relationship between dike and volcanic conduit distribution in a highly eroded monogenetic volcanic field san rafael utah usa we mapped 63 conduits 2000 dike segments and 12 sills in the san rafael subvolcanic field utah united states where this pliocene magmatic system is eroded to a depth of 0 8 km and is exceptionally well exposed although the number of mapped conduits dikes and sills might represent minimums depending on the level of erosion and exposure mapped dikes are more numerous around the areally extensive sills and interact with sills and conduits in complex ways we analyze conduit distribution using kernel density methods and compare results with dike and sill distribution we find that the distribution of conduits matches the major features of dike distribution including development of clusters and distribution of outliers these statistical models are then applied to the distributions of volcanoes in several recently active volcanic fields where intrusion distributions must be inferred from very sparse data and compared with san rafael conduit distribution this comparison supports the use of statistical models in probabilistic hazard assessment for distributed volcanism specifically renewed dike intrusion and potential eruptions in active basaltic systems can be assessed probabilistically from the distribution of older volcanoes in distributed volcanic systems

turbulent heat flux in the upper ocean under sea ice turbulence data from three arctic drift station experiments demonstrate features of turbulent heat transfer in the oceanic boundary layer time series analysis of several w t records shows that heat and momentum flux occur at nearly the same scales typically by turbulent eddies of the order of 10 20 m in horizontal extent and a few meters in vertical extent probability distribution functions of w t have large skewness and kurtosis where the latter confirms that most of the flux occurs in intermittent events with positive and negative excursions an order of magnitude larger than the mean value an estimate of the eddy heat diffusivity in the outer ekman part of the boundary layer based on measured heat flux and temperature gradient during a diurnal tidal cycle over the yermak plateau slope north of fram strait agrees reasonably well with the eddy viscosity with values as high as 0 15 m2 s 1 an analysis of measurements made near the ice ocean interface at the three stations shows that heat flux increases with both temperature elevation above freezing and with friction velocity at the interface it also reveals a surprising uniformity in parameters describing the heat and mass transfer e g the thickness of the transition sublayer from a modified version of the yaglom kader theory is about 10 cm at all three sites despite nearly a fivefold difference in the under ice roughness z0 which ranges from approximately 2 to 9 cm a much simplified model for heat and mass transfer at the ice ocean interface suggested by the relative uniformity of the heat transfer coefficients at the three sites is outlined

heat flux through sea ice in the western weddell sea convective and conductive transfer processes the heat flux through the snow and sea ice cover and at the ice ocean interface were calculated at five sites in the western weddell sea during autumn and early winter 1992 the ocean heat flux averaged 7 2 w m2 from late february to early june and average ice air heat flux in the second year floes depended on the depth of the snow cover and ranged from 9 to 17 0 8 w m2 in late february three of the five sites had an ice surface which was depressed below sea level resulting at two of the sites in a partially flooded snow cover and a slush layer at the snow ice interface as this slush layer froze to form snow ice the dense brine which was rejected flowed out through brine drainage channels and was replaced by lower salinity nutrient rich seawater from the ocean upper layer we estimate that about half of the second year ice in the region was covered with this slush layer early in the winter as the slush layer froze over a 2 to 3 week period the convection within the ice transported salt from the ice to the upper ocean and increased total heat flux through the overlying ice and snow cover on an area wide basis approximately 10 cm of snow ice growth occurred within second year pack ice primarily during a 2 to 3 week period in february and march this ice growth near the surface of the ice provides a salt flux to the upper ocean equivalent to 5 cm of ice growth despite the thick about 1 m ice cover in addition to the ice growth in the small area less than 5 open water regions

size distribution of scoria cones within the egrikuyu monogenetic field central anatolia turkey abstract egrikuyu monogenetic field emf is one of the five clusters of monogenetic volcanoes in quaternary central anatolian volcanic province cavp emf consists mainly of scoria cones and a few maars e g kutoren obruk previous studies on monogenetic volcanoes of cavp mainly focused on petrologic evolution of scoria cones rather than the statistical analyses of their morphological parameters using the database compiled by arcasoy 2001 for the morphometric parameters of the scoria cones in the emf we present the power law behavior of their size distribution with respect to basal diameters wco of 77 scoria cones from the whole database both empirical maximum likelihood estimation mle and graphical log log plot methods are used for the estimation of scaling parameter b value of power law for the scoria cones which have basal diameter greater than or equal to 0 36 km however graphical method gives the precise result with the b value of 2 78 0 08 for 77 scoria cones over the width range 0 1 1 23 km herein b value indicates the relative number of the small scoria cones with respect to large ones for a given area the power law behavior of the size distribution of scoria cones in the emf suggests that their occurrence is self organized critical phenomena similar to earthquakes since the size distribution of scoria cones provides information about their eruptive magnitude and occurrence mechanism our results can be directly applied to future risk assessment of the cavp

moho topography in the central andes and its geodynamic implications p to s converted waves at the continental moho together with waves multiply reflected between the earth s surface and the moho have been used to estimate the moho depth and average crustal vp vs variations in the central andes our analysis confirms and significantly complements the moho depth estimates previously obtained from wide angle seismic studies and receiver functions the resulting crustal thickness varies from about 35 km in the forearc region to more than 70 km beneath the plateau and thins 30 km further to the east in the chaco plains beneath the andean plateau the moho is deeper in the north altiplano and shallower in the south puna where the plateau attains its maximum elevation a non linear relation exists between crustal thickness and elevation and bouguer gravity suggesting that the crust shallower than 50 55 km is predominately felsic in contrast to a predominately mafic crust below such a relation also implies a 100 km thick thermal lithosphere beneath the altiplano and with a lithospheric thinning of a few tens of kilometers beneath the puna absence of expected increase in lithospheric thickness in regions of almost doubled crust strongly suggests partial removal of the mantle lithosphere beneath the entire plateau in the subandean ranges at 19 20 s the relation between altitude and crustal thickness indicates a thick lithosphere up to 130 150 km and lithospheric flexure beneath a relative topographic low at the salar de atacama a thick crust 67 km suggests that the lithosphere in this region is abnormally cold and dynamically subsided possibly due to coupling with the subducting plate this may be related to the strongest ms 8 0 known intra slab earthquake in the central andes that happened very close to this region in 1950 the average crustal vp vs ratio is about 1 77 for the altiplano puna and it reaches the highest values 1 80 1 85 beneath the volcanic arc indicating high ambient crustal temperatures and wide spread intra crustal melting 2002 elsevier science b v all rights reserved

relating arctic pack ice stress and deformation under winter conditions 1 together thermodynamic and dynamic processes determine the thickness distribution of the ice cover on polar oceans which governs the exchange of energy between the atmosphere and the ocean key to the dynamic processes is the mechanical behavior of the ice cover during the surface heat budget of the arctic ocean sheba field experiment we deployed sensors to measure the internal ice stress at several locations within a 15 15 km area these measurements are combined with satellite derived ice motion and imagery products the objective is to make a first step toward using these data sources for evaluating sea ice dynamics models by assessing whether the stress signal can be qualitatively linked to the regional scale 10 100 km deformation activity four case studies are presented each with distinguishing characteristics consolidation of the seasonal ice zone against the alaskan coast 5 7 december 1997 advancement of the consolidation zone into the perennial ice pack 11 13 december extreme divergence 14 17 january and consolidation of the pack against wrangel island and the siberian coast 20 23 february the results of this analysis 1 demonstrate that stress measurements are related to the regional deformation behavior of the ice cover 2 confirm that regional scale ice dynamics is primarily a function of coastal geometry and sustained large scale wind direction and magnitude 3 provide continued evidence that the ice pack behaves as a granular hardening plastic and 4 encourage pursuit of efforts to use direct measurements of ice stress and deformation in the formulation and development of sea ice dynamics models

computer simulation models of scoria cone degradation abstract long term erosional modifications of the relatively simple morphology of scoria cinder cones are ideally suited for study by field and computer simulation methods a series of temporally distinct cones in the san francisco and springerville volcanic fields of arizona provides the foundation for documenting the degradational evolution of scoria cones in a semi arid climate progressive changes due to erosion are illustrated by the systematic decrease with increasing age of various morphometric parameters including scoria cone height cone height width ratio hco wco crater depth width ratio and slope angle for example holocene latest pleistocene cones in the san francisco field have a mean hco wco value of 0 178 0 041 a mean maximum slope angle of 29 7 4 2 and a mean average slope angle of 26 4 7 3 whereas the group of pliocene cones have values of 0 077 0 024 20 5 5 8 and 8 7 2 7 respectively comparative morphology of scoria cones is a potentially useful dating tool for mapping volcanic fields in order to better understand the degradational modifications of these volcanic landforms we have developed a numerical approach to simulate the surficial processes responsible for the erosion of a typical scoria cone the simulation algorithm can apply either a linear diffusion equation model or a model with a nonlinear transport law using a finite difference formulation the simulation operates upon a three dimensional scoria cone input as a matrix of elevation values utilizing both field and model results the correlation between changing hco wco value cone age and computer time step was expressed graphically to derive comprehensive values of the transport or diffusion coefficient df for both volcanic fields for the san francisco volcanic field df had a calculated value of 21 4 m2 kyr for the linear model and 5 3 m kyr for the nonlinear model while for the springerville volcanic field df had a calculated value of 24 4 m2 kyr for the linear model and 6 3 m kyr for the nonlinear model

sea ice melting and floe geometry in a simple ice ocean model a coupled sea ice ocean numerical model has been developed that addresses the role of floe geometry during summertime melting the model contains a diagnostic equation for average floe diameter in addition to the usual prognostic equations for ice volume per unit area and ice concentration the partition between melting on the top bottom and lateral side surfaces of floes is examined using time dependent simulations with differing initial average floe diameters the different parameterizations for bottom and lateral melting in the literature are also compared and found to vary significantly the results show that lateral melting is important only for floes with diameters less than o 30 m given atmospheric thermal forcing typical of the central arctic in summer this means that the decrease in ice concentration over the summer is a strong function of floe diameter in keeping with simple geometrical arguments in all cases about 80 of the net thermal energy that enters the ocean through leads goes toward melting ice while the rest warms the ocean

polycyclic scoria cones of the antofagasta de la sierra basin southern puna plateau argentina fil baez walter ariel consejo nacional de investigaciones cientificas y tecnicas centro cientifico tecnologico conicet salta instituto de investigaciones en energia no convencional universidad nacional de salta facultad de ciencias exactas departamento de fisica instituto de investigaciones en energia no convencional argentina

geochemical isotopic and single crystal 40ar 39ar age constraints on the evolution of the cerro galan ignimbrites the giant ignimbrites that erupted from the cerro galan caldera complex in the southern puna of the high andean plateau are considered to be linked to crustal and mantle melting as a consequence of delamination of gravitationally unstable thickened crust and mantle lithosphere over a steepening subduction zone major and trace element analyses of cerro galan ignimbrites 68 71 sio2 that include 75 new analyses can be interpreted as reflecting evolution at three crustal levels afc modeling and new fractionation corrected 18o values from quartz 7 63 8 85 are consistent with the ignimbrite magmas being near 50 50 mixtures of enriched mantle 87sr 86sr 0 7055 and crustal melts 87sr 86sr near 0 715 0 735 processes at lower crustal levels are predicated on steep heavy ree patterns sm yb 4 7 high sr contents 250 ppm and very low nb ta 9 5 ratios which are attributed to amphibolite partial melts mixing with fractionating mantle basalts to produce hybrid melts that rise leaving a gravitationally unstable garnet bearing residue processes at mid crustal levels create large negative eu anomalies eu eu 0 45 0 70 and variable trace element enrichment in a crystallizing mush zone with a temperature near 800 850 c the mush zone is repeatedly recharged from depth and partially evacuated into upper crustal magma chambers at times of regional contraction crystallinity differences in the ignimbrites are attributed to biotite zoned plagioclase and other antecrysts entering higher level chambers where variable amounts of near eutectic crystallization occurs at temperatures as low as 680 c just preceding eruption 40ar 39ar single crystal sanidine weighted mean plateau and isochron ages combined with trace element patterns show that the galan ignimbrite erupted in more than one batch including a 2 13 ma intracaldera flow and outflows to the west and north at near 2 09 and 2 06 ma episodic delamination of gravitationally unstable lower crust and mantle lithosphere and injection of basaltic magmas whose changing chemistry reflects their evolution over a steepening subduction zone could trigger the eruptions of the cerro galan ignimbrites

teleseismic tomography of the southern puna plateau in argentina and adjacent regions abstract we performed a teleseismic p wave tomography study using seismic events at both teleseismic and regional distances recorded by a temporary seismic array in the argentine puna plateau and adjacent regions the tomographic images show the presence of a number of positive and negative anomalies in a depth range of 20 300 km beneath the array the most prominent of these anomalies corresponds to a low velocity body located in the crust most clearly seen in the center of the array 27 s 67 w between the cerro peinado volcano the cerro blanco caldera and the farallon negro in the east this anomaly southern puna magmatic body extends from the northern most part of the array and follows the line with the highest density of stations towards the south where it becomes smaller it is flanked by high velocities on the west and the east respectively on the west the high velocities might be related to the subducted nazca plate on the northeast the high velocity block coincides with the position of the hombre muerto basin in the crust and could be indicating an area of lithospheric delamination where we detected a high velocity block at 100 km depth on the eastern border of the puna plateau north of galan this block might be related to a delamination event in an area with a thick crust of paleozoic metamorphic rocks at the border between puna and eastern cordillera in the center of the array the southern puna magmatic body is also flanked by high velocities but the most prominent region is located on the east and is interpreted as part of the sierras pampeanas lithosphere with high velocities the position of the sierras pampeanas geological province is key in this area as it appears to limit the extension of the plateau towards the south

new criteria for systematic mapping and reliability assessment of monogenetic volcanic vent alignments and elongate volcanic vents for crustal stress analyses abstract linear arrays of monogenetic volcanic vent alignments represent an important source of stress strain data from volcanic regions of the earth and other planets currently however there is no standard methodology for mapping vent alignments or for assessing alignment reliability which are essential to defining a robust stress datum from vent alignments here we define a systematic method for defining monogenetic vent alignments by mapping the locations and shapes of vents elongation of vents into elliptical shapes is directly related to the trend of subsurface fissures that control alignments elongated vents therefore are critical for defining reliable regional vent alignments and also provide an independent means for assessing stress directions our reliability assessment system a b c d for vent alignments is based on the number of vents the standard deviation of vent center points from a best fit line the numbers and types of elongate vents the standard deviation of long axes of elliptical vents from a best fit line and in cases where alignments lack elongate vents by vent spacing distances we quantified morphometric parameters of well defined fissure fed vent alignments from polygenetic volcanoes and platform volcanic fields to establish appropriate threshold values for reliability assessments in this new method the combined analysis of vent locations and shapes optimizes the process of alignment mapping and the assessment of the reliability of alignments to be incorporated in stress analyses we provide quality ranking schemes for stress data derived from reliability assessed vent alignments and from elongate vents we demonstrate the utility of this new mapping and assessment methodology by analyzing monogenetic cinder cone fields within a platform volcanic field the san francisco volcanic field in arizona and within a volcanic field on the flank of a polygenetic volcano mount morning in antarctica

scaling laws of the size distribution of monogenetic volcanoes within the michoacan guanajuato volcanic field mexico abstract the michoacan guanajuato volcanic field displays about 1040 monogenetic volcanoes mainly composed of basaltic cinder cones this monogenetic volcanic field is the consequence of a dextral transtensive tectonic regime within the transmexican volcanic belt tmvb the largest intra continental volcanic arc around the world related to the subduction of the rivera and cocos plates underneath the north american plate we performed a statistical analysis for the size distribution of the basal diameter wco for cinder cones dataset used here was compiled by hasenaka and carmichael 1985 monogenetic volcanoes obey a power law very similar to the gutenberg richter law for earthquakes with respect to their size distribution log 10 n wco log 10 wco with 5 01 and 2 98 therefore the monogenetic volcanoes exhibit a wco size distribution empirical power law suggesting a self organized criticality phenomenon

delamination of southern puna lithosphere revealed by body wave attenuation tomography the southern puna plateau has been proposed to result from a major pliocene delamination event that has previously been inferred from geochemical geological and some preliminary geophysical data seventy five seismic stations were deployed across the southern puna plateau in 2007 2009 by scientists from the u s germany chile and argentina to test the delamination model for the region the puna passive seismic stations were located between 25 and 28 s using the seismic waveform data collected from the puna experiment we employ attenuation tomography methods to resolve both compressional and shear quality factors qp and qs respectively in the crust and uppermost mantle the images clearly show a high q nazca slab subducting eastward beneath the puna plateau and another high q block with a westward dip beneath the eastern cordillera we suggest that the latter is a piece of delaminated south american lithosphere a significant low q zone lies between the nazca slab and the south american lithosphere and extends southward from the northern margin of the seismic array at 25 s before vanishing around 27 5 s this low q zone extends farther west in the crust and uppermost mantle at the southern end of the seismic array the low q zone reaches 100 km depth beneath the northern part of the array but only 50 km depth in the south lateral variations of the low q zone reflect the possible mechanism conversion between mantle upwelling related to delamination and dehydration the depth of the nazca slab as defined by q images decreases from north to south beneath the plateau which is consistent with the steep flat transition of the angle of the subducting slab as defined by previous earthquake studies

morphometry of scoria cones and their relation to geodynamic setting a dem based analysis abstract the morphometry of a great number of scoria cones belonging to volcanic fields of various geodynamic settings has been measured and analyzed addressing the question whether there is a relation between the prevalent cone shape in a given field and the geodynamic setting of the field itself morphometric analysis was carried out on freely downloadable digital elevation models dems the accuracy of the used dems and the associated error in scoria cone morphometry were determined by cross comparing high resolution lidar derived dems usgs ned tinitaly dem and aster gdem the 10 m tinitaly 01 and usgs ned dems are proven to be suitable for scoria cone morphometry whereas aster gdem can be used reliably for cones with volume greater than 30 10 6 m 3 according to a detailed morphometry of all scoria cones we propose that the cones related to subductional setting show relatively higher values of h c o w co and lower values of w cr w co than the cones related to extensional setting the detected differences can be imputable to peculiar eruption dynamics resulting in slight but systematic changes in shape and differences in lithological and sedimentological characteristics that govern post eruptive erosion to constrain the pathway of scoria cone erosion the detected morphometric changes were also interpreted using a simple linear degradation model utilizing the obtained simulation results the inferred initial cone base and the age of scoria cones we calculated a diffusion coefficient k for several dated cones which are related to the prevalent climate our results despite the high error associated allow to assess the median k for all volcanic fields due to the complexity of the factors behind it is not easy to understand if the prevalent shape characterizing a certain volcanic field is due mainly to sin eruptive or post eruptive mechanisms however our distinction between the two main geodynamic settings may be the first step to decipher these factors

geomorphology morphometry spatial distribution and ages of mafic monogenetic volcanoes of the peinado and incahuasi fields southernmost central volcanic zone of the andes abstract the back arc southern puna region south of 24 s in the central volcanic zone of the andes contains hundreds of miocene to quaternary mafic monogenetic volcanoes roughly distributed in several volcanic fields analysis of the geomorphology morphometry spatial distribution and age of 36 mafic monogenetic centers in the peinado and incahuasi fields at the southwestern margin of the puna plateau gives insights on the links that mafic monogenetic volcanism can have with main and secondary structures and the effects of degradation on scoria cone shape degree of preservation morphometry and six new unspiked k ar ages indicate two distinct age groups old centers 2 ma and young centers 1 ma the older mafic centers consist of degraded scoria cones and lava flows with an estimated cumulative bulk volume of 2 2 km3 the younger mafic centers display a variety of well preserved landforms scoria cones lava flows maars tuff rings domes and have an estimated cumulative volume of 6 2 km3 their distribution in a main nne ssw and secondary ene wsw trends suggests a control by the regional nne ssw striking peinado and san francisco fault systems in a dextral strike slip configuration scoria cone and lava flow morphometries are similar in both fields but a marked difference indicating hydrovolcanic activity is the presence of tuff rings maars and tephra fallout deposits only in the peinado field morphometric analysis of dated pristine and degraded scoria cones of the southern puna region shows that parameters related to crater depth and inner crater steepness decrease consistently with age suggesting that crater infilling is the degradation related process that is most sensitive to age at scoria cones in the southern puna high values of crater depth crater width crater depth cone height and mean inner crater slope are indicative of a young 1 ma age as young cones can have initially low values

uplift of the central andean plateau and bending of the bolivian orocline the topography of the central andes can be considered the primary tectonic signal of late cenozoic mountain building in an arid region where the effects of uplift and magmatism are little obscured by denudation the spatial coverage of the topographic signal is more complete than that for sparsely sampled geological and geophysical data a color coded image of digitized topography between 12 s and 37 s highlights the altiplano puna one of the world s most remarkable plateaus and reveals important physiographic clues about the formation of that major feature the topographic data combined with information on structure magmatism seismicity and paleomagnetism support a simple kinematical model for the late cenozoic evolution of the central andes the model does not require collisional effects or enormous volumes of intrusive additions to the crust but instead calls upon plausible amounts of crustal shortening and lithospheric thinning the model interrelates andean uplift a changing geometry of the subducted nazca plate and a changing outline in map view of the leading edge of the south american plate crustal shortening has accommodated convergence between the chilean peruvian forearc and the south american foreland the altiplano puna plateau can be constructed by a combination of crustal shortening and thickening and lithospheric thinning above a shallow dipping 20 30 subducted plate the seawardly concave bend of western south america the bolivian orocline was enhanced but not completely produced by an along strike variation in the amount of late cenozoic shortening maximum shortening in bolivia both produced the widest part of the plateau and increased the seaward concavity of the bolivian orocline the along strike variations of shortening are hypothesized to result from corresponding along strike variations in the width of a weakened zone in the overriding plate weakening occurs above the wedge of asthenosphere located between the subducted and overriding plates hence the width of the zone of weakening depends upon the dip of the subducted plate two types of shortening are recognized 1 a widespread basin and range laramide like shortening that characterizes modem activity in the sierras pampeanas and late miocene deformation of the altiplano puna and 2 on the eastern side of the cordilleras and plateau an east verging foreland fold thrust belt in which the underthrust foreland compresses and thickens the ductile lower crust and produces a plateau uplift of the upper crust the second type of shortening can be applied to plio quaternary deformations throughout the central andes but with a substantial narrowing of the region of plateau uplift in peru and south of 28 s a proposed monoclinal flexure of the upper crust on the western side of the plateau uplift explains the remarkably simple and regular morphology of the main western slope of the central andes the monocline is located above the tip of the asthenospheric wedge between the converging plates it is postulated to occur above the western limit of lower crustal thickening in the regions of horizontal subduction the monocline can be associated with a late miocene asthenospheric wedge tip

shallowing and steepening subduction zones continental lithospheric loss magmatism and crustal flow under the central andean altiplano puna plateau

geomorphology and spatial distribution of monogenetic volcanoes in the southern puna plateau nw argentina abstract monogenetic volcanoes are the most common volcanic landforms on earth several works have shown that the study of geomorphology and spatial distribution of such small volcanoes reveals important aspects related to the volcanic field from eruption dynamics to tectonic processes the altiplano puna plateau 15 to 27 s central andes comprises the largest non collisional plateau on earth characterized by intensive deformation uplift and volcanism this region is marked by the presence of hundreds of mafic monogenetic volcanoes despite its discrete occurrence the monogenetic volcanoes show a close relationship with large scale lithospheric foundering events in the region in this contribution we applied a geographic information system gis approach in order to build the first complete catalog of monogenetic landforms present in the southern puna plateau 24 30 to 27 00 s nw argentina exploring their evolution and relationship with geotectonic events combining spatial analysis with a geomorphological study of each volcano it was possible to identify the presence of 285 monogenetic volcanoes in the region which could be grouped in seven clusters southern puna shows a predominance of cinder cones and lava domes suggesting a small influence of water in the eruption dynamics despite its high clustering degree southern puna monogenetic vents present a low density 8 3 10 3 vents km2 when compared to other monogenetic fields around the world in addition puna plateau cones show a close relationship with monogenetic cones associated with an extensional environment considering their back arc context based on relative and available absolute ages it was possible to map the volcanism evolution through time the results indicate that the first monogenetic volcanoes appeared in the central region of the plateau sierra de calalaste mainly associated with large scale nne ssw reactivated faults the activity then expanded antofalla and antofagasta regions and finally reached the borders of the plateau pasto ventura and arizaro regions which show volcanoes associated with nw se normal faults

identification of volcanic rootless cones ice mounds and impact craters on earth and mars using spatial distribution as a remote sensing tool 1 this study aims to quantify the spatial distribution of terrestrial volcanic rootless cones and ice mounds for the purpose of identifying analogous martian features using a nearest neighbor nn methodology we use the statistics r ratio of the mean nn distance to that expected from a random distribution and c a measure of departure from randomness we interpret r as a measure of clustering and as a diagnostic for discriminating feature types all terrestrial groups of rootless cones and ice mounds are clustered r 0 51 0 94 relative to a random distribution applying this same methodology to martian feature fields of unknown origin similarly yields r of 0 57 0 93 indicating that their spatial distributions are consistent with both ice mound or rootless cone origins but not impact craters each martian impact crater group has r 1 00 i e the craters are spaced at least as far apart as expected at random similar degrees of clustering preclude discrimination between rootless cones and ice mounds based solely on r values however the distribution of pairwise nn distances in each feature field shows marked differences between these two feature types in skewness and kurtosis terrestrial ice mounds skewness 1 17 1 99 kurtosis 0 80 4 91 tend to have more skewed and leptokurtic distributions than those of rootless cones skewness 0 54 1 35 kurtosis 0 53 1 13 thus nn analysis can be a powerful tool for distinguishing geological features such as rootless cones ice mounds and impact craters particularly when degradation or modification precludes identification based on morphology alone

velocity structure beneath the southern puna plateau evidence for delamination 1 the high elevation of the southern puna plateau the widespread melting of its crust the gap in intermediate depth seismicity and the recent eruptions of ignimbrite complexes can be explained by delamination of the lithospheric mantle beneath it to test this hypothesis an array consisting of 73 broad band and short period seismic stations was deployed in the region for a period of 2 years starting in 2007 we inverted the data using the two plane wave approach and obtained 1 d and 3 d rayleigh wave phase velocities our dispersion curve shows that at short periods 70 s the phase velocities are slightly higher than those of the tibetan plateau and lower than those of the anatolian plateau at periods of 100 140 s we observe a low velocity zone that might be remnant hot asthenosphere below a flat slab 7 10 ma we estimate the average continental lithosphere thickness for the region to be between 100 and 130 km our three dimensional rayleigh wave phase velocities show a high velocity anomaly at low frequencies 0 007 0 008 and 0 009 hz slightly to the north of cerro galan this would be consistent with the hypothesis of delamination in which a piece of lithosphere has detached and caused upwelling of hot asthenosphere which in turn caused widespread alkaline collision related volcanism this interpretation is also corroborated by our shear wave velocity model where a high velocity anomaly beneath the northern edge of cerro galan at 130 km depth is interpreted as the delaminated block on top of the subducting nazca slab

gis methods applied to the degradation of monogenetic volcanic fields a case study of the holocene volcanism of gran canaria canary islands spain abstract modeling of volcanic morphometry provides reliable measurements of parameters that assist in the determination of volcanic landform degradation variations of the original morphology enable the understanding of patterns affecting erosion and their development facilitating the assessment of associated hazards a total of 24 volcanic holocene eruptions were identified in the island of gran canaria canary islands spain 87 of these eruptions occurred in a wet environment while the rest happened in a dry environment 45 of holocene eruptions are located along short barrancos s type less than 10 km in length 20 along large barrancos l type 10 17 km in length and 35 along extra large barrancos xl type more than 17 km in length the erosional history of holocene volcanic edifices is in the first stage of degradation with a geomorphic signature characterized by a fresh young cone with a sharp profile and a pristine lava flow after intensive field work a careful palaeo geomorphological reconstruction of the 24 holocene eruptions of gran canaria was conducted in order to obtain the digital terrain models dtms of the pre and post eruption terrains from the difference between these dtms the degradation volume and the incision rate were obtained the denudation of volcanic cones and lava flows is relatively independent both their geographical location and the climatic environment however local factors such as pre eruption topography and ravine type have the greatest influence on the erosion of holocene volcanic materials in gran canaria although age is a key factor to help understand the morphological evolution of monogenetic volcanic fields the gran canaria holocene volcanism presented in this paper demonstrates that local and regional factors may determine the lack of correlation between morphometric parameters and age consequently the degree of transformation of the volcanic edifices evolves in many cases independently of their age

structure of the crust and the lithosphere beneath the southern puna plateau from teleseismic receiver functions abstract we present a teleseismic p and s receiver function study using data from a temporary passive source seismic array in the southernmost puna plateau and adjacent regions the p receiver function images show the distribution of crustal thickness and v p v s ratio for this area over much of the southern puna plateau the crustal thickness is 50 55 km whereas to the west a thicker crust 60 to 75 km is observed beneath much of the andean volcanic arc region from the puna southward there is little obvious change in the crustal thickness across the border of the plateau south of 28 s the crust is seen to progressively thin towards the east in the pampean ranges where it is 35 40 km thick the southern puna plateau is characterized overall by a low crustal v p v s ratio less than 1 70 implying a felsic crustal composition an anomalously high v p v s ratio of 1 87 is observed beneath the cerro galan volcanic center in the region where a prominent crustal low velocity zone identified below 10 km depth probably extends into the lower crust the crustal thickness determined under the cerro galan area 59 km is close to that of the rest of the southern puna the prominent high v p v s ratio and low velocity zone beneath the galan region implies the presence of a zone of partial melt or a magma chamber is consistent with hypothesis calling for lithospheric delamination beneath the galan caldera a widespread crustal low velocity layer observed beneath much of the southern puna correlates well with crustal low velocity anomalies observed by teleseismic tomography the lithosphere asthenosphere boundary beneath the array can be clearly observed by both p and s receiver functions at depths of 70 90 km in agreement with previous studies suggesting a thin lithosphere beneath the high elevated plateau the mantle transition zone discontinuities appear at expected depths

self similar clustering of cinder cones and crust thickness in the michoacan guanajuato and sierra de chichinautzin volcanic fields trans mexican volcanic belt abstract the spatial clustering of basaltic vents in monogenetic volcanic fields has been used as a proxy for crustal thickness in extensional and back arc tectonic settings the basaltic vents have a fractal clustered distribution self similar clustering described by a power law the power law is defined over a range the size range of the distribution of values in this case the vents separation delimited by a lower and an upper cut offs here we apply the fractal clustering analysis to the two largest monogenetic volcanic fields of the trans mexican volcanic belt tmvb a continental arc built on different crustal terranes the michoacan guanajuato volcanic field mgvf located in the central western tmvb includes over 1000 vents of late pliocene to quaternary age built on attenuated crust of mesozoic to tertiary age the sierra de chichinautzin volcanic field scvf in the central eastern tmvb is composed of 220 late pleistocene to holocene vents laying above thicker crust of precambrian to tertiary age monogenetic vents in both volcanic fields show self similar clustering with fractal exponent d 1 67 in the range 1 3 38 km mgvf and d 1 56 in the range 1 5 32 km scvf the upper cut off uco for the power law distribution of the mgvf well fits the crustal thickness below the volcanic field as derived from independent geophysical data the uco value of scvf indicates a crust thickness of about 32 km this value is in agreement with new geophysical data that indicate magma underplating the crust beneath the volcanic field area

on the record reduction in 1998 western arctic sea ice cover during summer 1998 record reductions in ice cover occurred in the beaufort and chukchi seas open water formed earlier than in prior years and september ice extent in this region was 25 percent less than the previous minimum for 1953 1997 seven percent of the arctic basin that had been perennially ice covered was ice free in 1998 this reduction in western arctic ice extent can be attributed in part to preconditioning by light ice cover in autumn 1997 and to atmospheric circulation patterns during the following winter through autumn that favored southerly and easterly winds such decreases in northerly winds and the associated weakening or displacement of the beaufort gyre is found to be typical of winters that precede years with below normal ice extent in the western arctic

fracture control on type morphology and distribution of parasitic volcanic cones an example from mt etna italy abstract this paper uses a coupled morphometric and stratigraphic analysis of several tens of parasitic pyroclastic cones of the se flank of mt etna volcano italy to explain the structure of a poorly understood actively deforming zone of the volcano moreover we present a new general classification of pyroclastic cones based on the parameterisation of coeval eruption points along the same magma feeding fracture each cone has been studied in detail in order to define its stratigraphic position morphometric characteristics growth evolution in relation to fracture distribution and orientation stress field and morphology of the substratum end members of this classification are at one side a simple circular or elongated edifice that grew around a single eruption point and can be related to a magma feeding fracture constrained by a relatively high confining stress in the substratum or a low magma pressure the other end member is a multiple rifted strongly elongated cone formed along multiple eruption points of a magma feeding fracture constrained by a relatively low confining stress or a high magma pressure lithostratigraphic and historical analyses demonstrate that the cones in this area developed between 15 ka bp and historical times the most recent one in 1669 ad testifying to a high rate of lateral eruption occurrence in the area these cones show n s elongated maximum crater axes n s trending axis of the depressed points of the crater rim and southward and southeastward breaching directions while coeval cones are n s aligned these morphometric characteristics reflect the geometry of n s magma feeding fractures the area can be regarded as a transitional weakness zone between the n s rift and the releasing system represented by the transtensional trecastagni and mascalucia faults indicating an e w oriented local component of extension possibly related to the interplay between the regional timpe fault system and the eastward gravitational spreading of the volcano the azimuth of breaching is controlled by magma feeding fracture orientation and substrate morphology especially in the eastern part of the area where it is influenced by the scarps related to the timpe regional fault system but it is also sensitive to cone development

pulsating flow dynamics of sustained forced pyroclastic density currents insights from a facies analysis of the campo de la piedra pomez ignimbrite southern puna argentina the quaternary campo de la piedra pomez ignimbrite cppi is a superbly exposed partially indurated rhyolitic ignimbrite emplaced on the southern puna of argentina it is characterized by a variety of facies that record in unprecedented detail the flow dynamics of the parent pyroclastic density currents pdcs detailed facies analysis and internal architecture defined using a sequential stratigraphy approach reveal that cppi was formed by sustained pdcs generated from a low fountain eruptive style boiling over the pdcs had overall flow conditions characterized by high particle concentration and limited capability to surmount topographic obstacles the mobility of the pdcs was largely controlled by high pore pressure and the continuous supply at the source sustained forced convection dominated pdcs the successive forestepping backstepping stacking patterns identified in the cppi reflect a marked unsteadiness of its parent pdcs due to a pulsating discharge rate at the source the lateral facies variations in the cppi record the non uniform character of its parent pdcs as they flowed outward from the base of the collapsing fountain proximal medial areas characterized by steady aggradation rates pass through to distal braided thalwegs with highly variable aggradation rates to frontal edges characterized by the step aggradations of secondary decoupled pumice rich lobes collectively the facies variations in the cppi record the complex dynamics of sustained pdcs that include pulsating discharge rate at the source progressive modification of the original topography and lateral flow transformations

miocene pliocene shortening extension and mafic magmatism support small scale lithospheric foundering in the central andes nw argentina

thin and thinner sea ice mass balance measurements during sheba 1 as part of a large interdisciplinary study of the surface heat budget of the arctic ocean sheba we installed more than 135 ice thickness gauges to determine the sea ice mass balance while installing these gauges during the fall of 1997 we found that much of the multiyear ice cover was only 1 m thick considerably thinner than expected over the course of the yearlong field experiment we monitored the mass balance for a wide variety of ice types including first year ice ponded ice unponded ice multiyear ice hummocks new ridges and old ridges initial ice thicknesses for these sites ranged from 0 3 to 8 m and snow depths varied from a few centimeters to more than a meter however for all of their differences and variety these thickness gauges sites shared a common trait at every site there was a net thinning of the ice during the sheba year the thin ice found in october 1997 was even thinner in october 1998 the annual cycle of ice thickness was also similar at all sites there was a steady increase in thickness through the winter that gradually tapered off in the spring this was followed by a steep drop off in thickness during summer melt and another tapering in late summer and early fall as freeze up began maximum surface melting was in july while bottom ablation peaked in august combining results from the sites we found an average winter growth of 0 51 m and a summer melt of 1 26 m which consisted of 0 64 m of surface melt and 0 62 m of bottom melt there was a weak trend for thicker ice to have less winter growth and greater net loss for the year however ice growth was also impacted by the snow depth considerable variability was observed between sites in both accretion and ablation the total accretion during the 9 month growth season ranged from zero for thick ridged ice to more than a meter for young ice ponds tended to have a large amount of surface melting while ridges had considerable bottom ablation

clustering within rootless cone groups on iceland and mars effect of nonrandom processes 1 this study aims at quantifying the spatial distribution of cones within rootless cone groups rcgs our data set consists of 1 seven icelandic rcgs identified through field investigations 2 seven candidate rcgs on mars identified through mars orbiter camera moc and thermal emission imaging system themis images and 3 four groups of impact craters on mars also identified through moc and themis images to determine if they can be remotely distinguished from the rcgs purely on the basis of their spatial distribution several independent statistical techniques are used including nearest neighbor analysis analysis of variance anova and linear alignment detection analysis our results indicate that the spatial distribution of each rcg is not random within a cone group cones preferentially form near existing cones the presence of at least one significant linear cone alignment in each rcg and strong linear alignments in some groups suggests that rootless cones form as the surface signature of preferred lava pathways an anova on mean nearest neighbor distances reveals the martian cone groups to be statistically indistinguishable from the icelandic rcgs supporting existing interpretations that they represent rootless cone groups a similar anova showed that the martian cone groups do not resemble the martian impact crater clusters studied the impact craters have significantly greater nearest neighbor distances and show no evidence of aggregation within a crater group

recent volcano tectonic activity of the ririba rift and the evolution of rifting in south ethiopia abstract the relationships between volcanic activity and tectonics at the southernmost termination of the main ethiopian rift mer east africa still represent a debated problem in the mer evolution new constraints on the timing evolution and characteristics of the poorly documented volcanic activity of the dilo and mega volcanic fields vf near the kenya ethiopia border are here presented and discussed the new data delineate the occurrence of two distinct groups of volcanic rocks 1 pliocene subalkaline basalts observed only in the dilo vf forming a lava basement faulted during a significant rifting phase 2 quaternary alkaline basalts occurring in the two volcanic fields as pyroclastic products and lava flows issued from monogenetic edifices and covering the rift related faults 40ar 39ar dating constrains the emplacement time of the large basal lava plateau to 3 7 ma whereas the youngest volcanic activity characterising the two areas dates back to 134 ka dilo vf to as recent as the holocene mega vf volcanic activity developed along tectonic lineaments independent from those of the rift no direct relations are observed between the pliocene roughly n s trending major boundary faults of the ririba rift and the ne sw oriented structural trend characteristic of the quaternary volcanic activity we speculate that this change in structural trend may be the expression of 1 inherited crustal structures affecting the distribution of the recent volcanic vents and 2 a local stress field controlled by differences in crustal thickness following a major episode of reorganization of extensional structures in the region due to rift propagation and abandonment

morphology of pyroclastic cones and tectonics the relationships between morphology and spatial distribution of 1315 quaternary pyroclastic cones and coeval faulting of the volcanic substrate are analyzed in the following regions with different structural settings tepic rift mexico ethiopian rift mexican volcanic belt canary archipelago and mount etna field data and analog experiments of tephra cone emplacement and collapse enable the definition of a number of parameters which can be used to infer the geometry of the fracture feeding the magma to a pyroclastic cone the strike of the feeding plane is directly related to 1 the elongation of cone base and crater 2 the location of depressions on the crater rim and 3 the alignment of pyroclastic cones in relation to a given vent spacing in addition the strike and dip of faults affect the direction of cone breaching these relationships are valid for volcanic substrate topographic surfaces with an inclination of less than 9 and are especially sensitive to fault escarpment and cone height lava and cone density and fault orientation with respect to the dip of the volcanic substrate topography relations 1 and 2 become more pronounced for regions undergoing extensional tectonics where edifices also have a larger dimension whereas breaching in the direction of the fault dip is more widespread in regions under extension breaching along the fault strike as well as the coincidence between fault strike and vent alignment are more frequent in regions with transcurrent or transtensional tectonics

syn eruptive morphometric variability of monogenetic scoria cones according to wood s model morphometric parameters such as slope angle can provide valuable information about the age of conical volcanic edifices such as scoria cones assuming that their initial slopes range from 30 to 33 measured manually on topographic maps and assuming that their inner architectures are homogenous this study examines the morphometric variability of nine young a few thousand years old small volume scoria cones from tenerife canary islands using high resolution digital elevation models in order to assess their slope angle variability because of the young age and minimal development of gullies on the flanks their morphometric variability can be interpreted as the result of syn eruptive processes including 1 pre eruptive surface inclination 2 vent migration and lava outflow with associated crater breaching and 3 diversity of pyroclastic rocks accumulated in the flanks of these volcanic edifices results show that slope angles for flank sectors differ by up to 12 among the studied volcanoes which formed over the same period of time this range greatly exceeds the 2 3 indicated by wood the greater than expected original slope range suggests that use of morphometric data in terms of morphometry based relative dating and detection of erosional processes and settings must be done with great care or detailed knowledge about absolute ages and eruption history especially in field scale morphometric investigation

normal faulting along the southern margin of the puna plateau northwest argentina 1 though orogen parallel shortening and vertical extension have dominated the tectonic evolution of the central andes a significant kinematic shift from horizontal contraction to extension appears to have occurred within the high puna altiplano plateau with the establishment of extension oblique to the orogen since late miocene time we present data from the southern margin of the puna plateau nw argentina where new normal faults have been documented in the fiambala punta negra and la quebrada areas the unifying characteristics of these areas are that young normal faults reactivate or crosscut older thrust and reverse faults the relationship between the faults and the late miocene pliocene punaschotter conglomerate suggests that the extensional faulting must be younger than 3 5 to 7 ma existing data are incomplete but indicate that similar horizontal extension has occurred in many regions throughout the puna altiplano plateau while shortening continues along the plateau margins given the spatial and temporal distribution of this late miocene to pliocene kinematic shift both lithospheric loss in the puna plateau and plateau wide gravitational extensional spreading enhanced by slowing of plate convergence rate could be responsible the young disorganized horizontal extension in the andes today may be the precursor to more pronounced extension such as observed on the tibetan plateau since mid miocene time

evaluation of morphometry based dating of monogenetic volcanoes a case study from bandas del sur tenerife canary islands morphometry based dating provides a first order estimate of the temporal evolution of monogenetic volcanic edifices located within an intraplate monogenetic volcanic field or on the flanks of a polygenetic volcano two widely used morphometric parameters namely cone height width ratio hmax wco and slope angle were applied to extract chronological information and evaluate their accuracy for morphometry based ordering based on these quantitative parameters extracted from contour based digital elevation models dems two event orders for the bandas del sur in tenerife canary islands were constructed and compared with the existing k ar paleomagnetic and stratigraphic data the results obtained suggest that the commonly used hmax wco ratio is not reliable leading to inappropriate temporal order estimates while the slope angle gives slightly better results the overall performance of such descriptive parameters was however generally poor i e there is no strong correlation between morphometry and age the geomorphic morphometric mismatches could be the result of 1 the diversity of syn eruptive processes i e diverse initial morphologies causing geomorphic morphometric variability 2 contrasting edifice specific degradation that depends partly upon the inner facies architecture of the volcanic edifices 3 various external environmental controls e g tephra mantling from pyroclastic density currents unrelated to the edifice evaluated and 4 differences in the scale resolution of input data the observed degradation trend and changes in morphometric parameters over time do not support a simple degradation model for monogenetic scoria cones volcanoes

winter snow cover on the sea ice of the arctic ocean at the surface heat budget of the arctic ocean sheba temporal evolution and spatial variability 1 the evolution and spatial distribution of the snow cover on the sea ice of the arctic ocean was observed during the surface heat budget of the arctic ocean sheba project the snow cover built up in october and november reached near maximum depth by mid december then remained relatively unchanged until snowmelt ten layers were deposited the result of a similar number of weather events two basic types of snow were present depth hoar and wind slab the depth hoar 37 of the pack was produced by the extreme temperature gradients imposed on the snow the wind slabs 42 of the snowpack were the result of two storms in which there was simultaneous snow and high winds 10 m s 1 the slabs impacted virtually all bulk snow properties emphasizing the importance of episodic events in snowpack development the mean snow depth n 21 169 was 33 7 cm with a bulk density of 0 34 g cm 3 n 357 r2 of 0 987 giving an average snow water equivalent of 11 6 cm 25 higher than the amount record by precipitation gauge both depth and stratigraphy varied significantly with ice type the greatest depth and the greatest variability in depth occurring on deformed ice ridges and rubble fields across all ice types a persistent structural length in depth variations of 20 m was found this appears to be the result of drift features at the snow surface interacting with small scale ice surface structures a number of simple ways of representing the complex temporal and spatial variations of the snow cover in ice ocean atmosphere models are suggested

structural and morphometric irregularities of eroded pliocene scoria cones at the bakony balaton highland volcanic field hungary abstract scoria cones of the mio pliocene bakony balaton highland volcanic field bbhvf are built up by wide range of volcanic rocks including intercalated lava flows dykes pyroclastic breccias and scoriaceous lapilli with various degrees of welding or agglutination according to k ar and ar ar dating ages of the fourteen scoria cones within the field span between 5 2 and 2 5 ma from these fourteen seven cones were selected which are suitable for morphometric analysis i e visible in the field and have identifiable boundaries the morphometric data were either derived by manual measurement on topographic maps and by digital elevation model based calculations using the same input contour line data from 1 10 000 maps basic cone parameters such as cone height basal and crater width have been measured in order to calculate parameters like h co w co ratio and average slope angle the results of these three parameter based manual calculations have been compared to the dem based results in order to highlight the controls of degradation pitfalls in morphometric parameterization and the differences between these two calculation methods based on the results three main controlling conditions have been identified that are together responsible for the preservation and erosion of the scoria cones located in the bbhvf 1 age of the cone 2 climate during the degradation and the 3 inner architecture of the edifice in terms of morphometric dating the traditional three parameter based method tends to give inaccurate results on 1 scattered and or truncated cones and 2 on the edifices characterised by highly effusive behaviour during the emplacement

recent slow normal and strike slip faulting in the pasto ventura region of the southern puna plateau nw argentina 1 recent normal and strike slip faulting on the puna plateau of nw argentina has been linked to lithospheric foundering gravitational spreading plate boundary forces and a decrease in crustal shortening from north to south however the timing kinematics and rate of extension remain poorly constrained we focus on the pasto ventura region nw argentina located on the southern puna plateau and recent deformation 1 ma field mapping and kinematic analysis across offset volcanic cinder cones show that the overall extension direction is subhorizontal is oriented ne sw to nne ssw and occurs at a slow time integrated rate of 0 02 to 0 08 mm yr since at least 0 8 0 5 ma a regional compilation from this study and existing data shows that recent extension across the puna plateau is subhorizontal but varies in azimuthal orientation dramatically data from the pasto ventura region are consistent with a number of models to explain normal and strike slip faulting on the puna plateau all of which likely influence the region some role for lower lithospheric foundering through dripping appears to be seen based on the regional extension directions and ages of mafic volcanism in the southern puna plateau

volcano tectonic setting of the intraplate pliocene holocene newer volcanic province southeast australia role of crustal fracture zones 1 the pliocene holocene newer volcanic province in victoria southeast australia is a wide volcanic field site of the most recent volcanic activity of australia the intraplate signature and the localization on the northern side of the southern ocean have been used in the past to ascribe the volcanic activity either to the presence of a mantle hot spot or to thermal anomalies inherited from the seafloor spreading that separated australia from antarctica during the gondwana breakup the spacing and distribution of groups of eruption points suggests the presence of a 32 km deep mantle thermal anomaly alignments of eruption points indicate a strong tectonic control on magma emplacement mainly along nw se mesozoic cenozoic structures and along n s palaeozoic and e w late cretaceous structures this volcano tectonic setting relates to the interference of the left lateral kinematics of the major n s trending faults associated with the tasman fracture zone and the extensional structures of the otway basin this interpretation is also coherent with stress in situ data and focal mechanisms of earthquakes shmax oriented n150 this interpretation enhances the role of the tasman fracture zone a major sinistral transform on the reactivation of transtensional structures and on triggering the magmatism of the newer volcanic province

the albedo of arctic leads in summer this is the publisher s final pdf the published article is copyrighted by the international glaciological society and can be found at http www igsoc org annals

heat flux at the ice ocean interface the role of the oceanic heat flux fw in the sea ice energy and mass balance is discussed and a method is described for determining fw from measurements of the temperature and thickness of sea ice results obtained using this method and data collected in the fall of 1988 during a drift in the eastern arctic northeast of fram strait are presented estimates of fw ranged from 0 to 37 w m 2 and varied in both time and space the gradual variation over the course of the drift reflects transformation of the west spitsbergen current into arctic water masses a significant intersite variability on horizontal scales of 10 to 100 m is ascribed to the interaction between under ice topographic features and turbulent energy and mass transfer in the boundary layer in addition there is a variability in the ice growth rate on horizontal scales of 0 1 to 1 m which is ascribed to the instability of the ice ocean phase boundary in the presence of turbulent flow these observations have implications for modeling and future experiments

monogenetic volcanism personal views and discussion monogenetic volcanism produces small volume volcanoes with a wide range of eruptive styles lithological features and geomorphic architectures they are classified as spatter cones scoria or cinder cones tuff rings maars maar diatremes and tuff cones based on the magma water ratio dominant eruption styles and their typical surface morphotypes the common interplay between internal such as the physical chemical characteristics of magma and external parameters such as groundwater flow substrate characteristics or topography plays an important role in creating small volume volcanoes with diverse architectures which can give the impression of complexity and of similarities to large volume polygenetic volcanoes in spite of this volcanic facies complexity we defend the term monogenetic volcano and highlight the term s value especially to express volcano morphotypes this study defines a monogenetic volcano a volcanic edifice with a small cumulative volume typically 1 km3 that has been built up by one continuous or many discontinuous small eruptions fed from one or multiple magma batches this definition provides a reasonable explanation of the recently recognized chemical diversities of this type of volcanism

morphometric and morphological development of holocene cinder cones a field and remote sensing study in the tolbachik volcanic field kamchatka article i nfo the evolution of landscape over time is a central aspect of geological paleogeographical and geomorphological studies volcanic features like cinder cones offer the opportunity to monitor the processes and development of the landscape cinder cones are perhaps the simplest and most common volcanic landforms in the world morphological and morphometric study of cinder cones has proven an efficient tool for determining their relative dates and the erosional processes affecting them the extensive kamchatka volcanic province russian far east with its large tolbachik cinder cone field is an excellent case study for spatial and temporal classification and calibration of changes in morphometric values with time we show how the morphological and morphometric values of the monogenetic cinder cones measured in the field and by digital elevation models can be used to validate their age and erosional processes field data were gps measurements of cinder cones formed at the tolbachik 1975 1976 eruption and of holocene cinder cones erosion processes on the cinder cones and lava flows were identified and evaluated for every studied cinder cone morphometric parameters were assessed on the basis of remotely sensed data and digital elevation model morphometric measurements were taken of cone height and slope and average axis diameter and the height width ratio was obtained the comparison of morphometric parameters calculated from aster dem and topographic map clearly supports the concept of relative morphometric dating as the most recent cinder cones are always associated with the highest slopes and h w ratio the measured morphometric values of the recent tolbachik cinder cones are valuable benchmark data for determining erosion rates such as the measured values for the paricutin cone in mexico after the 1943 eruption the variability of the morphometric values of the recent cinder cones is due to their lithological coarse composition a comparison with the older cinder cones in the area shows that the climatic conditions of the kamchatka peninsula and the slow development of vegetation cover determine a high rate of erosion and rapid change in the morphometric values as compared to published values for other volcanic fields

a unique volcanic field in tharsis mars pyroclastic cones as evidence for explosive eruptions based on theoretical grounds explosive basaltic volcanism should be common on mars yet the available morphological evidence is sparse we test this hypothesis by investigating a unique unnamed volcanic field north of the shield volcanoes biblis patera and ulysses patera on mars where we observe several small conical edifices and associated lava flows twenty nine volcanic cones are identified and the morphometry of many of these edifices is determined using established morphometric parameters such as basal width crater width height slope and their respective ratios their morphology morphometry and a comparison to terrestrial analogues suggest that they are martian equivalents of terrestrial pyroclastic cones the most common volcanoes on earth the cones are tentatively interpreted as monogenetic volcanoes according to absolute model age determinations they formed in the amazonian period our results indicate that these pyroclastic cones were formed by explosive activity the cone field is superposed on an old elevated window of fractured crust which survived flooding by younger lava flows it seems possible that a more explosive eruption style was common in the past and that wide spread effusive plain style volcanism in the late amazonian has buried much of its morphological evidence in tharsis

late miocene early pliocene onset of n s extension along the southern margin of the central andean puna plateau evidence from magmatic geochronological and structural observations abstract extensional faulting typifies many of the earth s cenozoic orogenic plateaus the altiplano puna plateau in the southern central andes is the world s second largest orogenic plateau it contains a rich array of extensional fractures and normal faults with closely associated mafic volcanic flows dykes and cones this is in stark contrast to the foreland areas which record protracted shortening and continuous eastward growth of the mountain belt within the puna area a kinematic change over from shortening to extension has previously been inferred to have occurred during the quaternary however our research in the southern puna together with earlier petrologic investigations in the south central part of the plateau indicates an earlier onset for the extensional tectonism our analysis has focused on the eastern portion of the cordillera de san buenaventura in the southernmost part of the plateau where we mapped two upper miocene pliocene volcanic units associated with extensional faulting the aguada alumbrera ignimbrite and the la hoyada volcanic complex the structural inventory of these units records n s extensional deformation in the puna associated with the development of e w oriented fractures dykes normal and strike slip faults and folds new 40ar 39ar dating of magmatic rocks together with their relationships with the mapped structures reveal that widespread extension in the southern puna had already commenced by 5 ma and possibly as early as 7 ma although the extensional structures on the puna are typically associated with mafic volcanism the upper miocene pliocene la hoyada volcanic complex hosts dykes of intermediate compositions mafic to intermediate magmatism and extensional tectonism in this region is thus contemporaneous with and structurally akin to that in the central and northern parts of the plateau the ubiquitous cogenetic relationship between mafic volcanism and extensional tectonism both within the puna plateau and along its eastern flanks clearly indicates that the normal faulting is a regional phenomenon that is broadly coeval with an inferred rapid and large scale uplift of the altiplano puna plateau and a decrease in plate convergence rates these observations are compatible with a mantle delamination scenario in which the delamination of lithospheric mantle may have produced an ensuing weakening of the crust and regional uplift which may in turn have generated the conditions necessary to trigger gravitational extensional collapse beginning in the late miocene to early pliocene

the relations between faulting and mafic magmatism in the altiplano puna plateau central andes mafic lava flows and scoria cone on the altiplano puna plateau correlate spatially and temporalily with late pliocene quternary strike slip faulting thrust faulting dominated deformation in the plateau and adjacent foreland during the miocene pliocene the relations between faulting and mafic magmatism may be explained by a change from vertical to horizontal least principal compression during the pliocene quaternary a model in which mantle derived mafic magma ascends through the thick less dense continental crust of the altiplano puna plateau suggests that nonlithostatic stress in the crust may have controlled the depth and geometry of intrusion horizontal nonlithostatic compression favored the formation of horizontal mafic intrusions in the lower crust which may have thermally weakened the crust localized crustal thickening and caused crustal anatexis horizontal nonlithostatic tension favored vertical intrusions in the crust and surface eruption

a simple model for deglacial meltwater pulses evidence from radiocarbon dating and complex ice sheet modeling suggests that the fastest rate of sea level rise in earth s recent history coincided with collapse of the ice saddle between the laurentide and cordilleran ice sheets during the last deglaciation in this study we derive a simple two equation model of two ice sheets intersecting in an ice saddle we show that two conditions are necessary for producing the acceleration in ice sheet melt associated with meltwater pulses the positive height mass balance feedback and an ice saddle geometry the amplitude and timing of meltwater pulses is sensitively dependent on the rate of climate warming during deglaciation and the relative size of ice sheets undergoing deglaciation we discuss how simulations of meltwater pulses can be improved and the prospect for meltwater pulses under continued climate warming

thickness structure and properties of level summer multiyear ice in the eurasian sector of the arctic ocean in august and september 1991 thickness structure and properties of level multiyear ice were studied at 66 locations in the eurasian sector of the arctic ocean the mean ice thickness was 2 86 m with 0 31 m of freeboard including 0 08 m deteriorated ice of mean density 370 kg m 3 on the basis of the study of ice cores 61 of the ice cover consisted of undeformed columnar ice the remaining 39 consisted of a mixture of ice types including frazil 18 and deformed ice 9 through microstructural studies six main classes of pores could be identified the mean density of the ice cover increased from 720 kg m 3 at the top to 880 kg m 3 below 0 4 m depth sea ice salinities mean value 2 1 correlate with ice thickness on average salinity profiles exhibit a linear increase from values close to 0 at the top to 2 at 1 m depth with less steep salinity gradients below sampling from different depths within the ice cover indicates that the brine in summer sea ice is strongly stratified the influence of meltwater percolation is evident with salinities around 5 and ph values 15 and 8 at greater depths brine volumes ranging from 80 to 150 are controlled by the thermodynamic equilibrium between the solid and liquid phases gas volumes decrease from 200 at the top to 50 below 1 m depth pore microstructure is highly variable even on small scales salinity and other ice properties do not vary to a large degree between different regions the evolution of level multiyear sea ice is discussed with particular reference to hidden occurrence of deformed ice and the importance of ablation processes

the role of shortwave radiation in the summer decay of a sea ice cover heat balance models of ice leads and the underlying water column were used to investigate the role of shortwave radiation in the summer decay of a sea ice cover because of the potential importance of positive feedback between decreasing ice concentration and increasing solar input to the ocean particular emphasis was given to the treatment of heat transfer and lateral melting in leads the rate of heat loss to floe edges was calculated from lead temperatures using an empirical boundary layer parameterization coefficients for this parameterization were obtained from field measurements in the dynamically active ice cover of the greenland sea during the 1984 marginal ice zone experiment and in the static ice of mould bay northwest territories field coefficients were found to be considerably larger than those previously obtained in the laboratory suggesting that heat transfer rates near floe edges were controlled more by winds and currents than by local density differences model studies of individual leads indicate that heat losses to the atmosphere cause lateral melt rates to asymptotically approach a constant value as lead size increases thus although very wide leads transmit considerable energy to the underlying ocean they have relatively little effect on lateral melting other results provide information on the relative importance of horizontal heat transfer rates ice thickness floe perimeter atmospheric forcing and oceanic heat flux in general the calculations indicate that much of the shortwave radiation entering the ocean is absorbed below the ice where it contributes to bottom ablation rather than lateral melting this suggests that previous work has seriously overestimated the magnitude of the feedback between ice concentration and incident shortwave radiation

semi automatic delimitation of volcanic edifice boundaries validation and application to the cinder cones of the tancitaro nueva italia region michoacan guanajuato volcanic field mexico abstract the shape and size of monogenetic volcanoes are the result of complex evolutions involving the interaction of eruptive activity structural setting and degradational processes morphological studies of cinder cones aim to evaluate volcanic hazard on the earth and to decipher the origins of various structures on extraterrestrial planets efforts have been dedicated so far to the characterization of the cinder cone morphology in a systematic and comparable manner however manual delimitation is time consuming and influenced by the user subjectivity but on the other hand automatic boundary delimitation of volcanic terrains can be affected by irregular topography in this work the semi automatic delimitation of volcanic edifice boundaries proposed by grosse et al 2009 for stratovolcanoes was tested for the first time over monogenetic cinder cones the method based on the integration of the dem derived slope and curvature maps is applied here to the tancitaro nueva italia region of the michoacan guanajuato volcanic field mexico where 309 plio quaternary cinder cones are located the semiautomatic extraction allowed identification of 137 of the 309 cinder cones of the tancitaro nueva italia region recognized by means of the manual extraction this value corresponds to the 44 3 of the total number of cinder cones analysis on vent alignments allowed us to identify ne sw vent alignments and cone elongations consistent with a ne sw max and a nw se min constructing a vent intensity map based on computing the number of vents within a radius r centred on each vent of the data set and choosing r 5 km four vent intensity maxima were derived one is positioned in the nw with respect to the volcano tancitaro one in the ne one to the s and another vent cluster located at the se boundary of the studied area the spacing of centroid of each cluster 24 km can be related to the thickness of the crust 9 10 km overlying the magma reservoir

geomorphometric variability of monogenetic volcanic cones evidence from mauna kea lanzarote and experimental cones abstract volcanic cones are the most common volcanic constructs on earth their shape can be quantified using two morphometric ratios the crater cone base ratio wcr wco and the cone height width ratio hco wco the average values for these ratios obtained over entire cone fields have been explained by the repose angle of loose granular material i e scoria controlling cone slopes the observed variability in these ratios between individual cones has been attributed to the effect of erosional processes or contrasting eruptive conditions on cone morphometry using a gis based approach high spatial resolution digital elevation models and airphotos two new geomorphometry datasets for cone fields at mauna kea hawaii usa and lanzarote canary islands spain are extracted and analyzed here the key observation in these datasets is the great variability in morphometric ratios even for simple shape and well preserved cones simple analog experiments are presented to analyze factors influencing the morphometric ratios the formation of a crater is simulated within an analog cone i e a sand pile by opening a drainage conduit at the cone base results from experiments show that variability in the morphometric ratios can be attributed to variations in the width height and horizontal offset of the drainage point relative to the cone symmetry axis to the dip of the underlying slope or to the influence of a small proportion of fine cohesive material gis analysis and analog experiments together with specific examples of cones documented in the field suggest that the morphometric ratios for well preserved volcanic cones are controlled by a combination of 1 the intrinsic cone material properties 2 time dependent eruption conditions 3 the local setting and 4 the method used to estimate the cone height implications for interpreting cone morphometry solely as either an age or as an eruption condition indicator are highlighted

the luingo caldera the south easternmost collapse caldera in the altiplano puna plateau nw argentina abstract this article identifies the pucarilla cerro tipillas volcanic complex and its major eruptive source the luingo caldera 26 10 s 66 40 w detailed geological mapping stratigraphic sections facies analysis and correlations including the identification of typical caldera components allow us to infer the position of a collapse caldera elongated at n65 and with a diameter of 19 km 13 km which is responsible for an eruption of 135 km 3 dre of magma the high crystal contents of the associated ignimbrites combined with its tectonic setting indicate that regional and local tectonic structures played a crucial role in the formation of the caldera the luingo caldera is located on the south eastern border of the puna and is the south easternmost recognised caldera of the altiplano puna plateau the age of the caldera and its products is 12 1 to 13 5 ma based on its location near the cerro galan complex 2 to 6 5 ma we can imply that volcanism existed in the area for about 10 ma the caldera morphology and product distribution account for a middle miocene paleao topography similar to the present one

spatial distribution and alignments of volcanic centers clues to the formation of monogenetic volcanic fields monogenetic basaltic volcanic fields occur worldwide in tectonic environments ranging from extensional to convergent understanding similarities and differences between these fields may help to characterize key controls on their generation such volcanic fields consist of numerous volcanic centers each of which represents a pathway of magma from its source to the surface we analyzed the spatial distribution of volcanic centers in 37 monogenetic volcanic fields and assuming that the distribution of volcanic centers relative to each other is matched by a similar source pattern within the mantle applied the following methods for each 1 the poisson nearest neighbor pnn analysis representing the degree to which the distribution of the volcanic centers departs from a predicted poisson distribution and 2 a volcanic alignment analysis to ascertain the preferential pathways if any used by the magma to reach the surface this is the first comprehensive global comparison of such analyses magma pathways within the brittle upper crust are influenced to various degrees by two end member situations 1 formation of new extension fractures perpendicular to the least compressive stress 3 and 2 re activation of pre existing fractures that are near parallel to the maximum principal stress 1 the results of the pnn analysis show that independently of the tectonic environment most volcanic fields display a clustered distribution of their volcanic centers alignment analysis shows that either the ambient tectonic environment exerts a strong influence on the preferential orientations of the volcanic alignments or that it is in competition with other factors e g pre existing structures local stress changes due to older intrusions overall these results indicate that the propagation of the magma and therefore the spatial distribution of the volcanic centers within volcanic fields is the product of an interplay between deep level influences i e nature of the magma source and shallow level influences i e stress field pre existing crustal structures of the lithosphere