evidence of earthquake triggering by the solid earth tides article i nfo clearevidence forearthquake triggeringbythe earth tides hasremained elusive for morethan a century using the largest global earthquake catalog available the neic catalog with 442412 events we observe a clear correlation with 99 confidence between the phase of the solid earth tide and the timing of seismic events earthquakes occur slightly more often at the time of ground uplift by the earth tide i e when normal stresses are reduced within the lithosphere we observe that this phase distribution anomaly is larger for smaller and shallowerearthquakes although earthquakes inregionswithdominantlynormalandstrike slip faulting seem to exhibit more tidal triggering than regions dominated by thrust faulting there is no statistically significant evidence for a focal mechanism dependence on earthquake triggering finally we show here that it is highly probablethat the observedtriggeringiscaused bythe solid earth tide ratherthan byloading fromthe oceanor atmospheric tides although an additional impact due to loading from ocean tides is possible and probable we cannot detect it here because the earthquake database is not sufficiently complete and homogeneous more smallmagnitudeearthquakesinoceanicareasareneeded ourresultsareconsistentwiththeideaofadamped

transfer of basal sliding variations to the surface of a linearly viscous glacier on etudie pour une plaque a faces paralleles d epaisseur h et de viscosite lineaire l effet en surface des fluctuations de la vitesse de derapage

predicting coastal hazards for sandy coasts with a bayesian network abstract low frequency high impact storm events can have large impacts on sandy coasts the physical processes governing these impacts are complex because of the feedback between the hydrodynamics of surges and waves sediment transport and morphological change predicting these coastal changes using a numerical model requires a large amount of computational time which in the case of an operational prediction for the purpose of early warning is not available for this reason morphodynamic predictions are not commonly included in early warning systems ewss however omitting these physical processes in an ews may lead to potential under or over estimation of the impact of a storm event to solve this problem a method has been developed to construct a probabilistic bayesian network bn this bn connects three elements offshore hydraulic boundary conditions characteristics of the coastal zone and onshore hazards such as erosion and overwash depths and velocities the hydraulic boundary conditions are derived at a water depth of approximately 20 m from a statistical analysis of observed data using copulas and site characteristics are obtained from measurements this bn is trained using output data from many pre computed process based model simulations which connect the three elements once trained the response of the bn is instantaneous and can be used as a surrogate for a process based model in an ews in which the bn can be updated with an observation of the hydraulic boundary conditions to give a prediction for onshore hazards the method was applied to praia de faro portugal a low lying urbanised barrier island which is subject to frequent flooding using a copula based statistical analysis which preserves the natural variability of the observations a synthetic dataset containing 100 events was created based on 20 years of observations but extended to return periods of significant wave height of up to 50 years these events were transformed from offshore to onshore using a 2d xbeach roelvink et al 2009 model three bn configurations were constructed of which the best performing one was able to predict onshore hazards as computed by the model with an accuracy ranging from 81 to 88 and predict events with no significant onshore hazards with an accuracy ranging from 90 to 95 two examples are presented on the use of a bn in operational predictions or as an analysis tool the added value of this method is that it can be applied to many coastal sites 1 limited observations of offshore hydrodynamic parameters can be extended using the copula method which retains the original observations natural variability 2 the transformation from offshore observations to onshore hazards can be computed with any preferred coastal model and 3 a bn can be adjusted to fit any relevant connections between offshore hydraulic boundary conditions and onshore hazards furthermore a bn can be continuously updated with new information and expanded to include different morphological conditions or risk reduction measures as such it is a promising extension of existing ewss and as a planning tool for coastal managers

deepening of inner gorges through subglacial meltwater an example from the unesco entlebuch area switzerland this paper explores the mechanisms by which inner gorges in the alps were formed it focuses on the ca 1 5 km long 80 m deep and a few hundred meter wide lammschlucht located in the northern foothills of the central alps we reconstructed the glacial cover using lateral moraines and hanging talus cones that record the elevation of the ice surface at the deglaciation stage of the lgm last glacial maximum we used the reconstructed ice thickness patterns to calculate the erosional potential of the subglacial meltwater the applied model is based on the principle of energy conservation and yields the pattern of downstream changes of the dynamic pressure which is considered a measure for erosion potential the model results suggest a maximum of the dynamic pressure at the end of the inner gorge we interpret therefore that the subglacial meltwater scoured the reach toward the end of the lammschlucht because of the enhanced dynamic pressure which was ultimately controlled by the ice overburden post glacial fluvial erosion then resulted in a readjustment through a regressive shift of the erosional front along the inner gorge farther upstream the current location of this front lies almost in the middle of the lammschlucht inner gorge where a step pool channel changes into a straight plane bed channel flowing on a deeply scoured bedrock

the extreme 2013 2014 winter storms hydrodynamic forcing and coastal response along the southwest coast of england the southwest coast of england was subjected to an unusually energetic sequence of atlantic storms during the 2013 2014 winter with the 8 week period from mid december to mid february representing the most energetic period since at least 1953 a regional analysis of the hydrodynamic forcing and morphological response of these storms along the sw coast of england highlighted the importance of both storm and site specific conditions the key factor that controls the atlantic storm wave conditions along the south coast of southwest england is the storm track energetic inshore wave conditions along this coast require a relatively southward storm track which enables offshore waves to propagate up the english channel relatively unimpeded the timing of the storm in relation to the tidal stage is also important and coastal impacts along the macro tidal southwest coast of england are maximised when the peak storm waves coincide with spring high tide the role of storm surge is limited and rarely exceeds 1 m the geomorphic storm response along the southwest coast of england displayed considerable spatial variability this is mainly attributed to the embayed nature of the coastline and the associated variability in coastal orientation on west facing beaches typical of the north coast the westerly atlantic storm waves approached the coastline shore parallel and the prevailing storm response was offshore sediment transport many of these north coast beaches experienced extensive beach and dune erosion and some of the beaches were completely stripped of sediment exposing a rocky shore platform on the south coast the westerly atlantic storm waves refract and diffract to become southerly inshore storm waves and for the southeast facing beaches this results in large incident wave angles and strong eastward littoral drift many south coast beaches exhibited rotation with the western part of the beaches eroding and the eastern part accreting 2015 the authors earth surface processes and landforms published by john wiley sons ltd

an analytical model to predict dune erosion due to wave impact an analytical model is developed to calculate recession distance and eroded volume for coastal dunes during severe storms the transport relationship used in the model is based on wave impact theory where individual swash waves hitting the dune face induce the erosion combining this relationship with the sediment volume conservation equation describes the response of the dune to high waves and water levels four different data sets on dune erosion originating from the laboratory and the field were employed to validate the model and to determine the value of an empirical transport coefficient appearing in the analytical solutions the time evolution of dune recession observed in the different data sets was well described by the model but the empirical coefficient showed some variation between cases especially for the field data in practical applications of the model it is recommended to use a range of coefficient values to include an uncertainty estimate of calculated quantities such as recession distance and eroded volume

the effect of the subglacial water pressure on the sliding velocity of a glacier in an idealized numerical model in order to interpret observed short term variations of the sliding velocity of a glacier the effect of a variable subglacial water pressure on the sliding velocity has been studied using an idealized numerical model in particular the transient stages of growing or shrinking water filled cavities at the ice bedrock interface were analysed it was found that the sliding velocity was larger when cavities were growing than when they had reached the steady state size for a given water pressure the smallest sliding velocities occurred while cavities were shrinking when cavitation is substantial a small drop of water pressure below the steady state value e g by 0 5 bar can temporarily cause backward sliding a limiting water pressure at which sliding becomes unstable is derived the consequences of more realistic assumptions than those of the model are discussed

analysis of time series of glacier speed columbia glacier alaska during the summers of 1984 and 1985 laser measurements were made of the distance from a reference location to markers on the surface of the lower reach of columbia glacier alaska the data have numerous gaps mostly because of inclement weather the laser measurements were corrected for variations in atmospheric temperature and pressure and for the trajectory of the marker the marker speed was calculated by using a combination of cubic splines and digital filters to arrive at a data set with 1 hour time intervals the speed varies from 7 to 15 m d and has three noteworthy components 1 a low frequency perturbation in speed with a time scale of days related to increased precipitation 2 semidiurnal and diurnal variations related to sea tides and 3 diurnal variations related to glacier surface melt the low frequency and tidal period variations are separated by low pass filtering and subtracting the filtered data from the original data the variations from melt runoff and tides have the same frequency range and are examined using harmonic analysis and multiple regression with the various forcing functions the high frequency portion of the ice speed signal is dominated by tidal influences and to a lesser extent by meltwater influences the low frequency portion of the signal is dominated by the effects of precipitation

links between short term velocity variations and the subglacial hydrology of a predominantly cold polythermal glacier the surface velocity of a predominantly cold polythermal glacier john evans glacier ellesmere island canada varies significantly on both seasonal and shorter time scales seasonal variations reflect the penetration of supraglacial water to the glacier bed through significant thicknesses of cold ice shorter term events are associated with periods of rapidly increasing water inputs to the subglacial drainage system earlyseason short term events immediately follow the establishment of a drainage connection between glacier surface and glacier bed and coincide with the onset of subglacial outflow at the terminus a mid season short term event occurred as surface melting resumed following cold weather and may have been facilitated by partial closure of subglacial channels during this cold period there is a close association between the timing and spatial distribution of horizontal and vertical velocity anomalies the temporal pattern of surface water input to the glacier and the formation seasonal evolution and distribution of subglacial drainage pathways these factors presumably control the occurrence of highwater pressure events and water storage at the glacier bed the observed coupling between surface water inputs and glacier velocity may allow predominantly cold polythermal glaciers to respond rapidly to climate induced changes in surface melting

influence of increasing surface melt over decadal timescales on land terminating greenland type outlet glaciers over recent decades greenland ice sheet surface melt has shown an increase both in intensity and spatial extent part of this water probably reaches the bed and can enhance glacier speed advecting a larger volume of ice into the ablation area in the context of a warming climate this mechanism could contribute to the future rate of thinning and retreat of land terminating glaciers of greenland these changes in ice flow conditions will in turn influence surface crevassing and thus the ability of water to reach the bed at higher elevations here using a coupled basal hydrology and prognostic ice flow model the evolution of a greenland type glacier subject to increasing surface melt is studied over a few decades for different scenarios of surface melt increase over the next decades the evolution of crevassed areas and the ability of water to reach the bed is inferred our results indicate that the currently observed crevasse distribution is likely to extend further upstream which will allow water to reach the bed at higher elevations this will lead to an increase in ice flux into the ablation area which in turn accelerates the mass loss of land terminating glaciers

links between acceleration melting and supraglacial lake drainage of the western greenland ice sheet 1 the impact of increasing summer melt on the dynamics and stability of the greenland ice sheet is not fully understood mounting evidence suggests seasonal evolution of subglacial drainage mitigates or counteracts the ability of surface runoff to increase basal sliding here we compare subdaily ice velocity and uplift derived from nine global positioning system stations in the upper ablation zone in west greenland to surface melt and supraglacial lake drainage during summer 2007 starting around day 173 we observe speedups of 6 41 above spring velocity lasting 40 days accompanied by sustained surface uplift at most stations followed by a late summer slowdown after initial speedup we see a spatially uniform velocity response across the ablation zone and strong diurnal velocity variations during periods of melting most lake drainages were undetectable in the velocity record and those that were detected only perturbed velocities for 1 day suggesting preexisting drainage systems could efficiently drain large volumes of water the dynamic response to melt forcing appears to 1 be driven by changes in subglacial storage of water that is delivered in diurnal and episodic pulses and 2 decrease over the course of the summer presumably as the subglacial drainage system evolves to greater efficiency the relationship between hydrology and ice dynamics observed is similar to that observed on mountain glaciers suggesting that seasonally large water pressures under the ice sheet largely compensate for the greater ice thickness considered here thus increases in summer melting may not guarantee faster seasonal ice flow

a modeling study of the effect of runoff variability on the effective pressure beneath russell glacier west greenland basal sliding is a main control on glacier flow primarily driven by water pressure at the glacier base the ongoing increase in surface melting of the greenland ice sheet warrants an examination of its impact on basal water pressure and in turn on basal sliding here we examine the case of russell glacier in west greenland where an extensive set of observations has been collected these observations suggest that the recent increase in melt has had an equivocal impact on the annual velocity with stable flow on the lower part of the drainage basin but accelerated flow above the equilibrium line altitude ela these distinct behaviors have been attributed to different evolutions of the subglacial draining system during and after the melt season here we use a high resolution subglacial hydrological model forced by reconstructed surface runoff for the period 2008 to 2012 to investigate the cause of these distinct behaviors we find that the increase in meltwater production at low elevation yields a more efficient drainage system compatible with the observed stagnation of the mean annual flow below the ela at higher elevation the model indicates that the drainage system is mostly inefficient and is therefore strongly sensitive to an increase in meltwater availability which is consistent with the observed increase in ice velocity

evidence of both m2 and o1earth tide waves in radon 222 air concentration measured in a subglacial laboratory 1 many earthquake related radon 222 temporal changes have been recorded since the 1960s and are frequently discussed sometimes initiating a controversial debate on the relevance of radon 222 as an earthquake precursory signal the diurnal s1 o1 and semidiurnal s2 m2 earth tide signatures in radon signals are acquired in a natural context this can be used to calibrate the radon changes under strain accumulation close to epicentral areas which are often discussed but are rarely evidenced by experimental data the analysis of a 10 month time series acquired in the subglacial laboratory of the argentiere glacier mont blanc massif french alps demonstrates here the unambiguous episodic appearance of the m2 o1 waves in the radon signal with significant amplitudes of 36 and 50 bq m 3 respectively we thus prove that radon variations induced by gravitational m2 and o1 waves are detectable in a natural environment in this particular place the radon response is probably amplified by cyclic stress variations applied on the upstream side of the natural rock dam into which the laboratory is drilled the amplification of the radon signal is induced by poroelastic deformation under this particular mechanical forcing this can elucidate why most precedent studies failed to detect m2 o1 signatures in radon signals recorded in other underground laboratories

satellite derived volume loss rates and glacier speeds for the juneau icefield alaska we provide a high resolution map of elevation change rates dh dt at the juneau icefield jif southeastern alaska in order to quantify its contribution to sea level rise between 2000 and 2009 2013 we also produce the first high resolution map of ice speeds at the jif which we use to constrain flux and look for acceleration we calculate dh dt using stacked digital elevation models dems from the advanced spaceborne thermal emission and reflection radiometer aster instrument and the shuttle radar topography mission srtm taking into account srtm c band penetration via comparison with srtm x band elevations overall the jif is losing mass less rapidly 0 13 0 12mw e a than other alaskan icefields 0 79mw e a we determine glacier speeds using pixel tracking on optical image pairs acquired from 2001 to 2010 by aster from radar image pairs acquired between 2007 and 2011 and from radar interferometry in 1995 we detect seasonal speed variations but no interannual acceleration ruling out dynamics as the cause of the observed thinning thinning must therefore be due to the documented warming in the region flux measurements confirm this for mendenhall glacier showing that calving constitutes only 2 5 5 of mass loss there

seismic electric signals ses and earthquakes a review of an updated van method and competing hypotheses for ses generation and earthquake triggering abstract electromagnetic phenomena are sometimes associated with seismic events but earthquake prediction using seismic electric signals ses has not been seriously considered since the early 1990s there are several causes 1 false alarms that have created panics in greece and 2 a strong critique of the varotsos alexopoulos nomicos van method used there an updated van method that includes time series analysis has made successful medium range predictions and short range predictions when coupled with seismic time series analysis four types of potential mechanisms to create precursory ses relying on deformation effects temperature effects ore mineral movement or groundwater variation are reviewed data relevant to each are insufficient to favor a single mechanism records of the number of false positive and missed events for an updated van method have not been well maintained false positives appear to be abundant and render the method unusable co seismic groundwater fluctuations are addressed and two novel hypotheses of earthquake trigger mechanism are also presented ionospherically induced electric and resultant magnetic fields to weaken rock thereby causing failure and volatiles liberated from minerals additionally promoting rock failure recommendations for further study are included

modelling storm impacts on beaches dunes and barrier islands a new nearshore numerical model approach to assess the natural coastal response during time varying storm and hurricane conditions including dune erosion overwash and breaching is validated with a series of analytical laboratory and field test cases innovations include a non stationary wave driver with directional spreading to account for wave group generated surf and swash motions and an avalanching mechanism providing a smooth and robust solution for slumping of sand during dune erosion the model performs well in different situations including dune erosion overwash and breaching with specific emphasis on swash dynamics avalanching and 2dh effects these situations are all modelled using a standard set of parameter settings the results show the importance of infragravity waves in extending the reach of the resolved processes to the dune front the simple approach to account for slumping of the dune face by avalanching makes the model easily applicable in two dimensions and applying the same settings good results are obtained both for dune erosion and breaching

modeling the effect of water excavation sequence and rock reinforcement with discontinuous deformation analysis abstract a powerful numerical method that can be used for modeling rock structure interaction is the discontinuous deformation analysis dda method developed by shi in 1988 in this method rock masses are treated as systems of finite and deformable blocks large rock mass deformations and block movements are allowed although various extensions of the dda method have been proposed in the literature the method is not capable of modeling water block interaction sequential loading or unloading and rock reinforcement three features that are needed when modeling surface or underground excavation in fractured rock this paper presents three new extensions to the dda method the extensions consist of hydro mechanical coupling between rock blocks and steady water flow in fractures sequential loading or unloading and rock reinforcement by rockbolts shotcrete or concrete lining examples of application of the dda method with the new extensions are presented simulations of the underground excavation of the unju tunnel in korea were carried out to evaluate the influence of fracture flow excavation sequence and reinforcement on the tunnel stability the results of the present study indicate that fracture flow and improper selection of excavation sequence could have a destabilizing effect on the tunnel stability on the other hand reinforcement by rockbolts and shotcrete can stabilize the tunnel it is found that in general the dda program with the three new extensions can now be used as a practical tool in the design of underground structures in particular phases of construction excavation reinforcement can now be simulated more realistically however the method is limited to solving two dimensional problems

calving processes and the dynamics of calving glaciers abstract calving of icebergs is an important component of mass loss from the polar ice sheets and glaciers in many parts of the world calving rates can increase dramatically in response to increases in velocity and or retreat of the glacier margin with important implications for sea level change despite their importance calving and related dynamic processes are poorly represented in the current generation of ice sheet models this is largely because understanding the calving problem involves several other long standing problems in glaciology combined with the difficulties and dangers of field data collection in this paper we systematically review different aspects of the calving problem and outline a new framework for representing calving processes in ice sheet models we define a hierarchy of calving processes to distinguish those that exert a fundamental control on the position of the ice margin from more localised processes responsible for individual calving events the first order control on calving is the strain rate arising from spatial variations in velocity particularly sliding speed which determines the location and depth of surface crevasses superimposed on this first order process are second order processes that can further erode the ice margin these include fracture propagation in response to local stress imbalances in the immediate vicinity of the glacier front undercutting of the glacier terminus by melting at or below the waterline and bending at the junction between grounded and buoyant parts of an ice tongue calving of projecting submerged ice feet can be regarded as a third order process because it is paced by first or second order calving above the waterline first order calving can be represented in glacier models using a calving criterion based on crevasse depth which is a function of longitudinal strain rate modelling changes in terminus position and calving rates thus reduces to the problem of determining the ice geometry and velocity distribution realistic solutions to the problem of modelling ice flow therefore depend critically on an appropriate choice of sliding law models that assume that basal velocities are controlled by basal drag can replicate much of the observed behaviour of calving glaciers with grounded termini but an important limitation is that they cannot be used to model floating glacier termini or ice shelves alternative sliding laws that parameterise drag from the glacier margins provide more flexible and robust ways of representing calving in ice sheet models such models can explain a remarkable range of observed phenomena within a simple unifying framework including downglacier increases in velocity and strain rates where basal and or lateral drag diminishes flow acceleration in response to thinning through time the tendency for glaciers to stabilise at pinning points in relatively shallow water or fjord narrowings the constraints on ice shelf stability and the contrasts in calving rates between tidewater and freshwater calving glaciers many unresolved issues remain however including the role played by the removal of backstress in the acceleration of retreating calving glaciers and the controls on melting at and below the waterline

modifications to the theory of intraglacial waterways for the case of subglacial ones on defend l idee que dans les glaciers de montagne temperes les voies d eau sont sous glaciaires pour un conduit noye sous glaciaire il faut introduire deux processus importants l accroissement de la deformation plastique sur les cotes amont des bosses et la chaleur apportee par l eau des sources qui en hiver rend compte de la plus grande partie du debit la theorie explique pourquoi rothlisberger 1972 dut adopter une valeur non realiste pour le parametre rheologique de la glace elle conduit a la conclusion que dans les zones non surcreusees la plus grande partie de l annee les conduits sous glaciaires doivent rester non noyes et a la pression atmospherique cas des surcreusements l incidence de ce nouveau modele sur la theorie du glissement des glaciers

simulation of storm induced barrier island morphodynamics and flooding abstract prediction of coupled storm hydrodynamics and morphodynamics is essential for accurately designing coastal flood protection measures a numerical simulation methodology was developed and implemented to evaluate and assess engineering design solutions for storm damage reduction along the south shore of long island new york usa this simulation methodology was applied to compute bay water levels for two major coastal storms taking into account contributions from storm surge waves wind and barrier island overwash and breaching simulation results for breaching and bay flooding compare well to historically documented barrier island morphological change and bay high water marks

statistical simulation of wave climate and extreme beach erosion abstract recent developments in extreme values modelling have been used to develop a framework for determining the coastal erosion hazard on sandy coastlines this framework quantitatively reproduced the extreme beach erosion volumes obtained from field measurements at narrabeen beach australia this encouraging finding was achieved using kriebel and dean s kriebel d l and dean r g 1993 convolution method for time dependent beach profile response journal of waterway port coastal and ocean engineering 119 2 204 226 simple beach erosion and accretion model the method includes allowances for joint probability between all basic erosion variates including wave height period and direction event duration tidal anomalies and event spacing a new formulation for the dependency between wave height and period has been developed it includes the physical wave steepness limitation event grouping where significantly more erosion can occur from two closely spaced storms is handled by temporally simulating the synthetic wave climate and the resulting beach erosion and accretion

radon surveys and real time monitoring at stromboli volcano influence of soil temperature atmospheric pressure and tidal forces on 222rn degassing abstract we used a network of stations to perform systematic radon surveys at stromboli volcano the time series of periodic measurements show that monthly average 222rn emissions reflect changes in volcanic activity and exhibit increasing trends prior and during the last major eruptive cycles maps of radon emissions indicate that diffuse degassing is operative at stromboli volcano concentrated degassing essentially occurs in the summit area and within a sector proximal to the two major ne trending faults these sites were chosen for deploying the two real time stations that are currently operating at stromboli in these devices the 222rn electronic dosimeters are connected to a radiomodem for wireless data transfer to a receiving station at the volcano observatory radon activity soil temperature and atmospheric pressure data are sampled and instantaneously transferred via web so that they can be checked remotely collected time series reveal an overall inverse correlation between radon emissions and seasonal temperature variations radon emissions in sectors of diffuse degassing are modulated by tidal forces as well radon activities recorded at the summit station located along the fracture zone where the gas flux is concentrated are positively correlated with changes in atmospheric pressure and confirm the occurrence of the atmospheric stack effect we finally emphasize that real time radon monitoring is an innovative technique that may be systematically applied in volcano surveillance

the importance of pressurized subglacial water in separation and sliding at the glacier bed l effet de l eau sous glaciaire sous pression sur le processus de glissement est examine a partir d un parametre appele indice de decollement du lit qui exprime les contraintes perpendiculaires au lit et la pression d eau les donnees proviennent de trois glaciers de formes differentes une loi puissance du type de weertman avec un exposant voisin de 3 modifiee pour tenir compte de l effet de la pression des eaux sous glaciaires apparait comme etant la meilleure

two dimensional time dependent hurricane overwash and erosion modeling at santa rosa island abstract a 2dh numerical model which is capable of computing nearshore circulation and morphodynamics including dune erosion breaching and overwash is used to simulate overwash caused by hurricane ivan 2004 on a barrier island the model is forced using parametric wave and surge time series based on field data and large scale numerical model results the model predicted beach face and dune erosion reasonably well as well as the development of washover fans furthermore the model demonstrated considerable quantitative skill upwards of 66 of variance explained maximum bias 0 21 m in hindcasting the post storm shape and elevation of the subaerial barrier island when a sheet flow sediment transport limiter was applied the prediction skill ranged between 0 66 and 0 77 in a series of sensitivity tests in which several hydraulic forcing parameters were varied the sensitivity studies showed that the variations in the incident wave height and wave period affected the entire simulated island morphology while variations in the surge level gradient between the ocean and back barrier bay affected the amount of deposition on the back barrier and in the back barrier bay the model sensitivity to the sheet flow sediment transport limiter which served as a proxy for unknown factors controlling the resistance to erosion was significantly greater than the sensitivity to the hydraulic forcing parameters if no limiter was applied the simulated morphological response of the barrier island was an order of magnitude greater than the measured morphological response

microseismic activity within a serac zone in an alpine glacier glacier d argentiere mont blanc france a passive seismic study was carried out underneath glacier d argenti ere mont blanc france where an array of seismometers was installed in a subglacial access tunnel the data show a very high emissivity from the glacier fracturing can be discriminated from serac falls using the signal characteristics we apply seismic array methods to locate the sources of these signals using a two step grid search in the parameter space four clusters of activity are found close to the network showing that this fracturing does not take place uniformly over the glacier but rather in isolated small zones we compute a local magnitude using regional earthquakes for calibration the magnitudes follow a classical gutenberg richter law in the range ml 3 to 0 15 showing that no characteristic size events dominate the process we suggest that those spatial clusters of icequakes could reveal the heterogeneous nature of the friction at the base of the glacier with patches of high frictional stresses locally generating intense fracturing within the ice mass

beach erosion and recovery during consecutive storms at a steep sloping meso tidal beach this study analyses beach morphological change during six consecutive storms acting on the meso tidal faro beach south portugal between 15 december 2009 and 7 january 2010 morphological change of the sub aerial beach profile was monitored through frequent topographic surveys across 11 transects measurements of the surf swash zone dimensions nearshore bar dynamics and wave run up were extracted from time averaged and timestack coastal images and wave and tidal data were obtained from offshore stations all the information combined suggests that during consecutive storm events the antecedent morphological state can initially be the dominant controlling factor of beach response while the hydrodynamic forcing and especially the tide and surge levels become more important during the later stages of a storm period the dataset also reveals the dynamic nature of steep sloping beaches since sub aerial beach volume reductions up to 30 m3 m were followed by intertidal area recovery 2 z 3 m with rates reaching 10 m3 m however the observed cumulative dune erosion and profile pivoting imply that storms even of regular intensity can have a dramatic impact when they occur in groups nearshore bars seemed to respond to temporal scales more related to storm sequences than to individual events the formation of a prominent crescentic offshore bar at 200 m from the shoreline appeared to reverse the previous offshore migration trend of the inner bar which was gradually shifted close to the seaward swash zone boundary the partially understood nearshore bar processes appeared to be critical for storm wave attenuation in the surf zone and were considered mainly responsible for the poor interpretation of the observed beach behaviour on the grounds of standard non dimensional morphological parameters copyright 2011 john wiley sons ltd

earth science radon and rock deformation researchers working around a reservoir in the french alps find that changes in certain phenomena such as emissions of radon gas from the ground in the vicinity follow variations in the reservoir s water level the water level reflects the amount of stress being applied to the underlying earth s crust so this approach may provide clues as to geophysical signals evident when crust deforms in the build up to an earthquake

variability in ice motion at a land terminating greenlandic outlet glacier the role of channelized and distributed drainage systems we use a combination of field observations and hydrological modelling to examine the mechanisms through which variability in meltwater input affects ice motion at a land terminating greenlandic outlet glacier we find a close agreement between horizontal ice velocity vertical ice velocity and modelled subglacial water pressure over the course of a melt season on this basis we argue that variation in horizontal and vertical ice velocity primarily reflects the displacement of basal ice during periods of cavity expansion and contraction a process itself driven by fluctuations in basal water pressure originating in subglacial channels this process is not captured by traditional sliding laws linking water pressure and basal velocity which may hinder the simulation of realistic diurnal to seasonal variability in ice velocity in coupled models of glacial hydrology and dynamics

abrupt glacier motion and reorganization of basal shear stress following the establishment of a connected drainage system three episodes of strong basal motion occurred at trapridge glacier yukon territory canada on 11 june 1995 following the establishment of a connected subglacial drainage system responses to these spring events are noted in the records for 42 instruments and were recorded throughout the 60 000 m study area strong basal motion during the events is indicated by ploughmeter load bolt and vertical strain records and abrupt pressure changes in several transducer records denote damage caused by extreme pressure pulses these pressure pulses generated by the abrupt basal motion also resulted in the failure of seven pressure sensors records for pressure turbidity and conductivity sensors indicate that basal drainage patterns did not change significantly during the events geophone records suggest that the episodes of basal motion were precipitated by the gradual failure of a sticky spot following hydraulic connection of part of the study area this failure resulted in the transfer of basal stress to the unconnected region of the bed during the course of the events no evidence for strong basal motion is seen in the instrument records for several weeks following the events suggesting that the mechanical adjustments resulted in a stable configuration of basal stresses this event illustrates how unstable situations can be quickly accommodated by mechanical adjustments at the glacier bed

short term variations in glacier flow controlled by subglacial water pressure at lauteraargletscher bernese alps switzerland short term variations in horizontal and vertical surface motion were studied with high temporal resolution during the ablation season in lauteraargletscher bernese alps switzerland horizontal surface flow speed oscillated diurnally showing a correlation with the water level in a borehole flow speed increased as a function of the water level with an asymptote at the ice overburden level this observation implied that the flow variations were principally controlled by the local water pressure which enhanced basal motions detailed examination of the diurnal variations however showed that the speed was larger when the pressure was increasing than when it was decreasing greater speed with increasing pressure was interpreted by subglacial watercavity opening and or longitudinal stress coupling with the upper reaches of the glacier upward surface movements were observed when the glacier flow speed increased simultaneous measurement of internal vertical strain in a borehole showed that the uplift had two different sources vertical straining of ice and volume increase of subglacial water cavities the vertical surface movement was largely affected by the vertical strain and the uplift events could not be simply attributed to cavity opening

coupling between a glacier and a soft bed ii model results the relation between the local effective pressure and shear stress on till beneath storglaciaren sweden discussed in iverson and others 1999 provides an empirical basis for studying the processes that control the strength of the ice bed coupling particles in the bed that protrude into the glacier sole support shear stresses that are limited by either ploughing or the traditional sliding mechanisms model calculations based on studies of cone penetration through fine grained sediment and sliding theory agree with the observed relation between shear stress and effective pressure if the water layer at the ice bed interface is assumed to thicken rapidly as the effective pressure approaches zero studies of the hydraulics of linked cavities provide support for this assumption if the mean thickness of the water layer reflects the extent of microcavity development at the interface comparison of the calculated shear stress with the ultimate strength of till suggests that bed deformation limits the shear stress on till beneath storglaciaren only at intermediate effective pressures at very low effective pressures like those inferred at the site of the tiltmeter discussed in iverson and others 1999 and at sufficiently high effective pressures ploughing and sliding should focus motion near the glacier sole a calculation using parameter values appropriate for ice stream b west antarctica suggests that ploughing may occur there at shear stresses not sufficient to deform the bed at depth this conclusion is reinforced by the likelihood that pore pressures in excess of hydrostatic should develop down glacier from ploughing particles thereby weakening the bed near the glacier sole however given the apparent sensitivity of the ice bed coupling to basal conditions that may be highly variable any blanket assumption regarding the flow mechanism of ice masses on soft beds should probably be viewed with skepticism

radon changes associated with the earthquake sequence in june 2000 in the south iceland seismic zone an earthquake sequence at the transform plate boundary in south iceland that included two magnitude 6 5 earthquakes in june 2000 was anticipated on the basis of a centuries long seismicity pattern in the area a program of radon monitoring in geothermal water from drill holes initiated in 1999 rendered distinct and consistent variations in radon in association with these events all seven sampling stations in a 50 30 km zone covering the epicentral area showed a consistent pattern four types of change could be identified 1 preseismic decrease of radon anomalously low values were measured 101 167 days before the earthquakes 2 preseismic increase spikes appear in the time series at six stations 40 144 days prior to the earthquakes these anomalies were large and unusual if compared to a 17 years history of radon monitoring in this area 3 coseismic step most likely related to the coseismic change in groundwater pressure observed over the entire area 4 postseismic return of the radon values to the preseismic level about three months later also concurrent with groundwater pressure changes

radon and thoron emission from lithophysae rich tuff under increasing deformation an experimental study 1 radon and thoron emissions from lithophysae rich tuff under increasing deformation are measured to determine how mechanical damage affects gas emission levels in tuffs mechanical properties of rocks under stresses should be carefully considered to properly interpret data from geochemical field monitoring two samples are uniaxially loaded up to failure while two others are unloaded at the end of the elastic phase in order to achieve the highest compaction of existing pores changes in the porosity of deformed samples are evidenced by helium pycnometer and microscopy analyses radon and thoron exhalation rates are measured on groups of two samples by alpha spectrometer technique results show that tuff samples are characterised by a dual porosity consisting of a macroporosity given by isolated large pores with sizes from mm up to cm scale and a microporosity ranging between microns to hundreds of microns at the end of the elastic phase pervasive pore collapse is observed due to the closure of the cm scale macropores this is mirrored by a significant decrease of radon and thoron release after failure a further reduction of porosity in the rock adjacent to the fault planes is observed due to extensive closure of both macropores and micropores at this stage radon and thoron emissions increase the formation of new exhaling surfaces is the main carrier of the bulk increase of radon and thoron exhalations strongly prevailing over the densification carried out from the compaction mechanisms in terms of volcanic hazard negative anomalies in radon emissions should be considered as indicators of forthcoming ruptures key words radon and thoron exhalation tuff deformation seismic precursor

a two dimensional coupled hydro mechanical finite discrete model considering porous media flow for simulating hydraulic fracturing abstract in this study we propose a new coupled hydro mechanical model considering porous media flow fdem flow for simulating hydraulic fracturing which makes full use of the unique topological connection between joint elements and solid elements in the combined finite discrete element method fdem the joint elements form the flow channel for fluid through which flow obeys the cubic law in addition viscous forces of fluid are taken into account in fdem flow a simple example with analytical solution is given to verify the model then the effects of fluid viscosity on hydraulic fracturing are investigated by this model the simulated results show that when a low viscosity fluid is injected the fluid infiltrates the fracture rapidly the initiation pressure is lower than the theoretical value and the breakdown pressure is slightly larger than the initiation pressure when high viscosity fluid is injected fluid infiltrate into the cracks very slowly the initiation pressure is close to the theoretical value and the breakdown pressure is much larger than the initiation pressure

gas geochemistry and seismotectonics a review abstract publications on soil and spring gases have been examined regarding their relationships with both tectonic and seismic activities the main sources behaviours and uses of species detected in soils and springs are displayed and their mode of sampling and analysing briefly described the main patterns of degassing in soils are described and we outline the wide range of geochemical signatures as the result of both permeability and mineralogical contrasts because thermomineral waters have been in contact with great volumes of crustal rocks at various depths spring gases might be more representative of the local environment than soil gases moreover gas signature comparisons show that spring gases are much more enriched with deep gases and slightly contaminated by atmospheric gases therefore they can be considered as better samples for identifying precursors of earthquakes environmental perturbations are examined and it is shown from divergent cases that pressure temperature soil moisture or earth tides may generate very high perturbations of the degassing process such effects demonstrate that no systematic correction law can be proposed and that removing external contributions from gas concentrations must be performed case by case this demonstrates therefore the need for the simultaneous measurement of external parameters during gas monitoring a qualitative examination of about 150 claimed precursors proposed in the literature has been reviewed as noted by previous authors anomalies appear at distances sometimes much greater than typical source dimensions and occur in the field of strain higher than 10 9 most of them being in the field of strain higher than 10 8 taking into account the very high heterogeneity of such a set of data we can suggest that amplitudes of gas anomalies are independent of both magnitudes and epicentral distances of related earthquakes suggesting local conditions to control amplitudes on the contrary precursory time and duration of anomalies seem to increase both with magnitudes and epicentral distances abundant evidence demonstrates the major role of crustal fluids in the earthquake cycle many works have outlined the fact that crustal instabilities can appear as the result of low stress strain perturbations during loading it has been suggested that motion of fluids may occur at various scales from microcrack fluid transfer up to changes of hydraulic levels of water tables the study of subsequent anomalies is expected to supply a tool for earthquake prediction following previous authors we outline the need for further methodological improvements including the setting up of multiparameter station networks and the simultaneous recording of the main external parameters atmospheric pressure water and air temperature soil moisture for signal processing

the predictability of cross shore bed evolution of sandy beaches at the time scale of storms and seasons using process based profile models deterministic and probabilistic profile models have been compared with hydrodynamic and morphodynamic data of laboratory and field experiments on the time scale of storms and seasons the large scale laboratory experiment is a pure 2d case and offers and ideal test case for cross shore profile models as disturbing alongshore non uniformities are absent the field experiments are performed at the egmond site the netherlands during the eu coast3d project and represent storm time scale oct nov 1998 as well as seasonal time scale conditions may 1998 sep 1999 the objective of the paper is to present information of coastal processes on these time scales and to assess the predictive capabilities coastal process based profile models with respect to hydrodynamics and morphodynamics at sandy beaches on the time scales of storms and seasons profile models can quite accurately errors smaller than 10 represent the cross shore significant wave height distribution in the surf zone if the wave breaking model is properly calibrated the wave breaking coefficient should be a function of local wave steepness and bottom slope for most accurate results profile models can reasonably represent the cross shore and longshore currents undertow in a pure 2d case and in 3d field conditions profile models including cross shore mixing effects and breaker delay effects do not produce better predictions of the longshore and cross shore current velocities profile models using default settings can quite reasonably simulate the behaviour of the outer and inner bars on the storm time scale the behaviour of the beach cannot be modelled with sufficient accuracy on the storm time scale profile models can reasonably simulate the post storm onshore bar migration provided that the near bed orbital velocities and wave asymmetry related sand transport are represented in a sufficiently accurate way using non linear wave theories profile models cannot simulate the beach recovery processes on the post storm time scale because these essentially 3d processes are not sufficiently known to be included in the models profile models using default settings cannot simulate the behaviour of the outer and inner bars and the beach on the seasonal time scale the behaviour of the outer bar on the seasonal time scale can only be represented properly after tuning using measured bed profiles the simulation of the inner bar and beach morphology on the seasonal time scale could not be improved by tuning

sliding phenomena in a steep section of balmhorngletscher switzerland annual aerial photographs of balmhorngletscher available since 1973 have furnished data on large ice avalanches originating in one particular location the avalanches characteristically occur during an active phase of fast sliding the analysis of a photogrammetric 1 2000 bedrock map of longitudinal ice surface profiles from photographs taken at various times and of velocity measurements by theodolite has shown that the fast sliding and the release of the avalanches in an area of about 250 by 100 m is quite independent of ice thickness it is suggested that besides the slope of the bed rock roughness and topographical features the particular structure of the rock surface in the fashion of tiles on a roof is a factor which influences the processes of fast sliding and avalanche formation it is suggested that meltwater gains access to cavities at the rock steps from where it is dragged along on the ice rock interface getting slowly worked into the basal ice layer many weeks after the beginning of the melt season the evolving acceleration becomes apparent characteristically at the beginning of september once the surface meltwater gains direct access to the bed through fresh crevasses the glacier accelerates progressively as water enters cracks faults and microfissures water pressure effects may become important as cavities grow while the gradual development of the active phase permits to forecast the growing avalanche risk the prediction of the event in time is a long way off if practical at all

detectability and significance of 12 hr barometric tide in radon 222 signal dripwater flow rate air temperature and carbon dioxide concentration in an underground tunnel summary searching for small periodic signals such as the 12 hr s2 barometric tide and monitoring their amplitude as a function of time can provide important clues on the complex processes affecting fluid transport in unsaturated fractured media under multiple influences here first we show that a modified spectrogram analysis msa is more efficient than simple fourier transform to reveal weak periodic signals secondly we show how transient periodic signals can be monitored as a function of time using spectrograms these methods are applied to time series of radon and carbon dioxide concentration dripwater flow rates and air temperature measured during several years in the roselend dead end tunnel located in the french alps near an artificial lake a weak s2 line is evidenced in radon concentration with enhanced amplitude during transient radon bursts similarly the s2 line is observed using msa in dripwater flow rates which sample mainly fracture flow as suggested by a hydrochemical analysis while it is not seen in dripwater flow rates sampling matrix flow in the absence of a strong 24 hr line the presence of a s2 line suggests sensitivity to barometric pressure and thus a significant advective contribution in radon and some dripwater transport no s2 line is observed in the carbon dioxide time series the temporal structure of the s2 component however is not similar in the radon concentration and the dripwater flow rates suggesting in particular that dripwater does not play a significant role in the generation of radon bursts temperature time series exhibit a significant s2 contribution induced by atmospheric pressure spatially organised in the tunnel decreasing vertically upwards a remarkable transient temperature inversion during radon bursts suggests that the additional advective air contributions responsible for the radon bursts occur from the non saturated rocks below the tunnel

genesis stability and preservation potential of large lateral moraines of alpine valley glaciers towards a unifying theory based on findelengletscher switzerland abstract lateral moraines are prominent features of glaciated landscapes in high mountain environments and key landforms in glacier and palaeoclimatic reconstructions yet compared to smaller moraines they have been little studied and several aspects are not well understood we here present detailed sedimentological results from the lateral moraines of findelengletscher in sw switzerland to gain new insights into the formation of these landforms the lateral moraines studied here stand up to 140 m above the valley floor are over 3 km long and strongly asymmetrical in cross profile with distal slopes between 29 and 36 and proximal slopes that are commonly 41 64 but locally reach angles of up to 80 recorded lithofacies comprise loose clast and matrix supported stratified diamicts and intercalated sorted sediments in the distal slopes and near the crestline overconsolidated matrix supported massive and weakly stratified diamicts and streaked out sorted sediment lenses in the core and proximal slopes and partly intercalated dark brown layers overlain by loose and consolidated diamicts exposed in near vertical walls in the proximal flank these are interpreted as supraglacial debris flow units with intercalated fluvial wash horizons glaciotectonised and subglacial traction till with boudinaged and streaked out sediment lenses and palaeosoils overlain by sediment produced by overtopping of the former moraine surface during a subsequent advance of the glacier clast shape analysis and process observations reveal that the dominant mode of transport is subglacial and glaciofluvial and that the main mode of sediment delivery to the moraines is by debris flows after the material has been transferred from the bed via englacial debris bands and meltout at the surface this differs from previous studies that found that a supraglacial source was dominant sedimentary structures clast fabric and process observations during the 1979 1980 readvance of findelengletscher strongly suggest that proximal layers of reworked pre existing sediments and or basal traction zone till have been plastered onto the moraine core in several locations causing a high degree of overconsolidation and strongly clustered fabric eigenvalues s 1 0 94 with clustering parallel to the moraine crestline this suggests that a combination of basal lateral drag and lateral plastering produces the observed proximal stability and ensures a high preservation potential we develop a conceptual model that describes alpine lateral moraines as structurally complex landforms that do not just record a single event as often surmised and we discuss implications for palaeo glacier reconstruction and the application of numerical dating methods

the effects of storm clustering on beach profile variability abstract impacts of storms in reshaping coastlines are well known also the far greater impact of clusters of storms where storms occur at close succession has been noted in a number of previous studies in this paper we analyse and discuss the storm wave climate and the beach profile response to clusters of storms at narrabeen beach new south wales australia narrabeen beach is subjected to frequent storms all year round and the beach undergoes substantial variability as a result the impact of storm clusters with closely spaced individual storms reaching the beach is investigated by combining historic measurements of beach profile surveys and numerical modelling of storm induced beach change our analysis of storm power index of storm clusters and its correlation with the change in beach width reveals that the strengths of single storms in a storm cluster alone are not the reason for beach change but time interval between successive storms and the post storm recovery speed of the beach concerned also play important roles we have quantified and compared beach erosion return levels resulting from single storms and storm clusters it was found that beach erosion volumes resulting from storm clusters with two or more storms resemble potential beach erosion volumes induced by single storms of far higher return periods

caterpillar like ice motion in the ablation zone of the greenland ice sheet current understanding of ice dynamics predicts that increasing availability and variability of meltwater will have an impact on basal motion and therefore on the evolution and future behavior of the greenland ice sheet we present measurements of ice deformation subglacial water pressure and surface velocity that show periodic and episodic variations on several time scales seasonal multiday and diurnal these variations observed with gps and sensors at different depths throughout the ice column are not synchronous but show delayed responses of ice deformation with increasing depth and basal water pressure in antiphase with surface velocity with the help of a full stokes ice flow model these observations are explained as ice motion in a caterpillar like fashion caused by patches of different basal slipperiness horizontal stress transfer through the stiff central part of the ice body leads to spatially varying surface velocities and ice deformation patterns variation of this basal slipperiness induces characteristic patterns of ice deformation variability that explain the observed behavior ice flow in the ablation zone of the greenland ice sheet is therefore controlled by activation of basal patches by varying slipperiness in the course of a melt season leading to caterpillar like ice motion superposed on the classical shear deformation

the effect of stress on radon emanation from rock a uranium bearing granitic rock of known radon emanation was deformed to failure under uniaxial stress radon emanation and microcrack activity were recorded continuously during the test radon concentration in the closed system was measured by an alpha detector a decrease in emanation was observed during the initial loading of the sample and is interpreted as associated with the closure of pre existing cracks within the rock at a uniaxial stress equal to approximately one half the ultimate strength a temporary increase 50 in the radon emanation was observed that correlated with an increase in microcracking within the sample when the stress was removed for several hours the original emanation was restored however once the specimen failed a temporary emanation increase of 120 was observed the emanation then decreased to a level nearly 5 greater than the prefailure specimen emanation

earth tide forcing of glacier drainage 1 fourier analysis reveals that winter electrical self potential sp water pressure pw and electrical conductivity ec time series collected beneath haut glacier d arolla switzerland are forced by earth and atmospheric tides forcing is dominant during periods of expanding bedrock consistent with glacier substrate deformation periodically driving water from the ice body into the bed this may modify the strength of subglacial sediments and could therefore influence glacier drainage and motion on a global scale

increase in radon emission due to rock failure an experimental study 1 radon anomalies are commonly observed prior to dynamic failure in the crust and are interpreted as cracking of the medium thus attracting considerable attention in understanding the precursory phenomena of earthquakes and volcanic activity in this study we have compared the starting radon emissions from low porosity crystalline lava phonolite samples with those from damaged and failed samples the damaged sample was loaded up to just beyond the end of the linear elastic phase as evidenced by the output of ae energy the increase in total porosity and a decrease in p wave and s wave velocity relative to the intact sample whereas the failed sample showed deformation behaviour characteristically brittle with increasing values of ae output and porosity as the sample approached macroscopic failure radon measurements have evidenced that dilatational microcracking of deformed sample produced no significant variation in radon emanation with respect to the intact sample in contrast after macroscopic failure radon emanation drastically increased therefore major finding from this study is that in the case of low porosity and relatively high strength crystalline lavas the development of a macroscopic fracture provides new large exhaling surface resulting in a substantial increase in radon emission rate

ground water radon anomaly before the kobe earthquake in japan radon concentration in ground water increased for several months before the 1995 southern hyogo prefecture kobe earthquake on 17 january 1995 from late october 1994 the beginning of the observation to the end of december 1994 radon concentration increased about fourfold on 8 january 9 days before the earthquake the radon concentration reached a peak of more than 10 times that at the beginning of the observation before starting to decrease these radon changes are likely to be precursory phenomena of the disastrous earthquake

impact of the winter 2013 2014 series of severe western europe storms on a double barred sandy coast beach and dune erosion and megacusp embayments abstract the winter of 2013 2014 was characterized by a striking pattern of temporal and spatial extreme storm wave clustering in western europe the 110 km long gironde coast sw france was exposed to the most energetic wave conditions over the last 18 years the period was outstanding in terms of the available energy to move sediment and cause large scale erosion with the 2 month average significant wave height hs exceeding 3 6 m just below the 0 95 quantile and 4 distinct 10 year return period storms with hs 9 m these storm waves caused unprecedented beach and dune erosion along the gironde coast including severely damaged sea defences at the coastal towns at the end of the winter dune erosion scarp height was highly variable alongshore and often exceeded 10 m megacusp embayments were observed along the gironde coast with an average alongshore spacing of 1000 m in the south progressively decreasing to 500 m in the north with an average cross shore amplitude of 20 m while beach megacusps were previously observed to systematically couple to the inner bar along the gironde coast during low to moderate energy wave conditions severe storm driven megacusp embayments cutting the dune were found to be enforced and coupled to the outer crescentic bar a detailed inspection of the 1500 m long bimonthly topographic surveys of truc vert beach shows that in early january 2014 the outstanding shore normal incident storm swell hercules with hs and peak wave period tp peaking at 9 6 m and 22 s respectively triggered the formation of a localized megacusp embayment with the erosion scarp height exceeding 6 m in its centre where the dune retreat reached 30 m the subsequent storms progressively smoothed the megacusp by the end of the winter mostly through severe erosion of the megacusp horns because of the very long period 16 s

thresholds for storm impacts on an exposed sandy coastal area in southern portugal abstract storms are one of the most important phenomena responsible for coastal erosion their destructive power presents major challenges for coastal management and knowledge of their characteristics and associated consequences is therefore of paramount importance in this study thresholds for storm impacts are defined for a sandy coast in southern portugal faro beach ria formosa using two different approaches i hydrodynamic conditions associated with historical storm impacts i e infrastructural damage and ii computed maximum wave run up values r high compared with beach morphology damage thresholds are defined as limits above which the action of a storm exceeds beach front response capability and starts to act directly on human infrastructures according to method i four different thresholds were defined for individual storms directed from the sw the threshold is a significant wave height of 4 7 m with a storm duration of 2 days and for storms directed from the se is a significant wave height of 6 m with a storm duration of at least 2 days regarding storm groups for those directed from the sw the threshold is 2 storms lasting at least 2 days each with significant wave heights greater than 3 5 m whilst for those directed from the se the threshold is 3 short storms lasting 1 day each with significant wave height over 3 9 m the return period for the sw storm group threshold is just 1 7 years for method ii beach morphological parameters d high highest elevation of the frontal dune d low elevation of the dune base and tan f foreshore slope were determined for five chosen cross shore profiles along the study area and r high computed for different hydrodynamic conditions results were validated through field observations of storm impacts the lowest thresholds for overwash are along the central part of the study area where a dune crest is absent due to human occupation the highest thresholds for overwash are on those profiles where a frontal dune is well developed or a foredune ridge is present western and eastern parts of the study area this study presents a methodological strategy to compute realistic thresholds for storm impacts along faro beach based on historical datasets of hydrodynamics and storm impacts information the approach could be implemented in other coastal areas to provide a comprehensive assessment of the storm impact requiring only simple information like offshore storm hydrodynamics characteristics beach morphology and reports of coastal infrastructure damage

a systematic compilation of earthquake precursors article a survey of published scientific literature was undertaken to identify and catalog observed earthquake pre cursors the earthquake precursors selected for analysis included electric and magnetic fields gas emissions groundwater level changes temperature changes surface deformations and seismicity for each of these precursors the published scientific literature was searched to document the statistics of each reported earth quake precursor spatial extent time duration amplitude signal noise ratio to analyze dependence of the observable for each precursor on earthquake magnitude and to explore proposed physical models to explain eachearthquakeprecursor somegeneralcharacteristics wereobservedfortheseprecursoryphenomena first the largest amplitude precursory anomalies tend to occur before the largest magnitude earthquakes also the number of precursory anomalies tends to increase the closer in time to the occurrence of the earthquake finally theprecursoryanomaliestendtooccurclosetotheeventualepicenterof theearthquake ingeneral the physical models indicate that all of the precursory phenomena are related to deformation that occurs near the fault prior to the main earthquake while the models provide plausible physical explanations for the pre cursors there are many free parameters in the models that are poorly resolved

geoscience the plumbing of greenland s ice observations of the water pressure in drilled boreholes and natural moulins on the greenland ice sheet show how its underlying plumbing system controls ice motion during the course of the summer melt season see letter p 80 increased meltwater delivery to the base of the greenland ice sheet will increase the ice sheet velocity accelerating its inevitable rush towards the ocean and subsequent sea level rise or will it debate on this topic is at the forefront of cryospheric research but has been hampered by the lack of simultaneous observations of hydraulic head in moulins vertical shafts that deliver water to the base of the ice sheet and boreholes which monitor basal water pressure lauren andrews and colleagues now provide these observations from a small region in western greenland and reveal that water delivery by moulins into channelized basal flow is indeed linked to short term fluctuations in ice velocity late season decelerations in ice velocity however seem to be controlled by changes in unchannelized flow rather than any shifts in the moulin system

numerical simulation of a low lying barrier island s morphological response to hurricane katrina abstract tropical cyclones that enter or form in the gulf of mexico generate storm surge and large waves that impact low lying coastlines along the gulf coast the chandeleur islands located 161 km east of new orleans louisiana have endured numerous hurricanes that have passed nearby hurricane katrina landfall near waveland ms 29 aug 2005 caused dramatic changes to the island elevation and shape in this paper the predictability of hurricane induced barrier island erosion and accretion is evaluated using a coupled hydrodynamic and morphodynamic model known as xbeach pre and post storm island topography was surveyed with an airborne lidar system numerical simulations utilized realistic surge and wave conditions determined from larger scale hydrodynamic models simulations included model sensitivity tests with varying grid size and temporal resolutions model predicted bathymetry topography and post storm survey data both showed similar patterns of island erosion such as increased dissection by channels however the model under predicted the magnitude of erosion potential causes for under prediction include 1 errors in the initial conditions the initial bathymetry topography was measured three years prior to katrina 2 errors in the forcing conditions a result of our omission of storms prior to katrina and or errors in katrina storm conditions and or 3 physical processes that were omitted from the model e g inclusion of sediment variations and bio physical processes

factors constraining the geographic distribution of earthquake geochemical and fluid related precursors abstract earthquake precursors are elusive and this elusiveness has hampered earthquake prediction in this paper the available catalogues of historical and contemporary geochemical and fluid related precursors of earthquakes are considered the locations of recording sites are mapped and compared with data concerning volcanic locations heat flows crustal velocities and the depth of seismic events possible relations among the considered geophysical parameters and the occurrence of fluid related earthquake precursors are discussed only some geological and geophysical conditions may allow for the occurrence of fluid related earthquake precursory phenomena as a consequence the geophysical models utilized to explain the occurrence of earthquake precursors should be updated furthermore only some areas of the world are deemed suitable for earthquake fluid related precursor monitoring

an implicitly coupled hydro geomechanical model for hydraulic fracture simulation with the discontinuous deformation analysis in this article we present and verify an algorithm for modeling hydraulic fracturing in complex fracture geometries the method is built upon an existing model which uses the discontinuous deformation analysis for simulation of rock mechanics and upon a finite volume fracture network model for simulation of compressible fluid flow in fractures improvements are made to the fluid contact and coupling components of the existing algorithm to increase its accuracy and stability the model is successfully benchmarked against the analytical solution for the opening profile of an internally pressurized griffith fracture and against the semi analytical solution for the pressure and opening profile of a bi wing hydraulic fracture propagating under conditions of no leakoff and no toughness additionally the model is verified through comparison with the results of a hydraulic fracturing experiment that examined propagation of a high viscosity fracturing fluid in an impermeable medium

a clear case of radon anomaly associated with a micro earthquake event in a stable continental region 1 though many worldwide attempts to establish radon anomalies in soil and groundwater as precursors for major earthquakes are made yet practically no such work has been reported for micro earthquakes in a stable continental region scr from the continuous radon measurements for five months at a depth of 1 m in fractured granitic area we report for the first time that enhanced radon concentration preceded seventeen hours the occurrence of micro earthquake the peak radon level twice the normal concentration was reached thirteen hours before the occurrence of the event and decayed exponentially during the next 5 days to come to normal level this radon precursor pertains to a dry period unaffected by meteorological factors thus exemplifies clearly its association with micro earthquake

glacial hydrology and erosion patterns a mechanism for carving glacial valleys article i nfo article history most glacial erosion models assume that erosion rates are proportional to ice sliding velocity while recent studies have shown that water plays a major role in modulating sliding velocities the impact it might have on erosion rates is still unclear here we incorporate subglacial hydrology into a glacial erosion model that is based on a sliding rule our results explicitly highlight that adding subglacial hydrology has profound impacts on the temporal and spatial patterns of glacial erosion first it suggests that erosion might mainly occur during melting seasons when subglacial water pressure is large and effective pressure is low i e before the channels fully develop and reduce the water pressure at the ice bedrock interface which promotes sliding and erosion second the distribution of erosion is bimodal with a peak at the equilibrium line altitude and as we demonstrate enhanced erosion at much lower altitudes within the ablation area where water due to melting abounds this has important implications because it explains why glacial erosion can simultaneously

response of glacier basal motion to transient water storage the speed of a glacier is affected most by sudden jumps in the water supply to the glacier but it goes back to previous levels if high water inputs are sustained because the glacier s plumbing system adjusts

on the instability of avalanching glaciers the instability of hanging glaciers and more generally of avalanching glaciers is discussed on the basis of observations performed on several glaciers located in the european alps a classification of avalanching glaciers is proposed which allows a primary appreciation of the danger inherent in these glaciers on the basis of field observations and results of numerical simulations of crevassing the fracture processes which lead to major icefalls as well as their recurrence are analyzed a method for predicting the time of failure is then discussed the disaggregation of the unstable ice masses usually observed prior to large icefalls is investigated and its implications for the forecasting of icefalls analyzed

glacier velocity and water input variability in a maritime environment franz josef glacier new zealand short term glacier velocity variations typically occur when a water input is accommodated by an increase in the subglacial water pressure although these velocity variations have been well documented on many glaciers few studies have considered them on glaciers where heavy rain and glacier melt occur year round this study investigates the relationship between water inputs and glacier velocity on franz josef glacier new zealand we installed six gnss stations across the lower glacier during austral summer 2010 11 and one station during summer 2012 13 glacier velocity remained elevated at all stations for 7 days following large rain events during diurnal melt events we find velocity variations in the early afternoon 12 00 16 00 at 600 m a s l and in the late evening 20 00 01 00 at 400 m a s l we hypothesize that the late evening velocity variations occurred as an upstream region of high subglacial water pressures and accelerated ice motion propagated downstream this mechanism may also explain the increased longitudinal compression and transverse extension across the lower glacier during speed up events our results indicate that the subglacial drainage system likely decreases in efficiency upstream and that the water input variability can still cause short term velocity variations despite the large year round water inputs

glacial abrasion and sliding their dependence on the debris concentration in basal ice a model of bedrock abrasion by a temperate glacier is developed that takes into account the significant impeding effect of scattered rock fragments at the ice rock interface on glacier sliding an increase in the debris concentration above a relatively low value can reduce the abrasion rate by decreasing both the flux of rock fragments and the effective forces which press fragments against the bed abrasion of a simple wavy bed is shown to be most rapid for a relatively low debris concentration above which the abrasion varies inversely with the debris content a similar concentration dependence of abrasion is expected for beds of arbitrary geometry but low roughness sliding glaciers will tend to abrade until the basal ice is nearly stagnant at which point rocks of all sizes start to lodge against the bed

the distribution of basal motion beneath a high arctic polythermal glacier the longitudinal pattern of surface velocity of a large predominantly cold polythermal glacier john evans glacier ellesmere island canada was measured over summer and winter periods inthe accumulation and upper ablationareas where ice is predominantly cold based summer velocities were slightly higher than overwinter velocities predicted velocities due to ice deformation alone in these areas closely matched these observations in the winter with limited basal motion likely in the summer in the lower ablation area where ice is likely warm based measured summer velocities were up to double overwinter velocities predicted ice deformationcould notaccountforall of these measured velocities in either summer or winter this suggests that basal motion occurs throughout the year over at least part of the lower ablation area this finding is supported by radio echo sounding subglacial drainage reconstructions and analyses of early summer meltwater chemistry which suggest that subglacial water is present throughout the year in thisregion insummer basalmotionmayaccountforupto75 ofthetotalsurfacevelocity throughoutthelowerablationarea the inferred rate of basal motionincreasessharplydir ectly below a setof moulinsby which most surface meltwater reachestheglacierbed

predicting coastal cliff erosion using a bayesian probabilistic model abstract regional coastal cliff retreat is difficult to model due to the episodic nature of failures and the along shore variability of retreat events there is a growing demand however for predictive models that can be used to forecast areas vulnerable to coastal erosion hazards increasingly probabilistic models are being employed that require data sets of high temporal density to define the joint probability density function that relates forcing variables e g wave conditions and initial conditions e g cliff geometry to erosion events in this study we use a multi parameter bayesian network to investigate correlations between key variables that control and influence variations in cliff retreat processes the network uses bayesian statistical methods to estimate event probabilities using existing observations within this framework we forecast the spatial distribution of cliff retreat along two stretches of cliffed coast in southern california the input parameters are the height and slope of the cliff a descriptor of material strength based on the dominant cliff forming lithology and the long term cliff erosion rate that represents prior behavior the model is forced using predicted wave impact hours results demonstrate that the bayesian approach is well suited to the forward modeling of coastal cliff retreat with the correct outcomes forecast in 70 90 of the modeled transects the model also performs well in identifying specific locations of high cliff erosion thus providing a foundation for hazard mapping this approach can be employed to predict cliff erosion at time scales ranging from storm events to the impacts of sea level rise at the century scale

morphological response of a sandy barrier island with a buried seawall during hurricane sandy abstract coastal populations continue to increase globally causing potential damage costs of coastal hazards to rise and community resiliency to become a worldwide priority recently hurricane sandy 2012 devastated areas of new york and new jersey and caused overwash and breaching of several urbanized barrier islands along the u s eastern seaboard this study focuses on the morphological response of bay head nj a township on a barrier island fronted with a buried seawall the hydrodynamics and morphology of bay head during hurricane sandy are simulated with xbeach a numerical model designed to study these processes during storm events from the simulations the seawall protected bay head by effectively dissipating wave energy during the peak of the storm and from rapidly increasing bay water levels that flood the backbarrier region of the island when the seawall is removed from the simulation dune heights are lowered allowing bay side flooding to cause a devastating erosive event that completely destroys the remaining dune system xbeach indicates severe erosion seaward of oceanfront buildings in the absence of a seawall vertical erosion under the dune peak about 15 m more than in the presence of the seawall and wave energy propagates further inland even after the storm has passed however with the seawall present wave attack is reduced on the island by a factor of 1 7 and prevents bay side flooding from causing significant morphological change on the island therefore the seawall increased resiliency of the bay head community during and after peak hurricane sandy forcing by preserving the dune system

subglacial modulation of the hydrograph from glacierized basins the extent of basin glacierization has important implications for the hydrograph in part because snow firn and ice impart different delays in water transport through the system here the significance of subglacial drainage morphology in modulating the hydrograph is examined with a one dimensional physically based model the conceptual model of subglacial drainage comprises both fast and slow elements respectively associated with summer and winter drainage regimes the additional possibility of a permeable glacier substrate is taken into account by allowing water transport in a subglacial aquifer forced by prescribed rates of melt water delivery to the glacier bed the model predicts glacier discharge by drainage system provenance the effects of 1 hard versus soft glacier beds 2 subsurface permeability and groundwater flow and 3 glacier geometry are then investigated hydrograph character in the form of peak timing and amplitude symmetry with respect to the forcing and the amplitude of diurnal fluctuations is affected by the partitioning of water through the various flow elements hard beds and impermeable substrates maximize the discharge routed through the fast drainage system in the simulations generally resulting in higher seasonal discharge maxima and stronger diurnal variations in discharge high hydraulic transmissivities either at the glacier bed or in underlying strata hinder the development of the fast drainage system in the simulations producing hydrographs of lower amplitude glacier geometry has a modest effect with adverse bed slopes very thick or very thin ice and short glacier lengths favouring prolonged drainage through the slow system these results suggest that the morphology and evolution of the subglacial drainage system may play a significant role in determining the character of the hydrograph from glacierized basins

extreme wave activity during 2013 2014 winter and morphological impacts along the atlantic coast of europe studies of coastal vulnerability due to climate change tend to focus on the consequences of sea level rise rather than the complex coastal responses resulting from changes to the extreme wave climate here we investigate the 2013 2014 winter wave conditions that severely impacted the atlantic coast of europe and demonstrate that this winter was the most energetic along most of the atlantic coast of europe since at least 1948 along exposed open coast sites extensive beach and dune erosion occurred due to offshore sediment transport more sheltered sites experienced less erosion and one of the sites even experienced accretion due to beach rotation induced by alongshore sediment transport storm wave conditions such as were encountered during the 2013 2014 winter have the potential to dramatically change the equilibrium state beach gradient coastal alignment and nearshore bar position of beaches along the atlantic coast of europe

detecting and characterising an englacial conduit network within a temperate swiss glacier using active seismic ground penetrating radar and borehole analysis englacial hydrology plays an important role in routing surface water to the glacier s bed and it consequently affects the glacier s dynamics however it is often difficult to observe englacial conduit conditions on temperate glaciers because of their short lived nature we acquired repeated active surface seismic data over the rhone glacier switzerland to monitor and characterise englacial conduit conditions amplitude versus angle analysis suggested that the englacial conduit is water filled and between 0 5 and 4 m thick a grid of gpr profiles acquired during the 2018 melt season showed the englacial conduit network persisting and covering 14 000 m 2 in late summer 2018 several boreholes were drilled into the conduit network we observed generally stable water pressure but there were also short sudden increases a borehole camera provided images of a fast flowing englacial stream transporting sediment through the conduit from these observations we infer that the englacial conduit network is fed by surface meltwater and morainal streams the surface and morainal streams merge together enter the glacier subglacially and flow through subglacial channels along the flank these subglacial channels flow into highly efficient englacial conduits traversing the up glacier section of the overdeepening before connecting with the subglacial drainage system

radon anomaly in the soil of taal volcano the philippines a likely precursor of the m 7 1 mindoro earthquake 1994 1 the soil gas 222rn concentration had been monitored almost continuously from june 1993 till november 1996 on taal volcano luzon island the philippines during this measurement period a singular mb 7 1 earthquake occurred on november 15 1994 between luzon and mindoro 48 km south of the volcano twenty two days before the earthquake an anomalous increase in soil gas radon peak to background ratio 6 was recorded unique in the whole time series the possible generation of this anomaly by typhoon teresa which struck luzon island a few days before was ruled out one year later when super typhoon angela the most powerful storm to hit the philippines in ten years crossed luzon island along almost the same track without triggering a similar disturbance in the radon signal consequently there is strong evidence that the taal radon anomaly originated in stress accumulation preceding the mindoro earthquake

a simple model for the spatially variable coastal response to hurricanes abstract the vulnerability of a beach to extreme coastal change during a hurricane can be estimated by comparing the relative elevations of storm induced water levels to those of the dune or berm a simple model that defines the coastal response based on these elevations was used to hindcast the potential impact regime along a 50 km stretch of the north carolina coast to the landfalls of hurricane bonnie on august 27 1998 and hurricane floyd on september 16 1999 maximum total water levels at the shoreline were calculated as the sum of modeled storm surge astronomical tide and wave runup estimated from offshore wave conditions and the local beach slope using an empirical parameterization storm surge and wave runup each accounted for 48 of the signal the remaining 4 is attributed to astronomical tides indicating that wave driven process are a significant contributor to hurricane induced water levels expected water levels and lidar derived measures of pre storm dune and berm elevation were used to predict the spatially varying storm impact regime swash collision or overwash predictions were compared to the observed response quantified using a lidar topography survey collected following hurricane landfall the storm averaged mean accuracy of the model in predicting the observed impact regime was 55 4 a significant improvement over the 33 3 accuracy associated with random chance model sensitivity varied between regimes and was highest within the overwash regime where the accuracies were 84 2 and 89 7 for hurricanes bonnie and floyd respectively the model not only allows for prediction of the general coastal response to storms but also provides a framework for examining the longshore variable magnitudes of observed coastal change for hurricane bonnie shoreline and beach volume changes within locations that experienced overwash or dune erosion were two times greater than locations where wave runup was confined to the foreshore swash regime during hurricane floyd this pattern became more pronounced as magnitudes of change were four times greater within the overwash regime than in the swash regime comparisons of pre storm topography to a calm weather survey collected one year after hurricane floyd s landfall show long term beach volume loss at overwash locations here the volume of sand eroded from the beach was balanced by the volume of overwash deposits indicating that the majority of the sand removed from the beach was transported landward across the island rather than being transported offshore in overwash locations sand was removed from the nearshore system and unavailable for later beach recovery resulting in a more permanent response than observed within the other regimes these results support the predictive capabilities of the storm scaling model and illustrate that the impact regimes provide a framework for explaining the longshore variable coastal response to hurricanes

investigations of glacier hydrological systems using dye tracer techniques observations at pasterzengletscher austria a l aide de traceurs colores on a mis en evidence une division laterale du drainage dans le bas de la langue qui n est pas determinee par la direction des crevasses obliques la reapparition de l eau dans les differents moulins est complexe bien qu elle reste constante dans le temps

sedimentation in a drumlin lee side subglacial wave cavity northwest ireland abstract lee side stratification sequences in a late pleistocene drumlin in northwest ireland are used to assess sedimentation patterns in subglacial wave cavities formed on the lee sides of drumlins three major subglacial cavity sub environments are identified 1 high energy divergent trough like closed conduit characterised by channel fill pebbly sand facies 2 low energy closed conduit characterised by alternating sand silts 3 trough margin dominated by stratified diamicts facies arrangements suggest two major transient states reflecting variations in subglacial meltwater flux the active phase showed meltwater flow directed across the drumlin apex suggesting complete uncoupling from the glacier bed supercavitation as flow velocities waned pebbly sand facies were deposited by in situ freezing of within conduit sediment admixtures the later quiescent phase was characterised by meltwater flow directed transverse to ice flow cavity shrinkage and concomitant deposition of subglacial sheetwash and cohesive sediment flows along cavity margins cavity closure resulted in complete coupling at the ice substrate interface with localised glaciotectonic loading on underlying lee side stratification sequences and concomitant till deposition these late stage sedimentation events at shinnan hill produced a very complex polygene endform which cannot be simply attributed to one formative process more realistically they reflect the influence of a rather complex and very dynamic subglacial system subject to complex spatial and temporal variations in subglacial erosion deposition and meltwater flux at the time of drumlinisation

radon daily signals in the elat granite southern arava israel 1 high time resolution monitoring of radon 222rn in three boreholes 4 10 and 53 m deep along a 0 6 km transect is carried out in massive granite in southern israel three components of variation occur in the measured signal ms seasonal radon sr periodic multiday md and daily radon dr periodic temporal variation of the components suggests an association between the overall level of the long term variation and the amplitude of the daily variation the daily mean level of radon and the daily standard deviation vary periodically throughout the year time offsets occur among time series of the ms and were investigated also for the md and dr components using consecutive 20 day intervals spanning 900 days the resulting time series show that systematic time offsets occur whereby the radon signal always occurs first at the easternmost site the md shows a gradually varying lag of 0 12 h and the dr a stable 1 3 h lag spectral analysis shows that diurnal 24 h and semidiurnal 12 h periodic components characterize the dr the amplitudes of these components exhibit regular temporal variation having a seasonal pattern the ratios of co occurring amplitudes of these components define a linear pattern indicating a fundamental statistical property in the frequency domain of the radon time series the results indicate that unrecognized dynamic processes are driving the radon signal in the subsurface regime of the pluton suggesting new prospects for radon behavior in the frame of interacting geodynamic tectonic and earth sun system related processes

combined measurements of subglacial water pressure and surface velocity of findelengletscher switzerland conclusions about drainage system and sliding mechanism interpretation des mesures de pression dans les forages et des vitesses superficielles la comparaison avec les modeles suggere que l on a neglige le frottement du aux debris dans les modeles et qu il n existe jamais de chenaux cylindriques rectilignes