role of geological inheritance in australian beach morphodynamics the australian coast contains 10 685 beaches which occupy 49 of the 30 000 km coast and average 1 37 km in length their relatively short length is largely due to the presence of bedrock calcarenite and laterite which form boundaries to many of the beaches as well as occurring as rocks reefs and islands along and off the beaches this geological inheritance plays a major role in australian beach systems determining their length and through wave refraction and attenuation influencing beach location shape type morphodynamics and circulation which in turn influence sediment transport and the backing dune and barrier systems this paper uses a database covering every australian beach to review the role of headlands rocks and reefs on australian beaches major effects are the short average beach length reduction in breaker height resulting in lower energy beach types wave refraction resulting in increased beach curvature the presence of topographic rips on moderate and higher energy beaches and megarips during high wave conditions and the interruption of and or trapping of longshore sand transport leading to beach rotation

the cooling of frontal flow ramps a calorimetric study on the rocche rosse rhyolite flow lipari aeolian islands italy relaxation geospeedometry using differential scanning calorimetry dsc has been applied to quantify the cooling history across the glass transition of flow ramps at the front of the calcalkaline rhyolite rocche rosse flow of lipari aeolian islands italy modelled cooling rates for the obsidian retrieved from two profiles range between 0 2 and 0 03 k min 1 cooling at the flow front appears to be dominated by conductive heat loss of individual flow ramps forming individual cooling units cooling rates of tens of kelvins per day appear to have controlled the last stage of viscous deformation before the entire flow came to rest it is inferred that cooling rates slower than those modelled are required to sustain flow in highly viscous rhyolitic lavas

cooling rates of lunar orange glass beads abstract it is widely accepted that the apollo 17 orange glass beads are of volcanic origin the degree of degassing of the glass beads depends on their cooling rates so the estimation of volatile contents in the parental magmas of these lunar pyroclastic glasses also depends on the cooling rates the cooling rate can be estimated using the calorimetric properties of the glass across the glass transition in this study a series of heat capacity measurements were carried out on hand picked lunar volcanic orange glass beads during several cycles of heating to temperatures above their glass transition using a differential scanning calorimeter the cooling rate of orange glass beads sample 74220 867 was calculated to be 101 k min using the correlation between glass cooling rates and fictive temperatures estimated from their heat capacity temperature paths this cooling rate is close to the lower end of the range that best fits the diffusion profiles of several volatile species in the glass beads and at the upper end of the cooling rate range recorded in glasses quenched subaerially on earth the cooling rate is likely to be controlled by the cooling environment cooling medium such that the lunar volcanic glass beads could have been cooled in a gaseous medium released from volcanic eruptions on the moon but not during free flight in vacuum the existence of a gas medium suggests in turn that there may have been at least a short lived or episodic atmosphere on the early moon at around 3 5 ga

holocene coastal dune formation in southern australia a case study abstract the 14 500 km long southern australian coast is exposed to high energy wave and wind regimes which have mobilized shelf derived sediments to produce extensive holocene shoreface deposits the 8000 km of sandy coast are backed by over 2000 km 2 of holocene dunes of varying degrees of stability in places dune deposition above present sea level accompanied the post glacial marine transgression commencing as early as 10 ka b p and has continued episodically to the present day the dunes are widespread in extent but vary in type size and evolution the oldest and often most extensive primary dune fields accompanied the post glacial marine transgression they occurred and in some places continue to form in areas of high wave and wind energy and abundant sand supply many of these systems exhausted their sediment supply by mid holocene and remain as stranded clifftop dunes where sand ramps were eroded or as eroding barriers secondary phases of dune activity occurred on moderate to high energy coasts following an initial period of post stillstand barrier progradation diminished sediment supply resulted in shoreline erosion and secondary dune formation the location size and evolution both of dunes types is largely controlled by the breaker wave regime which in turn influences the rate and volume of sediment supply beach morphodynamics and resulting aerodynamic boundary conditions and foredune erosion a study of dune formation along the 3700 km long south australian coast provides a basis for an overview of dune formation throughout southern australia

giant gas bubbles in a rheomorphic vent fill at the las canadas caldera tenerife canary islands during rheomorphism subsequent to fallout deposition a portion of the densely welded fallout of the la grieta member flowed back into the vent from where it was erupted while the rest of it flowed down the outer slopes of the las canadas caldera in tenerife the welded fallout and conduit vent structure are physically connected and constitute a rare example of this type of deposits rooted to its feeder conduit and exposed in the caldera wall the lower part of the vent filling rheomorphic rocks shows gas bubbles and cavities that increase in size up to 4 m down vent bubbles are deformed against other bubbles against the steep vent walls flattened parallel to the flow foliation planes and elongated parallel to the flow lineation and flow fold axes the preservation of such giant bubbles rather than their formation seems to be a pretty unique feature of the phonolitic products investigated here and it is likely the result of the combination of factors that acted to preserve in the surrounding of the glass transition interval the sealing and the late stage cooling of a pressurized system in addition strain drop at the base of the vent filling rheomorphic flow caused by flow stopping against vertical vent walls may have promoted rapid gas exsolution and the formation of large bubbles

the southern oscillation index wave climate and beach rotation short embayed beaches bounded by headlands are a common feature along the southern and central coastline of new south wales australia many of these embayed beaches have experienced severe erosion at their southern end over the last decade previous studies have suggested that this erosion may be the result of an oscillatory medium term phenomenon known as beach rotation the present study was undertaken with the objectives of 1 establishing definitive links between the southern oscillation index soi wave climate and beach rotation and 2 determining the physical processes governing beach rotation data from two similar new south wales beaches were analysed using time series analysis techniques and image processing techniques using argus video images in this study the results indicate that the northern end of this type of beach accretes during el nino phases while the southern end erodes resulting in a net clockwise rotation of the beach the opposite occurs during la nina phases resulting in a net anti clockwise rotation of the beach the beach response at the northern and southern ends lags soi trend shifts by 3 and 17 months respectively waves are predominantly incident from the southeast during both el nino and la nina phases offshore wave height is positively correlated with the soi while offshore wave direction is negatively correlated with the soi on average the number of storms per year doubles from el nino to la nina based on these links between beach width fluctuations soi and incident wave conditions a conceptual model of beach rotation is presented the model describes the combinations of cross shore and longshore sediment transport and hydrodynamic processes that are expected to result in the observed clockwise and anti clockwise beach rotation during el nino and la nina phases respectively

cooling dynamics of spatter fed phonolite obsidian flows on tenerife canary islands abstract relaxation geospeedometry has been applied to two series of clastogenic obsidian flows on tenerife to determine their thermal history across the glass transition the phonolite flows investigated were both generated by lava fountaining activity followed by rheomorphism of the deposits the detailed sampling resolution within the two series enabled an accurate quantification of their thermal history cooling rates within the investigated spatter fed flows vary over more than two orders of magnitude the highest cooling rates of 0 39 k min were modeled for the central vesiculated part of one flow the dense basal obsidian layers of both flows were cooled at substantially lower rates of 0 0042 and 0 0028 k min respectively there appears to be an influence of in situ vesiculation processes on the thermal budget of the investigated flows in addition the slow cooling rates for the basal portions of both flows seem to be associated with a stage of thermal buffering continual advective heat transport of hot material along a basal shear plane may sustain elevated temperatures associated with quasi isothermal annealing within this decollement numerical simulations based on conductive heat loss concepts fail to resolve the cooling history quantified through relaxation geospeedometry for the investigated flows the effects of vesiculation and thermal annealing on the cooling behavior of the clastogenic flows across the glass transition are discussed in the light of these new data in addition viscometric data on these phonolites are used to correlate the known cooling rates to viscosities at the glass transition

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

welding and rheomorphism of phonolitic fallout deposits from the las canadas caldera tenerife canary islands the las canadas caldera is a nested collapse caldera formed by the successive migration and collapse of shallow magmatic chambers among the pyroclastic products of this caldera are phonolitic fallout deposits that crop out in the caldera wall and on the extracaldera slopes these deposits exhibit an uninterrupted facies gradation from nonwelded to lava like and record continuous volcanic deposition densely welded and lava like facies result from the extreme attenuation and complete homogenization of juvenile clasts that destroy original clast outlines and any evidence of fallout deposition agglutination contributes significantly to the final degree of flattening observed in the welded facies after deposition rheomorphic flowage occurs emplacement temperatures for one of the welding sequences are calculated from magmatic temperatures and a model of tephra cooling during fallout results are 486 c for the nonwelded facies and 740 c for the moderately welded facies for the same welding sequence a cooling time between 25 and 54 days is estimated from published experimental and computational data as the possible duration of welding and rheomorphism following deposition and agglutination the lava like pyroclastic facies had the rheological properties of viscous lavas and flowed down the outer slopes away from the caldera some lava like masses detached from proximal areas to more distal regions during deposition the eruptive style evolved from plinian fallout to fountain fed spatter deposition this evolution was accompanied by a decrease in explosive power and a lower height of the eruptive column which produce higher emplacement temperatures and more effective heat retention of pyroclasts

evaluation of a relaxation geospeedometer for volcanic glasses abstract the cooling of silicate melts influences the character of volcanic processes primarily through the effect of temperature on melt viscosity but also through the derivative thermal properties expansivity and heat capacity if the cooling rates of volcanic facies can be established then the undoubtedly complex processes of erupting cooling and degassing magmas can be more readily understood the frozen structure of every glass volcanic or synthetic is influenced by the previous cooling history moreover the relaxation of the glass structure back to equilibrium during reheating across the glass transition is also dependent on the quenched in structure and thus can be used to determine the cooling rate history in this study differential scanning calorimetry dsc measurements have been used to determine the enthalpic relaxation of four volcanic glasses each glass has been heated at known heating rates in the calorimeter to temperatures above the glass transition interval the first heating of the glass involves the relaxation of the structure frozen in during the volcanic cooling subsequent controlled heating and cooling in the calorimeter enables the determination of a set of kinetic parameters which can be used to model the heat capacity curves by modeling the transient values of heat capacity across the glass transition interval the relaxation of enthalpy and the volcanic cooling rate across the glass transition interval can be obtained from our study we can demonstrate four different cooling rates for volcanic glasses over a range of three orders of magnitude from 4 c min 1 to 2 c day 1 we propose that the enthalpic relaxation of silicate melts can be applied as a geospeedometer to the study of volcanic rocks from a variety of occurrences

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

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

high and highly variable cooling rates during pyroclastic eruptions on axial seamount juan de fuca ridge abstract we present a calorimetric analysis of pyroclastic glasses and glassy sheet lava flow crusts collected on axial seamount juan de fuca ridge ne pacific ocean at a water depth of about 1400 m the pyroclastic glasses subdivided into thin limu o pele fragments and angular blocky clasts were retrieved from various stratigraphic horizons of volcaniclastic deposits on the upper flanks of the volcanic edifice each analysed pyroclastic sample consists of a single type of fragment from one individual horizon the heat capacity c p was measured via differential scanning calorimetry dsc and analysed using relaxation geospeedometry to obtain the natural cooling rate across the glass transition the limu o pele samples 1 mm grain size fraction and angular fragments 0 5 mm grain size fraction exhibit cooling rates of 10 4 3 to 10 6 0 k s 1 and 10 3 9 to 10 5 1 k s 1 respectively a coarser grain size fraction 2 mm for limu o pele and 1 mm for the angular clasts yields cooling rates at the order of 10 3 7 k s 1 the range of cooling rates determined for the different pyroclastic deposits presumably relates to the size or intensity of the individual eruptions the outer glassy crusts of the sheet lava flows were naturally quenched at rates between 63 k s 1 and 10 3 k s 1 by comparing our results with published data on the very slow quenching of lava flow crusts we suggest that 1 fragmentation and cooling appear to be coupled dynamically and 2 ductile deformation upon the onset of cooling is restricted due to the rapid increase in viscosity lastly we suggest that thermally buoyant plumes that may arise from rapid heat transfer efficiently separate clasts based on their capability to rise within the plume and as they subsequently settle from it

influence of cooling on lava flow dynamics experiments have been carried out to determine the effects of cooling on the flow of fluids with strongly temperature dependent viscosity radial viscous gravity currents of warm glucose syrup were erupted at constant rate into a flat tank filled with a cold aqueous solution cold viscous fluid accumulates at the leading edge altering the flow shape and thickness and slowing the spreading the flows attain constant internal temperature distributions and bulk viscosities the value of the bulk viscosity depends on the peclet number which reflects the advective and diffusive heat transport properties of the flow the flow skin viscosity which reflects cooling and the eruption viscosity our results explain why most lava flows have bulk viscosities much higher than the lava eruption viscosity the results can be applied to understanding dynamic lava features such as flow front thickening front avalanches and welded basal breccias

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

cooling process recorded in subglacially erupted rhyolite glasses rapid quenching thermal buffering and the formation of meltwater the thermal histories of two subglacial rhyolite glasses from torfajokull complex of south central iceland have been determined from changes in the relaxation of enthalpy in the calorimetric glass transition interval heat capacity measurements of bulk glass samples from rau ufossafjoll sample number js 1 1 and blahnukur sample number js 2 1 by differential scanning calorimetry show marked differences in the temperature of the onset of glass transition tg on reheating the average tg is 750 k for js 1 1 whereas it is 850 k for js 2 1 these differences in the onset of tg are related to quench rate through considerations of the activation energy and timescales for structural relaxation modeled using the kohlrausch williams watt function multiple glass samples from the two torfajokull locations recover different average values and distributions of a fictive temperature t f which we interpret in terms of differences in the thermal histories of the glasses in both glass samples the range of fictive temperatures and by implication apparent cooling rates is lower than those estimated for a glass rapidly quenched by contact with cold glacial melt water and requires that the glass was annealed at temperatures in the glass transition interval associated with relaxation times of the order of 1000 10 000 s the complex cooling histories of the torfajokull samples show that the products of subglacial eruptions may be held at elevated temperatures for several hours and as a result may drive vigorous convection in the ice bound vaults above erupting rhyolite deposits

temperature dependent thermal expansivities of silicate melts the system anorthite diopside abstract the temperature dependent thermal expansivities of melts along the join anorthite diopside have been determined on glassy and liquid samples using a combination of calorimetry dilatometry and pt double bob archimedean densitometry supercooled liquid volumes and molar thermal expansivities were determined using scanning calorimetric and dilatometric measurements of properties in the glass region and their behavior at the glass transition the extraction of low temperature liquid molar expansivities from dilatometry calorimetry is based on an assumed equivalence of the relaxation of volume and enthalpy at the glass transition using a method developed and tested by webb et al 1992 this method corrects for transient effects at the glass transition which can lead to serious overestimates of liquid thermal expansivity from peak values superliquidus volumes were determined using double pt bob archimedean densitometry at temperatures up to 1650 c the resulting data for liquid volumes near glass transition temperatures 810 920 c and at superliquidus temperatures 1400 1650 c are combined to yield thermal expansivities over the entire supercooled and stable liquid range the molar expansivities are in general temperature dependent the temperature dependence of thermal expansivity increases from anorthite to diopside composition the thermal expansivity of anorthite is essentially temperature independent whereas that of diopside decreases by 50 between 800 and 1500 c with the consequence that the thermal expansivities of the liquids in the anorthite diopside system converge at high temperature

senonian basin inversion and rejuvenation of rifting in africa and arabia synthesis and implications to plate scale tectonics abstract the late paleozoic to tertiary stratigraphic record of much of the african plate reflects the effects of continental rifting and passive margin development several short lived but widespread and tectonically important compressional or wrench dominated events occurred however during the permian to recent evolution of africa we focus here on the best documented of these events which occurred during the late santonian at that time older sedimentary basins mostly ene wsw trending were folded and inverted including some basins along the tethyan margin from morocco to the syrian arc and the intraplate benue southern chad basins and the lugh mandera basin in oman ophiolites were obducted following the santonian tectonism an extensive phase of rifting occurred in central and north africa and northern arabia spanning from campanian to maastrichtian or paleocene times rejuvenation or acceleration of subsidence occurred in several basins located along the tethyan margin along the atlantic and indian ocean margins as well as within the intraplate domain rifting was sometimes accompanied by magmatic activity especially in offshore northern libya and along the indian ocean margin compressional deformations rejuvenated or developed by latest maastrichtian times along the tethyan margin and locally within the intraplate domain one of the most remarkable attributes of the santonian tectonic event which we consider representative of the major trans african stress field changes is the rapidity with which the change was reflected stratigraphically across north and central africa and its short duration the cause of the santonian compressional event is directly linked to the change in poles of rotation for the opening of the atlantic at 83 85 ma the end of the cretaceous normal magnetic quiet zone this was also synchronous with the obduction of ophiolites along the northeast margin of arabia oman the onset of separation between india and madagascar with formation of the mascarene oceanic basin and the development of the european alpine chain we interpret these phenomena as causally related aspects of a global tectonic event the santonian compressional event as well as the campanian maastrichtian rifting event and the end cretaceous compressional event illustrate the critical connection between intraplate tectonic histories and processes occurring at sometimes very distant plate boundaries

the thermal history of a spatter fed lava flow the 8 ka pantellerite flow of mayor island new zealand the thermal history of the 8 ka spatter fed lava flow of mayor island new zealand has been investigated via relaxation geospeedometry cooling rates extant during the vitrification of the clastogenic pantellerite flow have been quantified cooling rates modelled for two obsidian layers at the top and the base of the flow vary over four orders of magnitude the flow base defined by a lower obsidian layer shows a gradual increase in cooling rates from 0 00072 k min adjacent to the crystalline core of the flow to 0 017 k min at the contact to a basal crumble breccia cooling rates of flow ridges formed by an upper obsidian layer vary between 0 001 and 6 k min based on field observation and thermal modelling cooling rates of kelvins to tens of kelvins per day for both upper and lower obsidians are difficult to interpret as simple cooling processes instead we propose a thermal history involving thermal annealing as an alternative explanation for these slow effective cooling rates such thermal annealing appears to have facilitated welding and rheomorphism of the spatter deposit leading to the development of a coherent lava sheet based on the results obtained here we present a quantitative scenario of the thermal history during the final stages of flow emplacement as a contribution to understanding the rheology of rheomorphic spatter deposits associated with explosive peralkaline rhyolitic volcanism and briefly address the hazard potential of such deposits

cooling rates of hyaloclastites applications of relaxation geospeedometry to undersea volcanic deposits glass fragments from three different hyaloclastites have been used to evaluate the range of cooling rates experienced by undersea volcanic deposits we found that the glass fragments retain structures with a range of apparent quench rates from 25 to 0 15 k min 1 the most rapid cooling rates are interpreted to be those resulting from cooling of the lava near the water interface simple conductive cooling models produce a range of quench rates comparable to those of the more rapidly cooled samples the very slow apparent quench rates are unlikely to result from simple linear cooling through the glass transition because of the onset of crystallization instead they are indicators of a more complex thermal history that involves the annealing of glasses at temperatures within the glass transition interval for a dwell time sufficient to allow the relaxation of the glass to lower temperature structures the thermal history recorded in these samples illustrates the complexity of eruptive processes and demonstrates that quench rates for natural glasses retain information relevant to more complex cooling models

lava and ice interaction at stratovolcanoes use of characteristic features to determine past glacial extents and future volcanic hazards structures resulting from lava and ice interaction are common at glaciated stratovolcanoes during summit eruptions at stratovolcanoes meltwater is produced and travels freely down steep slopes and thin permeable valley glaciers eroding the ice and enlarging preexisting glacial drainages as a result eruptions in this environment have produced few catastrophic floods lava flowing into the open channels and voids in the glaciers becomes confined and grows thicker filling the available space and producing steep sided bodies with smooth bulbous contact surfaces quenching of lava against ice or by water forms small scale features such as tensional fractures and glass as the amount of meltwater in contact with the lava increases the type and abundance of smaller scale features become similar to those produced during subglacial eruptions into meltwater lakes identification of large and small scale lava ice contact features in the field can be used to reconstruct paleoglacial extent and combined with geochronology of lavas to determine past paleoclimate an understanding of lava ice interaction allows us to better assess the hazards posed by future eruptions at glaciated volcanoes

glass transition temperatures of natural hydrous melts a relationship with shear viscosity and implications for the welding process abstract glass transition temperatures tg have been determined for natural multicomponent melts using differential scanning calorimetry trachytic dacitic phonolitic and basaltic base compositions have been analysed over a range of water contents up to 3 75 wt for each sample tg has been obtained over a range of cooling heating rates using the extrapolated onset and the peak temperatures in heat capacity temperature curves tg of all compositions are strongly reduced by increasing water content particularly for the first 1 wt added base composition also has an effect with the lowest tg occurring in the peralkaline phonolite suite for all samples a clear dependence on the cooling heating rate has been recorded these results have been compared with rheological investigations on the same samples on the basis of the equivalence of the shear and enthalpic relaxation process timescales we provide a method to predict the shear viscosity at the glass transition for all the melts investigated in this study both dry and hydrous our determinations of tg provide a lower limit for the time temperature envelope that gives rise to densely welded deposits and constraints on their emplacement temperature furthermore by using the viscosity values predicted at the glass transition we suggest that welding processes may occur over timescales on the order of tens of seconds to tens of minutes at tg

time dependent profiles of lava flows this work investigates the combined effects of a time dependent effusion rate and a spatially varying viscosity on the thickness profile of a flowing lava we formulate relatively simple governing equations as a primitive dynamical model for these two influences on lava flow morphology free boundary solutions for the profile of the flow and its extent are presented and analyzed for different boundary conditions at the source of the flow and several models for the spatial dependence of the viscosity the results presented here suggest that time dependence in the flow depth at the source and the form of the viscosity variation are significant influences on the morphology and dimensions of lava flows moreover this analysis implies that time dependent source conditions may contribute to the scatter in plots of eruption rate versus flow length and disparities between field and laboratory estimates of lava viscosity

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

nonisothermal viscous sintering of volcanic ash volcanic ash is often deposited in a hot state volcanic ash containing glass deposited above the glass transition interval has the potential to sinter viscously both to itself particle particle and to exposed surfaces here we constrain the kinetics of this process experimentally under nonisothermal conditions using standard glasses in the absence of external load this process is dominantly driven by surface relaxation in such cases the sintering process is rate limited by the melt viscosity the size of the particles and the melt vapor interfacial tension we propose a polydisperse continuum model that describes the transition from a packing of particles to a dense pore free melt and evaluate its efficacy in describing the kinetics of volcanic viscous sintering we apply our model to viscous sintering scenarios for cooling crystal poor rhyolitic ash using the 2008 eruption of chaiten volcano as a case example we predict that moderate linear cooling rates of 0 1 c min 1 can result in the common observation of incomplete sintering and the preservation of pore networks

cooling rate variation in natural volcanic glasses from tenerife canary islands silicate melts form glasses in a variety of geological environments the relaxation equilibration of the frozen glass structure provides a means of investigating the quench rates of natural glasses and this cooling history provides an important constraint for models of melt dynamics phonolite glasses from the central volcanic edifice of tenerife canary islands indicate a range of five orders of magnitude cooling rate determined by modeling the relaxation of the structure dependent property enthalpy h across the glass transition the relaxation of enthalpy is determined by heat capacity c p h t measurement of natural glass samples by differential scanning calorimetry dsc upon heating the heat capacity curve in the vicinity of the glass transition has a geometry characteristic of the previous cooling rate a series of thermal treatments applied to each individual sample results in a set of sample specific parameters which are used to model the heat capacity curve of the naturally cooled glass the cooling rate is then derived the equivalence of shear and enthalpic relaxation enables the relaxation of enthalpy for these volcanic samples to be described by a general term for the evolution of fictive temperature quench rates for thirty one glasses are calculated to be within the range 10 c s 1 to 7 c per day the cooling rates quoted are linear approximations across the glass transition within different volcanic facies cooling rates depend on several factors the most rapidly cooled glasses occur where samples lose heat by radiation from the surface our analyses indicate that in certain environments a natural annealing process results in slow quench rates this is interpreted as either a slow initial cooling process or the reheating of a glass to an annealing temperature within the glass transition interval the latter results in relaxation to a lower temperature structure controls on these processes include the initial temperature and dissipation of thermal energy from the volcanic body our results are consistent with an influence of volatiles on quench rates in volcanic bombs where glass adjacent to vesicular layers is relatively rapidly quenched we interpret this as a rapid quench rate frozen into the glass resulting from a change in viscosity due to volatile degassing in lava flows the conduction of heat from the hot flow interior controls the cooling process and diminishes the effect of volatile exsolution relaxation geospeedometry can be applied to glass samples from a variety of geological environments where cooling rates cannot be measured directly such measurements provide a means of determining cooling rates for a variety of volcanic processes an independent calibration for existing temperature and time data and a means for testing cooling rate dependent models

paleointensities of phonolitic obsidian influence of emplacement rotations and devitrification 1 a paleomagnetic study on phonolitic obsidian from six sites in tenerife spain is presented two sites are located at the 750 ka el pasajiron at the southern wall of las canadas caldera four sites correspond to the 115 17 bce montana blanca complex paleointensity determinations are performed with a modified thellier technique using checks for alteration and domain state additionally the anisotropy of the thermoremanence and the magnetic cooling rate dependency of each specimen are measured it was not possible to obtain good quality paleointensity data for el pasajiron thermal alteration was observed in most measurements systematic changes in rock magnetic properties and paleointensities within the profile of one site also suggest the presence of a chemical remanence crm which was probably acquired during devitrifiction of the upper part of the flow this crm cannot be seen in the arai plots themselves but only by comparison of data from different samples this underlines the importance of sampling only fresh glassy looking obsidians and not devitrified ones paleointensity determinations at montana blanca are of very good quality leading to an high success rate of 82 samples at one site show acquisition of trm during emplacement rotations however it could be shown that paleointensity data of rotated samples are reliable if the remanence carriers are in the single domain range an atrm anisotropy tensor of thermoremanent magnetization and cooling rate corrected paleointensity of 48 4 2 1 t and a vdm of 9 64 0 42 1022am2 were determined which are in very good agreement with other data from spain and morocco and to various geomagnetic field models