sediment resuspension by surface wave action an examination of possible mechanisms abstract detailed spectral and coherence analyses of both nephelometer data and near bottom acoustic concentration profiles support the conclusion of lesht et al 1980 that surfacewave activity is the most important input to the sediment resuspension process the sand sized fraction is suspended primarily by bursts of turbulence which are related to peak values of the envelope of surface waves two mechanisms for the resuspension of fine sediment are considered when the bed is bimodal sand and silt pore water motion induced by wave pressure fluctuations may carry fine particles into the boundary layer where they are suspended motion of the sand matrix as bedload will also expose fine particles to the flow so that they become suspended the combination of these two mechanisms accounts for the observed quasi linear relation between wave orbital velocity and suspended sediment concentration for the long island data the second mechanism is also consistent with observations of near bottom fluid velocity and suspended sediment concentration in norton sound alaska

permafrost and climate in europe monitoring and modelling thermal geomorphological and geotechnical responses we present a review of the changing state of european permafrost within a spatial zone that includes the continuous high latitude arctic permafrost of svalbard and the discontinuous high altitude mountain permafrost of iceland fennoscandia and the alps the paper focuses on methodological developments and data collection over the last decade or so including research associated with the continent scale network of instrumented permafrost boreholes established between 1998 and 2001 under the european union pace project data indicate recent warming trends with greatest warming at higher latitudes equally important are the impacts of shorter term extreme climatic events most immediately reflected in changes in active layer thickness a large number of complex variables including altitude topography insolation and snow distribution determine permafrost temperatures the development of regionally calibrated empirical statistical models and physically based process oriented models is described and it is shown that though more complex and data dependent process oriented approaches are better suited to estimating transient effects of climate change in complex mountain topography mapping and characterisation of permafrost depth and distribution requires integrated multiple geophysical approaches and recent advances are discussed we report on recent research into ground ice formation including ice segregation within bedrock and vein ice formation within ice wedge systems the potential impacts of climate change on rock weathering permafrost creep landslides rock falls debris flows and slow mass movements are also discussed recent engineering responses to the potentially damaging effects of climate warming are outlined and risk assessment strategies to minimise geological hazards are described we conclude that forecasting changes in hazard occurrence magnitude and frequency is likely to depend on process based modelling demanding improved understanding of geomorphological process response systems and their impacts on human activity

tide modulated ice flow variations drive seismicity near the calving front of bowdoin glacier greenland glacier microseismicity is a promising tool to study glacier dynamics however physical processes connecting seismic signals and ice dynamics are not clearly understood at present particularly the relationship between tide modulated seismicity and dynamics of calving glaciers remains elusive here we analyze records from an on ice seismometer placed 250 m from the calving front of bowdoin glacier greenland using high frequency glacier flow speed measurements we show that the microseismic activity is related to strain rate variations the seismic activity correlates with longitudinal stretching measured at the glacier surface both higher melt rates and falling tides accelerate glacier motion and increase longitudinal stretching long term microseismic monitoring could therefore provide insights on how a calving glacier s force balance and flow regime react to changes at the ice ocean interface

seismicity related to the glacier of cotopaxi volcano ecuador 1 significant seismic activity is generally recorded on volcanoes covered by an icecap this work was carried out in order to quantify the role of the glaciers in the generation of seismicity for cotopaxi volcano we compared the seismic activity registered on the glacier and on the rock near the snout of the north flank glacier we focused on the analysis of low frequency events 5 hz similar to volcanic lp events when recorded on rock base the particle motion analysis helps to estimate source locations which are distributed in crevasses areas high incident angles suggest a superficial origin these events are interpreted as icequakes for which we propose as source mechanism a fluid driven crack model triggered by ice cracking or hydraulic transients the low quality factor values estimated are consistent with the resonance of an ice crack filled with water this work shows that low frequency icequakes can be confusingly taken as volcanic lp events

pattern of cryospheric seismic events observed at ekstrom ice shelf antarctica mobility of glaciers such as rapid retreat or disintegration of large ice volumes produces a large variety of different seismic signals thus evaluating cryospheric seismic events e g changes of their occurrence in space and time allows to monitor glacier dynamics we analyze a one year data span recorded at the neumayer seismic network in antarctica events are automatically recognized using hidden markov models in this study we focused on a specifc event type occurring close to the grounding line of the ekstrom ice shelf observed waveform characteristics are consistent with an initial fracturing followed by the resonance of a water filled cavity resulting in a so called hybrid event the number of events detected strongly correlates with dominant tide periods we assume the cracking to be driven by existing glacier stresses through bending voids are then filled by sea water exciting the observed resonance in agreement with this model events occur almost exclusively during rising tides where cavities are opened at the bottom of the glacier i e at the sea ice interface

observations and analysis of b type earthquakes explosions and volcanic tremor at pavlof volcano alaska an eight station network of short period seismometers has been operated near pavlof volcano 55 25 n 161 54 w alaska peninsula since 1976 high quality analog to digital and direct digital data were recorded during eruptions in 1980 through 1983 data are analyzed from explosions with distinct air phases b type volcanic earthquakes shallow low frequency events lacking clear s phases and volcanic tremor to determine source and propagation effects between zero and several hundred b type events and explosions per day are recorded with higher numbers during eruptions magnitudes range between 0 5 and 1 3 and b values range between 1 9 0 1 and 2 6 0 1 with no systematic relation to eruptive activity six results are most important 1 data from a recently installed three component station reveal that the highest amplitude waves of the b type events show retrograde elliptical particle motion and normal dispersion and are hence probably rayleigh waves 2 stacking of the events enhances the p wave which has a velocity of 3 1 0 1 km sec 1 3 the explosions and b type events have similar hypocenters as evidenced by signal characteristics and wave arrival times 4 the b type events contain virtually no high frequency energy even when allowing for attenuation effects in particular we estimate the anelastic attenuation coefficient q to have a value of 45 20 for rayleigh waves in the shallow part of the volcano 5 volcanic tremor spectra exhibit evenly spaced narrow peaks which we model as eigenvalues of organ pipe resonance in the magma conduit we estimate the length of the conduit to be a maximum of 1 6 km 6 the volcano shows evidence of extreme lateral variation of velocity and attenuation in its shallow structure

localised thickening and grounding of an antarctic ice shelf from tidal triggering and sizing of cryoseismicity abstract we observe remarkably periodic patterns of seismicity rates and magnitudes at the fimbul ice shelf east antarctica correlating with the cycles of the ocean tide our analysis covers 19 years of continuous seismic recordings from antarctic broadband stations seismicity commences abruptly during austral summer 2011 at a location near the ocean front in a shallow water region dozens of highly repetitive events occur in semi diurnal cycles with magnitudes and rates fluctuating steadily with the tide in contrast to the common unpredictability of earthquake magnitudes the event magnitudes show deterministic trends within single cycles and strong correlations with spring tides and tide height the events occur quasi periodically and the highly constrained event sources migrate landwards during rising tide we show that a simple mechanical model can explain most of the observations our model assumes stick slip motion on a patch of grounded ice shelf which is forced by the variations of the ocean tide height and ice flow the well fitted observations give new insights into the general process of frictional triggering of earthquakes while providing independent evidence of variations in ice shelf thickness and grounding

recognition of spatial structures and ensemble averages in the benthic boundary layer simultaneous high frequency spatial and temporal measurements of benthic boundary layer bbl velocity and sediment concentration generate complex data sets in order to investigate the various spatial and temporal structures a pattern recognition method is for the first time adapted and used to investigate different and similar structures patterns of velocity and acoustically measured suspended sediment concentration profiles in the lowest 2 m of the bbl at tiana beach long island this layer is subject to interactions between differently scaled forcing fields which result in structures difficult to predict using existing time average or boundary layer methods under the assumption of no a priori knowledge about either the spatial or temporal structures in the bbl a deterministic mathematical methodology is implemented to recognize spatial structures in the data and classify them in an optimum number of classes the spatial pattern analysis in this paper indicates that 70 of the above mentioned data are represented by only 5 20 of its size spatial patterns different from those predicted from theory or experience are recognized

monitoring rock freezing and thawing by novel geoelectrical and acoustic techniques automated monitoring of freeze thaw cycles and fracture propagation in mountain rockwalls is needed to provide early warning about rockfall hazards conventional geoelectrical methods such as electrical resistivity tomography ert are limited by large and variable ohmic contact resistances requiring galvanic coupling with metal electrodes inserted into holes drilled into rock and which can be loosened by rock weathering we report a novel experimental methodology that combined capacitive resistivity imaging cri ert and microseismic event recording to monitor freeze thaw of six blocks of hard and soft limestones under conditions simulating an active layer above permafrost and seasonally frozen rock in a nonpermafrost environment our results demonstrate that the cri method is highly sensitive to freeze thaw processes it yields property information equivalent to that obtained with conventional ert and offers a viable route for nongalvanic long term geoelectrical monitoring extending the benefits of the methodology to soft hard rock environments contact impedances achieved with cri are less affected by seasonal temperature changes the aggregate state of the pore water liquid or frozen and the presence of low porosity rock with high matrix resistivities than those achieved with ert microseismic monitoring has the advantage over acoustic emissions that events were recorded in relevant field distances of meters to decameters from cracking events for the first time we recorded about 1000 microcracking events and clustered them in four groups according to frequency and waveform compared to previous studies mainly on ice cracking in glaciers the groups are attributed to single or multiple stage cracking events such as crack coalescence

a simple model for the influence of push morainal banks on the calving and stability of glacial tidewater termini push morainal banks at the grounding lines of tidewater termini of temperate glaciers are the source of two types of restraining forces operating at the glacier terminus horizontal normal forces derive from the lateral support and transport of the bank of sediment at the terminus whereas a horizontal shear force operates along the base of a bank pushed in front of an advancing glacier the simple model we present suggests that bank related restraining forces are significantly larger than the restraining force derived from the hydrostatic pressure of water adjacent to the submerged terminus of a glacier during glacier advance restraining forces continually increase resulting in decreasing flow rates glacier thickening and the eventual cessation of advance during retreat restraining forces continually decrease resulting in increasing flow rates glacier thinning and the potential for unstable rapid sustained retreat the normal seasonal oscillatory advance retreat cycle of a glacier is moderated by restraining forces associated with push moraines unstable retreat is likely initiated when bank related restraining forces fall below some threshold value during the seasonal retreat cycle calving is not a primary cause of glacier retreat but is more likely a short term response to increased flow rates increased flow rates result in glacier thinning and an approach toward buoyancy both of which fluctuate seasonally in accordance with bank related restraining forces

calving signature in ocean waves at helheim glacier and sermilik fjord east greenland abstractwhen glaciers calve icebergs a fraction of the released potential energy is radiated away via gravity waves the characteristics of such waves caused by iceberg calving on helheim glacier in east greenland are investigated observations were collected from an array of five high frequency bottom pressure meters placed along sermilik fjord calving generated tsunami waves were identified and used to construct a calving event catalog calving events are observed to cluster around high and low semidiurnal tides and around high and prior to low semimonthly tides in the postcalving ocean state discrete spectral peaks associated with calving events are observed and they are consistent among all the events a numerical model is used to compute the resonant modes of the fjord and to simulate calving generated ocean waves damped oscillator boundary forcing with 5 to 10 min periods is found to reproduce well the observed properties of calving waves these observations and modeling are relevant for be

effective discrimination of icequakes on seismic records from mawson station abstract the telemetered seismic station at mawson antarctica was one of the primary australian stations participating in the group of scientific experts technical test gsett experiment to test an international seismic monitoring system mawson signals are continuously transmitted to the national data center ndc in canberra and also forwarded to the international data centre idc in washington where further event analysis is performed numerous seismic signals are recorded on seismograms from the mawson station with a likely mechanism of sudden fracturing of ice the aim of this study was to find a procedure which will effectively discriminate seismic signals from these icequakes and thus speed up the analysis of the other detected events an automatic algorithm was designed to identify icequakes according to their characteristics frequency content duration azimuth inclination and magnitude the program was tested on a few datasets of randomly selected periods and one comprised of records of nuclear explosions detonated in the period of 1995 96 the preliminary results showed that this method was capable of distinguishing icequakes and could substantially improve the production of an automated event list

bedrock fracture by ice segregation in cold regions the volumetric expansion of freezing pore water is widely assumed to be a major cause of rock fracture in cold humid regions data from experiments simulating natural freezing regimes indicate that bedrock fracture results instead from ice segregation fracture depth and timing are also numerically simulated by coupling heat and mass transfer with a fracture model the depth and geometry of fractures match those in arctic permafrost and ice age weathering profiles this agreement supports a conceptual model in which ice segregation in near surface permafrost leads progressively to rock fracture and heave whereas permafrost degradation leads episodically to melt of segregated ice and rock settlement

a numerical model of fine sediment transport on the continental shelf a numerical model of fine grained sediment dispersion in the new york bight of the north american continental shelf is presented large amounts of waste material have been dumped in this region and the dispersal patterns of this material are of great interest to environmental managers the model assumes that fine sediment resuspension is determined by surface wave activity and that transport is determined by tidal currents considering surface wave activity to be a random process reduces sediment motion to a random walk which is governed by a diffusion equation the diffusion equation is solved numerically by an implicit time difference finite element algorithm for a number of initial conditions

rock moisture measurements techniques results and implications for weathering rock moisture is an important factor for the intensity and distribution of frost weathering processes however quantitative measurements are scarce which is partly due to the lack of reliable measurement techniques this paper presents five different techniques for obtaining rock moisture data while collecting rock pieces and two dimensional geoelectric measurements allow determination of the spatial moisture distribution the temporal variability can be derived from conductivity and time domain reflectometry records computer simulations using rock properties and climatic records as input data render it possible to clarify the important aspects that are responsible for the moisture distribution it proved to be advisable to use several methods to check and validate the results the results obtained in study areas in the bavarian alps make it clear that direct rainfall is the main source of rock moisture the influence of snow is limited to the immediate vicinity of the snow fields and is not equally pronounced at different times and positions rock moisture levels are higher in summer than they are in winter since in winter less water is supplied in liquid form northerly exposed rockwalls are generally more moist than those exposed in a southerly direction which is due to the different insolation as well as to the wind direction during rainfall in every position the rock is on average wetter on the inside than it is on the surface this means that shallow frost cycles as typical for south exposed sites are not affecting weathering since they take place at a depth level that is mostly dried out numerous spatial and temporal patterns of rockfall found in the same study areas can be explained through variations in rock moisture thus the moisture content of the rock is considered to be one of the major controlling factors of the frost shattering rate copyright 2005 john wiley sons ltd

seismic and geodetic evidence for grounding line control of whillans ice stream stick slip events the tidally modulated stick slip events of whillans ice stream in west antarctica produce seismic energy from three locations near the grounding line using ice velocity records obtained by combining time series from colocated broadband seismometers and gps receivers installed on the ice stream during the 2010 2011 and 2011 2012 austral summers along with far field seismic recordings of elastic waves we locate regions of high rupture velocity and stress drop these regions which are analogous to asperities in traditional seismic fault studies are areas of elevated friction at the base of the ice stream slip events consistently initiate at one of two locations near the center of the ice stream where events associated with the ross sea high tide originate or a grounding line spot where events associated with the ross sea low tide initiate as well as occasional high tide events following a skipped low tide event the grounding line site but not the central site produces rayleigh waves observable up to 1000 km away through fast expansion of the slip area grounding line initiation events also show strong directivity in the downstream direction indicating initial rupture propagation at 1 5 km s compared to an average of 0 150 km s for the entire slip event following slip initiation additional seismic energy is produced from two sources located near the grounding line first at the downstream end of subglacial lake engelhardt and second toward the farthest downstream extent of the ice stream this evidence suggests that the stronger higher friction material along the grounding line controls motion throughout the stick slip region

imaging radar observations and theory of type i and type ii quasi periodic echoes 1 midlatitude e region plasma irregularities have been investigated using the middle and upper atmosphere mu radar in shigaraki japan and the clemson 30 mhz radar in south carolina usa a new in beam imaging technique has been incorporated in the data analysis radar images reveal that the coherent backscatter associated with quasi periodic qp echoes mainly arrives from spatially localized elongated scattering regions and that striations in radar range time intensity rti maps are the signatures of the migrations of these regions through the sparsely filled illuminated volume the scattering regions in question appear to maintain altitude as they drift refraction and finite aspect angle sensitivity permit field aligned irregularities in the regions to be detected by radars over a broad range of zenith angles circulation observed within the scattering regions is consistent with simulations of polarized e region plasma clouds described in a companion paper as is the occasional appearance of type i echoes several long continuous bands of scatterers are also evident in the radar images

microseismic investigation of an unstable mountain slope in the swiss alps 1 risks associated with unstable rocky slopes are growing as a result of climate change and rapid expansions of human habitats and critical infrastructure in mountainous regions to improve our understanding of mountain slope instability we developed a microseismic monitoring system that operates autonomously in remote areas afflicted by harsh weather our microseismic system comprising 12 three component geophones was deployed across 60 000 m 2 of rugged crystalline terrain above a huge 30 million m 3 recent rockfall in the swiss alps during its 31 month lifetime signals from 223 microearthquakes with approximate moment magnitudes ranging from 2 to 0 were recorded determining the hypocenters was challenging for several reasons 1 p wave velocities were highly heterogeneous varying abruptly from 3 8 km s 2 first break picks were either inaccurate or lacking for some microearthquakes 3 there were no reliable s wave picks 4 numerous microearthquakes occurred just outside the network boundaries these issues were addressed by using a three dimensional 3 d p wave velocity model of the mountain slope determined from refraction tomography in a nonlinear inversion for hypocenter parameters and their probability density functions recordings from geophones at different altitudes and in boreholes constrained microearthquake depth estimates most microearthquakes were concentrated within 50 100 m of the surface in two zones one that followed the recent rockslide scarp and one that spanned the volume of highest fracture zone fault density these two active zones delineated a mass of rock that according to geodetic measurements has moved toward the scarp at 1 2 cm yr

electrical resistivity tomography monitoring of permafrost in solid rock walls 1 this article describes the first attempt to conduct electrical resistivity tomography ert in solid permafrost affected rock faces electrode design instrument settings and processing routines capable of measuring under relevant conditions were developed four transects with nw ne east e and south s aspects were installed in solid rock faces between matter valley and turtmann valley switzerland at 3070 3150 m above sea level dc resistivity in the transects was measured repeatedly during the summer and compared by applying a time lapse inversion routine resistivity values were calibrated using observed rock surface conditions of thawed damp rocks 1 8 k m deeply frozen rocks 18 80 k m and the transition from damp thawed to frozen rocks 8 18 k m mean surface layer resistivities of transects respond to air temperatures below 0 c with a rapid increase by a factor of 1 4 to 2 9 from values of 12 15 k m to values of 22 31 k m rock layers at depths of 2 6 m display a general trend of resistivity decrease in summer corresponding to a persistent thawing process their response to anomalously cool august temperatures occurs with a time lag of 2 to 4 weeks only transects e ne and nw display persistent high resistivity permafrost bodies 50 k m mostly at depths of 6 10 m the maximum thaw depth of a continuous thawing front above permafrost is 6 m however the ert results emphasize the role of heat transfer by deep reaching cleft water systems thus permafrost occurs in lenses rather than layers ert provides rapid detection of ice and water distribution in permafrost affected bedrock

source mechanics for monochromatic icequakes produced during iceberg calving at columbia glacier ak 1 seismograms recorded during iceberg calving contain information pertaining to source processes during calving events however locally variable material properties may cause signal distortions known as site and path effects which must be eliminated prior to commenting on source mechanics we applied the technique of horizontal vertical spectral ratios to passive seismic data collected at columbia glacier ak and found no dominant site or path effects rather monochromatic waveforms generated by calving appear to result from source processes we hypothesize that a fluid filled crack source model offers a potential mechanism for observed seismograms produced by calving and fracture processes preceding calving

identification of new events in apollo 16 lunar seismic data by hidden markov model based event detection and classification detection and identification of interesting events in single station seismic data with little prior knowledge and under tight time constraints is a typical scenario in planetary seismology the apollo lunar seismic data with the only confirmed events recorded on any extraterrestrial body yet provide a valuable test case here we present the application of a stochastic event detector and classifier to the data of station apollo 16 based on a single waveform example for each event class and some hours of background noise the system is trained to recognize deep moonquakes impacts and shallow moonquakes and performs reliably over three years of data the algorithm s demonstrated ability to detect rare events and flag previously undefined signal classes as new event types is of particular interest in the analysis of the first seismic recordings from a completely new environment we are able to classify more than 50 of previously unclassified lunar events and additionally find over 200 new events not listed in the current lunar event catalog these events include deep moonquakes as well as impacts and could be used to update studies on temporal variations in event rate or deep moonquakes stacks used in phase picking for localization no unambiguous new shallow moonquake was detected but application to data of the other apollo stations has the potential for additional new discoveries 40 years after the data were recorded besides the classification system could be useful for future seismometer missions to other planets e g the insight mission to mars

motion of an antarctic glacier by repeated tidally modulated earthquakes subglacial seismicity reveals information about glacier behaviour analysis of repeated seismic events beneath an antarctic outlet glacier is consistent with sliding of debris laden ice over a bedrock asperity with an event frequency that is modulated by the ocean tides

a new tide model for the antarctic ice shelves and seas we describe a new tide model for the seas surrounding antarctica including the ocean cavities under the floating ice shelves the model uses data assimilation to improve its fit to available data typical peak to peak tide ranges on ice shelves are 1 2 m but can exceed 3 m for the filchner ronne and larsen ice shelves in the weddell sea spring tidal ranges are about twice these values model performance is judged relative to the 5 10 cm accuracy that is needed to fully utilize ice shelf height data that will be collected with the geoscience laser altimeter system scheduled to be launched on the ice cloud and land elevation satellite in late 2002 the model does not yet achieve this level of accuracy except very near the few high quality tidal records that have been assimilated into the model some improvement in predictive skill is expected from increased sophistication of model physics but we also require better definition of ice shelf grounding lines and more accurate water column thickness data in shelf seas and under the ice shelves long duration tide measurements bottom pressure gauge or gps in critical data sparse areas particularly near and on the filchner ronne and ross ice shelves and pine island bay are required to improve the performance of the data assimilation model

experimental design for a pilot study on bedrock weathering near the permafrost table an experimental design is described to test the hypothesis that ice segregation near the top of permafrost and in the lower part of the active layer can brecciate frost susceptible bedrock seasonal temperature cycles in the active layer and the top of permafrost were simulated to a first approximation within a block of chalk measuring 30 m 31 m wide and 33 m high and insulated around the sides to minimize lateral heat transfer the block moistened first by capillary rise was initially frozen from the surface downwards simulating permafrost aggradation thereafter the upper half of the block was cycled above and below 0 c simulating seasonal freezing and thawing of the active layer while the lower half remained below 0 c simulating permafrost during thaw cycles water was supplied to the surface and base of the simulated active layer temperature unfrozen water content surface frost heave and porewater pressure within the chalk were monitored during the experiment

predicting suspended sediment concentration on continental shelves field observations of the near bottom suspended sediment concentration current and wave at a depth of 90 m on the washington shelf and at a depth of 1 5 m on the coastal beaufort sea show that wave induced oscillatory flow plays a dominant role in resuspending bottom sediment the suspended sediment concentration can be reasonably predicted from the measured flow data by applying a diffusion model good agreement between the predicted and observed concentrations is obtained by using a reference concentration proportional to the square root of the excess boundary shear stress for a sediment bed consisting of multiple grain sizes the differential rate at which material is eroded leads to a significant change in the surfacial grain size composition the fraction of the fine grain sediment in the surface layer decreases sharply with increasing boundary shear stress a procedure is presented to model this change of the grain size distribution in the surface layer the analysis indicates that neglecting the change of the surfacial grain size distribution with flow may overestimate the erosion depth by a factor of 10 at bottom orbital velocities exceeding 70 cm s 1

imaging the midlatitude sporadic e plasma patches with a coordinated observation of spaceborne insar and gps total electron content kilometer scale fine structures of midlatitude sporadic e es plasma patches have been directly imaged for the first time by an interferogram derived from l band advanced land observation satellite phased array type l band synthetic aperture radar data obtained over southwestern japan the synthetic aperture radar interferogram captured the eastern part of a large scale frontal structure of daytime midlatitude es which spans over 250 km in the east northeast to west southwest direction fine structures are characterized by frontal and disc shaped patches which are elongated in the same direction as the large scale frontal structure length and width of the disc shaped patches are 10 20 km and 5 10 km respectively and they are quasi periodically located with a typical separation of 10 15 km the kelvin helmholtz instability with the vertical shear of zonal winds is considered to be the most likely candidate for the generation mechanism of the frontal patch and disc shaped patches aligned in the zonal direction

acoustic profiling of suspended sediments in the marine bottom boundary layer an acoustic 3 mhz backscattering profilometer has been developed for study of sediment transport in the bottom boundary layer laboratory experiments indicate reasonable correlations between backscattering intensity and mass concentrations for well sorted fine to coarse quartz sands typical of those found in marine sediments departure of the calibration curves from their expected values is thought to be due to the non spherical shape of the quartz grains field experiments on the inner shelf using the profilometer combined with velocity profiles show individual profiles taken at 1 hz during erosion events are characterized by highly variable concentrations surface wave groups rather than individual waves appear to be correlated with groups of profiles with high concentrations extending 25 100 cm above bottom averaging produces smooth profiles which fit well log normal distributions predicted by steady flow suspended load theories

icequakes and glacier motion the hans glacier spitsbergen the recording of glacier icequakes has been carried out on the hans glacier spitsbergen the icequakes have been connected with the formation of open cracks the energy of the main group of icequakes has ranged from 0 01 j to 6 j their seismic moment being from 0 5 1014 dyne cm to 26 1014 dyne cm the nonelastic volume increase corresponding to each crack has ranged from 0 2 10 2 m3 to 8 8 10 2 m3 the stresses released due to extensional faulting ranged from 25n m2 to 500 n m2 these values are so small that they suggest an incomplete release of the medium the contribution into the glacier flow rate of the deformation in the surface glacier layer due to extensional faulting is lower by 2 to 3 orders of magnitude than the total plastic deformation associated with the ice creeping

continuous hmm based seismic event classification at deception island antarctica this paper shows a complete seismic event classification and monitoring system that has been developed based on the seismicity observed during three summer antarctic surveys at the deception island volcano antarctica the system is based on the state of the art in hidden markov modeling hmm techniques successfully applied to other scenarios a database that contains a representative set of different seismic events including volcano tectonic earthquakes long period lp events volcanic tremor and hybrid events that were recorded during the 1994 1995 and 1995 1996 seismic surveys was collected for training and testing simple left to right hmms and multivariate gaussian probability density functions with a diagonal covariance matrix were used the feature vector consists of the log energies of a filter bank that consists of 16 triangular weighting functions that were uniformly spaced between 0 and 20 hz and the first and second order derivatives the system is suitable to operate in real time and its accuracy for this task is about 90 on the other hand when the system was tested with a different data set including mainly lp events that were registered during several seismic swarms during the 2001 2002 field survey more than 95 of the recognized events were marked by the recognition system

imaging coherent scatter radar incoherent scatter radar and optical observations of quasiperiodic structures associated with sporadic e layers 1 during june and july 2002 a 30 mhz imaging coherent scatter radar was installed and operated on the island of st croix to view the e region ionosphere above arecibo puerto rico during the observing period 10 events with discernible quasiperiodic echo structure were observed with the coherent scatter radar in six of those events simultaneous measurements were made with the arecibo 430 mhz incoherent scatter radar the imaging coherent scatter radar allows us to locate and track the echo structures within the volume illuminated by the transmitter which shows structures that are generally aligned along wavefronts a slight preference for motion of the structures toward the southwest is evident throughout the period but the propagation directions and speeds vary greatly the incoherent scatter radar measurements show a close correspondence between the occurrence of the coherent echoes and the location of the enhanced electron density structures in particular the coherent echoes occur when the electron density layers show uplifts

antarctic icebergs a significant natural ocean sound source in the southern hemisphere in late 2007 two massive icebergs c19a and b15a drifted into open water and slowly disintegrated in the southernmost pacific ocean archived acoustic records show that the high intensity underwater sounds accompanying this breakup increased ocean noise levels at mid to equatorial latitudes over a period of 1 5 years more typically seasonal variations in ocean noise which are characterized by austral summer highs and winter lows appear to be modulated by the annual cycle of antarctic iceberg drift and subsequent disintegration this seasonal pattern is observed in all three oceans of the southern hemisphere the life cycle of antarctic icebergs affects not only marine ecosystem but also the sound environment in far reaching areas and must be accounted for in any effort to isolate anthropogenic or climate induced noise contributions to the ocean soundscape

range imaging of e region field aligned irregularities by using a multifrequency technique validation and initial results this paper reports the first use of a multifrequency range imaging rim technique for observing e region field aligned irregularities fais in the midlatitude ionosphere the middle and upper atmosphere radar mur 34 85 n 136 10 e was used to conduct experiments with five equally spaced frequencies between 46 25 and 46 75 mhz three types of rim data were examined data with 13 element binary barker codes with 16 element binary complementary codes and without phase codes moreover two calibration approaches were adopted to validate the applicability of the rim technique which functioned as intended excellent rim performance such as the ability to resolve several striations in an echo region of fais was demonstrated however sidelobe echoes caused by pulse coding mechanisms were occasionally observed at altitudes above and below the source regions in the coded data therefore a procedure was developed according to one of the calibration approaches to identify and remove such kind of sidelobe echoes which was shown to be applicable for the complementary coded data in addition to fais a thin plasma layer with a thickness of approximately 1 km was identified as being structured with some tilted finer structures which could not be observed in the original intensity images with a range resolution of 600 m preliminary estimates of the doppler velocities indicated that a wind shear effect could be the cause of such tilted finer structures

evidence for deep icequakes in an alpine glacier to obtain more reliable information about the focal depth distribution of icequakes in april 1997 we operated an array of seven portable digital seismographs on unteraargletscher central swiss alps over 5000 events were detected by at least two instruments during the 9 day recording period p wave velocities 3770 m f were determined from several calibration shots detonated at the glacier surface as well as in a 49 m deep borehole whereas s wave velocities 1860 ms 1 were derived from a simultaneous inversion for vp vs6 applied to 169 icequakes so far hypocentral locations have been calculated for over 300 icequakes besides confirming the occurrence of shallow events associated with the opening of crevasses our results show that a small but significant fraction of the hypocenters are located at or near the glacier bed one event was found at an intermediate depth of about 120 m three dimensional particle motion diagrams of both explosions and icequakes clearly demonstrate that all vertical component seismograms from shallow sources are dominated by the rayleigh wave on the other hand for events occurring at depths greater than about 40 m the rayleigh wave disappears almost entirely therefore a qualitative analysis of the signal character provides direct information on the focal depth of an event and was used as an independent check of the locations obtained from traditional arrival time inversions thus our results demonstrate that deep icequakes do occur and that simple rheological models according to which brittle deformation is restricted to the uppermost part of a glacier may need revision

antarctic grounding line mapping from differential satellite radar interferometry 1 the delineation of an ice sheet grounding line i e the transition boundary where ice detaches from the bed and becomes afloat in the ocean is critical to ice sheet mass budget calculations numerical modeling of ice sheet dynamics ice ocean interactions oceanic tides and subglacial environments here we present 15 years of comprehensive high resolution mapping of grounding lines in antarctica using differential satellite synthetic aperture radar interferometry dinsar data from the earth remote sensing satellites 1 2 ers 1 2 radarsat 1 and 2 and the advanced land observing system alos palsar for years 1994 to 2009 dinsar directly measures the vertical motion of floating ice shelves in response to tidal oceanic forcing with millimeter precision at a sample spacing better than 50 m simultaneously over areas several 100 km wide in contrast with earlier methods that detect abrupt changes in surface slope in satellite visible imagery or altimetry data on stagnant and slow moving areas we find that breaks in surface slope are reliable indicators of grounding lines but on most fast moving glaciers and ice streams our dinsar results reveal that prior mappings have positioning errors ranging from a few km to over 100 km a better agreement is found with icesat s data also based on measurements of vertical motion but with a detection noise one order of magnitude larger than with dinsar overall the dinsar mapping of antarctic grounding lines completely redefines the coastline of antarctica

the random redistribution of sediment by wind in a lake the total sedimentation rate was measured fortnightly for a year in a large shallow lake lough neagh northern ireland surface area 383 km2 mean depth 8 9 m at five sites using 10 sediment traps the total sedimentation rate included both primary and secondary sedimentation as the annual average total sedimentation rate 53 2 44 1 g m 2 d 1 is more than 25 times the primary value secondary sedimentation due to wind induced resuspension is very important the average of the largest 30 of wave mixed layer wml values a function of wind speed and effective fetch strongly correlates with the total sedimentation rate r2 values of 0 69 and 0 98 at two westerly sites at most of the sites as the wml value approaches the water depth then the orbital motion of the waves and the associated turbulence cause sediment disturbance and resuspension changing wml values then provide a basis to describe the random redistribution rr of sediment in lakes and these resuspension events can occur as frequently as 2 3 times every two weeks this study provides for the first time clear results and a description of the process of rr of sediment in a lake particularly the link between wind and sediment resuspension

temperature calibrated imaging of seasonal changes in permafrost rock walls by quantitative electrical resistivity tomography zugspitze german austrian alps 1 changes of rock and ice temperature inside permafrost rock walls crucially affect their stability permafrost rocks at the zugspitze were involved in a 0 3 0 4 km3 rockfall at 3 7 ka b p whose deposits are now inhabited by several thousands of people a 107 year climate record at the summit 2962 m asl shows a sharp temperature increase in 1991 2007 this article applies electrical resistivity tomography ert to gain insight into spatial thaw and refreezing behavior of permafrost rocks and presents the first approach to calibrating ert with frozen rock temperature high resolution ert was conducted in the north face adjacent to the zugspitze rockfall scarp in february and monthly from may to october 2007 a smoothness constrained inversion is employed with an incorporated data error model calibrated on the basis of normal reciprocal measurement discrepancy laboratory analysis of zugspitze limestone indicates a bilinear temperature resistivity relationship divided by a 0 5 0 1 c and 30 3 k m equilibrium freezing point and a twentyfold increase of the frozen temperature resistivity gradient 19 3 2 1 k m c temperature dominates resistivity changes in rock below 0 5 c while in this case geological parameters are less important ert shows recession and readvance of frozen conditions in rock correspondingly to temperature data maximum resistivity changes in depths up to 27 m coincide with maximum measured water flow in fractures in may here we show that laboratory calibrated ert does not only identify frozen and unfrozen rock but provides quantitative information on frozen rock temperature relevant for stability considerations

tide modulated ice motion and seismicity of a floating glacier tongue in east antarctica we recorded the ice motion and icequakes on the floating part of langhovde glacier in east antarctica to better understand the dynamic behavior of ice shelves and floating tongues diurnal and semi diurnal variations in ice motion and seismicity were simultaneously observed at all four global navigation satellite system and three seismic stations over 2 weeks the short term along flow ice motion is explained by the elastic response of the glacier to ocean tide induced hydrostatic stress variations which decayed at a rate of 0 8 km 1 toward the grounding line we observed a large number of icequakes during mid rising and high tides that covered a broad frequency range and formed two major groups of events centered at 10 and 120 hz respectively the hourly occurrence rates were 500 events h 1 with the observed seismicity consistent with fracture due to floating tongue bending we also observed minor secondary peaks at high ice speeds which could reflect surface cracking due to stretching or basal friction our observation demonstrates that tidal modulation was the main factor to fracture the floating tongue of langhovde glacier

hokkaido hf radar signatures of periodically reoccurring nighttime medium scale traveling ionospheric disturbances detected at short ranges the super dual auroral radar network hokkaido hf radar often detects periodically reoccurring e region echoing regions propagating toward or away from it in this work we consider 117 of such events identified for 2008 2012 these are shown to occur at nighttime preferentially during summer although significant number for events was found for winter statistics for the local time of occurrence magnitude of the speed and polarity of progressions and temporal and spatial periodicities are presented we show that the power of echoes is linearly related to their doppler velocity which makes it possible to identify the events on both power and doppler velocity plots other peculiar characteristics of echoes are discussed the onset of events is associated with gravity waves propagation through the radar field of view

flow dynamics of tidewater glaciers a numerical modelling approach the dynamics of grounded tidewater glaciers is investigated with a time dependent numerical flow model which solves the full equations for the stress and velocity fields and includes a water pressure dependent sliding law the calving criterion implemented in the model shifts the calving front at each time step to the position where the frontal ice thickness exceeds flotation height by a prescribed value with this model the linear relation between calving rate and water depth proposed on empirical grounds is qualitatively reproduced for the situation of a slowly retreating or advancing terminus but not for situations of rapid changes length changes of tidewater glaciers i e especially rapid changes are dominantly controlled by the bed topography and are to a minor degree a direct reaction to a mass balance change thus accurate information on the near terminus bed topography is required for reliable prediction of the terminus changes due to climate changes the results also confirm the suggested cycles of slow advance and rapid retreat through a basal depression rapid changes in terminus positions preferably occur in places where the bed slopes upwards in the ice flow direction

bed load transport under waves and currents the data from the flume experiments of kalkanis 1964 and abou seida 1965 giving the rates of accumulation of sand in recessed traps in oscillating sand beds have been reassessed in contrast to the work of madsen and grant 1976 the accumulation rate is interpreted as a measure of the average concentration of bed load per unit area during the period of oscillation for which the shields number t exceeds the threshold shields number th for the experimental runs where the reynolds number 35 the volume concentration of bed load c t cm3 cm 2 was found to be directly proportional to the excess shields number ex t t th c t 0 09 0 03 ext and the volume transport rate q t under instantaneous flow velocity u t was therefore q t 0 09 0 03 ex t u t for t th the rate of transport predicted by this equation was tested against the data of manohar 1955 and good agreement found showing a closer match between calculated and observed transport at high rates than found by the equation of madsen and grant 1976 the form of the transport rate equation proposed here q t u2 t u2th u t is compared with the form of the bedload transport equation for unidirectional flow and is found to have a firmer physical basis than some other wave transport equations presently in use

barrier island evolution middle atlantic shelf u s a part i shoreface dynamics abstract in part i of this paper near bottom fluid velocity and sediment concentration measurements from the shoreface of a middle atlantic barrier long island coast are analyzed to provide insight into the dynamics of erosional shoreface retreat in part ii these data are combined with observations of coastal stratigraphy in order to construct a model for the evolution and behavior of middle atlantic barriers wave motions on the long island shoreface tend to drive sediment onshore calculations of the onshore sediment flux driven by asymmetrical shoaling waves show that for the wave states commonly encountered on the middle atlantic shelf values become strongly positive landward of approximately 10 m water depth upper shoreface but drop to very low values shortly seaward of that isobath on the lower shoreface and inner shelf floor fair weather wave current interaction tends to cause a landward creep of sediment even though the wave orbital component of the near bottom velocity field is nearly symmetrical this movement occurs because the wave approach direction generally lies within 90 of the direction up coast or down coast of the alongshore wind driven current therefore fluid shear stress acting on the sediments tends to be reinforced during the shoreward stroke of the wave orbital motion and partially cancelled during the seaward stroke during major storms the rate of sediment transport increases by at least an order of magnitude and the role of wind driven currents becomes important much more sediment is resuspended by the wave orbital current component because storm waves are more powerful than fair weather swells but the wind driven flow component is also much stronger and is now available for transporting the resuspended sediment storm flows over the shoreface occur in distinct dynamic zones surf zone friction dominated zone transition zone geostrophic zone the zones are defined by dynamical considerations and expand or contract with the intensity of the causative wind stress during peak flow events the characteristic length scales of the friction dominated and geostrophic zones tend to correspond with the morphologic zones of the shoreface and inner shelf the storm intensified wind driven alongshore flows of the lower shoreface are frequently jet like in nature and may be upwelling or downwelling wind driven coastal flows with a strong downwelling component occur during most storms on the long island coast and are particularly important to the coastal sand budget during these events sand is entrained by the storm intensified upper shoreface circulation system of wave driven alongshore currents and rip currents and is fed into the main wind driven coastal current because of the offshore component of bottom flow sand is swept down the lower shoreface and onto the adjacent inner shelf fair weather processes may be unable to return storm deposited sand to the beach from such an offshore position the shoreface transport regime of the long island barrier coast thus consists of long periods of time months during which sand moves slowly toward the beach punctuated by short intense periods hours or days during which sand is transferred from the shoreface to the adjacent inner shelf the long term sense of movement of the shoreface whether retreating the long island case or prograding must depend on the loss or gain of sand by shoreface with respect to the inner shelf the data shows that the coastal sand budget is controlled not only by the upper shoreface cycle withdrawl of sand from the beach prism storage in the breakpoint bar and its subsequent return to the beach but by a cycle of larger spatial and temporal scale in which sand is exchanged between the shoreface as a whole and the adjacent inner shelf

simultaneous middle and upper atmosphere radar and ionospheric sounder observations of midlatitude e region irregularities and sporadic e layer 1 we made middle and upper atmosphere mu radar observations of midlatitude e region field aligned irregularities fais in the summer of 1999 and 2000 sporadic e es layer was monitored with a routine ionosonde and its altitude was measured with an fm cw sounder fcs in this paper we draw attention to two findings first we show that quasiperiodic qp radar echoes appearing before 0200 lt are more enhanced with increasing foes fbes which means that the fai generation is closely related to localized density gradients within es and extend from 100 to 130 km in altitude while es altitudes determined from the fcs soundings are between 100 and 110 km the latter fact suggests that existing models for the qp echo generation which require a deep modulation of es altitude are not applicable to our observational results we propose a new working model for generating qp echoes in which polarization electric fields originated from high density plasma clouds within es are mapped upward along the geomagnetic field to produce relatively weak irregularities above the es layer second we show new findings obtained from the current observations namely two types of qp echoes that occur below 100 km in the morning one is the morning qp mqp echoes with periods of 4 8 min and the other is the qp echoes with periods of 1 min the latter type can be categorized as low altitude qp echoes that were found from previous nighttime mu radar observations until now the mu radar qp echoes have been believed to occur above 100 km for the period from sunset to midnight although we do not know the generation mechanisms of the low altitude mqp echoes we suppose that these echoes might be caused by a weak es that exists below 100 km

sediment transport in the mouth of the eden estuary abstract observations of water movement and sediment transport were made from a fixed platform at an intertidal location in the mouth of the eden estuary the effects of wave activity on water movement and suspended sediment fluxes were evaluated and an empirical relationship between suspended sediment concentrations and near bed water movement is described the circulation of water in st andrews bay indicates a residual movement onshore near to the bed onshore movement of sediment in the mouth of the estuary is indicated by suspended sediment fluxes and bedload transport determined from bedform migration the relative roles of suspended sediment and bedload transport are discussed morphological changes in the estuary mouth over the three year survey period are relatively small and indicate a stable environment

automatic detection of alpine rockslides in continuous seismic data using hidden markov models data from continuously recording permanent seismic networks can contain information about rockslide occurrence and timing complementary to eyewitness observations and thus aid in construction of robust event catalogs however detecting infrequent rockslide signals within large volumes of continuous seismic waveform data remains challenging and often requires demanding manual intervention we adapted an automatic classification method using hidden markov models to detect rockslide signals in seismic data from two stations in central switzerland we first processed 21 known rockslides with event volumes spanning 3 orders of magnitude and station event distances varying by 1 order of magnitude which resulted in 13 and 19 successfully classified events at the two stations retraining the models to incorporate seismic noise from the day of the event improved the respective results to 16 and 19 successful classifications the missed events generally had low signal to noise ratio and small to medium volumes we then processed nearly 14 years of continuous seismic data from the same two stations to detect previously unknown events after postprocessing we classified 30 new events as rockslides of which we could verify three through independent observation in particular the largest new event with estimated volume of 500 000 m3 was not generally known within the swiss landslide community highlighting the importance of regional seismic data analysis even in densely populated mountainous regions our method can be easily implemented as part of existing earthquake monitoring systems and with an average event detection rate of about two per month manual verification would not significantly increase operational workload

greenland rumbles louder as glaciers accelerate flow rates of many large glaciers in greenland and antarctica have accelerated recently greenland earthquakes produced from glacier motion and calving have also increased dramatically

observation of three dimensional structures of quasi periodic echoes associated with mid latitude sporadic e layers by mu radar ultra multi channel system 1 quasi periodic qp backscatter observed by vhf radars associated with the mid latitude sporadic e es layers is characterized by distinct striations on range time intensity rti plots two competing models claim to explain the structure of unstable regions that scatter the radar waves horizontally drifting patches at an almost constant altitude and unstable regions elongated in altitude along the geomagnetic field line we have conducted interferometric imaging observations of qp radar echoes to investigate spatial structures of qp echoes precisely kyoto university s newly developed ultra multi channel receiving system of middle and upper atmosphere mu radar was used we used 19 independent channels for the radar imaging and determined the three dimensional structure and the motion of the qp echoes during the observation from 30 may to 02 june 2005 well defined qp echoes were observed on the nights of 31 may 01 june and 02 june 2005 some of qp echoes were found at altitudes higher than 120 km and appeared to descend in altitude as they approached the radar this result suggests that backscatter regions are developed along the geomagnetic field line from es layer altitudes to as high as 130 km and that the fluctuations in plasma density and electric field observed by pfaff et al 2005 using in situ measurements form a part of qp echoes

observations of bottom currents and estimates of resuspended sediment transport at the new york bight 12 mile dumpsite to document storm events that may induce a redistribution of sediment in the vicinity of the new york bight 12 mile sewage sludge dumpsite current meter moorings were deployed in water depths from 20 m near the mouth of new york harbor to 53 m within the hudson shelf valley from july 1986 through june 1989 ten usable instrument records ranging from one month to one year in duration were obtained eight of them near bottom records seasonal and geographic variability of wind induced flow were examined the wind is most efficient in driving the subtidal currents in the 2 10 day frequency band during winter when the water column is well mixed and when the eastward component of the wind often induces and sustains an up valley northward bottom flow maximum efficiency occurs for wind from 300 wnw and at sites located within the hudson shelf valley a continental shelf bottom boundary layer model glenn and grant 1987 was used to estimate resuspended sediment transport model inputs include bottom currents observed orbital wave velocities estimated and sediment grain size from the literature model output indicates that sediment resuspension at the current meter sites occurs approximately 5 of the time primarily during winter months the difference in along valley flux between two moorings provides a rough estimate 6 month time series of deposition and erosion the net deposition 02 mm was no greater than the deposition and erosion resulting from individual storms a three dimensional circulation model you et al 1991 is applied to increase the spatial resolution of the near bottom current field 4 km grid for a storm event in may of 1987 given these velocities that vary in space and time the redistribution of sediment was modeled for different surface wave conditions areas of deposition aligned with the hudson shelf valley due to less wave induced resuspension in deeper waters given all the uncertainties in the input variables grain size surface waves and the simplistic assumptions made in modeling the deposition and erosion it is still uncertain how much sludge is permanently removed from the area but episodic redistribution of surficial sediment evidently occurs throughout the inner new york bight

seismic detection and analysis of icequakes at columbia glacier alaska 1 contributions to sea level rise from rapidly retreating marine terminating glaciers are large and increasing strong increases in iceberg calving occur during retreat which allows mass transfer to the ocean at a much higher rate than possible through surface melt alone to study this process we deployed an 11 sensor passive seismic network at columbia glacier alaska during 2004 2005 we show that calving events generate narrow band seismic signals allowing frequency domain detections detection parameters were determined using direct observations of calving and validated using three statistical methods and hypocenter locations the 1 3 hz detections provide a good measure of the temporal distribution and size of calving events possible source mechanisms for the unique waveforms are discussed and we analyze potential forcings for the observed seismicity

characteristics of tide water calving at glaciar san rafael chile glacial calving is a poorly understood process this study tests the influence of local environmental variables on the magnitude and frequency distributions of calving behaviour at glaciar san rafael chile near the terminus of the glacier surface speeds average 17 m d 1 in summer and calving is profuse and continual the size location and characteristics of over 7000 calving events were recorded during 32 d in 1991 and 1992 together with meteorological bathymetric and oceanographic data mean daily calving exceeds 400 events per day and the mean calving flux is more than 2 mm 3 d 1 mean annual calving speed and calving flux are about 4500 m a 1 and 2 0 km 3 a 1 respectively this calving speed is higher than that predicted by the established empirical relationship between tide water calving speed and water depth this is surprising given the low salinity of laguna san rafael and that fresh water calving speeds are commonly much lower than those in tide water daily patterns of calving frequency and flux correlate poorly or not at all with meteorological variables but tidal stage may have some control over the timing of large submarine calving events submarine calving produced the largest bergs however the relatively small total flux recorded from the submerged part of the ice cliff may imply unusually rapid melt rates

rapid retreat and acceleration of helheim glacier east greenland 1 a significant amount of the measured coastal thinning of the greenland ice sheet may be due to recent acceleration of outlet glaciers using remote sensing we measured two major periods of speedup on helheim glacier between 2000 and 2005 that increased peak speeds from approximately 8 to 11 km yr these speedups coincided with rapid retreats of the calving front totaling over 7 5 km the glacier also thinned by over 40 m from 2001 to 2003 retreat of the ice front appears to decrease resistance to flow and concentrates the gravitational driving force over a smaller area farther up glacier acceleration may be a delayed response to surface draw down and steepening of the glacier s main trunk if the 2005 speedup also produces strong thinning then much of the glacier s main trunk may un ground leading to further retreat citation howat i m i joughin s tulaczyk and s gogineni 2005 rapid retreat and acceleration of helheim glacier east greenland geophys res lett 32 l22502 doi 10 1029 2005gl024737

a stochastic modeling approach to the fine sediment budget of the new york bight a stochastic model of fine sediment transport on the continental shelf is modified to incorporate the effects of storm flows the model based on surface gravity wave resuspension now includes transport by both tides and episodic storm flows effects of gravity wave storm flow correlation as deduced from near bottom current meter measurements are also included sediment dispersion is significantly faster when the effects of storm flows are included the effects of the gravity wave storm flow correlation and the regional net flow pattern are small the model is solved numerically for equilibrium dispersal patterns for sediment entering at estuary inlets bordering the new york bight region additional dispersal patterns are found for upcoast and downcoast sources as well as the dredge spoil dump site combinations of these dispersal patterns are least squares fit to the observed fine sediment distribution in the new york bight to evaluate the magnitudes of the sources of sediment negative source magnitudes are interpreted as sediment sinks the results are consistent with other estimates of sediment sources and sinks in the new york bight

tide induced microseismicity in the mertz glacier grounding area east antarctica the deployment of a seismic network along the adelie and george v coasts in east antarctica during the period 2009 2012 provides the opportunity to monitor cryoseismic activity and to obtain new insights on the relationship between tidal cycles and coastal glacier dynamics here we focus on records from a seismometer located on a rocky outcrop in the vicinity of the grounding line of the 35 km broad mertz glacier a major outflow of this region we detect numerous icequakes 50 000 events within 10 months and up to 100 events h and demonstrate their clear tidal modulation we suggest that they result from ice friction and fracturing around the rocky peak and from the glacier flexure in response to the falling and rising tides at its grounding area we propose that such icequake monitoring could be used as a climate proxy since grounding lines are subject to migrate with sea level changes

acoustic and microseismic characterization in steep bedrock permafrost on matterhorn ch understanding of processes and factors in uencing slope stability is essential for assessingthe stability of potentially hazardous slopes passive monitoring of acoustic emissions and microseismologyprovides subsurface information on fracturing timing and identi cation of the mechanism and thereforecomplement surface displacement data this study investigates for the rst time acoustic and microseismicsignals generated in steep frac tured bedrock permafrost covering the broad frequency range of 1 105hz the analysis of arti cial forcing experiments using a rebound hammer in a controlled setting led to twomajor ndings first statistically insigni cant cross correlation between signals indicates that waveformschange strongly with propagation distance second a sign cant ampli cation is found in the frequencyband 33 67 hz this nding is strongly supported by evidence from arti cial rockfall events and moreimportantly by naturally occurring fracture events identi ed in fracture displacement data thus lteringthis frequency band enables enhanced detection of microseismic events relevant for slope stabilityassessment the analysis of 2 year time series in this frequency band further suggests that the detectedenergy rate baseline of all automatically triggered events using the sta lta algorithm is not sensitive totemperature forcing an observation of primary importance for long term data collection analysis andinterpretation the event detection in the established frequency band is not only improved but also nota ected by the short and long term temperature changes in such a rapidly changing environment

evolving force balance at columbia glacier alaska during its rapid retreat 1 changes in driving and resistive stresses play an essential role in governing the buoyancy forces that are important controls on the speed and irreversibility of tidewater glacier retreats we describe changes in geometry velocity and strain rate and present a top down force balance analysis performed over the lower reach of columbia glacier our analysis uses new measurements and estimates of basal topography and photogrammetric surface velocity measurements made between 1977 and 2001 while assuming depth independent strain sensitivity tests show that the method is robust and insensitive to small changes in the calculation parameters spatial distributions of ice speed show little correspondence with driving stress instead spatial patterns of ice speed exhibit a nonlinear correspondence with basal drag primary resistance to flow comes from basal drag but lateral drag becomes increasingly more important throughout the retreat which may account for observed increases in speed maximum basal drag is always located in a prominent constriction located 12 km upstream from the preretreat terminus once the terminus retreated into deep water off the terminal moraine marking the modern maximum extent the upstream location of this maximum basal drag helped to promote thinning and decrease effective pressure in the lower region by limiting replenishing ice flow from upstream an increase in both ice velocity and calving resulted initiating what appears to be an irreversible retreat

calving icebergs a source of low frequency seismic signals from columbia glacier alaska low frequency icequakes produced by columbia glacier alaska are caused by large icebergs which break off the glacier terminus into prince william sound occasionally many ice seracs fall in rapid succession producing complex low frequency icequake signals with durations sometimes exceeding 10 min an empirical relationship v 4000 t between the volume v of an iceberg in cubic meters and the duration t of the seismic signal in seconds can be used to estimate the calving rate of columbia glacier from seismological data alone during 1984 and 1985 a period of rapid retreat of the glacier the calculated number of icequakes per month showed seasonal fluctuations that corresponded to variations in calving rate determined by photogrammetry it is likely that most previously reported low frequency icequakes in southern alaska are produced by calving tidewater glaciers

seasonality and increasing frequency of greenland glacial earthquakes some glaciers and ice streams periodically lurch forward with sufficient force to generate emissions of elastic waves that are recorded on seismometers worldwide such glacial earthquakes on greenland show a strong seasonality as well as a doubling of their rate of occurrence over the past 5 years these temporal patterns suggest a link to the hydrological cycle and are indicative of a dynamic glacial response to changing climate conditions

acoustic measurements of suspended sand on the shoreface and the control of concentration by bed roughness acoustic backscatter measurements of the concentrations of sand in suspension on the shoreface seawards of the breaking zone during a mild storm event show that sand concentrations increase initially but then rapidly decrease as the wave energy increases it is suggested that the bed roughness is a major control on suspended sand concentration and that the decrease in concentration is due to decreasing ripple steepness after the break off bed shear stress is exceeded no direct measurements of bedforms were available and the combined wave current interaction model of grant and madsen j geophys res vols 84 1979 and 87 1982 with extensions to movable bed roughness ripple dimensions from carstens et al s 1969 laboratory data u s army corps eng cerc tech mem 28 and to sediment induced self stratification glenn and grant j geophys res vol 92 1983 was used to predict the current and suspended sand concentration profile matching the measured and modeled concentrations at 2 cm above the bed the values of the resuspension coefficient 0 were found to decrease as excess skin friction increased in a manner similar to that suggested by drake and cacchione cont shelf res vol 9 1989 but were an order of magnitude larger using the much smaller ripple dimensions of nielsen j geophys res vol 86 1981 changed the model results very little significant differences were found between the time averaged suspended sand profiles and those predicted by the model sand transport fluxes have also been computed using the instantaneous products of measured suspended concentrations and currents the current being the sum of steady and wave induced components the wave induced fluxes show considerable variability from run to run but the general pattern is of a transport profile having a shoreward maximum at 5 10 cm above the bed and offshore transport in the few centimetres closest to the bed little net transport occurred above 15 cm these fluxes show a weak dependence on the wave energy becoming more shoreware and the height of the maximum shoreward transport decreasing as the wave energy increased again consistent with the influence of the ripple steepness

seismic and hydroacoustic tremor generated by colliding icebergs 1 iceberg harmonic tremor iht emanating from tabular icebergs in the southern ocean and along calving margins of the antarctic ice sheet is a complex evolving signal at frequencies above approximately 0 5 hz iht has been observed as t phases on islands in the equatorial pacific as hydroacoustic signals in the indian ocean and by local and regional antarctic seismic networks to identify the iht source mechanism and to understand its relevance to iceberg calving evolution and breakup we deployed seismometers on a giant 25 by 50 km tabular iceberg called c16 in the ross sea antarctica during a uniquely accessible period austral summer 2003 2004 when it was aground against the northern shore of ross island during the deployment period c16 was in sporadic contact with another giant tabular iceberg b15a that was moving under the influence of local ocean currents this study reveals that the c16 associated iht was a manifestation of extended episodes of discrete repeating stick slip icequakes typically thousands of individual subevents per hour produced when the cliff like edges of the tabular icebergs underwent glancing strike slip collisions the iht signal that we observed is thus not a phenomenon associated with iceberg elastic or fluid resonance modes but is instead the consequence of long sequences of very regularly spaced and similar pulses of seismic radiation from these constituent stick slip subevents iht represents a newly identified glaciogenic source of seismicity that can be used to improve our understanding of iceberg dynamics and possibly of ice shelf disintegration processes

3 d radar imaging of e region field aligned plasma irregularities by using multireceiver and multifrequency techniques this paper reports the first use of a 3 d radar imaging for observing e region field aligned plasma irregularities fais in the midlatitude ionosphere five carrier frequencies equally spaced between 46 25 and 46 75 mhz were transmitted alternately with consecutive radar pulses and 20 receivers were employed for receiving the radar echoes the experiments were carried out using the middle and upper atmosphere radar 34 85 n 136 10 e with the radar beams steered to the geographic north and 6 6 north by east at the zenith angles of 51 0 and 51 5 respectively the 2 d imaging with the echoes collected by the 19 of the 20 receivers revealed that in zonal dimension the off beam direction of arrival doa of the echo region changed alternately between positive and negative values which can be attributed to the highly localized fais drifting zonally through the radar beam on the other hand the off beam doa in meridional dimension was negative and positive respectively at higher and lower range locations which were supposed to be due to the meridional drift component of fais a combination of 5 frequencies and 19 receivers achieved a 3 d imaging of the fai structures illustrating small scale fai striations and bubblelike plasma structures in the radar volume moreover declination of geomagnetic field line was examined from the imaged 3 d brightness distribution in the radar volume the estimated declination of geomagnetic field line was in agreement with that computed from the international geomagnetic reference field model in 2011 this paper has demonstrated some capabilities of radar imaging for ionospheric investigation

mid latitude e region field aligned irregularities observed with the mu radar fine structures e region field aligned irregularities were observed on june 24 25 1989 with the mu radar at shigaraki japan 34 9 n 136 1 e geomagnetic latitude 25 0 n the 3 2 m scale irregularities were observed with the mu radar in five main beam directions each of which was nearly perpendicular to the geomagnetic field at 100 km altitude doppler spectra were obtained every 20 s with a range resolution of 600 m field perpendicular echoes appeared from 2130 to 2330 lt and from 0400 to 1100 lt times that correspond to postsunset and postsunrise period in the e region a preliminary examination of the doppler spectra indicates spectral widths of 50 120 m s 1 and the mean doppler velocities are well below the ion acoustic speed these spectral characteristics are consistent with those obtained in the equatorial and auroral electrojets and have been attributed to the gradient drift instability the echoes observed during the postsunset and postsunrise periods showed quite different morphologies in the time height distribution for this reason they are classified into two types continuous and quasi periodic the appearance of the continuous echoes was mainly continuous in time and situated between 90 and 100 km altitude during the postsunrise period the appearance of the quasi periodic echoes was intermittent with periods of 5 10 min and situated above 100 km altitude during the postsunset period the quasi periodic echoes showed phase propagation toward the radar while the averaged mean doppler velocity was away from the radar by measuring the time delays in echo regions from five directions an apparent westward motion approximately 120 m s 1 of the irregularity regions was estimated

potential use of time domain reflectometry for measuring water content in rock abstract quantifying water movement through bedrock materials requires a technique which can accurately measure water content at precise locations within the medium time domain reflectometry tdr is widely used to measure the water content of soil and has a measurement sensitivity which is tightly confined to the area immediately surrounding the probes this study applies tdr to the measurement of water content in rocks the technique was evaluated using sandstone and welded tuff in a series of laboratory experiments a block of each rock type was instrumented with a series of evenly spaced tdr probes each block was first saturated with water and then allowed to air dry the water content was determined gravimetrically using the tdr over a period of several weeks the results indicate that the tdr technique can be used to determine the water content of rock with an accuracy comparable with that reported for the technique used in soils