understanding coastal change using shoreline trend analysis supported by cluster based segmentation abstract shoreline change analysis is a well defined and widely adopted approach for the examination of trends in coastal position over different timescales conventional shoreline change metrics are best suited to resolving progressive quasi linear trends however coastal change is often highly non linear and may exhibit complex behaviour including trend reversals this paper advocates a secondary level of investigation based on a cluster analysis to resolve a more complete range of coastal behaviours cluster based segmentation of shoreline behaviour is demonstrated with reference to a regional scale case study of the suffolk coast eastern uk an exceptionally comprehensive suite of shoreline datasets covering the period 1881 to 2015 is used to examine both centennial and intra decadal scale change in shoreline position analysis of shoreline position changes at a 100 m alongshore interval along 74 km of coastline reveals a number of distinct behaviours the suite of behaviours varies with the timescale of analysis there is little evidence of regionally coherent shoreline change rather the analyses reveal a complex interaction between met ocean forcing inherited geological and geomorphological controls and evolving anthropogenic intervention that drives changing foci of erosion and deposition

the properties and geological environments of helicoids axially symmetric surfaces in torsional and non torsional deformations abstract a helicoid is a non developable surface swept out by a line the generator which rotates with constant sense about another non parallel line the heliaxis whilst moving parallel to that line in a constant direction torsion may produce helicoids though this is not a necessity previous references to helicoids and helices in structural geology are reviewed and the basic properties of helicoids are compared with those of cylindrical and conical surfaces a map and stereogram technique is developed for the recognition of nested initially parallel equally rotated coaxial macroscopic helicoids the typically sigmoidal outcropping traces of nested helicoids show dip direction reversals along trend on stereograms linear loci each representing the poles from a single helicoid trace diverge from a common pole a nested set of macroscopic helocoidal cleavage surfaces from the hill end trough southeastern australia are modelled and interpreted to have formed in two stages of torsion associated with accommodation of an adjacent granitoid intrusion the volume affected by torsion is bound by curviplanar scissor faults helicoids may be found associated with rotational porphyroblasts deformed cylindrical bodies or strip like surfaces e g intrafolial fold axial planes cylindrical diapirs with helical flow patterns cylindrical scissor faults ductile shear zones zones of constrictional strain and en echelon segmented dykes and fracture planes

experimental and theoretical basis of self potential phenomena in volcanic areas with reference to results obtained on mount etna sicily abstract self potential anomalies observed on volcanoes may be closely associated with thermoelectric electrochemical or electrokinetic couplings calculations based on irreversible thermodynamics and on laboratory measurements of streaming potentials allow us to estimate the amplitude of the anomalies generated by each mechanism in order to obtain realistic results values of the parameters used in the calculations or used to draw conclusions from the streaming potential measurements were chosen according to in situ tests or laboratory measurements with samples of volcanic origin results show clearly the pronounced predominance of the streaming potentials effects 300 mv upon thermoelectric 30 mv and electrochemical 10 mv couplings

phase equilibrium constraints on the viscosity of silicic magmas 1 volcanic plutonic comparison by using recently determined experimental phase equilibria we show that the viscosity of granitic magmas emplaced at upper crustal levels is approximately constant at 104 5 pa s irrespective of their temperature and level of emplacement magmas crystallizing as granitic plutons are not water poor and thus not more viscous than their extrusive equivalents instead comparison between pre eruption magma viscosities of extrusive silicic intermediate and intrusive granitic magmas shows that the former are on average slightly more viscous given the typical strain rates in silicic magma chambers magma rheological behavior is expected to be dominantly newtonian bubbles having a minor rheological influence at depth although exceptions can exist thus whether a silicic intermediate magma is erupted or frozen at depth depends primarily on the rheological properties of surrounding terranes or on external tectonic factors but not on the rheology of the magma itself however preemptive viscosities of extrusive magmas rarely exceed 106 pa s which suggests that crystal melt mushes with higher viscosities cannot leave the magma storage regions beneath volcanoes the narrow range of viscosities displayed by silicic intermediate magmas results from both the strong control that pressure exerts on volatile solubilities in silicate melts and thermal limitations required to produce acid magmas considerations of the relationships between magma crystallinities bulk sio2 and preemptive melt h2o contents show that the higher the melt h2o content is the higher the maximum crystallinity that a given magma will be while still being potentially erupted an empirical correlation is proposed that enables us to estimate preemptive melt h2o contents of erupted magmas by knowing their crystallinity and bulk sio2

spatial analysis of sand dunes with a new global topographic dataset new approaches and opportunities on june 29 2009 version 1 of the aster gdem advanced spaceborne thermal emission and reflection radiometer global digital elevation model was made available at no cost or restrictions to users worldwide via electronic download the aster gdem provides expanded spatial coverage and better resolution than other global digital elevation models dems in this paper we demonstrate how the aster gdem provides new opportunities for investigating large aeolian sand dunes in three dimensions two dune specific spatial analysis methods are presented to illustrate potential applications of these data for discriminating dune generations and quantifying spatial variations of sediment supply moreover we review how existing and emerging fields of dune pattern analysis and simulation modeling will be able to make significant advances through application of these data potentially leading to future progress in studies of dune morphodynamics environmental controls and paleoenvironmental reconstructions copyright 2010 john wiley sons ltd

ground deformation and gravity changes accompanying the march 1981 eruption of mount etna abstract we present reults from simultaneous precise levelling and gravity surveys on mount etna covering the period august 1980 august 1981 the flank eruption of march 1981 erupted 18 35 10 5 m 3 of lava following it upward movements of more than 17 cm were observed close to the new fissure and a broad apparently independent uplift of 5 cm was observed 4 km to the west a zone of about 2 cm depression to the east of the fissure is insufficient to account for the volume of magma erupted gravity results show positive changes of up to 63 microgal and display good positive correlation with elevation changes both sets of measurements appear to be due to new intrusion of magma rather than subsurface magma drainage ground deformation close to the new fissure is well modelled by intrusion of a dyke in the zone 100 500 m below the surface striking along the fissure and of dip between 75 90 the gravity changes are modelled as due to a deeper intrusion of magma along the same line but some 1500 m below the surface the changes were not present immediately after the eruption but occurred during the ensuing 5 months it is proposed that this introduction of matter occurred by crack propagation along the fissure in the aftermath of the eruption towards the west of the fissure and some 4 km west of the summit ground deformation is modelled by intrusion of a dyke in the zone 300 1500 m below the surface and dipping at 80 85 again gravity changes appear to be due to magma intrusion at greater depth close to sea level in this case gravity changes are interpreted as due to magma density changes as a result of pressure increase in a larger scale fissure zone this same pressure increase may be forcing the new intrusion close to the surface and makes this part of the volcano a region of especially high risk

the march 1981 mount etna eruption inferred through ground deformation modelling abstract the march 1981 eruption of mt etna was characterised by the fast propagation of a long eruptive fissure approximately 7 km and by an unusually high eruption rate the continuous tilt recorded by a bore hole station located on the southern flank showed a small inflation 3 4 months before the eruption followed by a rapid deflation during the fissure opening the discrete deformation measurements electroptical distance measurements edm and levelling showed large horizontal changes in the volcano flanks and smaller vertical ones close to the eruptive fissure we modelled the deformation pattern associated with the 1981 eruption using horizontal 57 data and vertical 50 data measurements two geometric constraints were considered for the eruptive fissure the dislocation theory was used to model the intrusion by characterising it in two parts as a double tensile crack which represents the initial deeper intrusion first crack and then the final shallower part associated with the eruptive fissure second crack an analytic inversion was performed obtaining a very good solution and then the robustness of this result was verified through an accurate trial and error search the first deeper crack extends vertically from about 300 to 1700 m above sea level a s l it was widely opened opening 5 m dipping w and radiating from the summit of the volcanic edifice in the nnw direction for approximately 3 km in the shallowest part last 500 m the intrusion propagated radially in the northern sector along the nnw direction second crack matching the surface location of the observed eruptive fissure we interpret that the deeper crack formed during the 3 4 months preceding the eruption

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

sr nd isotopic constraints on the petrogenesis of the central bohemian pluton czech republic the sr nd isotopic data for selected granitoids of the central bohemian pluton show a broad negative correlation with the total range of 87sr 86sr 330 0 7051 0 7129 and nd330 0 2 to 8 9 the older intrusions have more depleted sr nd compositions and calc alkaline geochemistry sazava suite whereas the younger intrusions shift towards k rich calc alkaline blatna suite and shoshonitic rocks icany and certovo b emeno suites with more evolved isotopic signatures the distribution of the data is interpreted as reflecting a diversity of sources and processes rather than a single progressive crustal contamination trend the sazava suite could have originated by partial melting of metabasites or of a mantle source with an isotopic composition close to bulk earth or by hybridization of crustally derived tonalitic and mantle derived magmas variation within the blatna suite is modelled by mixing between a moderately enriched 87sr 86sr 330 0 708 nd330 3 mantle component with either an isotopically evolved metasedimentary component or with more evolved magmas of the suite the icany suite was most probably produced by partial melting of peraluminous lithologies possibly of the adjacent moldanubian unit the certovo b emeno suite evolved from strongly enriched mantle derived magmas 87sr 86sr 330 0 7128 end330 7 either through closed system fractional crystallization or interaction with magma corresponding to leucogranites of the central bohemian pluton

interpreting magmatic fabric patterns in plutons abstract most plutons have widespread magmatic fabrics the interpretation of which remains controversial we propose a method to constrain likely causes of fabric patterns the application of which indicates the following 1 preserved fabric patterns often form after chamber construction and only rarely provide information about ascent or emplacement 2 fabrics are poor recorders of total strain and are easily reset preserving only the last increment of strain during crystallization 3 in magmatic systems mechanically decoupled from host rocks patterns may result from strain during internally driven flow filter pressing or porous flow in relatively static chambers or by final increments of strain during emplacement 4 with greater emplacement depths fabric patterns increasingly reflect strain caused by regional deformation and 5 given that magmatic fabrics are easily reset and reflect only the last increment of strain of comparatively weak materials they may provide a relatively direct record of paleostress in orogenic belts

geographic information systems applied to integrated coastal zone management abstract the littoral is the area where marine and terrestrial processes superpose and interact limits of their respective actions are imprecise as processes which are characteristic of each of these environments do overlap this particular characteristic makes the littoral zone complex and vulnerable to human activity which in many cases causes irretrievable damage to the natural equilibrium integrated coastal zone management iczm promotes sustainable coastal development by adapting the use of natural resources in a way that avoids serious damage to the natural environment this requires an integrated and organized action of all institutions that are involved in coastal development geographic information systems gis besides being a useful tool for drawing maps on different scales and projections constitutes an excellent instrument for data analysis and integration due to its ability to identify spatial connections between different information layers in this way it is possible to build models for geomorphological evolution and predict changes in the coastal areas in order to illustrate this three examples of gis applications are presented which are currently being developed in different areas of the spanish littoral coastal hazards shoreline evolution and coastal sand dune evolution respectively

rheology of granitic magmas during ascent and emplacement flow abstract considerable progress has been made over the past decade in under standing the static rheological properties of granitic magmas in the continental crust changes in h2o content co2 content and oxidation state of the interstitial melt phase have been identified as important compositional factors governing the rheodynamic behavior of the solid fluid mixture although the strengths of granitic magmas over the crystallization interval are still poorly constrained theoretical investigations suggest that during magma ascent yield strengths of the order of 9 kpa are required to com pletely retard the upward flow in meter wide conduits in low bagnold number magma suspensions with moderate crystal contents solidosities 0 1 0 3 viscous fluc tuations may lead to flow differentiation by shear enhanced diffusion ams and mi crostructural studies support the idea that granite plutons are intruded as crystal poor liquids 50 with fabric and foliation development restricted to the final stages of emplacement if so then these fabrics contain no information on the ascent verti cal transport history of the magma deformation of a magmatic mush during pluton emplacement can enhance significantly the pressure gradient in the melt resulting in a range of local macroscopic flow structures including layering crystal alignment and other mechanical instabilities such as shear zones as the suspension viscosity varies with stress rate it is not clear how the timing of proposed rheological transitions formulated from simple equations for static magma suspensions applies to mixtures undergoing shear new theories of magmas as multiphase flows are required if the full complexity of granitic magma rheology is to be resolved

techniques for gis modeling of coastal dunes coastal dunes present a unique problem to coastal scientists because of the dynamic nature of most coastal dune systems coastal dunes can change shape quickly and frequently due to storm generated winds and waves prevailing winds can transport significant amounts of sand throughout the dune system topographic and volumetric changes in a 150 40 m site on the outer banks of north carolina were assessed through a series of monthly field surveys conducted over a 1 year period from may 1997 to may 1998 this paper discusses the geographic information system gis methodology used for data acquisition and analysis and presents one methodology developed to measure 3 d dune morphodynamics using a 2 d and 3 d gis it serves as a guide for other coastal researchers who may have limited surveying or gis experience issues concerning sampling routine data density and grid cell size are discussed the methodology followed results in the production of a grid of interpolated elevation values that can be represented in a variety of ways including as topographic maps digital elevation models dem or two dimensional cross sections of the dune system the grid from the may 1998 survey is subtracted from the may 1997 grid to obtain elevation change information that in turn can be represented graphically the results of the analysis show that volumetric change over the 1 year period was dominated by erosion along the seaward face of the dune the monthly surveys show that this erosion was the result of two northeasters in january and february 1998 the loss of volume is partially compensated for by accumulation to the rear of the foredune ridge primarily in locations where blowouts facilitate aeolian transport of sediment from the beach the implication is that the dune system is eroding rapidly due to storm activity it also suggests that there is a mechanism for offsetting some of the volumetric loss through aeolian transport into the dune system

the case of the 1981 eruption of mount etna an example of very fast moving lava flows 1 mount etna despite being an extremely active volcano which during the last 400 years has produced many lava flow flank eruptions has rarely threatened or damaged populated areas the reconstruction of the temporal evolution of potentially hazardous flank eruptions represents a useful contribution to reducing the impact of future eruptions by and analyzing actions to be taken for protecting sensitive areas in this work we quantitatively reconstructed the evolution of the 1981 lava flow field of mt etna which threatened the town of randazzo this reconstruction was used to evaluate the cumulated volume the time averaged discharge rate trend and to estimate its maximum value the analysis was conducted by comparing pre and post eruption topographic surfaces extracted by processing historical photogrammetric data sets and by utilizing the eruption chronology to establish the lava flow front positions at different times an unusually high discharge rate for etna of 640 m3 s was obtained which corresponds well with the very fast advance rate observed for the main lava flow a comparison with other volcanoes presenting high discharge rate was proposed for finding a clue to unveil the 1981 etna eruptive mechanism a model was presented to explain the high discharge rate which includes an additional contribution to the lava discharge caused by the interception of a shallow magma reservoir by a dike rising from depth and the subsequent emptying of the reservoir

mid crustal magmatic sheets in the cascades mountains washington implications for magma ascent abstract diking diapirism ascent along faults and ascent during heterogeneous ductile flow have all been championed as the most important means of magma ascent in the crust we suggest that these mechanisms are end members in a complex spectrum of ascent processes in an attempt to evaluate which combination of ascent processes formed sheet like bodies in the mid crustal 20 25 km entiat pluton washington we examined the tip regions of these sheets the sheets have length width ratios ranging from 6 to 75 with increasing ratios strongly correlated to decreasing sheet tip radii from 850 to 100 m and decreasing ratios of tip diameter sheet width from 0 66 to 0 33 thus these bodies have geometries falling between those of dikes and those associated with elliptical diapirs the sheets are not associated with faults or fracture zones extending from their tips instead sheet walls are oriented parallel to the axial planes of upright syn emplacement folds in sheets with high length width ratios magmatic foliations in sheets are folded or parallel to axial planes of host rock folds with decreasing length width ratios margin parallel foliations in both sheet and host rock are increasingly common our studies indicate that the sheets are emplaced at high angles to 1 not 3 as proposed in elastic dike models and are always associated with complex viscoelastic flow of host rock these observations rule out elastic dike and fault models and instead favor diapiric rise of magma sheets during viscoelastic behavior of host rock

multiobjective genetic algorithm inversion of ground deformation and gravity changes spanning the 1981 eruption of etna volcano 1 during the last few decades joint investigations of microgravity and surface deformation measurements have played an increasingly important role in studying the internal dynamics of active volcanoes deformation and microgravity observations have been accomplished at mt etna since the eighties past data sets collected during important paroxysmal events can be utilized as case studies to both 1 test the possibilities of nowadays more powerful inversion tools and improved analytical formulations to model the source mechanisms of volcano related deformation and gravity changes and 2 in turn obtain new insights into the functioning of the plumbing system of the volcano here we analyze a data set spanning the march 1981 eruption of mt etna large horizontal displacements were evidenced on the ne and sw flanks of the volcano through electrooptical distance measurements edm during two 20 month periods both encompassing the march 1981 eruption elevation changes evidenced through leveling measurements during a 12 month period spanning the eruption were in general smaller than horizontal displacements with important amplitudes only close to the eruptive fissure gravity measurements carried out together with leveling measurements evidenced positive changes spatially well correlated with elevation changes but having a larger wavelength the joint inversion of the multimethod geophysical data is regarded as a multiobjective optimization problem and solved through a genetic algorithm technique of the nondominated type we conclude that a composite intrusive mechanism with two tensile cracks each associated to a zone where preexisting microfractures were filled with new magma leaded to the 1981 eruption the results of the present study highlight the advantages of multiobjective evolutionary algorithms as a powerful tool to jointly invert multimethod geophysical data and pose important issues on the subject of volcano monitoring

overprinting of magnetic fabrics in granites by small strains numerical modelling abstract the anisotropy of magnetic susceptibility ams is used to determine weakly defined mineral preferred orientation fabrics in granites however the effects of small strains superimposed on the low intensity ams fabrics typical of these rocks is not well understood numerical simulations are presented which investigate the effects of small superimposed strains on the shapes magnitudes and orientations of pre existing ams fabrics which are similar to those reported in the literature for undeformed granites a computer generated biotite petrofabric is subjected to progressive strain using march s strain response model for pure shear plane strain axially symmetric shortening and simple shear regimes results indicate that a pre existing ams fabric might be significantly modified or overprinted by small strains 10 15 strain in the pure shear and axially symmetric shortening regimes 0 5 1 0 for simple shear a new ams fabric may develop with an orientation similar to that expected for shearing of an initially isotropic petrofabric at low strains the evolution of the shape of the ams ellipsoid depends strongly on the orientation of the initial petrofabric with respect to the strain framework the ams ellipsoid may evolve towards either oblate or prolate shapes and the evolution in the ellipsoid shape may be reversed during progressive strain this modelling suggests that small strains affecting a pluton following its emplacement could mask ams fabrics developed earlier the results also suggest that in simple shear the orientation of the ams ellipsoid may serve as a shear sense indicator for small strains even if the earlier fabric is not isotropic

magma mixing in the genesis of hercynian calc alkaline granitoids an integrated petrographic and geochemical study of the sazava intrusion central bohemian pluton czech republic the devonian early carboniferous 354 1 3 5 ma conventional zircon u pb age sazava intrusion biotite amphibole quartz diorite tonalite and granodiorite of the central bohemian pluton cbp associated with bodies of olivine pyroxene amphibole gabbro gabbrodiorite quartz diorite and rare hornblendite gives an opportunity for a comparative study of a rather shallow calc alkaline magma mixing zone at two levels separated by a vertical difference of approximately 1 km the deeper section p ibram displays the direct evidence for the existence of a long lived periodically tapped and replenished floored magma chamber masli the contacts between the subhorizontal sheet like basic bodies and the surrounding commonly cumulus rich sazava granitoid are arcuate and cut by a series of veins and ascending pipes shallow dipping swarms of strongly elongated and flow aligned mafic microgranular enclaves mme concordant with the contacts of the basic bodies are commonplace the higher level teletin section shows relatively independent basic intrusions some of them distinctly hybrid in character and mainly of quartz dioritic composition surrounded by relatively homogeneous nearly cumulus free sazava tonalite rich in texturally variable mme larger quartz microdiorite bodies and the mme both interpreted as hybrids contain varying proportions of highly heterogeneous plagioclase megacrysts with complex zoning particularly well shown by cathodoluminescence cl most often the megacrysts have cores of labradorite anorthite partly resorbed and overgrown by andesine rims but some are strongly brecciated and fragments have been annealed by rim growth also characteristic are long prisms of apatite oikocrysts of quartz and k feldspar and zoned amphibole the latter has brown pargasite and magnesiohastingsite cores resorbed and overgrown by magnesiohornblende compositionally similar to the amphibole in the sazava tonalite the brown cores are probably relics of a higher p t stage with temperature exceeding 900 c plots of major element analyses of the teletin quartz microdiorite and the mme fall close to the line joining the compositions of the evolved sazava granodiorite tonalite and the associated gabbros the estimated minimal proportions of the acidic end member range from ca 15 to 20 for the quartz microdiorite and ca 40 to 60 for the enclaves field relationships macroscopic and mineralogical features and whole rock geochemistry are consistent with a hybrid origin of the quartz microdiorite masses and enclaves unzoned calcic plagioclase cores are interpreted as having crystallized from a basic magma prior to its injection into a high level acidic magma chamber the sudden decrease in ca activity and introduction of water due to magma mixing with tonalitic melt led to their resorption and brecciation quartz ocelli that are abundant locally in some basic bodies are most likely xenocrysts introduced from the felsic magma in the basic melt they were resorbed and became a substrate for heterogeneous nucleation of the amphibole or pyroxene coronas strong undercooling of the basic magma resulted in the growth of long prismatic apatite together with dendritic boxy cellular plagioclase both types of plagioclase cores were subsequently overgrown by more sodic mantles at the same time small unzoned plagioclase crystals nucleated in the groundmass following thermal re adjustment crystallization of the hybrid magma ended with considerably slower growth of quartz and k feldspar oikocrysts

bursting the bubble of ballooning plutons a return to nested diapirs emplaced by multiple processes a popular model for the emplacement of roughly spherical plutons is that of ballooning or in situ inflation of a magma chamber in a common version of this model magma ascends until loss of heat or buoyancy causes the outermost magma to crystallize and cease ascent while the hotter tail of magma continues to rise and expand the already crystallized outer margin this expansion forms a concentric gneissic to mylonitic foliation and flattening type strain in the outer margin of the pluton by means of subsolidus deformation and pushes aside the surrounding country rock to form a dynamothermal aureole that postdates regional structures our reexamination of three supposedly ballooned plutons ardara ireland cannibal creek australia papoose flat california and evaluation of published descriptions of many others indicate that this model is largely incorrect deflections of country rock structures strains and porphyroblast matrix relationships indicate that only minor to moderate expansion usually 30 or less occurred during emplacement that other emplacement mechanisms must have occurred and that regional deformation continued during and after emplacement internal structures indicate that when magma chamber expansion did occur it did so by flow of magma that magmatic foliations and lineations formed late in the magma chamber evolution that enclave shapes are neither good strain markers nor indicators of the magnitude of expansion and that only minor internal subsolidus deformation results from emplacement this study indicates that many plutons previously interpreted as post tectonic ballooning plutons are better viewed as syntectonic nested diapirs emplaced by a variety of country rock material transfer processes this nested diapir model implies that magma ascent may occur by rise of large magma batches instead of transport in dikes followed by ballooning that magma chamber dynamics differ from that in the ballooning model and that normally zoned plutons may form by intrusion of several pulses of magma rather than by in situ crystal fractionation from a single parent melt

cryptic trace element variation as an indicator of reverse zoning in a granitic pluton the ricany granite czech republic cryptic variation recognized on the basis of trace element patterns shows the oieany granite in the northeastern part of the hercynian central bohemian pluton to be a reversely zoned high level intrusion unlike many other reversely zoned plutons there are no marked differences in modal composition between the margins and the centre of the intrusion the granite is generally peraluminous and geochemically evolved as demonstrated by its restricted and high sio 2 range and low k rb ratio coupled with a c two fold variation in ba and sr concentrations modelling shows that the geochemical variations can be most readily explained by k feldspar dominated fractionation in a magma chamber below the present level of exposure the reverse zoning is interpreted as the product of emplacement of an essentially single pulse of magma from a deeper level magma chamber in which fractionation has led to a vertical compositional gradient the least evolved magma was emplaced in the centre of the high level pluton with the more evolved magma around it recognition of cryptic reverse zoning in granites has major implications for granite petrogenesis in that the magmatic evolution of such bodies has to be established before assessing potential mechanisms of emplacement

twentieth century dune migration at the great sand dunes national park and preserve colorado relation to drought variability abstract the great sand dunes national park and preserve in southern colorado contains a large dune mass banked against the sangre de cristo mountains the dune mass is bounded for hundreds of kilometers by a vegetated low relief sand sheet with abundant active parabolic and barchanoid dunes the clear morphology of these dunes formed by winds mostly from the southwest and the unambiguous identification of these forms in remotely sensed images provide straightforward targets to assess temporal changes in dune position a digital database of georeferenced remote sensing images from 1936 to 1999 is used to quantify parabolic and barchan dune migration rates and surface reflectance an indicator of vegetation cover with evolving drought conditions in the twentieth century the total net migration of 13 parabolic dunes in 63 years is 0 31 to 0 66 km whereas 11 barchan dunes moved an average of 0 12 to 0 47 km compared to intervening wet year there is at least a three fold increase in average parabolic dune migration during well documented droughts in the 1930s 1950s and 1990s with a concomitant reduction in vegetation cover and surface water resources the landscape response to the most recent drought in the late twentieth century is documented by an average parabolic dune migration rate of 30 m year which is a six fold acceleration over prior wet years and similar to dune response during the 1930s a nonlinear threshold for parabolic dune migration is indicated with lower quartile palmer drought severity index values of

magnetic fabrics and their relationship with the emplacement of the piracaia pluton se brazil magnetic fabric and rock magnetism studies were performed on the four units of the 578 3 ma old piracaia pluton nw of sao paulo state southern brazil this intrusion is roughly elliptical 32 km2 composed of i coarse grained monzodiorite mzd c ii fine grained monzodiorite mzd f which is predominant in the pluton iii monzonite heterogeneous mzn het and iv quartz syenite qz sy magnetic fabrics were determined by applying both anisotropy of low field magnetic susceptibility ams and anisotropy of anhysteretic remanent magnetization aarm the two fabrics are coaxial the parallelism between ams and aarm tensors excludes the presence of a single domain sd effect on the ams fabric of the units several rock magnetism experiments performed in one specimen from each sampled units show that for all of them the magnetic susceptibility and magnetic fabrics are carried by magnetite grains which was also observed in the thin sections foliations and lineations in the units were successfully determined by applying magnetic methods most of the magnetic foliations are steeply dipping or vertical in all units and are roughly parallel to the foliation measured in the field and in the country rocks in contrast the magnetic lineations present mostly low plunges for the whole pluton however for eight sites they are steep up to vertical thin section analyses show that rocks from the piracaia pluton were affected by the regional strain during and after emplacement since magmatic foliation evolves to solid state fabric in the north of the pluton indicating that magnetic fabrics in this area of the pluton are related to this strain otherwise the lack of solid state deformation at outcrop scale and in thin sections precludes deformation in the sw of the pluton this evidence allows us to interpret the observed magnetic fabrics as primary in origin magmatic acquired when the rocks were solidified as a result of magma flow in which steeply plunging magnetic lineation suggests that a feeder zone could underlie this area

breaching in a wave dominated barrier spit the trabucador bar north eastern spanish coast the trabucador bar is a barrier coast linking the main lobe of the ebro delta with its southern spit this coastal stretch which may be considered as a microtidal transgressive barrier is the most vulnerable area of the deltaic coast to storm induced geomorphologic changes during the second week of october 1990 a severe storm affected the ebro delta causing serious erosion in which the trabucador bar was one of the most damaged zones a breach 800 m long and with a maximum depth of 0 4 m below the mean water level was created during the breaching process approximately 70 000 m3 of sand were removed from the subaerial barrier in a few hours three factors are normally responsible for the loss of sediment longshore transport gradient offshore transport and overwash processes most of the eroded sediment 60 000 m3 was transported towards the inner bay due to overwash processes the post storm recovery of the zone was slow and far from complete as the breach remained a conduit for onshore sediment transport under a regime of breaking and reforming waves an artificial dune was subsequently constructed to close the breach and thus allow beachface recovery

flow lobes in granite the determination of magma flow direction in the trawenagh bay granite northwestern ireland using anisotropy of magnetic susceptibility anisotropy of magnetic susceptibility ams has been determined from 152 sites over the 64 km2 trawenagh bay granite part of the 400 ma caledonian donegal batholith microscopic observations thermomagnetic analyses high field torque magnetometry and heating experiments demonstrate that the ams fabric is carried by biotite with varying amounts of mimetic magnetite in the biotite cleavage planes the ams fabric is interpreted as a flow fabric because microstructures indicate magmatic state deformation it defines large scale macroscopic flow features flow lobes in this weakly deformed granite at pluton scale the data set shows a gentle westward plunging lineation at a smaller scale many lobate magnetic foliation patterns can be discerned in which the magnetic lineation is usually symmetrically disposed about the long axes of the lobes in three dimensions the lobes are tongue like 1500 m wide subunit scale and elongated east west parallel with the general lineation they close consistently westward and younger lobes in the east appear to deflect older lobes in the west the trawenagh bay granite is west of a major synplutonic shear zone that hosts the main donegal granite pluton these structures are interpreted as frozen flow lobes and indicate that the magma flowed in a westward direction from within the active shear zone of the main donegal granite into the weakly deformed wall rock trawenagh bay granite intra unit pulses or surges have long been suspected in granite plutons however this study reports the most detailed description of such structures to date

volcanism and the dynamics of open magma chambers the repeated eruption of many volcanoes is now accounted for by events taking place in a subterranean magma chamber which is open in the sense that the inflow of material to the chamber from below leads to a magma pressure p which exceeds the lithostatic pressure pl by an amount greater than the tensile strength of the chamber walls before the contents of the magma chamber have reached thermodynamic and geochemical equilibrium this is the condition which must be satisfied when an eruption occurs we have now derived a relationship giving the critical volume of added material v required to cause an eruption as a function of magma compressibility and the volume by which the chamber expands

modelling diverse processes in the petrogenesis of a composite batholith the central bohemian pluton central european hercynides the multiple intrusions making up the central bohemian pluton in the central european hercynides have petrographic and geochemical features consistent with the presence of four main granitoid suites major element trace element and sr nd isotopic compositions are used to model their petrogenesis partial melting of metabasic locks or of a chur like mantle source are interpreted to have produced melts parental to the most primitive calc alkaline sazava suite interaction of basic with more acidic magmas followed by extensive amphibole plagioclase dominated fractionation accounts for the production of trondhjemites alternatively the trondhjemites correspond to small degree melts of a metabasic source afc assimilation fractional crystallization modelling with a paragneiss as a contaminant and increasing d nd values simulates the characteristics of the blatna suite closed system fractionation of strongly enriched mantle derived magmas or their interaction with leucogranitic melts is deduced for the petrogenesis of the shoshonitic certovo bremeno suite partial melting of a metasedimentary source followed by k feldspar dominated fractionation accounts for the granites of rite ricany suite the progression from relatively primitive calc alkaline granitoids towards evolved k rich calc alkaline and shoshonitic rocks is interpreted to reflect the increasing enriched mantle input in the petrogenesis of the later suites the evidence for hercynian subduction is equivocal and the mantle enrichment could have been significantly older

shallow miocene basaltic magma reservoirs in the bahia de los angeles basin baja california mexico the basement in the bahia de los angeles basin consists of paleozoic metamorphic rocks and cretaceous granitoids the neogene stratigraphy overlying the basement is formed from the base to the top by andesitic lava flows and plugs sandstone and conglomeratic horizons and miocene pyroclastic flow units and basaltic flows basaltic dikes also intrude the whole section to further define its structure a detailed gravimetric survey was conducted across the basin about 1 km north of the sierra las flores in spite of the rough and lineal topography along the foothills of the sierra la libertad we found no evidence for large scale faulting gravity data indicates that the basin has a maximum depth of 120 m in the valle las tinajas and averages 75 m along the gravimetric profile high density bodies below the northern part of the sierra las flores and valle las tinajas are interpreted to be part of basaltic dikes the intrusive body located north of the sierra las flores is 2 5 km wide and its top is about 500 m deep the lava flows of the top of the sierra las flores together with the distribution of basaltic activity north of this sierra suggests that this intrusive body continues for 20 km along a nnw trending strike between the sierras las flores and las animas a 0 5 km wide 300 m thick intrusive body is interpreted at a depth of about 100 m this dike could be part of the basaltic activity of the cerro las tinajas and the small mounds along the foothills of western sierra las animas the observed local normal faulting in the basin is inferred to be mostly associated with the emplacement of the shallow magma reservoirs below las flores and las tinajas

comparing magnetic and magmatic fabrics to constrain the magma flow record in la gloria pluton central chile abstract this contribution illustrates a case study of a pluton la gloria pluton lgp where magnetic and magmatic fabrics are locally decoupled we compare the magmatic fabric with the available magnetic fabric data to explore their abilities and elucidate the magma flow record of lgp results indicate that magnetic controlled by multi domain magnetite and magmatic fabrics are generally consistent throughout lgp foliations define an axisymmetric pattern that gradually changes from vertical near lateral margins to less steep in the pluton interior whereas lineations are subhorizontal following the elongation direction of the pluton however samples at the pluton center show marked differences between both fabrics magnetic fabrics indicate subhorizontal magnetic lineations and foliations and magmatic fabrics indicate subvertical lineations and foliations both magnetic and magmatic fabrics are interpreted to record strain caused by magma flow during thermal convection and lateral magma propagation at the transition between low and high crystallinity stages we suggest that fabrics acquisition and consistency were determined by shear conditions pure simple shear rates ratio and the orientation of the magma flow direction with respect to a rigid boundary critical crystalline region of the pluton magmatic fabric differs at the center of the pluton because pure shear is dominant and ascendant flows are orthogonal to the horizontal rigid boundary lgp represents a whole scale partly molten magma reservoir where both thermal convection and lateral propagation of the magma are recorded simultaneously this study highlights the importance of characterizing both fabrics to properly interpret magma flow recorded in plutons

in defense of magmatic diapirs abstract diapirism as a crustal magma ascent mechanism has been recently criticized we contend that this reflects an overly simplistic view that diapirs must resemble modeled hot stokes diapirs and the perception that magma ascent in dikes is a more problem free mechanism for the construction of plutons we describe four cordilleran plutons that have characteristics much more compatible with diapirs than dike fed chambers these plutons were emplaced at depths ranging from 10 to 30 km and record different parts of diapiric ascent paths most ascended during complex visco elastic flow of host rock during regional deformation have narrow structural aureoles indicating power law behavior of host rock and were constructed of multiple batches of magma attributes enabling them to ascend greater distances than single hot stokes diapirs some features of these plutons are not typically attributed to diapirs and thus we introduce the term visco elastic diapir for bodies consisting of one or more batches of magma rising together with length to width ratios

intrusive mechanism of the 2002 ne rift eruption at mt etna italy modelled using gps and gravity data summary microgravity and gps data collected at mt etna during a 1 yr time interval encompassing the 2002 ne rift eruption are analysed the common gps gravity profile traverses the summit area of mt etna between the summit craters about 3000 m and the northernmost tip of the eruptive fractures 2500 m displacements up to 2 m in both the horizontal and vertical directions and gravity variations up to 350 gal after having removed the effect of elevation changes observed during this period are among the largest ever recorded at etna displacements and gravity changes have been modelled separately assuming a magma influx from the summit feeder pipe to the ne rift models obtained through surface deformation data partially overlap with those explaining the gravity data but in general are narrower and extend to a greater depth the discrepancies found between gravity and deformation models are significant and can be regarded as due to the different structural features encountered by the intruding magma during its downslope propagation along the ne rift in particular on the grounds of our result we infer that both the eastward sliding of the east flank of the volcano and the curved shape of the ne rift influenced the 2002 intrusive process

dynamics of magma storage in the summit reservoir of kilauea volcano hawaii an eruption of kilauea volcano hawaii normally results in a decrease in the internal pressure of a summit magma reservoir as it partly drains the interior of the volcano responses to the decrease in pressure 1 by elastic expansion of remaining magma and gas 2 additional exsolution of gas dissolved in the magma and 3 by contraction of the volcanic edifice this process is modeled here using gravity geodetic and observational data for recent events at kilauea during magma removal the ratio of pressure change in the magma reservoir to the volume of associated summit subsidence ranges from less than 0 22 pa m3 to more than 0 43 pa m3 lower ratios occur during large subsidences because of a large effective volume of the reservoir small events may involve source volumes of only 2 km3 in contrast a volume of near 13 km3 is associated with larger events because the boundary between plastic and elastic behavior may migrate outward with increased time and strain the aggregate compressibility of kilauea s reservoir is significantly increased by volumetric changes of the co2 gas phase by bulk compression and solution with pressure this effect is more pronounced for relatively shallow sources because the bulk modulus of gas is proportional to pressure the average reservoir co2 weight fraction may be near 0 0005 to 0 0009 co2 appears to accumulate in the upper portion of the reservoir where the concentration reaches 0 0030 weight fraction gradual long term subsidences are different from the short term deflations associated with specific eruptions during long term subsidence no net change in mass or pressure occurs within the summit reservoir rifting of the summit area which may tend to shorten the reservoir as it widens or slow degassing and contraction of stored magma may cause long term subsidence

magnetic fabric of the řicany granite bohemian massif a record of helical magma flow abstract a highly unusual fabric pattern and inferred flow mechanism was discovered in the shallow level icany granite pluton bohemian massif using an integrated structural and anisotropy of magnetic susceptibility ams study the pluton consists of an outer strongly porphyritic and an inner weakly porphyritic biotite granite separated by a wide gradational contact both varieties share a steep margin parallel magmatic foliation defined by k feldspar phenocrysts and biotite and magnetic ams foliation carried by biotite the steep foliation bears a shallowly plunging magnetic lineation arranged parallel to the circumference of the pluton margin and a steep magnetic lineation in the weakly porphyritic pluton center we propose a new mechanism of magma flow in which the bulk ascent along a steep sided cylindrical conduit was partitioned into a high viscosity phenocryst rich outer margin flowing helically and a low viscosity phenocryst poor center flowing vertically this interpretation is supported quantitatively by a simple model of magma flow within a cylindrical pipe in which the linear decrease in phenocryst content from the pluton margin inwards causes a power law decrease in the effective viscosity of the magma according to the poiseuille equation such a power law viscosity distribution across the conduit produces a central zone of high magma ascent velocity the magnetic ams fabric pattern in the icany pluton may thus preserve a record of helical magma ascent driven by viscosity partitioning in a steep sided conduit which presumably linked an underlying magma chamber with a volcanic feeder at the surface except for one deep seated granite migmatite complex no such helical fabric pattern has been documented in a granite pluton as of yet we propose that the viscosity partitioned helical flow may be a more common magma ascent mechanism in shallow level volcano plutonic systems than previously envisaged

origin ascent and oblique emplacement of magmas in a thickened crust an example from the cretaceous fangshan adakitic pluton beijing abstract the fangshan pluton in the western hills of beijing records a history of emplacement from primarily vertical ascent to oblique injection along a detachment fault thus the pluton provides a classic example answering the room problem this pluton and the nanjiao apophyse were produced by cretaceous magmatism that formed the regionally extrusive east china mesozoic igneous province the fangshan pluton includes two intrusive phases a 136 ma monzodiorite phase intruded by a 131 ma quartz monzodiorite phase rocks from both phases have chondrite normalized ree patterns enriched in lree and depleted in hree they have primitive mantle normalized trace element patterns with distinct negative nb and ti anomalies and high sr 1067 1348 ppm and low y 8 17 ppm with high sr y ratios 71 137 these features are characteristic of adakites and suggest that the magmas were derived by partial melting of the lower part of a thickened continental crust the pluton has magmatic foliations and lineation indicative of the intrusion of the earlier magmas slightly obliquely from se to nw the magmatic fabrics have enclave ratios rfmag rp of 3 0 3 5 asymmetric solid state deformational fabrics and strains rs for the northwestern 3 5 4 0 and southeastern parts 1 5 2 0 again suggest a later oblique injection of magmas from se to nw both the fangshan pluton and nanjiao apophyse suggest that magmas migrated most probably along the pre existing detachment fault such an emplacement is also supported by the aeromagnetic polarization data and strong deformation of the beiling syncline thus magma emplacement in the fangshan pluton probably involved creation of space by both faulting and wallrock strain

a review of criteria for the identification of magmatic and tectonic foliations in granitoids abstract foliations in granitoids can form by magmatic flow submagmatic flow high temperature solid state deformation and moderate to low temperature solid state deformation a review of previous work suggests that no single criterion can consistently distinguish foliations in granitoids formed by flow during ascent diapiric emplacement and expansion emplacement during regional deformation or regional deformation post dating emplacement however a magmatic origin is favoured for foliations defined by the alignment of igneous commonly euhedral minerals particularly where the foliation is parallel to internal or external pluton contacts foliations formed during expansion or ballooning of diapirs may be strictly magmatic in origin although some studies suggest that solid state deformation also may occur if so we would hope to find evidence of deformation of crystal melt systems and that the solid state deformation occurred at high temperatures the inference of syntectonic foliations is most convincing where magmatic and high temperature solid state foliations are subparallel these foliations are continuous with regionally developed foliations in the wall rocks synkinematic porphyroblasts are present in the wallrocks and igneous minerals have the same age as metamorphic minerals associated with the regional cleavage a strictly tectonic origin for foliations in granitoids is favoured when the foliation is defined by metamorphic minerals no alignment of igneous minerals occurs the foliation is locally at high angles to pluton wallrock contacts and the foliation is continuous with a regionally developed cleavage

structures indicative of helicoidal flow in a migmatitic diapir bacao complex southeastern brazil abstract the migmatitic bacao complex southeastern brazil shows foliation and lineation patterns that depict an internal flow structure with helicoidal geometry microstructures show that a rheological transition exists from a predominantly magmatic flow represented by isotropic undeformed granitic textures to solid state flow mylonites towards the diapir margins nebulites and contorted migmatites occur in the diapir core whereas the peripheral domains show different kinds of banded migmatites gneisses and high temperature mylonites along the margins low temperature mica rich mylonites and phyllonites occur two major flow domains were recognized the central cell and the peripheral cell each cell is characterized by one or more systems of concentric foliations subcells the mineral lineation produced by the morphological alignment of biotite flakes on the foliation planes defines helicoidal geometries in all subcells this lineation was interpreted as being parallel to the local flow vector the foliation and lineation patterns suggest that the principal ascent trunk occurred along a medium plunge spiral in the central cell a dip flow regime the constant injection of molten material in the central cell pushed the material previously emplaced into the peripheral cell where flow upwards continued through a shallower plunge spiral a strike flow regime

timing and nature of magmatic fabrics from structural relations around stoped blocks abstract structural relations around several large 100 m stoped blocks in the granodiorite of castle creek sierra nevada california suggest that magmatic fabrics formed as or after the space making phase of pluton emplacement had ended the stoped granite blocks are approximately 360 m below the exposed pluton roof magmatic foliations in granodiorite surrounding the blocks commonly follow km scale orientation trends to within 1 m of block contacts where they become deflected parallel to the block boundaries locally undeflected foliations occur within a few centimeters of block contacts mafic enclave fabric ellipsoid intensities 0 2 we draw the following conclusions concerning magmatic fabrics in the granodiorite of castle creek 1 magmatic fabrics formed during and or after the latest stages of pluton emplacement and thus contain little or no information about space making processes 2 magmatic fabrics had poor strain memory and 3 during magmatic fabric formation pluton strains were partially decoupled from host rock strains published data from other plutons indicate that these relationships may be common particularly in the brittle upper crust it follows from these conclusions that even in the best case magmatic fabrics contain only qualitative information about pluton emplacement mechanisms regional tectonics and internal magma chamber processes interpretations of magmatic fabrics must be corroborated by evaluating causes kinematics and magnitudes of syn emplacement host rock deformation in the worst case the causes of magmatic fabrics cannot be uniquely determined

emplacement and magnetic fabrics of rapakivi granite intrusions within wiborg and aland rapakivi granite batholiths in finland abstract anisotropy of magnetic susceptibility ams studies were carried out in two areas in finland the ruotsinpyhtaa intrusion within the wiborg rapakivi granite batholith and the saltvik intrusions within the aland rapakivi granite batholith the main aim of this study was to understand the emplacement history of these mid proterozoic rapakivi granites aeromagnetic images reveal structures of ca 5 10 km intrusions that build up the large rapakivi granite batholiths of aland and wiborg magnetic susceptibility data from the database of the geological survey of finland including more than 1700 samples from the wiborg rapakivi batholith and almost 900 samples from the aland rapakivi batholith were compared with measurements from the present study the mean susceptibility is ca 1500 si for the wiborg batholith and ca 10 000 si for the aland batholith samples taken for this study demonstrate that the mean value for the ruotsinpyhtaa intrusion is ca 1200 si and for the saltvik intrusions ca 24 000 si thermomagnetic measurements reveal that the magnetic susceptibility is mainly derived either from paramagnetic minerals or from magnetite the absence of solid state deformation features such as breccia or contact deformation indicates a cauldron type subsidence emplacement the ams measurements from ruotsinpyhtaa confirm these proposals with concentric gently dipping magnetic foliations that support a ring complex structure above a piston type subsidence system the saltvik area consists of a number of smaller elliptical intrusions of different rapakivi granites forming a multiple intrusive complex the magnetic fabric shows a general westward dipping of the pyterlite and eastward dipping of the contiguous even grained rapakivi granite which indicates a central inflow of magma batches towards the east and west resulting from a laccolitic emplacement of magma batches while the main mechanism for space creation was derived from subsidence

age and magnetic fabric of the tres corregos granite batholith evidence for ediacaran transtension in the ribeira belt se brazil anisotropy of magnetic susceptibility ams and u pb shrimp zircon ages in the eastern part of the tres corregos batholith ribeira belt se brazil indicate a well defined fabric pattern acquired between 600 and 595 ma the batholith consists mostly of porphyritic granites distributed in the ribeirao branco barra do chapeu and itaoca plutons late fluorite bearing alkaline granites some containing sn polymetallic greisen type deposits intruded the ribeirao branco pluton and the low grade metasedimentary host rocks the magnetic fabric of the ribeirao branco granite is dominantly oblate and oblique to the pluton elongation while that in barra do chapeu is mostly concentric on both plutons ams records the preferred orientation of coarse homogeneous ti poor magnetite grains such fabric patterns indicate a partitioned strain field dominated by strike slip left lateral shear deformation in the ribeirao branco and extension in the barra do chapeu pluton the zircon ages of these plutons are 600 6 ma and 595 4 ma likewise the ages of alkaline plutons were in the range of 597 and 595 ma registering a fast transition between the typical syntectonic batholithic magmatism to the late highly evolved and specialized magmas these results indicate that the ribeira belt was deformed by transtension in the middle ediacaran the geological setting is consistent with a continental arc with the tres corregos batholith emplacing at the middle upper crust

mt etna volcano modelling of ground deformation patterns of recent eruptions and considerations on the associated precursors abstract the study of the ground deformation associated with the recent eruptions of the etna volcano 1981 1989 1991 93 furnished the opportunity to observe different behaviour relating to the eruptive activity and suggested different feeding and penetration mechanisms inside the volcano edifice in particular the analytical modelling of geodetic data was applied to study the strain sources of these eruptions by the application of single and multiple source models i e composed of two single sources in particular a single tensile dislocation was used to model the se fracture associated with the 1989 eruption a double tensile dislocation was adopted to interpret and model the deformation pattern of the 1981 eruption a double source composed of a tensile dislocation for the final eruptive fracture and a depressuring body for the deflation during the eruption course was considered for the 1991 93 eruption the results of this modelling show that however the final uprising system i e the tensile mechanisms inside the volcano edifice involved the same structure oriented approximately nnw sse this structure was activated by different eruption mechanisms with associated different deformation patterns during these three recent eruptions a review of the methodologies applied and main results obtained in modelling of different sources and mechanisms is presented here the analysis of the deformation data and the performed modelling evidence that the associated precursors can strongly change for the different eruptions in addition the implications both in terms of how the volcano works and in terms of ground deformation precursors are discussed

deformation induced gravity changes in volcanic regions summary we analyse a new model to estimate the change in gravity and in elevation caused by volcanic eruption or inflation in the new model a permeable porous zone surrounds a spherical magma chamber magma may enter or leave the magma chamber and independently the permeable zone this arrangement simulates the flow processes inferred from field studies and provides a degree of freedom not available in the classic model proposed by mogi and used by many others since then we find in agreement with field data and previous analyses of the mogi model that the change in edifice volume is smaller than the volume of magma which produces it the local change in gravity is found to be proportional to the local elevation change the constant of proportionality being positive or negative depending on whether magma flow is directed into or out of the chamber or infiltrated zone

geospatial analysis of a coastal sand dune field evolution jockey s ridge north carolina preservation and effective management of highly dynamic coastal features located in areas under development pressures requires in depth understanding of their evolution modern geospatial technologies such as lidar real time kinematic gps and three dimensional gis provide tools for efficient acquisition of high resolution data geospatial analysis feature extraction and quantification of change these techniques were applied to the jockey s ridge north carolina the largest active dune field on the east coast of the united states with the goal to quantify its deflation and rapid horizontal migration digitized contours photogrammetric lidar and gps point data were used to compute a multitemporal elevation model of the dune field capturing its evolution for the period of 1974 2004 in addition peak elevation data were available for 1915 and 1953 analysis revealed possible rapid growth of the dune complex between 1915 1953 followed by a slower rate of deflation that continues today the main dune peak grew from 20 1 m in 1915 to 41 8 m in 1953 and has since eroded to 21 9 m in 2004 two of the smaller peaks within the dune complex have recently gained elevation approaching the current height of the main dune steady annual rate of main peak elevation loss since 1953 suggests that increase in the number of visitors after the park was established in 1974 had little effect on the rate of dune deflation horizontal dune migration of 3 6 m yr in southerly direction has carried the sand out of the park boundaries and threatened several houses as a result the south dune section was removed and the sand was placed at the northern end of the park to serve as a potential source sand fencing has been an effective management strategy for both slowing the dune migration and forcing growth in dune elevation understanding the causes of the current movements can point to potential solutions and suggest new perspectives on management of the dune as a tourist attraction and as a recreation site while preserving its unique geomorphic character and dynamic behavior d 2005 elsevier b v all rights reserved

the cryptic summit graben of mt etna volcano abstract previous studies have inferred the likelihood of a summit graben at mt etna but until now there has been no direct observation or evidence of such a feature here the results of 43 years of deformation measurements at the summit are reported in which the presence of an actively forming north south graben 1 5 km wide is evident with a maximum subsidence of nearly 4 m in 43 years its bounding faults have in most places been hidden by the eruptive deposits of 190 summit eruptions but horizontal measurements across these faults show a maximum value of nearly 9 m of east west extension most of the subsidence and extension has taken place during the injection of eruption feeder dykes with extreme values for single events of 1 7 m subsidence during the injection of the 2002 2003 dyke and 4 4 m extension across the 1989 feeder dyke but subsidence and extension continues to take place slowly during inter eruptive periods analogue modelling indicates that its origin is probably a consequence of the gravitational spreading and downslope sliding of the etna edifice on its clay rich substrate aided by magmatic pressure from feeder dykes intruded into individual faults and by downward pressure from surface loading of erupted lava this study clarifies the way in which the mechanism of gravitational spreading is maintained throughout the lifetime of this and other spreading volcanoes and rifts on earth and mars

fracture controlled magma conduits in an obliquely convergent continental magmatic arc magnetic fabric patterns of two mid cretaceous nested plutons 102 1 and 96 3 ma in the central sierra nevada batholith provide evidence that felsic magma emplacement and ascent occurred via north trending steeply dipping planar fracture conduits oriented obliquely to the arc u pb geochronology data indicate that emplacement of the plutons was separated by 2 to 10 m y and that they were emplaced in part via the same conduit magnetic fabrics in the younger pluton are related to its final emplacement which was strongly influenced by a system of host rock joints formation of the north trending conduits at 100 ma can be related to a small arc parallel dextral shear component that produced tension fractures and that was associated with high angle oblique convergence by 90 ma convergence had become sufficiently oblique for the development of nearly arc parallel structures which were then favored as magma conduits