surface energy balance and melt thresholds over 11 years at taylor glacier antarctica 11 years ablation 18 cm a 1 was dominated by sublimation with very few occurrences of melt 42 days during 11 years results also indicated that above freezing air temperatures did not necessarily result in melt and in turn melt occurred during subfreezing air temperatures under some conditions for air temperatures near freezing low wind speed was critically important for melt initiation according to the model subsurface melt away from rocks and sediment in the ice occurred three times more frequently than surface melt occurs no deeper than 50 cm below the glacier surface and was small never exceeding 8 by mass the magnitude of subsurface melting and the energy balance indicate that taylor glacier ice is intermediate in optical properties between snow and blue ice

seismic velocity changes concentrated at the shallow structure as inferred from correlation analyses of ambient noise during volcano deformation at izu oshima japan we investigate the stress sensitivity of velocity changes at izu oshima in japan using seismic interferometry method we calculate cross correlation functions ccfs of ambient noises recorded by four seismic stations on the active volcano from 1 january 2012 to 31 december 2015 at 0 5 1 hz 1 2 hz and 2 4 hz applying moving time windows to calculate cross spectrum between daily ccfs and reference ccf which is the average for the all observation period we compute daily velocity changes the obtained velocity changes vary from 1 to 3 with a dominant period of about 1 year we calculate areal strains by using global navigation satellite systems data at the volcano it is evident that the velocity changes are well correlated with the areal strain changes whose linear trend is removed the stress sensitivity of velocity changes which are obtained from the observed velocity changes and areal strains is lower at 0 5 1 hz than that at higher frequencies 7 1 1 3 10 8 pa 1 at 0 5 1 hz 1 4 0 1 10 7 pa 1 at 1 2 hz and 1 3 0 1 10 7 pa 1 at 2 4 hz modeling the velocity changes of rayleigh wave propagating in layered structures we find that the observed velocity changes are concentrated in the upper 1 km of the structure since similar frequency dependency is recognized among the stress sensitivity of velocity changes reported in previous studies we conclude that the velocity changes are localized in the shallow depth because of the increase of confining pressure

inflation deflation cycles revealed by tilt and seismic records at stromboli volcano 1 strombolian activity is driven by gas dynamic where large quantities of volatiles are first exsolved and then suddenly released ejecting fragmented lava at 100 300 m height with exit velocities of 20 70 m s this conduit process is detected as vlp seismicity only in the final stage 10 s before the explosion when the rising gas slug interacts with the shallower part last 200 300 m of the feeding conduits we present new ground deformation recorded with high resolution tiltmeters 1 nrad sampled at 1 hz and detected by broad band seismometers that extends the perception of this explosive process tiltmeters and seismometers reveal that the explosive process is accompanied by a persistent deformation of the ground detected as small 100 nrad inflation deflation cycles 250 s long and associated with the constant process of gas recharge and discharge of the magma conduit

detecting seasonal variations in seismic velocities within los angeles basin from correlations of ambient seismic noise summary we analyse 3 yr of continuous seismic records from broad band stations of the caltech regional seismic network ci in vicinity of the los angeles basin using correlations of ambient seismic noise relative velocity variations in the order of 0 1 per cent can be measured between all interstation pairs it is the first time that such an extensive study between 861 interstation pairs over such a large area has been carried out we perform these measurements using the stretching technique assuming that one of the two waveforms is merely a stretched version of the other obviously this assumption is always violated and the two waveforms are generally decorrelated due to temporal changes in the earth crust due to different sources or simply because the cross correlations are not fully converged we investigate the stability of these measurements by repeating each measurement over various time windows of equal length on average between all interstation pairs in the los angeles basin a seasonal signal in the relative velocity variation is observed with peaks and troughs during winter and summer time respectively generally the observed signal decreases with increasing interstation distance and relative traveltime perturbations can only be measured up to an interstation distance of 60 km furthermore the traveltime perturbations do not depend on azimuth of station pairs suggesting that they are not related to seasonal variations of the noise sources performing a simple regionalization by laterally averaging measurements over a subset of stations we found the sedimentary basin showing the most consistent signal and conclude that the observed seasonality might be induced either by changes in the ground water aquifer or thermo elastic strain variations that persist down to a depth of 15 22 km

three dimensional shear velocity anisotropic model of piton de la fournaise volcano la reunion island from ambient seismic noise we cross correlate 4 years of seismic noise from the seismic network of piton de la fournaise volcano la reunion island to measure the group velocity dispersion curves of rayleigh and love waves we average measurements from vertical and radial components to obtain 577 rayleigh wave dispersion curves the transverse components provided 395 love wave dispersion curves we regionalize the group velocities measurements into 2 d velocity maps between 0 4 and 8 s finally we locally inverted these maps for a pseudo 3 d anisotropic shear velocity model down to 3 km below the sea level using a neighborhood algorithm the 3 d isotropic shear wave model shows three distinct high velocity anomalies surrounded by a low velocity ring the anomaly located below the present plaine des sables could be related to an old intrusive body at the location of the former volcanic center before it migrated toward its present location the second high velocity body located below the summit of the volcano likely corresponds to the actual preferential dyke intrusion zone as highlighted by the seismicity the third high velocity anomaly located below the grandes pentes and the grand brule areas and is an imprint of the solidified magma chamber of the dismantled les alizes volcano radial anisotropy shows two main anomalies positive anisotropy above sea level highlighting the recent edifice of piton de la fournaise with an accumulation of horizontal lava flows and the second one below the sea level with a negative anisotropy corresponding to the ancient edifice of piton de la fournaise dominated by intrusions of vertical dykes

high resolution hydrothermal structure of hansbreen spitsbergen mapped by ground penetrating radar detailed ground penetrating radar gpr surveys at 50 and 200 mhz on hansbreen a polythermal glacier in southern svalbard are presented and interpreted comparison of the variations in character of the radar reflections with borehole thermometry and water levels in moulins suggests that gpr can be used to study the hydrothermal properties of the glacier the high resolution of the gpr data shows that the hydrothermal structure of the glacier is highly variable both along the centre line and on transverse profiles water contents for many places and depths within the glacier were calculated by estimating radar wave velocities to point reflectors we find typical water contents of 1 2 for the temperate ice but wetter ice associated with surface crevassing and moulins typically 4 water content there is evidence that wet ice sometimes overlays drier ice the hydrothermal structure is thus shown to be very complex temperature gradients in the cold ice indicate freezing rates of temperate ice below cold ice of 0 1 0 5 m a while isolated point reflectors within the cold ice indicate large water filled bodies that are probably related to the regular drainage structure of the glacier

monitoring velocity variations in the crust using earthquake doublets an application to the calaveras fault california we present a technique that greatly improves the precision in measuring temporal variations of crustal velocities using an earthquake doublet or pair of microearthquakes that have nearly identical waveforms and the same hypocenter and magnitude but occur on different dates we compute differences in arrival times between seismograms recorded at the same station in the freqency domain by cross correlation of short windows of signal a moving window analysis of the entire seismograms including the coda gives t the difference in arrival times versus running time along the seismogram the time resolution of the method is an order of magnitude better than the digitization interval the t technique is illustrated with a pair of microearthquakes m 1 7 and 2 0 that occurred before and after the coyote lake california earthquake m 5 9 of august 6 1979 and on the same segment of the calaveras fault that ruptured during the earthquake the coda wave arrivals for some stations are progressively delayed for the second earthquake in the doublet so that its seismogram appears as a stretched version of the earlier event we interpret this systematic variation in t along the coda as a change in the average s velocity in the upper crust in the time interval between the two doublets s wave velocities appear to have decreased by 0 2 in an oblong region 5 10 km in radius at the south end of the aftershock zone

modelling the long term mass balance and firn evolution of glaciers around kongsfjorden svalbard we analyse the long term 1961 2012 distributed surface mass balance and firn evolution of the kongsvegen and holtedahlfonna glacier systems in northwestern svalbard we couple a surface energy balance model to a firn model with forcing provided from regional climate model output in situ observational data are used to calibrate model parameters and validate the output the simulated area averaged surface mass balance for 1961 2012 is slightly positive 0 08 m w e a 1 which only fractionally compensates for mass loss by calving refreezing of percolating water in spring summer 0 13 m w e a 1 and stored water in fall winter 0 18 m w e a 1 provides a buffer for runoff internal accumulation i e refreezing below the previous year s summer surface in the accumulation zone peaks up to 0 22 m w e a 1 and is unaccounted for by stake observations superimposed ice formation in the lower accumulation zone ranges as high as 0 25 m w e a 1 a comparison of the periods 1961 99 and 2000 12 reveals 21 higher annual melt rates since 2000 and a 31 increase in runoff which can only in part be ascribed to recent warmer and drier conditions in response to firn line retreat both albedo lowering snow ice albedo feedback and lower refreezing rates refreezing feedback further amplified runoff

bed properties and hydrological conditions underneath mccall glacier alaska usa during three summer field seasons 2003 2005 and 2006 we carried out radio echo sound ing measurements with a 5 mhz central frequency ice penetrating radar on mccall glacier arctic alaska usa along the central flowline and 17 cross profiles two way travel time was after migration converted to ice thickness which in combination with a recent digital elevation model of the surface of the glaciated area resulted in a detailed map of the bed topography this reveals a complex basal topography in the confluence area of the different glacial cirques the pattern of subglacial water flow following the hydraulic potential gradient was calculated for the whole glacier area and shows a confluence of subglacial water downstream from the confluence of the glacier cirques from the ice thickness map the total ice volume was estimated as slightly less than 0 5 km 3 bed reflection power brp was determined for the glacier after correction for ice thickness dependence results reveal a clear relationship between the brp pattern and basal sliding anomalies along the central flowline

temporal changes in the radiophysical properties of a polythermal glacier in spitsbergen in order to study the seasonal and inter seasonal variations in radio wave velocity rwv radiophysical investigations were made at hansbreen a polythermal glacier in spitsbergen in july august 2003 and april 2004 these investigations included repeated radar profiling 20 and 25mhz along a transverse profile repeated common midpoint measurements continuous radar measurements during 8 days at a fixed site meteorological observations and continuous ice surface velocity monitoring by differential gps seasonal and inter seasonal rwv changes in the temperate ice layer are attributed respectively to rapid water redistribution within it during the summer and to variations in water content from 2 1 in summer to 0 4 in spring the reflection properties of the temperate ice layer correlate well with the air temperature with a nearly semi diurnal time lag the temporal variability of the reflection properties of the internal horizon suggests enlargement of water inclusions or water drainage from the horizon repeated profiling shows a stable spatial pattern in bed reflection power interpreted as changes in water content controlled by bedrock topography the spatial variations of internal reflection energy along the repeated profile correlate with the thickness of the cold ice layer and the occurrence of drainage and crevasse systems

penetration depth of interferometric synthetic aperture radar signals in snow and ice digital elevation models of glaciated terrain produced by the nasa jet propulsion laboratory jpl airborne interferometric synthetic aperture radar insar instrument in greenland and alaska at the c 5 6 cm wave length and l band 24 cm frequencies were compared with surface elevation measured from airborne laser altimetry to estimate the phase center of the interferometric depth or penetration depth p on cold polar firn at greenland summit p 9 2m at c and 14 4m at l band on the exposed ice surface of jakobshavn isbrae west greenland p 1 2 m at c and 3 3 m at l band except on smooth marginal ice where p 15 5 m on colder marginal ice of northeast greenland p reaches 60 to 120 m at l band on the temperate ice of brady glacier alaska p is 4 2 m at c and 12 6 m at l band with little dependence on snow ice conditions the implications of the results on the scientific use of insar data over snow ice terrain is discussed

use of c band ground penetrating radar to determine backscatter sources within glaciers the question of penetration of synthetic aperture radar sar signals at c band frequency into polar glaciers is addressed by comparing ground penetrating radar gpr and sar backscatter signatures profiles of the kongsvegen glacier svalbard were obtained with a c band gpr the received signal is converted to the equivalent radar cross section using the standard radar equation thus mapping the effective scattering sources within the glacier at this frequency the depth of the observed scattering sources is greatest in the superimposed ice where layers are clearly seen to a depth of approximately 14 m the very high scattering properties of the upper firn layers preclude layers deeper than approximately 6 m from being imaged integrating the radar cross sections over the depth gives a single backscatter value that we compare with the backscatter coefficient scattering cross section per unit area of the processed sar data for the same profile the comparison indicates that for coincidentally acquired gpr and sar data the radar cross section measured by the gpr does represent the features that contribute to the sar signal

tidal asymmetry in sediment resuspension on a macrotidal beach in northwestern australia abstract a field experiment was conducted on a macrotidal beach in northwestern australia to investigate the relation between sediment resuspension and sea bed morphology continuous measurements of waves currents and suspended sediment concentrations were carried out over a period of several hours around high tide concurrent with half hourly visual observations of the sea bed morphology the incident waves had a significant wave height of 0 35 m and period 11 s most of the data were collected outside the surf zone where sediment resuspension was mainly by wave groups and suspended sediment transport was primarily accomplished by mean longshore and cross shore currents the sediment resuspension process was further characterised by a pronounced tidal asymmetry with suspended sediment concentrations and transport rates during the falling tide significantly larger than during the rising tide the asymmetry is attributed to the combined effects of a larger bed roughness and stronger mean nearshore flows during the falling tide the increase in bed roughness occurred during the rising tide under the influence of decreasing bed shear stresses when post vortex ripple morphology developed on a previously plane bed around high tide the ripples were fully developed and had attained a ripple height of approximately 0 005 m and a ripple length of 0 06 0 08 m application of the van rijn van rijn l c 1989 handbook sediment transport by currents and waves delft hydraulics report h461 sediment transport model further confirmed that enhanced sediment resuspension during the falling tide was primarily the result of the development of ripple morphology with increased mean current strengths playing a secondary role the results have major implications for modelling suspended sediment transport on macrotidal beaches

a new mechanism for seaward dispersion of midshelf sediments silt to sand size particles may be transported across middle continental shelves by currents forced by the radiation stress of variable amplitude swell with the passage of each group of waves of sufficient amplitude for the high waves in the group to resuspend bottom sediments there is a seaward bias in the return of sediments to the seafloor over a storm season with the passage of many wave groups the net seaward sediment displacement may be 1 5 km

spatial mapping of multi year superimposed ice on the glacier kongsvegen svalbard ground penetrating radar gpr and satellite ers 2 synthetic aperture radar sar are used to map the thickness and extent of the superimposed ice si zone on the surge type glacier kongsvegen svalbard gpr imagery shows sub horizontal si layers lying unconformably above a discrete boundary below this boundary the ice has a gpr signature similar to that of ice further down glacier in the ablation zone this boundary is posited to represent the closing of crevasses that were created during the last surge of kongsvegen in 1948 open crevasses would have interrupted the formation of sheet layers of si due to efficient vertical drainage of the snowpack aerial photographs suggest that the crevasses closed sometime in the period 1956 66 a classified sar image from 2003 is used to delineate the extent of the si zone the si extent in the sar image agrees well with the si zone mapped by gpr using the si spatial depth distribution we estimate the mean annual accumulation of superimposed ice to be 0 16 0 06 m w e a 1 locally up to 0 43 m a 1 w e this corresponds to 15 33 of the local winter balance and 5 10 of the total winter balance measured since 1987

medium term frequency distributions of cross shore suspended sediment transport rates in water depths of 3 to 9 m abstract a data set of several thousands of hours of near bed flow obtained at three cross shore positions in 3 to 9 m water depth in the multiple bar system of terschelling netherlands was used to estimate the medium term years frequency distribution of the cross shore suspended sediment transport rates induced by short waves infragravity waves and cross shore mean flows predictions of an energetics based transport model were categorised into groups of the local height over depth ratio with a width of 0 02 and were subsequently coupled to the discrete medium scale probability distribution of this ratio at all depths the estimated medium scale sediment transport rate by the short waves q ms h and mean flows q ms mf were of approximately equal magnitude and were about three times as large as that of the infragravity waves in general the medium term sediment transport rates were dominated neither by the most extreme conditions nor by day to day situations this was related to the infrequent recurrence of the most energetic events and by the predicted negligible transport rates under daily conditions in 9 m depth breaking conditions contributed to about 90 of both q ms h and q ms mf in shallower water 3 5 m non breaking conditions became increasingly important for q ms h whereas q ms mf remained fully dominated by surf zone conditions this observation as well as literature findings for water depths less than about 3 m suggest that the range of small scale conditions that contribute most to q ms h and q ms mf changes in the onshore direction from mainly breaking conditions at depths in excess of 5 7 m towards prolonged non breaking periods for q ms h and short breaking events for q ms mf on the beach

lapse time dependent coda wave depth sensitivity to local velocity perturbations in 3 d heterogeneous elastic media in the context of seismic monitoring recent studies made successful use of seismic coda waves to locate medium changes on the horizontal plane locating the depth of the changes however remains a challenge in this paper we use 3 d wavefield simulations to address two problems first we evaluate the contribution of surface and body wave sensitivity to a change at depth we introduce a thin layer with a perturbed velocity at different depths and measure the apparent relative velocity changes due to this layer at different times in the coda and for different degrees of heterogeneity of the model we show that the depth sensitivity can be modelled as a linear combination of body and surface wave sensitivity the lapse time dependent sensitivity ratio of body waves and surface waves can be used to build 3 d sensitivity kernels for imaging purposes second we compare the lapse time behaviour in the presence of a perturbation in horizontal and vertical slabs to address for instance the origin of the velocity changes detected after large earthquakes

modes of cross shore sediment transport on the shoreface of the middle atlantic bight the mechanisms responsible for onshore and offshore sediment fluxes across the shoreface zone seaward of the surf zone were examined in a 3 year field study the study was conducted in the southern part of the middle atlantic bight in the depth region 7 17 m using instrumented tripods supporting electromagnetic current meters pressure sensors suspended sediment concentration sensors and sonar altimeters the observations embraced fairweather moderate energy swell dominated and storm conditions cross shore mean flows ranged from near zero during fairweather to 20 cm s 1 during the storm oscillatory flows were on the order of 10 cm s 1 during fairweather and 100 cm s 1 during the storm suspended sediment concentrations at about 10 cm above the bed were 5 kg m 3 during the storm three methods were applied to evaluate the relative importance of incident waves long period oscillations mean flows and gravity in effecting shoreward or seaward sediment flux 1 an energetics transport model was applied to instantaneous near bottom velocity data 2 higher moments of near bottom flows were estimated and compared and 3 suspended sediment fluxes were estimated directly from the instantaneous products of cross shore velocity and suspended sediment concentration the results show that measurable contributions were made by all four of the processes most significantly mean flows were seen to dominate and cause offshore fluxes during the storm and to contribute significantly to onshore and offshore flux during fairweather and moderate energy incident waves were in all cases the major source of bed shear stress but also caused shoreward as well as seaward net sediment advection low frequency effects involving wave groups and long period waves made secondary contributions to cross shore sediment flux contrary to expectations low frequency fluxes were just as often shoreward as seaward whereas cross correlations between suspended sediment concentration and the instantaneous near bottom current speed were high and in phase under storm conditions they were weak and out of phase during fairweather conditions this suggests that simple energetics models are probably inadequate for predicting fairweather transport of suspended sediment

frequency dependent cross shore suspended sediment transport 1 a non barred shoreface abstract the local time varying and time averaged suspended sediment transports across a marine non barred shoreface were obtained from field measurements of the near bed velocity and sediment concentration vectors using electromagnetic current meters and optical backscatterance suspended solids sensors co spectral analyses of velocity and sediment concentration revealed the contributions of waves of different frequencies to the total transport the transport attributable to quasi steady currents was determined from the product of the time averaged cross shore velocity and sediment concentration estimates of the local time integrated sediment volume flux total and net and the associated erosion or accretion were determined using depth of activity rods suspended sediment transport was associated with 1 local wind forced waves 2 swell 3 low frequency waves group bound long waves and 4 offshore directed mean currents undertow these transport components varied spatially and temporally in response to changes in the wave height to water depth ratio the local net oscillatory transport rate at wind wave and swell wave frequencies was directed onshore predominantly and increased as water depth decreased in association with wave shoaling the local mean sediment transport rate was predominantly offshore and dominated the net transport rate wherever wave induced components were weak relative to the mean currents under breaking waves the suspended sediment transport contribution associated with wind waves and swell waves was reduced as a result of dissipation the net suspended sediment transport rate exhibited a distinct vertical structure reflecting the balance at each elevation between the opposing mean and oscillatory components of transport the local time averaged total and net sediment volume flux and resulting erosion and accretion patterns support the hypothesis of a near balance in sediment flux for the complete storm event

body and surface wave reconstruction from seismic noise correlations between arrays at piton de la fournaise volcano body wave reconstruction from ambient seismic noise correlations is an important step toward improving volcano imaging and monitoring here we extract body and surface waves that propagate in piton de la fournaise volcano on la reunion island using ambient noise cross correlation and array processing techniques ambient noise was continuously recorded at three dense arrays each comprising 49 geophones to identify and enhance the green s function from the ambient noise correlation we apply a double beamforming dbf technique between the array pairs the dbf allows us to separate surface and body waves direct and reflected waves and multipathing waves based on their azimuths and slownesses we successfully extract body waves between all the combinations of arrays including the wave that propagates through the active magmatic system of the volcano additionally we identify the effects of uneven noise source distribution and interpret the surface wave reflections

magma transport and storage at piton de la fournaise la reunion between 1972 and 2007 a review of geophysical and geochemical data abstract since the middle of the 20th century improvement in volcano monitoring techniques has provided large data sets that can be used to evaluate the evolution of magma plumbing systems at piton de la fournaise volcano abundant eruptive activity and a dense monitoring network are especially conducive to such research analysis of the extensive set of geophysical and geochemical data associated with the last 35 years of activity provides new insights into magma transport and storage at piton de la fournaise two periods of frequent eruptions separated by 6 years of inactivity can be distinguished 1972 1992 and 1998 2007 considering these two periods we show evidence of major changes in the shallow plumbing system in 2000 during 1972 1992 and 1998 2000 lava compositions and weak long term eruptive precursors lasting few days to three weeks characterized by no significant summit inflation and about ten volcano tectonic earthquakes per day suggest that eruptions were fed by the progressive drainage of an occasionally recharged shallow magma reservoir geophysical evidence of shallow magma reservoir recharge was only recorded in 1986 and 1998 in contrast from 2000 to 2007 geophysical data highlight the appearance of long term precursors 1 to 5 months of summit inflation and strong seismicity up to one hundred events per day preceding cycles of successive eruptions each cycle of eruptions was characterized by a sequence 3 to 10 months in duration of summit and near summit proximal eruptions and ended with a distal low altitude oceanite olivine abundances 20 vol eruption on the eastern flank of the volcano within each of these eruptive cycles lavas became progressively more magnesian over time the preferential motion of the eastern flank caused by continuous recharging of the shallow reservoir since 2000 would favour the occurrence of distal eruptions towards this flank at the end of a cycle

recent fluctuations in the extent of the firn area of austfonna svalbard inferred from gpr in spring during 2004 07 we conducted ground penetrating radar gpr measurements on the austfonna ice cap svalbard with the original aim of mapping the thickness and distribution of winter snow here we further exploit the information content of the data and derive a multi year sequence of glacier facies distribution that provides valuable spatial information about the total surface mass balance smb of the ice cap beyond the usually evaluated winter balance we find that following an initial decrease in the extent of the firn area 2003 04 the firn line lowered within two subsequent years by 40 100m elevation in the north and west and 150 230 m in the south and east of the ice cap corresponding to a lateral expansion of the firn area along the profiles by up to 7 3 and 13 3 km respectively the growth of the firn area is in line with stake measurements from etonbreen that indicate a trend towards less negative smb over the corresponding period

the systematic contribution of transporting mechanisms to the cross shore sediment transport in water depths of 3 to 9 m the systematic contributions of short waves infragravity waves and mean flows to the cross shore sediment transport were studied with direct measurements of instantaneous near bed sediment concentrations and velocities as well as with an energetics based sediment transport model using measured time series of near bed cross shore flow as input the study was conducted at four cross shore positions in the multiple bar system of terschelling netherlands during three field campaigns each with a five week duration the data were collected in 3 to 9 m water depth during a wide range of conditions from low energy non breaking conditions to almost fully saturated breakers the height over depth ratio hs h was applied at all four measuring stations as a local conditional parameter all model predictions were grouped into hs h classes with a width of 0 02 to highlight the generality of the data the energetics approach predicted that the suspended load dominated over the bedload at all four stations both the sediment flux measurements as well as the model predictions showed that the largest contributors to the gross suspended sediment transport were made by the short waves and the undertow inducing an onshore and offshore transport respectively their contributions to the gross suspended transport were about 40 to 50 under surf zone conditions bound infragravity waves were observed and predicted to result in an offshore directed transport that was of subordinate magnitude compared to the observed and estimated magnitudes by the short waves and the undertow however as these transports almost cancelled out because of their about equal magnitude but opposite sign the suspended transport by bound infragravity waves may not be ignored and may rather paradoxically have a relatively large influence on the net suspended sediment transport hydrodynamical processes that do not seem to be of importance to the onshore and offshore sediment transport in 3 to 9 m water depth in the long run are mean flows under non breaking conditions and free infragravity motions a direct comparison between measured sediment fluxes and the model predictions suggests that simple energetics models are suitable for predicting cross shore sediment transport in 3 to 9 m water depth

imaging the dynamics of dyke propagation prior to the 2000 2003 flank eruptions at piton de la fournaise reunion island 1 the relationship between shallow magma storage and flank injections in volcanic edifices is rarely documented we analyse the time series of geodetic and seismic data collected at piton de la fournaise volcano la reunion during 9 flank eruptions from 2000 to 2003 the data depicts how magma injections supplied flank eruptions at piton de la fournaise volcano and allows to precisely determine the direction and duration of dike intrusions indicating a two phases pattern consistent over all the eruptions 1 fast vertical migration of the dyke 2 m s from the magma chamber to the surface in 10 to 50 minutes and 2 slower lateral migration 0 2 0 8 m s in tens of minutes to hours controlled by the rift zone geometry

monitoring glacier changes using multitemporal multipolarization sar images this paper presents a processing chain for the change detection of arctic glaciers from multitemporal multipolarization synthetic aperture radar sar images we produce terrain corrected multilook complex covariance data by including the effects of topography on both geolocation and sar radiometry as well as azimuth slope variations on polarization signature an unsupervised contextual non gaussian clustering algorithm is employed for the segmentation of each terrain corrected polarimetric sar image and subsequently labeled with the aid of ground truth data into glacier facies we demonstrate the consistency of the segmentation algorithm by characterizing the expected random error level for different sar acquisition conditions this allows us to determine whether an observed variation is statistically significant and therefore can be used for the postclassification change detection of arctic glaciers subsequently the average classified images of succeeding years are compared and changes are identified as the detected differences in the location of boundaries between glacier facies in the current analysis a series of dual polarization c band envisat asar images over the kongsvegen glacier svalbard is used for demonstration

reverse sediment transport induced by amplitude modulated waves abstract amplitude modulated waves can induce bedload and suspended load transports of sediment in the reverse direction of the wave propagation the reverse transport rate is mainly controlled by the magnitude of the bottom orbital velocity the mechanism is most effective in transporting silts and fine sands offshore but not clays the sorting characteristic may be amplified when non uniform size sediments are present in the sea bed the mechanism provides a feasible explanation for two shelf sedimentation patterns difficult to understand using conventional seaward sediment transport models

svalbard glacier elevation changes and contribution to sea level rise 1 we compare satellite altimetry from the ice cloud and land elevation satellite icesat 2003 2007 to older topographic maps and digital elevation models 1965 1990 to calculate long term elevation changes of glaciers on the svalbard archipelago results indicate significant thinning at most glacier fronts with either slight thinning or thickening in the accumulation areas except for glaciers that surged which show thickening in the ablation area and thinning in the accumulation areas the most negative geodetic balances occur in the south and on glaciers that have surged while the least negative balances occur in the northeast and on glaciers in the quiescent phase of a surge cycle geodetic balances are related to latitude and to the dynamical behavior of the glacier the average volume change rate over the past 40 years for svalbard excluding austfonna and kvitoya is estimated to be 9 71 0 55 km3 yr 1 or 0 36 0 02 m yr 1 w equivalent for an annual contribution to global sea level rise of 0 026 mm yr 1 sea level equivalent

anisotropic radio wave scattering from englacial water regimes mýrdalsjokull iceland colinear polarized 5 mhz radar profiling data were obtained on m rdalsjokull a temperate glacier in iceland radar transects and therefore polarization planes were aligned approximately parallel transverse and oblique to the ice flow direction echoes from the shallower half to two thirds of the ice were 10 20db stronger on the oblique and longitudinal transects than those on the transverse transects anisotropy as a function of depth is clearly seen at the sites where the transects cross strong scattering on longitudinal transects apparently caused extinction of a radar reflecting layer that was continuously profiled on the transverse transects a radio wave scattering model shows that scattering from a longitudinal water filled conduit parallel to the glacier surface can explain the observed azimuthal variations of the echo we conclude that low frequency mhz radio waves can help to characterize englacial water regimes

from glacier facies to sar backscatter zones via gpr we present a comparison between data acquired with frequency modulated ground penetrating radar gpr and satellite synthetic aperture radar sar both radars are polarimetric and operate at a center frequency of 5 3 ghz the field site is the polythermal glacier kongsvegen svalbard along glacier gpr profiles cover the ablation area and the accumulation area where the latter consists of superimposed ice si and firn the glacier facies are clearly identifiable on the gpr profiles although we show that the copolarized response is better for distinguishing different ice zones whereas the si firn boundary is most obvious in the cross polarized response a calibrated backscatter coefficient is calculated for the gpr data and compared with the sar backscatter coefficient the sar zones are in very good agreement with the gpr derived glacier facies we show that in the ablation area the sar response is dominated by backscatter from the previous summer surface in the si and firn areas it is dominated by sources below the previous summer surface

bed reflectivity beneath inactive ice streams in west antarctica radio echo sounding res techniques are used to examine spatial changes inbed reflectivityacrossrelictice streams inwest antarctica measurementsfrom adjacent interstream ridgesare usedto correctthe measuredpower returned fromthebed for attenuation and losses due to geometric spreading scattering and absorption res measurements near boreholes drilled on ice stream c isc indicate high coefficients of bed reflectivity r40 1 in locations where the bed wasthawed and boreholes connected to thebasalwatersystem andlow reflectivitycoefficients r50 02 atlocationsthat were frozen and not connected intermediate values of bed reflectivity were measured at locations where the connection to the basal water systemwas weak measurements across four relictmargins show thatbedreflectivity usuallyjumpsfromlow tohighvaluesseveral kilometers inside the outermost buried crevasses we interpret this to be a transition from frozento thawedbasal conditions anddiscuss implications of these observations

improving temporal resolution in ambient noise monitoring of seismic wave speed 1 the use of ambient seismic noise has been intensively investigated to perform passive tomography at various scales besides passive tomography passive monitoring is another application of seismic noise correlation as was shown by the recent observation of postseismic velocity changes around the san andreas fault in parkfield california one of the drawbacks of using ambient noise correlation for passive monitoring is the need to average the correlations over a long time period in order to obtain a sufficient signal to noise ratio snr for the phase fluctuations to be measured accurately for the application to passive monitoring one wants the possibility of following short term velocity variations 1 day or less using noise correlation functions calculated on short time windows another difficulty may then appear when the spatial distribution of noise sources also evolves with time the aim of this paper is to introduce an adaptive filter to the parkfield data set in order to improve the snr output of the ambient noise correlation functions when applied to passive monitoring the temporal resolution can be increased from 30 days up to 1 day with this improved temporal resolution the velocity drop observed at parkfield is shown to be cosesimic with the 24 september 2004 mw 6 0 event the relationship between the measured velocity fluctuations and the time evolution of the spatial distribution of the noise wavefield is also investigated finally the error bar in the amplitudes of the velocity variations is compared with a theoretical expectation

imaging the internal structure of an alpine glacier via l band airborne sar tomography in this paper we report results from the analysis of 3 d l band airborne synthetic aperture radar sar acquisitions acquired in march 2014 over the mittelbergferner glacier austrian alps during the european space agency esa campaign alptomosar the campaign included coincident in situ measurements of snow and ice properties and ground penetrating radar gpr data acquired at 600 and 200 mhz over a total length of 18 km radar data were acquired by repeatedly flying an l band sar along an oval racetrack at an altitude of about 1300 m over the glacier such that two data stacks from opposite views are obtained data from all passes were coherently combined to achieve 3 d resolution capabilities resulting in the generation of 3 d tomographic sar tomosar cubes where each voxel represents l band radar reflectivity from a particular location in the 3 d space at a spatial resolution on the order of meters tomosar cubes were finally corrected to account for wave propagation velocity into the ice which was a necessary step to associate the observed features with their geometrical location hence enabling a direct comparison to gpr data the tomosar cubes show the complexity of the glacier subsurface scattering most areas are characterized by surface scattering in proximity of the ice surface plus a complex pattern of in depth volumetric scattering beneath and scattering at the ice bedrock interface various subsurface features observed in gpr transects at 200 mhz clearly showed up in tomosar sections as well particularly firn bodies crevasses layer transitions and bedrock reflection down to 50 m below the ice surface

coast formation in an arctic area due to glacier surge and retreat the hornbreen hambergbreen case from spistbergen glacierized coasts undergo faster geomorphic processes than unglaciated ones we have studied changes of the coastal area in southern svalbard with the glacier bridge between torell land and sorkapp land since the beginning of the 20th century the existence of a continuous subglacial depression beneath the hornbreen hambergbreen system has been debated since the 1960s with inconclusive results in this study we assess both the subglacial topography and the bathymetry of hornsund fjord and hambergbukta bay this included 40 km of radar surveys over the glacial system and sea depth sounding the extent of the glaciers from maps and satellite images together with digital terrain models and surface elevation data based on gps profiling were used to analyse geometry changes of the glacier surfaces the results confirm the existence a continuous subglacial depression below sea level c 40 m deep between hornsund and the barents sea the hornbreen hambergbreen system has changed in shape over the past century reflecting its dynamic origin and activity also exemplified by the sequential surges identified since 1899 there was a pre surge build up event of flatbreen causing a surge and subsequent lowering of the hornbreen hambergbreen terminus by the 1960s after the entire surface lowered albeit with a delay in the hornbreen terminal zone since the year 2000 hornbreen terminus has retreated at an average rate of 106 m a 1 50 faster than that of hambergbreen if the retreat continues at the 2000 2015 average rate the ice bridge between hornsund and hambergbukta will be broken sometime between 2055 and 2065 and the hornsund strait will separate sorkapp land from the spitsbergen island the processes and events described in this study particularly the effects of the glacier surge may provide a model for changes likely to occur in other coastal glaciated regions experiencing rapid change

glacier facies of vestfonna svalbard based on sar images and gpr measurements abstract the warming climate of the arctic affects the mass budget of glaciers and changes in the distribution of glacier facies are indicative of their response to climate change the glacial mass budget over large land ice masses can be estimated by remote sensing techniques but selecting an efficient remote sensing method for recognizing and mapping glacier facies in the arctic remains a challenge in this study we compared several methods of distinguishing the facies of the vestfonna ice cap svalbard based upon synthetic aperture radar sar images and terrestrial high frequency ground penetrating radar gpr measurements glacier zones as determined using the backscattering coefficient sigma0 of sar images were compared against gpr data and an alternative application of internal reflection energy ire calculated from terrestrial gpr data was also used for differentiating the extent of glacier facies the ire coefficient was found to offer a suitable method for distinguishing glacier zones and for validating sar analysis furthermore results of analysis of fully polarimetric phased array type l band synthetic aperture radar alos palsar and european remote sensing synthetic aperture radar ers 2 sar images were compared with the ire coefficient classification especially promising method is h segmentation where the glacier zone boundaries corresponded very well with both gpr visual interpretation and ire classification results the ire coefficient s simplicity of calculation makes it a good alternative to the subjective gpr visual interpretation method where results strongly depend on the operator s level of experience we therefore recommend for gpr profiles to be used for additional validation of sar image analysis in studies of glacier facies on the high arctic ice masses

bar formation due to wave groups and associated long waves abstract field observations reveal that waves propagating onto a beach from deeper water have a grouped structure associated with this pattern of alternating high and low waves is a long wave forced by radiation stress variations due to the changing short wave height as the wave groups propagate onshore the relationship between the variation in the short wave height and the long wave motion is complicated by breaking of the short waves reflection of the long wave and the generation of a free long wave by time variation of the breakpoint position nevertheless there may still be a fixed phase relation between the short wave envelope and the long wave motion at any particular location resulting in a net transport of sediment over the timescale of the short wave groups this transport arises from sediment grains mobilised by short waves and moved by the long wave motion model predictions of wave group propagation onto a beach and the associated long wave motions are presented which suggest that sediment transport due to short wave long wave coupling may result in the formation of a bar within the inner surf zone and the possibility of additional bars further offshore outside the surf zone this mechanism for bar formation may provide a new framework for understanding bar morphodynamics

sudden drop of seismic velocity after the 2004 mw 6 6 mid niigata earthquake japan observed with passive image interferometry 1 passive image interferometry pii is a seismological method employing ambient seismic noise to monitor the temporal evolution of mean shear wave velocity within the earth first the elastic green s tensor between two seismometers is computed from the cross correlation of seismic noise recorded during a certain period second the constructed seismograms of different time periods are treated as earthquake multiplets and small time shifts in their coda are used to invert a relative change in mean shear wave velocity when applied to the source region of the 2004 mw 6 6 mid niigata earthquake japan centroid depth 5 km we used noise recorded at six seismometers located at a distance of less than 25 km from the epicenter daily inversions during the 2 months before and after the earthquake show a sudden drop of mean shear wave velocity of some tenths of a percent at the time of the mid niigata earthquake using noise in two frequency bands 0 1 0 5 hz and 2 8 hz we find similar amplitudes for the velocity drop which indicates that changes are not restricted to the shallow subsurface possible interpretations of this velocity decrease are a decrease of crustal stress after the earthquake a nonlinear site response in the shallow subsurface layer due to strong ground motion or structural weakening due to the creation of new fractures in the source area of the earthquake

changes of glacier facies on hornsund glaciers svalbard during the decade 2007 2017 abstract changes in glacier facies glacier zones such as firn or superimposed ice si are good indicators of glacier response to climate change they are especially important for fast warming svalbard where only a few glaciers are under glaciological mass balance monitoring this paper presents a first study of changes of glacier facies extent for three tidewater glaciers located in southern spitsbergen svalbard and it is based on both satellite remote sensing and terrestrial data analysis covering two time spans 2007 2017 for hansbreen and 2012 2017 for storbreen and hornbreen satellite remote sensing analysis include unsupervised classification of synthetic aperture radar sar data from both decommissioned envisat asar and modern satellite missions radarsat 2 sentinel 1 the results of the sar classification are compared to the information on glacier zones retrieved from terrestrial data i e shallow cores and visual interpretation of 800 mhz ground penetrating radar gpr profiles in addition a novel application of the internal reflection power irp coefficient as an objective method of distinguishing glacier zones based on gpr data is discussed changes in glacier facies areas over time are analysed as well as their correlation to hansbreen s mass balance the main finding of the study is that firn and si of hansbreen storbreen and hornbreen significantly decreased over the study period for example due to continuous negative mass balance between 2010 and 2017 the contribution of firn area to hansbreen s total area decreased ca 14 cumulative firn area loss during that time 45 whereas since 2012 si has not been distinguished as a vast area on this glacier in addition an east west gradient of firn area loss was observed as a result of differences in local climate conditions therefore for the common time span i e 2012 2017 hansbreen recorded a ca 12 loss of firn contribution to glacier area whereas hornbreen recorded ca 9 finally application of the irp coefficient as an objective method of glacier zones discrimination by gpr data gave very good results so the method is recommended for future analysis of glacier zones instead or as a support to popular visual interpretation of the gpr profiles

equilibrium slopes and cross shore velocity asymmetries in a storm dominated barred nearshore system abstract the near bed 0 10 m elevation horizontal velocities were measured across a two barred lacustrine shoreface during a storm and reveal a spatially coherent but temporally variable pattern in the low order moments of the velocity field large cross shore velocity asymmetries indicated 1 1 spatially extensive and temporally persistent offshore mean flows up to 0 18 m s 1 across the landward slope of the linear outer bar reflecting an undertow driven by a wave induced setup 2 2 an onshore directed skewness opposing the mean flow of wind wave origin and persistent under propagating bores in the inner bar system long after this asymmetry had disappeared from the outer bar extensive sediment reactivation with near zero net sediment flux over the whole of the upper shoreface indicated a sediment prism in a steady state volumetrically over the storm cycle uniform depths of sediment reactivation with zero bed elevation change over the storm cycle revealed local slopes in a steady state in the outer linear bar however time integration of the near bed velocity field at this location indicated an offshore net flux of water while sedimentary structures indicated bedform migration and thus at least bedload almost uniformly onshore when ripples and megaripples were present the sediment transport giving rise to the local equilibrium cannot be explained therefore on the basis of the mean properties of the near bed velocity vector but requires knowledge of the time varying instantaneous sediment transport vector onshore migration of the inner bar correlated well with the large and persistent onshore skewness of the velocity distribution in the inner surf zone associated with translatory surf bores throughout the storm decay period low frequency oscillations were only significant close to the shoreline but may have influenced the development of a sinuous three dimensional inner bar form as it migrated onshore

mapping thermal and hydrological conditions beneath a polythermal glacier with radio echo sounding spatial patterns in residual bed reflection power brp r derived from ground based radio echo sounding were mapped and interpreted in terms of the thermal and hydrological conditions at the base of a high arctic polythermal glacier john evans glacier ellesmere island canada brp r is the residual from a statistical relationship between measured bed reflection power and ice thickness that describes the rate of dielectric loss with depth in the glacier we identified three types of thermal structure a positive brp r and an internal reflecting horizon occur over the glacier terminus the reflecting horizon is interpreted as the boundary between warm and cold ice and suggests the presence of a warm basal layer b positive brp r occurs without an internal reflector in the upper part of the ablation zone this suggests that ice is at the pressure melting point only at the bed c negative brp r without an internal reflector occurs in all other regions suggesting cold ice at the bed where brp r is positive its pattern is similar to the pattern of subglacial water flow predicted from the form of the subglacial hydraulic equipotential surface this suggests that hydrological conditions at the glacier bed are a major control on brp r probably because the dielectric contrast between ice and water is higher than that between ice and other subglacial materials

polythermal glacier hydrology a review 1 the manner by which meltwater drains through a glacier is critical to ice dynamics runoff characteristics and water quality however much of the contemporary knowledge relating to glacier hydrology has been based upon and conditioned by understanding gleaned from temperate valley glaciers globally a significant proportion of glaciers and ice sheets exhibit nontemperate thermal regimes the recent growing concern over the future response of polar glaciers and ice sheets to forecasts of a warming climate and lengthening summer melt season necessitates recognition of the hydrological processes in these nontemperate ice masses it is therefore timely to present an accessible review of the scientific progress in glacial hydrology where nontemperate conditions are dominant this review provides an appraisal of the glaciological literature from nontemperate glaciers examining supraglacial englacial and subglacial environments in sequence and their role in hydrological processes within glacierized catchments in particular the variability and complexity in glacier thermal regimes are discussed illustrating how a unified model of drainage architecture is likely to remain elusive due to structural controls on the presence of water cold ice near glacier surfaces may reduce meltwater flux into the glacier interior but observations suggest that the transient thermal layer of near surface ice holds a hydrological role as a depth limited aquifer englacial flowpaths may arise from the deep incision of supraglacial streams or the propagation of hydrofractures forms which are readily able to handle varied meltwater discharge or act as locations for water storage and result in spatially discrete delivery of water to the subglacial environment the influence of such drainage routes on seasonal meltwater release is explored with reference to summer season upwellings and winter icing formation moreover clear analogies emerge between nontemperate valley glacier and ice sheet hydrology the discussion of which indicates how persistent reassessment of our conceptualization of glacier drainage systems is required there is a clear emphasis that continued integrated endeavors focused on process glaciology at nontemperate glaciers are a scientific imperative to augmenting the existing body of research centered on ice mass hydrology

tidal asymmetry in suspended sand transport on a macrotidal intermediate beach abstract time series of nearbed horizontal flow velocities and suspended sediment concentrations obtained from a colocated electromagnetic current meter emcm and optical backscatter sensor obs respectively are used to examine the relative importance of steady and fluctuating components to the total sediment transport over a full tidal cycle on a macrotidal intermediate beach spurn head uk fluctuating sediment fluxes are decomposed into gravity and infragravity contributions using co spectral techniques the relative importance of the oscillatory gravity and infragravity and steady mean transport components to the total sediment transport is analysed throughout the tidal cycle a continuum of 34 discrete suspended sediment cross shore velocity co spectra are computed over a full tidal cycle for the obs and emcm measurements 0 10 m above the bed these net transport spectra vary greatly both with cross shore location and tidal state in particular a marked asymmetry in transport processes is evident between the flood and ebb tides with high levels of sediment resuspension and transport occurring on the ebbing tide approximately two hours after high water just seaward of the breakpoint at this time the dominant transport was directed offshore co spectral peak 0 04 kg m 2 s at incident wave frequency typical patterns are observed in transport spectra outside the surf zone and within the inner surf zone outside the narrow surf zone cross shore transport spectra show weak offshore transport co spectral peak 0 002 kg m 2 s associated with bound long waves and stronger onshore transport co spectral peak 0 006 kg m 2 s at incident wave frequencies conversely co spectra computed within the inner surf zone show the offshore sediment fluxes spectral peak 0 010 kg m 2 s at infragravity frequencies to be greater in magnitude than the corresponding onshore transport co spectral peak 0 008 kg m 2 s occurring at incident wave frequencies

a three component scattering model for polarimetric sar data an approach has been developed that involves the fit of a combination of three simple scattering mechanisms to polarimetric sar observations the mechanisms are canopy scatter from a cloud of randomly oriented dipoles evenor double bounce scatter from a pair of orthogonal surfaces with different dielectric constants and bragg scatter from a moderately rough surface this composite scattering model is used to describe the polarimetric backscatter from naturally occurring scatterers the model is shown to describe the behavior of polarimetric backscatter from tropical rain forests quite well by applying it to data from nasa jet propulsion laboratory s jpls airborne polarimetric synthetic aperture radar airsar system the model fit allows clear discrimination between flooded and nonflooded forest and between forested and deforested areas for example the model is also shown to be usable as a predictive tool to estimate the effects of forest inundation and disturbance on the fully polarimetric radar signature an advantage of this model fit approach is that the scattering contributions from the three basic scattering mechanisms can be estimated for clusters of pixels in polarimetric sar images furthermore it is shown that the contributions of the three scattering mechanisms to the hh hv and vv backscatter can be calculated from the model fit finally this model fit approach is justified as a simplification of more complicated scattering models which require many inputs to solve the forward scattering problem

cross shore sand transport by infragravity waves as a function of beach steepness two field data sets of near bed velocity pressure and sediment concentration are analyzed to study the influence of infragravity waves on sand suspension and cross shore transport on the moderately sloping sand motor beach 1 35 the local ratio of infragravity wave height to sea swell wave height is relatively small hig hsw 0 4 most sand is suspended during negative infragravity velocities and qig is offshore directed the infragravity contribution to the total sand flux is considerably larger and reaches up to 60 during energetic conditions on the whole hig hsw is a good indicator for the infragravity related sand suspension mechanism and the resulting infragravity sand transport direction and relative importance

two methods for firn area and mass balance monitoring of svalbard glaciers with sar satellite images this paper presents two methods for glacier monitoring on svalbard using synthetic aperture radar sar satellite images both methods were developed on glaciers in the kongsfjorden area the first method monitors the firn area extent and the firn line over time by thresholding and filtering the sar image manual detection of the threshold is preferable but using a constant threshold for all images also gives adequate results a retreat of the fire line position is visible especially on kongsvegen corresponding to consecutive years of negative mass balance the second method applies a k means classification to three clusters on the glacier surface the areal extent of the resulting class on the upper part of the glacier correlates remarkably well with the independently measured mass balance of kongsvegen having a correlation coefficient of around 0 89 for the various glaciers this is because the snow from the accumulation area influences the k means classification thus on glaciers where mass balance values are available new mass balance values can be predicted solely from sar images for glaciers where no mass balance is available the area change cannot be calibrated to absolute mass balance values but relative changes can be predicted

recent elevation changes of svalbard glaciers derived from icesat laser altimetry abstract we have tested three methods for estimating 2003 2008 elevation changes of svalbard glaciers from multi temporal icesat laser altimetry a linear interpolation of crossover points between ascending and descending tracks b projection of near repeat tracks onto common locations using digital elevation models dems and c least squares fitting of rigid planes to segments of repeat track data assuming a constant elevation change rate the two repeat track methods yield similar results and compare well to the more accurate but sparsely sampled crossover points most glacier regions in svalbard have experienced low elevation thinning combined with high elevation balance or thickening during 2003 2008 the geodetic mass balance excluding calving front retreat or advance of svalbard s 34 600 km2 glaciers is estimated to be 4 3 1 4 gt y 1 corresponding to an area averaged water equivalent w e balance of 0 12 0 04 m w e y 1 the largest ice losses have occurred in the west and south while northeastern spitsbergen and the austfonna ice cap have gained mass winter and summer elevation changes derived from the same methods indicate that the spatial gradient in mass balance is mainly due to a larger summer season thinning in the west and the south than in the northeast our findings are consistent with in situ mass balance measurements from the same period confirming that repeat track satellite altimetry can be a valuable tool for monitoring short term elevation changes of arctic glaciers

stereo video observation of nearshore bedforms on a low energy beach abstract a new technique utilising underwater stereo video was tested for its ability to measure nearshore bed morphology at high frequency and high resolution a stereo video system was used to monitor small scale ripple morphology wavelengths 0 05 0 10 m heights 5 mm in the nearshore of a low energy beach in southwestern australia waves currents and suspended sediment concentrations were also monitored bed morphology could be measured with a mean accuracy of 2 mm with the stereo video system measurements in the field were limited to ripple crest positions since targets over the entire ripple profiles could not be identified in both the left and right stereo images this limitation could be overcome in the future by use of laser stripes to illuminate the profiles and the generation of epipolar lines within the analysis software to match corresponding targets in each of the images ripple crest positions were measured at 1 hz and the relationship between ripple movement and near bed hydrodynamics was investigated to test the applicability of the stereo video system to make high frequency bedform observations ripple crests were found to oscillate at the same frequency as the swell waves the magnitude of the ripple movement at swell wave frequencies was an order of magnitude greater than ripple movement at wind wave frequencies net onshore migration of the ripples corresponded to onshore wave asymmetry very weak mean cross shore currents and net onshore suspended sediment flux measured at an elevation of 0 05 m

near surface weakening in japan after the 2011 tohoku oki earthquake 1 the magnitude mw 9 0 tohoku oki earthquake on 11 march 2011 was one of the largest in recent history ground motion caused by the seismicity around the time of the main shock was recorded by kik net the strong motion network that covers most of japan by deconvolving waveforms generated by earthquakes that are recorded at the surface and in a borehole at kik net station fksh18 we detect a reduction of shear wave velocity in the upper 100 m of about 10 and a subsequent healing that varies logarithmically with time using all available borehole and surface records of more than 300 earthquakes that occurred between 1 january 2011 and 26 may 2011 we observe a reduction in the shear wave velocity of about 5 in the upper few hundred meters after the tohoku oki earthquake throughout northeastern japan the area of the velocity reduction is about 1 200 km wide which is much wider than earlier studies reporting velocity reductions following other larger earthquakes the reduction of the shear wave velocity is an indication that the shear modulus and hence the shear strength is reduced over a large part of japan

a new index of glacier area change a tool for glacier monitoring since the mid 19th century most glaciers have been losing area and volume this loss of area has not been homogeneous in time and space and direct observations are sparse making regional and global estimates of glacier change difficult this paper focuses on developing a single index for monitoring glacier change one that would be particularly useful for remote sensing applications we combine the results of direct glacier mass balance observations b total glacier area s and accumulation area sc derived from maps or remotely sensed images using the accumulation area ratio aar sc s we note the differences between observed aar time averaged aar hi and the equilibrium state aar0 as determined by its value at b 0 from a regression of b aar we suggest that d aar hi aar0 aar0 quantifies the difference between the currently observed state of glaciers and their equilibrium state and measures the delay in the dynamic response of s relative to the climatic response of sc using all available observations for the period 1961 2004 d 65 for tropical glaciers which implies their rapid shrinkage as s continues to decrease and catch up with sc during the same period mid latitude and polar glaciers show less negative values of d of 86 glaciers from all latitudes and regions only 11 show positive d at any time between 1961 and 2004 averaged over 1961 2004 d is 15 1 2 2 and b hi is 360 42 mm a 1 w e values for aar0 range between about 40 and 80 but the bulk of the equilibrium values are between 50 and 60 the average aar0 is 57 9 0 9 and has remained stable over time the equilibrium aar has not changed with climate overall the observed negative d suggests a committed retreat of glaciers and their continuing contribution to sea level even if global temperature is held constant