viscosity of microlite bearing rhyolitic obsidians an experimental study to investigate the influence of microlites on lava flow rheology the viscosity of natural microlite bearing rhyolitic obsidians of calc alkaline and peralkaline compositions containing 0 1 0 4 wt water was measured at volcanologically relevant temperatures 650 950 c stresses 103 105 pa and strain rates 10 5 to 10 7 s 1 the glass transition temperatures t g were determined from scanning calorimetric measurements on the melts for a range of cooling heating rates based on the equivalence of enthalpic calorimetric and shear viscosity relaxation we calculated the viscosity of the melt in crystal bearing samples from the t g data the difference between the calculated viscosity of the melt phase and the measured viscosity for the crystal bearing samples is interpreted to be the physical effect of microlites on the measured viscosity the effect of 45 vol crystals for both of these samples a connectivity factor is apparent with for the latter a close packing framework of crystals which is interpreted to influence the apparent viscosity

propagation of acoustic waves in a viscoelastic two phase system influence of gas bubble concentration abstract volcanic explosions generate pressure perturbations in the atmosphere and a seismic wavefield in the ground the source is therefore well coupled with the atmosphere and the ground the acoustic and elastic wavefields reflect dynamical processes at the source and the viscoelastic properties of the magma gas medium at low pressure 70 strongly affect the propagation properties of the acoustic wavefield we found that the amplitude of the infrasonic wavefield in the atmosphere typically recorded in case of strombolian explosions 2 105 pa can be explained by a deep 50 m source embedded in the magma conduit only if a very large unrealistic pressure drop 1013 pa is assumed the strong damping linked to the poor elastic properties of the shallow magma gas mixture prevents the efficient propagation of the acoustic waves in the magma gas mixture and resonance of body waves cannot occur infrasonic waves can be transmitted from the magma to the atmosphere only when the source is very shallow

global biogeochemical cycle of boron 1 the global boron b cycle is primarily driven by a large flux 1 44 tg b yr through the atmosphere derived from seasalt aerosols other significant sources of atmospheric boron include emissions during the combustion of biomass 0 26 0 43 tg b yr and coal which adds 0 20 tg b yr as an anthropogenic contribution these known inputs to the atmosphere cannot account for the boron removed from the atmosphere during rainfall 3 0 tg b yr and estimated dry deposition 1 3 2 7 tg b yr in addition to atmospheric deposition rock weathering is a source of boron 0 19 tg b yr for terrestrial ecosystems and humans mine about 0 31 tg b yr from the earth s crust more than 4 8 tg b yr circulates in the biogeochemical cycle of land plants and about 0 53 0 63 tg b yr is carried from land to sea by rivers the biogeochemical cycle of boron in the sea includes 4 4 tg b yr circulating in the marine biosphere and an annual loss of 0 47 tg b yr to the oceanic crust via a variety of sedimentary processes that collectively remove only a small fraction of the total annual inputs to the oceans thus with our current understanding of the global biogeochemistry of b the atmospheric budget shows outputs inputs while the marine compartments show inputs outputs despite these uncertainties it is clear that the human perturbation of the global b cycle has more than doubled the mobilization of b from the crust and contributes significantly to the b transport in rivers

scaling behavior and source mechanism of tremor recorded at erebus volcano ross island antarctica abstract erebus is an intraplate stratovolcano of phonolitic composition located at the southern end of terror rift within the west antarctica rift system the volcanic edifice of erebus exhibits a summit plateau that hosts the main crater and a smaller inner crater that contains a persistent lava lake volcano seismic signals are recorded at erebus by a permanent network of short period and broadband seismometers installed around the volcano edifice we investigate the duration amplitude scaling of tremor recorded by the closest 0 6 2 km broadband stations to the inner crater during may 2002 april 2004 in order to elucidate the physical processes taking place at its source after screening the data for signals related to non volcanic sources such as iceberg calving we obtained 72 tremor events spectral analysis reveals that these events were either harmonic exhibiting several overtones or broadband but there were also mixed events that contained both of these two states all tremor episodes considered in this study follow an exponential duration amplitude distribution that implies a scale bound source process this precludes the possibility that any of these signals is related to iceberg calving near ross island or that rock fracturing processes play any role in tremor generation the large viscosity of phonolitic magma 105 3 pa s suggests that source mechanisms which require high flow speeds in order to excite tremor are unlikely to operate at erebus on the other hand oscillations of co2 bubble clouds formed at localized asperities within the magma chamber represent a scale bound source that is also consistent with the observed oxidation state of ascending gas and with the deep 5 7 km location of the tremor source these results are important for understanding tremor processes at volcanoes which similar to erebus exhibit vigorous convection in their shallow plumbing system

the edges of large earthquakes and the epicenters of future earthquakes stress induced correlations in elastodynamic fault models fault models can generate complex sequences of events from frictional instabilities even when the material properties are completely uniform along the fault these complex sequences arise from the heterogeneous stress and strain fields which are produced through the dynamics of repeated ruptures on the fault visual inspection of the patterns of events produced in these models shows a striking and ubiquitous feature future events tend to occur near the edges of where large events died out in this paper we explore this feature more deeply first using long catalogues generated by the model we quantify the effect we show interestingly that it is an even larger effect for future small events than it is for future large events then using our ability to directly measure all aspects of the model we find a physical explanation for our observations by examining the stress fields associated with large events looking at the average stress field we see a large stress concentration left at the edge of the large events out of which the future events emerge further we see the smearing out of the stress concentration as small events occur this indicates why the epicenters of future small events are more correlated with the edges of large events than are the epicenters of future large events finally we discuss how results from our simple model may be relevant to the more complicated case of the earth

non newtonian rheology of igneous melts at high stresses and strain rates experimental results for rhyolite andesite basalt and nephelinite the stress strain rate relationships of four silicate melt compositions high silica rhyolite andesite tholeiitic basalt and nephelinite have been studied using the fiber elongation method measurements were conducted in a stress range of 10 400 mpa and a strain rate range of 10 6 to 10 3 s 1 the stress strain rate relationships for all the melts exhibit newtonian behavior at low strain rates but non newtonian nonlinear stress strain rate behavior at higher strain rates with strain rate increasing faster than the applied stress the decrease in calculated shear viscosity with increasing strain rate precedes brittle failure of the fiber as the applied stress approaches the tensile strength of the melt the decrease in viscosity observed at the high strain rates of the present study ranges from 0 25 to 2 54 log10 pa s the shear relaxation times of these melts have been estimated from the low strain rate newtonian shear viscosity using the maxwell relationship s g non newtonian shear viscosity is observed at strain rates time 1 equivalent to time scales that lie 3 log10 units of time above the calculated relaxation time brittle failure of the fibers occurs 2 log10 units of time above the relaxation time this study illustrates that the occurrence of non newtonian viscous flow in geological melts can be predicted to within a log10 unit of strain rate high silica rhyolite melts involved in ash flow eruptions are expected to undergo a non newtonian phase of deformation immediately prior to brittle failure

model of earthquake recurrence role of elastic wave radiation relaxation of friction and inhomogeneity we have constructed a dynamical model of seismicity wherein a fault is embedded in an infinite continuous elastic medium therefore the influence of the energy dissipated in seismic wave radiation oil the sequential history of model earthquakes is fully taken into account in this model the drop in friction at rupture takes place gradually thus introducing a relaxation dimension as an example we consider a finite homogeneous fault that is terminated by infinitely strong barriers at the ends the features of the seismicity are dominated by the stresses that are reflected from the unbreakable barriers there is a strong dependence of the patterns of seismicity on the ratio of the relaxation dimension to the distance between the barriers at the ends for large values of this parameter we find that periodicity begins after a short transient interval and a dominance of the statistical distributions by large events that break completely through the fault from end to end for small values of this parameter smaller scale seismicity is interspersed with the large events and no periodicity is observed within the time spanned by the computations we conclude that major unquenched heterogeneities such as those found at barriers which we suppose arise in nature due to the nonuniform geometry of faults are vital ingredients for generating complex seismic histories as well as giving rise to the complex features of individual earthquake source time functions in models of seismicity as a dynamical process

theory of the airborne sound field generated in a resonant magma conduit abstract explosive sources triggered inside a magma conduit may excite the conduit into acoustic resonance the acoustic field in the conduit can propagate into the atmosphere through an open vent and ensonify the overlying atmosphere the character of the airborne sound field is determined by a combination of propagation and source effects the resonance of the magmatic conduit and the diffraction of the sound field at the volcanic vent are acoustic propagation effects whereas the explosion pressure signature and the firing rate of the explosions define the source characteristics for wavelengths larger than the conduit radius only the longitudinal resonances of the magmatic conduit are relevant and the open vent radiates like a piston surrounded by an infinite baffle in this case the fluid particle velocities are directed along the axis of the conduit and the sound field may propagate into the surrounding bedrock through the conduit wall displacement induced by the fluid overpressure this coupling may produce seismic signals with banded spectra such as volcanic tremor and long period events the airborne pressure field retains the modal structure of the sound field in the magmatic conduit which contains information on the conduit geometry and geo acoustic properties of the magma the seismic wavefield is driven by the acoustic field in the magma and also contains this information although it may be filtered by propagation effects in the bedrock the theoretical sound field in the magma conduit is used to interpret seismic tremor signals recorded at mt spurr volcano alaska rapid variations in the acoustic impedance of the magma conduit terminations can create systematic changes in the tremor spectra which can be used to monitor changes in the magmatic system the results of the modelling illustrate the difference between source effects and conduit resonance as well as the value of seismoacoustic measurements in volcanic environments

chemical weathering of basalts southwest iceland effect of rock crystallinity and secondary minerals on chemical fluxes to the ocean river ground and peat water from a basaltic catchment area laxa in kjos southwest iceland were sampled and analyzed for major element concentrations to define the effect of glassy versus crystalline basalt the formation of secondary minerals and runoff on fluxes of dissolved elements to the ocean the proportions of the dissolved solids in the water samples derived from precipitation air and rock weathering were estimated the amounts of na mg ca k and s originating from precipitation were calculated from the respective solute cl marine ratios and the estimated aqueous cl originated from precipitation which was calculated using measured b content of the waters and b cl molal marine and rock ratios the rock contribution from weathering ranged from 22 to 46 percent of the total dissolved solids of the waters iron and al showed low mobility compared to na this was primarily due to consumption of these elements by ferrihydroxides allophane imogolite and clay minerals also si and to a lesser degree ca show apparent slightly lower mobility than na these results are in good agreement with these phases being dominant in the soils of the study area wada and others 1992 and the main secondary minerals of basaltic glass in iceland crovisier and others 1992 reaction progress calculations support these findings according to a model interaction of basaltic glass and meteoric water al fe and si are consumed by amorphous fe and al hydroxides and imogolite and allophane at low reaction progress with increasing reaction progress ca fe mg smectite became the primary secondary minerals limiting the mobility of ca fe mg si and al these findings suggest that the weathering in the laxa in the kjos catchment area has evolved into the beginning of the smectite weathering stage and that it is dominated by a relatively low reaction progress and a high water to rock ratio in the present study the effect of runoff and rock crystallinity was quantified for dissolved elemental fluxes temperature lithology other than rock crystallinity and rock age were similar in all of the catchment areas in this study silica ca f s al k mg and b had a very similar dependence on runoff on the other hand na fluxes were found to be less dependent on runoff and fe fluxes were found to be independent of runoff basaltic glass dissolves faster than fully crystallized basaltic rocks gislason and eugster 1987a therefore increased glass content of the primary rocks is thought to increase the leaching and elemental fluxes at constant runoff however because some of the solutes particularly al and fe were highly influenced or even controlled by the formation of secondary minerals this increasing dissolution with increasing glass content was hidden on the other hand basaltic glass was observed to enhance the fluxes of more mobile elements like na si ca f and s by a factor of 2 to 5 at a constant runoff of 200 cm yr constant vegetative cover and 0 to 100 percent glass content of the rocks the k and mg fluxes were found to be independent of rock crystallinity however runoff alone cannot explain the fluxes of these elements and it seems that vegetative cover and seasonal variations in biomass activities influence the k and mg fluxes

fracture and surface crust development in a holocene pahoehoe lava flow on the island of tenerife canaries abstract an almost horizontal pahoehoe surface in a holocene plagioclase basanite lava on tenerife displays three scales of fracture within the surface crust an early formed set of large scale fractures divides up the surface into an orthogonal set of rectangular slabs with dimensions of several metres and depths of 10 12 cm the shortest slab dimension is parallel to the flow emplacement direction inferred from a strong surface lineation the slabs are domed with the centre an average of 9 6 cm with range 4 19 6 cm above the edges of the slabs profiles of the slabs normal and perpendicular to the margins and through the crest indicate that they can be described by a power law in which the deflection of the slab h is related to the distance from the crest x with an exponent between 2 and 3 analysis of joints within the slabs indicates two smaller scale networks an intermediate scale joint network bounds blocks with rectilinear to polygonal shapes in plan view and has a characteristic mean spacing of 24 2 cm range 10 5 48 cm the major fractures in this set are normal and parallel to the slab margins a smaller scale joint network bounds polygonal equant blocks in plan view and has characteristic spacing of 6 4 cm range 3 7 10 5 cm a model of cooling from the pahoehoe surface is used to constrain the growth of the crust and timing of fracture development the large scale slabs are attributed to localised accumulation of gas beneath the growing crust causing buoyant forces the tensile stresses caused by uplift are sufficient to form the large scale fractures after 2 or 3 h of cooling the intermediate scale fracture network is attributed to the flexure of the slab crust the smaller scale polygonal joint network is related to the build up of isotropic tensile stresses in the cooling slab crust due to thermal contraction with fracture development being promoted by the flexure of the slabs an analysis of the slab deformation indicates that lava crust is weak the weakness is explained by division of the crust into three zones an outer zone with small scale joints that cause negligible strength a middle zone of elastic behaviour in which stress can build up and a lower zone of plastic deformation the crustal slabs display profiles similar to that expected in a bending elastic plate the deformation of the 10 cm thick crust can be explained if the elastic zone was about 2 cm thick this result agrees with an independent calculation of elastic zone thickness based on the position of the brittle ductile transition being located at the 600 c isotherm at a depth of about 2 cm when the crustal slabs were rifted apart

implications of the 26 december 2004 sumatra andaman earthquake on tsunami forecast and assessment models for great subduction zone earthquakes results from different tsunami forecasting and hazard assessment mod els are compared with observed tsunami wave heights from the 26 december 2004 indian ocean tsunami forecast models are based on initial earthquake information and are used to estimate tsunami wave heights during propagation an empirical forecast relationship based only on seismic moment provides a close estimate to the observed mean regional and maximum local tsunami runup heights for the 2004 indian ocean tsunami but underestimates mean regional tsunami heights at azimuths in line with the tsunami beaming pattern e g sri lanka thailand standard forecast models developed from subfault discretization of earthquake rupture in which deep ocean sea level observations are used to constrain slip are also tested forecast models of this type use tsunami time series measurements at points in the deep ocean as a proxy for the 2004 indian ocean tsunami a transect of deep ocean tsunami amplitudes recorded by satellite altimetry is used to constrain slip along four subfaults of the m 9 sumatra andaman earthquake this proxy model performs well in comparison to observed tsunami wave heights travel times and inundation patterns at banda aceh hypothetical tsunami hazard assessments models based on end member estimates for average slip and rupture length m w 9 0 9 3 are compared with tsunami observations using average slip low end member and rupture length high end member m w 9 14 consistent with many seismic geodetic and tsunami inversions adequately estimates tsunami runup in most regions except the extreme runup in the western aceh province the high slip that occurred in the southern part of the rupture zone linked to runup in this location is a larger fluctuation than expected from standard stochastic slip models in addition excess moment release 9 deduced from geodetic studies in comparison to seismic moment estimates may gen erate additional tsunami energy if the exponential time constant of slip is less than approximately 1 hr overall there is significant variation in assessed runup heights caused by quantifiable uncertainty in both first order source parameters e g rupture length slip length scaling and spatiotemporal complexity of earthquake rupture

numerical modelling of stress generation and microfracturing of vesicle walls in glassy rocks abstract in the absence of stress concentrating flaws such as microfractures vesicular glassy materials can withstand gas pressures within vesicles in excess of 100 mpa however vesicles within such materials are known to decrepitate explosively at much lower internal gas pressures both in natural systems and in the laboratory here we present a model that quantitatively predicts the generation of microfractures in vesicle walls during cooling cooling of gas bearing vesicles in glassy rock has little effect on water solubility in the glass but leads to a rapid decrease in gas pressure in the vesicles the drop in pressure causes disequilibrium between the water in the glass and in the vesicle dehydration of the glass in a diffusive boundary layer around the vesicle leads to elastic shrinkage the resulting strain generates large tensile tangential stresses which can exceed the strength of the glass causing microfracturing such microfractures present a possible means by which glassy rock surrounding vesicles could be weakened enough to permit explosive decrepitation at low pore vapor pressures the results have implications wherever hydrous vesicular glasses are formed for example rocks formed in shallow subvolcanic intrusions or vent plugs may spontaneously disintegrate with explosive emission of vapor glassy submarine lavas spontaneously decrepitate upon dredging from the ocean floor popping rock vesicular glasses produced in laboratory experiments investigating vapor melt phase equilibria have been observed to contain abundant fractures surrounding vesicles and to dehydrate at anomalously high rates

frequency dependent rheology of vesicular rhyolite frequency dependent rheology of magmas may result from the presence of inclusions bubbles crystals in the melt and or from viscoelastic behavior of the melt itself with the addition of deformable inclusions to a melt possessing viscoelastic properties one might expect changes in the relaxation spectrum of the shear stresses of the material e g broadening of the relaxation spectrum resulting from the viscously deformable geometry of the second phase we have begun to investigate the effect of bubbles on the frequency dependent rheology of rhyolite melt the present study deals with the rheology of bubble free and vesicular rhyolite melts containing spherical voids of 10 and 30 vol we used a sinusoidal torsion deformation device vesicular rhyolite melts were generated by the melting at 1 bar of an armenian obsidian dry fountain erevan armenia and little glass mountain obsidian california the real and imaginary parts of shear viscosity and shear modulus have been determined in a frequency range of 0 005 10 hz and temperature range of 600 900 c the relaxed shear viscosities of samples obtained at low frequencies and high temperatures compare well with data previously obtained by parallel plate viscometry the relaxed shear viscosity of vesicular rhyolites decreases progressively with increasing bubble content the relaxation spectrum for rhyolite melt without bubbles has an asymmetric form and fits an extended exponent relaxation the presence of deformable bubbles results in an imaginary component of the shear modulus that becomes more symmetrical and extends into the low frequency high temperature range the internal friction q 1 is unaffected in the high frequency low temperature range by the presence of bubbles and depends on the bubble content in the high temperature low frequency range the present work in combination with the previous study of stein and spera 1992 illustrates that magma viscosity can either increase or decrease with bubble content depending upon the rate of style of strain during magmatic flow

the generation of gas overpressure in volcanic eruptions abstract observations of natural eruption products show that different parts of a single magma batch may experience different degassing histories during ascent in a volcanic conduit in non explosive eruptions lava issuing from a volcanic vent may contain overpressured gas bubbles these important features of volcanic eruptions cannot be accounted for by existing flow models which rely on simplifying hypotheses for the relationship between pressures in the gas phase and in the bulk flow volcanic flows involve highly compressible material which undergoes large viscosity variations as degassing proceeds we show that these properties may lead to large gas overpressures in erupting lava the magnitude of this overpressure depends on the initial volatile content of magma and is largest for relatively volatile poor magmas due to the extreme viscosity variations at water contents less than 1 wt we develop a simple analytical model to illustrate the main features of compressible viscous flows 1 at any level gas pressure is larger near the conduit axis than at the walls 2 gas overpressure is an increasing function of mass discharge rate

models of tremor and low frequency earthquake swarms on montserrat recent observations from soufriere hills volcano in montserrat reveal a wide variety of low frequency seismic signals we discuss similarities and differences between hybrid earthquakes and long period events and their role in explosions and rockfall events these events occur usually in swarms and occasionally merge into tremor an observation that can shed further light on the generation and composition of harmonic tremor we use a 2d finite difference method to model major features of low frequency seismic signatures and compare them with the observations a depth dependent velocity model for a fluid filled conduit is introduced which accounts for the varying gas content in the magma and the impact on the seismic signals is discussed we carefully analyse episodes of tremor that show shifting spectral lines and model those in terms of changes in the gas content of the magma as well as in terms of a time dependent triggering mechanism of low frequency resonances in this way we explain the simultaneous occurrence of low frequency events and tremor with a spectral content comprising integer harmonics

thermal properties of vesicular rhyolite abstract thermal diffusivity of rhyolite melt and rhyolite foam 70 80 porosity has been measured using the radial heat transfer method cylindrical samples length 50 55 mm diameter 22 mm of rhyolite melt and foam have been derived by heating samples of little glass mountain obsidian using available data on heat capacity and density of rhyolite melt the thermal conductivity of samples has been determined the difference in thermal conductivity between rhyolite melt and foam at igneous temperatures 1000 c is about one order of magnitude the effect of thermal insulation of magmas due to vesiculation and foaming of the top layer is discussed in terms of the data obtained using a simple illustrative model of magma chamber convection

magnesium isotope geochemistry in the han river south korea abstract magnesium mg isotopes can be a proxy for directly constraining the sources of riverine mg but the dominant controls on riverine mg isotope ratios are still uncertain here we report mg isotope ratios for river waters experimental leachates and digestions bulk rocks and fertilizers in the han river hr south korea the hr is composed of two lithologically distinct tributaries the north han river nhr that flows over only silicate rocks and the south han river shr that flows over silicate and carbonate rocks the lithological differences between the nhr and shr are reflected in major ion 87sr 86sr and 26mg geochemistry in particular the nhr has lower major ion concentrations but higher 87sr 86sr ratios and 26mg values than the shr simple mass balances and mixing equations indicate that if the riverine 26mg values in the hr system are mainly controlled by conservative mixing between silicate and carbonate weathering the average carbonate end member 26mg value should be unlikely lower than what are measured in this study although multiple process related fractionations occur in the hr system the enrichment of 24mg in river waters relative to silicate rocks they drain could be mostly controlled by either fractionation or mixing between isotopically distinct reservoirs such as minerals or fractions labile and structural mg during dissolution while the little depletion of 24mg in the shr waters relative to carbonate rocks they drain could be likely due to the input of groundwater with lower 26mg value rather than fractionation however it is difficult to identify the contribution of anthropogenic inputs to riverine 26mg because their effects are little this study suggests that the potential of mg isotopes for constraining mg sources in a lithologically varied river basin can be enhanced with a better understanding of process related fractionation

major ion chemistry of the ganga brahmaputra river system weathering processes and fluxes to the bay of bengal the ganga brahmaputra one of the world s largest river systems is first in terms of sediment transport and fourth in terms of water discharge a detailed and systematic study of the major ion chemistry of these rivers and their tributaries as well as the clay mineral composition of the bed sediments has been conducted the chemistry of the highland rivers upper reaches of the ganga the yamuna the brahmaputra the gandak and the ghaghra are all dominated by carbonate weathering ca mg and hco3 account for about 80 of the cations and anions in the lowland rivers the chambal the betwa and the ken hco3 excess over ca mg and a relatively high contribution of na k to the total cations indicate that silicate weathering and or contributions from alkaline saline soils and groundwaters could be important sources of major ions to these waters the chemistry of the ganga and the yamuna in the lower reaches is by and large dictated by the chemistry of their tributaries and their mixing proportions illite is the dominant clay mineral about 80 in the bedload sediments of the highland rivers kaolinite and chlorite together constitute the remaining 20 of the clays in the chambal betwa and ken smectite accounts for about 80 of the clays this difference in the clay mineral composition of the bed sediments is a reflection of the differences in the geology of their drainage basins the highland rivers weather acidic rocks whereas the others flow initially through basic effusives the ganga brahmaputra river system transports about 130 million tons of dissolved salts to the bay of bengal which is nearly 3 of the global river flux to the oceans the chemical denudation rates for the ganga and the brahmaputra basins are about 72 and 105 tons km yr 1 respectively which are factors of 2 to 3 higher than the global average the high denudation rate particularly in the brahmaputra is attributable to high relief and heavy rainfall

complexity of seismicity due to highly rate dependent friction we study a simple antiplane fault of finite length embedded in a homogeneous isotropic elastic solid in order to understand the origin of seismic source heterogeneity in the presence of nonlinear rate dependent friction all the mechanical properties of the medium and friction are assumed to be homogeneous starting from a heterogeneous initial stress distribution we apply a slowly increasing uniform stress load far from the fault and we simulate the seismicity for more than 20 000 events in some cases the style of seismicity produced by this model is determined by a control parameter which measures the degree of rate dependence of friction for classical friction models with rate independent friction no complexity appears and seismicity is perfectly periodic for weakly rate dependent friction seismicity becomes slightly nonperiodic but most events are still characteristic earthquakes when friction is highly rate dependent seismicity is completely irregular and ruptures of all sizes occur inside the fault highly rate dependent friction destabilizes the healing process producing premature healing of slip and partial stress drop premature healing causes rupture to take the form of narrow propagating slip episodes the so called heaton s 1990 pulses partial stress drop produces large variations in the state of stress which in turn produce earthquakes of different sizes we make the conjecture that all models in which static stress drop is only a fraction of the dynamic stress drop produce stress heterogeneity

ultrasonic measurements of vp and qp relaxation spectrum of complex modulus on basalt melts abstract ultrasonic compressional wave velocity v p and quality factor q p have been measured in alkali basalt olivine basalt and basic andesite melts in the frequency range of 3 4 22 mhz and in the temperature range of 1100 1400 c velocity and attenuation of the melts depend on frequency and temperature showing that there are relaxation mechanisms in the melts complex moduli are calculated from the ultrasonic data the results fit well a complex modulus of arrhenius temperature dependence with log normal gaussian distribution in relaxation times of attenuation the analysis yields average relaxation time its activation energy relaxed modulus unrelaxed modulus and width of gaussian distribution in relaxation times relaxed modulus is smaller 17 5 gpa for basic andesite melt of high silica and high alumina contents than for the other two basalt melts 18 1 18 4 gpa the most probable relaxation times decrease from 3 10 10 s for basic andesite to 10 11 s for alkali basalt at 1400 c activation energies of attenuation ranging from 270 to 340 kj mol 1 in the three melts are highest in basic andesite longitudinal viscosity values and their temperature dependences are also calculated from v p and q p data the volume viscosity values are estimated from the data using the shear viscosity values longitudinal volume and shear viscosities and their activation energies are highest in the basic andesite melt of the most polymerized structure

tectonic and sedimentary evolution of the korean peninsula a review and new view abstract this review focuses on the tectonics and sedimentation of major sedimentary basins and orogenic belts late proterozoic neogene in the korean peninsula the korean peninsula is part of the amuria plate and represents an important link between continental blocks of north and south china and the island arcs of japan the basement rocks exposed in the kyonggi and yongnam massifs consist of 2 7 to 1 1 ga high grade gneiss and schist these massifs are separated by the okchon fold belt which comprises metasedimentary rocks and bimodal meta volcanic rocks the stratigraphy of the okchon group is unclear at present the okchon basin was probably initiated as an intraplate rift prior to the late proterozoic the hwanggangri formation clast bearing phyllite most likely represents deposition by subaqueous debris flows in slope environments of an enclosed basin the stratigraphic relationship between the okchon group and the choson supergroup cambro ordovician of the taebaeksan basin is poorly constrained the choson supergroup unconformably overlies the yongnam massif and consists mainly of carbonate sequence that formed mostly in shallow marine and tidal environments reflecting numerous sea level fluctuations the sequence is disconformably overlain by siliciclastic sequence of pyongan supergroup carboniferous triassic which formed most likely in shallow marine deltaic and fluvial environments the imjingang belt is an east trending fold and thrust zone and consists of metasedimentary rocks and volcaniclastics devonian carboniferous underlain unconformably by proterozoic basement rocks late proterozoic amphibolites of oceanic affinity were metamorphosed at about 8 13 kbar and 630 740 c during the late permian to the early triassic the south vergent contraction and top down to the north normal faulting are suggestive of a suture belt between the north china block sino korea craton and the south china block yangtze craton an extension of sulu belt across the yellow sea entire peninsula experienced strong deformation and metamorphism during the suturing event namely songrim orogeny during this orogenic event the kyonggi massif and the okchon basin accreted to the yongnam massif and taebaeksan basin along the south korean tectonic line running northeast southwest a series of northward trending thrust formed along the boundary zone to the east kaktong and kongsuwon thrusts and others piggyback basins locally developed along the thrust faults forming the taedong group the crustal deformation resumed in the early to late jurassic daebo event under contractional setting dextral ductile shearing associated with thrusting and folding continued in the mid southern part of the peninsula it was due to orthogonal northwestward subduction of the izanagi plate under the asian continent the yongnam massif experienced continuous dextral offset along the honam shear zone in the early cretaceous the izanagi plate began to subduct northward and caused formation of strike slip basins in retroarc setting i e kyongsang basin in the southeastern part and a number of small scale basins in the mid southwestern part of the peninsula small scale alluvial fans and fluvial channel networks formed in the basin margin and were transitional to ephemeral lacustrine systems under semiarid to arid conditions extensive intrusion of granitoids occurred from triassic to early tertiary with a gap between 160 and 100 ma representing continental magmatic arc in the tertiary the southeastern margin of the korean peninsula experienced back arc opening pull apart basins formed in the miocene bounded by the yangsan and hupo faults the yonil group sedimentary fill of the pohang basin comprises more than 1 km thick siliciclastic sequence which represents deposition in fan delta systems on the hanging wall of the yangsan fault thick more than 10 km thick sediments in the ulleung basin margin were deformed in the late miocene due to the northward movement of kyushu block quarternary volcanic events in cheju island represent intraplate hot spots

high temperature deformation of volcanic materials in the presence of water we describe an experimental apparatus used to perform deformation experiments relevant to the volcanological sciences the apparatus supports low load high temperature deformation experiments under dry and wet conditions on natural and synthetic samples the experiments recover the transient rheology of complex melt porosity solids volcanic materials during uniaxial deformation the key component to this apparatus is a steel cell designed for high temperature deformation experiments under controlled water pressure experiments are run under constant displacement rates or constant loads the range of accessible experimental conditions include 25 1100 c load stresses 0 to 150 mpa strain rates 10 6 to 10 2 1 s and fluid pressures 0 150 mpa the apparatus is calibrated against standard values of viscosity using constant load experiments on cores of nist nbs 717a borosilicate glass we also report results of constant displacement rate 10 6 m s experiments on porous 70 sintered cores of ash from the rattlesnake tuff the cores of volcanic ash were deformed in experiments under ambient dry and elevated water pressures wet dry experiments at 870 c show an increase in effective viscosity 10 9 5 to 10 10 4 pa s with increasing strain 30 due to porosity reduction during compaction experiments under 1 3 mpa p h 2 o recover lower values of apparent viscosity 10 9 2 to 10 9 4 pa s despite being run at lower temperatures 640 665 c the wet experiments also do not show a rise in viscosity with increased strain decreasing porosity as observed in dry experiments rather the presence of an h 2 o fluid phase expands the window of viscous deformation and delays the onset of strain hardening that normally accompanies porosity reduction

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

magma fragmentation by rapid decompression the processes leading to magma fragmentation and the generation of pyroclastic debris during explosive volcanic eruptions are of fundamental importance in volcanology observations of explosive eruptions1 3 as well as theoretical analyses of the underlying processes4 have raised the question of whether the rapid decompression of highly viscous vesicular magma that results from the collapse of a lava dome or volcanic edifice can in itself produce explosive magma fragmentation and pyroclast formation here we report the results of a laboratory investigation of pyroclast formation following rapid decompression samples of magma from the 1980 eruption of mount st helens when rapidly depressurized from initial pressures of up to 12 mpa and at temperatures in the range 750 825 c fragmented to form pyroclastic products that are in many respects similar to those formed in real eruptions moreover we observe explosive fragmentation at temperatures well below those normally associated with magmatic processes suggesting that even relatively cool magma bodies can be very hazardous when subjected to rapid unloading events

bubble growth in visco elastic magma implications to magma fragmentation and bubble nucleation we present a visco elastic bubble growth model accounting for viscous and elastic deformations and for volatile mass transfer between bubbles and melt we define the borders between previous bubble growth models accounting for incompressible viscous melt and our new model accounting also for elastic deformation this is done by a set of end member analytical solutions and numerical simulations elastic deformation is most prominent for magma of small vesicularity where the growth regime depends on the shear modulus for high shear modulus bubble growth is slow and follows an exponential law in a viscous growth regime while for low shear modulus bubbles quickly follow a square root diffusive solution our model provides all the elastic components stresses strains and strain rates required for defining criteria for failure and magma fragmentation we suggest two failure criteria a stress related one based on the internal friction and the mohr coulomb failure theory and a strain related one based on fibre elongation experiments we argue that both criteria are equivalent if we consider their shear modulus dependency and its effect on magma rheology last we apply our model to the process of bubble nucleation in the incompressible case following nucleation growth is slow and leads to long incubation times during which bubbles may be dissolved back into the melt the elastic response in magmas with low shear modulus results in a short incubation time increasing the probability of survival the above effects emphasize the significance of visco elasticity for the dynamic processes occurring in magmas during volcanic activity

natural versus anthropogenic sources in the surface and groundwater dissolved load of the dommel river meuse basin constraints by boron and strontium isotopes and gadolinium anomaly summary the river dommel a tributary of the meuse river drains an area of intensive agriculture livestock farming maize and grassland over 50 of the basin and a dense population of about 600 000 people representing 20 of the total area the combined human activities in the dommel catchment lead to a large amount of dissolved elements and compounds released in surface and groundwaters the aim of this study was to discriminate the natural including infiltration of meuse water versus anthropogenic sources of the dissolved load and to identify the various pollution sources such as agriculture industrial activity and wastewater treatment plants using geochemical tools including major and trace elements sr and b isotopes and rare earth elements ree for that purpose a same day geochemical snapshot picture of the entire basin was combined with monthly monitoring in strategic points the major and trace elements analyses allowed discriminating the main pollution sources affecting the basin i e point versus diffuse sources strontium isotopes helped to identify each tributary and to calculate mixing proportions combining these calculations with the sr isotopic data obtained from the snapshot sampling campaign during a low flow period shows that meuse water infiltration represents 25 of the total dommel discharge boron isotopes used for assessing the amount of water affected by anthropogenic input cannot discriminate between the two main anthropogenic inputs i e urban wastewater and the zinc smelter effluent as they have similar 11 b values finally the ree and especially the use of gd anomalies gd demonstrated the generalized impact of urban wastewater on the streams of the dommel basin the coupled use of different geochemical tracers sr and b isotopes together with gd in addition to the standard major element analyses led to discriminating the various anthropogenic components influencing the dommel basin water quality with these tools it also became possible to assess the complex water circulation and exchanges between water compartments including the major role of meuse water through the bocholt herenthals canal

brittleness of fracture in flowing magma 1 understanding the transition to brittle fracture of flowing magma is essential for estimating the explosiveness of a volcanic eruption in order to quantify brittleness of flowing magma a new parameter is introduced which is a function of the ratio of the rate of change of the strain energy due to elastic distortional deformation to the mechanical power due to total distortional deformation rate from the perspective of dependence of brittle fracture of magma on stress decompression rate strain rate and shear thinning effects are reviewed the experimental data of kameda et al 2008 for rapid decompression of simulants of bubbly magma have also been reexamined the results show that exhibits a strong transition that correlates well with the observed transition between ductile expansion to brittle fragmentation moreover is useful in considering the effects of shear thinning and steady creep conditions on brittle fracture statements in the literature that suggest that materials behave in a brittle manner at sufficiently high strain rate are correct however these statements do not precisely quantify the notion of high strain rate so they are easy to misinterpret when considering the effect of shear thinning although shear thinning tends to increase the absolute magnitude of the total strain rate it does not necessarily increase brittleness also in principle it is unlikely for brittle fracture to occur at steady creep cracking observed in steady creep experiments of magma lavallee et al 2007 2008 may be attributed to small fluctuations with sufficiently high frequencies to satisfy the conditions for brittle fracture

extremely fluid behavior of hydrous peralkaline rhyolites the viscosities of a series of water bearing peralkaline rhyolitic melts have been experimentally determined the dry melt compositions are composed of a series of additions of na2o to a metaluminous base composition the melts initially hydrated at high pressures and quenched isobarically have been prepared by cutting and polishing then reheating across the glass transition at 1 atm where they are annealed to a relaxed metastable state and then investigated dilatometrically using micropenetration methods the measurements have been performed in the viscosity range of 108 5 1011 5 pa s which corresponds to temperatures in the range of 675 220 c for these compositions despite the relatively low viscosities of dry peralkaline melts in comparison with metaluminous melts of similar sio2 content the viscosities of peralkaline rhyolitic melts also decrease strongly and non linearly with the addition of water the resulting viscosity temperature relationships for water bearing peralkaline rhyolitic melts are shifted to much lower temperatures such that glass transition temperatures for moderate cooling rates correspond to extraordinarily low temperatures a model is presented for the calculation of melt viscosities in the range of 108 5 1011 5 pa s for peralkaline rhyolites with up to 7 wt h2o the very fluid nature of these peralkaline rhyolites over a wide range of water contents may facilitate a very efficient degassing history of glassy peralkaline rhyolites in nature efficient degassing might explain the apparent contradiction of the presence of common water rich melt inclusions in phenocryst phases hosted in water free glassy rhyolites versus the absence of vesicular layers or textural evidence for a vesicular past for the glassy 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

propagation of acoustic waves in a visco elastic two phase system influences of the liquid viscosity and the internal diffusion abstract the main purpose of the present paper is to present the mathematical expression for the frequency dependent effective acoustic properties of a liquid bubble mixture effects of the bubble resonance the heat and mass transfer between the liquid and bubbles and the viscoelasticity of the liquid are included in the expression several characteristic frequencies associated with these internal processes are represented by simple functions of the material and condition parameters using these expressions the acoustic properties of bubbly magmas are calculated and analyzed it is shown that the dispersion and attenuation of the pressure wave are particularly considerable in the frequency range lower than the characteristic frequency of the mass transfer and in the range near the characteristic frequency of the viscous response of the bubble radius in the frequency range bounded by these two frequencies the bubbly magma can be regarded as an elastic medium with the slow sound speed the significance of such acoustic properties on resonance of a body of bubbly magma is demonstrated in a simple one dimensional system

dynamic heterogeneities versus fixed heterogeneities in earthquake models summary a debate has raged over whether fixed material and geometrical heterogeneities or alternatively dynamic stress heterogeneities arising through frictional instabilities dominate earthquake complexity it may also be that both types of heterogeneities interact and are important this paper makes a first step in examining this interaction combining two previously separate lines of research one line examined friction which has attractors the subset of the phase space that the system evolves towards in the long run on homogeneous faults which are simple and then added fixed heterogeneities to the faults to obtain complex attractors another line examined frictions which produced complex attractors on homogeneous faults here we examine frictions which produce complex attractors on homogeneous faults and study them on heterogeneous faults in order to study the interaction of dynamic stress heterogeneities and fixed fault heterogeneities we consider two types of fixed heterogeneities an additive noise and a multiplicative noise to the frictional strength of the fault because of the linearity of the bulk elastodynamics the attractor is unaffected by additive fixed noise in the strength of the fault adding an arbitrary function of space fixed in time to the friction leaves the resulting attractor unchanged in contrast multiplicative fixed noise multiplying the friction can have a profound effect on the resulting attractor in the small multiplicative noise amplitude limit the frictional weakening attractor is little perturbed at finite amplitudes fixed heterogeneities substantially alter the attractor we see as one consequence a shift toward longer length events at larger amplitudes fixed heterogeneities are seen to reduce the irregularities created by the frictional instability we study but by no means destroy them we quantify this by examining a measure of variability of the importance in hazard estimates the coefficient of variation of large event recurrence times the coefficient of variation is seen to remain substantial even for large fixed heterogeneities for friction that weakens with time so the underlying uniform fault attractor is simple fixed heterogeneities increase irregularity for all frictions examined at low fixed heterogeneity the stress concentrations left over by the ends of the large events dominate where most of the small events occur while at higher heterogeneity the stress irregularities left over by fixed fault heterogeneities begin to dominate where the small events occur this may be the strongest signature of fixed heterogeneities and should be examined further in the earth finally in what may have important implications for more sophisticated estimates of earthquake hazard we see a correlation of locations with lower strength drop having higher variation in large event repeat times

a rheological investigation of vesicular rhyolite abstract the rheology of vesiculating rhyolitic systems exerts a strong control on the transport of silicic magmas in the subvolcanic to volcanic environments we present here an investigation of vesiculating and vesiculated rhyolites using dilatometric methods this study examines the effect of vesicle content on the viscosity of a natural supercooled rhyolitic liquid with 0 70 vesicles the experimental samples of rhyolitic glass are derived from fusion of a natural obsidian from little glass butte oregon crystal free rhyolite glasses of varying porosity were prepared by fusing obsidian powder in a pt crucible differing porosities were obtained by varying the temperature 1300 1650 c and duration 0 5 6 h of the fusions cylindrical samples of the resulting vesiculated rhyolites were cored from the crucible using diamond tools and their ends were ground flat and parallel for dilatometry the porosity of each sample was determined from archimedean buoyancy density determinations and comparison with bubble free rhyolite 2 331 g cm 3 porosity 1 p p o the density of foamed samples was determined using their mass volume and regular geometry viscosities were determined in the parallel plate mode at stresses of 5 10 3 to 10 5 pa the viscosimeter was calibrated using nbs 711 glass the bubble contents were microscopically investigated using a video reflected light system and image analysis software distribution functions of the size orientation aspect ratio and surface porosity were obtained the viscosity of rhyolite decreases with increasing bubble content a general relationship of the form 0 1 c describes the effect of porosity in volume fraction on the viscosity where c is a dimensionless constant 22 4 2 9 and log 10 0 10 94 0 04 pa s at 850 c

pressure waves in a supersaturated bubbly magma summary we study the interaction of acoustic pressure waves with an expanding bubbly magma the expansion of magma is the result of bubble growth during or following magma decompression and leads to two competing processes that affect pressure waves on the one hand growth in vesicularity leads to increased damping and decreased wave amplitudes and on the other hand a decrease in the effective bulk modulus of the bubbly mixture reduces wave velocity which in turn reduces damping and may lead to wave amplification the additional acoustic energy originates from the chemical energy released during bubble growth we examine this phenomenon analytically to identify conditions under which amplification of pressure waves is possible these conditions are further examined numerically to shed light on the frequency and phase dependencies in relation to the interaction of waves and growing bubbles amplification is possible at low frequencies and when the growth rate of bubbles reaches an optimum value for which the wave velocity decreases sufficiently to overcome the increased damping of the vesicular material we examine two amplification phase dependent effects 1 a tensile phase effect in which the inserted wave adds to the process of bubble growth utilizing the energy associated with the gas overpressure in the bubble and therefore converting a large proportion of this energy into additional acoustic energy and 2 a compressive phase effect in which the pressure wave works against the growing bubbles and a large amount of its acoustic energy is dissipated during the first cycle but later enough energy is gained to amplify the second cycle these two effects provide additional new possible mechanisms for the amplification phase seen in long period lp and very long period vlp seismic signals originating in magma filled cracks

the equivalence of enthalpy and shear stress relaxation in rhyolitic obsidians and quantification of the liquid glass transition in volcanic processes abstract the relaxation of enthalpy and shear stress has been investigated for six silicic volcanic obsidians calc alkaline rhyolitic obsidians from ben lomond dome new zealand erevan dry fountain armenia and little glass butte usa peralkaline obsidians from mayor island new zealand and eburru kenya and a macusanite obsidian from se peru the temperature dependences of enthalpy and shear stress relaxation are obtained from the dependence of the calorimetric heat capacity peak temperature on heating rate and the dependence of shear viscosity on temperature respectively both processes enthalpy relaxation and shear stress relaxation can be approximated to be arrhenian in the investigated temperature ranges relevant to volcanological processes activation energies derived for enthalpy and shear stress relaxation for each sample are equal this equality permits the calculation of viscosity at the glass transition as a function of cooling rate of a volcanic melt the relationship between viscosity at the glass transition and the cooling rate is given by log10 s at tg k log10 q where s the shear viscosity at the glass transition q is the cooling rate in c s 1 and k is a constant the six melt compositions investigated here exhibit a value of k 10 49 0 31 for the modeling of volcanic processes this equation allows the prediction of the viscosity at the glass transition temperature for a given value of cooling rate taken together with the maxwell relation an effective relaxation time can be obtained for the cooling rate prediction of the glass transition temperature permits the allotment of temperature ranges for the liquid and glassy segments of the cooling history of the volcanic melt and thus for the correct assignment of glassy and liquid values of the derivative thermodynamic properties such as expansivity and heat capacity in thermodynamic modeling of late stage volcanic processes

diffusion of a multi species component and its role in oxygen and water transport in silicates an important but poorly understood factor that affects diffusion rates is the role of speciation during diffusion of a multi species component the diffusion of such a component is complicated by the different diffusion coefficient of each species and the interconversion reactions among the species these complexities can be treated by a diffusion equation that incorporates the diffusive fluxes of all species contributing to the concentration of the component the effects of speciation on the diffusion of the component can be investigated experimentally in some simple cases by measuring concentration profiles of all species developed during diffusion experiments or by studying some of their other consequences experimental data on water diffusion in rhyolitic glasses indicate that although dissolved water is present as two species h 2o molecules and oh groups molecular h 2o is the dominant diffusing species at very low to high water concentrations this explains the apparently complex behavior of water diffusion experimental data on oxygen diffusion in some silicates using 18 o tracers in the form of h 2 18 o are consistent with the idea that 18 o transport is dominated by diffusion of h 2o molecules even at lower water contents ppm or less this explains why oxygen transport depends on the presence of water and generally depends on water fugacity linearly for this mode of oxygen transport there is a simple theoretical relationship between the effective total oxygen diffusion coefficient and the total water diffusion coefficient that is a function of only the water concentration of the silicate at low water content this relationship appears to describe quantitatively the existing data over a wide range in water contents and diffusion coefficients in several phases

delayed brittle like fragmentation of vesicular magma analogue by decompression abstract a rapid decompression experiment using syrup containing gas bubbles was conducted in order to clarify the fragmentation of vesicular magma which is a key phenomenon in volcanic eruptions we focus on brittle like fragmentation which occurs with a longer time scale than brittle fragmentation the response of the bubbly syrup to the decompression for various viscosities and porosities was tested under various initial pressures pressure differences and decompression times the response observed by high speed photography was classified using the deborah number de dt which is defined as the ratio of the viscoelastic relaxation time of the syrup to the decompression time the maximum differential stress at the bubble surface max and a measure of instantaneous brittleness at the bubble surface c at the time when the differential stress at the surface reaches the critical fracture stress c in a number of the experimental runs in which both de dt and c indicated ductile response of the material brittle like fragmentation occurred when max substantially exceeded c for all of the runs in which brittle like fragmentation was observed the onset of fragmentation was delayed substantially from the relaxation time whereas the onset occurred within the characteristic time for viscous expansion of the bubbles in many cases of brittle like fragmentation fragmentation continued after the onset triggered by a single decompression event detailed analysis indicates that brittle like fragmentation started with a sudden release of the gas in the bubbly syrup through a surface crack which might lead to an increase in local brittleness magma fragmentation may be viewed as sequential brittle like fragmentation this view may provide an explanation for the observed time delay for the onset of an explosive eruption after a triggering decompression event

infrasonic tremor wavefield of the pu u ō ō crater complex and lava tube system hawaii in april 2007 1 long lived effusive volcanism at the pu u crater complex kilauea volcano hawaii produces persistent infrasonic tremor that has been recorded almost continuously for months to years previous studies showed that this infrasonic tremor wavefield can be recorded at a range of 10 km however the low signal power of this tremor relative to ambient noise levels results in significant propagation effects on signal detectability at this range in april 2007 we supplemented a broadband infrasound array at 12 5 km from pu u mene with a similar array at 2 4 km from the source kipu the additional closer range data enable further evaluation of tropospheric propagation effects and provide higher signal to noise ratios for studying volcanic source processes the infrasonic tremor source appears to consist of at least two separate physical processes we suggest that bubble cloud oscillation in a roiling magma conduit beneath the crater complex may produce a broadband component of the tremor low frequency sound sourced in a shallow magma conduit may radiate infrasound efficiently into the atmosphere due to the anomalous transparency of the magma air interface we further propose that more sharply peaked tones with complex temporal evolution may result from oscillatory interactions of a low velocity gas jet with solid vent boundaries in a process analogous to the hole tone or whistler nozzle the infrasonic tremor arrives with a median azimuth of 67 at kipu additional infrasonic signals and audible sounds originating from the extended lava tube system to the south of the crater complex median azimuth 77 coincided with turbulent degassing activity at a new lava tube skylight our observations indicate that acoustic studies may aid in understanding persistent continuous degassing and unsteady flow dynamics at kilauea volcano

crumbling of dacite dome lava and generation of pyroclastic flows at unzen volcano recent modelling of volcanic eruptions has shown that the efficiency of subsurface degassing of magmas determines whether magma erupts explosively or effuses quietly1 2 slow uprise of magma is often accompanied by effective degassing leading to the extrusion of lava flows and domes although lava dome extrusion is one of the less explosive modes of eruption it is often accompanied by explosive pyroclastic activities3 5 the 1991 eruption of unzen volcano provided an opportunity to observe at close range several types of small scale pyroclastic flow glowing avalanches originating from lava domes most of the pyroclastic flows are of merapi type caused by blocks falling from a collapsing dome others are of pelean type originating in an explosion from the side of a dome the lavas apparently show variable degrees of self explosivity we suggest that variable degrees of degassing of the magma produced a wide range of excess pore pressures in the extruded lava domes resulting in both merapi type and pelean type pyroclastic flows from the domes

damping of pressure waves in visco elastic saturated bubbly magma the attenuation of pressure waves in a saturated bubbly magma is examined in a model coupling seismic wave propagation with bubble growth dynamics this model is solved analytically and numerically including effects of diffusion of volatiles visco elasticity and bubble number density we show that wave attenuation is controlled mainly by the peclet and deborah numbers the peclet number is a measure of the relative importance of advection to diffusion the deborah number is a visco elastic measure describing the importance of elasticity in comparison to viscous melt deformation we solve numerically for wave attenuation for various magma properties corresponding to a wide range of peclet and deborah numbers we show that the numerical solution can be approximated quite well for frequencies above 1 hz by an analytical end member solution obtained for high peclet and low deborah numbers for lower frequencies volatile transport should be accounted for leading to higher attenuation with respect to the analytical solution however if the deborah number is increased either by longer relaxation time or by higher frequencies then attenuation decreases with respect to the analytical solution therefore visco elasticity leads to a significant improvement of the resonating qualities of a magma filled conduit and widens the depth and frequency ranges where pressure waves will propagate efficiently through the conduit the interaction of pressure waves with bubbly liquids has been discussed in the literature it was confronted either by studying non linear radial oscillations of a single bubble keller kolodner 1956 keller miksis 1980 accounting also for liquid compressibility prosperetti lezzi 1986 lezzi prosperetti 1987 and including the effect of heat transfer between bubble and liquid prosperetti et al 1988 or by exploring linear pressure waves in bubbly liquids caflisch et al 1985a b present a rigorous mathematical approach while commander prosperetti 1989 present a more heuristic approach following the suspension model of van wijngaarden 1968 commander prosperetti 1989 focused on linear pressure waves propagating in liquids containing small concentrations of gas bubbles they constrained their treatment to conditions of no volatiles flux between bubble and melt and to wavelengths that are much longer than the typical radius of bubbles ichihara et al 2004 presented a model accounting for effects of bubble resonance and scattering of pressure waves propagating through a visco elastic bubbly liquid this model was further developed by ichihara kameda 2004 to include also thermal effects and non ideality of the gas in the bubble on the acoustic bulk properties of a bubbly magma the problem of mass transfer between bubbles and melt in volcanic systems was confronted by collier et al 2006 in order to obtain the attenuation of pressure waves propagating through a magma filled conduit assuming an incompressible bubbly magma they concluded that there is a very limited range in depth which allows waves to propagate with minimum damping in this study we integrate the theory of pressure waves propagating in bubbly liquids commander prosperetti 1989 with the theory of bubble growth in magmas navon lyakhovsky 1998 analytical solutions are presented table 1 for four bubble growth end member regimes viscous diffusive equilibrium and no mass flux viscoelasticity and melt compressibility are introduced by a new visco elastic bubble growth model this model is used to generate a visco elastic numerical solution for the q factor and to understand better the physics of seismic wave attenuation in a saturated visco elastic bubbly magma

magma fragmentation speed an experimental determination abstract the propagation speed of a fragmentation front combined with the ascent velocity of magma is in all likelihood a controlling factor in the dynamics of explosive volcanic eruptions direct measurement of the fragmentation speed in natural systems appears to be impossible at present fortunately laboratory experiments can provide information on the propagation speed of the fragmentation front here we present the results of fragmentation speed determinations using a so called fragmentation bomb these are to the best of our knowledge the first in situ fragmentation speed determinations performed on magma natural magma samples merapi basaltic andesite mount st helens dacite and unzen dacite have been investigated in the temperature range of 20 950 c and at pressures up to 25 mpa two techniques have been employed firstly in experiments at 20 c dynamic pressure transducers were placed above and below the magma samples and the fragmentation speed of the magma sample was derived from an analysis of the decompression curves secondly at elevated temperatures an alternative technique was introduced and successfully employed this involved the severing via fragmentation of conducting wires placed within the samples at various heights fragmentation speeds are very low falling in the range of 2 70 m s and increasing with an increase in the magnitude of the decompression step responsible for the fragmentation the first high temperature determination seems consistent with low temperature results implications for explosive volcanism are discussed briefly

geochemistry of dissolved and suspended loads of the seine river france anthropogenic impact carbonate and silicate weathering this study focuses on the chemistry of the seine river system one of the major rivers in europe and constitutes the first geochemical investigation of both suspended and dissolved loads of this river the seine river drains a typical mesozoic cenozoic sedimentary basin the paris basin constituted of limestones mixed or interbedded with terrigenous sediments derived from the paleoreliefs bordering the mesozoic and cenozoic seas in the context of quantifying the global influence of carbonate and silicate weathering on atmospheric co2 consumption the seine river offers the possibility of examining weathering rates in a flat sedimentary environment under temperate climatic conditions one of the major problems associated with the seine river as with many temperate rivers is pollution we propose in this paper 2 approaches in order to correct the dissolved load of the seine river for anthropogenic inputs and to calculate weathering rates of carbonates and silicates the first uses the dissolved load of rivers and tries to allocate the different solutes to different sources a mixing model based on elemental ratios is established and solved by an inversion technique the second approach consists in using the suspended load geochemistry under steady state conditions we show that the geochemistry of suspended sediments makes it possible to estimate the amount of solutes released during the chemical weathering of silicates and thus to calculate weathering rates of silicates the total dissolved load of the seine river at paris can be decomposed into 2 of solutes derived from natural atmospheric sources 7 derived from anthropogenic atmospheric sources 6 derived from agriculture 3 derived from communal inputs and 82 of solutes derived from rock weathering during high floods the contribution of atmospheric and agriculture inputs predominates the weathering rate of carbonates is estimated to be 48 t km2 yr 25 mm 1000 yr only 10 of carbonates are transported in a solid form the rest being transported in solution co2 consumption by carbonate weathering approaches 400 103 mol km2 yr in the seine river at paris about 2 3 mg l of dissolved cations are found to originate from the chemical weathering of silicates by taking dissolved silica into accounts the total dissolved load derived from silicate weathering is about 6 7 mg l this value is minimal because biological uptake of silica probably occur in the seine river the chemical weathering rate of aluminosilicates is estimated to be 2 t km2 yr the ratio of physical over chemical weathering of silicates range between 1 and 3 and the total chemical and physical erosion rates of sedimentary silicates are about 2 3 mm kyr the co2 consumption by silicate weathering 15 24 103 mol km2 yr and is independent of dissolved silica concentration silicate consumption is thus 20 times less than carbonate consumption in the paris basin compared to the neighboring granitic areas the sedimentary region drained by the seine river has 2 to 3 times lower co2 consumption rates we attribute this difference to the cation depleted nature of the seine basin aluminosilicates which are of sedimentary origin at a world scale the chemical denudation rates found for the seine basin are very low and comparable to those given for tropical lowland rivers draining silicates such as the rivers of the congo and amazon basins in spite of huge climatic differences we attribute this similarity to the low mechanical denudation that characterizes these two types of regions

transfer of atmospheric boron from the oceans to the continents an investigation using precipitation waters and epiphytic lichens 1 the variation of b concentration in atmospheric deposition was studied from the analysis of 35 individual rain events 17 snow packs and 17 lichens sampled over ne north america south from hudson bay and asia from the coast of bangladesh to the high himalayas of nepal rain samples show a range of b concentration between 0 3 and 9 4 g l average of 1 8 1 7 g l excluding two rains with higher b contents of 17 and 37 5 g l most likely reflecting anthropic contamination snowpacks and lichens which average atmospheric deposition over periods of a few months to a few years show a smaller range of variation from 0 1 to 2 3 g l average 1 1 0 8 g l for snowpacks and from 1 to 25 9 ppm for lichens the lichens have elemental ratios such as b cl similar to the average of rains showing that they are good monitors of atmospheric b deposition without significant biofractionation of elements this is also demonstrated by their halogen contents which follow the systematics of the atmospheric distribution of these elements previously derived from the study of rains and atmospheric particles though individual rains do not show systematic decrease in b concentration with distance to the sea this behavior is clearly shown by samples having longer integration times snowpacks and lichens the snow and lichen data show that seawater is a major source of atmospheric b using the lichen data the enrichment factor normalized to na of marine air masses relative to seawater is estimated to be 13 average b na of 5 6 10 3 this implies that the fractionation factor of atmospheric suspended marine particles relative to seawater fx x na particle x na seawater is 0 177 thus b transfer from seawater to the atmosphere occurs mostly via degassing of sea salts the residence time of gaseous b being estimated at 15 9 fold that of particulate b the distribution of b in the atmosphere between gaseous b and degassed sea salts can be used to model the large range of b concentrations measured in single rain events by selective removal of one of the two b components in this model unfractionated marine air masses can reach the continents with very variable b concentrations between 0 2 and 20 g l

thermal effects of magma degassing abstract the thermodynamics of diffusive bubble growth is dominated by latent heat of water exsolution vaporization and the work of gas expansion p dv work a numerical assessment of the effects of these on cooling of bubbly magma water in albite indicates that a magma can exsolve volatiles at equilibrium or with varying degrees of oversaturation depending on decompression history and degassing kinetics heat of water exsolution vaporization from magmatic melts has not previously been experimentally or analytically determined and we have evaluated it from others thermodynamic functions known for the albite water system heat of exsolution is small for pressures over 100 mpa but can reach 20 kj mole at 1 2 mpa 10 20 bar oversaturation degassing at 10 20 bar can cause cooling of albite by 8 k wt of exsolved water the thermal effect of equilibrium degassing depends on the starting pressure of decompression because it follows the solubility curve for a saturated melt at 100 mpa 4 wt water it can cool a magma at least by 35 k before it disrupts into spray as gas volume fraction exceeds 0 8 although we do not specifically consider the dynamics of bubble interactions in this study our results suggest that the dynamic cooling rate could be significant at the vent of an erupting magma column and under extreme eruption conditions can lead to glass formation around fast growing bubbles of magmatic foam this could cause fragmentation into fine ash by brittle failure conversely bubble wall cooling even before glass formation can serve to reduce diffusive volatile flux into bubbles decreasing the overall cooling of the system and lead to solidification of oversaturated magmas as occasionally observed in eruption products

chemical weathering rates of a soil chronosequence on granitic alluvium iii hydrochemical evolution and contemporary solute fluxes and rates although long term changes in solid state compositions of soil chronosequences have been extensively investigated this study presents the first detailed description of the concurrent hydrochemical evolution and contemporary weathering rates in such sequences the most direct linkage between weathering and hydrology over 3 million years of soil development in the merced chronosequence in central california relates decreasing permeability and increasing hydrologic heterogeneity to the development of secondary argillic horizons and silica duripans in a highly permeable younger soil 40 kyr old pore water solutes reflect seasonal to decadal scale variations in rainfall and evapotranspiration et this climate signal is strongly damped in less permeable older soils 250 to 600 kyr old where solutes increasingly reflect weathering inputs modified by heterogeneous flow elemental balances in the soils are described in terms of solid state exchange and pore water reservoirs and input output fluxes from precipitation et biomass solute discharge and weathering solute mineral nutrients are strongly dependent on biomass variations as evidenced by an apparent negative k weathering flux reflecting aggradation by grassland plants the ratios of solute na to other base cations progressively increase with soil age discharge fluxes of na and si when integrated over geologic time are comparable to solid state mass losses in the soils implying similar past weathering conditions similarities in solute and sorbed ca mg ratios reflect short term equilibrium with the exchange reservoir long term consistency in solute ratios when contrasted against progressive decreases in solid state ca mg requires an additional ca source probably from dry deposition amorphous silica precipitates from thermodynamically saturated pore waters during periods of high evapotranspiration and result in the formation of duripans in the oldest soils the degree of feldspar and secondary gibbsite and kaolinite saturation varies both spatially and temporally due to the seasonality of plant respired co2 and a decrease in organically complexed al in deeper pore waters k feldspar is in equilibrium and plagioclase is about an order of magnitude undersaturated hydrologic heterogeneity produces a range of weathering gradients that are constrained by solute distributions and matrix and macropore flow regimes plagioclase weathering rates based on precipitation corrected na gradients vary between 3 and 7 10 16 mol m 2 s 1 these rates are similar to previously determined solid state rates but are several orders of magnitude slower than for experimental plagioclase dissolution indicating strong inhibitions to natural weathering partly due to near equilibrium weathering reactions

identification of sources affecting water chemistry in the nakdong river south korea the sources impacting the water chemistry of the nakdong river nr in south korea were investigated in order to examine the pollution mechanism including the fate and transport of the contaminants and how much such sources may affect its main channel of water resource water samples were collected between 2007 and 2008 from 8 sites along a 510 km downstream transect of the nr and chemical and isotopic compositions of the water samples were evaluated to identify natural and anthropogenic sources contributing to the water chemistry of the nr the results showed that the major ion concentrations were mainly controlled by chemical weathering that occurred in the watershed in which a silicate weathering is more dominant than a carbonate weathering the 87sr 86sr ratios of the water samples were in a range from 0 71043 to 0 71520 within those of the mesozoic volcanogenic sedimentary rocks long developed in the watershed thereby supporting the fact that the water chemistry is governed by a chemical weathering the 34s values varied in a narrow range of 1 8 3 1 regardless of spatial and seasonal variations mass balance calculations indicated that the contributions of chemical weathering and anthropogenic sources during summer time increased along a downstream transect from 67 3 1 3 to 73 6 0 5 and from 6 0 to 15 7 respectively in contrast the contribution of chemical weathering during winter time decreased from 82 7 0 8 to 72 5 0 3 while anthropogenic contribution increased up to 22 2 these results indicated that the water chemistry of the nr was mainly caused by a chemical weathering followed by anthropogenic inputs and rainwater this study will provide baseline information for comparing the water quality issue before and after the implementation of the four rivers restoration project of south korea

chemical dynamics of the st lawrence riverine system δdh2o δ18oh2o δ13cdic δ34ssulfate and dissolved 87sr 86sr chemical and stable isotope analyses of the st clair detroit niagara and st lawrence rivers st lawrence system and their tributaries show that the chemical and isotopic compositions of the waters are strongly controlled by the geology of their drainage basins tributaries draining the canadian shield have very low tds hco3 so42 ca2 mg2 no3 sr2 higher si and fetotal and high 87sr 86sr ratios 0 710 0 713 the grand and thames rivers that drain paleozoic limestones dolostones and evaporites are characterized by opposite attributes the st lawrence and the tributaries draining the canadian appalachians fall between these two endmembers the st clair detroit and niagara rivers do not show any pronounced seasonal variations in major component chemistry due to buffering by the great lakes in contrast pronounced seasonal variations characterize the lower st lawrence mainly because of significant tributary inputs into the overall water budget the d and 18o in the st lawrence range from 60 9 to 44 5 and from 8 5 to 6 1 smow respectively much heavier than the comparative values measured for the tributaries 92 8 to 58 3 and 13 1 to 8 5 this is a consequence of evaporative loss that over the residence time of water of 102 years equals about 7 of the water volume in the great lakes the strontium and sulfur isotopic values for the st lawrence system are relatively uniform with measured values from 0 70927 to 0 71112 for 87sr 86sr and from 4 3 to 5 6 for sulfate 34s their seasonal variations are also minor the strontium and sulfur fluxes of the st lawrence river are calculated to be 7 84 108 and 1 09 1011 mol a respectively the relative contributions of the great lakes tributaries and other sources to these fluxes are 73 16 11 for strontium and 64 13 23 for sulfur isotopic composition of dissolved inorganic carbon 13cdic in the st lawrence system ranges from 4 7 to 0 7 considerably heavier than the values for the tributaries 16 5 to 6 7 the light 13cdic values for the tributaries suggest that co2 from bacterial respiration plays an important role in the isotopic composition of riverine dic however in the main stem river s this bacterial signal is masked by isotopic equilibration with atmospheric co2 due to the long residence time of water in the great lakes seasonally the main stem river s have heavier 13c values in the fall than in the spring a consequence of preferential 12c consumption by photosynthetic plants in the epilimnion of the great lakes during the growth season in the down stream portion of the st lawrence river influx of isotopically light tributary waters causes progressive 13c depletion from 1 3 to 2 0 and 1 4 to 3 0 in the fall and spring respectively the total dic carbon flux of the st lawrence river is calculated to be 3 9 1011 mol a mass balance calculations show that the relative contributions of the great lakes tributaries decay of organic matter exchange with the atmosphere and dissolution of carbonates to this total dic flux are 81 13 2 6 10 in the spring and 83 15 2 4 0 in the fall respectively

silicate weathering and co2 consumption deduced from the seven chinese rivers originating in the qinghai tibet plateau abstract we present river chemical data for the seven chinese rivers the jinsha jiang yalong jiang min jiang dadu he lancang jiang nu jiang and huang he originating in the qinghai tibet plateau our sampling locations are near sites where the seven rivers flow down the plateau water samples were collected in both high water periods summer and low water periods winter our study shows that most of the ca mg and hco 3 in the seven rivers are derived from the carbonate weathering and only small fractions 10 of the cations are derived from silicate weathering the chemical erosion rates of silicate and carbonate range from 1 1 mm ka 1 to 3 4 mm ka 1 and from 7 5 mm ka 1 to 29 9 mm ka 1 respectively the long term co 2 consumption by silicate weathering in the seven chinese river basins ranges from 0 7 10 5 mol km 2 a 1 to 3 7 10 5 mol km 2 a 1 based on our analysis of chemical data from the seven chinese rivers and the previously published data of the ganges brahmaputra and indus the main ten rivers originating in the himalaya and qinghai tibet plateau consume 328 10 9 mol a 1 of atmospheric co 2 this is only 3 8 of the co 2 consumption derived from global silicate weathering 8700 10 9 mol a 1 indicating that the chemical weathering of the himalaya and qinghai tibet plateau makes a very small contribution to the reduction of the global atmospheric co 2 concentration

chemical weathering and associated co2 consumption in six major river basins south korea abstract we report the chemical strontium sr and sulfur s isotopic compositions of water samples collected from six major south korean rivers to investigate seasonal and spatial variations in water chemistry and to estimate the chemical weathering rates and associated co 2 consumption overall the chemical compositions of river water exhibited significant temporal and spatial variations the magnitude of which varied depending on river size and geology the 87 sr 86 sr ratios and 34 s values of the rivers varied only spatially in close relation to basin lithology a mass balance calculation indicated that the dissolved loads of the six rivers were controlled by atmospheric 4 3 18 4 anthropogenic 6 0 27 2 and chemical weathering inputs 66 1 83 3 the average rates of carbonate weathering by sulfuric scw and carbonic acids ccw and silicate weathering by sulfuric ssw and carbonic acids csw were 4 50 and 11 0 t km 2 yr and 5 77 and 10 8 t km 2 yr respectively the associated mean co 2 consumption rates by ccw and csw were 312 10 3 and 471 10 3 mol km 2 yr respectively the calculated chemical weathering rates were closely related to runoff and the associated co 2 consumption rates tended to be higher in summer than in winter this study highlights the role of sulfuric acid in chemical weathering suggesting that it should be carefully considered in studies of co 2 consumption rate

deformation of foamed rhyolites under internal and external stresses an experimental investigation the style of magma eruption depends strongly on the character of melt degassing and foaming depending on the kinetics of these processes the result can be either explosive or effusive volcanism in this study the kinetics of foaming due to the internal stresses of gas expansion of two types of obsidian have been investigated in time series experiments 2 min 24 h followed by quenching the samples the volumetric gas melt ratio has been estimated through the density measurements of foamed samples

on the volcanic waveguide an analytical solution for the sound field in a resonant magma conduit with depth dependent magma properties provides a versatile interpretative tool for the analysis of seismoacoustic signals generated by fluid processes in active volcanoes expressions are given for the acoustic field in the atmosphere and the seismic field in the ground radiated through the magma conduit vent and walls respectively a new source model allows the resonance in the conduit to be excited by the vertical fluid velocity at the bottom of the conduit this source model represents acoustic excitation induced by low frequency fluid oscillations or large volume fluctuations originating at depth the magma conduit is modeled as a three section duct with each section having a different density sound speed viscosity and dimension the modal structure of the coupled resonant system is retained as the sound field in the conduit propagates into the surrounding bedrock and the overlying atmosphere the source time function permits estimates of the total mass injected or removed from the magmatic system and the source spectrum acts as a band pass filter on the resonant modes of the conduit theoretical or empirical source functions can be used to drive the seismoacoustic wave field and the amplitude of the source velocity may be constrained by the ballistics of pyroclasts and the height of ash plumes the acoustic properties of the melt may be predicted from the temperature composition and flow conditions of the magma as a function of depth comparisons of synthetic waveforms and spectra with those of seismic and acoustic signals recorded on active volcanoes permit estimates of the conduit geometry density sound speed and attenuation properties of the melt and characterize the temporal and spectral features of the source function the ability to extract this information accurately and efficiently from seismic and acoustic data streams may permit near real time modeling of fluid driven processes in active volcanoes

characteristics of carbonate evaporite and silicate weathering in huanghe river basin a comparison among the upstream midstream and downstream abstract to systematically study chemical weathering in the entire huanghe river basin we divided the basin into three parts with significant differences in geology and climate we collected 38 water samples from the main channel and its main tributaries spread between the upstream above lanzhou midstream from lanzhou to huayuankou and downstream from huayuankou up to river mouth segments of the river the concentrations of major elements and h o isotopic compositions were obtained from the samples and the total dissolved solids tds and co2 consumption budget were calculated from the aggregated data of each of the three segments the results demonstrate that the tds are mainly derived from carbonate weathering in upper huanghe river evaporite dissolution is predominately occurred in the midstream and there is almost no additional contribution from rock weathering in the downstream an increasing trend of co2 consumption rate by silicate weathering is observed from 0 14 105 mol km2 yr in the upstream to 5 62 105 mol km2 yr in the downstream and the budget of co2 consumption by silicate weathering is estimated to be 26 2 109 mol yr in contrast the co2 consumption rate by carbonate weathering decreases from 3 04 105 mol km2 yr in the upstream to near zero in the downstream and the budget of co2 consumption is estimated to be 100 5 109 mol yr as a whole in the entire huanghe river basin the co2 consumption budget and tds yield are estimated to be 126 7 109 mol yr and 27 5 106 t yr respectively these results indicate that evaporite dissolution in the midstream is responsible for the high tds in the huanghe river basin while carbonate weathering in the upstream plays the most significant role in co2 consumption

earthquakes on dipping faults the effects of broken symmetry dynamic simulations of earthquakes on dipping faults show asymmetric near source ground motion caused by the asymmetric geometry of such faults the ground motion from a thrust or reverse fault is larger than that of a normal fault by a factor of 2 or more given identical initial stress magnitudes the motion of the hanging wall is larger than that of the footwall in both thrust reverse and normal earthquakes the asymmetry between normal and thrust reverse faults results from time dependent normal stress caused by the interaction of the earthquake generated stress field with earth s free surface the asymmetry between hanging wall and footwall results from the asymmetric mass and geometry on the two sides of the fault

scaling relations of strike slip earthquakes with different slip rate dependent properties at depth abstract empirical observations suggest that earthquake stress drop is generally constant to investigate the effect of rupture width on earthquake scaling relations we analyze synthetic seismicity produced by a 3d vertical strike slip fault model using two different profiles of frictional slip rate behavior below the seismogenic zone within the rate and state framework a relatively abrupt transition of the a b profile from velocity weakening to strengthening at the base of the seismogenic crust produces increasing slip and stress drop with increasing event size choosing a smoother transition allows large earthquakes to propagate deeper leading to similar slip length scaling but constant stress drop scaling our numerical experiments support the idea that the maintenance of constant stress drop across the entire range of observed earthquake magnitudes may be achieved by allowing coseismic slip to rupture to depths below the seismogenic layer

slip patterns and earthquake populations along different classes of faults in elastic solids numerical simulations of slip instabilities on a vertical strike slip fault in an elastic half space are performed for various models belonging to two different categories the first category consists of inherently discrete cellular fault models such are used to represent fault systems made of segments modeled by numerical cells that can fail independently of one another their quasi independence is assumed to provide an approximate representation of strong fault heterogeneity due to geometric or material property disorder that can arrest ruptures at segment boundaries the second category consists of models having a well defined continuum limit these involve a fault governed by rate and state dependent friction and are used to evaluate what types of property heterogeneity could lead to the quasi independent behavior of neighboring fault segments assumed in the first category the cases examined include models of a cellular fault subjected to various complex spatial distributions of static to kinetic strength drops and models incorporating rate and state dependent friction subjected to various spatial distributions of effective stress normal stress minus pore pressure the results indicate that gradual effective stress variations do not provide a sufficient mechanism for the generation of observed seismic response strong and abrupt fault heterogeneity as envisioned in the inherently discrete category is required for the generation of complex slip patterns and a wide spectrum of event sizes strong fault heterogeneity also facilitates the generation of rough rupture fronts capable of radiating high frequency seismic waves the large earthquakes in both categories of models occur on a quasi periodic basis the degree of periodicity increases with event size and decreases with model complexity however in all discrete segmented cases the models generate nonrepeating sequences of earthquakes and the nature of the large quasi periodic events is highly variable the results indicate that expectations for regular sequences of earthquakes and or simple repetitive precursory slip patterns are unrealistic the frequency size fs statistics of the small failure episodes simulated by the cellular fault models are approximately self similar with b 1 2 and ba 1 where b and ba are b values based on magnitude and rupture area respectively for failure episodes larger than a critical size however the simulated statistics are strongly enhanced with respect to self similar distributions defined by the small events this is due to the fact that the stress concentrated at the edge of a rupture expanding in an elastic solid grows with the rupture size when the fault properties e g geometric irregularities are characterized by a narrow range of size scales the scaling of stress concentrations with the size of the failure zone creates a critical rupture area terminating the self similar earthquake statistics in such systems events reaching the critical size become on the average unstoppable and they continue to grow to a size limited by a characteristic model dimension when however the system is characterized by a broad spectrum of size scales the above phenomena are suppressed and the range of apparent self similar fs statistics is broad and characterized by average b and ba values of about 1 the simulations indicate that power law extrapolations of low magnitude seismicity will often underestimate the rate of occurrence of moderate and large earthquakes the models establish connections between features of fs statistics of earthquakes range of self similar regimes local maxima and structural properties of faults dominant size scales of heterogeneities dimensions of coherent brittle zones the results suggest that observed fs statistics can be used to obtain information on crustal thickness and fault zone structure

frictional weakening and slip complexity in earthquake faults previous work has shown that velocity weakening friction produces slip complexity in simple dynamical models of earthquake faults carlson and langer 1989 here i show that a different type of dynamical instability caused by slip weakening friction also produces slip complexity the deterministically chaotic slip complexity produced by slip weakening friction in a simple one dimensional model is studied and the scaling of the distribution of sizes of events with the parameters in the model examined in addition a possible physical origin of frictional weakening is examined through a very simplified mathematical representation of a physical process proposed by sibson 1973 whereby frictional heating causes an increase in pore fluid temperature and pressure thereby reducing the effective normal stress and friction the two different types of frictional weakening are derived from two opposing limits with slip weakening occurring when the dissipation of heating is slow compared to the rupture timescale as lachenbruch 1980 has shown while velocity weakening is shown to occur when the dissipation is fast compared to the rupture timescale since both end member cases of frictional weakening are seen to produce slip complexity slip complexity is argued to be a generic feature of frictional weakening and elastodynamics on a fault

temporal evolution of a magmatic dike system inferred from the complex frequencies of very long period seismic signals 1 i present a detailed description of temporal variations in the complex frequencies of very long period vlp events observed in association with an earthquake swarm that occurred beneath hachijo island japan the individual vlp signals show simple decaying harmonic oscillations with periods near 10 s and they last for about 300 s the vlp activity began on 20 august 2002 and continued until 2 april 2003 spectral analysis of the vlp waveforms identifies two spectral peaks of which the complex frequencies show systematic temporal variations at the beginning of the vlp activity the q values of both the peaks show increasing trends from roughly 15 to 35 in the time period between 22 and 26 august the frequency of one peak shows a decreasing trend from 0 1 to 0 09 hz while the frequency of the other peak shows an increasing trend from 0 128 to 0 136 hz during this time after these systematic variations the frequencies and q values of the two peaks remain roughly constant waveform simulations based on a fluid filled crack model indicate that the observed systematic temporal variations can be reasonably explained by gradual expansion of a crack containing a basalt gas mixture the roughly constant frequencies and q values of the two peaks after these systematic variations suggest that the magmatic dike persistently existed beneath hachijo island for more than 6 months mass and heat advection is required to sustain the dike system implying magmatic flow and convection in the dike and magma chamber beneath this island

microlites and nanolites in rhyolitic glass microstructural and chemical characterization we used transmission electron microscopy tem and scanning electron microscopy sem to study magmatic crystals in the ben lomond rhyolite lava dome taupo volcanic center new zealand using tem and sem to investigate the size distributions of these crystals we identified three size populations microphenocrysts 1 2 m wide microlites 0 6 m wide and smaller crystals 0 6 m wide which we term nanolites the predominant mineral phases of the microlites and nanolites are augites pigeonites and hypersthenes the compositions and microstructures within these pyroxenes indicate disequilibrium crystallization at approximately 850 900 c and undercoolings as high as 300 c from equilibrium crystallization temperatures complex microstructures resulting from subsolidus reactions in augite and pigeonite are consistent with moderate cooling rates within the upper obsidian layer of the ben lomond rhyolite dome this study demonstrates the existence of sub micron magmatic crystals in a rhyolite and illustrates the potential of tem to provide unique information about the crystallization and cooling histories of glassy volcanic rocks

hyperquenched volcanic glass from loihi seamount hawaii abstract explosive submarine basaltic eruptions occurring in water depths of several kilometres commonly result in the formation of layered volcaniclastic deposits in order to quantify the cooling of such volcaniclastics we have identified and separated two types of glassy fragments from these deposits on loihi seamount 1 fine 30 80 m limu o pele bubble wall fragments and 2 coarser 0 8 1 2 mm dense angular fragments these pristine basaltic glasses have been subjected to differential scanning calorimetry dsc from room temperature up to temperatures above their glass transition heat capacity c p in j g 1 k 1 data reveal glassy and liquid regimes separated by clear hysteresis behaviour within the glass transition the transient c p in the glass transition interval exhibits a deep trough before the peak indicating very high cooling rates it is a classic feature of so called hyper quenching having been observed in dsc experiments on glasses produced using the splat quench d b dingwell p courtial d giordano and a r l nichols viscosity of peridotite liquid earth and planetary science letters 226 1 2 127 138 2004 and cascade fibre spinning y z yue j d christiansen and s l jensen determination of the fictive temperature for a hyperquenched glass chemical physics letters 357 1 2 20 24 2002 techniques the trough is deepest for the limu o pele fragments energy matching methods developed for the estimation of cooling rates for such glasses yield a rate of 10 5 31 k s 1 for the cooling of the fine sieve fraction of limu glass on the sea floor at loihi thus limu o pele volcaniclastics believed to be formed during mild submarine pyroclastic eruptions have experienced the fastest cooling of any natural volcanic glass measured to date such extreme cooling rates are likely to impact on many chemical and physical aspects of the stability of these glasses on the sea floor as well as their use as proxies for field variables of the earth s physical state and as monitors of the efficiency of chemical lithosphere hydrosphere exchange

the influence of trace amounts of water on the viscosity of rhyolites as a major volatile in volcanic systems water has a significant influence on the rheological properties of silicic magmas this is especially so at minor water contents relevant to the emplacement of silicic lavas to investigate the influence of water on the viscosity of natural rhyolitic obsidians a novel strategy has been adopted employing parallel plate and micropenetration techniques viscosities have been determined on three types of material a raw water bearing obsidians b remelted 1650 c 1 atm degassed glasses of the obsidians and c hydrothermally hydrated 1300 c 3 kbar obsidians ten natural rhyolitic obsidians peraluminous calc alkaline and peralkaline were employed seven originated from lava flows and contained 0 2 wt h2o two samples were f rich from pyroclastic successions and one was an obsidian cobble with 1 5 wt water also associated with pyroclastic units melt compositions and water contents were stable during viscometry the measured decreases in activation energies of viscous flow and viscosity with small amounts of water are much greater than the shaw calculation scheme predicts in addition a marked non linear decrease in exists with increasing water content in contrast to the case for peralkaline rhyolites 0 1 0 2 wt water decreases activation energies significantly up to 30 for calc alkaline compositions these results have important implications for the ease of near surface degassing of silicic magmas during emplacement and permit the testing of calculational models for viscosity largely based on synthetic systems

stability of foams in silicate melts bubble coalescence and the spontaneous disruption of high porosity foams in silicate melts are the result of physical expulsion of interpore melt syneresis leading to bubble coalescence and diffusive gas exchange between bubbles melt expulsion can be achieved either along films between pairs of bubbles or along plateau borders which represent the contacts between 3 or more bubbles theoretical evaluation of these mechanisms is confirmed by experimental results enabling us to quantify the relevant parameters and determine stable bubble size and critical film thickness in a foam as a function of melt viscosity surface tension and time foam stability is controlled primarily by melt viscosity and time melt transport leading to coalescence of bubbles proceeds along inter bubble films for smaller bubbles and along plateau borders for larger bubbles thus the average bubble size accelerates with time in silicate melts the diffusive gas expulsion out of a region of foam is effective only for water and even then only at small length scales as the diffusion of co2 is negligible the results of our analyses are applicable to studies of vesicularity of lavas melt degassing and eruption mechanisms

pyroclastic surges and flows from the 8 10 may 1997 explosive eruption of bezymianny volcano kamchatka russia the 8 10 may 1997 eruption of bezymianny volcano began with extrusion of a crystallized plug from the vent in the upper part of the dome progressive gravi tational collapses of the plug caused decompression of highly crystalline magma in the upper conduit leading at 13 12 local time on 9 may to a powerful vertical vulcanian explosion the dense pyroclastic mixture col lapsed in boil over style to generate a pyroclastic surge which was focused toward the southeast by the steep walled 1956 horseshoe shaped crater this surge with a temperature 30 km 2 with deposits as much as 30 cm thick and extending 7 km from the vent the surge deposits comprised mas sive to vaguely laminated gravelly sand md 1 2 to 3 7 sorting 1 2 to 3 of poorly vesiculated andesite mean density 1 82 g cm 3 vesicularity 30 vol sio2 content 58 0 wt the deposits with a volume of 5 15 106 m3 became finer grained and better sorted with distance the maximal diameter of juvenile clasts decreased from 46 to 4 cm the transport and deposition of the surge over a snowy landscape generated extensive lahars which traveled 30 km immediately following the surge semi vesiculated block and ash flows were emplaced as far as 4 7 km from the vent over time the juvenile lava in clasts of these flows became progres sively less crystallized apparently more silicic 59 0 to 59 9 wt sio 2 and more vesiculated density 1 64 to 1 12 g cm 3 vesicularity 37 to 57 vol at this stage the eruption showed transitional behavior with mass di vided between collapsing fountain and buoyant column the youngest pumice and ash flows were accompanied by a sustained sub plinian eruption column 14 km high from which platy fallout clasts were deposited 59 7 sio 2 density 1 09 g cm 3 vesicularity 58 vol the explosive activity lasted about 37 min and produced a to tal of 0 026 km 3 dense rock equivalent of magma with an average discharge of 1 2 104 m3 s 1 a lava flow 200 m long terminated the eruption the evolutionary succession of different eruptive styles during the explo sive eruption was caused by vertical gradients in crystal lization and volatile content of the conduit magma which produced significant changes in the properties of the erupting mixture

relative source locations of continuous tremor before and after the subplinian events at shinmoe dake in 2011 volcano monitoring systems are not always ready to resolve signals at the onset of eruptive activity this study makes use of stations installed later to calibrate the performance of the stations that had been operated before the eruption seven stations recorded continuous volcanic tremor before and during the subplinian eruptions of shinmoe dake japan in 2011 we estimated the source locations of the tremor using the amplitude distribution the stability of the analysis was obtained by careful selection of time windows in which signals from a single source are dominated the site effects and the regional attenuation factor were evaluated using tremor recorded after the major eruptions by a dense seismic array and a good number of stations a tremor source changed its depth beneath the crater for one week before the major eruption rising from a depth of a few kilometer to the water layer three times each of which occurred following shallow inflation and minor eruptions it is interpreted as migration of gas probably with magma which further transported heat to the water layer and triggered the subplinian eruptions

sulphur isotopic and chemical compositions of the natural waters in the chuncheon area korea abstract the contribution of chinese sources to the acid deposition in neighbouring countries in far east asia has been disputed this study is to examine the isotopic composition of the s in the natural waters in the chuncheon area to see if the isotopic composition can be an indicator of the pollution sources in the area meteoric water sampled between september 2000 and july 2001 and surface water sampled in december 2000 and april 2001 in the area were collected to examine their chemical and isotopic compositions the ph values of the meteoric water lie between 4 02 and 6 89 but mostly lower than 5 6 indicating considerable acid deposition the ph of the surface water is generally higher than that of the atmospheric water factor analysis on the concentrations of the dissolved components suggests that the surface water chemistry depends principally on the chemistry of the atmospheric water the dissolution of carbonate minerals and silicate water interaction plays a rather minor role in affecting the water chemistry 18 o and d of all the natural water samples align fairly well along the global meteoric water line the 34 s of the dissolved so4 in the meteoric water has values ranging from 3 4 to 8 2 showing little seasonal difference the contribution from sea salt to the total atmospheric s is estimated to be less than 10 the 34 s of the anthropogenic s in the chuncheon atmosphere is calculated to be 2 5 to 7 2 which partly overlaps the reported values of s in chinese coal chinese rainfall and japanese fallout appropriate tracking and quantitative estimation of the contribution from possible pollution sources to the local s concentrations requires more information on the isotopic compositions of the potential pollution sources the 34 s of the dissolved so4 in the surface water has values ranging from 3 2 to 6 2 which is a little narrower than that of the meteoric water the 34 s and the concentration range of the dissolved so4 in the stream water the results from factor analysis on the compositional variables and observations from geological field work suggest that most so4 comes from the meteoric input and that the 34 s of the surface water may be utilized for the investigation of tracing and identifying the sources of the atmospheric pollutant s in the study area

an experimental facility for the investigation of magma fragmentation by rapid decompression a special experimental facility has been developed to investigate the fragmentation of vesicular magma undergoing rapid decompression the facility operates in a regime similar to that of shock tubes and at temperatures up to 950 c and pressures up to 200 bar cylindrical samples diameter ca 17 mm length ca 50 mm undergo rapid decompression in a high temperature high pressure section of the facility following the disruption of a diaphragm separating that section from a low pressure low temperature section actual vesicular magma samples have been experimentally fragmented at elevated temperatures and pressures corresponding to those observed during explosive volcanic eruptions and the resulting pyroclastics have been photographically resolved in flight and collected for physical characterization the results of these experiments show that the rapid decompression of highly viscous vesicular magma can generate pyroclastic ejecta via rapid and complete fragmentation of magma at high temperature this new fragmentation facility is presented as a tool for experimental volcanology under well constrained conditions