a lower palaeolithic industry from the cromerian mis 13 baginton formation of waverley wood and wood farm pits bubbenhall warwickshire uk artefacts of cromerian mis 13 age recovered from extensions to the classic site of waverley wood farm pit warwickshire give new insights into the lower palaeolithic and pleistocene geological record of the english midlands the baginton formation in the area to the south and southwest of coventry has been the major source of lower palaeolithic artefacts in the midlands since the first discoveries in the 1930s current sand and gravel workings at waverley wood and wood farm pits near the village of bubbenhall have provided artefacts of quartzite andesite and flint together with sparse large mammal material some of the lower palaeolithic finds were in situ in the succession providing for the first time firm evidence of their geological provenance the variety and number of the artefacts allows detailed evaluation of the largest group of lower palaeolithic tools to be found in the west midlands the petrology of some of the tools and associated clasts in the gravels at the base of the baginton formation allow speculation on the origin of the rock types from northwest and eastern england which may have been brought to the west midlands by a pre anglian glaciation or just possibly by human transport copyright 2006 john wiley sons ltd

holocene coastal glaciation of alaska holocene uctuations of the three cirque glaciers on the seward peninsula and ve groups of tidewater and land terminating glaciers along the northernmost gulf of alaska provide a proxy record of late holocene climatic change furthermore the movements of the coastal glaciers were relevant to late holocene native american migration the earliest expansion was recorded about 6850 yr bp by hubbard glacier at the head of yakutat bay in the gulf of alaska however its down fjord advance to the bay mouth was delayed until 2700 bp similarly expansions of the icy bay bering and mccarty glaciers occurred near their present termini by 3600 3000 bp compatible with marked cooling and precipitation increases suggested by the alaskan pollen record decrease in glacier activity 2000 bp was succeeded by advances of gulf coastal glaciers between 1500 and 1300 bp correlative with early medieval expansions across the northern hemisphere a medieval optimum encompassing at least a few centuries prior to ad 1200 is recognized by general retreat of land terminating glaciers but not of all tidewater glaciers little ice age advances of land based glaciers many dated with the precision of tree ring cross dating were centered on the middle 13th or early 15th centuries the middle 17th and the last half of the 19th century a d strong synchrony of these events across coastal alaska is evident 2000 elsevier science ltd all rights reserved

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

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

submarine melting at the terminus of a temperate tidewater glacier leconte glacier alaska u s a heat fresh and sea water balances indicate that the late summer rate of submarine melting at the terminus of tidewater leconte glacier alaska u s a in 2000 was about 12md 1 w e averaged over the submerged face this is 57 of the estimated total ice loss at the terminus calving plus melting at this time submarine melting may thusprovidea significantcontributiontotheoverallablationofatidewaterglacier oceano graphic measurements conductivity temperature depth made 200 500m from the ter minus identified an isohaline 27ppt and isothermal 7 2 c layer extending from 130m depthto the fjord floor capping this is a 40mthick overflow plume distinguishedby high outflow rates low salinity 22 25ppt and lower temperatures 5 6 c mixing models indicate that fresh water comprised about11 of this plume it originates mostly as sub glacial discharge whose buoyancy drives convection at the terminus deep warm saline watersareincorporatedintotheplumeasitascends causingsubstantialmeltingoficealong the submarine face the calving terminus undergoes seasonal changes that coincide with changes in subglacial discharge and fjord water temperatures and we suggest that these fluctuations interminuspositionare directly relatedto changes in submarine melting

a revised model for the pleistocene development of the river avon warwickshire a re examination of the pleistocene river deposits in the valley of the midland avon indicates that the conventional post hoxnian model for their development has to be revised reinvestigation of two key localities cropthorne in the lower avon valley and ailstone on the warwickshire stour a left bank tributary of the avon shows that the deposits of at least two separate temperate episodes are represented within the sequence amino acid ratios on non marine mollusca from the temperate deposits allow these episodes to be correlated with oxygen isotope stages 5 and 7 since the stage 7 temperate deposit lies within sediments which post date the wolston glacial sequence an older age is indicated for that sequence than is proposed in the conventional stratigraphic succession of the british pleistocene

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

icequakes coupled with surface displacements for predicting glacier break off a hanging glacier at the east face of weisshorn switzerland broke off in 2005 we were able to monitor and measure surface motion and icequake activity for 25 days up to 3 days prior to the break off the analysis of seismic waves generated by the glacier during the rupture maturation process revealed four types of precursory signals of the imminent catastrophic rupture 1 an increase in seismic activity within the glacier 2 a change in the size frequency distribution of icequake energy 3 a modification in the structure of the waiting time distributions between two successive icequakes and 4 a correlation between the seismic activity and the log periodic oscillations of the surface velocities superimposed on the global acceleration of the glacier during the rupture maturation analysis of the seismic activity led us to identify two regimes a stable phase with diffuse damage and an unstable and dangerous phase characterized by a hierarchical cascade of rupture instabilities where large icequakes are triggered

calving flux estimation from tsunami waves abstract measuring glacier calving magnitude frequency and location in high temporal resolution is necessary to understand mass loss mechanisms of ocean terminating glaciers we utilized calving generated tsunami signals recorded with a pressure sensor for estimating the calving flux of bowdoin glacier in northwestern greenland we find a relationship between calving ice volume and wave amplitude this relationship was used to compute calving flux variation the calving flux showed large spatial and temporal fluctuations in july 2015 and in july 2016 with a mean flux of 2 3 0 15 105 m3 d 1 calving flux was greater during periods of fast ice flow high air temperature and at low falling tide indicating the importance of increased longitudinal strain due to glacier acceleration and or submarine melting at the calving front long term measurements with the method introduced here are promising for understanding the complex interplay of ice dynamics melting and calving at glacier fronts

mis 13 12 in britain and the north atlantic understanding the palaeoclimatic context of the earliest acheulean research over the last two decades has revealed a rich record of lower palaeolithic occupation in britain before 450 000 years acheulean industries mode ii first appear in the later part of the early middle pleistocene marine isotope stage mis 19 13 this paper reviews i the age of the earliest acheulean in britain ii the climates under which the earliest acheulean industries occur as recorded by the palaeoecological assemblages that are found at key archaeological sites and iii the spatial and temporal pattern of regional climate change i e the magnitude of glacial interglacial cycles that occurred as a backdrop to the first arrival of mode ii archaeology in britain this review suggests that in britain the earliest acheulean populations arrived during mis 13 and that early occupation occurred under a range of climatic environmental settings but frequently under post temperate late interglacial or interstadial type cool boreal environments furthermore this review shows that the pattern of climate forcing in western europe during mis 13 12 was not analogous to the interglacial cycles of the past 450 000 years as latitudinal climate gradients appear to have been less pronounced the paper concludes by discussing the significance of these observations for understanding the arrival of the earliest acheulean in britain

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

ice front variation and tidewater behavior on helheim and kangerdlugssuaq glaciers greenland we used satellite images to examine the calving behavior of helheim and kangerdlugssuaq glaciers greenland from 2001 to 2006 a period in which they retreated and sped up these data show that many large iceberg calving episodes coincided with teleseismically detected glacial earthquakes suggesting that calving related processes are the source of the seismicity for each of several events for which we have observations the ice front calved back to a large pre existing rift these rifts form where the ice has thinned to near flotation as the ice front retreats down the back side of a bathymetric high which agrees well with earlier theoretical predictions in addition to the recent retreat in a period of higher temperatures analysis of several images shows that helheim retreated in the 20th century during a warmer period and then re advanced during a subsequent cooler period this apparent sensitivity to warming suggests that higher temperatures may promote an initial retreat off a bathymetric high that is then sustained by tidewater dynamics as the ice front retreats into deeper water the cycle of frontal advance and retreat in less than a century indicates that tidewater glaciers in greenland can advance rapidly greenland s larger reservoir of inland ice and conditions that favor the formation of ice shelves likely contribute to the rapid rates of advance

the british pleistocene fluvial archive east midlands drainage evolution and human occupation in the context of the british and nw european record this paper reviews the pleistocene evolution and human occupation of the river trent the major fluvial artery draining midland britain and places it within a modern quaternary context in contrast to the sedimentary records of the river thames and the erstwhile bytham system which extend back to the early pleistocene present knowledge of the terrace sequence of the trent its tributary systems and associated ancestral courses extends back only to the anglian glaciation marine isotope stage mis 12 although the regional pre anglian drainage configuration is demonstrably complex the post anglian sequence is well developed with major terrace sand and gravel aggradations associated with each subsequent cold stage temperate climate sediments correlating with mis 7 and 5e have been recorded although deposits relating to earlier interglacials during mis 11 and 9 have yet to be identified evidence for human occupation in the form of lower and middle palaeolithic artefacts has been recorded from terrace sediments correlated with mis 8 and mis 4 but the majority of this material is heavily rolled and abraded suggesting significant reworking from older deposits this review demonstrates that there is a rich palaeo environmental record from the trent but the lack of a high resolution chronostratgraphic framework raises issues about correlation with other systems

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

the british lower palaeolithic of the early middle pleistocene the archaeology of britain during the early middle pleistocene mis 19 12 is represented by a number of key sites across eastern and southern england these sites include pakefield happisburgh 1 high lodge warren hill waverley wood boxgrove kent s cavern and westbury sub mendip alongside a background scatter lithic record associated with the principal river systems bytham pre diversion thames and solent and raised beaches westbourne arundel hominin behaviour can be characterised in terms of preferences for temperate or cool temperate climates and open woodland mosaic habitats indicated by mammalian fauna mollusca insects and sediments a biface dominated material culture characterised by technological diversity although with accompanying evidence for distinctive core and flake pakefield and flake tool high lodge assemblages probable direct hunting based subsistence strategies with a focus upon large mammal fauna and generally locally focused spatial and landscape behaviours principally indicated by raw material sources data although with some evidence of dynamic mobile and structured technological systems the british data continues to support a modified short chronology to the north of the alps and the pyrenees with highly sporadic evidence for a hominin presence prior to 500 600 ka although the ages of key assemblages are subject to ongoing debates regarding the chronology of the bytham river terraces and the early middle pleistocene glaciations of east anglia

automated detection of basal icequakes and discrimination from surface crevassing thomas s hudson jonathan smith alex m brisbourne robert s white journal annals of glaciology

a 15 year record of frontal glacier ablation rates estimated from seismic data we present a unique time series of continuous glacier frontal ablation rates with weekly resolution over 15 years estimated from seismic calving observations at kronebreen svalbard using linear statistical models we calibrate the seismic record with seven years of satellite derived frontal ablation measurements the two basic input parameters required for our models are the cumulative duration of individual seismic calving events and the incompleteness of the seismic record to correct for the effect of seismic background noise frontal ablation follows the seasonal glacier speed up peaking 1 2 months after the melt season maximum short lived peaks are associated with melt and rain events cumulative frontal ablation of kronebreen between 2001 and 2015 is about 4 0 km3 3 7 gt with the greatest annual loss 0 45 km3 between 2013 and 2014 at the onset of the recent accelerated retreat of the glacier our approach provides a potential method for monitoring tidewater glaciers worldwide that have sufficiently close seismic instrumentation

a unifying framework for iceberg calving models we propose a general framework for iceberg calving models that can be applied to any calving margin the framework is based on mass continuity the assumption that calving rate and terminus velocity are not independent and the simple idea that terminus thickness following a calving event is larger than terminus thickness at the event onset the theoretical near steady state analysis used to support and analyze the framework indicates that calving rate is governed to first order by ice thickness thickness gradient strain rate mass balance rate and backwards melting of the terminus the analysis furthermore provides a physical explanation for a previously derived empirical relationship for ice shelf calving alley and others 2008 in the calving framework the pre and post calving terminus thicknesses are given by two unknown but related functions the functions can vary independently of changes in glacier flow and geometry and can therefore account for variations in calving behavior due to external forcings and or self sustaining calving processes positive feedbacks although the calving framework does not constitute a complete calving model any thickness based calving criterion can easily be incorporated into the framework the framework should be viewed as a guide for future attempts to parameterize calving

numerical modeling of iceberg capsizing responsible for glacial earthquakes the capsizing of icebergs calved from marine terminating glaciers generate horizontal forces on the glacier front producing long period seismic signals referred to as glacial earthquakes these forces can be estimated by broadband seismic inversion but their interpretation in terms of magnitude and waveform variability is not straightforward we present a numerical model for fluid drag that can be used to study buoyancy driven iceberg capsize dynamics and the generated contact forces on a calving face using the finite element approach we investigate the sensitivity of the force to drag effects iceberg geometry calving style and initial buoyancy we show that there is no simple relationship between force amplitude and iceberg volume and similar force magnitudes can be reached for different iceberg sizes the force history and spectral content varies with the iceberg attributes the iceberg aspect ratio primarily controls the capsize dynamics the force shape and force frequency whereas the iceberg height has a stronger impact on the force magnitude iceberg hydrostatic imbalance generates contact forces with specific frequency peaks that explain the variability in glacial earthquake dominant frequency for similar icebergs top out and bottom out events have significantly different capsize dynamics leading to larger top out forces especially for thin icebergs for realistic iceberg dimensions we find contact force magnitudes that range between 5 6 1011 and 2 1014 kg m consistent with seismic observations this study provides a useful framework for interpreting glacial earthquake sources and estimating the ice mass loss from coupled analysis of seismic signals and modeling results

glacier generated earthquakes from prince william sound alaska analysis of seismic records from stations near the prince william sound supports the association of monochromatic low frequency signals with tidewater glaciers in the area thirty three of the larger better recorded signals with corresponding earthquake magnitudes of ml 1 5 to 2 5 were located using routine seismological techniques epicenters for these glacierquakes clustered in the vicinity of the harvard columbia yale and barry glaciers monthly counts from one station for 1975 1979 and part of 1976 range from less than 4 to 248 events a sudden decrease in the number of events per month in mid 1979 raises the possibility of a single source or a common source mechanism for these glacier related signals the monochromatic nondispersive waveforms which characterize these 1 to 2 hz signals may result from harmonic resonance of the glaciers in the epicentral region we speculate that a variety of source mechanisms within or near the glaciers may provide the initial impulse for these events however the characteristic observed waveform is most likely the result of seismic energy which is internally reflected within the ice at fundamental resonant frequencies boundary conditions associated with tidewater glaciers may also allow the ice body to act as a wave guide for shear or surface waves the signal we observe therefore appears to be a source site phenomenon

biostratigraphic and aminostratigraphic constraints on the age of the middle pleistocene glacial succession in north norfolk uk considerable debate surrounds the age of the middle pleistocene glacial succession in east anglia following some recent stratigraphical reinterpretations resolution of the stratigraphy here is important since it not only concerns the glacial history of the region but also has a bearing on our understanding of the earliest human occupation of north western europe the orthodox consensus that all the tills were emplaced during the anglian marine isotope stage mis 12 has recently been challenged by a view assigning each major till to a different glacial stage before during and after mis 12 between trimingham and sidestrand on the north norfolk coast datable organic sediments occur immediately below and above the glacial succession the oldest glacial deposit happisburgh till directly overlies the sidestrand unio bed here defined as the sidestrand hall member of the cromer forest bed formation dating of these sediments therefore has a bearing on the maximum age of the glacial sequence this paper reviews the palaeobotany and describes the faunal assemblages recovered from the sidestrand unio bed which accumulated in a fluvial environment in a fully temperate climate with regional deciduous woodland there are indications from the ostracods for weakly brackish conditions significant differences are apparent between the sidestrand assemblages and those from west runton the type site of the cromerian stage these differences do not result from contrasting facies or taphonomy but reflect warmer palaeotemperatures at sidestrand and a much younger age this conclusion is suggested by the higher proportion of thermophiles at sidestrand and the occurrence of a water vole with unrooted molars arvicola rather than its ancestor mimomyssavini with rooted molars amino acid racemisation data also indicate that sidestrand is significantly younger than west runton these data further highlight the stratigraphical complexity of the cromerian complex and support the conventional view that the happisburgh till was emplaced during the anglian rather than the recently advanced view that it dates from mis 16 moreover new evidence from the trimingham lake bed sidestrand cliff formation above the youngest glacial outwash sediments briton s lane formation indicates that they also accumulated during a middle pleistocene interglacial probably mis 11 all of this evidence is consistent with a short chronology placing the glacial deposits within mis 12 rather than invoking multiple episodes of glaciation envisaged in the new glacial stratigraphy during mis 16 12 10 and 6 copyright 2009 john wiley sons ltd

basal icequakes recorded beneath an alpine glacier glacier d argentiere mont blanc france evidence for stick slip motion while basal icequakes associated with glacier motion have been detected under antarctica for several decades there remains very little evidence of stick slip motion for alpine glaciers here we analyzed 2357 basal icequakes that were recorded at glacier d argenti ere mont blanc massif between february and november of 2012 and that are likely to be associated with basal sliding these events have been classified into 18 multiplets based on their waveforms the strong similarity of the waveforms within each multiplet suggests an isolated repeating source despite this similarity the peak amplitude within each multiplet varies gradually in time by up to a factor of 18 the distribution of these events in time is relatively complex for long time scales we observe progressive variations in the amplitudes of events within each multiplet for intermediate time scales hours the events occur regularly in time with typical return times of several minutes up to several hours for short time scales from 0 01 to 100 s the largest multiplet shows clus tering in time with a power law distribution of the interevent times the location of these events and their focal mechanisms are not well constrained because most of these events were detected by a single seismometer nevertheless the locations can be estimated with an accuracy of a few tens of meters using a polarization analysis the estimated average depth of the basal events is 179 m which is in good agreement with the estimated glacier thickness the relative changes in distance between the source and the sensor can be measured accurately by correlating separately the p wave and s wave parts of the seismograms of each event with the template waveforms which are obtained by averaging the signals within each multiplet we observed small variations in the times between the p wave and the s wave of up to 0 6 ms over 50 days these variations cannot be explained by displacement of the sensor with respect to the glacier but might be due to small changes in the seismic wave velocities with time finally we found using numerical simulations that the observed signals are better explained by a horizontal shear fault with slip parallel to the glacier flow than by a tensile fault these results suggest that the basal events are associated with stick slip motion of the glacier over rough bedrock the rupture length and the slip are difficult to estimate nonetheless the rupture length is likely to be of the order of meters and the total seismic slip accumulated over one day might be as large as the glacier motion during the most active bursts

changes in the velocity structure of the greenland ice sheet using satellite radar interferometry observations of greenland we detected widespread glacier acceleration below 66 north between 1996 and 2000 which rapidly expanded to 70 north in 2005 accelerated ice discharge in the west and particularly in the east doubled the ice sheet mass deficit in the last decade from 90 to 220 cubic kilometers per year as more glaciers accelerate farther north the contribution of greenland to sea level rise will continue to increase

hydrospheric modulation of stress and seismicity on shallow faults in southern alaska abstract shallow 40 km low magnitude m 2 0 seismicity in southern alaska is examined for seasonal variations during the annual hydrological cycle the seismicity is declustered with a spatio temporal epidemic type aftershock sequence model the removal of aftershock sequences allows detailed investigation of seismicity rate changes as water snow and ice loads modulate crustal stresses throughout the year the grace surface loads are obtained from the jpl global land and ocean mass concentration blocks mascon solutions the stress changes at a depth of 10 km are calculated using a 1d spherical layered earth model to evaluate the induced seasonal stresses of 10 kpa we use 30 yr of earthquake focal mechanisms to constrain the tectonic background stress field orientation and assess the seasonal stress change with respect to the principal stress orientations the background stress field is assumed to control the preferred orientation of faulting and stress perturbations are expected to increase or decrease seismic activity on the faults the number of excess earthquakes is calculated with respect to the background seismicity rates for discrete stress intervals the results indicate a 25 increase in regional seismicity rates that correlate with a 3 month time lag following failure encouraging annual mean normal stress differential stress and least principal compressive stress no immediate earthquake rate variations are observed in this region wide analysis the correlation with a 3 month time lag suggests increased mobility of preexisting fluids at seismogenic depths is varying the pore pressure within fault zones to modulate the seismicity rates throughout the seasonal loading cycle

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

iceberg calving as a primary source of regional scale glacier generated seismicity in the st elias mountains alaska 1 since the installation of the alaska regional seismic network in the 1970s data analysts have noted nontectonic seismic events thought to be related to glacier dynamics while loose associations with the glaciers of the st elias mountains have been made no detailed study of the source locations has been undertaken we performed a two step investigation surrounding these events beginning with manual locations that guided an automated detection and event sifting routine results from the manual investigation highlight characteristics of the seismic waveforms including single peaked narrowband spectra emergent onsets lack of distinct phase arrivals and a predominant cluster of locations near the calving termini of several neighboring tidewater glaciers through these locations comparison with previous work analyses of waveform characteristics frequency magnitude statistics and temporal patterns in seismicity we suggest calving as a source for the seismicity statistical properties and time series analysis of the event catalog suggest a scale invariant process that has no single or simple forcing these results support the idea that calving is often a response to short lived or localized stress perturbations our results demonstrate the utility of passive seismic instrumentation to monitor relative changes in the rate and magnitude of iceberg calving at tidewater glaciers that may be volatile or susceptible to ensuing rapid retreat especially when existing seismic infrastructure can be used

improved age constraint for pre and post anglian temperate stage deposits in north norfolk uk from analysis of serine decomposition in bithynia opercula the new glacial stratigraphy ngs of britain postulates that deposits hitherto assigned to the anglian glaciation in marine isotope stage mis 12 represent mis 16 12 10 and 6 this controversial idea can be tested at sidestrand in north norfolk where fossiliferous temperate stage deposits underlie the oldest and overlie the youngest of the glacial deposits previous work has considered biostratigraphy and amino acid dating of these temperate stage deposits but did not achieve tight age constraint using the amino acid evidence alone the total hydrolysable amino acid fraction in intra crystalline protein from bithynia tentaculata opercula has previously been analysed for concentrations of serine and alanine statistical screening of these data gives alanine serine ratios of 4 572 0 114 for the sidestrand hall member beneath the glacial deposits and 3 564 0 091 for the sidestrand cliff formation overlying the glacial deposits these ratios imply ages of mis 13a and 11c respectively indicating the latest cromerian and early hoxnian interglacials and invalidating the ngs copyright 2009 john wiley sons ltd

amino acid geochronology of the type cromerian of west runton norfolk uk aminostratigraphic studies of continental deposits in the uk have hitherto relied almost exclusively on data from the aragonitic shells of non marine molluscs for dating pleistocene sequences this is usually based on the d l value of a single amino acid d alloisoleucine l isoleucine a i in the total shell proteins two genera of freshwater gastropods valvata and bithynia are used to explore the value of using multiple amino acids from the intra crystalline fraction which should be more protected from the effects of diagenesis than the inter crystalline component results are compared from both the aragonitic shells and opercula composed of calcite a more stable form of calcium carbonate in order to put the amino acid data from the west runton freshwater bed into perspective statistical analyses are used to compare them with results from the hoxnian mis 11 site at clacton on sea essex twelve protein decomposition indicators revealed that the results from the shells were not as clear cut as those from the opercula five indicators from the valvata shell suggest that west runton is older than clacton at a 95 significance level but two actually suggested a younger age seven indicators show that the bithynia shells from west runton are older than congeneric shells from clacton in marked contrast all 12 indicators isolated from the opercula demonstrate that west runton is significantly older than clacton the data are also compared with results from waverley wood an important archaeological site in the english midlands falling within the cromerian complex contrary to earlier interpretations the new amino acid data from bithynia opercula indicate that west runton is older than waverley wood a relationship now consistent with the available biostratigraphy

tidal and seasonal variations in calving flux observed with passive seismology the seismic signatures of calving events i e calving icequakes offer an opportunity to examine calving variability with greater precision than is available with other methods here using observations from yahtse glacier alaska we describe methods to detect locate and characterize calving icequakes we combine these icequake records with a coincident manually generated record of observed calving events to develop and validate a statistical model through which we can infer iceberg sizes from the properties of calving icequakes we find that the icequake duration is the single most significant predictor of an iceberg s size we then apply this model to 18 months of seismic recordings and find elevated iceberg calving flux during the summer and fall and a pronounced lull in calving during midwinter calving flux is sensitive to semidiurnal tidal stage large calving events are tens of percent more likely during falling and low tides than during rising and high tides consistent with a view that deeper water has a stabilizing influence on glacier termini multiple factors affect the occurrence of mechanical fractures that ultimately lead to iceberg calving at yahtse glacier seismology allows us to demonstrate that variations in the rate of submarine melt are a dominant control on iceberg calving rates at seasonal timescales on hourly to daily timescales tidal modulation of the normal stress against the glacier terminus reveals the nonlinear glacier response to changes in the near terminus stress field

distribution and provenance of the baginton sand and gravel in the wreake valley northern leicestershire england implications for inter regional correlation the baginton sand and gravel is traced along the lower wreake valley as a continuous water laid stratum at the base of the drift succession its properties closely resemble those previously described from the proto soar valley namely an upward fining sequence and a composition dominated by pebbles of triassic and carboniferous origin such a provenance is consistent with the idea that the proto soar once followed a route eastwards past melton mowbray and that the drainage along the lower wreake valley has been reversed in the course of pleistocene times however the slope of the sand and gravel train appears to be to the west rather than the east and the rockhead relief is also inconsistent with an eastward flowing proto soar until this enigma is resolved it would be imprudent to use the baginton sand and gravel as the basis for inter regional correlations the issue is further complicated by the preservation at brooksby of earlier interglacial or interstadial deposits whose temporal affinities remain unclear

major river systems of central and southern britain during the early and middle pleistocene central and southern britain was drained by two main river systems during the larger part of the early and middle pleistocene the thames and bytham rivers evidence for these rivers and their quaternary history is represented by their sediments the kesgrave and bytham sands and gravels respectively the geomorphological position of the sediments biostratigraphy and amino acid geochronology evidence from the earlier parts of the early pleistocene tiglian c4b and earlier indicates low energy river systems and marine conditions over much of east anglia for most of the early pleistocene tiglian c4c to the cromerian complex the ancestral thames was the main river with at its maximal extent a catchment that extended into wales and across east anglia and what is now the north sea to join the ancestral rhine during this period glaciers in the uplands of wales and periglacial mass movement elsewhere supplied material to the catchment and it was at this time that the bulk of the sorted quaternary ssediments of lowland britain were deposited the bytham river system has no successor because the landscape now in existence has been fundamentally altered by glacial erosion this catchment drained most of midland england and joined the thames in central east anglia initially the bytham river was a tributary of the thames but over time it extended its catchment and at the beginning of the cromerian complex it became the main river of southern britain with the anglian glaciation 01 stage 121 the bytham river was destroyed and the thames was diverted to its present route through london

seventeen antarctic seismic events detected by global surface waves and a possible link to calving events from satellite images 1 we detect 17 seismic events in antarctica from 1997 to 2009 by applying a surface wave detector to global seismic data we locate these events using a waveform cross correlation method and find that most occurred near the coast of antarctica and are clustered in three regions four events are on the ronne ice shelf close to the location of a 1998 calving event five events are near the vanderford glacier and eight events are near the ninnis glacier the observed rayleigh and love waves for these events have similar amplitudes and a two lobed radiation pattern matching the expected amplitude behavior of a single force source model using such a model we obtain best fitting horizontal force directions for the 14 events that have relatively better signal to noise ratios analysis of coastline changes from modis images before and after the detected events show that two events on vanderford glacier and one event near ninnis glacier are likely associated with calving events moreover the inferred force directions for the seismic events appear consistent with local ice flow directions both satellite observations and modeling results strongly suggest a link between seismic events and calving processes in the two regions however the force directions on the ronne ice shelf are aligned with observed rift propagation directions suggesting that these events may arise from rifting processes

alaska tidewater glacier terminus positions 1948 2012 a significant portion of the world s glacier ice drains through tidewater outlets though much remains unknown about the response to recent climate change of tidewater glaciers we present a 64 year record of length change for 50 alaska tidewater glaciers we use u s geological survey topographic maps to provide a base length for glaciers before 1970 using all available cloud free landsat images we manually digitize calving front outlines for each glacier between 1972 and 2012 resulting in a total of more than 10 000 outlines tidewater glacier lengths vary seasonally focusing on the 36 glaciers terminating in tidewater throughout the study period we find a mean standard deviation seasonal variation of 60 85 m a 1 we use these oscillations to determine the significance of interannual changes in glacier length all 36 glaciers underwent at least one period 1 year of significant advance or retreat 28 glaciers underwent at least one period of both significant advance and retreat over the entire period 1948 2012 24 of these glaciers retreated a total uncertainty of 107 95 0 29 km 11 advanced a total of 7 71 0 20 and one chenega glacier did not change significantly retreats and advances are highly variable in time several glaciers underwent rapid short term retreats of a few years duration these retreats occurred after large changes in summer sea surface temperature anomalies further study is needed to determine what triggered these retreats no coherent regional behavior signal is apparent in the length record although two subregions show a coherence similar to recent observations in greenland

interpretation of amplitude data from a ground based radar in combination with terrestrial photogrammetry and visual observations for calving monitoring of kronebreen svalbard a ground based radar has been used successfully for monitoring calving events and velocities at kronebreen svalbard for two test seasons in 2007 and 2008 we use daily terrestrial optical photogrammetry and continuous visual observation to validate the interpretation of a 116 hour ground based radar amplitude of return signal data recorded from 26 to 30 august 2008 the radar was placed 4 km from the glacier it measured at high temporal rate 2 hz and the antenna lobe covered a width of 700 m of the front the calving front geometry was extracted from the optical images and its effect on radar backscatter together with the movement of the glacier was identified in the plot of the amplitude of the radar return signal calving events were detected applying an automated change detection technique to the radar dataset this technique allowed us to detect 92 of the events that were observed during the same time in this paper we focus on the method rather than on data interpretation however future use of this method combined with meteorological data tides and ocean temperature will be valuable for calving process studies

the bytham river reconsidered abstract the english midlands is one of the most important regions for british pleistocene geology the middle pleistocene glacial sediments of the region termed the wolston formation overlie deposits of a pre existing river system the baginton formation the latter are characteristically composed of quartz rich sediment derived from underlying triassic bedrock this sw ne aligned proto soar system was overridden by the wolstonian ice its lack of terraces or discrete sedimentary units implies that the river can only have existed for a limited period the deposits accumulated during a period of climate change from boreal interstadial to subarctic conditions a reinterpretation of these sediments as the headwaters of a pre anglian bytham river aligned towards east anglia across the fenland where they were linked to the ingham formation deposits found favour for two decades this was especially so when the wolston formation sediments were reassigned to the earlier anglian stage however recent work has shown that the bytham river could not have existed in the form suggested by some authors since pre anglian age fluvial sediments are absent from the eastern fenland margin except possibly certain deposits at high lodge suffolk therefore a re examination of the evidence is required it is concluded that the wolstonian glaciation late saalian marine isotope stage mis 6 indeed post dates that during the anglian stage elsterian mis 12 in addition it appears that the baginton proto soar stream as originally conceived almost certainly did not exist before the early wolstonian early saalian stage following a significant period of fluvial incision rather than being aligned towards east anglia the substantial proto soar flowed into south lincolnshire and thence potentially to the north sea via the wash and the silver pit depression by contrast the pre anglian ingham formation deposits of central east anglia were almost certainly deposited by a separate proto trent river that drained the east midlands over an extended period as a left bank thames tributary together these conclusions reinforce the view that the main drainage alignment in southern england during the pre anglian period was nw to se parallel to the regional tilt of the landmass

the early and early middle pleistocene context of human occupation and lowland glaciation in britain and northern europe abstract this paper reviews the stratigraphical and environmental contexts of early human occupation and lowland glaciation in britain and northern europe it highlights the fragmentary nature of most of the critical sequences and the inadequacy of existing stratigraphical frameworks the earliest archaeology known from nw europe has been reported from happisburgh 3 a site on the norfolk coast the flint artefacts from here were recovered from sediments previously assigned to the pastonian stage of the early pleistocene however the mammalian assemblage from happisburgh 3 differs from other local sites attributed to the pastonian indicating a younger age within the early pleistocene the sediments have reversed palaeomagnetic polarity and have palynological features inviting correlation with the leerdam interglacial in the dutch bavelian complex the interglacials of the british cromerian complex are compared and their archaeological record reviewed at most of these sites the archaeology includes hand axes associated with a mammalian assemblage containing the water vole arvicola but at pakefield suffolk a core and flake industry is associated with the ancestral mimomys savini this together with the even older record from happisburgh 3 indicates earlier periods of human occupation than previously known from nw europe at least five temperate episodes with distinct faunal assemblages are now recognized in the british early middle pleistocene but these are unlikely to equate directly with odd numbered stages of the marine isotope record this biostratigraphical framework conflicts with a new glacial stratigraphy for east anglia which proposes glaciations during mis 16 12 10 and 6 evidence is reviewed from sidestrand and trimingham where datable organic sediments occur directly beneath and above the middle pleistocene glacial succession indicating that it was emplaced entirely during the anglian glacial stage mis 12 a new stratigraphical framework is provided ranking british sites in order of relative age which is then compared with a revised scheme for the dutch late early and early middle pleistocene succession the revisions involve the relocation of the waardenburg interglacial interglacial 1 to the bavelian complex and the use of the brunhes matuyama palaeomagnetic reversal to define both the base of the dutch cromerian complex and the early middle pleistocene boundary moreover following recent re interpretation the noordbergum interglacial interglacial iv and glacial c are removed from the cromerian complex and are correlated with mis 11 and mis 12 respectively this scheme imposes greater consistency between the british and dutch successions as well as conformity with guidelines recommended by the international stratigraphic commission

characteristics of seismic and acoustic signals produced by calving bering glacier alaska 1 we recorded 126 calving and iceberg breakup events from the terminus of the bering glacier during five days in august 2008 using seismometers and three small aperture arrays of infrasound sensors the seismic signals were typically emergent narrow band and lower frequency similar to records at other glaciers the acoustic records were characterized by shorter duration higher frequency signals with more impulsive onsets we demonstrate that triangular infrasound arrays permit improved locations of calving events over seismic arrivals that rely on a relatively complicated poorly known velocity model twenty six of 35 well located events occurred on icebergs in vitus lake rather than the glacier face while our data do not permit a complete description of the source process the distinctive frequency contents and durations in the seismic and infrasound data suggest that the two data types record different aspects of the same process

a conceptual model of valley incision planation and terrace formation during cold and arid permafrost conditions of pleistocene southern england staircases of gravelly river terrace deposits in southern england occupy valleys typically underlain by frostsusceptible and brecciated bedrocks the valleys developed during the quaternary by alternating episodes of 1 brecciation incision and planation through the bedrock forming wide low relief erosion surfaces and 2 aggradation in braidplains of gravel a few meters thick that bury the erosion surfaces a conceptual model to account for some of the terraces proposes that brecciation resulted from ice segregation in the ice rich layer in the upper meters of pleistocene permafrost making them vulnerable to fluvial thermal erosion and therefore predisposing the bedrock to planation the low gradients of the valleys were adjusted such that rivers transferred fine materials out of the basins but lacked the competence to remove gravel which therefore accumulated within floodplains the model challenges the prevailing view of incision during climate transitions it attributes incision and planation to very cold and arid permafrost conditions when rivers had limited discharges and hillslopes supplied limited volumes of stony debris into valley bottoms

greenland ice sheet increased coastal thinning repeated laser altimeter surveys and modelled snowfall summer melt show average ice loss from greenland between 1997 and 2003 was 80 12 km3 yr 1 compared to about 60 km3 yr 1 for 1993 4 1998 9 half of the increase was from higher summer melting with the rest caused by velocities of some glaciers exceeding those needed to balance upstream snow accumulation velocities of one large glacier almost doubled between 1997 and 2003 resulting in net loss from its drainage basin by about 20 km3 of ice between 2002 and 2003 copyright 2004 by the american geophysical union

underwater acoustic signatures of glacier calving climate driven ice water interactions in the contact zone between marine terminating glaciers and the ocean surface show a dynamic and complex nature tidewater glaciers lose volume through the poorly understood process of calving a detailed description of the mechanisms controlling the course of calving is essential for the reliable estimation and prediction of mass loss from glaciers here we present the potential of hydroacoustic methods to investigate different modes of ice detachments high frequency underwater ambient noise recordings are combined with synchronized high resolution time lapse photography of the hans glacier cliff in hornsund fjord spitsbergen to identify three types of calving events typical subaerial sliding subaerial and submarine a quantitative analysis of the data reveals a robust correlation between ice impact energy and acoustic emission at frequencies below 200 hz for subaerial calving we suggest that relatively inexpensive acoustic methods can be successfully used to provide quantitative descriptions of the various calving types

glacier calving observed with time lapse imagery and tsunami waves at glaciar perito moreno patagonia calving plays a key role in the recent rapid retreat of glaciers around the world however many processes related to calving are poorly understood since direct observations are scarce and challenging to obtain when calving occurs at a glacier front surface water waves arise over the ocean or a lake in front of glaciers to study calving processes from these surface waves we performed field observations at glaciar perito moreno patagonia we synchronized time lapse photography and surface waves record to confirm that glacier calving produces distinct waves compared with local noise a total of 1074 calving events were observed over the course of 39 d during austral summer calving occurred twice more frequently than in spring the cumulative distribution of calving interevent time interval followed exponential model implying random occurrence of events in time we further investigated wave properties and found that source to sensor distance can be estimated from wave dispersion within 20 error we also found that waves produced by different calving types showed similar spectra in the same frequency range between 0 05 0 2 hz and that the amplitude of surface waves increased with the size of calving this study demonstrates the potential of surface wave monitoring for understanding calving processes

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

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

iceberg calving during transition from grounded to floating ice columbia glacier alaska 1 the terminus of columbia glacier alaska unexpectedly became ungrounded in 2007 during its prolonged retreat visual observations showed that calving changed from a steady release of low volume bergs to episodic flow perpendicular rifting propagation and release of very large icebergs a style reminiscent of calving from ice shelves here we compare passive seismic and photographic observations through this transition to examine changes in calving mechanical changes accompany the visible changes in calving style post flotation generation of seismic energy during calving is substantially reduced we propose this is partly due to changes in source processes

well dated fluvial sequences as templates for patterns of handaxe distribution understanding the record of acheulean activity in the thames and its correlatives the use of acheulean handaxe typology as a cultural and temporal marker has been a topic of controversy in recent decades with many archaeologists continuing to reject such an approach out of hand much of the controversy stems however from difficulties in reconciling the archaeological record from quaternary sediments with a flawed and overly simplified chronostratigraphical template with the adoption of the expanded chronology based on the marine oxygen isotope record underpinned by biostratigraphical and geochronological dating has come the recognition of a meaningful progression of artefact types such as the first appearance of levallois technique attributed to mis 9 8 over widespread parts of the old world more recently it has been established that assemblages in britain with twisted ovate handaxes in significant numbers represent mis 11 occupation while those with significant proportions of cleavers and ficron handaxes appear to be correlated with deposits formed at around the time of the mis 9 interglacial the recognition of such patterns stems largely from the well dated thames sequence it should not be confused with the previous use in the mid 20th century of archaeological typology as a crude dating indicator based on a relative refinement of tool making key means of age constraint for the thames sequence have been mammalian assemblage zones representing the last four interglacial cycles molluscan biostragraphy and amino acid racemization dating of molluscan material especially the calcitic opercula of the gastropod bithynia tentaculata thus providing a framework within which the archaeological patterns can be identified

the middle pleistocene deposits of waverley wood pit warwickshire england a complex of channels underlying the baginton lillington gravel baginton formation at waverley wood quarry warwickshire is described fossil pollen and plant macrofossils coleoptera ostracoda mollusca and mammalia are described from the channel fill deposits consideration of all the evidence allows the identification of four separate stages of channel fill which largely occurred under a cool temperate climate at the top of channel 2 evidence for a cold continental climatic episode can be recognised suggesting that the whole complex was deposited under a fluctuating climate at the end of a temperate stage at two levels in the channels human artefacts were recovered confirming the presence of palaeolithic people in warwickshire during the deposition of the sediments amino acid geochronology suggests an age within the cromerian complex stage for the channels the small vertebrate and molluscan faunas indicate that the deposits are no older than the latter part of the cromerian complex stage of east anglia the regional stratigraphic significance of the waverley wood succession is outlined

intermediate depth icequakes and harmonic tremor in an alpine glacier glacier d argentiere france evidence for hydraulic fracturing we detected several thousand deep englacial icequakes on glacier d argentiere mont blanc massif between 30 march and 3 may 2012 these events have been classified in eight clusters inside each cluster the waveforms are similar for p waves and s waves although the time delay between the p waves and s waves vary by up to 0 03 s indicating an extended source area although these events were recorded by a single accelerometer they were roughly located using a polarization analysis the deepest events were located at a depth of 130 m 60 m above the ice bed interface the clusters are separated in space the largest cluster extends over about 100 m for this cluster the strike of the rupture plane is nearly parallel to the direction of the open crevasses and the dip angle is 56 deep icequakes occur in bursts of activity that last for a few hours and are separated by quiet periods many events occurred on 28 29 april 2012 during the warmest days when snow melting was likely important the distribution of events in time and space obeys a power law as also observed for earthquakes but with larger exponents the polarity of the p waves for all of the events is consistent with tensile faulting finally between 25 april and 3 may we observed a gliding harmonic tremor with a fun damental resonance frequency that varied between 30 hz and 38 hz with additional higher frequency harmonics during this time we also observed shallow hybrid events with high frequency onsets and a monochromatic coda these events might be produced by the propagation of fractures and the subsequent flow of water into the fracture the strongest resonance was observed just after a strong burst of deep icequakes and during an un usually warm period when the snow height decreased by 60 cm in one week the res onance frequency shows a succession of several sharp decreases and phases of progressive increases one of the strongest negative steps of the resonance frequency on 28 april coincides with a burst of deep icequakes these events appear to be associated with the propagation of fractures which can explain the decrease in the resonance frequency finally we observed an acceleration of glacier flow on 29 april and suggested that melt water had reached the ice bed interface these observations suggest that deep icequakes are due to hydraulic fracturing and that they can be used to track fluid flow inside glaciers

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

seismic activity and surface motion of a steep temperate glacier a study on triftgletscher switzerland the tongue of triftgletscher switzerland is particularly susceptible to major break off events due to its steep slope in order to detect precursors of such an event we monitored the local seismic activity and detected 2426 icequakes with sources located in an area ranging between 2050 and 2350ma s l events triggered by cracks and icefalls were recorded but no precise distinction between the two sources was possible using duration or frequency criteria clusters of seismic activity were located and confirmed by visual observations we performed a surface motion analysis and found that surface motion was driven significantly by runoff changes at a timescale of 2 3 days by means of a statistical analysis a power law behaviour of the released seismic energy distribution was discerned at certain times during the period investigated variations in power law exponent values indicated that low and high energy events predominantly occurred during phases of enhanced and reduced surface motion respectively substantial releases of seismic energy likely to signal the glacier recoupling were detected during phases of decreasing runoff clues to potential seismic precursors of break off events are discussed

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

analysis of low frequency seismic signals generated during a multiple iceberg calving event at jakobshavn isbrae greenland 1 we investigated seismic signals generated during a large scale multiple iceberg calving event that occurred at jakobshavn isbrae greenland on 21 august 2009 the event was recorded by a high rate time lapse camera and five broadband seismic stations located within a few hundred kilometers of the terminus during the event two full glacier thickness icebergs calved from the grounded or nearly grounded terminus and immediately capsized the second iceberg to calve was two to three times smaller than the first the individual calving and capsize events were well correlated with the radiation of low frequency seismic signals 0 1 hz dominated by love and rayleigh waves in agreement with regional records from previously published glacial earthquakes these low frequency seismic signals had maximum power and or signal to noise ratios in the 0 05 0 1 hz band similarly full waveform inversions indicate that these signals were also generated by horizontal single forces acting at the glacier terminus the signals therefore appear to be local manifestations of glacial earthquakes although the magnitudes of the signals twice time integrated force histories were considerably smaller than previously reported glacial earthquakes we thus speculate that such earthquakes may be a common if not pervasive feature of all full glacier thickness calving events from grounded termini finally a key result from our study is that waveform inversions performed on low frequency calving generated seismic signals may have only limited ability to quantitatively estimate mass losses from calving in particular the choice of source time function has little impact on the inversion but dramatically changes the earthquake magnitude accordingly in our analysis it is unclear whether the smaller or larger of the two calving icebergs generated a larger seismic signal

calving event detection by observation of seiche effects on the greenland fjords with mass loss from the greenland ice sheet accelerating and spreading to higher latitudes the quantification of mass discharge in the form of icebergs has recently received much scientific attention here we make use of very low frequency 0 001 0 01 hz seismic data from three permanent broadband stations installed in the summers of 2009 10 in northwest greenland in order to monitor local calving activity at these frequencies calving seismograms are dominated by a tilt signal produced by local ground flexure in response to fjord seiching generated by major iceberg calving events a simple triggering algorithm is proposed to detect calving events from large calving fronts with potentially no user interaction our calving catalogue identifies spatial and temporal differences in calving activity between jakobshavn isbrae and glaciers in the uummannaq district similar to 200 km to the north the uummannaq glaciers show clear seasonal fluctuations in seiche based calving detections as well as seiche amplitudes in contrast the detections at jakobshavn isbrae show little seasonal variation which may be evidence for an ongoing transition to winter calving activity the results offer further evidence that seismometers can provide efficient and inexpensive monitoring of calving fronts

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

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

eight hundred years of summer temperature variations in the southeast of the iberian peninsula reconstructed from tree rings july to october temperature variations are reconstructed for the last 800 years based on tree ring widths from the cazorla range annual tree ring width at this site has been found to be negatively correlated with temperature of the previous summer this relationship is genuine metabolically plausible and cannot be explained as an indirect correlation mediated by hydroclimate the resulting reconstruction ncz tjaso represents the southernmost annually resolved temperature record based on tree rings in europe and provides detailed information on the regional climate evolution during the late holocene in the southeast of the iberian peninsula the tree ring based temperature reconstruction of cazorla range reveals predominantly warm summer temperatures during the transition between the medieval climate anomaly mca and the little ice age lia from the 13th to the mid of the sixteenth century the lia spanned a slightly longer time 1500 1930 ce than in other european summer temperature reconstructions from the alps and pyrenees the twentieth century though warmer than the preceding centuries does not show unprecedented warmth in the last 800 years three ensembles of climate simulations conducted with two global atmosphere ocean general circulation climate models gcms considering different external forcings were used for comparison echo g erik and mpi esm e1 and e2 additionally individual simulations were available from gcm included in the fifth coupled model intercomparison project as well as single forcing simulations performed with mpi esm the comparison of the reconstructed and simulated temperatures revealed a close agreement of ncz tjaso with the simulations performed with total solar irradiance forcing with wider amplitude furthermore the correlations with single forcing simulations suggest volcanism as the main factor controlling preindustrial summer temperature variations in the cazorla range over the last five centuries the persistent anti correlation between ncz tjaso and simulated temperatures during the mca lia transitional period underlines the current limitations for attributing temperature variations during that period to internal variability or external forcing

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

the earliest occupation of north west europe a coastal perspective recent discoveries from pakefield and happisburgh britain have provided clear evidence for an unexpectedly early hominin occupation of north west europe the sites found in the deposits of interglacial rivers and estuaries on the southern rim of the ancient north sea coast span the older and younger parts of the cromerian complex stage the older of these sites pre date 0 5 ma based on the presence of a mimomys micromammal fauna and may be as old as 0 78 1 0 ma on the european continent stone artefacts unambiguously as old derive from the mediterranean the earliest archaeological evidence that has been discovered inland in europe north of the alps is associated with an arvicola fauna younger than 0 5 ma and was deposited in temperate conditions near rivers that flowed into the north sea only after the cromerian complex is there evidence for hominin activity in cooler conditions and also in locations east of the rhine valley this spatial and temporal pattern in site distribution occurs despite the long history of research in north west europe and the presence of deposits of the same age from both the coast and rivers this paper explores the idea that the changes in site distribution before and after the cromerian complex signal that early hominin occupation in northern europe during the earlier period was an atlantic phenomenon i e restricted to the milder temperate climates in the coastal continental regions dispersal to more inland habitats originated in the coastal regions the conditions explaining preservation of the oldest sites from a geological perspective are investigated providing a geographical climatological and habitat context for the wider surroundings of the sites because of differences in the potential for preserving archaeology in fluvial and coastal contexts poor long term preservation of coastal depositional contexts and low numbers of sites it is difficult to disentangle the influence of hominin habitat preference or even tolerance from habitat preservation however the hypothesis that the earliest hominins in europe were restricted to the temperate atlantic parts of europe provides a testable framework for evaluating future archaeological discoveries and makes it possible to formulate research strategies for locating new hominin occupation sites in europe especially its atlantic regions

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

updated estimates of glacier volume changes in the western chugach mountains alaska and a comparison of regional extrapolation methods and 2001 2004 average net balance rates ranged between 3 1 to 0 16 m yr 1 for the tidewater and 1 5 to 0 02 m yr 1 for the nontidewater glaciers we tested several methods for extrapolating these measurements to all the glaciers of the western chugach mountains using a process similar to cross validation predictions of individual glacier changes appear to be difficult probably because of the effects of glacier dynamics which on long multidecadal timescales complicates the response of glaciers to climate in contrast estimates of regional contributions to rising sea level were similar for different methods mainly because the large glaciers whose changes dominated the regional total were among those measured for instance the above sea level net balance rate of columbia glacier 3 1 0 08 km 3 yr 1 water equivalent weq or an equivalent rise in sea level sle of 0 0090 0 0002 mm yr 1 was nearly half of the total regional net balance rate of the western chugach mountain glaciers 7 4 1 1 km 3 yr 1 weq or 0 020 0 003 mm yr 1 sle between 1950 1957 and 2001 2004 columbia glacier is a rapidly retreating tidewater glacier that has lost mass through processes largely independent of climate tidewater glaciers should therefore be treated separately when performing regional extrapolations

how oceanic melt controls tidewater glacier evolution the recent rapid retreat of many arctic outlet glaciers has been attributed to increased oceanic melt but the relationship between oceanic melt and iceberg calving remains poorly understood here we employ a transient finite element model that simulates oceanic melt and ice break off at the terminus the response of an idealized tidewater glacier to various submarine melt rates and seasonal variations is investigated our modeling shows that for zero to low oceanic melt the rate of volume loss at the front is similar or higher than for intermediate oceanic melt rates only very high melt rates lead to increasing volume losses these results highlight the complex interplay between oceanic melt and calving and question the general assumption that increased submarine melt leads to higher calving fluxes and enhanced retreat models for tidewater glacier evolution should therefore consider calving and oceanic melt as tightly coupled processes rather than as simple additive parametrizations

an aminostratigraphy for the british quaternary based on bithynia opercula aminostratigraphies of quaternary non marine deposits in europe have been previously based on the racemization of a single amino acid in aragonitic shells from land and freshwater molluscs the value of analysing multiple amino acids from the opercula of the freshwater gastropod bithynia which are composed of calcite has been demonstrated the protocol used for the isolation of intra crystalline proteins from shells has been applied to these calcitic opercula which have been shown to more closely approximate a closed system for indigenous protein residues original amino acids are even preserved in bithyniid opercula from the eocene showing persistence of indigenous organics for over 30 million years geochronological data from opercula are superior to those from shells in two respects first in showing less natural variability and second in the far better preservation of the intra crystalline proteins possibly resulting from the greater stability of calcite these features allow greater temporal resolution and an extension of the dating range beyond the early middle pleistocene here we provide full details of the analyses for 480 samples from 100 horizons 75 sites ranging from late pliocene to modern these show that the dating technique is applicable to the entire quaternary data are provided from all the stratotypes from british stages to have yielded opercula which are shown to be clearly separable using this revised method further checks on the data are provided by reference to other type sites for different stages including some not formally defined additional tests are provided by sites with independent geochronology or which can be associated with a terrace stratigraphy or biostratigraphy this new aminostratigraphy for the non marine quaternary deposits of southern britain provides a framework for understanding the regional geological and archaeological record comparison with reference to sites yielding independent geochronology in combination with other lines of evidence allows tentative correlation with the marine oxygen isotope record

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

fast tidewater glaciers some iceberg calving outlet glaciers flow continuously at speeds normally associated with surging glaciers arid exhibit dramatic instability scenarios related to those suggested for marine ice sheets no temperate tidewater glaciers are known to have floating termini but many polar and subpolar tidewater glaciers do the fast flow of temperate calving glaciers is almost entirely due to basal sliding and appears to be a function of the effective pressure on the bed which may approach zero and the longitudinal back stress on the terminus the terminus boundary condition the calving relation is imperfectly known yet is vital to the dynamics of these glaciers calving relations for grounded tidewater glaciers have been suggested on empirical grounds but have not been rigorously tested the calving relations for floating termini are virtually unknown this together with the imperfect understanding of basal sliding inhibits confidence in our understanding of the stability of these glaciers columbia glacier alaska is an instructive example because observations have been made on the major changes in its geometry calving rate and dynamics that have occurred in less than 10 years the calving flux has increased more rapidly than the glacier flux causing thinning and retreat as a result the ice velocity has increased markedly the short term velocity changes relate to changes in back pressure ice recession tidal changes and the flux of water injected to the bed these results have relevance to the mechanisms of basal sliding glacier surges and the stability of marine ice streams

calving seismicity from iceberg sea surface interactions 1 iceberg calving is known to release substantial seismic energy but little is known about the specific mechanisms that produce calving icequakes at yahtse glacier a tidewater glacier on the gulf of alaska we draw upon a local network of seismometers and focus on 80 hours of concurrent direct observation of the terminus to show that calving is the dominant source of seismicity to elucidate seismogenic mechanisms we synchronized video and seismograms to reveal that the majority of seismic energy is produced during iceberg interactions with the sea surface icequake peak amplitudes coincide with the emergence of high velocity jets of water and ice from the fjord after the complete submergence of falling icebergs below sea level these icequakes have dominant frequencies between 1 and 3 hz detachment of an iceberg from the terminus produces comparatively weak seismic waves at frequencies between 5 and 20 hz our observations allow us to suggest that the most powerful sources of calving icequakes at yahtse glacier include iceberg sea surface impact deceleration under the influence of drag and buoyancy and cavitation numerical simulations of seismogenesis during iceberg sea surface interactions support our observational evidence our new understanding of iceberg sea surface interactions allows us to reattribute the sources of calving seismicity identified in earlier studies and offer guidance for the future use of seismology in monitoring iceberg calving

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

land sea correlations in the pleistocene based on isoleucine epimerization in non marine molluscs the correlation between the oxygen isotope stratigraphy of the oceans and continental stratigraphic records is one of the main challenges for quaternary research most continental classifications however are based on techniques and hypotheses that predate recent advances nevertheless the deep sea oxygen isotope global stratigraphic framework has been extended to the continents by means of some long sequences1 but these are exceptional and regional geology is unsatisfactorily classified for correlation with the oxygen isotope signal because successive geological events produced similar evidence homotaxis geochronometric dating is essential for correlation but available methods are highly site regional or sample specific fortunately non marine molluscs are ubiquitous in time and space and here we use the time dependent epimerization of l isoleucine in these fossils to subdivide the pleistocene of the british isles and to identify more events than recognized by the existing classification2 by calibrating the relative aminostratigraphic scale with independent dating methods we have set up a geochronology which is the basis for land sea correlations back to oxygen isotope stage 15

glacier fjord and seismic response to recent large calving events jakobshavn isbrae greenland 1 the recent loss of jakobshavn isbrae s extensive floating ice tongue has been accompanied by a change in near terminus behavior calving currently occurs primarily in summer from a grounded terminus involves the detachment and overturning of several icebergs within 30 60 min and produces long lasting and far reaching ocean waves and seismic signals including glacial earthquakes calving also increases near terminus glacier velocities by 3 but does not cause episodic rapid glacier slip thereby contradicting the originally proposed glacial earthquake mechanism we propose that the earthquakes are instead caused by icebergs scraping the fjord bottom during calving

avalanching glacier instabilities review on processes and early warning perspectives avalanching glacier instabilities are gravity driven rupture phenomena that might cause major disasters especially when they are at the origin of a chain of processes reliably forecasting such events combined with a timely evacuation of endangered inhabited areas often constitute the most efficient action recently considerable efforts in monitoring analyzing and modeling such phenomena have led to significant advances in destabilization process understanding improving early warning perspectives the purpose of this paper is to review the recent progress in this domain three different types of instabilities can be identified depending on the thermal properties of the ice bed interface if cold 1 the maturation of the rupture is associated with a typical time evolution of surface velocities and passive seismic activity a prediction of the final break off is possible using these precursory signs for the two other types water plays a key role in the development of the instability if the ice bed interface is partly temperate 2 the presence of meltwater may reduce the basal resistance which promotes the instability no clear and easily detectable precursory signs are known in this case and the only way to infer any potential instability is to monitor the temporal evolution of the thermal regime the last type of instability 3 concerns steep temperate glacier tongues switching for several days weeks during the melting season into a so called active phase followed in rare cases by a major break off event although the prediction of such events is still far from being achievable critical conditions promoting the final instability can be identified

glacial earthquakes in greenland and antarctica glacial earthquakes are a new class of seismic events first discovered as signals in long period seismograms recorded on the global seismographic network most of these events occur along the coasts of greenland where they are spatially related to large outlet glaciers glacial earthquakes show a strong seasonality with most events occurring during the late summer the rateofglacial earthquakeoccurrenceincreasedbetween2000and2005 with a stabilization of earthquake frequency at 2003 2004 levels in 2006 2008 recent observations establish a strong temporal correlation between the distinct seismic signals of glacial earthquakes and large ice loss events in which icebergs of cubic kilometer scale collapse against the calving face linking the seismogenic process to the force exerted by these icebergs on the glacier andtheunderlyingsolidearth asuddenchangeinglacierspeedresultsfrom these glacial earthquake calving events seasonal and interannual variations in glacier terminus position account for general characteristics of the temporal variation in earthquake occurrence glacial earthquakes in antarctica are less well studied but they exhibit several characteristics similar to glacial earthquakes in greenland