combined discrete and continuous gravity observations at mount etna systematic investigation of discrete gravity measurements has continued at mount etna since 1986 the network now covers an area of 400 km2 with about 70 stations 0 5 3 km apart mass redistributions occurring at depths ranging between about 8 km below sea level and a few hundred metres below the surface magma level changes within the shallower parts of the feeding conduits have been identified from these data conventional discrete microgravity monitoring on a network of stations furnishes only instantaneous states of the mass distribution at continuously active systems in order to obtain information on the rate at which the volcanic processes and thus mass transfers occur three stations for continuously recording gravity where installed on mount etna in 1998 a 16 month long sequence from one of the continuously running stations pdn located 2 km from the active northeast crater at the summit of etna volcano is presented after removing the effects of earth tide and tilt the correlation of the residual gravity sequence with simultaneous recordings of meteorological parameters acquired at the same station was analysed once the meteorological effects have also been removed continuous gravity changes are within 10 gal of gravity changes measured using conventional microgravity observations at sites very close to the continuous station this example shows how discrete and continuous gravity observations can be used together at active volcanoes to get a fuller and more accurate picture of the spatial and temporal characteristics of volcanic processes

rheology of the ronne ice shelf antarctica inferred from satellite radar interferometry data using an inverse control method 1 the antarctic ice sheet is surrounded by large floating ice shelves that spread under their own weight into the ocean ice shelf rigidity depends on ice temperature and fabrics and is influenced by ice flow and the delicate balance between bottom and surface accumulation here we use an inverse control method to infer the rigidity of the ronne ice shelf that best matches observations of ice velocity from satellite radar interferometry ice rigidity or flow law parameter b is shown to vary between 300 and 900 kpa a 1 3 ice is softer along the side margins due to frictional heating and harder along the outflow of large glaciers which advect cold continental ice melting at the bottom surface of the ice shelf increases its rigidity while freezing decreases it accurate numerical modelling of ice shelf flow must account for this spatial variability in mechanical characteristics citation larour e e rignot i joughin and d aubry 2005 rheology of the ronne ice shelf antarctica inferred from satellite radar interferometry data using an inverse control method geophys res lett 32 l05503 doi 10 1029 2004gl021693

tidally driven stick slip motion in the mouth of whillans ice stream antarctica we show that the ice plain in the mouth of whillans ice stream formerly ice stream b antarctica moves by stick slip motion during a spring tide period rapid motions regularly occur near high tide and during falling tide this correlation is weaker during a neap tide period when the tidal magnitudes are less precise timing of these motion events suggests that they propagate through the region with a mean velocity of 88 ms 1 we hypothesize that this speed is associated with the propagation of shear waves through a wet subglacial till motion events are also seen on more smoothly flowing floating ice event delays are very short between grounded and floating stations suggesting the events propagate through the ice shelf as an elastic wave we further hypothesize the events are caused by the interaction of a sticky bed the accumulation of stored elastic strain through the compression of ice by upstream inflow and tidal forcing motion events seem to be triggered either by reduction of vertical normal stresses at high tide or by the increase of shear stresses from sub shelf ocean currents during falling tide event magnitudes are not related to the length of the preceding quiescent period suggesting significant viscous dissipation within the till

externally triggered renewed bubble nucleation in basaltic magma the 12 october 2008 eruption at halema uma u overlook vent kīlauea hawai i usa 1 from october 2008 until present dozens of small impulsive explosive eruptions occurred from the overlook vent on the southeast side of halema uma u crater at k lauea volcano usa these eruptions were triggered by rockfalls from the walls of the volcanic vent and conduit onto the top of the lava column here we use microtextural observations and data from clasts erupted during the well characterized 12 october 2008 explosive eruption at halema uma u to extend existing models of eruption triggering we present a potential mechanism for this eruption by combining microtextural observations with existing geophysical and visual data sets we measure the size and number density of bubbles preserved in juvenile ejecta using 2d images and x ray microtomography our data suggest that accumulations of large bubbles with diameters of 50 m to at least millimeters existed at shallow levels within the conduit prior to the 12 october 2008 explosion furthermore a high number density of small bubbles 50 m is measured in the clasts implying very rapid nucleation of bubbles visual observations combined with preexisting geophysical data suggest that the impact of rockfalls onto the magma free surface induces pressure changes over short timescales that 1 nucleated new additional bubbles in the shallow conduit leading to high number densities of small bubbles and 2 expanded the preexisting bubbles driving upward acceleration the trigger of eruption and bubble nucleation is thus external to the degassing system

the knudsen theorem and the total exchange flow analysis framework applied to the baltic sea abstract the knudsen theorem for estuarine exchange flow based on mass conservation of water and salt and its generalization with resolution in salinity coordinates the total exchange flow tef analysis framework are reviewed here the former had been developed and applied to quantify exchange flow between the north sea and the baltic sea more than a century ago in this paper the underlying short research paper published in 1900 by martin knudsen originally written in german is translated into english reaching far beyond the knudsen relation in particular the extensive scientific achievements of martin knudsen on the salinity of seawater are reviewed using the knudsen theorem and the tef analysis framework validated multi decadal years 1949 2013 model simulations are analyzed in terms of exchange flow through straits of the western baltic sea when comparing the model results to the original findings of martin knudsen it is impressive to see how relevant his analysis of ratios of averaged inflowing and outflowing water masses still is today given that they were based on just a few salinity observations the model based long term knudsen and tef analyses of exchange flow in the western baltic sea reproduces the major baltic inflows mbis that have occurred since the 1950s for the complex inflow years 2002 2003 with two baroclinic summer inflows and one barotropic winter inflow in between the strong underestimation of the exchange flow by eulerian analysis as compared to tef analysis is demonstrated

ice stream d flow speed is strongly modulated by the tide beneath the ross ice shelf the flow velocity of ice stream d west antarctica has been measured to vary by a factor of three over the course of a day these fluctuations are measured at the grounding line as well as upstream of the grounding line in the ice plain of ice stream d the diurnal velocity fluctations appear to be driven by the tide beneath the ross ice shelf these results suggest that there is significant and heretofore poorly understood influence of the ocean tide and of the ice shelf on the dynamics of ice stream flow

geophysical indications of magma uprising at mt etna during the december 2005 to january 2006 non eruptive period 1 during the december 2005 january 2006 non eruptive period the tremor amplitude at etna markedly increased and negatively correlated with the gravity signal from one of the two summit station over 2 3 hour periods no correlation was found with the signal from the other gravity station we locate the tremor source by inverting the spatial distribution of seismic amplitudes relying on the relative position of the two stations we define a volume within which the gravity source must lie during the period of marked anti correlation the tremor sources intersect this volume in a region located 1 km s se of the summit craters and about 2 km beneath the surface this finding suggests that the anti correlation marks the activation of a joint source process possibly related to the arrival of fresh magma and the consequent gas separation our study has implications for the early recognition of gas segregation processes at active volcanoes

three dimensional flushing times of the persian gulf 1 a three dimensional hydrodynamic model is employed in a fully prognostic mode to derive flushing times of the persian gulf an evaporation driven inverse estuary that is governed by import of surface water from the adjacent ocean and export of saline bottom gulf water through the strait of hormuz during spring and summer a cyclonic overturning circulation establishes along the full length of the gulf during autumn and winter this circulation breaks up into mesoscale eddies laterally stirring most of the gulf s surface waters as a result of this 95 flushing times of surface waters are shortest 1 3 yr increasing with distance from the strait along the iranian coast but are much longer 5 yr along the coasts of kuwait and saudi arabia owing to density stratification introduced by the surface inflow of ocean water flushing times of bottom waters are 6 yr in most parts of the gulf

a numerical investigation of circulation in the arabian gulf a three dimensional hydrodynamic model is developed to study the circulation in the arabian gulf the model contains realistic basin geometries and bathymetries of the arabian gulf and a good portion of the gulf of oman and is driven by monthly climatological winds evaporation and net ocean heat gain in both gulfs and the shatt al arab discharge it is found that the cyclonic circulation in the southern portion of the gulf is primarily driven by the evaporation induced freshening from the strait of hormuz in the northwestern corner of the gulf the shatt al arab discharge maintains the cyclonic circulation which would otherwise be anticyclonic the northwestward intrusion of fresher water along the iranian coast is weakened by northwesterly winds in winter but strengthens and extends almost to the head of the gulf in summer owing to the warming of the gulf of oman waters the development of the summer thermocline in the arabian gulf and diminishing winds the southward coastal current along the arabian coast is most prominent between the head of the gulf and qatar the model also predicts a strong southward coastal jet east of qatar which is primarily wind driven no similar coastal jet can be developed in the gulf of salwa west of qatar

gravity fluctuations induced by magma convection at kīlauea volcano hawai i convection in magma chambers is thought to play a key role in the activity of persistently active volcanoes but has only been inferred indirectly from geochemical observations or simulated numerically continuous microgravity measurements which track changes in subsurface mass distribution over time provide a potential method for characterizing convection in magma reservoirs we recorded gravity oscillations with a period of 150 s at two continuous gravity stations at the summit of k lauea volcano hawai i the oscillations are not related to inertial accelerations caused by seismic activity but instead indicate variations in subsurface mass source modeling suggests that the oscillations are caused by density inversions in a magma reservoir located 1 km beneath the east margin of halema uma u crater in k lauea caldera a location of known magma storage

estimation of hydraulic properties of subglacial till from ploughmeter measurements force variations on a ploughmeter and fluctuations in subglacial water pressure have been measured in the same borehole at storglaciaren sweden to investigate hydraulic properties of the basal till layer a strong inverse correlation of the pressure and force records in conjunction with a significant time lag between the two signals suggests that pore water pressures directly affect the strength of the till variations in subglacial water pressure result in potential gradients across the water till interface at the bottom of the borehole that drive pressure waves downwards through the till layer when the borehole water level is high and back upwards when the water level is low analysis of the propagation velocity of this pressure wave indicates that the hydraulic diffusivity of storglaciaren till is in the range 1 9 3 6 10 6 m 2 s 1 in good agreement with estimates obtained in the laboratory hydraulic conductivity values associated with these diffusivities are between 10 and 10 m s 1 and thus are well within the range of values for other glacial tills

ca isotope study of ordovician dolomite limestone and anhydrite in the williston basin implications for subsurface dolomitization and local ca cycling abstract a difference of 0 61 is reported between dolomite 1 66 and its precursor limestone 1 05 in the yeoman formation red river equivalent of the williston basin southeastern saskatchewan the significance of the large difference found and the preference for light isotope enrichment in the dolomite is evaluated with assistance from 87 sr 86 sr ratios and dolomitization models previously proposed for the studied rocks in particular i explore the possibility that 44 ca values in dolomite reflect the 44 ca values of the dolomitizing fluids without any correction for mineral fluid fractionation this hypothesis is based on recent studies showing negligible isotopic fractionation between carbonates and ca 2 bearing waters at very low precipitation rates fantle and depaolo 2007 jacobson and holmden 2008 if correct calcium isotopes hold promise as a tool for discriminating among numerous hydrological models of dolomite formation as a case in point the 44 ca value of the yeoman dolomite 1 66 is too low to reflect ca derived from the following sources 1 the original limestone 1 05 2 overlying beds of anhydrite 1 28 or 3 evaporated seawater 0 25 paleozoic carbonates ranging as low as 1 7 appear to be the lightest source of ca in the basin succession suggesting that the mg containing dolomitizing fluid was a connate water with a previous history of water rock interactions with paleozoic carbonates possibly involving earlier episodes of dolomitization and light ca release into migrating basinal fluids the relatively high seawater 44 ca values inferred from measurements of yeoman limestone and lake alma anhydrite suggest that seawater in the williston basin 450 ma was 0 22 0 46 higher in 44 ca than the contemporaneous ocean based on globally distributed brachiopods farkas et al 2007 this finding suggests that 44 ca values preserved in the deposits of epeiric seas may bias the 44 ca reconstruction of the ocean secular record if local ca cycling effects are not taken into account equations describing the isotope balance of ca in an epeiric sea indicate that seawater 44 ca values may be higher lower or equal to the 44 ca value of the ocean depending on the sizes of local scale ca deposition and weathering fluxes in relation to seawater ca exchange fluxes

focused seismicity triggered by flank instability on kīlauea s southwest rift zone abstract swarms of earthquakes at the head of the southwest rift zone on k lauea volcano hawai i reveal an interaction of normal and strike slip faulting associated with movement of k lauea s south flank a relocated subset of earthquakes between january 2012 and august 2014 are highly focused in space and time at depths that are coincident with the south caldera magma reservoir beneath the southern margin of k lauea caldera newly calculated focal mechanisms are dominantly dextral shear with a north south preferred fault orientation two earthquakes within this focused area of seismicity have normal faulting mechanisms indicating two mechanisms of failure in very close proximity 10 s of meters to 100 m we suggest a model where opening along the southwest rift zone caused by seaward motion of the south flank permits injection of magma and subsequent freezing of a plug which then fails in a right lateral strike slip sense consistent with the direction of movement of the south flank the seismicity is concentrated in an area where a constriction occurs between a normal fault and the deeper magma transport system into the southwest rift zone although in many ways the southwest rift zone appears analogous to the more active east rift zone the localization of the largest seismicity m2 5 within the swarms to a small volume necessitates a different model than has been proposed to explain the lineament outlined by earthquakes along the east rift zone

gravity height correlations for unrest at calderas abstract calderas represent the sites of the world s most serious volcanic hazards although eruptions are not frequent at such structures on the scale of human lifetimes there are nevertheless often physical changes at calderas that are measurable over periods of years or decades such calderas are said to be in a state of unrest and it is by studying the nature of this unrest that we may begin to understand the dynamics of eruption precursors here we review combined gravity and elevation data from several restless calderas and present new data on their characteristic signatures during periods of inflation and deflation we find that unless the bouguer gravity anomaly at a caldera is extremely small the free air gradient used to correct gravity data for observed elevation changes must be the measured or calculated gradient and not the theoretical gradient use of which may introduce significant errors in general there are two models that fit most of the available data the first involves a mogi type point source and the second is a bouguer type infinite horizontal plane source the density of the deforming material usually a magma chamber is calculated from the gravity and ground deformation data and the best fitting model is to a first approximation the one producing the most realistic density no realistic density is obtained where there are real density changes or where the data do not fit the point source or slab model we find that a point source model fits most of the available data and that most data are for periods of caldera inflation the limited examples of deflation from large silicic calderas indicate that the amount of mass loss or magma drainage is usually much less than the mass gain during the preceding magma intrusion in contrast deflationary events at basaltic calderas formed in extensional tectonic environments are associated with more significant mass loss as magma is injected into the associated fissure swarms

characterizing long time scale hydrological effects on gravity for improved distinction of tectonic signals the influence of the hydrological noise on repeated gravity measurements has been investigated on the basis of the time series of 18 superconducting gravimeters sgs and on predictions inferred from the land dynamics lad world gascoyne land water energy balances model presently the global hydrologic models are not precise enough to fulfill the geodetic requirements and are not efficient enough to separate the hydrology from tectonic motion in the land based gravity time series however although the lad model predictions and the gravity observations present significant differences in the time domain it is shown that they have similar amplitudes in the frequency domain in most of the cases the time series of the global geodynamics project make it possible to investigate phenomena of a few years in the best case given the similarity between the power spectral densities psds of the lad model predictions and the sg measurements when taken at the same epoch it makes sense to use the lad model to study the spectral behavior of the hydrological effects down to the decadal time scale which is not yet possible with land based measurements it is shown that the psds of the hydrological effects flattens at low frequency and is characterized by a generalized gauss markov structure with such a noise level the time necessary to measure a gravity rate of change of 1 nm s 2 a at the 1 sigma level should not extend any longer than 17 years at the locations where the hydrological effects play a major role

shallowly driven fluctuations in lava lake outgassing gas pistoning kīlauea volcano abstract lava lakes provide ideal venues for directly observing and understanding the nature of outgassing in basaltic magmatic systems k lauea volcano s summit lava lake has persisted for several years during which seismic and infrasonic tremor amplitudes have exhibited episodic behavior associated with a rise and fall of the lava surface gas pistoning since 2010 the outgassing regime of the lake has been tied to the presence or absence of gas pistoning during normal behavior no gas pistoning the lake is in a spattering regime consisting of higher tremor amplitudes and gas emissions in comparison gas piston events are associated with an abrupt rise in lava level up to 20 m during which the lake enters a non spattering regime with greatly decreased tremor and gas emissions we study this episodic behavior using long term multidisciplinary monitoring of the lake including seismicity infrasound gas emission and geochemistry and time lapse camera observations the non spattering regime i e rise phase of a gas piston cycle reflects gas bubbles accumulating near the top of the lake perhaps as a shallow foam while spattering regimes represent more efficient decoupling of gas from the lake we speculate that the gas pistoning might be controlled by time varying porosity and or permeability in the upper portions of the lava lake which may modulate foam formation and collapse competing models for gas pistoning such as deeply sourced gas slugs or dynamic pressure balances are not consistent with our observations unlike other lava lakes which have cyclic behavior that is thought to be controlled by deeply sourced processes external to the lake itself we show an example of lava lake fluctuations driven by cycles of activity at shallow depth and close to the lake s surface these observations highlight the complex and unsteady nature of outgassing from basaltic magmatic systems

observations of seasonal exchange through the straits of hormuz and the inferred heat and freshwater budgets of the persian gulf the exchange between the persian arabian gulf and the indian ocean is investigated using hydrographic and moored acoustic doppler current profiler data from the straits of hormuz during the period december 1996 to march 1998 the moored time series records show a relatively steady deep outflow through the strait from 40 m to the bottom with a mean speed of approximately 20 cm s a variable flow is found in the upper layer with frequent reversals on timescales of several days to weeks the annual mean flow in the near surface layer is found to be northeastward out of the persian gulf in the southern part of the strait suggesting a mean horizontal exchange with the indian ocean that is superimposed on the vertical overturning exchange driven by evaporation over the gulf the salinity of the deep outflow varies from 39 3 to 40 8 psu with highest outflow salinities occurring in the winter months december march the annual mean deep outflow through the strait is estimated to be 0 15 0 03 sv calculation of the associated heat and freshwater fluxes through the strait yields estimates for the annual heat loss over the surface of the gulf of 7 4 w m2 and an annual water loss e p r of 1 68 0 39 m yr these values are shown to be in relatively good agreement with climatological surface fluxes derived from the southampton oceanography centre global flux climatology after known regional biases in the radiative budget are taken into account

volcano geodesy recent developments and future challenges abstract ascent of magma through earth s crust is normally associated with among other effects ground deformation and gravity changes geodesy is thus a valuable tool for monitoring and hazards assessment during volcanic unrest and it provides valuable data for exploring the geometry and volume of magma plumbing systems recent decades have seen an explosion in the quality and quantity of volcano geodetic data new datasets some made possible by regional and global scientific initiatives as well as new analysis methods and modeling practices have resulted in important changes to our understanding of the geodetic characteristics of active volcanism and magmatic processes from the scale of individual eruptive vents to global compilations of volcano deformation here we describe some of the recent developments in volcano geodesy both in terms of data and interpretive tools and discuss the role of international initiatives in meeting future challenges for the field

very long period conduit oscillations induced by rockfalls at kilauea volcano hawaii 1 eruptive activity at the summit of kilauea volcano hawaii beginning in 2010 and continuing to the present time is characterized by transient outgassing bursts accompanied by very long period vlp seismic signals triggered by rockfalls from the vent walls impacting a lava lake in a pit within the halemaumau pit crater we use raw data recorded with an 11 station broadband network to model the source mechanism of signals accompanying two large rockfalls on 29 august 2012 and two smaller average rockfalls obtained by stacking over all events with similar waveforms to improve the signal to noise ratio to determine the source centroid location and source mechanism we minimize the residual error between data and synthetics calculated by the finite difference method for a point source embedded in a homogeneous medium that takes topography into account we apply a new waveform inversion method that accounts for the contributions from both translation and tilt in horizontal seismograms through the use of green s functions representing the seismometer response to translation and tilt ground motions this method enables a robust description of the source mechanism over the period range 1 1000 s the vlp signals associated with the rockfalls originate in a source region 1 km below the eastern perimeter of the halemaumau pit crater the observed waveforms are well explained by a simple volumetric source with geometry composed of two intersecting cracks including an east striking crack dike dipping 80 to the north intersecting a north striking crack another dike dipping 65 to the east each rockfall is marked by a similar step like inflation trailed by decaying oscillations of the volumetric source attributed to the efficient coupling at the source centroid location of the pressure and momentum changes induced by the rock mass impacting the top of the lava column assuming a simple lumped parameter representation of the shallow magmatic system the observed pressure and volume variations can be modeled with the following attributes rockfall volume 200 4500 m3 length of magma column 120 210 m diameter of pipe connecting the halemaumau pit crater to the subjacent dike system 6 m average thickness of the two underlying dikes 3 6 m and effective magma viscosity 30 210 pa s most rockfalls occur during episodes of sustained deflation of the kilauea summit the mass loss rate in the shallow magmatic system is estimated to be 1400 15 000 kg s 1 based on measurements of the temporal variation of vlp period in the two large rockfalls that occurred on 29 august 2012

ice sheet grounding line dynamics steady states stability and hysteresis 1 the ice sheet ice shelf transition zone plays an important role in controlling marine ice sheet dynamics as it determines the rate at which ice flows out of the grounded part of the ice sheet together with accumulation this outflow is the main control on the mass balance of the grounded sheet in this paper we verify the results of a boundary layer theory for ice flux in the transition zone against numerical solutions that are able to resolve the transition zone very close agreement is obtained and grid refinement in the transition zone is identified as a critical component in obtaining reliable numerical results the boundary layer theory confirms that ice flux through the grounding line in a two dimensional sheet shelf system increases sharply with ice thickness at the grounding line this result is then applied to the large scale dynamics of a marine ice sheet our principal results are that 1 marine ice sheets do not exhibit neutral equilibrium but have well defined discrete equilibrium profiles 2 steady grounding lines cannot be stable on reverse bed slopes and 3 marine ice sheets with overdeepened beds can undergo hysteresis under variations in sea level accumulation rate basal slipperiness and ice viscosity this hysteretic behavior can in principle explain the retreat of the west antarctic ice sheet following the last glacial maximum and may play a role in the dynamics of heinrich events

ice shelf tidal flexure and subglacial pressure variations abstract we develop a model of an ice shelf ice stream system as a viscoelastic beam partially supported by an elastic foundation when bedrock near the grounding line acts as a fulcrum leverage from the ice shelf dropping at low tide can cause significant 1 cm uplift in the first few kilometers of grounded ice this uplift and the corresponding depression at high tide lead to basal pressure variations of sufficient magnitude to influence subglacial hydrology tidal flexure may thus affect basal lubrication sediment flow and till strength all of which are significant factors in ice stream dynamics and grounding line stability under certain circumstances our results suggest the possibility of seawater being drawn into the subglacial water system the presence of seawater beneath grounded ice would significantly change the radar reflectivity of the grounding zone and complicate the interpretation of grounded versus floating ice based on ice penetrating radar observations

elastic dynamics and tidal migration of grounding lines modify subglacial lubrication and melting 1 we combine the dynamics of ice bed and ocean in a new elastic model for the tidal timescale migration of grounding lines on deformable foundations previous interpretations of tidal flexure using models of elastic ice shelves with fixed grounding lines were found to be inconsistent suggesting an elasticity of ice that varies spatially and temporally and that is significantly smaller than measured experimentally we argue here that with our model a consistent purely elastic interpretation can be made combining this new approach with remote sensing measurements we show that the grounding line migrates several kilometers during a tidal cycle that we can infer the effective elastic properties of the bed and that the elastic pressure of the ice leads to a hydrological barrier near the grounding line that controls subglacial hydrology our findings imply that subglacial lubrication and melting induced by the ocean thermal forcing can increase substantially during high tide

magma reservoir failure and the onset of caldera collapse at kīlauea volcano in 2018 introduction the 2018 rift zone eruption of k lauea volcano hawai i drained large volumes of magma from the volcano s summit reservoir system causing high rate subsidence of the ground surface and withdrawal of an active lava lake over the span of 1 week the surface of the lava lake fell more than 300 m continued withdrawal of magma caused the rock above the reservoir to fail triggering the onset of episodic caldera collapse surface collapse began near the evacuated lava lake vent but as the eruption continued over 3 months the area of the new caldera expanded to 5 km2 and its volume grew to 0 8 km3 the precursory activity and subsequent growth of the caldera were recorded in far greater detail than was possible at the handful of other caldera collapses observed in the past century these comprehensive observations permit new insights into the conditions that lead to magma reservoir host rock failure and caldera collapse rationale volcanic caldera collapses can be highly destructive and create prominent topographic features but little is known about the architecture of subcaldera magma storage zones or the critical decrease in pressure that triggers collapse withdrawal of k lauea s lava lake in 2018 can be used to gauge pressure change in the underlying magma reservoir we developed a model of time evolving reservoir depressurization to jointly explain lava lake withdrawal rate and the rate and spatial pattern of ground subsidence obtained from radar satellites and a dense local monitoring network results we tracked the evolution of the magmatic system from steady elastic decompression to inelastic failure we were able to estimate the location geometry volume and time evolving pressure within the reservoir as well as conditions required to trigger failure of the overlying crust before the onset of collapse the ground at k lauea s summit was subsiding at nearly 10 cm day and the lava lake surface was retreating at 50 m day we found that these phenomena were caused by drainage of magma at a high rate from a storage reservoir centered 2 km below the surface with a volume of several cubic kilometers drainage rapidly reduced reservoir pressure stressing the surrounding crust two weeks after the rift zone intrusion and eruption began to drain magma from the summit withdrawal of conclusion our results tightly constrain the pressure decrease in the magma reservoir before the onset of collapse together with geodetic data this bounds the magma storage volume and the stress changes needed to cause failure of the host rock above the reservoir our results demonstrate that a magma reservoir s roof may begin to fail after withdrawal of only a small fraction of the stored magma at k lauea this process was likely influenced by a relatively thin and wide reservoir roof and preexisting crustal weaknesses including an established caldera ring fault system and the lava lake vent roof collapses maintained magma pressure sustaining the eruption but they did not as is sometimes assumed completely repressurize the reservoir this indicates residual frictional strength on the collapse bounding faults the eruption was not terminated by complete evacuation of stored magma contrary to assumptions sometimes made when interpreting data from past caldera collapses and indicates that a different process was responsible for the cessation of the eruption joint monitoring of ground deformation and lava lake elevation at other volcanoes when possible may yield rich insights into magmatic processes and conditions

shallow magma accumulation at kīlauea volcano hawai i revealed by microgravity surveys for vertical displacement at the summit of about 1 3 m and 160 gal respectively the volume of magma lost based on grav ity data and assuming a reasonable magma density exceeded the volume of summit col lapse suggesting the creation of 40 90 10 6 abstract using microgravity data collected at k lauea volcano hawai i united states between november 1975 and january 2008 we document signifi cant mass increase beneath the east margin of halema uma u crater within k lauea s summit caldera surprisingly there was no sustained uplift accompanying the mass accumulation we propose that the positive grav ity residual in the absence of signifi cant uplift is indicative of magma accumulation in void space probably a network of interconnected cracks which may have been created when magma withdrew from the summit in response to the 29 november 1975 m 7 2 south fl ank earthquake subsequent refi lling documented by gravity represents a gradual recovery from that earthquake a new eruptive vent opened at the summit of k lauea in 2008 within a few hundred meters of the positive gravity residual maximum probably tapping the reservoir that had been accumulating magma since the 1975 earthquake

observations beneath pine island glacier in west antarctica and implications for its retreat thinning ice in west antarctica is currently contributing about 10 of the observed rise in global sea level observations obtained from an autonomous underwater vehicle operating beneath pine island glacier west antarctica reveal that the glacier was recently grounded on a transverse ridge in the sea floor but now warm sea water flows through the widening gap above the ridge thinning ice in west antarctica resulting from acceleration in the flow of outlet glaciers is at present contributing about 10 of the observed rise in global sea level1 pine island glacier in particular has shown nearly continuous acceleration2 3 and thinning4 5 throughout the short observational record the floating ice shelf that forms where the glacier reaches the coast has been thinning rapidly6 driven by changes in ocean heat transport beneath it as a result the line that separates grounded and floating ice has retreated inland7 these events have been postulated as the cause for the inland thinning and acceleration8 9 here we report evidence gathered by an autonomous underwater vehicle operating beneath the ice shelf that pine island glacier was recently grounded on a transverse ridge in the sea floor warm sea water now flows through a widening gap above the submarine ridge rapidly melting the thick ice of the newly formed upstream half of the ice shelf the present evolution of pine island glacier is thus part of a longer term trend that has moved the downstream limit of grounded ice inland by 30 km into water that is 300 m deeper than over the ridge crest the pace and ultimate extent of such potentially unstable retreat10 are central to the debate over the possibility of widespread ice sheet collapse triggered by climate change11 12

a review of controls on lava lake level insights from halema uma u crater kīlauea volcano the height of the lava column is a fundamental measure of open vent volcanic activity but little continuous long term data exist to understand this parameter the recent 2008 2018 lava lake activity at the summit of k lauea volcano provides an opportunity to track and understand the processes that control lava level over timescales ranging from minutes to years we review recently published data as well as analyze the long term record of lava level at k lauea s summit during 2009 2017 longer timescale fluctuations over days to months have a strong positive linear correlation with ground deformation suggesting they reflect pressure changes in the summit magma reservoir shorter timescale fluctuations over minutes to hours have an inverse relationship with spattering i e outgassing intensity at the lake surface increased outgassing lowers the lake level and vice versa our analysis of the long term lava level data thus confirms that lava level at halema uma u is controlled by these two types of processes 1 those related to magma reservoir pressure changes such as magma supply rate and 2 shallow outgassing fluctuations such as gas pistoning frequency filtering can isolate pressure and outgassing driven components of lava level change time series analysis indicates that there was no large persistent periodicity in the lava level a minor fortnightly oscillation might be related to earth tides but was not continuously present the correlation between lava level and deformation of the summit indicates that the lava lake acts as a reliable piezometer tracking lava level over time may thus provide an indication of flank eruptive potential we show that long term interdisciplinary monitoring is necessary to discriminate the processes that control lava level

intrusive mechanism of the 2002 ne rift eruption at mt etna italy inferred through continuous microgravity data and volcanological evidences 1 in october 2002 a new eruption began at etna lava flows were issued from two different fissure systems on the ne and s flanks of the volcano a continuous microgravity sequence acquired at a station on the n slope 2800 m a s l shows a marked decrease about 400 gal in less than one hour about 4 hours before lava was first emitted from the eruptive fissures along the ne rift this anomaly reversed soon afterward at a high rate the strong gravity decrease is interpreted as the opening by external forces of a shallow fracture system 1 km w of the gravity station magma from the central conduit entered the new fracture system passively and propagated through it towards lower portions of the ne rift both the arrangement of the new fracture system and the eruptive dynamics are in keeping with the inferred intrusive mechanism

gravity steps at mt etna volcano italy instrumental effects or evidences of earthquake triggered magma density changes 1 on two occasions sudden gravity changes occurred simultaneously at two summit etna s stations during local low magnitude earthquakes a systematic coupling between earthquakes inducing comparable maximum acceleration and displacement at the observation points and gravity steps is missing implying 1 the non instrumental nature of the steps and 2 the need for particular underlying conditions for the triggering mechanism s to activate we review some of the volcanological processes that could induce fast underground mass redistributions resulting in gravity changes at the surface these processes involve bubbles and crystals present in the magma and require particular conditions in order to be effective as mass redistributing processes the gravity steps could be a geophysical evidence of the dynamical stress transfer between tectonic and magmatic systems at a local scale given the implications that these transfers may have on the volcanic activity routine volcano monitoring should include the observation of fast gravity changes

terrasar x interferometry reveals small scale deformation associated with the summit eruption of kīlauea volcano hawai i 1 on 19 march 2008 a small explosive eruption at the summit of k lauea volcano hawai i heralded the formation of a new vent along the east wall of halema uma u crater in the ensuing years the vent widened due to collapses of the unstable rim and conduit wall some collapses impacted an actively circulating lava pond and resulted in small explosive events we used synthetic aperture radar data collected by the terrasar x satellite a joint venture between the german aerospace center dlr and eads astrium to identify and analyze small scale surface deformation around the new vent during 2008 2012 lidar data were used to construct a digital elevation model to correct for topographic phase allowing us to generate differential interferograms with a spatial resolution of about 3 m in k lauea s summit area these interferograms reveal subsidence within about 100 m of the rim of the vent small baseline subset time series analysis suggests that the subsidence rate is not constant and over time may provide an indication of vent stability and potential for rim and wall collapse information with obvious hazard implications the deformation is not currently detectable by other space or ground based techniques

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

inferring shallow subsurface density structure from surface and underground gravity measurements calibrating models for relatively undeformed volcanic strata at the jemez volcanic field new mexico usa imaging shallow subsurface density structure is an important goal in a variety of applications from hydrogeology to seismic and volcanic hazard assessment we assess the effectiveness of surface and subsurface gravity measurements in estimating the density structure of a well characterized rock volume the mesa a small flat topped plateau upon which the town of los alamos new mexico usa is located our gravity measurements were made on the mesa surface above a horizontal tunnel and underground within the tunnel we demonstrate that in the absence of other geophysical data such as seismic data or muon attenuation subsurface tunnel gravity measurements are critical to accurately recovering geologic structure without the tunnel data our resolution is limited to roughly the surface gravity station spacing but by including the tunnel data we can resolve structure to a depth of 10 times the surface gravity station spacing densities were obtained using both forward modeling and a bayesian inverse modeling approach incorporating relevant constraints from geologic observations we find that bayesian inversion with geologically relevant prior is a superior approach to the forward models in terms of both robustness and efficiency and correctly predicts the orientation and elevation of important geologic features

pigeonholing pyroclasts insights from the 19 march 2008 explosive eruption of kīlauea volcano we think conventionally of volcanic explosive eruptions as being triggered in one of two ways by release and expansion of volatiles dissolved in the ejected magma magmatic explosions or by transfer of heat from magma into an external source of water phreatic or phreatomagmatic explosions we document here an event where neither magma nor an external water source was involved in explosive activity at k lauea instead the eruption was powered by the expansion of decoupled magmatic volatiles released from deeper magma which was not ejected by the eruption and the trigger was a collapse of near surface wall rocks that then momentarily blocked that volatile flux mapping of the advected fall deposit a day after this eruption has highlighted the difficulty of constraining deposit edges from unobserved or prehistoric eruptions of all magnitudes our results suggest that the dispersal area of advected fall deposits could be miscalculated by up to 30 of the total raising issues for accurate hazard zoning and assessment eruptions of this type challenge existing classification schemes for pyroclastic deposits and explosive eruptions and in the past have probably been interpreted as phreatic explosions where the eruptive mechanism has been assumed to involve flashing of groundwater to steam

oceanographic controls on shallow water temperate carbonate sedimentation spencer gulf south australia spencer gulf is a large ca 22 000 km2 shallow 60 m water depth embayment with active heterozoan carbonate sedimentation gulf waters are metahaline salinities 39 to 47 and warm temperate ca 12 to 28 c with inverse estuarine circulation the integrated approach of facies analysis paired with high resolution monthly oceanographic data sets is used to pinpoint controls on sedimentation patterns with more confidence than heretofore possible for temperate systems biofragments mainly bivalves benthic foraminifera bryozoans coralline algae and echinoids accumulate in five benthic environments luxuriant seagrass meadows patchy seagrass sand flats rhodolith pavements open gravel sand plains and muddy seafloors the biotic diversity of spencer gulf is remarkably high considering the elevated seawater salinities echinoids and coralline algae traditionally considered stenohaline organisms are ubiquitous euphotic zone depth is interpreted as the primary control on environmental distribution whereas seawater salinity temperature hydrodynamics and nutrient availability are viewed as secondary controls luxuriant seagrass meadows with carbonate muddy sands dominate brightly lit seafloors where waters have relatively low nutrient concentrations ca 0 to 1 mg chl a m 3 low diversity bivalve dominated deposits occur in meadows with highest seawater salinities and temperatures 43 to 47 up to 28 c patchy seagrass sand flats cover less illuminated seafloors open gravel sand plains contain coarse bivalve bryozoan sediments interpreted as subphotic deposits in waters with near normal marine salinities and moderate trophic resources 0 5 to 1 6 mg chl a m 3 to support diverse suspension feeders rhodolith pavements coralline algal gravels form where seagrass growth is arrested either because of decreased water clarity due to elevated nutrients and associated phytoplankton growth 0 6 to 2 mg chl a m 3 or bottom waters that are too energetic for seagrasses currents up to 2 m sec 1 muddy seafloors occur in low energy areas below the euphotic zone the relationships between oceanographic influences and depositional patterns outlined in spencer gulf are valuable for environmental interpretations of other recent and ancient particularly neogene high salinity and temperate carbonate systems worldwide

continuous gravity and tilt reveal anomalous pressure and density changes associated with gas pistoning within the summit lava lake of kīlauea volcano hawai i

continuous gravity measurements reveal a low density lava lake at kīlauea volcano hawai i abstract on 5 march 2011 the lava lake within the summit eruptive vent at k lauea volcano hawai i began to drain as magma withdrew to feed a dike intrusion and fissure eruption on the volcano s east rift zone the draining was monitored by a variety of continuous geological and geophysical measurements including deformation thermal and visual imagery and gravity over the first 14 hours of the draining the ground near the eruptive vent subsided by about 0 15 m gravity dropped by more than 100 gal and the lava lake retreated by over 120 m we used gps data to correct the gravity signal for the effects of subsurface mass loss and vertical deformation in order to isolate the change in gravity due to draining of the lava lake alone using a model of the eruptive vent geometry based on visual observations and the lava level over time determined from thermal camera data we calculated the best fit lava density to the observed gravity decrease to our knowledge the first geophysical determination of the density of a lava lake anywhere in the world our result 950 300 kg m 3 suggests a lava density less than that of water and indicates that k lauea s lava lake is gas rich which can explain why rockfalls that impact the lake trigger small explosions knowledge of such a fundamental material property as density is also critical to investigations of lava lake convection and degassing and can inform calculations of pressure change in the subsurface magma plumbing system

mapping the grounding zone of the ross ice shelf antarctica using icesat laser altimetry we use laser altimetry from the ice cloud and land elevation satellite icesat to map the grounding zone gz of the ross ice shelf antarctica at 491 locations where icesat tracks cross the grounding line gl ice flexure in the gz occurs as the ice shelf responds to short term sea level changes due primarily to tides icesat repeat track analysis can be used to detect this region of flexure since each repeated pass is acquired at a different tidal phase the technique provides estimates for both the landward limit of flexure and the point where the ice becomes hydrostatically balanced we find that the icesat derived landward limits of tidal flexure are in many places offset by several km and up to 60 km from the gl mapped previously using other satellite methods we discuss the reasons why different mapping methods lead to different gl estimates including instrument limitations variability in the surface topographic structure of the gz and the presence of ice plains we conclude that reliable and accurate mapping of the gl is most likely to be achieved when based on synthesis of several satellite datasets

insights into shallow magmatic processes at kīlauea volcano hawaiʻi from a multiyear continuous gravity time series continuous gravity data collected near the summit eruptive vent at k lauea volcano hawai i during 2011 2015 show a strong correlation with summit area surface deformation and the level of the lava lake within the vent over periods of days to weeks suggesting that changes in gravity reflect variations in volcanic activity joint analysis of gravity and lava level time series data indicates that over the entire time period studied the average density of the lava within the upper tens to hundreds of meters of the summit eruptive vent remained low approximately 1000 1500 kg m3 the ratio of gravity change adjusted for earth tides and instrumental drift to lava level change measured over 15 day windows rose gradually over the course of 2011 2015 probably reflecting either 1 a small increase in the density of lava within the eruptive vent or 2 an increase in the volume of lava within the vent due to gradual vent enlargement superimposed on the overall time series were transient spikes of mass change associated with inflation and deflation of k lauea s summit and coincident changes in lava level the unexpectedly strong mass variations during these episodes suggest magma flux to and from the shallow magmatic system without commensurate deformation perhaps indicating magma accumulation within and withdrawal from void space a process that might not otherwise be apparent from lava level and deformation data alone continuous gravity data thus provide unique insights into magmatic processes arguing for continued application of the method at other frequently active volcanoes

gravity changes and deformation at kīlauea volcano hawaii associated with summit eruptive activity 2009 2012 analysis of microgravity and surface displacement data collected at the summit of k lauea volcano hawaii usa between december 2009 and november 2012 suggests a net mass accumulation at 1 5 km depth beneath the northeast margin of halema uma u crater within k lauea caldera although residual gravity increases and decreases are accompanied by periods of uplift and subsidence of the surface respectively the volume change inferred from the modeling of interferometric synthetic aperture radar deformation data can account for only a small portion as low as 8 of the mass addition responsible for the gravity increase we propose that since the opening of a new eruptive vent at the summit of k lauea in 2008 magma rising to the surface of the lava lake outgasses becomes denser and sinks to deeper levels replacing less dense gas rich magma stored in the halema uma u magma reservoir in fact a relatively small density increase 200 kg m 3 of a portion of the reservoir can produce the positive residual gravity change measured during the period with the largest mass increase between march 2011 and november 2012 other mechanisms may also play a role in the gravity increase without producing significant uplift of the surface including compressibility of magma formation of olivine cumulates and filling of void space by magma the rate of gravity increase higher than during previous decades varies through time and seems to be directly correlated with the volcanic activity occurring at both the summit and the east rift zone of the volcano

shallow degassing events as a trigger for very long period seismicity at kīlauea volcano hawai i the first eruptive activity at k lauea volcano s summit in 25 years began in march 2008 with the opening of a 35 m wide vent in halema uma u crater the new activity has produced prominent very long period vlp signals corresponding with two new behaviors episodic tremor bursts and small explosive events both of which represent degassing events from the top of the lava column previous work has shown that vlp seismicity has long been present at k lauea s summit and is sourced approximately 1 km below halema uma u by integrating video observations infrasound and seismic data we show that the onset of the large vlp signals occurs within several seconds of the onset of the degassing events this timing indicates that the vlp is caused by forces sourced at or very near the lava free surface due to degassing transmitted down the magma column and coupling to the surrounding rock at 1 km depth

magma compressibility and the missing source for some dike intrusions 1 dike intrusions are often accompanied by localized deflation interpreted as depressurizing magma chambers feeding the dike in some cases the inferred volume decrease is a factor of 4 or 5 less than the volume increase of the dike here we explore whether this discrepancy can be explained by compressibility of the magma combined with the fact that cracks are much more compliant than equidimensional magma chambers if pressure changes are small the magma compressibility m is constant and the dike ends up in hydrostatic equilibrium with an ellipsoidal magma chamber at the same depth the ratio rv of the volume of the crack to the volume lost by the chamber is rv 1 4 m 3 1 where is the host rock rigidity for gas poor magmas m 0 6 2 10 10 pa 1 and 3 25 gpa we find 1 2 rv 7 7 large changes in magma compressibility due to gas exsolution increase rv

lava lake level as a gauge of magma reservoir pressure and eruptive hazard forecasting volcanic activity relies fundamentally on tracking magma pressure through the use of proxies such as ground surface deformation and earthquake rates lava lakes at open vent basaltic volcanoes provide a window into the uppermost magma system for gauging reservoir pressure changes more directly at k lauea volcano hawai i usa the surface height of the summit lava lake in halema uma u crater fluctuates with surface deformation over short hours to days and long weeks to months time scales this correlation implies that the lake behaves as a simple piezometer of the subsurface magma reservoir changes in lava level and summit deformation scale with and shortly precede changes in eruption rate from k lauea s east rift zone indicating that summit lava level can be used for short term forecasting of rift zone activity and associated hazards at k lauea

formation and circulation of dense water in the persian arabian gulf 1 the nature and circulation of water masses in the persian arabian gulf hereinafter referred to as the gulf is investigated by examination of a historic database of hydrographic observations the densest water forms in winter at the northern end of the gulf rather than along the warmer southern and western coasts with the exception of small amounts of water directly above the seafloor most water flowing out of the gulf mixes across a density front that separates gulf deep water within the gulf from the indian ocean surface water iosw contrary to previous inferences the seasonally variable incursion of iosw into the gulf peaks in late spring this timing may be due to seasonal changes in sea surface slope driven by variations in evaporation rate in order to explain mooring results published elsewhere that show relatively small seasonal changes in the volume flux through the strait of hormuz hereinafter referred to as the strait we suggest that this flux is driven by the difference between the density of gulf deep water in the interior of the basin and water at comparable depths outside the gulf this density difference varies less than 15 during the year high rates of vertical mixing in the strait extend about 200 km westward in response to topographic constriction of tidal flows by islands and shoals

an improved model for tidally modulated grounding line migration understanding grounding line dynamics is necessary for predictions of long term ice sheet stability however despite growing observations of the tidal influence on grounding line migration this short timescale migration is poorly understood with most modeling attempts assuming beam theory to calculate displacements here we present an improved model of tidal grounding line migration that treats migration as an elastic fracture problem forced by the additional ocean water pressure from the tide this new model predicts that the grounding line cannot be assumed to be in hydrostatic equilibrium and furthermore that migration is inherently asymmetric and nonlinear with migration distances that are not proportional to the tidal load specifically for constant surface slope the grounding line migrates upstream approximately ten times further as the tide rises from mean sea level to high tide than it migrates downstream as the tide falls from mean sea level to low tide and migration distances are substantially larger than simple flotation arguments suggest numerical tests also show that the dependence of migration distance on elastic moduli and ice sheet thickness are inconsistent with predictions of beam theory for a range of realistic values finally applying the new model to observations in antarctica results in new estimates of bed slopes though these estimates remain uncertain due to imperfect knowledge of the relevant rheological parameters