origin of maghaemite in chinese loess deposits aeolian or pedogenic maghaemite and magnetite common ferrimagnetic minerals in surficial soils have physical properties which are similar except for the thermal instability of the former utilising this exception a study of thermomagnetic properties has been made to systematically separate these two magnetic components in loess and palaeosol samples from the upper parts of the luochuan section of the central chinese loess plateau this investigation has shown that although maghaemite thermally unstable component occurs in greater amounts in palaeosols ms 0 0187 am2 kg 1 1 1 than in loess units ms 0 0156 am2 kg 1 1 1 in relative terms its contribution to the ferrimagnetic component of magnetisation is higher in the loess units ms 32 2 2 0 than the soils ms 23 5 3 7 such an observation suggests that much of the maghaemite component originates in the aeolian source area with some addition of pedogenic maghaemite occurring in the palaeosols

the 2005 eruption of sierra negra volcano galapagos ecuador sierra negra volcano began erupting on 22 october 2005 after a repose of 26 years a plume of ash and steam more than 13 km high accompanied the initial phase of the eruption and was quickly followed by a 2 km long curtain of lava fountains the eruptive fissure opened inside the north rim of the caldera on the opposite side of the caldera from an active fault system that experienced an mb 4 6 earthquake and 84 cm of uplift on 16 april 2005 the main products of the eruption were an a a flow that ponded in the caldera and clastigenic lavas that flowed down the north flank the a a flow grew in an unusual way once it had established most of its aerial extent the interior of the flow was fed via a perched lava pond causing inflation of the a a this pressurized fluid interior then fed pahoehoe breakouts along the margins of the flow many of which were subsequently overridden by a a as the crust slowly spread from the center of the pond and tumbled over the pahoehoe the curtain of lava fountains coalesced with time and by day 4 only one vent was erupting the effusion rate slowed from day 7 until the eruption s end two days later on 30 october although the caldera floor had inflated by 5 m since 1992 and the rate of inflation had accelerated since 2003 there was no transient deformation in the hours or days before the eruption during the 8 days of the eruption gps and insar data show that the caldera floor deflated 5 m and the volcano contracted horizontally 6 m the total eruptive volume is estimated as being 150 106 m3 the opening phase tephra is more evolved than the eruptive products that followed the compositional variation of tephra and lava sampled over the course of the eruption is attributed to eruption from a zoned sill that lies 2 1 km beneath the caldera floor

basaltic magma reservoirs factors controlling their rupture characteristics and evolution the manner in which magma enters and leaves a magma reservoir is a fundamental aspect of magmatic activity a quantitative model is developed to evaluate the variation of stress acting on the wall of a magma reservoir as a function of depth factors assessed include the size of the reservoir its depth of burial the strength of the country rocks and the variation with depth of the densities of the magma and country rocks it is shown that small magma reservoirs with halfheights less than 1 km centered at levels of neutral buoyancy can grow in all directions with nearly equal ease by injecting dikes into their surroundings at the sites of wall ruptures in larger reservoirs with half heights greater than 2 km however the stress required to cause wall failure is much less at the depth corresponding to the center of the reservoir than it is near the top or bottom thus larger reservoirs are likely to grow predominantly sideways by lateral dike injection in these cases vertical growth will not be important unless significant accumulation of low density material can occur in the upper part of the reservoir the formation of a low density layer due to gas exsolution or chemical differentiation of the magma can facilitate failure of the roof and upward dike migration from a mature reservoir as the reservoir grows and evolves through time the increasing magma pressure head at the depth corresponding to the center of the reservoir means that the amount of gas exsolution or chemical differentiation required to allow the occurrence of vertical dike emplacement also increases ultimately a vertical reservoir size is reached beyond which the excess stress required to cause lateral dike injection is so much less than that required to cause vertical injection that essentially no further vertical growth of the reservoir will occur the reservoir will thus develop a more laterally elongate shape with time the final aspect ratio will then depend mainly on the supply rate of magma to the reservoir from the mantle

volcanic eruption velocities measured with a micro radar a novel technique to quantitatively assess volcanic eruption dynamics is presented we report on measurements of volcanic eruption velocities with a modified micro radar doppler anemometer on stromboli volcano italy the mean vertical eruption velocity recorded during a four day period in late 1996 was around 10 m s which is somewhat on the small side for strombolian eruptions however the activity of stromboli volcano during this period was very weak explaining the relatively small velocities the technique used is much better in resolution than older techniques based on static photos and allows a continuous monitoring of the volcanic activity in addition to the velocity information recorded by the doppler spectrum it also contains information on the density of the ejected material and the size distribution of the particles in the volcanic jet

the velocity description of deformation paper 2 sediment geometries associated with fault bend and fault propagation folds abstract a general tectono sedimentary forward modelling equation is used to derive two dimensional numerical models of sediment geometries associated with developing fault bend and fault propagation folds these styles of folding are described in terms of velocity models of deformation and are linked with syn tectonic erosion transport and sedimentation the resultant two dimensional numerical models simulate pre growth and growth strata in both submarine and subaerial settings the geometries and relationships produced by the models are broadly similar to those seen in natural examples however complex stratal geometries may be generated which are significantly different to those produced by previous models growth strata associated with fault bend and fault propagation folds are also compared and the distinguishing features of each mode of folding discussed the forward models presented in this paper have predictive capabilities in terms of possible sediment geometries associated with fault bend and fault propagation folds and also in terms of the amount of deformation or erosion that a part of a structure may have undergone

lava fountain heights at pu u o o kilauea hawaii indicators of amount and variations of exsolved magma volatiles we review the factors determining lava fountain heights in hawaiian style basaltic eruptions such as those occurring during the recent series of eruptive episodes at the pu u o o vent east rift zone of kilauea volcano hawaii numerical solutions to the equations describing the fluid dynamics of such eruptions predict that lava fountain heights which are indicators of the velocity of magmas in vents should be controlled much more strongly by amounts of exsolved volatiles than by any other factors the next most important factor is the width of the conduit system which determines frictional losses and can be characterized by the volume flux of magma the diameter of the surface vent required to accommodate a given discharge i e instantaneous volume rate of eruption is also a function of exsolved magma volatile content but is less dependent on this factor than is the fountain height we simulate fountain heights for typical discharges at pu u o o and find implied exsolved gas contents very close to those determined by other methods the corresponding predicted vent diameters are comparable with and somewhat smaller than the observed diameter of the pu u o o vent the discrepancy is probably a consequence of processes occurring in the lava pond which is present over the vent during eruptions the variation of fountain height with time during eruptive episodes can be used as a measure of changing exsolved magma volatile content which can be related to processes occurring in the subsurface dike system

video monitoring reveals pulsating vents and propagation path of fissure eruption during the march 2011 pu u ō ō eruption kilauea volcano abstract lava fountains are a common eruptive feature of basaltic volcanoes many lava fountains result from fissure eruptions and are associated with the alignment of active vents and rising gas bubbles in the conduit visual reports suggest that lava fountain pulses may occur in chorus at adjacent vents the mechanisms behind such a chorus of lava fountains and the underlying processes are however not fully understood the march 2011 eruption at pu u kilauea volcano was an exceptional fissure eruption that was well monitored and could be closely approached by field geologists the fissure eruption occurred along groups of individual vents aligned above the feeding dyke we investigate video data acquired during the early stages of the eruption to measure the height width and velocity of the ejecta leaving eight vents using a sobel edge detection algorithm the activity level of the lava fountains at the vents was determined revealing a similarity in the eruption height and frequency based on this lava fountain time series we estimate the direction and degree of correlation between the different vents we find that the height and velocity of the eruptions display a small but systematic shift in time along the vents indicating a lateral migration of lava fountaining at a rate of 11 m s from w to e this finding is in agreement with a propagation model of a pressure wave originating at the kilauea volcano and propagating through the dyke at 10 m s from w to e based on this approach from videos only 30 s long we are able to obtain indirect constraints on the physical dyke parameters with important implications for lateral magma flow processes at depth this work shows that the recording and analysis of video data provide important constraints on the mechanisms of lava fountain pulses even though the video sequence is short it allows for the confirmation of the magma propagation direction and a first order estimation of the dyke dimensions

coupled textural and compositional characterization of basaltic scoria insights into the transition from strombolian to fire fountain activity at mount etna italy strombolian and fire fountain activities represent a common expression of explosive basaltic eruptions however the transition between these two eruptive styles and their source mechanisms are still debated we use textural and compositional studies to characterize pyroclastic material from both the strombolian and hawaiian style fire fountain phases of the january june 2000 etna activity we find that basaltic scoria presents distinctive textural and compositional features that reflect different modes of magma vesiculation and crystallization in the two eruptive regimes overall magma that forms strombolian scoria is far more crystallized less vesicular and more evolved indicating strong volatile depletion and longer residence time before being erupted fire fountain scoria indicates a fast rising magma with evidence of moderate syneruptive volatile exsolution the new textural and compositional data set is integrated with previous volcanological and geophysical investigations to provide further insights into the dynamics of fire fountains and to frame the transition from strombolian explosions to fire fountain activity into a model that may apply to future eruptions at mount etna as well as other active basaltic volcanoes

waves of bubbles in basaltic magmas and lavas initially homogeneous suspensions of bubbles in basaltic magmas and lava flows may become unstable and form rising waves or layers of bubbles we derive a set of model equations for the two phase bubble liquid system and present the results of a linear stability analysis and numerical simulations periodic vesicle layers are preserved in columbia liver flows with a spacing of 1 m the prediction of the stability analysis combined with a simple model for solidification of the lava suggests that vesicle layers may represent waves of bubbles formed within the flow the spacing of layers is determined by a balance between the growth of bubbles and hydrodynamic self diffusion vesicular layers preserved in columbia liver flows may thus form by hydrodynamic processes and do not require the repeated injection of fresh volatile rich magma or a periodic nucleation of bubbles waves of bubbles may also develop in magma chambers and conduits and could play a role in eruption dynamics

the formation of helgafell southwest iceland a monogenetic subglacial hyaloclastite ridge sedimentology hydrology and volcano ice interaction abstract helgafell a little eroded basaltic hyaloclastite ridge in southwest iceland formed in a single eruption under a pleistocene ice sheet the ice thickness at the eruption site was at least 500 m and it was probably located some 15 km from the glacier s snout the eruption created a 2 km long 0 8 km wide and initially 300 m high ridge gravity modelling indicates that helgafell has a bulk density of 1800 kg m 3 and that holocene lavas around it are 40 80 m thick this confirms that helgafell is predominantly made of hyaloclastite with pillow lavas and intrusions only making up a few percent of the total volume the southeast side is made of unsorted eruption fed hyaloclastites considered to have been piled up against an ice wall while moderately to well sorted water transported material is found on the northwest side glacier flow and meltwater drainage was towards the northwest the absence of basal pillow lavas suggests that magma fragmentation occurred from the onset of the eruption until its end the lithofacies preserved indicate a fully subglacial eruption although a final subaerial eruptive phase may have taken place through an ice chimney the volatile contents h 2 o 0 26 0 37 wt of several glass samples from the southeast side of the mountain indicate water pressures of 1 mpa throughout the eruption efficient syn eruptive drainage of meltwater coupled with rapid ice subsidence probably led to partial dynamic support of the ice causing water pressure in the vault to be much lower than the static load of the overlying ice observed lack of correlation between elevation and volatile content may be a consequence of gradual reduction in dynamic support as the eruption rate declined and the edifice grew higher helgafell demonstrates that explosive activity may occur under 500 m thick ice and it may be an analogue to the ridge formed in the gjalp eruption in 1996

sedimentary records of relative paleointensity of the geomagnetic field theory and practice sediments have proved irresistible targets for attempts at determining the relative variations in the earth s magnetic field because of the possibility of long and continuous sequences that are well dated and have a reasonable global distribution the assumption underlying paleointensity studies using sedimentary sequences is that sediments retain a record reflecting the strength of the magnetic field when they were deposited early theoretical work suggested that because the time required for an assemblage of magnetic particles in water to come into equilibrium with the ambient magnetic field was quite short no dependence on magnetic field was expected nonetheless a number of experiments showed that sedimentary magnetizations varied in accordance with the field albeit not always in a simple linear fashion experiments in which the sediments were stirred in the presence of a field to simulate bioturbation showed a reasonably linear relationship with the applied field and these results spurred the hope that variations in the earth s magnetic field might indeed be recoverable from appropriate sedimentary sequences examination of existing paleointensity data sets allows a few general conclusions to be drawn it appears that sedimentary sequences can and do provide a great deal of information about the variations in relative paleointensity of the earth s magnetic field the dynamic range of sedimentary data sets is comparable to those acquired from thermal remanences moreover when compared directly with such independent measures of magnetic field variations as beryllium isotopic ratios and thermally blocked remanences there is considerable agreement among the various records when viewed over timescales of hundreds to thousands of years relative paleointensity data sets from more than a few thousand kilometers apart bear little resemblance to one another suggesting that they are dominated by nondipole field behavior when viewed over timescales of a few tens of thousands to hundreds of thousands of years however the records show coherence over large distances at least thousands of kilometers and may reflect changes in the dipole field on the basis of a sequence spanning the brunhes and matuyama chrons the magnetic field has oscillated with a period of about 40 ka for the last few hundred thousand years but these oscillations are not clear in the record prior to about 300 ka thus they are probably not an inherent feature in the geomagnetic field and the correspondence of the period of oscillation to that of obliquity is probably coincidence

kinematic models of basement cover interaction insights from the malargue fold and thrust belt mendoza argentina abstract we investigate through natural examples from the malargue fold and thrust belt the manner in which the basement structures interact with the cover in a thick skinned fold and thrust belt our work suggests that there is a broad spectrum of basement cover interaction mechanisms with two end members coupled and uncoupled interactions the kind of bonding between basement and cover is related to the propagation to slip ratio p s because high values of this ratio indicate rapid forward propagation of shortening into the cover while low values favour welding between basement and cover structures we analyse the factors controlling the kinematics of basement cover deformation and find that not only the strength of the cover its thickness and its mechanical anisotropy control the p s and basement cover bonding but also the strain rate the thickness of synorogenic strata and the presence of pre existing faults

eruptive processes leading to the most explosive lava fountain at etna volcano the 23 november 2013 episode the 23 november 2013 lava fountain at etna volcano was the most explosive of the last 44 episodes that have occurred at etna in 2011 2013 we infer the total magma volume erupted by thermal images analysis and show that it was characterized by a very high time averaged discharge rate tadr of 360 m3 s 1 having erupted 1 6 106 m3 of dense rock equivalent magma volume in just 45 min which is more than 3 times the tadr observed during previous episodes two borehole dilatometers confirmed the eruption dynamics inferred from the thermal images when compared to the other lava fountains this episode can be considered as the explosive end member however the erupted volume was still comparable to the other lava fountain events we interpret that the 23 november explosive end member event was caused by more primitive and gas rich magma entering the system as demonstrated by the exceptional height reached by the lava fountain

spectroscopic evidence for a lava fountain driven by previously accumulated magmatic gas the eruption of mount etna in 2000 was notable for an exceptional series of 64 periodic lava fountains propelling lava fragments to heights of up to 900 metres it has been difficult to determine which of two suggested sources of power gas release from the magma itself during its rapid ascent or a build up of pressure from gas accumulated at depth is the driving force for these dramatic jets but one of the etna fountains provided volcanologists with the opportunity to use remote sensing not that remote see picture on the following page to determine the infrared spectra of the gas phase this revealed the chemical composition of the gas that powered this fountain as consistent with an origin in an accumulated gas layer lava fountains are spectacular continuous gas jets propelling lava fragments to heights of several hundred metres which occasionally occur during eruptions of low viscosity magmas1 2 3 4 5 whether they are generated by the effervescent disruption of fast rising bubbly melt2 3 4 5 or by the separate ascent of a bubble foam layer accumulated at depth6 7 still remains a matter of debate8 no field measurement has yet allowed firm discrimination between these two models a key insight into the origin of lava fountains may be gained by measuring the chemical composition of the driving gas phase this composition should differ markedly depending on whether the magma degassing occurs before or during eruption9 10 here we report the analysis of magmatic gas during a powerful 250 600 m high lava fountain measured with fourier transform infrared spectroscopy11 12 13 14 on mount etna sicily the abundances of volcanic gas species determined from absorption spectra of lava radiation reveal a fountain gas having higher co2 s and s cl ratios than other etnean emissions14 15 16 17 18 and which cannot derive from syn eruptive bulk degassing of etna basalt19 20 instead its composition suggests violent emptying of a gas bubble layer previously accumulated at about 1 5 km depth below the erupting crater

rock magnetism and geochemistry of two plio pleistocene chinese loess palaeosol sequences implications for quantitative palaeoprecipitation reconstruction abstract stratigraphic and spatial variations in the magnetic properties of chinese loess are widely accepted as reflecting changes in the intensity of soil forming processes over time and space recently several workers have used statistical correlations between the magnetic susceptibility and related parameters of modern loess plateau soils and modern climate to generate transfer functions to reconstruct past temporal and spatial trends in precipitation here we try to assess the viability of this approach by conducting magnetic and geochemical measurements of two long 2 5 my loess palaeosol sequences from different locations on the modern precipitation gradient across the loess plateau one site duanjiapo is located on the southern humid margin of the plateau and the other site luochuan is located in a drier modern environment some 160 km further north our results indicate discrepancies between magnetic and geochemical indicators of weathering and soil forming intensity and that any attempt to predict palaeoprecipitation at duanjiapo using published approaches would be significantly in error overall our results indicate a complex response of magnetic mineral transformations to climate including the production of both ferrimagnetic and antiferromagnetic minerals within the same climatic interval together with the destruction of magnetic material within some of the palaeosols therefore we suggest considerable caution should be exercised in generating quantitative climatic reconstructions from a single magnetic parameter

paleorainfall reconstructions from pedogenic magnetic susceptibility variations in the chinese loess and paleosols the rock magnetic properties of the chinese loess and paleosols constitute a unique and sensitive record of east asian paleoclimate through the quaternary period systematic variations in the concentration and grain size of the magnetic minerals in these sediments have produced systematic variations in the magnetic susceptibility signal which can be easily and rapidly measured at many sites across the loess plateau variations in many other rock magnetic properties can be used to identify the key shifts in ferrimagnetic grain size but magnetic susceptibility alone is sufficiently sensitive to record stadial and interstadial climate stages as well as glaciations and interglaciations past changes in rainfall and monsoon activity for this region are reconstructed from the susceptibility variations the susceptibility record is calibrated using the modern relationship between rainfall and pedogenic susceptibility on the loess plateau our rainfall reconstructions identify enhanced summer monsoonal activity in the chinese loess plateau region in the early holocene and the last interglaciation in the presently semiarid western area of the plateau annual precipitation in interglacial times was up to 80 higher than at present in the more humid southern and eastern areas values were up to 20 higher than today s levels during the last glaciation precipitation decreased across the entire plateau typically by 25 the relationship between pedogenic susceptibility climate and weathering age was examined over the northern hemisphere temperate zone and the observed positive correlation between rainfall and susceptibility indicates that climate rather than soil age is the predominant factor that controls pedogenic susceptibility enhancement in loess soils

dynamics of coupled diffusive and decompressive bubble growth in magmatic systems bubble growth in an ascending parcel of magma is controlled both by diffusion of oversaturated volatiles and decompression as the magma rises we have developed a numerical model which explores the processes involved in water exsolution from basaltic and rhyolitic melts rising at a constant rate from magma chamber depths of 4 and 1 km while the model does not attempt to simulate natural eruptions it sheds light on the processes which control eruptive behavior under various conditions ascent rates are defined such that a constant rate of decompression dp dt is maintained a variety of initial ascent rates are considered in the model from 1 m s to 100 m s for basalts and from a few centimeters per second to 10 m s for rhyolite at the base of the conduit the model results indicate that for any reasonable ascent rate basaltic melt degasses at a rate sufficient to keep the dissolved volatile concentration at equilibrium with the decreasing ambient pressure rhyolitic melt reaches the surface at equilibrium if its ascent rate is less than 1 m s but it can erupt with high oversaturation at greater ascent rates the latter may lead to explosive eruptions if the ascent rate of rhyolite is 10 m s or more then melt barely degasses at all in the conduit and erupts with the highest oversaturation possible for the case of slow magma rise bubble growth is limited by decompression for the case of rapid magma rise bubble growth is limited by diffusion the results of our simple model do not accurately simulate natural volcanic eruptions but suggest that subsequent more complex models may be able to simulate eruptions using the insights regarding diffusive and decompressive bubble growth processes explored in this study numerical modeling of volcanic degassing may eventually lead to better prediction of eruption timing energetics and hazards of active volcanoes

strains developed in the hangingwalls of thrusts due to their slip propagation rate a dislocation model reply abstract fault planes propagate radially from a point source and this failure propagation process is very similar to the movement of a dislocation through a crystal lattice an elastic strain represented by an extra half plane is necessarily imparted to the lattice at an edge dislocation and this is equivalent to the ductile bead which accompanies the propagating tip of a thrust fault this ductile bead migrates with the fault tip and imparts a characteristic internal strain to the thrust sheet a two dimensional model is presented to illustrate the inter relationship between fault plane slip fault tip propagation and internal strain in multilayered sequences internal strain is usually represented by asymmetric folds verging in the thrust transport direction a simple technique the displacement distance plot utilizes the fact that displacement dies out towards the fault tip this plot can be used to quantify the relative stretch measured parallel to the fault movement which is dependent on the slip propagation rate and it may be used to define exactly the position of the fault tip on a cross section examples of fold thrust structures from devon england and pembrokeshire wales are used to illustrate the technique

location of tremor sources and estimation of lava output using tremor source amplitude on the piton de la fournaise volcano 2 estimation of lava output abstract we propose several relations for estimating the amounts of lava emitted during eruptions of the piton de la fournaise volcano based on the use of tremor source amplitude sources for eruption tremor are located in several frequency bands with a location method based on the use of seismic amplitudes corrected for recording site effects sources are usually found at shallow depth and close to the eruptive vents suggesting that tremor is directly generated by the eruptive activity simultaneously with the location of the tremor sources our program gives the source amplitude of the phenomenon we assume a linear or a quadratic relation between the lava output and the tremor source amplitude both relations are calibrated using data for the march 1998 eruption and tested using the volumes emitted during the july and september 1999 and february 2000 eruptions we found that the 5 10 hz frequency band gives lava output much higher than for lower frequencies suggesting that for that band the tremor generation depends on the eruption site in addition to the lava output or that tremor at those frequencies is not directly caused by the outflow of lava but maybe rather by gas the best estimations are obtained using the quadratic relation for frequencies below 5 hz with an agreement better than 15 with the field observations for the july and september 1999 eruptions and 30 for the february 2000 eruption our results show that the cumulative amplitude of tremor recorded during eruptions of the piton de la fournaise is directly related to the amounts of lava erupted

magnetic enhancement is linked to and precedes hematite formation in aerobic soil 1 soil formation usually increases magnetic susceptibility most often by increasing the concentrations of magnetite and maghemite which are two ferrimagnetic iron oxides here we provide evidence that magnetic enhancement in aerobic soils not affected by detrital magnetic inputs or thermal transformation of other iron oxides is mostly due to the formation of maghemite which is later transformed into hematite the iron oxide that gives red color to soil we show that the maghemite hematite ratio is influenced by the particular environment and the degree of soil development so it constitutes an effective tool for paleoenvironmental and planetary studies

a study of clast size distribution ash deposition and fragmentation in a hawaiian style volcanic eruption ash deposits from hawaiian style eruptions are generally of small volume but are important in understanding the mechanisms of these eruptions an analysis of the ash deposit from the 1959 kilauea iki eruption of kilauea volcano is presented and the whole deposit grain size distribution for the eruption is calculated the grain size distribution is found to be heavily skewed towards the coarsest clast sizes and to differ considerably from size distributions for plinian deposits

the 1983 86 pu u o o eruption of kilauea volcano hawaii a study of dike geometry and eruption mechanisms for a long lived eruption abstract the 1983 1986 pu u o o eruption of kilauea volcano had a very distinctive episodic character which later changed to steady state activity in this paper we present a physical model of episodic activity which explains the process largely in terms of non uniform magma cooling and yield strength development resulting from variable dike width the model is applied to the pu u o o data set and shows that to explain the pressure variations within the summit magma reservoir and the patterns of summit deflation a yield strength of 80 to 200 pa needs to be developed this corresponds to a temperature decrease in the magma of 10 15 c consistent with temperature variations measured in the erupted lavas the model stimulates the variation in volume flux as a function of time through the eruption and produces results which agree well with observed patterns of magma movement gradual evolution of the dike system through the eruptive series is explained by progressive widening of its narrowest sections the loss of the episodic character and the transition to continuous activity is explained by a slight change in the thermal efficiency of the system the change in pattern of gas release from lava fountaining to gas pistoning and strombolian activity which accompanied the change from episodic activity to steady state eruption results from the reduction in magma flow rate at shallow levels in the dike system however we demonstrate that continuous eruptions do not inherently lack lava fountains higher magma supply rates and thus higher flow velocities would allow fountaining to occur during continuous eruption we demonstrate that episodic eruptions result from a fine balance between the effects of cooling of magma within the dike and the generation of pressure within the magma reservoir and thus that thermally episodic eruptions reflect a middle ground between short lived fissure eruptions in which magma cooling dominates and continuous eruption in which cooling is minimised the initial few months of an eruption being critical to establishing the thermal viability of the dike system

the velocity description of deformation paper 1 theory abstract there are several advantages in using velocities to describe the deformation of the crust and lithosphere induced by extension compression isostasy and other processes 1 the method is very general any deformation style can be described in this way simple examples are pure shear inclined or vertical simple shear bulk rotation airy or flexural isostasy and compaction 2 velocity fields can be combined to model more complex deformation 3 the syn tectonic evolution of parameters such as temperature pressure hydrocarbon maturity and porosity are easily modelled once the deformation velocities are specified 4 the syn tectonic evolution of sedimentary architectures can be modelled using a general tectono sedimentary forward modelling equation which incorporates the deformation velocities these advantages are illustrated by a computer model which simulates clastic sediments prograding into an active half graben formed by extension above a listric fault processes included in this model are compaction of the sediments hanging wall deformation by inclined simple shear and simultaneous footwall deformation to avoid space problems the velocity field for the hanging wall block above the non rigid footwall must obey a simple contact condition

explosive volcanic eruptions ix the transition between hawaiian style lava fountaining and strombolian explosive activity the commonest eruption styles of basaltic volcanoes involve hawaiian lava fountaining or intermittent strombolian explosions we investigate the ways in which magma rise speed at depth magma volatile content and magma viscosity control which of these eruption styles takes place we develop a model of the degree of coalescence between gas bubbles in the magma which allows us to simulate the transition between the two extreme styles of activity we find that magma rise speed is the most important factor causing the transition with gas content and viscosity also influencing the rise speed at which the transition occurs counter to intuitive expectations a decrease in gas content does not cause a transition from hawaiian to strombolian activity but instead causes a transition to passive effusion of vesicular lava rather a change from hawaiian to strombolian style requires a significant reduction in magma rise speed

a comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials some results from lake sediments abstract a new rapid method for identifying relative grain size variations in magnetic involves the parameter anhysteretic susceptibility arm i e specific arm obtained in a 1 oe steady field which is particularly sensitive to the single domain sd and small pseudo single domain psd grains of the finer magnetite fraction a second parameter low field susceptibility is relatively more sensitive to the coarser magnetite fraction larger psd and smaller multidomain md grains we can then obtain a measure of the ratio of coarse to fine grain magnetite for large numbers of samples by plotting arversus a simple idealized model based on sized magnetite samples is proposed to explain the use of the armversus plot for detecting relative grain size changes in the magnetic content of natural materials the sediments of three lakes that contain magnetite or a similar magnetic carrier and have a wide range of values of arm and are used to test the model the model is used to interpret the magnetic variations observed and the interpretations are supported by high field hysteresis measurements of the same sediments the combination of the high field hysteresis method of day et al 1 and the arm vs method is a powerful technique allowing the rapid identification of both the relative grain size and domain state for large numbers of samples containing magnetite the armvs method should be used as an intial means of identifying distinct groups of samples the high field hysteresis method should then be applied to a few representative samples from each group to confirm the initial interpretation

modelling magnetization data using simplex two new approaches to modelling magnetization data are described the first approach models the magnetic properties of natural materials in terms of mixtures of possible source materials the second approach models the magnetic properties of natural materials in terms of mixtures of magnetite and haematite crystals of varying concentrations and grain sizes in the second approach the magnetic characteristics of magnetite and haematite and their variation with grain size are described by bicubic spline functions the methods are applied to remanence and susceptibility measurements on a suite of lake sediment particle size fractions and on a set of samples from a soil profile

eruption dynamics of hawaiian style fountains the case study of episode 1 of the kīlauea iki 1959 eruption hawaiian eruptions are characterized by fountains of gas and ejecta sustained for hours to days that reach tens to hundreds of meters in height quantitative analysis of the pyroclastic products from the 1959 eruption of k lauea iki k lauea volcano hawai i provides insights into the processes occurring during typical hawaiian fountaining activity this short lived but powerful eruption contained 17 fountaining episodes and produced a cone and tephra blanket as well as a lava lake that interacted with the vent and fountain during all but the first episode of the eruption the focus of this paper microtextural analysis of hawaiian fountaining products from this opening episode is used to infer vesiculation processes within the fountain and shallow conduit vesicle number densities for all clasts are high 106 107 cm 3 post fragmentation expansion of bubbles within the thermally insulated fountain overprints the pre fragmentation bubble populations leading to a reduction in vesicle number density and increase in mean vesicle size however early quenched rims of some clasts with vesicle number densities approaching 107 cm 3 are probably a valid approximation to magma conditions near fragmentation the extent of clast evolution from low vesicle to melt ratio and corresponding high vesicle number density to higher vesicle to melt ratio and lower vesicle number density corresponds to the length of residence time within the fountain

variations in trace metal and halogen ratios in magmatic gases through an eruptive cycle of the pu u o o vent kilauea hawaii july august 1985 particle and gas samples were obtained before and after eruptive episode 35 in july and august 1985 at the fuming pu u o o vent kilauea volcano hawaii the sampling system employed consisted of a particle filter followed by four sup 7 lioh treated filters to collect acidic gases the filters were analyzed using instrumental neutron activation analysis inaa the results indicate that br cl and re cl ratios do not fluctuate through an eruption cycle but the f cl f br and metal cl ratios in and cd do change through the cycle an inverse relationship between f cl and metal cl was observed the changes are probably due to influxes of relatively undegassed magma during the repose period releasing fume with lower f cl f br and higher metal cl ratios as the magma in the pu u o o conduit gradually degasses either before or several days after an eruptive episode f cl and f br ratios increase and the metal cl ratios decrease one sample collected on july 24 two days before eruptive episode 35 did not follow this general trend this can be explained by a gas pulse from a deeper less degassed portion of magma making its way to the top of the conduit

interactions between bubbles in magmas and lavas effects of bubble deformation the interactions between two deformable bubbles are studied in order to determine the effects of deformation on bubble dynamics and to determine the limits in which the effects of deformation can be ignored deformation due to hydrodynamic interactions with other bubbles leads to alignment of horizontally offset bubbles and thus an enhanced rate of coalescence bubble alignment may produce spatial inhomogeneities in bubble concentrations in magmas which implies temporal variations in the concentration and size of bubbles in erupting magmas and spatial variations in solidified lavas an approximate quantitative model for the rate of coalescence of deformable bubbles is developed based on a series of experiments the effects of deformation can be ignored if the largest bubbles have radii less than about 5 mm in silicate magmas

a velocity description of constant thickness fault propagation folding abstract the expression of the geometric model of constant thickness fault propagation folding as a velocity description of deformation allows the derivation of rates of displacement uplift and fault propagation the velocity model of fault propagation folding and sedimentation are combined in a finite difference scheme and two examples of growth strata associated with overturned fold forelimbs illustrate the application of the model

radar doppler velocimetry of volcanic eruptions theoretical considerations and quantitative documentation of changes in eruptive behaviour at stromboli volcano italy summary the use of radar doppler velocimetry for the observation of volcanic activity is new we used this method to continuously observe the activity of one vent of stromboli volcano italy from the end of 2000 april until early may during this period we recorded 702 eruptions 132 of which occurred before a strong rain storm passed over the island on april 29 in order to interpret the recorded doppler data we developed a program that simulates different strombolian eruption scenarios for which we then calculate the theoretical doppler spectra comparing our theoretical data with the observed data we are able to show that most of the eruptions are nearly vertical although we did observe only one component of the eruption vector with our doppler radar one of the most interesting features of the data set is a significant change in eruptive behaviour that correlates with the occurrence of the rain storm we find that on average the eruption duration increased by a factor of 2 eruptive velocities were much higher and indirect evidence indicates that the average particle diameter of the erupted material decreased this change may have several causes but the coincidence with the rain storm may be evidence of magma water interaction and feedback on the volcanic activity if the fluid source rain changing the eruptive style is at the surface and in near surface layers then the main control on final eruption dynamics at stromboli volcano must also be in rather shallow regions

a new approach to investigate an eruptive paroxysmal sequence using camera and strainmeter networks lessons from the 3 5 december 2015 activity at etna volcano abstract explosive sequences are quite common at basaltic and andesitic volcanoes worldwide studies aimed at short term forecasting are usually based on seismic and ground deformation measurements which can be used to constrain the source region and quantify the magma volume involved in the eruptive process however during single episodes of explosive sequences integration of camera remote sensing and geophysical data are scant in literature and the total volume of pyroclastic products is not determined in this study we calculate eruption parameters for four powerful lava fountains occurring at the main and oldest mt etna summit crater voragine between 3 and 5 december 2015 these episodes produced impressive eruptive columns and plume clouds causing lapilli and ash fallout to more than 100 km away we analyse these paroxysmal events by integrating the images recorded by a network of monitoring cameras and the signals from three high precision borehole strainmeters from the camera images we calculated the total erupted volume of fluids gas plus pyroclastics inferring amounts from 1 9 10 9 m 3 first event to 0 86 10 9 m 3 third event strain changes recorded during the first and most powerful event were used to constrain the depth of the source the ratios of strain changes recorded at two stations during the four lava fountains were used to constrain the pyroclastic fraction for each eruptive event the results revealed that the explosive sequence was characterized by a decreasing trend of erupted pyroclastics with time going from 41 first event to 13 fourth event of the total erupted pyroclastic volume moreover the volume ratio fluid pyroclastic decreased markedly in the fourth and last event to the best of our knowledge this is the first time ever that erupted volumes of both fluid and pyroclastics have been estimated for an explosive sequence from a monitoring system using permanent cameras and high precision strainmeters during future explosive paroxysmal sequences this new approach might help in monitoring their evolution also to understand when if they are going to finish knowledge of the total gas and pyroclastic fractions erupted during each lava fountain episode would improve our understanding of their processes and eruptive behaviour

magnetic susceptibility evidence of monsoon variation on the loess plateau of central china during the last 130 000 years the magnetic susceptibility of loess and paleosols in central china represents a proxy climate index closely related to past changes of precipitation and vegetation and thus to summer monsoon intensity time series of magnetic susceptibility constructed for three loess paleosol sequences in the southern part of the chinese loess plateau document the history of summer monsoon variation during the last 130 000 yr they correlate closely with the oxygen isotope record of stages 1 to 5 in deep sea sediments soils were forming during intervals of strong summer monsoon whereas loess units were deposited at times of reduced monsoon intensity the chinese loess paleosol sequence can thus be viewed as a proxy record of asian monsoon variability extending over the last 2 5 myr

lithological factors affecting magnetic susceptibility of subtropical soils zhejiang province china abstract magnetic susceptibility was measured on subtropical soils formed on a range of parent materials in zhejiang province china to demonstrate the influence of parent material lithologies on the amount and vertical distribution of in the soils we found that the values of soils vary by up to two orders of magnitude with their parent material lithologies soils formed on igneous rocks with high values showed high absolute and distinctly decreased compared with values of parent materials the values of soils formed on basalt andesite and granodiorite were 250 10 8 m 3 kg 1 the values of soils formed on granite and other neutral and acid igneous rocks ranged from 50 10 8 to 120 10 8 m 3 kg 1 in most of the soils formed on sedimentary rocks enhancement in upper horizons of soils was found compared with parent material this enhancement was believed to be pedogenic formation of superparamagnetic sp stable single domain ssd magnetic grains which are characterized by high values of frequency dependent susceptibility fd and anhysteretic remanent magnetization arm soils formed on sedimentary rocks with a very low initial and iron content showed a low value throughout the profile it was found that there is a highly significant relationship between the values of soils and their dithionite citrate bicarbonate solution dcb soluble iron contents fe d the values of soils in chronosequences formed on alluvium and two marine deposits increased as soils became older it is suggested that the values can be used as a tool for determining the relative age in chronosequence studies

introduction to special section on how volcanoes work part 2 the special section on how volcanoes work is a collection of some of the nearly 300 papers presented at the hawaii symposium on how volcanoes work held in hilo in january 1987 tilling 1987a the response of the symposium participants to the invitation to submit their papers for consideration in the special section exceeded expectations in all more than 70 manuscripts were received reviewed and handled following regular jgr editorial procedures part 1 of the special section composed of the papers that were processed and accepted in time to meet the production schedule was published in the december 1987 issue of the journal of geophysical research solid earth and planets tilling 1987a even though part 1 contained only eight papers it nonetheless provided a representative sampling of the multidisciplinary nature of the investigations undertaken to improve our understanding of volcanic systems the papers published in part 1 included ground deformation studies on caldera systems dzurisin and yamashita 1987 mortensen and hopkins 1987 geochemical and observational studies of the lava fountains and of volcanic fume during the 1983 1984 activity of pu u o o in kilauea s east rift zone crowe et al 1987 head and wilson 1987 magmatic crystal stratigraphy and theoretical petrology pearce et al 1987 russell 1987 dynamics of active lava lakes tilling 1987b and seismic evidence for a subcrustal intrusive complex beneath the island of oahu hawaii ten brink and brocher 1987

lack of correlation between paleoprecipitation and magnetic susceptibility of chinese loess paleosol sequences we have conducted a detailed mineral magnetic study of loess unit 8 l8 and paleosol unit 8 s8 from three localities jingbian yichuan and duanjiapo along a n s transect in the chinese loess plateau as expected the low field magnetic susceptibility has higher values in s8 and lower values in l8 similarly superparamagnetic particle concentrations increase in s8 with increasingly humid cli mates along the n s transect which suggests that pedogenic magnetic enhancement is related to climate however in s8 at duanjiapo is so low that there is no correlation between and the degree of pedogenesis in this loess paleosol cycle it therefore appears that is not consistently the most suit able indicator of paleoclimate in chinese loess paleosol se quences our results indicate that there are complexities in the mineral magnetic response to pedogenesis which could invalidate interpretation of the record of chinese loess paleosol sequences in terms of paleoprecipitation

influence of the aging of fe oxides on the decline of magnetic susceptibility of the tertiary red clay in the chinese loess plateau abstract magnetic properties free and active fe oxides grain size distribution and mineral assemblage of a quaternary loess tertiary red clay trc section in lingtai county in the chinese loess plateau were studied the results suggest that the trc of the lingtai section shares similar aeolian characteristics with the overlying quaternary loess paleosol sequence qlps but the former is generally more intensively weathered than the latter as indicated by its higher citrate bicarbonate dithionite cbd extractable fe fe d finer grain size and lower content of easily weathered primary minerals however magnetic susceptibility lf and magnetic remanence arm sirm and soft etc of the main part of the trc are significantly lower implying the decline of ferrimagnetic minerals fm in contrast hematite and goethite in the trc is significantly enhanced as indicated by its higher hirm the acid ammonium oxalate aao extractable fe fe o of the whole section sharply decreases with increasing age fe o and fe o fe d values of the section are significantly correlated with lf especially in the trc the low values of fe o and fe o fe d correspond to weak lf this suggests a significant influence of the age related transformation of fe oxides on the decline of fm in the trc lower fm and higher hematite and or goethite in the trc further suggest the transformation of fm into hematite with the aging of fe oxides during post depositional processes though more evidence is needed to understand the processes involved lf of the trc in the chinese loess plateau mostly cannot be regarded as a promising paleoclimatic proxy because its weak magnetism does not correlate to its strong pedogenesis

a plinian treatment of fallout from hawaiian lava fountains a new model is presented which simulates the dispersal and deposition of material from a hawaiian eruption column the model treats the hawaiian column as a coarse grained plinian column and uses a modified version of the wilson and walker wilson l walker g p l 1987 explosive volcanic eruptions vi ejecta dispersal in plinian eruptions the control of eruption conditions and atmospheric properties geophys j r astron soc 89 657 679 plinian pyroclast dispersal model to simulate the fall out of material during a hawaiian eruption the model results are found to be in good agreement with independent estimates of various parameters made for the 1959 kilauea iki eruption of kilauea volcano the close agreement between the model results and these independent estimates shows that dynamically hawaiian eruptions are indistinguishable from plinian eruptions the major differences in the styles and deposits of these two types of eruptions are accounted for by differences in the mass fluxes and gas contents of the erupting magmas and most fundamentally by differences in the grainsize distribution of the erupted clasts plume heights predicted by the model are greater than those found for previous models of hawaiian eruptions this is because previous models did not allow for the progressive fall out of particles from the plume and more importantly made no correction for the velocity disequilibrium between gas and clasts when the grainsize distribution is coarse

new field and laboratory evidence for the origin of hyaloclastite flows on seamount summits new field observations with the submersible alvin and photographic evidence from a study of the summits of seamounts near the east pacific rise show that hyaloclastite deposits occur commonly hyaloclastite outcrops were found on six volcanoes at depths from 1240 to 2500 m these new observations plus laboratory study of new hyaloclastite specimens extend the results of previous studies most of the hyaloclastite samples are of hydrovolcanic eruptive origin but a few show evidence of a predominantly sedimentary origin primarily from morphology we identify several vent areas from which hyaloclastite presumably erupted the surface appearance of the hyaloclastite deposits varies with distance to these vents leading us to propose a facies model for deep sea hyaloclastites on seamount summits hyaloclastites of hydromagmatic origin exhibit weak normal grading and bedding parallel alignment of platy shards they consist of blocky sliver and fluidal basalt glass shards and lithics in a matrix that contains pelagic sediment the shards themselves are remarkably free of even the tiniest crystals and are usually chemically homogeneous we propose that the shards form mainly by cooling contraction granulation but cannot rule out the possibility of limited steam explosivity hyaloclastites are closely associated with submarine pahoehoe and we propose that a very rapid eruption rate promoting clastic dominated versus flow dominated eruptive behavior is the dominant control on hyaloclastite formation we propose that shard formation occurs during submarine lava fountaining gravitational instability of the resulting slurry of shards sea water and possibly steam causes gravity flow that carries the shards outward from the vent further field and modelling studies are needed to test these ideas and more quantitatively constrain the ascent mechanism eruption dynamics and deposition of deep sea hyaloclastites

magma reservoirs and neutral buoyancy zones on venus implications for the formation and evolution of volcanic landforms we examine the production of magma reservoirs and neutral buoyancy zones nbzs on venus and the implications of their development for the formation and evolution of volcanic landforms the high atmospheric pressure on venus reduces volatile exsolution and generally serves to inhibit the formation of nbzs and shallow magma reservoirs for a range of common terrestrial magma volatile contents magma ascending and erupting near or below mean planetary radius mpr should not stall at shallow magma reservoirs such eruptions would be characterized by relatively high total volumes and effusion rates for the same range of volatile contents at 2 km above mpr about half of the cases result in direct ascent of magma to the surface and half in the production of neutral buoyancy zones in general neutral buoyancy zones and shallow magma reservoirs begin to appear as gas content increases and are nominally shallower on venus than on earth for a fixed volatile content nbzs become deeper with increasing elevation over the range of elevations treated here 1 km to 4 4 km depths differ by a factor of 2 4 these analyses reveal several factors that may help to account for the low height of volcanoes on venus larger primary reservoirs cause the wide dispersal of conduits building edifices models of the position of the shallow nbz reservoir during edifice growth show that for earth the magma chamber center remains at a constant depth below the growing edifice summit thus keeping pace with the increasing elevation while on venus the chamber center becomes deeper relative to the summit of the growing edifice because of the major change in atmospheric pressure as a function of altitude therefore neutral buoyancy zones and magma reservoirs on venus will remain in the prevolcano substrate longer and in many cases may not emerge into the edifice at all the lower rate of vertical migration implies that magma reservoirs would tend to stabilize undergo greater lateral growth and become larger on venus than earth the proportion of the available magma going into production of the edifice relative to that intruded into the substrate is smaller on venus than earth large reservoirs would encourage multiple and more widely dispersed source vents and large volumes for individual eruptions in large reservoirs positively buoyant materials are likely to be produced from differentiation substrate remelting and volatile exsolution nonbuoyant materials exsolving volatiles in a shallow reservoir will need higher gas bubble concentrations to produce eruptions than on earth and when this gas enriched melt emerges at the surface it is more likely to retain its bubbles than to undergo explosive disruption due to the high surface atmospheric pressure therefore there is the potential for the production of a range of erupted lavas that have very high gas bubble concentrations leading to anomalous more viscous rheological properties inhibition of disruption of volatile rich magma for both basaltic and more evolved compositions can lead to the production of 1 more bubble rich vesicular flows characterized by higher viscosity and greater thicknesses the venus equivalent of effusions that would have lost much of their volatiles in the fire fountaining process on earth 2 high volume high discharge rate extremely gas rich basaltic effusions that increase viscosity considerably upon surface extrusion and produce domes whose volumes are considerably higher than their dense rock equivalent and 3 more evolved compositions that are gas rich but do not undergo disruption upon effusion and produce domes and flows of high viscosity the venus equivalent of terrestrial ignimbrites on the basis of these analyses we predict that intrusions and dike emplacement should be common particularly around both shallow and deep magma reservoirs and the tops of dikes should be manifested as radial fractures there should be a range of diameters of circular features associated with the presence of both shallow nbz related and deep plumerelated magma reservoirs large volume lava outpourings should be favored at lower elevations and shallow reservoirs and edifices should be more common at intermediate elevations at the highest elevations magma reservoirs are predicted to be large and relatively deep with low associated edifices direct ascent of magma where neutral buoyancy zones are unlikely low elevations and the propensity for relatively larger magma reservoirs on venus when they do form are both factors which will tend to favor high volume eruptions independent of variations in magma temperature or chemistry individual volcanic features should be interpreted in terms of regional geologic setting and the dynamics of elevation changes commonly associated with various scales of mantle processes and magma emplacement in order to assess global crustal growth processes on venus

dynamics of degassing at kilauea volcano hawaii at kilauea volcano hawaii the recent long lived eruptions of mauna ulu and pu u o o have occurred in two major stages defining a characteristic eruptive pattern the first stage consists of cyclic changes of activity between episodes of fire fountaining and periods of quiescence or effusion of vesicular lava the second stage consists only of continuous effusion of lava we suggest that these features reflect the dynamics of magma degassing in a chamber which empties into a narrow conduit in the volcano chamber gas bubbles rise through magma and accumulate at the roof in a foam layer the foam flows toward the conduit and its shape is determined by a dynamic balance between the input of bubbles from below and the output into the conduit the foam thickness is proportional to lq e2 l g 1 4 where l and l are the viscosity and density of magma e is the gas volume fraction in the foam g is the acceleration of gravity and q is the gas flux the bubbles in the foam deform under the action of buoyancy and the maximum permissible foam thickness is hc 2 e lgr where is the coefficient of surface tension and r is the original bubble radius if this critical thickness is reached the foam collapses into a large gas pocket which erupts into the conduit foam accumulation then resumes and a new cycle begins the attainment of the foam collapse threshold requires a gas flux in excess of a critical value which depends on viscosity surface tension and bubble size hence two different eruption regimes are predicted 1 alternating regimes of foam buildup and collapse leading to the periodic eruption of large gas volumes and 2 steady foam flow at the roof leading to continuous bubbly flow in the conduit the essential result is that the continuous process of degassing can lead to discontinuous eruptive behavior data on eruption rates and repose times between fountaining phases from the 1969 mauna uiu and the 1983 1986 pu u o o eruptions yield constraints on three key variables the area of the chamber roof must be a few tens of square kilometers with a minimum value of about 8 km2 magma reservoirs of similar dimensions are imaged by seismic attenuation tomography below the east rift zone close to the roof the gas volume fraction is a few percent and the gas bubbles have diameters lying between 0 1 and 0 6 mm these estimates are close to the predictions of models for bubble nucleation and growth in basaltic melts as well as to the observations on deep submarine basalts the transition between cyclic and continuous activity occurs when the mass flux of gas becomes lower than a critical value of the order of 103 kg s in this model changes of eruptive regime reflect changes in the amount and size of bubbles which reach the chamber roof

sulfur isotopic evidence for sources of volatiles in siberian traps magmas abstract the siberian traps flood basalts transferred a large mass of volatiles from the earth s mantle and crust to the atmosphere the eruption of the large igneous province temporally overlapped with the end permian mass extinction constraints on the sources of siberian traps volatiles are critical for determining the overall volatile budget the role of crustal assimilation the genesis of noril sk ore deposits and the environmental effects of magmatism we measure sulfur isotopic ratios ranging from 10 8 to 25 3 vienna canon diablo troilite v cdt in melt inclusions from siberian traps basaltic rocks our measurements which offer a snapshot of sulfur cycling far from mid ocean ridge and arc settings suggest the 34 s of the siberian traps mantle melt source was close to that of mid ocean ridge basalts in conjunction with previously published whole rock measurements from noril sk our sulfur isotopic data indicate that crustal contamination was widespread and heterogeneous though not universal during the emplacement of the siberian traps incorporation of crustal materials likely increased the total volatile budget of the large igneous province thereby contributing to permian triassic environmental deterioration

assessing uncertainties in balanced cross sections abstract balanced structural cross sections are models that are fit to incomplete data the models are under constrained with respect to any particular two dimensional line length model but enough data generally exists to yield a well constrained area balance solution furthermore the area balance encompasses all possible line length solutions therefore where the primary objective of section balancing is the determination of horizontal shortening magnitude area balancing provides an analytical solution we use this analytical solution to develop a comprehensive robust analysis of the uncertainty in shortening estimates resulting from cross section balancing the analytical solution allows us to propagate errors formally on the input parameters stratigraphic thicknesses depth to decollement eroded hanging wall cutoffs through the equations and produce the resulting uncertainty on the magnitude of shortening balanced cross sections from the subandean belt of the central andes are used to demonstrate the relative importance of stratigraphy and eroded hanging wall cutoffs in the contribution to the overall error

explosive volcanic eruptions viii the role of magma recycling in controlling the behaviour of hawaiian style lava fountains explosive eruptions of mafic magmas produce lava fountains whose heights are a function of the exsolved volatile content of the magma its erupted mass flux and the geometry of the vent which may be an elongate fissure or a localized near circular conduit the geometry of the initial vent and the eruptive behaviour can be distinctly modified by lava drainback and accumulating ejecta hot pyroclasts landing near the vent may coalesce to form rootless flows some of which may drain back into the vent to be recycled into the eruption products rootless flows may be at least partially confined by pre existing topographic features or by spatter or cinder ramparts being built up by the eruption itself so that they accumulate into a lava pond over and around the vent the erupting jet of magmatic gas and pyroclasts must force its way through such a pond and will entrain some of the pond lava as it does so the energy expended in entraining and accelerating previously erupted materials will reduce the eruption velocity and the lava fountain height by an amount which can be calculated as a function of the eruption conditions and the lava pond depth or lava drainback rate the results of such calculations are presented and are used to assess the influence of this process on attempts to infer magma volatile contents from field observations of lava fountain heights

magma flow between summit and pu u ō ō at klauea volcano hawai i 1 volcanic eruptions are often accompanied by spatiotemporal migration of ground deformation a consequence of pressure changes within magma reservoirs and pathways we modeled the propagation of pressure variations through the east rift zone erz of klauea volcano hawai i caused by magma withdrawal during the early eruptive episodes 1983 1985 of the ongoing pu u kupaianaha eruption eruptive activity at the pu u vent was typically accompanied by abrupt deflation that lasted for several hours and was followed by a sudden onset of gradual inflation once the eruptive episode had ended similar patterns of deflation and inflation were recorded at klauea s summit approximately 15 km to the northwest albeit with time delays of hours these delay times can be reproduced by modeling the spatiotemporal changes in magma pressure and flow rate within an elastic walled dike that traverses klauea s erz key parameters that affect the behavior of the magma dike system are the dike dimensions the elasticity of the wall rock the magma viscosity and to a lesser degree the magnitude and duration of the pressure variations themselves combinations of these parameters define a transport efficiency and a pressure diffusivity which vary somewhat from episode to episode resulting in variations in delay times the observed variations in transport efficiency are most easily explained by small localized changes to the geometry of the magma pathway

uplift rates of marine terraces as a constraint on fault propagation fold kinematics examples from the hawkswood and kate anticlines north canterbury new zealand abstract marine terraces on growing fault propagation folds provide valuable insight into the relationship between fold kinematics and uplift rates providing a means to distinguish among otherwise non unique kinematic model solutions here we investigate this relationship at two locations in north canterbury new zealand the kate anticline and haumuri bluff at the northern end of the hawkswood anticline at both locations we calculate uplift rates of previously dated marine terraces using dgps surveys to estimate terrace inner edge elevations we then use markov chain monte carlo methods to fit fault propagation fold kinematic models to structural geologic data and we incorporate marine terrace uplift into the models as an additional constraint at haumuri bluff we find that marine terraces when restored to originally horizontal surfaces can help to eliminate certain trishear models that would fit the geologic data alone at kate anticline we compare uplift rates at different structural positions and find that the spatial pattern of uplift rates is more consistent with trishear than with a parallel fault propagation fold kink band model finally we use our model results to compute new estimates for fault slip rates 1 2 m ka at kate anticline and 1 4 m ka at haumuri bluff and ages of the folds 1 ma which are consistent with previous estimates for the onset of folding in this region these results are consistent with previous work on the age of onset of folding in this region provide revised estimates of fault slip rates necessary to understand the seismic hazard posed by these faults and demonstrate the value of incorporating marine terraces in inverse fold kinematic models as a means to distinguish among non unique solutions

europa morphological characteristics of ridges and triple bands from galileo data e4 and e6 and assessment of a linear diapirism model galileo solid state imaging ssi images of europa provide high resolution data on the morphological characteristics of ridges and permit the development of nomenclatural schemes for their description and classification key observations are that ridges 1 are remarkably consistent in their along strike linearity width and height 2 form long linear features in which preexisting structures can sometimes be traced up the outer slopes of the ridges and in other cases appear to be buried 3 contain narrow apical zones of small scale ridge parallel faulting 4 are sometimes flanked by narrow troughs and ridge parallel fractures and 5 often display associated color variations on the basis of the characteristics and associated features of ridges we find that a process in which initial fracturing most plausibly related to tidal deformation of a brittle layer overlying a buoyant ductile substrate leading to linear diapiric upwelling provides a consistent explanation for the observed features in this process the upwelling linear diapir causes flexure bending and faulting of the region marginal to the fracture the deformation and uplift of adjacent plains material and its preexisting structures to form the apical part of the ridge the exposure of the inner walls of the crack and the mass wasting of the inner and outer walls of the ridge to modify but often not completely destroy the preexisting structure of the adjacent plains specifically this mechanism can account for many characteristics of the ridges including their linearity their consistent and regular morphology over their great lateral extent their positive topography the presence of preexisting structure on the outer ridges caused by upbowing of background ridged plains the formation of marginal troughs as diapiric rim synclines the detailed nature of their outer and inner slopes caused largely by faulting and mass wasting processes and their sequential formation with multiple orientations related to tidal deformation processes linear diapirism also provides a possible explanation for color and albedo characteristics related to thermal effects of the upwelling warm ice e g inducing volatile migration and grain size variations as the vast majority of deformation is vertical in this scenario this mechanism minimizes the necessity for complementary compressional deformation required by some other models

sycamore knoll a wave planed pop up structure in a sinistral oblique thrust system southern california continental borderland at the boundary between the western transverse ranges province and inner continental borderland of southern california strain is partitioned across the sinistral oblique anacapa dume fault system sycamore knoll a pop up structure 20 km west of point dume in the hanging wall of the north dipping anacapa dume fault stands out as an anomalous bathymetric high along the southern california coast we synthesize new and existing geophysical datasets including multibeam bathymetry backscatter and single multichannel seismic to understand the morphology and tectonic implications of sycamore knoll we identify a complete eustatic low stand submerged marine terrace package encircling sycamore knoll platform that corresponds to the last glacial maximum lgm the marine terrace deposits and wave planed surface of sycamore knoll require a late quaternary uplift rate of 0 55 0 5 0 3 mm yr relative to sea level by combining our uplift rate with previous estimates of basin subsidence and a revised structural model of the anacapa dume fault we determine a maximum slip rate in latest quaternary time of 1 50 0 5 0 3 mm yr and hence a post lgm rate of convergence across the anacapa dume fault of 0 60 0 2 0 1 mm yr

growth stratal records of instantaneous and progressive limb rotation in the precordillera thrust belt and bermejo basin argentina analysis of synorogenic deposits preserved near the thrust front zone of the precordillera fold and thrust belt and in the bermejo foreland basin in central argentina documents the evolution of deformation during the last 5 myr as well as the thrust system kinematics seismic lines across the area display examples of progressive and instantaneous limb rotations the easternmost thrust plate of the central precordillera the niquivil thrust experienced episodic motion in two main stages a first thrust movement as a fault propagation fold and a second movement as a high angle anticlinal breakthrough fault after a period of quiescence growth strata deposited in the la pareja intermontane basin and the las salinas and bermejo anticline recorded continuous growth of eastern precordilleran structures beginning at 2 7 ma with uplift rates of 0 3 mm yr for the niquivil anticline 1 08 mm yr for the las salinas anticline and between 0 6 and 0 38 mm yr during the last 2 myr for the bermejo anticline once the eastern precordillera began to grow the propagation of the niquivil thrust stopped restricting the deformation to the young vallecito out of sequence thrust the complex geometry of growth strata deposited on the back limb of the las salinas anticline can be explained by using a model of a two step fault propagation fold with constant layer thickness the bermejo anticline of the eastern precordillera is formed by the simultaneous propagation of a shallow fault responsible for the fold shape and a deep fault that produced vertical uplift a growth triangle that documents instantaneous forelimb rotation for a fault propagation fold is recorded for the first time in a published seismic line

magnetostratigraphy and paleoclimatic interpretation of a continuous 7 2 ma late cenozoic eolian sediments from the chinese loess plateau an almost 300m thick eolian sequence of late cenozoic sediments which includes 162 5m of quaternary loess paleosols and 126m of late tertiary eolian red clay from the central part of the chinese loess plateau was investigated to determine the magnetostratigraphy the results show that eolian dust accumulation and by inference the related east asia paleomonsoon had begun by 7 2ma as paleomonsoon are largely controlled by the tibetan plateau this implies that the plateau had reached some critical elevation by 7 2ma the section also documents a rapid increase in eolian dust accumulation in the late cenozoic at 3 2ma that is probably due to the influence of global ice volume on the east asian monsoon

multiple origins and interpretations of the magnetic susceptibility signal in chinese wind blown sediments abstract in most chinese loess paleosol sequences high magnetic susceptibility values are found in the soil horizons with low values in the loess layers the susceptibility signal has been widely used as a proxy climatic indicator however both the causes and mechanisms which control susceptibility still remain controversial our recent studies challenge some earlier interpretations of the magnetic susceptibility signal in chinese wind blown sediments first the prevailing hypothesis of pedogenic origin cannot totally account for the susceptibility variations in many sections second in some cases the principal carrier of the magnetization seems not to be the ultrafine pedogenic minerals rather coarse lithogenic magnetic minerals derived from local sources can also contribute significantly to the susceptibility signal finally not all the chinese soils have higher susceptibility values than that of loess or sand layers opposite relationships do exist it is concluded that the source and causes of susceptibility may be different from site to site or even at different times at a given site any single hypothesis cannot completely account for the susceptibility variations in the chinese loess plateau and its surrounding regions besides the previous explanations of carbonate leaching pedogenic processes and organic decomposition the contribution of source materials to magnetic susceptibility must also be taken into account

an analogue experimental model of depth fluctuations in lava lakes lava lakes consisting of molten degassing lava in summit craters of active basaltic volcanoes sometimes exhibit complex cycles of filling and emptying on time scales of hours to weeks such as recorded at pu u o o in hawaii and oldoinyo lengai in tanzania here we report on a new series of analogue laboratory experiments of two phase flow in a reservoir conduit lava lake system which spontaneously generates oscillations in the depth of liquid within the lake during the recharge phase gas supplied from a subsurface reservoir of degassing magma drives liquid magma up the conduit causing the lake to fill as the magmastatic pressure in the lake increases the upward supply of magma driven by the gas bubbles falls eventually the upflow becomes unstable and liquid drains downwards from the lake driven by the magmastatic pressure of the overlying lake suppressing the ascent of any more bubbles from the chamber at a later stage once the lake has drained sufficiently the descent speed of liquid through the conduit decreases below the ascent speed of the bubbles and the recharge cycle resumes application of a quantitative model of the experiments to the natural system is broadly consistent with field data

deep submarine pyroclastic eruptions theory and predicted landforms and deposits submarine pyroclastic eruptions at depths greater than a few hundred meters are generally considered to be rare or absent because the pressure of the overlying water column is sufficient to suppress juvenile gas exsolution so that magmatic disruption and pyroclastic activity do not occur consideration of detailed models of the ascent and eruption of magma in a range of sea floor environments shows however that significant pyroclastic activity can occur even at depths in excess of 3000 m in order to document and illustrate the full range of submarine eruption styles we model several possible scenarios for the ascent and eruption of magma feeding submarine eruptions 1 no gas exsolution 2 gas exsolution but no magma disruption 3 gas exsolution magma disruption and hawaiian style fountaining 4 volatile content builds up in the magma reservoir leading to hawaiian eruptions resulting from foam collapse 5 magma volatile content insufficient to cause fragmentation normally but low rise speed results in strombolian activity and 6 volatile content builds up in the top of a dike leading to vulcanian eruptions we also examine the role of bulk interaction steam explosivity and contact surface steam explosivity as processes contributing to volcaniclastic formation in these environments we concur with most earlier workers that for magma compositions typical of spreading centers and their vicinities the most likely circumstance is the quiet effusion of magma with minor gas exsolution and the production of somewhat vesicular pillow lavas or sheet flows depending on effusion rate the amounts by which magma would overshoot the vent in these types of eruptions would be insufficient to cause any magma disruption the most likely mechanism of production of pyroclastic deposits in this environment is strombolian activity due to the localized concentration of volatiles in magma that has a low rise rate magmatic gas collects by bubble coalescence and ascends in large isolated bubbles which disrupt the magma surface in the vent producing localized blocks bombs and pyroclastic deposits another possible mode of occurrence of pyroclastic deposits results from vulcanian eruptions these deposits being characterized by the dominance of angular blocks of country rocks deposited in the vicinity of a crater should be easily distinguishable from strombolian and hawaiian eruptions however we stress that a special case of the hawaiian eruption style is likely to occur in the submarine environment if magmatic gas buildup occurs in a magma reservoir by the upward drift of gas bubbles in this case a layer of foam will build up at the top of the reservoir in a sufficient concentration to exceed the volatile content necessary for disruption and hawaiian style activity the deposits and landforms are predicted to be somewhat different from those of a typical primary magmatic volatile induced hawaiian eruption specifically typical pyroclast sizes might be smaller fountain heights may exceed those expected for the purely magmatic hawaiian case cooling of descending pyroclasts would be more efficient leading to different types of proximal deposits and runout distances for density flows would be greater potentially leading to submarine pyroclastic deposits surrounding vents out to distances of tens of meters to a kilometer in addition flows emerging after the evacuation of the foam layer would tend to be very depleted in volatiles and thus extremely poor in vesicles relative to typical flows associated with hawaiian style eruptions in the primary magmatic gas case we examine several cases of reported submarine volcaniclastic deposits found at depths as great as 3000 m and conclude that submarine hawaiian and strombolian eruptions are much more common than previously suspected at mid ocean ridges furthermore the latter stages of development of volcanic edifices seamounts formed in submarine environments are excellent candidates for a wide range of submarine pyroclastic activity due not just to the effects of decreasing water depth but also to 1 the presence of a summit magma reservoir which favors the buildup of magmatic foams enhancing hawaiian style activity and episodic dike emplacement which favors strombolian style eruptions and 2 the common occurrence of alkalic basalts the co2 contents of which favor submarine explosive eruptions at depths greater than tholeiitic basalts these models and predictions can be tested with future sampling and analysis programs and we provide a checklist of key observations to help distinguish among the eruption styles

environmental magnetism past present and future environmental magnetism involves the application of rock and mineral magnetic techniques to situations in which the transport deposition or transformation of magnetic grains is influenced by environmental processes in the atmosphere hydrosphere and lithosphere the first explicit description of environmental magnetism as a distinct field was in 1980 since that time environmental magnetism has become a broad field that is finding application in an ever increasing array of scientific disciplines in this review of the present state of environmental magnetic studies we divide the field into three broad but arbitrary categories the first involves the use of mineral magnetic assemblages in the geological record to study physical processes in depositional environments this category includes the correlation of sediment cores using magnetic susceptibility measurements studies of geomagnetic field behavior the analysis of depositional and postdepositional mechanical processes that affect sediments and the examination of magnetic parameters that might represent proxies for paleoclimatic variation the second category encompasses studies of the processes responsible for variations in the magnetic minerals brought into a sedimentary environment these provenance investigations include studies of changes in catchment derived sediment in lakes fluctuations in contributions from terrigenous aeolian and glaciogenic components in deep sea sediments and the origin of atmospheric particulates the final category addresses in situ changes and transformations of magnetic minerals in sedimentary environments including pedogenesis authigenetic diagenetic formation of ferrimagnetic phases dissolution of magnetic minerals due to reductive diagenesis and contributions of biomagnetism to sedimentary magnetism because environmental magnetism can address problems in so many disciplines and because many of these problems may be inaccessible to other techniques it is likely that the scope of environmental magnetism will continue to expand rapidly environmental magnetism is capable of providing important data for studies of global environmental change climatic processes and the impact of humans on the environment all of which are major research initiatives in the international scientific community these factors suggest that environmental magnetism has a bright and diverse future

factors influencing the height of hawaiian lava fountains implications for the use of fountain height as an indicator of magma gas content the heights of lava fountains formed in hawaiian style eruptions are controlled by magma gas content volume flux and the amounts of lava re entrainment and gas bubble coalescence theoretical models of lava fountaining are used to analyse data on lava fountain height variations collected during the 1983 1986 pu u o o vent of kilauea volcano hawaii the results show that the variable fountain heights can be largely explained by the impact of variations in volume flux and amount of lava re entrainment on erupting magmas with a constant gas content of 0 32 wt h2o however the gas content of the magma apparently declined by 0 05 wt during the last 10 episodes of the eruption series and this decline is attributed to more extensive pre eruption degassing due to a shallowing of the sub vent feeder dike it is concluded that variations in lava fountain height cannot be simply interpreted as variations in gas content as has previously been suggested but that fountain height can still be a useful guide to minimum gas contents where sufficient data are available on eruptive volume fluxes and extent of lava entrainment greatly improved estimates can be made of magma gas content from lava fountain height

paleoclimatic significance of the temperature dependent susceptibility of holocene loess along a nw se transect in the chinese loess plateau we have conducted mineral magnetic investigations of samples of modern dune sand pristine loess and present day loess along a nw se transect from the northern to the central loess plateau in china the methods used include the temperature dependence of susceptibility tds before and after citrate bicarbonate dithionite cbd treatment as well as x ray diffraction xrd analysis the xrd analyses demonstrate that magnetite and hematite both exist in the chinese loess paleosol sequence and its modem source area but the tds measurements show that magnetite is the predominant contributor to magnetic susceptibility maghemite is present in the pristine loess and the present day loess due to pedogenesis the pedogenic processes that produce the maghemite are closely linked to paleoclimate and for this transect precipitation appears to be the most important climatic variable we suggest that tds can be used as a useful method for the analysis of pedogenesis and climatic change

fluidal clast breccia generated by submarine fire fountaining trooper creek formation queensland australia abstract a distinctive monomictic breccia composed of fluidal and blocky basaltic andesite clasts occurs in a cambro ordovician submarine volcanic succession in northern queensland australia associated with this fluvial clast buccia facies are coherent facies and coarse and fine breccia facies of the same composition the fluidal clast breccia facies is internally massive and 250 m thick varying only in the ratio of fluidal clasts to blocky clasts fluidal clasts range in size from 2 cm to 170 cm and have moderately to highly vesicular cores and thick up to 1 cm non vesicular formerly glassy rims blocky clasts are highly vesicular to non vesicular subaqueous fire fountain breccias are distinguished from subaerial fire fountain breccias by thick glassy margins on fluidal clasts the lack of welding and agglutination and the distinctive association of highly vesicular fluidal clasts with non vesicular angular blocky clasts recognition of submarine fire fountain breccias in volcanic successions constrains the eruption style proximity tens of metres to source and environment of deposition

mid ocean ridge eruptive vent morphology and substructure evidence for dike widths eruption rates and evolution of eruptions and axial volcanic ridges high resolution side scan sonar data of mid atlantic ridge mar inner valley floor axial volcanic ridges reveal details of their architectural elements we develop quantitative models for basaltic eruptions from dikes and compare the predicted products of these eruptions with the observed morphologic features inhibition of gas exsolution lack of magma disruption and hydrothermal effects combine to decrease the rise speed of magma in submarine dikes and enhance cooling leading to more rapid centralization of eruptions along the widest places in the dike dikes are predicted to initially feed eruptions from fissure vents producing lines of hummocky ridges centralization of activity to several adjacent vents produces chains of hummocky bulbous mounds and can enhance the effusion rate at a single vent to produce small seamounts the widest dikes are predicted to produce smooth flows up to several kilometers in length which should pond in adjacent lows edifice sizes predicted on the basis of volume fluxes and flow lengths implied by the widths of dikes observed on the seafloor in iceland and in ophiolite complexes are in quantitative agreement with the dimensions of observed features each ridge is made up of the products of a variety of these individual dike emplacement and extrusive events involving various dike widths cooling times and eruption durations on the basis of typical mar spreading rates about one dike emplacement event would be expected every 40 years since not all dikes reach the surface the actual mean interval between eruptions will exceed this mar dikes should solidify between average dike emplacement events dike emplacement events are more frequent on the east pacific rise epr and thus new dikes are more likely to reoccupy the sites of incompletely solidified older dikes differences between the morphology of the mar axial volcanic ridge and the sheet flow dominated epr are attributed to on average wider dikes erupting with greater frequency along the epr

nature of local magma storage zones and geometry of conduit systems below basaltic eruption sites pu u o o kilauea east rift hawaii example the fluid dynamics of the well documented eruptive episodes at pu u o o kilauea wolfe et at 1987 are used to investigate quantitativeely the size and shape of the shallow conduit system beneath the vent cooling calculations are employed to study the long term survival of conduits and the consequences of multiple dike injection events we find that the subvent conduit must have a planar geometry at depths greater than a few tens to at most a few hundreds of meters with a width of less than a few meters a length of the order of 100 m and a height of the order of 1 kin this structure is clearly the residue of the preeruption dikes although such a feature can be widened somewhat by repeated dike emplacement events there is no evidence to suggest that a larger and much more equant magma reservoir should develop at shallow depth the extensive degassing often occurring after single eruptions or between repeated eruptions previously thought to imply the presence of a large equidimensional shallow magma chamber can be readily explained by the volume of magma in a dikelike subvent planar magma storage zone on the basis of these observations which we infer to apply commonly to basaltic eruption sites we suggest that the terms chamber or reservoir be used with caution because they most often connote a relatively large equant magma body distinct from the feeder dike lying just below the vent we find that the subvent region has the same basic geometric characteristics as the parental dike and we propose that it be referred to as a planar magma storage zone

eruption of lava flows on europa theory and application to thrace macula europa on the basis of its spectral characteristics and its apparently young surface age is likely to be at least partially resurfaced by liquid water volcanic processes however convincing evidence for lava flow morphology in voyager data has not previously been found and the lower density of liquid water relative to an overlying solid water ice crust suggests that extrusive volcanism could be uncommon we examine a candidate lava flow like feature thrace macula and compare its characteristics with theoretical predictions for the ascent and eruption of water magma on europa outlining a range of conditions under which water ice magma could plausibly be erupted to the surface thrace macula 45 s 171 w is a dark lobate feature extending nnw to sse its northern part is centered in a 140 km diameter arcuate to circular lineament and within this zone are radial and concentric lineaments and three dark lobes similar in appearance to flow lobes extending away from a central region for distances of 40 50 and 160 km the 160 km lobe appears to follow local topographic features producing lobate margins at subdued structures broadening locally parallel to structural trends and terminating against a gray band models for the present structure and state of the predominantly h2o exterior of europa range from solid water ice to a thin ice layer overlying a liquid water layer and these conditions may even vary as a function of space and time ascent and eruption of h2o magma through a less dense water ice crust means that sustained effusive eruptions are very difficult to produce if a globally continuous liquid water or salt water layer exists e g crawford and stevenson 1988 kargel 1991 for flows as extensive as the thrace macula feature we thus require magma source regions sufficiently localized that excess pressure can be built up in the source region given the elastic properties of ice at these source depths the most likely scenario is intrusion of silicate magma into the base of an ice crust and melting and mobilization of water magma with this range of magma source settings we model plausible surface vent geometries for a water lava flow interpretation of thrace macula modeling calculations show that flow lobes with the above geometries and thicknesses on the order of 10 m could be formed in water eruptions on europa involving discharge rates of 2 105 m3 s through dikes with widths in the range 5 10 m these discharge rates about 3 times larger than those of terrestrial flood basalts should not be unusual for water eruptions on europa under these conditions and suggest that water volcanic resurfacing could be common on the satellite if source regions meeting these criteria were readily available the lack of abundant similar dark flows could be due to brightening with time or might imply that conditions for their formation grounded or nearly solid ice crust only evolved in the latter part of europan history

submarine eruption near socorro island mexico geochemistry and scanning electron microscopy studies of floating scoria and reticulite abstract products of an underwater eruption near socorro island in the ne pacific were observed directly on january 29 1993 ten days after precursors were first recorded by sofar sound fixing and ranging hydrophones located in hawaii and tahiti eruptive activity was noticed from boats and ships as small steam plumes rising from the sea at an area centered at 18 48 n 111 05 w 2 4 km nw of punta tosca and 4 6 km ssw of cape henslow on socorro island the observed steam was produced by 1 3 m large blocks of hot dark grey highly vesiculated basalt rising buoyantly to the surface from two submarine shallow vents at 210 and 30 m depth tens of blocks accompanied by bubbles could be observed rising to the surface in irregular pulses these scoriaceous blocks remained floating at the surface until they would crack into smaller pieces by thermal contraction emitting hissing noises from vapourizing seawater in contact with the hot interior of the blocks steam jets several metres in height were produced and occasionally blocks were propelled laterally by the steam jet depending on vesicularity and permeability blocks remained floating and drifting with the surface current for 1 15 minutes before sinking back floating rocks covered an area of about 6000 m2 this intermittent activity has been observed ever since and has not stopped as of april 1994 buoyant scoria and reticulite are indicative of volatile mostly co2 supersaturation and exsolution in the magma prior to rapid quenching which inhibits loss of volatiles by bubble escape a high velocity ascent of low viscosity magma in a relatively narrow conduit is also required to prevent substantial gas escape and allow formation of reticulite the buoyant scoria is most probably ejected by intermittent lava fountaining at fixed vents as a result of changes in eruption velocities due to changes in the exsolved gas content of the lava between january and july 1993 floating blocks of scoria and reticulite were collected on several occasions from the surface of the sea for chemical and mineralogical analyses major and minor element analyses including ree as well as electron microprobe analyses of different phases revealed that the composition of the emitted lava has not changed through time blocks of basalt sio2 45 47 are highly vitric and vesicular with tabular anorthite phenocrysts up to 3 mm in length and minor grains of forsteritic olivine ree and trace element composition of these rocks suggest an anomalous mantle source for the erupted alkali basalt lava the ongoing eruption will either continue in a similar fashion as described and eventually cease or built up a mound that reaches the surface and forms an island with accompanying change in eruptive style

magnetic properties of modern soils and quaternary loessic paleosols paleoclimatic implications the magnetic properties of paleosols developed in quaternary sequences of loess have been used for stratigraphic definition correlation with other terrestrial and deep sea sequences and paleoclimatic paleorainfall reconstruction in some loess paleosol sequences including those of the chinese loess plateau tajikistan and the czech republic maxima in magnetic susceptibility values correspond with the paleosol horizons and minima with the least weathered loess layers in other loess soil sequences including those of siberia alaska and argentina the relationship is completely opposite with susceptibility minima associated with the most developed paleosols to account for these opposite relationships the respective roles of 1 magnetic enhancement and 2 magnetic depletion and or dilution in determining soil magnetic properties are investigated for a range of modern soil types most magnetic enhancement is seen in the upper horizons of well drained cambisols absence or loss of magnetic iron oxides is apparent in acid podsol profiles and waterlogged soils for the cambisol profiles significant correlation is found between susceptibility and organic carbon cation exchange capacity and clay content the mineralogy morphology and grain size of soil magnetic carriers extracted from three modern enhanced soils and a paleosol from the chinese loess plateau are also identified by independent petrographic means microscopy and x ray diffraction of magnetic extracts magnetite and maghemite of ultrafine grain size from 0 4 to 0 001 i m are the major contributors to the magnetically enhanced soils weathering can concentrate detrital magnetic grains especially in the fine silt size fractions of soils the magnetic data from the modern soils indicate that interpretation of paleosol magnetic properties must be done on a site specific basis taking into account the possibilities of pedogenic enhancement pedogenic dilution or depletion and allochthonous inputs of magnetic minerals excessively arid wet or acid soils are unable to form significant amounts of pedogenic ferrimagnets well drained intermittently wet dry soils with reasonable buffering capacity and a substrate source of fe show most magnetic enhancement for those soils which favour magnetic enhancement processes correlation has been found between the maximum value of the pedogenic susceptibility and the annual rainfall the almost unique pedogenic system in the chinese loess plateau where variation in soil forming factors other than climate is reduced to a global minimum allows use of the paleo susceptibility values as proxy paleorainfall values to identify the mechanism of any link between magnetic properties for example susceptibility and climate change the mineralogy and grain size of soil magnetic carriers requires detailed investigation given the prospect of 1 quantitative paleorainfall records from continental loess records 2 predictions of present and future climate change and 3 the value of paleoclimate data for testing of numerical climate models such magnetic investigations can contribute significantly to our understanding of past and future environmental change

a quantitative reconstruction of a loess paleosol sequence focused on paleosol genesis an example from a section at chaoyang china abstract a typical loess paleosol sequence at chaoyang in china deposited continuously since 423 ka bp was examined to quantitatively reconstruct a loess paleosol sequence first particle size distribution was evaluated based on clay free fractions where the sum of sand silt 100 and fine earth fractions and used to characterize the parent material uniformity as well as field morphology geochemical features and micro morphology characteristics second mass balance mb and soil reconstruction sr approaches were employed to examine the linkage between pedogenesis and loess deposition the results indicated a uniform loess deposit below 228 cm depth and the presence of four reddish stratigraphic layers interbedded with four yellowish stratigraphic layers all derived mostly from silt eolian deposits the main soil pedogenic processes following silt deposition were clay eluviation illuviation silification and ferrallitization the strongest pedogenesis occurred for the s3 deposit layer during 225 243 ka bp and was associated with the greatest mass loss of non clay 7 6 na2o 42 cao 21 mgo 28 sio2 10 and at the same time with the greatest gains in clay 42 fe2o3 8 and al2o3 4 together with mass loss changes mc of 620 g 100 cm2 the greatest mass gain changes 234 g 100 cm2 occurred in the l4 deposit layer during 243 311 ka bp and were associated with gains in na2o 18 and p2o5 4 5 indicating the fastest deposition rate during the long period of sedimentation 423 ka bp loess deposition was predominant during dry cold periods whereas paleosol formation from pedogenic processes was predominant during wet warm periods thus the formation of paleosols and loess deposition were dependent on the relative rate of pedogenesis and deposition as controlled by climate change under an east asian summer monsoon eas paleosol formation dominated whereas loess deposition dominated under an east asian winter monsoon eaw quantification of the degree of loess development paleosols or loess deposits aids reconstructing soil genesis and understanding the loess paleosol formation sequence and its linkage to climate change

textural and geophysical characterization of explosive basaltic activity at villarrica volcano 1 villarrica volcano chile is one of the most active volcanoes in south america its activity is currently characterized by continuous degassing from a summit lava lake vent punctuated by explosive events during november 2004 a multidisciplinary experiment was deployed for a 10 d period to define the style of emission and infer shallow conduit dynamics at this basaltic center this involved collection of thermal seismic and infrasonic data to describe the background activity confined inside the crater and use of samples to texturally and chemically characterize the ejecta from more energetic explosions able to attain the crater rim the background activity was characterized by gas bursting with a frequency of 9 events per minute this involved emission of gas puffs fed by bubble bursting with larger bursts emplacing sheets of magma onto the lower crater walls the ejecta population from the more energetic events was characterized by the coexistence of both scoriae and golden pumice these two types of clasts have different textures but identical glass compositions suggesting that they underwent different conduit histories the golden pumice is interpreted as the expanding inner part of a short lived jet fed by a rapidly ascending magma batch the scoria forms the outer portion of the jet and comprises degassed material entrained during passage of the fresh batch through material residing in the upper most portion of the conduit we thus have a largely degassed upper column that feeds persistent bubble bursting through which fresh batches occasionally rise to feed events of relatively higher energy

pedostratigraphy and paleomagnetism of a 7 0 ma eolian loess red clay sequence at lingtai loess plateau north central china and the implications for paleomonsoon evolution abstract a 305 m thick loess red clay sequence was discovered recently at lingtai which is located in the middle part of the chinese loess plateau it consists of a complete pleistocene loess soil sequence with a thickness of about 175 m and 130 m of tertiary red clay deposits the red clay sequence at lingtai is the thickest one presently known in the loess plateau field observations show that the lingtai red clay contains over 110 couplets of pedogenic b horizons and horizontal carbonate nodule horizons and that it can be regarded as an extremely thick soil complex paleomagnetic studies of 680 samples suggest that the basal age of the lingtai loess red clay sequence is about 7 05 ma grain size analysis of samples taken at 3 3 cm intervals indicates that the red clay has the same sedimentological characteristics as those observed in the loess thus suggesting a wind blown origin of the tertiary red clay and continuous atmospheric dust deposition in the loess plateau during the last 7 05 ma the pedogenic characteristics of the paleosols within the pleistocene loess and the b horizons in the red clay suggest that the east asia summer monsoon in the latest miocene may have already been slightly stronger than that during the holocene this implies that at about 7 5 ma bp the tibetan plateau could have been uplifted to a critical height in maintaining the east asia summer monsoon system observations of the loess red clay sequence also suggest that the long term changes in the east asia summer monsoon strength have been nonlinear since the latest miocene

origin of the miocene pliocene red earth formation at xifeng in northern china and implications for paleoenvironments abstract in the eastern loess plateau region of northern china the quaternary loess soil sequences of the last 2 6 ma are underlain by the hipparion red earth formation magneto stratigraphic studies suggest that it is a near continuous terrestrial record for the period from 7 to 2 6 ma bp and therefore has great potential for the study of asian paleoclimates the origin of this formation is controversial and needs further study in this work the xifeng red earth section a type section for the eastern loess plateau region was studied using optical microscopic analysis grain size measurements and both major and trace element geochemical properties to address questions of its origin and environmental implications the results show that this formation consists of three parts the lower part 6 2 ma bp is a water reworked deposit related to alluvial and slope processes the middle part from 6 2 to 3 6 ma bp was derived from in situ eolian dust deposition but was significantly affected by groundwater oscillations and the upper part from 3 6 to 2 6 ma bp is an eolian formation similar to the quaternary loess soil sequence the grain size of the upper part is significantly coarser than for the middle part but finer than for the overlying loess because the eolian dust deposits in the middle reaches of the yellow river were mainly transported from the deserts in northern china by the northwesterly winter monsoon wind and the westerlies we interpret the eolian origin of the middle and upper red earth formation beginning approximately at 6 2 ma bp as an indication of the strengthening of the aridification of the asian continent desert lands in central asia must have been formed at or by that time to provide a significant source of dust however the generally finer grain size of the red earth suggests a weaker transporting wind and or a more remote source the latter implies a smaller extent of deserts than in the quaternary the high degree of similarity between the geochemical properties of the red earth and loess samples seems to suggest a rather similar source areas and comparable dust transporting trajectories the removal of the dust deposits from groundwater influence and the increase in grain size at 3 6 ma bp are attributable to both tectonic and climatic causes the initiation of these phenomena corresponds to an intensive uplift of the tibetan plateau and also to a simultaneous uplift of the sedimentary basins in the surrounding areas it is also approximately synchronous with an increase in eolian mass accumulation rate in the north pacific both suggesting an increased continental aridity in the asian dry lands and an increasing intensity of transporting winds

inverse modeling for possible rather than unique solutions abstract despite the implementation of several kinematic and mechanical models for fault related folding and the incorporation of structural uncertainty in geological models structural modeling is still too deterministic the current focus is on forward modeling of a unique fit we show the application of trishear inverse modeling global optimization and markov chain monte carlo mcmc methods to a clay model of basement involved compressional faulting from which we know both total and incremental deformation global optimization and mcmc methods provide a range of possible models rather than a unique fit total inversions give an average of the model s deformation while incremental inversions are more physically related to the model s evolution global optimization identifies the full range of possible models while mcmc characterizes expected parameter values and their uncertainties structural inversions without sound geology are meaningless a robust stratigraphy geomorphic markers mesoscopic structures analogue and mechanical modeling can all greatly improve the inversions

escarpment evolution on high elevation rifted margins insights derived from a surface processes model that combines diffusion advection and reaction experiments with a surface processes model of large scale 1 1000 km long term 1 100 m y erosional denudation are used to establish the controls on the evolution of a model escarpment that is related to the rifting of a continent the model describes changes in topographic form as a result of simultaneous short and long range mass transport representing hillslope diffusive processes and fluvial transport advection respectively fluvial entrainment is modeled as a first order kinetic reaction which reflects the credibility of the substrate and therefore the fluvial system is not necessarily carrying at capacity one dimensional and planform models demonstrate that the principal controls on the evolution of an initially steep model escarpment are 1 antecedent topography drainage 2 the timescale or equivalently a length scale in the fluvial entrainment reaction 3 the flexural response of the lithosphere to denudation and 4 the relative efficiencies of the short and long range transport processes when rainfall and substrate lithology are uniform a significant amount of discharge draining over the escarpment top causes it to degrade only when the top of the model escarpment coincides with a drainage divide can escarpment retreat occur for these conditions an additional requirement for retreat of a model escarpment without decline is a long reaction time scale for fluvial entrainment this corresponds to a substrate that is hard to detach by fluvial erosion and therefore to fluvial erosion that is not transport limited continuous backtilting of an escarpment due to flexural isostatic uplift in response to denudational unloading helps maintain the scarp top as a divide it is essential if the escarpment gradient is to be preserved during retreat in a uniform lithology low flexural rigidities promote steep and slowly retreating escarpments for given rainfall and substrate conditions the morphology of a retreating model escarpment is determined by the ratio of the short range diffusive and long range advective transport efficiencies a low ratio which is interpreted to correspond to a relatively arid climate and weathering limited conditions promotes steep sharp topped escarpments with straight main slopes and escarpment retreat occurs over a wide range of height scales a high ratio interpreted to correspond to a more humid temperate climate produces a convex upper slope and concave lower slope morphology and only major escarpments are predicted to preserve a high scarp gradient lithological contrasts in the model produce more complex morphologies and predict the formation of scarps crowned by an erosionally resistant caprock however resistant caprocks are not an essential requirement for model scarps to retreat we conclude that the inferred controls and model behavior are both consistent with the present day morphology of rifted continental margins and with modern conceptual models of landscape evolution

volumetric observations during paroxysmal eruptions at mount etna pressurized drainage of a shallow chamber or pulsed supply abstract the october 17 to november 5 1999 eruption of mount etna s bocca nuova crater emplaced a 15 10 6 m 3 flow field the eruption was characterized by 11 paroxysmal events during which intense strombolian and lava fountain activity fed vigorous channelized a a flows at eruption rates of up to 120 m 3 s 1 each paroxysm lasted between 75 and 450 min and was separated by periods of less intense strombolian activity and less vigorous 3 s 1 effusion ground based satellite and model derived volumetric data show that the eruption was characterized by two periods during which eruption rates and cumulative volume showed exponential decay this is consistent with a scenario whereby the system was depressurized during the first eruptive period october 17 23 repressurized during an october 24 pause and then depressurized again during the second period october 25 28 the imbalance between the erupted and supplied volumes mean that the two periods involved the collection of 1 5 5 7 10 6 m 3 and 1 2 3 6 10 6 m 3 respectively or an increase in the time averaged supply to 11 6 13 6 m 3 s 1 and 12 5 14 9 m 3 s 1 two models are consistent with the observed episodic fountaining derived volumetric trends and calculated volume imbalance a magma collection model and a pulsed supply model in the former case depressurization of a shallow reservoir cause the observed volumetric trends and foam collapse at the reservoir roof powers fountaining in the pulsing case variations in magma flux account for pressurization depressurization and supply the excess volume increases in rise rate and volatile flux coupled with rapid exsolution during ascent trigger fountaining limiting equations that define critical foam layer volumes and magma rise rates necessary for hawaiian style fountaining favor the latter model

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

magnetic susceptibility of the quaternary red clay in subtropical china and its paleoenvironmental implications abstract magnetic susceptibility lf and other magnetic parameters of 11 typical profiles of quaternary red clay qrc in subtropical china were measured lf curves of the qrc profiles show similar vertical variations lf of the uppermost yellow brown earth ybe and uniform red clay urc of the profiles is high mostly ranging from 50 to 150 10 8 m 3 kg 1 that of the reticulate red clay rrc sharply decreases downwards especially in the lower rrc lrrc with dense reticulate pattern lf is often less than 10 10 8 m 3 kg 1 grain size characteristics and geochemical properties of the qrc suggest that the sharp decrease of lf in the rrc is not related to sudden change of parent materials but to the formation of the reticulate pattern further study indicates that pedogenic fine ferrimagnetic minerals fm superparamagnetic particles sp and or stable single domain ssd are the main magnetic carriers of the qrc the ybe and urc with higher lf show low coercivity and magnetic soft behavior the rrc especially the lrrc with weak magnetism shows high coercivity and magnetic hard behavior the temperature dependent susceptibility tds of the qrc suggests that the dominant type of fm in the ybe and urc is pedogenic maghemite the rrc especially the lrrc however contains little maghemite but a trace amount of lithogenic multi domain md magnetite inherited from the parent rock during post depositional hydromorphic processes pedogenic maghemite was more easily dissolved than hematite which caused the sharp decrease of lf in the rrc as lf of the qrc was mainly controlled by the intensity of hydromorphic processes rather than the weathering degree lf of the qrc in subtropical china cannot accurately indicate the paleoclimate during the quaternary period when the red clay was initially formed

multidisciplinary investigation on a lava fountain preceding a flank eruption the 10 may 2008 etna case a multidisciplinary approach integrating a wide data set ranging from bulk rock compositions of the erupted products to volcanic tremor long period events and tilt and gravity signals is used to investigate the source depth and magma dynamics of the 10 may 2008 lava fountain at southeast crater sec of mount etna the investigation was undertaken in the framework of the previous 2007 explosive activity as well as the subsequent effusive eruption beginning 13 may 2008 and lasting up to july 2009 all the data concur in indicating that the 10 may lava fountain was generated by the fragmentation of a foam layer trapped at the top of a shallow reservoir about 1500 1700 m below the summit of sec the shift from the episodic strombolian lava fountain activity occurring in 2007 at sec to the more powerful 10 may 2008 lava fountain is explained by the intrusion of a new more primitive magma into the shallow reservoir data also indicate that an attempted magma intrusion east of the summit area occurred during the 10 may fire fountain this event caused the fracturing and weakening of the surrounding rocks and created a preferential pathway for the penetration of the magma that only 3 days later started to feed the 2008 2009 effusive eruption