salt weathering simulation using a single immersion technique samples of concrete were subjected in an environmental cabinet to six different diurnal cycles of temperature and humidity change representative of desert surface conditions in the presence of a range of saturated salt solutions the samples were not subjected to repeated immersion or continuous partial immersion as has been the case in most previous experiments breakdown did occur nonetheless the two most effective cycles were one from egypt with a very high daytime maximum and one from the negev with high nocturnal humidity conditions cycles with relatively modest temperature and humidity cycles were ineffective in causing debris liberation

preeruption conditions and timing of dacite andesite magma mixing in the 2 2 ka eruption at mount rainier analytical field and experimental evidence demonstrate that the mount rainier tephra layer c 2 2 ka preserves a magma mixing event between an andesitic magma whole rock sio 2 content of 57 60 wt and a dacitic magma whole rock sio 2 content of 65 1 wt the end member andesite a mix of an injected and chamber andesite and dacite can be characterized on the basis of the homogeneity of the matrix glass and phenocryst rim compositions many pumices however contain mixtures of the end members the end member dacite contains a microlite free matrix glass with 74 77 wt sio 2 orthopyroxene rims of mg 57 64 clinopyroxene rims of mg 66 74 and plagioclase rim anorthite contents of an 45 65 the temperature and oxygen fugacity from fe ti oxide compositions are 930 10 c and 0 5 0 75 log units above nno the mixed andesite contains mg 73 84 orthopyroxene rims mg 73 78 clinopyroxene rims an 78 84 plagioclase rims and mg 67 74 amphibole rims the temperature from fe ti oxides hornblendeplagioclase and two pyroxene geothermometry is 1060 15 c and the oxygen fugacity is approximately one log unit above nno for the injected andesite the chamber andesite is estimated to be a magma with a 64 65 wt sio 2 melt at 980 c and a nno oxygen fugacity we conclude that the andesitic and dacitic magmas are from separate magma storage regions at 7 km and 2 4 km due to differences in the bimodal whole rock matrix glass and phenocryst compositions and the presence or absence of stable hornblende the time involved from the mixing event through the eruption is limited to a period of 4 5 days based on fe ti oxide reequilibration phenocryst growth rates and hornblende breakdown the eruption sequence is interpreted as having been initiated by an injection of the 1060 15 c andesitic magma into the 980 c 7 km andesite storage region the mixed andesitic magma then intersected a shallow 2 4 km dacitic storage system on its way toward the surface the eruption became more dacitic over time and the final products some show evidence of partial reequilibration between the andesite and dacite

magma buoyancy and volatile ascent driving autocyclic eruptivity at hekla volcano iceland volcanic eruptions are typically accompanied by ground deflation due to the withdrawal of magma from depth and its effusion at the surface here based on continuous high resolution borehole strain data we show that ground deformation was absent during the major effusion phases of the 1991 and 2000 eruptions of hekla volcano iceland this lack of surface deformation challenges the classic model of magma intrusion withdrawal as source for volcanic ground uplift subsidence we incorporate geodetic and geochemical observables into theoretical models of magma chamber dynamics in order to constrain quantitatively alternative co and inter eruptive physical mechanisms that govern magma propagation and system pressurization we find the lack of surface deformation during lava effusion to be linked to chamber replenishment from below whilst magma migrates as a buoyancy driven flow from the magma chamber towards the surface we further demonstrate that inter eruptive pressure build up is likely to be generated by volatile ascent within the chamber rather than magma injection our model explains the persistent periodic eruptivity at hekla throughout historic times with self initiating cycles and is conceptually relevant to other volcanic systems

coastal processes and the development of shoreline erosion in 1971 the us army corps of engineers inventoried the stability of the nation s coastlines concluding in their final summary a report on the national shoreline study that of the 135 000 km of coastline some 33 000 km were seriously eroding more recently dolan et al 1983 assembled the existing data on shoreline changes for the united states reaffirming the magnitude of this problem although such inventories have not been undertaken for the entire world s shorelines coastal erosion is undoubtedly a global problem beach erosion is for the most part episodic with the major retreats in the shoreline occurring during unusually intense storms on the east coast of the united states beach erosion and property losses are produced by nor easters and hurricanes on the west coast intense storms move down from the gulf of alaska generating waves that attack the coastline this obvious association of beach erosion with the energy level of storm waves creates an oversimplified impression of the actual physical processes involved in the erosion only recently have we begun to understand and appreciatc the diversity of processes that are actually involved in coastal erosion it is now recognized that long period oscillations may dominate water motions in the nearshore sometimes containing more energy than the storm generated waves these oscillations as well as a variety of nearshore currents rearrange the beach sand to cause highly variable rates of shoreline retreat along even short stretches of beach although the long term rise in sea level has been recognized as an important factor in shoreline

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

petrologic and experimental evidence for the movement and heating of the pre eruptive minoan rhyodacite santorini greece hydrothermal experiments combined with petrologic observations form the basis for a new two stage model for the evolution of the pre eruption minoan magma chamber at santorini greece ninety nine percent of the erupted volume is two pyroxene rhyodacitic magma that had been stored at a temperature of 885 c based on magnetite ilmenite and quilf geothermometry the rest of the volume is basaltic to andesitic magma which occurs as 200 mpa in addition the composition of the plagioclase hosts an56 6 of the inclusions require temperatures of 825 25 c at pressures 200 mpa this demonstrates that the minoan rhyodacitic magma underwent a two stage evolution first crystallizing at 825 c and 200 mpa and then rinsing to a shallow 50 mpa storage region with a concomitant rise in temperature to 885 c we suggest that the episodic intrusion of mafic magmas provided the necessary heat and perhaps contributed to the ascent of the magma to shallow crustal depths where it reequilibrated before the cataclysmic eruption phase equilibria suggest that much of the heating of the rhyodacite occurred in the shallow storage region thermal budget calculations suggest that the rhyodacite magma could have been heated by intrusions of basalt rising at reasonable upwelling rates and injected into the storage zone over several hundred years preservation of amphibole in the mafic scoria indicate that injection of mafic magma continued up until days before the cataclysmic eruption perhaps triggering the event

along arc variations in the pre eruptive h2o contents of mariana arc magmas inferred from fractionation paths new experimental results are presented on the effects of dissolved h2o during low pressure 52 kbar crystal fractionation in mariana arc magmas the resulting fractionation paths are used to infer the pre eruptive h2o concentrations of mariana lavas from seamounts and islands estimated pre eruptive h2o concentrations for mariana seamounts 2 3 wt are relatively constant and similar to three out of eight of the subaerial volcanoes alamagan pagan and asuncion these h2o concentrations are also similar to measured h2o concentrations in mariana back arc lavas lavas from the remaining islands guguan agrigan uracas anatahan and possibly sarigan have significantly higher h2o 5 6 than the other seamounts and islands these high h2o islands are distributed throughout the arc and do not show any relation to variations in subduction parameters such as subduction angle or obliquity analysis of the h2o concentrations of olivine hosted melt inclusions from seven islands guguan pagan agrigan anatahan alamagan asuncion and sarigan and one seamount fukujin match the estimates inferred from the liquid lines of descent one interpretation of our results is that the flux of volatiles from the mariana sub arc mantle is fundamentally heterogeneous alternatively the variations in pre eruptive h2o concentrations could reflect variations in the depth and extent of fractionation of mariana magmas

an experimental investigation of the influence of water and oxygen fugacity on differentiation of morb at 200 mpa crystallization experiments were performed at 200mpa in the temperature range 1150 950 c at oxygen fugacities corresponding to the quartz fayalite magnetite qfm and mno mn3o4 buffers to assess the role of water and fo2 on phase relations and differentiation trends in mid ocean ridge basalt morb systems starting from a primitive mgo 9 8 wt and an evolved morb mgo 6 49 wt crystallization paths with four different water contents 0 35 4 7 wt h2o have been investigated in primitive morb olivine is the liquidus phase followed by plagioclase clinopyroxene amphibole is present only at water saturated conditions below 1000 c but not all fluid saturated runs contain amphibole magnetite and orthopyroxene are not stable at low fo2 qfm buffer residual liquids obtained at low fo2 show a tholeiitic differentiation trend the crystallization of magnetite at high fo2 mno mn3o4 buffer results in a decrease of melt feo mgo ratio causing a calc alkaline differentiation trend because the magnetite crystallization temperature is nearly independent of the h2o content in contrast to silicate minerals the calc alkaline differentiation trend is more pronounced at high water contents residual melts at 950 c in a primitive morb system have compositions approaching those of oceanic plagiogranites in terms of sio2 and k2o but have ca na ratios and feo contents that are too high compared with the natural rocks implying that fractionation processes are necessary to reach typical compositions of natural oceanic plagiogranites

crystal rich lava dome extrusion during vesiculation an experimental study abstract lava dome forming eruptions represent a common eruptive style and a major hazard at numerous active volcanoes worldwide the extrusion mechanics of crystal rich lava domes and the influence of volatiles on the transition from viscous to brittle behaviour during lava dome extrusion remain unclear understanding how gas exsolution and crystallinity control effusive versus explosive eruption behaviour is essential here we present new experimental results on the rheology of synthesised crystal rich 50 to 80 vol quartz crystals hydrous 4 2 wt h2o in the glass dacite samples which vesiculate from 5 to 27 vol gas bubbles at high temperatures from glass transition temperature to 797 c during deformation conducted in a parallel plate viscometer constant stress at 0 63 0 64 mpa and variable strain rates ranging from 8 32 10 8 to 3 58 10 5 s 1 the experiments reproduce certain aspects of lava dome deformation in volcanic conduits during vesiculation of the residual melt instigated in the experiments by increasing temperature during gas exsolution i e nucleation and growth of gas pressurised bubbles and volume inflation we find that the rheological lubrication of the system during deformation is strongly dictated by the initial crystallinity at crystal contents

precursory dike propagation control of viscous magma eruptions plinian eruptions of phenocryst rich viscous silicic magmas have been reported and in several cases the climactic eruptions were preceded by a small eruption of the magmas formed by mixing with more mafic magmas the eruptive sequence suggests that the less viscous mixed magmas formed a dike prior to the climactic eruption of the viscous silicic magmas the viscosities of seven sets of precursory and climactic magmas were investigated all the climactic silicic magmas had viscosities 10 6 pa s in contrast to the precursory mixed magmas which had viscosities one to five orders of magnitude smaller these viscosity contrasts can be interpreted by adopting a hypothesis of dike propagation limit for magma viscosity above which the magmas are too viscous to form dikes without freezing the dike propagation limit estimated by the dike propagation model of rubin and the maximum excess pressure retained by the tensile strength of a chamber9s wall rock are consistent with the observation of the threshold viscosity of 10 5 10 7 pa s between the precursory and climactic magmas the consistency of the seven examples with the physical model suggests that precursory dike formation by less viscous mixed magma is one of the effective mechanisms for tapping silicic viscous magma chambers

continuous mixing of crystal mush and replenished magma in the ongoing unzen eruption zoning profiles of magnetite phenocrysts in the successively effused dacite of the ongoing unzen eruption from 1991 wereanalyzed to estimate the time scale of magma mixing the dacite was formed by mixing of relatively high and low temperature t end member magmas the magnetite phenocrysts derived from the low t magma are reversely zoned by the mixing with high t magma a diffusion calculation for reequilibration of the reverse zonings gives the time interval from magma mixing to quenching for the mixed dacite erupted from may 1991 to may 1993 the typical diffusion time was estimated to be a few months regardless of the effused sequence for 2 yr this indicates that the mixing was continuous during the effusion the invariability of the other mixing signatures such as the thickness of reaction rims around biotite phenocrysts also supports the continuous mixing model low t end member magma is estimated by mass balance calculation to be a crystal rich mush of dacitic composition these observations lead to a model wherein the highly crystallized remnant magma of the preceding activity has been mixed with the newly injected hot magma of similar bulk composition just prior to the effusion the proposed mechanism implies that this type of magma mixing is an inevitable process in periodically erupting polygenetic volcanoes

cavernous weathering in the capitol reef desert utah tafoni and honeycomb weathering are abundant in sandstones at capitol reef national park cavities are particularly common in talus blocks resting on alkali rich soil in vertical walls of desert washes and in sandstones containing calcareous cement chemical analyses x ray diffraction data and field observations suggest that salt weathering is the most important cause of disintegration but dissolution of calcite cement also occurs in calcareous sandstones cavernous weathering at capitol reef produces cavities similar in appearance to features found in arkose outcrops along the coast of northwest washington even though the environmental conditions at these two locations are very different

petrological and experimental constraints on the pre eruption conditions of holocene dacite from volcan san pedro 36 s chilean andes and the importance of sulphur in silicic subduction related magmas we present an experimental and petrological study aimed at estimating the pre eruptive conditions of a holocene dacitic lava from volcan san pedro 36 s chilean andes phase equilibrium experiments were performed at temperatures t from 800 to 950 c and mainly at 200 mpa but also at 55 150 and 406 mpa oxygen fugacity fo2 ranged from the ni nio buffer nno to 3 5 log units above nno 3 5 and water contents from 3 to 6 wt we also report several experiments where we added sulphur 0 1 1 wt s to the dacite the main mineral assemblage of the dacite hornblende orthopyroxene plagioclase is stable at 200 50 mpa 850 10 c with 4 5 5 5 wt h2o in the melt and at fo2 of nno 1 2 0 2 in accord with the crystallinity mineral proportions and t fo2 determination from fe ti oxides of the lava however biotite which is also present in the dacite is stable at these same t fo2 conditions only in experiments with 0 1 wt s added this result is in accord with the occurrence of pyrrhotite in the lava and with the presence of s in glass inclusions and biotite 300 ppm and up 170 ppm respectively moreover the zoning patterns and compositions of plagioclase phenocrysts together with the presence of high temperature minerals e g clinopyroxene in the lava suggest that the petrological history of the dacite is more complex than a single near equilibrium crystallization stage and could be explained by short lived 100 years temperature fluctuations 50 c in the magma reservoir

evidence for limited zonation in silicic magma systems taupo volcanic zone new zealand smith 1979 suggested that all pyroclastic eruptions that exceed 1 km 3 will show pronounced systematic compositional zonation since then chemical and thermal zonation in large silicic magma bodies has become the expected condition in rhyolitic magma bodies however trace element chemistry and fe ti oxide geothermometry of quaternary rhyolitic plinian tephras from two volcanic centers in the taupo volcanic zone new zealand suggest that no strong systematic chemical or thermal zonation was present in either magma system of the plinian tephra units erupted over the past 50 ka from the taupo and okataina volcanoes 28 were sampled and most were analyzed for th pb rb sr y zr and nb as well as fe ti oxide composition taupo volcano tephras erupted over the past 10 ka have uniform compositions for all elements except sr and all these samples fall on the same t f o 2 buffer trend however pre 22 ka taupo tephras are mineralogically and chemically distinct from the younger group and fall on a different t f o 2 buffer trend this may be a result of the large eruption 155 km 3 of magma from the taupo volcano at 22 5 ka and subsequent reequilibration of the magmatic system the okataina volcano tephras erupted over the past 31 ka show slight systematic and considerable nonsystematic trace element variation but all fall on a single t f o 2 buffer trend this may indicate slight preeruptive alteration of a single okataina magma body

methods of determining the rheological properties of magmas at sub liquidus temperatures non vesicular basaltic melts behave as newtonian fluids at temperatures above their liquidus and their viscosities can be calculated using a method developed by shaw 1972 and bottinga and weill 1972 because many igneous processes involve the flow of silicates at sub liquidus temperatures numerous attempts have been made to calculate the interactive effects of the crystal phase however current methods are appropriate only for relatively low crystal concentrations and they assume newtonian behaviour we argue that this assumption is invalid when bubble or crystal concentrations exceed 30 at higher concentrations factors other than concentration become increasingly important these include particle shape and size distribution a method which takes these factors into account is tested on a range of suspensions including magmas at sub liquidus temperatures and rheological properties calculated using this method agree closely with the measured values we also demonstrate that an equation which was introduced to explain large differences in measured apparent viscosities during the cooling and crystallisation of mount st helens dacite murase et al 1985 and which is currently used to calculate the rheological properties of crystallising lavas generates viscosities which may be in error by several orders of magnitude this difference is argued to be caused by a combination of factors including the ten orders of magnitude range in the strain rates utilised during the mount st helens measurements causing orders of magnitude difference in the resulting apparent viscosities rheological data on crystallising silicic melts are reinterpreted taking into account the non newtonian rheology of the magmas and changes in activation energy of flow during crystallisation

salt weathering influence of evaporation rate supersaturation and crystallization pattern micro and macroscale experiments which document the dynamics of salt damage to porous stone have yielded data which expose weaknesses in earlier interpretations previously unexplained differences are found in crystal morphology crystallization patterns kinetics and substrate damage when comparing the growth of mirabilite na2so4 10h2o and thenardite na2so4 versus halite nacl the crystallization pattern of sodium sulphate was strongly affected by relative humidity rh while a lesser rh effect was observed for sodium chloride macroscale experiments confirmed that mirabilite crystallizing at rh 50 per cent and thenardite crystallizing at rh 50 per cent tend to form subflorescence in highly localized areas under conditions of constant rh and temperature this crystallization pattern was more damaging than that of halite since halite tended to grow as efflorescence or by filling the smallest pores of the stone in a homogeneous fashion a result which contradicts wellman and wilson s theoretical model of salt damage low rh promoted rapid evaporation of saline solutions and higher supersaturation levels resulting in the greatest damage to the stone in the case of both sodium sulphate and sodium chloride crystallization at any particular crystallization condition sodium chloride tended to reach lower supersaturation levels resulting in the crystallization of isometric crystals and created negligible damage while sodium sulphate reached higher supersaturation ratios resulting in non equilibrium crystal shapes resulting in significant damage esem showed no damage from sodium sulphate due to hydration instead after water condensation on thenardite crystals rapid dissolution followed by precipitation of mirabilite took place resulting in stone damage by means of crystallization pressure generation it is concluded that salt damage due to crystallization pressure appears to be largely a function of solution supersaturation ratio and location of crystallization these key factors are related to solution properties and evaporation rates which are constrained by solution composition environmental conditions substrate properties and salt crystallization growth patterns when combined with a critical review of salt damage literature these experiments allow the development of a model which explains variations in damage related to combinations of different salts substrates and environmental conditions

feasibility study of spectral pattern recognition reveals distinct classes of volcanic tremor abstract systematic investigations of the similarities and differences among volcanic tremor at a range of volcano types may hold crucial information about the plausibility of inferred source mechanisms which in turn may be important for eruption forecasting however such studies are rare in part because of an intrinsic difficulty with identifying tremor signals within very long time series of volcano seismic data accordingly we develop an efficient tremor detection algorithm and identify over 12 000h of volcanic tremor on 24 stations at k lauea okmok pavlof and redoubt volcanoes we estimate spectral content over 5 minute tremor windows and apply a novel combination of principal component analysis pca and hierarchical clustering to identify patterns in the tremor spectra analyzing several stations from a given volcano together reveals different styles of tremor within individual volcanic settings in addition to identifying tremor properties common to all stations in a given network we find localized tremor signals including those related to processes such as lahars or dike intrusions that are only observed on some of the stations within a network subsequent application of our analysis to a combination of stations from the different volcanoes reveals that at least three main tremor classes can be detected across all settings whereas a regime with a ridge of high power distributed over 1 2hz and a gradual decay of spectral power towards higher frequencies is observed dominantly at three volcanoes k lauea okmok redoubt with magma reservoirs centered at less than 5km below sea level b s l a spectrum with a steeper slope and a narrower peak at 1 2hz is observed only in association with open vents k lauea and pavlof a third regime with a peak at approximately 3hz is confined to two stratovolcanoes pavlof and redoubt these observations suggest generic relationships between the spectral character of the observed signals and volcano characteristics such as magma viscosity storage depths and the physical properties of volcanic edifices similarities among the spectral patterns detected at stations 4km and 8 10km distance from the centers of volcanic activity respectively indicate that path effects do not strongly influence spectral shapes at distances of a few kilometers from the inferred source of the signals our preliminary work shows that a global comparison of tremor is feasible our results suggest that further work on data from a larger sample and diverse range of volcano types will reveal additional classes of tremor signals and plausibly identify fingerprints of source processes that are specific to volcano type but independent of volcano location

weathering of coastal defensive structures in southwest england a 500 year stone durability trial historic structures can be viewed as exposure trials of the stone of which they are constructed as such they represent a geomorphological weathering experiment several structures of henrician sixteenth century and greater age on the coast of southwest england have been exposed to coastal salt weathering for 500 600 years long term weathering rates on five different rock groups are derived from careful study of weathering depths and forms there is significant variation in weathering rate between five major rock groups rank ordering of weathering rate values reveals a durability order of these rock groups which is confirmed by local juxtapositions controls on rock durability in the coastal weathering environment include both mechanical and mineralogical characteristics specific density and combined quartz and muscovite content are positively related to durability high feldspar and chlorite content are associated with low durability copyright 2000 john wiley sons ltd

preeruptive magma viscosity an important measure of magma eruptibility 1 using a compilation of melt compositions meltwater contents temperatures and phenocryst contents the preeruptive viscosities under magma reservoir conditions are calculated for 83 erupted magmas the basaltic to rhyolitic magmas have preeruptive viscosities over the range 101 to 108 pa s although bulk sio2 content has often been used as a qualitative measure of preeruptive magma viscosity the bulk sio2 content shows a weak correlation with magma viscosity correlation coefficient r 0 5 because of a wide range of phenocryst contents from 0 to 50 vol andesitic magmas have viscosities ranging from 102 to 107 pa s which are lower or higher than those of phenocryst poor rhyolitic magmas with 105 to 106 pa s focusing on andesitic to rhyolitic magmas the r between bulk sio2 contents and magma viscosities changes to 0 1 in contrast the melt only sio2 content from a basaltic to rhyolitic melt shows a good linear correlation with melt only viscosity r 0 9 although most of the calculated viscosities of erupted magmas fall below 106 pa s as consistent with the previous compilation study this paper describes 20 examples of highly viscous magmas with 106 pa s in most cases composed of mixtures of high silica rhyolitic melt 75 79 wt sio2 and abundant phenocrysts 30 55 vol in these highly viscous magmas 9 examples have erupted following the precursory eruption of less viscous magma suggesting that precursory dike propagation and conduit formation by the less viscous magma with 106 pa s induced the following eruption of less eruptible highly viscous magmas

salt as an agent in the development of cavernous weathering a well recognized spatial association exists between cavernous weathering and the presence of soluble salts disaggregation of rock in caverns is attributed to mechanical pressures exerted by crystallization and or hydration of salts however scanning electron micrographic analysis demonstrates that solutional etching is the major weathering process in caverns in near coastal locations in western australia and new south wales australia it is suggested here that the breakdown of the caverned sandstone is caused by sodium chloride which increases the rate of quartz dissolution

crystal capture sorting and retention in convecting magma the mystery of producing strong compositional diversity among suites of comagmatic igneous rocks is investigated by considering the dynamic evolution of basaltic magma in a sheet like chamber a central conclusion is that inward progressing crystallization produces strong viscosity and temperature gradients that promote convection only near the leading edge of the upper thermal boundary layer convection is apparently confined to an essentially isoviscous isothermal region that hugs the downward growing roof zone strong changes in viscosity with crystallization divide the upper and lower thermal boundary layers into regions of decreasing viscosity and crystallinity n called rigid crust n 0 5 mush 0 5 n 0 25 and suspension n 0 25 the strong increase in viscosity near the mush suspension interface acts as a capture front that overtakes and traps slowly settling crystals initial phenocrysts mostly escape capture but crystals nucleated and grown in the suspension zone can escape only if the capture front slows to a critical rate attainable only in bodies thicker than about 100 m escaping crystals are redistributed and sorted by convection driven by the advance of the capture front itself crystal laden plumes traverse the central hot core of the body and deposit partially resorbed and sorted crystals within the lower suspension zone convection is never vigorous but is part of an overall intimate balance between roofward heat loss rigid crust growth crystallization kinetics and transport and sorting of sinking escaped crystals there is a strong similarity between these processes and those producing both varves and saline pan deposits it is clear that lavas lava lakes and sills are indeed examples of true magma chambers strongly exhibiting certain aspects of this over all process these aspects commonly also characterize the large mafic magmatic bodies because strong compositional changes in the residual melt occur largely outward that is at lower temperatures and higher crystallinities of the capture front which is immobile and mostly within rigid crust the possible range in comagmatic compositions available for eruption anywhere within the active magma is very limited this is in broad agreement with the compositional range observed in basaltic lava lakes sills and plutons like skaergaard the tuning of convection crystallization kinetics and phase equilibria in chambers of this type can produce a variety of textures and layering but not a diversity of compositions

oscillatory rheology measurements of particle and bubble bearing fluids solid like behavior of a crystal rich basaltic magma the rheology of crystal and bubble bearing magmas governs the propagation of seismic waves as well as eruption dynamics here rheology includes viscous and elastic components and their ratio known as attenuation we perform an oscillatory rheology measurements which provide storage elastic component and loss viscous component moduli and attenuation with frequency dependence using particle and bubble bearing fluids whose liquid viscosity is in the range of that of a basaltic melt we find that both the storage and loss moduli dramatically increase with the particle fraction but weakly depend on the bubble fraction solid like behavior equivalent to attenuation 40 vol the shallow conduit of stromboli volcano filled by a crystal rich and low viscosity basaltic magma may be an example where shear waves propagate and brittle fractures occur to cause explosive eruptions because of its high crystallinity

laboratory simulation of rock weathering by salt crystallization and hydration processes in hot arid environments the results of a series of experiments are reported in this paper which were designed to differentiate between the forces of crystal growth and hydration in salt weathering using a single salt hydrate system sodium sulphate five contrasting rock types and several diurnal temperature relative humidity cycles which permitted or inhibited these processes and simulated ground surface climates in hot arid environments it was shown that hydration of sodium sulphate is an effective mechanism of rock disintegration but that it is significantly less destructive than crystal growth pressure crystallization of thenardite na2so4 is in turn more effective in rock weathering than the crystal growth of mirabilite na2so4 10h2o in general rates of disintegration were most rapid where the diurnal temperature range was extreme and relative humidity lowest

role of precursory less viscous mixed magma in the eruption of phenocryst rich magma evidence from the hokkaido komagatake 1929 eruption during the 1929 activity of hokkaido komagatake volcano the plinian eruption of a phenocryst rich andesite was preceded by a small eruption of more mafic magma formed by magma mixing a similar eruption sequence has been reported for some other eruptions pallister et al 1996 venezky and rutherford 1997 suggesting that eruption of a mixed magma is a precursor of phenocryst rich magmas for the purpose of understanding the tapping processes of the phenocryst rich magma chamber we investigated the temporal variation in the erupted magma and estimated the viscosity and density of the end member and mixed magmas with constraints drawn from petrography for the precursory mixed magma we estimate 33 4 vol phenocrysts andesitic dacitic melt composition 3 wt h2o content and temperature of 1040 c in comparison for the climactic silicic end member magma we estimate 48 3 vol phenocryst high silica rhyolitic melt 3 wt h2o and temperature of 950 c respectively the mafic end member magma which was not erupted is thought to be an almost aphyric basaltic andesitic magma based on mass balance calculation of the phenocryst content the proportion of the mafic end member magma component in the mixed magma was calculated to be 20 40 wt on the basis of these data we estimate magma viscosities of 103 9 106 9 and 102 0 pa s for the mixed silicic end member and mafic end member magmas respectively the calculated density differences among these magmas are inconsequential when possible errors are considered we calculate the minimum excess pressure required for dike propagation to be 31 mpa for the silicic end member magma and 8 mpa for the mixed magma using the estimated viscosity and dike propagation model of rubin 1995 if we assume that excess pressure is limited by the wall rock strength of the magma chamber excess pressure retainable in the magma chamber is less than ca 20 mpa this suggests that the mixed magma was able to ascend to the surface without freezing whereas the viscous silicic end member magma could not the formation and precursory eruption of the mixed magma are therefore effective and necessary initiation processes for the phenocryst rich viscous magma eruption

extensive young silicic volcanism produces large deep submarine lava flows in the ne lau basin new field observations reveal that extensive up to 402 km2 aphyric glassy dacite lavas were erupted at multiple sites in the recent past in the ne lau basin located about 200 km southwest of samoa this discovery of volumetrically significant and widespread submarine dacite lava flows extends the domain for siliceous effusive volcanism into the deep seafloor although several lava flow fields were discovered on the flank of a large silicic seamount niuatahi two of the largest lava fields and several smaller ones northern lava flow fields were found well north of the seamount the most distal portion of the northernmost of these fields is 60 km north of the center of niuatahi caldera we estimate that lava flow lengths from probable eruptive vents to the distal ends of flows range from a few km to more than 10 km camera tows on the shallower near vent areas show complex lava morphology that includes anastomosing tube like pillow flows and ropey surfaces endogenous domes and or ridges some with crease like extrusion ridges and inflated lobes with extrusion structures a 2 1 5 km 30 m deep depression could be an eruption center for one of the lava flow fields the lau lava flow fields appear to have erupted at presumptive high effusion rates and possibly reduced viscosity induced by presumptive high magmatic water content and or a high eruption temperature consistent with both erupted composition 66 sio2 and glassy low crystallinity groundmass textures the large areal extent 236 km2 and relatively small range of compositional variation 0 60 for wt si02 within the northern lava flow fields imply the existence of large eruptible batches of differentiated melt in the upper mantle or lower crust of the ne lau basin at this site the volcanism could be controlled by deep crustal fractures caused by the long term extension in this rear arc region submarine dacite flows exhibiting similar morphology have been described in ancient sequences from the archaean through the miocene and in small batches on present day seafloor spreading centers this study shows that extensive siliceous lavas can erupt on the modern seafloor under the right conditions

phase equilibria of the lyngdal granodiorite norway implications for the origin of metaluminous ferroan granitoids the proterozoic 950 ma lyngdal granodiorite of southern norway belongs to a series of hornblende biotite metaluminous ferroan granitoids hbg suite coeval with the post collisional rogaland anorthosite mangerite charnockite amc suite this granitoid massif shares many geochemical characteristics with rapakivi granitoids yet granodiorites dominate over granites to constrain both crystallization p t fo2 h 2o in melt and magma generation conditions we performed crystallization experiments on two samples of the lyngdal granodiorite with 60 and 65 wt sio2 at 4 2 kbar mainly at fo2 of nno nickel nickel oxide to nno 1 and under fluid saturated conditions with various h2o co2 ratios for each temperature comparison between experimental phase equilibria and the mineral assemblage in the lyngdal granodiorite indicates that it crystallized between 4 and 2 kbar from a magma with 5 6 wt h2 oa t an fo2 of nno to nno 1 these oxidized and wet conditions sharply contrast with the dry and reduced conditions inferred for the petrogenesis of the amc suite and many other rapakivi granites worldwide the high liquidus temperature and h2o content of the lyngdal granodiorite imply that it is not a primary magma produced by the partial melting of the crust but is derived by the fractionation of a mafic magma lyngdal type magmas appear to have volcanic equivalents in the geological record in particular our results show that oxidized high silica rhyolites such as the bishop tuff could be derived via fractionation of oxidized intermediate magmas and do not necessarily represent primary crustal melts this study underlines the great variability of crystallization conditions from anhydrous to hydrous and reduced to oxidized and petrogenetic processes among the metaluminous ferroan magmas of intermediate compositions granodiorites quartz mangerites quartz latites suggesting that there is not a single model to explain these rocks

rheology of crystal bearing silicate melts an experimental study at high viscosities the viscosity of partially crystallized mg3al2si3o12 melts has been measured under uniaxial compression in the interval 1010 1013 poise as a function of the volume fraction of crystals these inclusions are well rounded spherulites of aluminous enstatite having the same composition as the melt and whose growth rate is negligible at the temperature of the measurements the viscosity increases by less than 1 order of magnitude for crystal fractions of 40 vol and remains newtonian up to the maximum stress exerted namely 1 kbar the einstein roscoe equation 0 1 m n provides very good fits to the measurements only if either the m or n parameter is allowed to depend on temperature for modeling of magmatic processes however the widely recommended constant values m 0 6 and n 2 5 should be adequate the rheology changes abruptly when the clustered spherulites begin to oppose shear deformation at a crystal fraction of about 40 vol the viscosity becomes non newtonian with yield strengths of a few tens of bars at temperatures at which the viscosity of the melt is higher than 1010 poise as long as the crystal fraction remains lower than 70 vol the deformation proceeds in an irregular manner with a nonuniform distribution of crystals and melt the deformation becomes again regular at low stresses with lower melt fractions but samples undergo extensive fracturation along the direction of uniaxial stress similar rheology changes have been observed during the isothermal crystallization of li2si2o5 melts which produces small ellipsoidal inclusions these results suggest that the influence of solid suspensions on the rheology of magmas is primarily determined by the crystal fraction even though additional measurements would be useful to determine the possible influence of other factors such as the size distribution or the shape of the inclusions

variability of shoreline erosion and accretion within a beach compartment of flathead lake montana we measured shoreline reconfiguration and variability in shoreline retreat in flathead lake which is a large glacial lake regulated by a hydroelectric dam at its natural outlet wave induced erosion rates ranged from 0 5 to 2 5 m yr i at the northshore study site where fetch and hence wave energy was maximal shoreline retreat was not solely related to storm intensity or volumetric changes in nearshore bars three erosive processes were involved in the measured variability of shoreline retreat undercutting endstripping and ovcrwash wave scour on an exposed bank caused undercutting and endstripping while overwash resulted when water was forced over the top of the shoreline shoreline morphology and vegetation determined the type of erosion process and the rate of shoreline retreat shoreline retreat was offset by localized and dramatic accretion caused by sediment entrapment by drift logs bordering the shoreline the eroding shoreline and ncarshore bed were sediment sources for the accretion drift logs naturally protcctcd the shoreline from direct wave attack and stimulated sediment accretion providing new rccruitmcnt arca for riparian vegetation each stretch of sea coastline or lake shorcline uniquely responds to the physical processes associated with erosion and accretion change in shoreline position is one measurable response to the complex processes that continually shape the littoral zone shoreline erosion depends on many site specific factors such as ncarshore morphology relative changes in water levels varying wave energies patterns of net littoral drift and sediment composition and grain size warnkc et al 1966 sharaf el din 1974 sakalowsky 1975 morton 1979 therefore when addressing shoreline behavior it is necessary to examine and identify components and processes that determine the observed shoreline response on a local scale beach erosion and shoreline retreat are largely episodic corresponding to periods of intense storms however this general association of erosion with the cncrgy level of waves creates an oversimplified impression of the actual processes causing shoreline retreat

comagmatic granophyre and dacite from karymsky volcanic center kamchatka experimental constraints for magma storage conditions abstract despite a 30 000 years difference in age two caldera forming eruptions at karymsky volcanic center kamchatka karymsky 7900 yr bp and academy nauk ca 40 000 yr bp produced two pyroxene dacites with the same composition and mineralogy granophyric xenoliths of the identical whole rock chemistry were found in basalts erupted within academy nauk caldera in 1996 unlike the dacites however the granophyres are holo crystalline and contain biotite and amphibole large amphibole phenocrysts contain rare inclusions of clinopyroxenes which compositionally overlap with clinopyroxenes in the dacites the al content of the amphibole suggests it grew at a pressure of about 100 mpa results of hydrothermal experiments and petrologic observations indicate that academy nauk and karymsky dacites were last equilibrated at 883 19 c 100 15 mpa and 871 19 c 85 18 mpa respectively both at water saturated conditions the mineral assemblage of granophyre is reproduced by isobaric crystallization of the dacite at 100 mpa implying that the granophyres were sampled from the crystallized silicic reservoir that produced the caldera forming eruption of academy nauk similar chemical compositions of karymsky and academy nauk dacites indicate that both were derived from the same crustal level source the eruptive history of the calderas can best be explained by two 10 12 km 3 dacitic batches that detached from a parental body situated in the lower crust then ascended to 3 4 km depth re equilibrated and erupted

dehydration melting and water saturated melting of basaltic and andesitic greenstones and amphibolites at 1 3 and 6 9 kb

heterogeneous rheology controlled postseismic deformation of the 2011 tohoku oki earthquake using two dimensional finite element modeling we reproduced the observed postseismic deformation of the 2011 tohoku oki earthquake our model which accounts for the lithosphere asthenosphere boundary and weak zones beneath volcanoes was able to reproduce small scale 20 km perturbations in postseismic deformation observed by the dense geodetic network such as local subsidence around quaternary volcanoes the inverted afterslip has a peak at the downdip limit of the main rupture region on the subducting plate interface consistent with physical predictions the combination of afterslip and viscoelastic relaxation in a heterogeneous rheology model explains the observations well even on small scales

shear viscosity of rhyolite vapor emulsions at magmatic temperatures by concentric cylinder rheometry abstract the viscosity of natural rhyolitic melt from lipari aeolian islands and melt bubble emulsions 30 50 vol porosity generated from lipari rhyolite have been measured in a concentric cylinder rheometer at temperatures and shear rates in the range 925 1150 c and 10 3 10 1 2 s 1 respectively in order to better understand the dependence of emulsion shear viscosity on temperature and shear rate in natural systems bubble free melt exhibits newtonian arrhenian behavior in the temperature range 950 1150 c with an activation energy of 395 30 kj mol the shear viscosity is given by log m 8 320 20624 t suspensions were prepared from natural rhyolite glass to which small amounts of na2so4 were added as a foaming agent reasonably homogeneous magmatic mixtures with an approximate log normal distribution of bubbles were generated by this technique suspension viscosity varied from 106 1 to 108 37 pa s and systematically correlates with temperature and porosity in the shear stress range 104 26 105 46 pa of the experiments the viscosity of melt bubble emulsions is described in terms of the relative viscosity r e m where e is the emulsion viscosity and m is the viscosity of melt of the same composition and temperature the dependence of relative viscosity on porosity for magmatic emulsions depends on the magnitude of the capillary number ca g rb 1 m 1 the ratio of viscous forces acting to deform bubbles to interfacial forces resisting bubble deformation for inviscid bubbles in magmatic flows three regimes may be identified for ca 10 an asymptotic regime is reached in which relative viscosity decreases with increasing porosity and is independent of ca our experiments were carried out for 30

getting granite dikes out of the source region whether a dike can propagate far from a magma reservoir depends upon the competition between the rate at which propagation widens the dike and the rate at which freezing constricts the aperture available for magma flow various formulations are developed for a viscous fluid at temperature t sub m intruding a growing crack in an elastic solid the initial solid temperature equals t sub m at the source and decreases linearly with distance from the source if t sub m is the unique freezing temperature of the fluid dike growth is initially self similar and an essentially exact solution is obtained if t sub m is above the solidus temperature the solution is approximate but is designed to overestimate the distance the dike may propagate the ability of a dike to survive thermally depends primarily upon a single parameter that is a measure of the ratio of the dike frozen margin thickness to elastic thickness perhaps more intuitively one may define a minimum distance from the essentially solid reservoir wall to the point at which the host rock temperature drops below the solidus necessary for dikes to propagate far into subsolidus rock it is concluded that for reasonable material properties and source conditions most basalt dikes will have little difficulty leaving the source region but most rhyolite dikes will be halted by freezing soon after the magma encounters rock at temperatures below the magma solidus while these results can explain why granitic dikes are common near granitic plutons but rare elsewhere the potentially large variation in magmatic systems makes it premature to rule out the possibility that most granites are transported through the crust in dikes nonetheless these results highlight difficulties with such proposals and suggest that it may also be premature to rule out the possibility that most granite plutons ascend as more equidimensional bodies

a model for the rheology of particle bearing suspensions and partially molten rocks an edited version of this paper was published by agu copyright 2009 american geophysical union

gas saturation and evolution of volatile and light lithophile elements in the bandelier magma chamber between two caldera forming eruptions we have studied the distribution of light and volatile elements li be b h2o f cl in matrix glasses and melt inclusions in quartz and sanidine phenocrysts from tephras of the cerro toledo rhyolite which were erupted from the bandelier magma chamber between two caldera forming eruptions at 1 608 ma and 1 225 ma since the small volume tephras of the cerro toledo rhyolite record chemical evolution of the upper parts of the magma chamber during this 383 kyr period we can track volatile evolution in the magma during its differentiation specifically the development of a separate fluid phase from the magma the partitioning of volatile and light elements between this fluid and the magma and the timing of the second caldera eruption at 1 225 ma the melt inclusion data reveal that li be and b were progressively enriched with time at the top of the magma chamber showing a similar three fold enrichment by contrast f cl and f2o show more variable behavior f was enriched 3 6 times in the magma and cl increased 2 5 times while water concentrations remained constant evidence for a separate fluid phase includes 1 comparatively small magmatic enrichment factors for cl and h2o elements which are known to partition into fluid 2 decline of the cl be and cl b ratios in melt inclusions with time indicating preferential loss of cl and 3 maximum cl contents of 2900 3000 ppm in melt inclusions which are concentrations at or close to the saturation limit for cl in a two phase gas saturated magma the lack of temporal h2o enrichment in the magma suggests that it became gas saturated at an early stage the cl fluid magma partition coefficient was initially low due to the presence of a low salinity single phase vapor the fluid is calculated to have increased its salinity from 0 76 wt equivalent nacl to 3 1 wt nacl by crystallization and cl enrichment in the magma consequently the fluid was transformed to two immiscible phases as a result the cl partition coefficient increased and the cl content in the magma was buffered at 2900 3000 ppm overpressures in the magma chamber have been modeled as a function of crystallization total pressure and depth h2o solubility in rhyolite resurgence crystallization contraction and initial fluid mass for the large amounts of crystallization 40 70 required by the geochemical relations unrealistically large overpressures 75 mpa are indicated unless 1 the magma existed as a foam or 2 the chamber was able to degas passively and thus buffer the buildup of pressure to maintain realistic overpressures in the magma chamber 50 mpa an equilibrium was required between gas buildup by crystallization and volatile loss by passive degassing the change from a one phase vapor to a two phase immiscible fluid before the upper bandelier tuff eruption may have promoted partial or complete sealing of the magmatic hydrothermal system permitting significant overpressures to develop the result could have been a cataclysmic caldera forming eruption

experimental constraints on the deep magma feeding system at stromboli volcano italy new experiments have been performed on a high k basalt pst 9 from stromboli volcano italy to constrain the physical conditions of golden pumice magmas at their storage level and discuss their petrogenesis fluid present h2o and co2 bearing near liquidus experiments were performed at 11508c between 100 and 400mpa and under oxidizing conditions glasses were analyzed by fourier transform ir spectroscopy and their h2o and co2 concentrations compared with those in glass inclusions most glass inclusions cluster near the 200mpa isobar suggesting entrapment at a depth of 8 km golden pumice magmas have viscosities of 7 9 pa s and densities of 2 48 2 57 g cm3 compositions of experimental fluids coexisting with melts along the liquidus have been estimated by mass balance they range from co2 rich xh2o 0 2 at 400mpa to h2o rich xh2o 0 8 at 100mpa the free fluid phase present at the reservoir level has an xh2o of 0 6 consistent with equilibration with a near liquidus golden pumice magma below 300mpa clinopyroxene is the liquidus phase in all highpressure experiments either fluid absent h2o or fluid present h2o co2 in contrast at 0 1mpa cpx and ol appear together on the liquidus and olivines are more fo rich up to 89 1 than those crystallizing at high pressures up to 87 3 the composition of cotectic liquids multiply saturated in cpx and ol has been experimentally determined most pumices and a majority of melt inclusions have compositions of cotectic melts in contrast pst 9 plots in the cpx field and is representative of less evolved ankaramitic magmas parental to golden pumices melt inclusions trapped in fo 487 olivines form a group of ultra calcic compositions plotting in the cpx field interpreted as boundary layer melts locally generated by cpx dissolution in the deep reservoir ankaramitic melts in the stromboli feeding system are proposed to derive from primitive mantle melts by combined crystallization mixing wall rock interaction and assimilation

phase equilibria constraints on pre eruptive magma storage conditions for the 1956 eruption of bezymianny volcano kamchatka russia abstract phase equilibria experiments were performed on andesites from the catastrophic 1956 eruption of bezymianny volcano kamchatka russia to determine pre eruptive magma storage conditions fifteen experiments were conducted under water saturated conditions with oxygen fugacity equal to the ni nio oxygen buffer at temperatures between 775 and 1100 c and pressures between 50 and 200 mpa simultaneous amphibole and plagioclase crystallization is reproduced at 850 c and 200 mpa the simultaneous crystallization temperature range of the plagioclase clinopyroxene orthopyroxene fe ti oxide assemblage increases with decreasing pressure from 840 to 940 c at 150 mpa to 940 1020 c at 50 mpa melt inclusion compositions in plagioclase phenocrysts and matrix glass match experimental melt compositions reproduced at 50 100 mpa and 50 mpa respectively presence of the silica phase in groundmass and mature amphibole breakdown rims suggests that magma has been stored at ca 3 km depth prior to the final ascent for at least 40 days syn eruptive ascent led to decompression driven crystallization which caused a temperature increase from 850 900 c to 950 1000 c

rhyodacite magma storage conditions prior to the 3430 ybp caldera forming eruption of aniakchak volcano alaska this study presents a pre eruptive magma storage model for the rhyodacite and andesite magmas erupted during the 3430 ybp caldera forming eruption of aniakchak volcano alaska derived from phase equilibria experiments and petrological data the compositions of fe ti oxide pairs from the early erupted plinian rhyodacite pumice yield core temperatures of 871 900 c with rims up to 942 c and fo2 from 10 6 to 11 8 log units melt inclusions entrapped in plagioclase phenocrysts have h2o contents between 3 and 5 wt estimated by ftir and electron microprobe volatiles by difference methods with no detectable co2 assuming water saturation this corresponds to entrapment pressures between 65 and 150 mpa phase equilibria results reproduce the natural phase assemblages at p text h 2 text o of 95 150 mpa at 870 880 c assuming water saturation a mismatch in experimental versus natural glass sio2 and al2o3 and melts models for h2o undersaturated conditions indicate that the rhyodacite may not have been h2o saturated melts models with x text h 2 text o 0 8 and ptotal of 125 150 mpa at 870 880 c reproduce the natural groundmass glass al2o3 composition best indicating the magma may have been slightly h2o undersaturated those pressures correspond to storage at 4 5 5 4 km depth in the crust melts models and vbd estimates from melt inclusions in titanomagnetite grains from the andesite indicate pre eruptive conditions of 1 000 c and 110 mpa corresponding to a minimum residence depth of 4 1 km assuming water saturation or greater if the magma was h2o undersaturated previous geochemical studies indicate separate histories of the two magmas though they retain some evidence that they are ultimately related through fractional crystallization processes analogous to the 1912 novarupta magmas the rhyodacite and andesite presumably originated within the same crystal mush zone beneath the edifice yet were separated laterally and underwent different degrees of crustal assimilation the andesite must have resided in close proximity with ascent occurring in response to movement of the rhyodacite and resulting in extensive syn eruptive mingling

experimental constraints on the effects of pressure and h 2 o on the fractional crystallization of high mg island arc basalt h2o undersaturated melting experiments of synthesized basalt sio2 50 7 wt mgo 8 3 wt mg 60 were conducted at fo2 corresponding to nno 1 and nno 1 to clarify the effects of pressure 2 7 kbar and h2o on fractional crystallization in island arcs h2o content was ranged from nominally anhydrous to 4 4 wt differentiation trends namely the liquid lines of descent change sensitively according to pressure h2o relations tholeiitic differentiation trends are reproduced with h2o 2 wt in primary magma with such quantities of h2o fractional crystallization is controlled by olivine plagioclase at 2 kbar increasing the pressure from 2 to 4 kbar induces early crystallization of orthopyroxene instead of olivine and therefore sio2 enrichment in the residual melts is suppressed increasing h2o 2 wt in primary magma stabilizes clinopyroxene relative to orthopyroxene and or magnetite although the phase relations and proportions strongly depend on fo2 and h2o content differentiation trends are always calc alkaline

depth and evolution of a silicic magma chamber melting experiments on a low k rhyolite from usu volcano japan we estimated the depth of the magma chamber system beneath usu volcano one of the most active volcanoes injapan by melting experiments on the eruptive product of the ad 1663 plinian eruption us b pumice this pumice is a low k rhyolite with a k2o content of only 1wt the experiments were conducted using internally heated pressure vessels at 98 392mpa and 700 9008c under nickel nickel oxide nno buffered and water saturated conditions the pre eruptive conditions of the 1663 eruption were estimated to be 780 208c and around 200 250mpa the phase equilibria mineral compositions plagioclase orthopyroxene and fe ti oxides melt composition and melt fraction are all in agreement with this conclusion this pressure corresponds to a depth of 8 10 km assuming a lithostatic condition with an appropriate crustal density structure the magma was at near water saturated conditions deviation between the estimated pressure and the true total pressure was estimated to be less than 50mpa the us b magma was under very uniform conditions with a temperature variation of less than c 208c deduced from the narrow range of the phase equilibrium conditions crystallizing orthopyroxene without quartz and the homogeneous composition of plagioclase c an 41 45 we also estimated the pre eruptive conditions of post 1663 eruptions where it has been proposed that two magmas high p and low p members mixed prior to each eruption the pressure of the deep magma was also around 200 250mpa whereas that of the shallow magma was estimated to be 100 150mpa 4 6 km depth according to the pressure dependence of the plagioclase composition obtained in our experiments thus there appear to be two magma chambers beneath usu volcano our estimate is consistent with geophysical observations made during the 2000 eruption including identification of an inflation and deflation source at a depth of 10 km a low frequency 12 s tremor source at a depth of 5 6 km and an earthquake swarm at a depth of less than 4 km the depth of the rhyolitic magma chamber 8 10 km is deeper than the level of neutral buoyancy for the magma and is comparable with that of mafic magma that existed beneath the rhyolitic magma this suggests that the depth of the 8 10 km deep magma chamber was controlled by the emplacement of the mafic magma and that the rhyolitic magma was produced at that depth when compared with other silicic magma systems the usu magma system has similar characteristics including a similar pre eruptive pressure of around 200mpa and a pressure decrease with time suggesting upward magma movement towards a neutral buoyancy level the low potassium content of the usu magma prohibited crystallization of biotite k feldspar or hornblende which are common phases in magmas with intermediate to high potassium contents the absence of hydrous minerals at near liquidus conditions may cause a rapid increase in water content

degassing and microlite crystallization of basaltic andesite magma erupting at arenal volcano costa rica abstract volcanoes can erupt explosively in plinian style or effusively as lava flows most models for such ranges in activity are based on silicic magma which may not be appropriate for less viscous basic magma although basic magma erupting at arenal volcano has not varied significantly in bulk composition the volcano has exhibited a full range in eruptive style from plinian activity in 1968 to strombolian bursts to lava flows we examined groundmass textures of samples erupted over that range of activity to investigate the controls on the variability microlite textures in lavas collected both hot rapid quenched and cold show that most samples have textures that are overprinted by crystallization as a result of cooling despite that overprint microlites in the plinian sample have unique crystal morphologies and vesicles that are much smaller and more spherical than those in the other samples we interpret those differences as recording a change in degassing style as a result of changing ascent rate in the conduit to constrain the potential changes in ascent rate a limited number of decompression experiments were run at rates from 0 0013 to 0 25 mpa s crystal textures and morphologies vary greatly as decompression rates change and compared to our observed differences in the natural groundmass it appears that magma erupted in the plinian event decompressed between 0 0013 and 0 025 mpa s whereas magma erupted in non plinian events decompressed slower than 0 0013 mpa s the change in eruptive style from explosive plinian to lava effusion thus resulted from an order of magnitude decrease in magma ascent rate plinian magma probably rose too quickly to allow bubbles to coalesce and allow the magma to degas efficiently whereas at other times magma rose more slowly which allowed bubbles to coalesce and gas to escape leading to less explosive activity

wave set up on a natural beach wave set up the superelevation of mean water level owing to the presence of breaking incident waves was measured at the shoreline of a natural beach offshore pressure sensors monitored incident wave conditions the set up of the shoreline was found to be about 0 17hs where hs is the significant wave height in deep water

plinian airfall deposits of basaltic composition two widespread scoria fall deposits locally known as the fontana lapilli and san judas formation are demonstrated to have issued from masaya caldera complex nicaragua and to be the first documented plinian airfall deposit of basaltic composition data from maps of median grain size average maximum pyroclast diameter and average maximum diameter of lithic fragments provide conclusive evidence of the plinian nature of both deposits the volume within the 1 mm isopach of the fontana lapilli is 12 km3 3 4 km3 dense rock equivalent and within the san judas formation it is 1 2 km3 0 35 km3 dre theoretical eruption parameters calculated for the fontana lapilli and san judas formation respectively include muzzle velocity 170 m s and 150 m s column height 50 km and 18 km volume eruption rate 2 105 m3 s and 1 104 m3 s and duration 2 h and 10 h these are all similar to the calculated parameters for silicic plinian eruptions basaltic magmas are generally considered incapable of erupting in the manner characteristic of plinian eruptions recognition of them argues that factors other than high viscosity may be of fundamental importance

phase relations and liquid lines of descent in hydrous ferrobasalt implications for the skaergaard intrusion and columbia river flood basalts crystallization experiments using a hydrous ferrobasalt as starting material conducted at 200mpa 940 12008c at a wide range of water activities 0 1 1 and redox conditions qfm 3 to qfm 4 where qfm is the quartz fayalite magnetite oxygen buffer show that h2o influences significantly the differentiation history of ferrobasaltic magmas a combination of our data with published experiments on dry ferrobasalt at 1atm provides an extensive experimental database for modeling and quantifying crystallization and differentiation processes within a typical fe rich tholeiitic system under both dry and hydrous conditions the addition of h2o decreases liquidus temperatures and changes significantly the proportions temperature range and sequence of crystallizing mineral phases the dry liquidus is at about 11708c whereas the liquidus for h2o saturated melts is at 10608c the main phases crystallizing from h2o bearing ferrobasalt at the investigated conditions are olivine ol clinopyroxene cpx plagioclase pl magnetite mt hematite hm ilmenite ilm and amphibole am the phase assemblage is similar to that of the dry system except for the presence of hm at extremely oxidizing conditions and am at low temperatures 59508c and h2o saturated conditions the important observation made in this study is that the stability of fe ti oxides and in particular mt as well as the simultaneous coprecipitation of mtand ilm are almost independent of the activity of h2o ah2o in the system whereas the liquidus temperatures of the silicate minerals are dramatically depressed by increasing ah2o the stabilities of oxides are controlled mainly by the redox conditions prevailing in the system the most pronounced effect of ah2o on the liquidus temperatures of silicates is observed for pl which shows a considerable delay in crystallization with progressive magma differentiation early crystallization of fe ti oxides in h2o bearing ferrobasaltic compositions precludes any significant fe enrichment during differentiation as fe enrichment is a characteristic feature of the skaergaard intrusion it implies that the skaergaard parental magma did not contain considerable amounts of water on the other hand our experiments indicate that the differentiation of some ferrobasaltic series from the columbia river flood basalt province might have occurred in magmatic systems containing significant amounts of volatiles 0 5 3 wt h2o

sulphur solubility in andesitic to basaltic melts implications for hekla volcano the solubility of sulphur in sulphide saturated h2o bearing basaltic andesitic and basaltic melts from hekla volcano iceland has been determined experimentally at 1 050 c 300 and 200 mpa and redox conditions with oxygen fugacity logfo2 between qfm 1 2 and qfm 1 1 qfm is a quartz fayalite magnetite oxygen buffer in the systems containing various amounts of s and h2o the s content of the h2o rich glasses saturated with pyrrhotite decreases from 2 500 ppm in basalt to 1 500 ppm in basaltic andesite at the investigated conditions furthermore the reduction of water content in the melt at pyrrhotite saturation and fixed t p and redox conditions leads to a decrease in s concentration from 2 500 to 1 400 ppm for basaltic experiments for h2o decrease from 7 8 to 1 4 wt and from 1 500 to 900 ppm for h2o decrease from 6 7 to 1 7 wt for basaltic andesitic experiments our experimental data combined with silicate melt inclusion investigations and the available models on sulphide saturation in mafic magmas indicate that the parental basaltic melts of hekla were not saturated with respect to sulphide during magmatic differentiation the s content in the residual melts increased and might have reached sulphide saturation with 2 500 ppm dissolved s with further magma crystallization the s concentration in the melt was controlled by the sulphide saturation of the magma decreasing from 2 500 to 900 ppm s

a melt viscosity scale for preeruptive magmas a simplified method to estimate preeruptive melt viscosity by using only melt sio2 content groundmass sio2 content is proposed for sub alkaline magmas melt viscosity is controlled by many magmatic properties e g melt composition melt water content and temperature however these properties are linked by phase equilibrium in preeruptive magmas in this study the magmatic properties were investigated by compiling data of phase equilibria experiments performed under preeruptive conditions negative correlations are found between melt sio2 contents and liquidus temperatures and between liquidus temperatures and melt water contents both increasing melt sio2 content and decreasing liquidus temperature have the effect of increasing the melt viscosity producing a linear positive correlation between logarithmic values of melt viscosity and linear values of melt sio2 content for a specific melt sio2 content an increase in liquidus temperature causes a decrease in melt viscosity whereas a decrease in water content causes an increase in melt viscosity as a result of this opposing effect the melt viscosity is strongly correlated with the melt sio2 content the correlation coefficient of 1 based on this relationship an empirical equation predicting logarithmic values of preeruptive melt viscosity is proposed as a linear function of melt sio2 content referred to as the melt viscosity scale the equation reproduces melt viscosities for compiled experimental melts and natural melts with root mean square deviation of 0 4 and 0 5 log units respectively this method provides order of magnitude estimates for preeruptive melt viscosity its strength is in being applicable to examples for which a full dataset of preeruptive magmatic properties is lacking or has large uncertainties e g slowly cooled lavas the simplicity of this method enables us to easily and promptly estimate preeruptive melt viscosity combined with rheological models for multiphase magmas the present method can be applied widely and thus greatly increase the number of case studies which include evidence based estimates of preeruptive magma viscosity

non newtonian behavior of plagioclase bearing basaltic magma subliquidus viscosity measurement of the 1707 basalt of fuji volcano japan abstract laboratory measurements of viscosity were done for basalt erupted in 1707 ad from fuji volcano japan using a concentric cylinder rotational viscometer at temperatures of 1297 1157 c 1 atm pressure and fo 2 near the ni nio buffer on cooling elongated plagioclase crystals with a mean length width ratio of ca 8 5 appeared at 1237 c followed by olivine at 1157 c at progressively lower temperatures the total crystal volume fraction increased monotonously to ca 0 25 viscosity increased from 38 9 to 765 pa s at a shear strain rate of 1 s 1 this basalt magma behaves as a newtonian fluid at temperatures greater than 1217 c but shear thinning behavior occurs at temperatures less than 1197 c because of the suspended plagioclase crystals this behavior is well approximated as a power law fluid at the onset of shear thinning the crystal volume fraction was between 0 06 and 0 13 which is attributed to the pronounced lath shape of plagioclase crystals the relative viscosity increases monotonously with increase of crystal volume fraction at a constant shear strain rate and with decrease of shear strain rate at a constant crystal volume fraction a modified form of the krieger dougherty equation is introduced herein it enables us to describe the dependencies of relative viscosity on both the crystal volume fraction and shear strain rate and consequently the onset of shear thinning behavior

a preliminary scanning electron microscope study of honeycomb weathering of sandstone in a coastal environment honeycomb weathering has been observed in a carboniferous sandstone at a coastal location near ballycastle on the north coast of northern ireland specimens of this sandstone have been analysed by x ray diffraction scanning electron microscopy and energy dispersive spectrometry results reveal that calcium sulphate gypsum is the only salt present and is found only at and immediately below the rock surface sem observations suggest that crystallization of salts in pores could easily dislodge quartz grains to promote granular disintegration whilst etching of quartz grain surfaces attests to chemical weathering activity within the rock however the reason for the development of the honeycomb pattern is not known

preferential eruption of andesitic magmas through recharge filtering at subduction zones andesite lavas erupt in greater abundance than the individual magmas that mix to produce them textural and geochemical analyses of andesites from mount hood oregon reveal that injection and mixing of iron and magnesium rich magma in the magma chamber can initiate the volcanic eruption andesitic volcanic rocks are common in subduction zones and are argued to play an important role in the formation and evolution of the continental crust at convergent margins1 2 3 4 andesite formation is dominated by mixing between iron and magnesium rich mafic magmas and silica rich felsic magmas1 2 4 the abundance of andesites in many subduction zones suggests they erupt in preference to the magmas that mix to produce them4 however the reasons for this remain unclear here we use textural and geochemical analyses of andesites from mount hood oregon to show that eruptions are closely linked with episodes of mafic recharge the intrusion of mafic magma into a shallow felsic magma reservoir the felsic and mafic magmas involved rarely erupt by themselves probably because the former are too viscous and the latter too dense mafic recharge overcomes these barriers to eruption and as it also promotes efficient mixing results in preferential eruption of mixed andesitic magmas the abundance of andesites therefore relates to local crustal conditions and the ability of magmas to erupt we suggest that volcanoes such as mount hood that erupt homogeneous andesitic compositions through time are those that are the most reliant on mafic recharge to initiate eruptions

numerical modeling of moisture transport in sandstone the influence of pore space fabric and clay content in the present study a numerical modeling of moisture distribution under real climate conditions within sandstone monoliths is accomplished based on detailed material specific transport and storage functions the impact of lithology and pore radii distributions is modeled with consideration of 1 the single sandstone monolith 2 the sandstone monolith with clay layers and 3 the sandstone monolith with clay layers and hydrophobic treatment the results reveal that the unimodal equal pore radii distribution of the quartz arenite promotes quickly a capillary water uptake during driving rain liquid stage but due to its missing smaller capillaries a high drying velocity leads to an almost dry pore space since moisture can only be absorbed via gaseous stage e g during summer on the contrary the sublitharenite with a unimodal unequable pore radii distribution is characterized by a distinctly higher water content since in addition smaller pores also allow the absorption of moisture via sorption moreover the high clay content promotes a retarded interaction with the environment which is also reflected by the high vapor diffusion resistance the highest water content shows the feldspathic litharenite with highest clay content and bimodal pore size distribution here over nine magnitudes of water transporting pores is involved at water transport and storage results also reveal that moisture accumulations during droughts trace the deterioration shape of rounding for all sandstones highest annual fluctuations are observable within the rim zone of the monolith while the center is characterized by more stable moisture content which mainly depends on rising water content of the bedrock the presence of clay layers has for each sandstone specific consequences however within the whole sandstone the stress index is increased and stress location is displaced to the boundaries of clay layers results of modeling the hydrophobic treatment reveal that this conservation strategy is only useful for sandstones where all moisture is absorbed in liquid stage why then all water absorption is hindered in case of sandstones with bimodal and unimodal unequal pore size distributions moisture uptake is possible also via sorption accordingly moisture accumulates behind the zone of hydrophobic treatment this finally will lead to stress transfer to the outer rim during salt or ice crystallization and will be responsible for flaking

variable weathering response in sandstone factors controlling decay sequences differences in weathering response characteristics of fine and coarse grained stanton moor sandstone samples were assessed in a laboratory weathering simulation experiment using a variable combination of salt weathering and freeze thaw cycles preliminary analysis of permeability characteristics identified similar mean values for each type of stanton sandstone but significant differences in the range of values between the two sample sets with coarse grained samples of stanton moor sandstone displaying a restricted range of values in comparison to fine grained samples which showed much greater within block variation data indicated that the greater the range in initial permeability values the greater the potential for salt and moisture ingress and retention and hence eventual disruption of the fabric of the stone experimental data also identified different stages in decay sequences with significant structural change occurring during the initial preparatory stage before material breakdown and loss became apparent evidence suggests that relatively minor structural and mineralogical differences between samples of the same stone type can have a significant influence on weathering behaviour resulting in distinct rates and patterns of breakdown copyright 2005 john wiley sons ltd

water co2 cl and f in melt inclusions in phenocrysts from three holocene explosive eruptions crater lake oregon rare melt inclusions 100 m in diameter trapped near the boundaries of corroded patchy zones in plagioclase phenocrysts from plinian pumice of three holocene eruptions were analyzed by ir spectroscopy for molecular h 2o oh groups and co 2 and by electron microprobe for cl and f the three rhyodacitic eruptions each of which began with aplinian phase occurred over 200 yr the llao rock and cleetwood eruptions ended with degassed lava flows and the subsequent climactic eruption with voluminous ignimbrite groundmass glass and melt inclusion compositions anhydrous are similar inclusions with total h 2o concentrations of 1 2 3 4 wt are adjacent to fractures or are hourglass inclusions suggesting partial degassing caused by depressurization melt inclusions in phenocrysts in climactic ignimbrite may have vesiculated for the same reason intact inclusions in plinian pumices have total h 2o concentrations believed to represent magmatic h 2o contents wt llao rock 5 3 5 3 cleetwood 3 8 4 7 climactic 3 9 0 2 l n 6 ratios of or molecular h 2o indicate closure temperatures of 200 500oc that reflect syn or posteruptive cooling co 2 concentrations are 25 ppm h 2o and co 2 concentrations indicate saturation pressures of 1 0 1 8 kbar or depths 5 km six inclusions from climactic pumice average 400 40 l ppm f 1880 70 ppm cl f and cl concentrations of the other samples are similar and not well correlated with each other or with total h 2o location of melt inclusions near boundaries of patchy zones which are mantled by oscillatory zoned overgrowths suggests that their h 2o concentrations represent magmatic values significantly before eruption although mean h 2o concentrations of analyzed melt inclusions decrease for the three successive eruptions it is not certain that this indicates a corresponding change in magmatic h 2o content during the interval between eruptions

storage conditions and evolution of andesitic magma prior to the 1991 95 eruption of unzen volcano constraints from natural samples and phase equilibria experiments the compositions of homogenized melt inclusions trapped in plagioclase pl microphenocrysts 40 200 m length from mafic enclaves within dacitic rocks erupted at unzen volcano in 1991 95 were investigated the sio2 contents of the melt inclusions vary from 58 to 70 wt and pl anorthite content is an50 70 the stability fields in terms of temperature and water activity of natural pl and coexisting melts from the melt inclusions were estimated from data of phase equilibria experiments performed with a synthetic andesite composition at t 900 1140 c p 200 mpa log fo2 nno 2 nno and water activity of about 0 1 this composition is representative of the average composition of mafic enclaves from the 1991 95 eruption and nearly identical to the composition of andesitic lavas from 1663 unzen eruption the temperatures and h2o melt concentrations calculated using the compositions of coexisting pl and melt inclusions provide an estimation of the conditions of andesitic magma evolution within the mafic enclaves prior to eruption the formation of melt inclusions in plagioclase microphenocrysts occurred at a maximum temperature of 1010 35 c for a melt containing 2 wt h2o and a minimum temperature of 945 c 30 c for a melt with 4 wt dissolved h2o the compositional range of the melt inclusions indicates that the composition of the mafic enclave was not significantly contaminated by the host magma when inclusions were formed the difference between concentrations of dissolved s up to 0 06 wt and cl up to 0 05 wt in melt inclusions in pl of mafic enclaves and concentrations of s 0 005 wt and cl 0 05 0 11 wt in melt inclusions in phenocrysts of the dacitic magma clearly implies that two distinct sources for s and cl in the 1991 95 eruption of unzen volcano need to be considered sulfur degassing was generated by a release of fluids from the high temperature andesitic magma whereas cl was degassed from the low temperature silicic magma the combination of data from melt inclusions and phase equilibria experiments indicates that the mafic end member magma at unzen was already partially crystallized and contained significant proportions 20 to 40 wt of pl and orthopyroxene opx when melt inclusions started to form since clinopyroxene cpx and magnetite mt crystallize after pl and opx the temperatures derived for the mafic end member magma from coexisting opx cpx and ilm mt pairs do not represent temperatures near to the liquidus assuming that the injected mafic magma was nearly aphyric its initial temperature might have been higher than estimated in previous studies

chemical textures on quartz grains an experimental approach using salts two groups of fresh crushed brazilian quartz grains 0 4 0 6 mm were placed in 10 ml of various saturated salt solutions sodium sulphate sodium chloride magnesium sulphate sodium carbonate and sodium carbonate and soil one group was placed in an environmental cabinet programmed to simulate summer diurnal temperature and relative humidity values recorded in wheeler valley a dry valley in southern victoria land antarctica the other group was allowed to remain at normal laboratory conditions quartz grains from both groups were removed at pre selected intervals for examination using the scanning electron microscope after 50 hours chemical surface textures were formed on the quartz grains in all but the sodium sulphate solution at the 140 hour interval all the salt solutions used were producing chemical surface textures on the quartz grains this paper demonstrates that chemical surface textures can be produced on quartz grain surfaces by saturated salt solutions in a short period of time and may prove to be representative of chemical surface textures produced in a saturated saline environment

rheology of bubble bearing magmas abstract the physical effects of air or argon bubbles on the rheology of a calcium aluminosilicate melt have been measured at temperatures ranging from 830 to 960 c at 1 bar pressure the melt composition is sio 2 64 al 2 o 3 23 and cao 13 wt while bubble volume fractions are 0 0 06 0 13 0 32 0 41 and 0 47 measured newtonian viscosities range from 10 10 to 10 14 dpa s melts with bubble fractions of 0 06 and 0 13 show with increasing temperature t an increasing relative viscosity for t t 850 c for all bubble fractions the viscosity decreases markedly with temperature the observed maximum decrease of the relative viscosity is 75 for a bubble fraction of 0 47 at 907 c at all bubble fractions the viscosity is independent of the applied stress which ranged from 11 to 677 bars no clear indications were observed of non newtonian rheological behavior under our experimental conditions the relative viscosity of the two phase liquid depends primarily on the bubble fraction physical and volcanological implications of these measurements are discussed

storage and eruption of near liquidus rhyolite magma at cordon caulle chile the last three eruptions at the cordon caulle volcanic complex chile have been strikingly similar in that they have started with relatively short pre eruptive warning and produced chemically homogeneous rhyolite to rhyodacite magma with glassy to aphyric texture these characteristics collectively call for an understanding of the storage conditions leading to the rise and extraction of crystal poor silicic magma from volcanoes we have analyzed and experimentally reproduced the mineral assemblage and glass chemistry in rhyolite magma produced in the most recent eruption of cordon caulle and we use these to infer magma storage and ascent conditions fe ti oxide mineral geothermometry suggests that the rhyolite was stored at 870 920 c at these temperatures the phenocryst assemblage plag an37 cpx opx mag ilm can be reproduced under h2o saturated conditions of between 100 and 50 mpa corresponding to crustal depths between about 2 5 and 5 0 km the shallow and relatively hot magma storage conditions have implications for the rapid onset degassing efficiency and progression from explosive to mixed pyroclastic effusive eruption style at cordon caulle

pre eruptive conditions of dacitic magma erupted during the 21 7 ka plinian event at nevado de toluca volcano central mexico abstract the nevado de toluca volcano in central mexico has been active over the last ca 42 ka during which tens of km 3 of pyroclastic material were erupted and two important plinian type eruptions occurred at ca 21 7 ka lower toluca pumice ltp and ca 10 5 ka upper toluca pumice utp samples from both the ltp and utp contain plagioclase amphibole iron titanium oxides and minor anhedral biotite set in a vesicular rhyolitic glassy matrix in addition utp dacites contain orthopyroxene analysis of melt inclusions in plagioclase phenocrysts yields h 2 o contents of 2 3 5 wt for ltp and 1 3 3 6 wt for utp samples ilmenite ulvospinel geothermometry yields an average temperature of 868 c for the ltp magma hotter than the utp magma 842 c arce et al 2006 whereas amphibole plagioclase geothermometry yields a temperature of 825 859 c for the ltp magma water saturated experiments using ltp dacite suggest that i amphibole is stable above 100 mpa and below 900 c ii plagioclase crystallizes below 250 100 mpa at temperatures of 850 900 c and iii pyroxene is stable only below pressures of 200 100 mpa and temperatures of 825 900 c comparison of natural and experimental data suggests that the ltp dacitic magma was stored at 150 200 mpa 5 8 7 7 km below the volcano summit no differences in pressure found between 21 7 ka and 10 5 ka suggest that these two magmas were stored at similar depths orthopyroxene produced in lower temperature ltp experiments is compositionally different to those found in utp natural samples suggesting that they originated in two different magma batches whole rock chemistry petrographic features and mineral compositions suggest that magma mixing was responsible for the generation of the dacitic plinian ltp eruption

micro environmental change as a trigger for granite decay in offshore irish lighthouses implications for the long term preservation of operational historic buildings following automation of lighthouses around the coastline of ireland reports of accelerated deterioration of interior granite stonework have increased significantly with an associated deterioration in the historic structure and rise in related maintenance costs decay of granite stonework primarily occurs through granular disintegration with the effective grusification of granite surfaces a decay gradient exists within the towers whereby the condition of granite in the lower levels is much worse than elsewhere the lower tower levels are also regions with highest relative humidity values and greatest salt concentrations data indicate that post automation decay may have been triggered by a change in micro environmental conditions within the towers associated with increased episodes of condensation on stone surfaces this in turn appears to have facilitated deposition and accumulation of hygroscopic salts e g nacl giving rise to widespread evidence of deliquescence in the lower tower levels evidence indicates that the main factors contributing to accelerated deterioration of interior granite stonework are changes in micro environmental conditions salt weathering chemical weathering through the corrosive effect of strongly alkaline conditions on alumino silicate minerals within the granite and finally the mica rich characteristics of the granite itself which increases its structural and chemical susceptibility to subaerial weathering processes by creating points of weakness within the granite this case study demonstrates how seemingly minor changes in micro environmental conditions can unintentionally trigger the rapid and extensive deterioration of a previously stable rock type and threaten the long term future of nationally iconic operational historic structures

pre eruptive water content of rhyolitic magmas as determined by ion microprobe analyses of melt inclusions in phenocrysts abstract the ion microprobe was used to analyze trapped melt inclusions in phenocrysts from two rhyolitic eruptions for h2o f and incompatible trace elements eleven melt inclusions from phenocrysts in air fall tephra from obsidian dome near long valley usa gave an average of 4 1 1 2 wt h2o and showed large variations in f and incompatible trace elements reflecting a complex history reported to involve mixing of at least two magma types eight inclusions in phenocrysts from the taupo ultraplinian event new zealand gave 4 5 0 8 wt h2o with small variations in the other elements analyzed measured water contents are similar to earlier estimates of the pre eruptive water contents of these and similar rhyolites and major and trace element analyses of inclusions compare closely with bulk analyses suggesting that the analyses of inclusions represent the chemistry of the magma at the time of entrapment

shoreline erosion and aeolian deposition along a recently formed hydro electric reservoir blondulon iceland abstract erosion and deposition processes have been active along the shores of the blondulon hydro electric reservoir in the icelandic highlands since its formation nearly two decades ago in this study bluff development and distribution of aeolian material along the shores of the reservoir is related to erosive forces and source materials the 57 km 2 reservoir was formed in the glacial river blanda in 1991 and enlarged in 1996 bluff erosion and aeolian deposition has been monitored since 1997 field observations meteorological data gis analyses and calculations of wave power were used to measure and describe erosive processes along the new shoreline wave induced bluff erosion was most rapid during the first years after impoundment and was most active at sites with glacial till substrate high cumulative wave power and long fetches along the dominant wind direction in recent years relatively high erosion rates have continued at bluffs of fluvioglacial material under low cumulative wave power the fluvioglacial material has low resistance to wave activity creating unstable bluffs whereas bluffs made of glacial till are more stable aeolian sandy sediment mainly volcanic tephra eroded from soils has been deposited at sites open towards dry strong winds during low water levels in inlets of low wave energy slope and aspect against wind direction restricted the sediment distribution to 212 000 m 2 21 ha of the heathland along the reservoir by 2008 a volume of 11 000 m 3 had accumulated the continued redistribution of aeolian sediments and processes of bluff erosion were controlled by the water level fluctuations in the reservoir

a morphological study of greenschist weathering on dated coastal structures south devon uk three dated structures up to 450 years in age display the effects of coastal weathering of the greenschist of which they are constructed a variety of weathering forms is present the various topographic surfaces of the structures create variation in weathering environments and consequent weathering processes and rates weathering is enhanced by direct exposure to salt bearing spray and by humid conditions and apparently limited by direct exposure to solar radiation the maximum rates of weathering on the three surfaces approximate to 0 6 mm a 1 over this period consistent with measured contemporary weathering rates for a natural surface formed by this rock type in a nearby coastal location 1997 by john wiley sons ltd