class of smooth plains that were likely emplaced volcanically a lower reflectance material with a lesser spectral slope may represent a distinct crustal component enriched in opaque minerals possibly more common at depth a spectrally intermediate terrain probably forms most of the upper crust three other spectrally distinct but spatially restricted units include fresh crater ejecta less affected by space weathering than other surface materials high reflectance deposits seen in some crater floors and moderately high reflectance relatively reddish material associated with rimless depressions

debris avalanche deposits of the milo lahar sequence and the opening of the valle del bove on etna volcano italy previously undescribed debris avalanche deposits occur in two locations downslope from the open end of the valle del bove these outcrops comprise unstratified ungraded deposits of metre scale lava blocks in a matrix of weathered and fractured lava clasts the avalanche deposits are unconformably overlain by matrix to clast supported conglomerates representing debris flow and interbedded fluvial deposits that constitute most of the milo lahar sequence we present evidence that the milo lahar sequence which crops out just at the exit of the valle del bove formed during the opening and enlargement of this depression the presence of the avalanche deposits at the base of the milo lahar sequence indicates that catastrophic landslides were involved in the formation of the valle del bove the composition of lavas in the debris avalanche deposits is similar to that of most of the ellittico volcanic sequence exposed along the northern wall of the valle del bove radiocarbon dates of 8400 and 5300 years bp from the base and top respectively of the debris flow sequence indicate that the milo lahars are correlative with the exposed part of the chiancone deposit the basal lahars of the chiancone which contain lava blocks whose compositions partially overlap that of blocks in the avalanche deposits may have formed by water concentration in the distal end of the avalanche causing transformation to debris or alternatively by reworking of the avalanche deposit

geological and geomorphological evolution of the etna volcano ne flank and relationships between lava flow invasions and erosional processes in the alcantara valley italy abstract in this paper the interrelationships between volcanic activity and fluvial events in the alcantara valley are investigated based on the correlation between the stratigraphy of the ne flank of mt etna and subsurface data the geological and geomorphological evolutions of the valley are reconstructed new 1 10 000 scale geological mapping shows that the bulk of this sector of the volcano is made up of the ellittico volcano lava flows though they are widely covered by the products of the eruptive activity of the last 15 ka the present day morphological setting of the alcantara valley is the result of two main evolutionary phases initiated during the activity of the ellittico volcano only one lava flow invasion of the valley floor occurred in the first phase this phenomenon was followed by a long period of erosional processes leading to the entrenchment of the drainage pattern and the erosion of the ellittico lava flow about 20 25 ka ago an important change in the frequency of the lava flow invasions into the valley occurred associated with the final stage of the ellittico volcano activity marking the beginning of the second phase during this phase volcanic processes became predominant with respect to other morphogenetic processes in the alcantara valley lava flows coming from the ne flank of the ellittico volcano caused a radical modification of the morphological setting of this area even though only one lava flow emitted by an eruptive fissure located within the valley partially filled the riverbed during the eruptive activity of the last 15 ka the complete filling of the alcantara valley floor occurred in particular between 15 and 7 ka a lava flow originated from the mt moio scoria cone filled the valley floor for a distance of about 9 km following a short period of erosion an eruptive fissure located within the valley generated a 20 21 km long lava flow that was channelled along the full extent of the alcantara valley and stretches for about 3 km offshore in the ionian sea in the last 7 ka lava flows originating from the ne rift zone produced only temporary damming of the riverbed without any important contribution to the filling of the alcantara valley

the origin of lunar concentric craters abstract lunar concentric craters are a unique class of impact craters because the interior of the craters contains a concentric ridge but their formation mechanism is unknown in order to determine the origin of concentric craters we examined multiple working hypotheses which include eight impact related and endogenic processes we analyzed data sets that originated from instruments onboard clementine kaguya and the lunar reconnaissance orbiter to characterize the morphology spatial distribution composition and absolute model ages of 114 concentric craters concentric craters contain five key properties 1 a concentric ridge 2 anomalously shallow floors 3 their occurrence is concentrated near mare margins and in mare pond regions 4 the concentric ridge composition is similar to the surrounding area and 5 concentric crater ages are eratosthenian and older these five key properties served as constraints for testing impact related and endogenic mechanisms of formation we find that most impact related hypotheses cannot explain the spatial and age distribution of concentric craters as for endogenic hypotheses we deduce that igneous intrusions are the likely mechanism that formed concentric craters because of the close relationship between concentric craters and floor fractured craters and the concentration of both features near mare highland boundaries and in mare ponds furthermore we observe that floor fractured craters are common at crater diameters 15 km whereas concentric craters are common at crater diameters 15 km produce floor fractured craters

multispectral images of mercury from the first messenger flyby analysis of global and regional color trends abstract we have analyzed messenger multispectral images of mercury in order to gain information on the nature of materials present on the planet s surface the quantitative analysis tools of lucey which are built on the hapke conceptual framework for the reflectance of a silicate regolith allow us to derive spectral parameter images that are sensitive to the abundance of ferrous iron in silicates the abundance of opaque phases and the state of maturity of the surface consistent with previous estimates we conclude that the silicate portion of mercury s surface is low in ferrous iron with a small range of variation the spectral changes that accompany regolith maturation on mercury are consistent with lunar style space weathering via the accumulation of nanophase iron the spectral character of mercury s major surface units high reflectance plains intermediate terrain and low reflectance material can be attributed to variations in the abundance of an opaque phase s a class of minor color unit the red spots occurs in at least three morphological varieties two of which are associated with deposits interpreted to be of pyroclastic origin the bright crater floor deposits a second type of minor unit have extremely shallow blue spectral slopes that are unrelated to the presence of immature material

intercrater plains on mercury insights into unit definition characterization and origin from messenger datasets abstract orbital observations by the mercury surface space environment geochemistry and ranging messenger spacecraft are used to re evaluate the nature and origin of the oldest mapped plains deposits on mercury the intercrater and intermediate plains units defined by mariner 10 investigators despite the large areal extent of these plains which comprise approximately one third of the planetary surface area viewed by mariner 10 their formation mechanism was not well constrained by mariner 10 imaging one hypothesis attributed plains formation to ponding of fluidized impact ejecta to create relatively smooth surfaces another hypothesis was that these plains are of volcanic origin to assess the origin of these older plains and the contribution of early volcanism to resurfacing on mercury we have used messenger data to analyze the morphology spectral properties impact crater statistics and topography of mariner 10 type areas of intercrater and intermediate plains on the basis of new criteria for the identification of intercrater and intermediate plains derived from these observations we have remapped 18 of the surface of mercury we find that the intercrater plains are a highly textured unit with an abundance of secondary craters whereas the intermediate plains are composed of both intercrater and smooth plains we suggest that the term intermediate plains not be used to map the surface of mercury henceforth but rather this unit should be subdivided into its constituent intercrater and smooth plains units we argue that a substantial percentage of the intercrater plains are composed of volcanic materials on the basis of 1 examples of areas where ejecta from a small number of superposed craters have transformed smooth plains deposits of volcanic origin into a unit indistinguishable from intercrater plains 2 the range in ages of intercrater plains deposits as interpreted from crater size frequency distributions and 3 the near global distribution of intercrater plains compared with the uneven distribution of impact basins and their associated ejecta deposits

the geochemistry of indian bole horizons palaeoenvironmental implications of deccan intravolcanic palaeosurfaces deccan intravolcanic bole horizons represent weathering products formed during major hiatuses of a major volcanic episode in these quiescent periods weathering processes pervasively altered the newly formed volcanic landscape and subsequent flows covered and effectively fossilized the resulting weathered palaeosurfaces the current work is a detailed geochemical study which examines patterns of element mobilization during these intravolcanic weathering events the bole horizons normally rest on top of altered basaltic lavas both boles and altered lavas represent a comparatively early stage in weathering because the content of chemically residual elements such as aluminium and iron are closer to fresh basalt than laterite nevertheless these is clear evidence for significant chemical alteration because the more mobile elements such as calcium and sodium have been substantially removed a chemically distinctive nature for some boles can be demonstrated from chondrite normalized ree plots and in these instances strontium and neodymium isotopic compositions demonstrate that the fine grained bole material is derived from a chemically distinct source in addition thin sections reveal that these fine grained portions commonly contains glass shards and occasionally fresh phenocrysts it is therefore suggested that many deccan boles are in fact weathered pyroclastic material and that the pyroclastic content of the basaltic succession may be greater than previously supposed a significant pyroclastic input during the deccan eruptions has important palaeoenvironmental implications for the fate of late cretaceous flora and fauna in peninsular india

relevance of the chiancone volcaniclastic deposit in the recent history of etna volcano italy abstract the chiancone ch deposit is a volcaniclastic fan on the eastern flank of mt etna it crops out from the exit of the depression of the valle del bove 350 m a s l to the sea in an area which covers about 40 km 2 with a maximum thickness of about 30 m and a slope of 3 4 towards the east the total volume of the deposit is unknown because the base does not crop out but some geophysical data suggest a maximum thickness of about 300 m leading to an estimated maximum volume of about 12 km 3 which is comparable to the volume of the valle del bove vdb since this horseshoe shaped valley is considered to be the ch s source region a study of this deposit may allow an understanding of the mechanisms responsible for the origin of the vdb on the basis of stratigraphic and sedimentary studies we divided the ch sequence into two main parts the basal portion lithofacies 1 is visible only along the coast and has a width of about 6 5 km a thickness of 1 4 m and appears as an indurated horizontal deposit with a flat locally eroded upper surface we consider lithofacies 1 as a huge mud flow which may be associated with an important eruptive event the upper part lithofacies 2 5 is mainly composed of fluvial beds 63 of measured thicknesses that we attribute to events reworking the previously deposited layers the less abundant 23 very coarse grained lenses were caused by fluvial floods thin and discontinuous pyroclastic layers are accidentally 3 interbedded into the sequence the upper portion of the ch sequence is up to 30 m thick and formed after 7590 130 yr b p as established by our new radiocarbon dating when the chemical data obtained on lava blocks sampled from lithofacies 1 4 are compared with products of older eruptive centres it may be argued that the major direction of transport occurred from west to east and involved erosion of those old eruptive centres which were located in the central northern part of the vdb our data suggest the occurrence of an important eruptive event at least 7590 yr b p which may be associated with the deposition of the huge basal mud flow this event was followed by fluvial reworking and deposition at a rate of at least 4 mm yr extending this deposition rate to the whole thickness of the ch deposit 300 m would imply a maximum age of 80 000 70 000 yr b p however the deposition rate of the hidden part of the ch deposit was almost certainly much greater than 4 mm yr implying an age for the onset of the ch sequence significantly less than 80 000 70 000 yr b p this very strongly suggests that the trifoglietto volcano which is older than 80 000 yr was not involved in the opening of the vdb and the formation of the ch deposit it also suggests that the first event of the opening of the vdb was much older than the 5000 yr proposed by some authors it is possible that the ch was deposited during or slightly later than the life span of the ellittico volcano 40 000 15 000 yr b p

characteristics of lunar mare deposits in smythii and marginis basins implications for magma transport mechanisms an analysis of 34 lunar lava flows and ponds in the eastern limb smythii and marginis basins was undertaken to examine and model the first stages of secondary crustal formation and assess processes involved in magma transport and eruption in order to isolate the characteristics of single eruptive episodes we focused on discrete mare ponds adjacent to the major mafia mean values for areas and volumes of deposits estimated to be good candidates for single eruptive phases are large approximately 950 1000 km 2 and 200 km 3 respectively these eruptive volumes are commensurate with the largest known terrestrial eruptions flood basalts the lack of geomorphological structures indicative of shallow magma reservoirs indicates that deep probably subcrustal source regions are prevalent with respect to crustal thickness relationships the magnitude and frequency of eruptive events are observed to be greatest in areas of thinnest crust specifically regions of major maria mare smythii mare marginis occur in areas of thinnest crust while isolated ponds occur where the crust is relatively thicker this is consistent with the correlation observed globally between crustal thickness and the magnitude and frequency of eruptive events ages of volcanic flows and pyroclastic events range from early imbrian to imbfian eratosthenian but are concentrated most heavily between 3 80 3 60 ga suggesting a period of peak volcanism beginning around 3 85 ga and lasting approximately 200 ma however the existence of dark halo crater clusters in non mare units within the region suggests the presence of cryptomaha which would indicate an earlier onset of volcanism and a volume of mare matehal potentially greater than that currently exposed on the surface typical nearest neighbor distances suggest deposits derive from reservoirs 100 km in diameter the observations made here are consistent with a magma transport model in which plumes rising diapirically stall at a density boundary under the lunar crust and propagate dikes to the surface through overpressufization

impact induced thermal effects in the lunar and mercurian regoliths while the moon and mercury are similar objects in a geomorphologic sense they also possess important differences particularly in the context of small scale impact phenomena not only is the surface of mercury notably hotter than that of the moon but the impact flux is also more intense at mercury due to higher impact velocities and a greater spatial density of micrometeoroids by extrapolating the terrestrial micrometeoroid flux to the moon and mercury it is found that the impact rate at mercury is 5 5 times greater and the mean impact velocity more than 60 percent higher than at the moon a model of impact melting and vaporization applied to the lunar and mercurian environments indicates that almost 14 times more impact melt and over 20 times more vapor are generated per unit time in the mercurian regolith although the surface temperature plays a role in determining the melt and vapor volumes the difference in impact velocity appears to be markedly more important average craters formed by identical projectiles under the two velocity distributions on the two planets should be very similar in size because differences in the kinetic energy of the average impactors will be offset by the differences in gravitational acceleration as a result variations in regolith mixing should depend more on the actual impact rates than on disparities in excavated volumes each average impact on mercury however will produce more than twice as much impact melt as its lunar counterpart introducing more glass into the mercurian regolith although substantial quantities of impact vapor are produced on both planets mixing of the regolith should occur quickly enough in each case to spread the deposited vapor over large surface areas the resulting vapor coatings should be negligibly small for most purposes a much larger agglutinate population should exist on mercury and individual agglutinates should be similar to those of the lunar highlands reflectance spectra and visual albedos indicate that the mercurian crust possesses relatively small quantities of fe perhaps similar to those of apollo 16 light and dark matrix breccias laboratory studies have demonstrated that as the magnetic fractions which are correlated with agglutinate abundances of soils derived from these breccias increase the differences in 0 565 mm visible light reflectivity between the soils diminish should the regional variations in fe content of the mercurian crust be similar to those of these apollo 16 samples then the intense agglutination environment could account for the lack of optical contrast across the mercurian surface at the same time the very large fraction of impact glass in the regolith would imply that most pyroxenes have been fused and incorporated into these glasses seriously attenuating the fe2 crystal field absorption near 0 9 mm supporting this picture are the most recently published spectral observations of mercury which provide little or no evidence of such an absorption feature

tephra layers in bannock basin eastern mediterranean several volcanic ash layers were identified in cores collected in the bannock basin eastern mediterranean during cruises ban 84 ban 86 and ban 88 of the r v bannock lithological microscopic mineralogical and chemical analyses together with stratigraphic position help in identifying them as tephra layers y 1 y 5 x 2 and w 1 of keller et al gsa bull 89 1978 tephra layer y 1 is stiff and usually deformed and is black to very dark brown in colour it is mainly composed of highly vesicular micropumice with dark brown and colourless limpid glass and it has a benmoritic chemical composition which is typical of mt etna material tephra layer y 5 is composed of soft limpid vitric shards and subordinate micropumice ranging in composition from alkaliphonolitic trachyte to latite and may be correlated with the campanian ignimbrite eruption which occurred about 35 000 years ago in the phlegrean fields the campanian volcanic area in italy tephra layer x 2 is olive grey in colour and is composed of micropumice and glass shards with a chemical composition ranging from alkali phonolitic trachyte to latite its source is probably the campanian volcanic area tephra layer w 1 is dark grey and made up of micropumice and glass shards with a chemical composition ranging from tephrite phonolite to alkali phonolitic trachyte its source is probably the roman volcanic area in italy the volcanic layers have been identified in cores of the basin sill in the central bulge of the basin and on the basin flanks leading up to the cobblestone topography of the mediterranean ridge they could not however be identified in any core raised from beneath the anoxic hypersaline brines important volcanological results are a an extension of the areal distribution of y 1 x 2 and w 1 b correlation of y 1 with the biancavilla ignimbrite of mt etna dated in previous works at about 14 000 yrs b p and c determination of the bimodal chemical composition of y 5 showing that the latter has a composition in accordance with that of the campanian ignimbrite in the phlegrean fields

stratigraphy of the caloris basin mercury abstract the 1300 km diameter caloris impact basin is surrounded by well defined ejecta units that can be recognized from more than 1000 km radially outward from the basin edge a formal rock stratigraphic nomenclature is proposed for the caloris ejecta units which are collectively called the caloris group each of the individual formations within the group are described and compared to similar rock units associated with the lunar imbrium and orientale basins a crater degradation chronology linked the the caloris event is also proposed to assist in stratigraphic correlation on a mercury wide basis

image processing analysis in reconstructing fragmentation and transportation mechanisms of pyroclastic deposits the case of monte pilato rocche rosse eruptions lipari aeolian islands italy abstract a quantitative study of particle morphology of samples from monte pilato rocche rosse deposits lipari aeolian islands italy shows a significant variability in particle structure and texture the study consisted of image processing techniques and multivariate statistical methods in analysis of the quantitative particle morphology data with the goal of identifying the genetic processes responsible for the formation of the deposits from these investigations we numerically define the form of the clasts thus avoiding subjectivity in the classification of clast morphology starting from this clast definition we then construct diagrams in which clasts due to different genetic processes i e magmatic vs hydromagmatic fragmentation are discriminated based on simple nondimensional parameters the application of the methods used seems to be of general interest in discriminating the fragmentation and transportation dynamics responsible for the formation of pyroclastic deposits