the steensby inlet ice stream in the context of the deglaciation of northern baffin island eastern arctic canada deglaciation of northern baffin island involved several large ice streams with contrasting histories three north flowing marine based ice streams were in place during the last glacial maximum but they retreated at widely varying rates during the early and middle holocene the steensby inlet ice stream formed in response to over steepening of the ice front during deglaciation of foxe basin it caused an abrupt change in places a general reversal of flow about 6 ka bp and operated across its full width for only about 500 years nevertheless it left a distinct subglacial footprint including an hourglass shaped bedform set a dense network of till samples from the region of the ice stream reveals a sharp sided pluglike dispersal of carbonate debris that was sustained by erosion in the source area of about 5 mm a 1 the ice stream devolved into valley controlled ice streams separated by cold based ice over interfluves the former evacuated debris along valleys and left erosional till scarps along the sides of sliding ice post ice stream end moraines including the large gifford moraine require later cold based flow across the drumlins formed by the ice stream copyright 2008 john wiley sons ltd

comment on converging ice streams a new paradigm for reconstructions of the laurentide ice sheet in southern ontario and deposition of the oak ridges moraine

southern laurentide ice lobes were created by ice streams des moines lobe in minnesota usa abstract regional mapping in southern minnesota has illuminated a suite of landforms developed by the des moines lobe that delimit the position of the lobe at its maximum and at lesser readvances the ice lobe repeatedly advanced discharged its subglacial water and subsequently stagnated recent glaciological research on antarctic ice streams has led some glacial geologists to postulate that ice streams drained parts of the marine based areas of the laurentide ice sheet i postulate that such ice streams may develop in land based areas of an ice sheet as well and that the des moines lobe 200 km wide and 900 km long was an outlet glacier of an ice stream it appears to have been able to advance beyond the laurentide ice sheet as long as adequate water pressure was maintained however the outer part of the lobe stagnated because subglacial water that facilitated the flow was able to drain away through tunnel valleys stagnation of the lobe is not equivalent to stoppage of the ice stream because ice repeatedly advanced into and onto the stagnant margins stacking ice and debris similar landforms are also seen in other lobes of the upper midwestern united states

a small baseline approach for investigating deformations on full resolution differential sar interferograms this paper presents a differential synthetic aperture radar sar interferometry difsar approach for investigating deformation phenomena on full resolution difsar interferograms in particular our algorithm extends the capability of the small baseline subset sbas technique that relies on small baseline difsar interferograms only and is mainly focused on investigating large scale deformations with spatial resolutions of about 100 spl times 100 m the proposed technique is implemented by using two different sets of data generated at low multilook data and full single look data spatial resolution respectively the former is used to identify and estimate via the conventional sbas technique large spatial scale deformation patterns topographic errors in the available digital elevation model and possible atmospheric phase artifacts the latter allows us to detect on the full resolution residual phase components structures highly coherent over time buildings rocks lava structures etc as well as their height and displacements in particular the estimation of the temporal evolution of these local deformations is easily implemented by applying the singular value decomposition technique the proposed algorithm has been tested with data acquired by the european remote sensing satellites relative to the campania area italy and validated by using geodetic measurements

multidimensional time series analysis of ground deformation from multiple insar data sets applied to virunga volcanic province summary a novel multidimensional small baseline subset msbas methodology is presented for integration of multiple interferometric synthetic aperture radar insar data sets for computation of 2 or 3 d time series of deformation the proposed approach allows the combination of all possible air borne and space borne sar data acquired with different acquisition parameters temporal and spatial sampling and resolution wave band and polarization the produced time series have improved temporal resolution and can be enhanced by applying either regularization or temporal filtering to remove high frequency noise we apply this methodology to map 2003 2010 ground deformation of the virunga volcanic province vvp north kivu democratic republic of congo the horizontal and vertical time series of ground displacement clearly identify lava compaction areas long term deformation of mt nyamuragira and 2004 2006 and 2010 pre and coeruptive deformation providing that enough sar data is available the method opens new opportunities for detecting ground motion in the vvp and elsewhere

recent advances in sar interferometry time series analysis for measuring crustal deformation abstract synthetic aperture radar sar interferometry is a technique that permits remote detection of deformation at the earth s surface and has been used extensively to measure displacements associated with earthquakes volcanic activity and many other crustal deformation phenomena analysis of a time series of sar images extends the area where interferometry can be successfully applied and also allows detection of smaller displacements through the reduction of error sources here we review recent advances in time series sar interferometry methods that further improve accuracy this is particularly important when constraining displacements due to processes with low strain rates such as interseismic deformation we include examples of improved algorithms applied to image deformation associated with the 2010 eruption of eyjafjallajokull volcano in iceland slow slip on the guerrero subduction zone in mexico and tectonic deformation in western anatolia turkey

discussion streamlined erosional residuals and drumlins in central british columbia canada by j donald mcclenagan 2013 geomorphology 189 41 54 abstract mcclenagan 2013 presents a model to explain streamlined erosional residuals or drumlins on uplands and lowlands in the plateau region of central british columbia canada in this discussion paper we note that mcclenagan 2013 has not adequately discussed previous relevant work in the region and we argue that additional analyses and evidence are required to substantiate this new model the hypothesis offered for the origin of the plateau landscape specifically catastrophic glaciofluvial activity differs significantly from a model based on glacial erosion and deformation that has been developed from field based research over the past six decades we discuss four critical points relating to the proposed model 1 the current geological model for the plateau region of central british columbia 2 theory of glacial dispersal 3 existing hypotheses for the formation of drumlins and other glacial landforms and 4 theoretical glacial erosion modeling we further suggest that the model cannot be substantiated without sedimentological or morphological field evidence for water bodies argued to be the source of the proposed megaflood or megafloods

monitoring the fate of injected co2 using geodetic techniques author s vasco dw dixon th ferretti a samsonov sv abstract 2020 by the society of exploration geophysicists geodetic methods comprise one class of geophysical data that are sensitive to changes in effective pressure within operating reservoirs albeit indirectly through induced deformation geodetic observations which have observation intervals that vary from seconds to days weeks or months generally provide more frequent sampling compared to existing geophysical methodologies such as seismic time lapse monitoring which typically invoke repeat times of months to years these differences in sampling intervals are primarily due to the extensive effort and hence cost of conducting geophysical field operations which often precludes executing a large number of surveys satellite based interferometric synthetic aperture radar insar is cost effective and used in many applications including monitoring the injection of carbon dioxide co2 for both long term storage and enhanced oil production an application to the geologic sequestration of co2 in algeria revealed northwest migration along a fault fracture zone intersected by the injection well a study in a texas field demonstrated that enhanced oil recovery utilizing co2 leads to observable surface deformation that may be used to characterize the sequestered co2 and to estimate the pressure changes within the reservoir induced by injection and production

fresh arguments against the shaw megaflood hypothesis a reply to comments by david sharpe on paleohydraulics of the last outburst flood from glacial lake agassiz and the 8200 bp cold event

thin film channelized drainage or sheetfloods beneath a portion of the laurentide ice sheet an examination of glacial erosion forms northern new york state usa abstract morphologic analyses of characteristic bedrock erosion forms found in northern new york state usa were used to reconstruct the subglacial conditions under which they may have been produced observations from sites on wellesley island n y at point salubrious n y and at an open pit mine near balmat n y were combined with regional mapping of a diverse suite of glacial erosion forms in order to establish the areal extent and significance of subglacial drainage in northern new york results of these site specific and regional studies are the basis for discussion of the probable role of subglacial meltwater in the region bedrock erosion forms preserved at various locations in northern new york are interpreted as products of flow separation of localized subglacial meltwater during ice bed decoupling the regional distribution of these forms indicates that they are largely restricted to pre existing subglacially modified bedrock valleys that served as subglacial tunnel channels regionally extensive deep subglacial meltwater flow characterized as sheetfloods is not required to account for the erosional features described from specific sites in northern new york state

rocks under strain strain induced time lapse time shifts are observed for depleting reservoirs pressure depletion as a result of oil and gas production creates changes in the stress and strain fields of the rock material both inside and outside the reservoir seismic waves propagating through these rocks have different traveltimes before and after depletion because the layer thicknesses change and the seismic velocity is altered by the changes in the stress and strain fields the cumulative change in two way traveltimes with depth is referred to as time lapse time shift

formation of mega scale glacial lineations on the dubawnt lake ice stream bed 2 sedimentology and stratigraphy mega scale glacial lineations msgls are highly elongate subglacial landforms produced beneath zones of fast flowing ice while qualitative data on their morphology have existed for several decades studies of their composition and sedimentology are comparatively rare sediment exposures along the course of the finnie river in nunavut northern canada provide a window into the internal stratigraphy and sedimentology of msgls formed by the dubawnt lake palaeo ice stream during regional deglaciation of the laurentide ice sheet stratigraphic sections record evidence for an initial advance of ice into the study area followed by ice sheet recession and deposition of glacifluvial and glacilacustrine outwash subsequently the dubawnt lake palaeo ice stream overrode and reworked this outwash subglacially forming an msgl till this till comprises a sandy red diamicton facies forming the core of the msgl ridges and containing variably deformed lenses stringers and rafts of outwash the sedimentology of this diamicton is consistent with an origin as a glacitectonite and hybrid till formed by a combination of non pervasive subglacial sediment deformation and lodgement facies variations from stratified to massive diamicton reflect in turn variations in strain and subglacial transport distance the occurrence of stratified glacifluvial sediments within these ridges and the well preserved nature of many of the sandy inclusions within the diamicton imply relatively short transport distances and incomplete mixing msgls under the dubawnt lake palaeo ice stream formed through a combination of subglacial erosion and deposition this included non pervasive subglacial sediment deformation and the reworking of pre existing sediment depocentres during streaming flow these results highlight the importance of sediment supply to msgl formation with the presence of abundant pre existing sediments which were subsequently overridden being critical to lineation formation

middle wisconsinan marine shells near repulse bay nunavut canada implications for marine isotope stage 3 ice free conditions and laurentide ice sheet dynamics in north west hudson bay

monitoring pressure depletion and improving geomechanical models of the shearwater field using 4d seismic dedicated 4d seismic data have been used to investigate horizontal and vertical compartmentalization in the high pressure high temperature hpht shearwater field in the u k central north sea geomechanical modeling and conversion of model results to synthetic seismic time shifts allow quantitative comparison of models with real 4d seismic time shifts drilling in and around heavily depleted reservoirs is very challenging and matching the geomechanical model to all data sets including 4d provides the best possible constraints on the likely stress fields an infill well will encounter in the overburden and the reservoir

a critical assessment of subglacial mega floods a case study of glacial sediments and landforms in south central alberta canada the existing subglacial megaflood explanation of glacial sediment deposition and landform production in south central alberta relies upon four sets of observations and associated interpretations 1 a subglacial genesis for all glacilacustrine sediments lying stratigraphically below a local melt out till or ice stagnation facies 2 a melt out genesis for the ice stagnation facies 3 a syn depositional status for the glacitectonic disturbance visible in most exposures due to periodic ice bed re coupling and 4 a subglacial megaflood origin for a truncation surface and clast lag that occurs at the top of the sedimentary exposures and the carving of hummocky terrain and flutes in the area we provide alternative interpretations of the sediment landform assemblages of the area and demonstrate that alternative simpler interpretations of the evidence can be proposed specifically we propose 1 a proglacial rather than subglacial origin of glacilacustrine sediments 2 a glacilacustrine origin for the melt out till and its subsequent glacitectonic disturbance by minor glacier readvances 3 postdepositional rather than syn depositional glacitectonic disturbance due to a significant advance by glacier ice after the accumulation of a thick sequence of glacilacustrine sediments 4 that some linear chains of hummocks are the morphological expression of glacitectonic folding and thrusting 5 that the use of the truncation surfaces to propose a subglacial fluvial origin for hummocky moraine is flawed logic because they do not constitute the tops of hummocks but rather occur on the interfluves that separate the numerous small coulees incised into the valley sides during postglacial time truncation surfaces and clast lags occur locally on the beds of spillway tracts and can be explained as the products of erosion by subaerial spillway water the mega flood explanation of flutings and hummocky moraine in the region is also questioned because these landforms record a regional ice flow imprint of mis aligned and cross cutting flow sets terminating at series of inset and locally cross cutting and lobate transverse ridges moraines these landform associations preclude a subglacial flood origin for the flutings and demonstrate that the transverse ridges are more appropriately interpreted as recessional push moraines the similarity of the glacial landforms of this region to the active temperate glacial landsystem produced by historical glacier recession in modern glacierized catchments where sheetfloods have not been influential in subglacial landform production allows us to apply a modern analogue to landscape interpretation that does not include subglacial sheetflooding

regional unconformities and the sedimentary architecture of the oak ridges moraine area southern ontario seismic stratigraphy geometry and sediment facies within the oak ridges moraine orm area of ontario record major structural elements and surfaces of the quaternary sedimentary sequence the derived stratigraphic architecture can be used to identify the key elements of a regional erosional surface represented by an unconformity in the subsurface and associated overlying channel sediments the erosional surface unconformity forms a distinct time datum in the quaternary sequence which provides an important aid to lithostratigraphic correlation the architecture also gives improved understanding of the effects of erosion on the late glacial landscape the surfaces of erosional drumlins and intervening troughs and the beds and banks of meltwater channels in the orm area define the regional unconformity highlighted by seismic profiles linked to continuously cored boreholes these features are attributed to regional scale subglacial meltwater flow events the sculpted surfaces which are analogous to water eroded forms the presence of boulder lags and coarse grained deposits on the regional erosional surface and the channels with undulating profiles provide the vital supporting evidence for a meltwater interpretation the inter regional extent of the unconformity is inferred from the coherence of regional paleoflows and the extent of drumlinized uplands tunnel channels and scoured bedrock terrain across 75 of the landscape from the orm area east and south to the finger lakes new york the implied magnitude of erosion suggests a pressing need for directed sedimentological study in those ocean basins that were probable depositional sites for flood deposits

monitoring primary depletion reservoirs using amplitudes and time shifts from high repeat seismic surveys in the high porosity poorly consolidated turbidites of the deepwater gulf of mexico production induced compaction is the main production drive mechanism when aquifer support is weak and prior to pressure support by secondary recovery water injection time lapse 4d seismic monitoring of this class of reservoirs has provided several new learning opportunities the time lapse amplitude response of these fields can be complicated due to saturation changes water replacing oil inside the reservoir rock compaction causing density and velocity changes inside the reservoir stress relief and associated deformation of the rock outside the reservoir and changes in reservoir fluid pressures due to pore pressure decrease methods that rely on time lapse amplitude changes with offset to discriminate pressure and saturation changes can help separate and thus simplify the interpretation of some of these effects tura and lumley 1999 landro 2001

drumlinized tunnel valleys in south central ontario abstract a network of late wisconsin valleys deeply incise thick successions up to 200 m of quaternary sediment and paleozoic bedrock across south central ontario the valleys have previously been interpreted as an integrated network of tunnel channels recording catastrophic releases of subglacial meltwater across the bed of the laurentide ice sheet lis recent geologic investigations in the western part of the valley network integrate information gained from surficial sediment and landform mapping continuously cored boreholes that penetrate the entire quaternary sediment succession in valleys as well as intervening uplands and both water borne and land based geophysical surveys together these data provide new insights and a refined interpretation of the genesis timing and paleoglaciological significance of these valleys valleys within the study area are some of the largest observed within the regional network up to 30 km long 7 km wide and 175 m deep they are oriented both north south and in a radial pattern varying from ne sw in the southern part of the study area to ese wnw in the north an undulating late wisconsin till sheet newmarket till caps the regional uplands and is commonly observed along the flanks and floors of the valleys all of which show evidence of a drumlinization phase that postdates excavation of most of the valleys at least two generations of valleys are interpreted from cross cutting relationships with abrupt heads and locally perched downflow ends of some valley forms radiocarbon age determinations of organic material from both below and above the newmarket till constrain the timing of valley excavation to between 28 05 and 12 81 14c kyr bp borehole and outcrop data within the valleys reveal four stratigraphic units su1 su4 that form the floor and sediment infill of the valleys the newmarket till su1 is commonly underlain by deformed substrates the till is absent in parts of some valleys and the lowermost parts of the valley fill commonly consist of coarse grained gravels su2 that pass upwards into sands su3 the bulk of the sediment infill consists of glaciolacustrine silt clay rhythmites su4 that pass upwards into organic and mollusk bearing nearshore and fluviodeltaic deposits that record drainage of proglacial lakes from the study area during deglaciation it is proposed that these features are a previously unrecognized type of tunnel valley that developed subglacially during late wisconsin ice cover meltwater surpluses would be generated at the ice bed interface due to the low transmissivity substrate in the study area with flow preferentially routed into lows on the bed downward incision into confined and pressurized aquifers likely facilitated rapid headward erosion of the valleys enhanced by piping waning meltwater flow velocities discharges allowed ice creep to re occupy newly formed valleys permitting renewed till deposition and subsequent drumlinization of the valleys the valleys also provided efficient routing for meltwater draining the retreating ice marginal zone during deglaciation and allowed localised sand and gravel deposition as eskers and ice proximal subaquatic fans in the oak ridges moraine and within proglacial lakes that developed during ice retreat however there is no evidence for regional scale catastrophic release of subglacial meltwater in the valley infills this integrated dataset represents one of the most complete characterizations of subglacial valleys in a terrestrial setting in north america

comment on shaw j pugin a and young r 2008 a meltwater origin for antarctic shelf bedforms with special attention to megalineations geomorphology 102 364 375 the submarine glacial geomorphology and sedimentology of the cross shelf troughs and the adjacent continental slope around the antarctic peninsula and west antarctica have been the focus of a series of marine geophysical and geological investigations over the last decade e g shipp et al 1999 canals et al 2000 wellner et al 2001 lowe and anderson 2002 o cofaigh et al 2002 dowdeswell et al 2004 heroy and anderson 2005 evans et al 2005 domack et al 2006 mosola and anderson 2006 wellner et al 2006 dowdeswell et al 2006 o cofaigh et al 2007 o cofaigh et al 2008 c o cofaigh j a dowdeswell j evans and r d larter geological constraints on antarctic palaeo ice stream retreat earth surface processes and landforms 33 2008 pp 513 525 o cofaigh et al 2008 and dowdeswell et al 2008 these studies have interpreted sets of characteristic streamlined glacial bedforms and sediments on the shelf which in numerous cases occur in front of modern ice streams as largely the product of fast flowing palaeo ice streams that drained across the shelf during or following the last glacial maximum a key feature of these studies is the observation of highly attenuated bedforms known as mega scale glacial lineations msgl formed in soft sediment on the outer continental shelf these lineations are regarded as key evidence for streaming flow in their recent paper shaw et al present a radically different interpretation of the glacial geomorphology of antarctic cross shelf troughs in terms of catastrophic discharge of subglacial meltwater floods across the shelf in their interpretation msgl are regarded as the product of erosion by turbulent meltwater flow the following comment discusses a number of the key assertions made in their paper

formation of mega scale glacial lineations observed beneath a west antarctic ice stream most discharge from large ice sheets takes place through fast flowing ice streams and their speed is strongly modulated by interactions between the ice and the underlying sediments seismic surveys and investigations through boreholes have revealed a spatial association between fast ice flow and saturated deformable sediments nevertheless our knowledge of the morphology of the interface between ice and sediments is still limited resulting in only rudimentary understanding of the basal boundary conditions beneath ice streams and the generation of subglacial bedforms here we present radar data from the bed of a west antarctic ice stream that reveal the presence of mega scale glacial lineations we combine these data with previously published seismic data and show that these lineations develop in areas of dilatant deforming till and are part of a dynamic sedimentary system that undergoes significant change by erosion and deposition on decadal timescales we find that the mega scale glacial lineations are indistinguishable from those found on beds of palaeo ice streams providing conclusive evidence for the hypothesis that highly elongate bedforms are a characteristic of fast flow regions in ice sheets

inverting for reservoir pressure change using time lapse time strain application to genesis field gulf of mexico there are increasing numbers of published examples from around the world in which significant 4d time shifts have been observed in the overburden above producing reservoirs

palaeo ice streams in the northern keewatin sector of the laurentide ice sheet evidence for ice streams in the laurentide ice sheet is widespread in the region of northern keewatin and the boothia peninsula nunavut canada palaeo ice streams have been recognized but their location size and potential role in ice sheet dynamics are poorly constrained based on the interpretation of satellite imagery we produce a palaeo ice stream map of this region glacial directional landforms eskers and moraines were mapped and integrated into landform assemblages using a glacial geological inversion model palaeo frozen bed areas were also identified relative age of the geomorphic swarms was assessed by cross cutting relationships and radiocarbon ages where available using this information we obtained a glaciologically plausible picture of ice stream evolution within the northernmost laurentide ice sheet on the m clintock channel corridor three generations of pure ice streams are found on baffin island and the gulf of boothia glaciation was dominated by frozen bed zones located on high plateaus and ice streams running along the troughs i e topographic ice streams a massive convergent pattern at the head of committee bay drained ice from both the keewatin and foxe sectors and was probably one of the main deglaciation channels of the laurentide ice sheet finally our results indicate that streaming flow was present in the deep interior of the laurentide ice sheet as recently shown for the greenland and antarctic ice sheets

variations in the composition of the clay fraction of the cenozoic pagodroma group east antarctica implications for determining provenance abstract the cenozoic pagodroma group in the northern prince charles mountains east antarctica is a glaciomarine succession of fjordal character comprising four uplifted formations of different ages the composition of the the assemblage of the upper oligocene to lower miocene mount johnston formation is characterised by the dominance of illite and intermediate concentrations of chlorite similar to that assemblage is the clay mineral suite of the middle miocene fisher bench formation where illite and chlorite together account for 95 of the clay minerals the middle to upper miocene battye glacier formation is the only formation with significant and persistent smectite concentrations although illite is still dominant the kaolinite concentration is also high and is even higher than that of chlorite the clay fraction of the upper pliocene to lower pleistocene bardin bluffs formation is characterised by maximum kaolinite concentrations and relatively low illite and chlorite concentrations the bulk of the clay fraction in each formation can be explained by the physical weathering and erosion of a nearby source under glacial conditions in the case of mount johnston formation and fisher bench formation this source may be situated in the metavolcanic and gneissic rocks of fisher massif the sediments of the bardin bluffs formation indicate a local source within the amery oasis where proterozoic granitoid rocks and gneisses and permo triassic fluvial rocks of the amery group are exposed these results suggest a strong local imprint on the glacial sediments as northwards flowing ice eroded the bedrock in these areas the origin of the clay fraction of the battye glacier formation is a matter of debate the smectite and kaolinite content most easily can be explained by erosion of sources largely hidden beneath the ice upstream less likely these clay minerals reflect climatic conditions that were much warmer and wetter than today facilitating chemical weathering

geospatial analysis of controls on subglacial bedform morphometry in the new york drumlin field implications for laurentide ice sheet dynamics the outline and trend of 6566 subglacial bedforms in the new york drumlin field have been digitized from digital elevation data a spatial predictive model has been used to extend values of bedform elongation over an area measuring 200 km 110 km the resulting surface is used in conjunction with depth to bedrock data and an assumed duration of ice residence to test three proposed controls on bedform elongation upon comparison the resulting display of morphometry is best explained by differences in ice velocity across the field of study the existence of multiple zones of fast moving ice located along the southern margin of the laurentide ice sheet is implied by the observed patterns of bedform elongation and orientation we present two interpretations that are consistent with the observations first enhanced basal sliding caused by decreasing effective pressure near a calving margin is suggested as a possible mechanism by which localized fast ice flow is initiated and maintained second topographically controlled ice streams likely occupied the fjord like troughs of the appalachian upland northern rim contrary to previous understanding of the laurentide southern margin in new york state the resulting palaeoglaciological reconstruction illustrates a dynamic mosaic of ice stream and or outlet glacier activity copyright 2009 john wiley sons ltd

seafloor features delineate late wisconsinan ice stream configurations in eastern parry channel canadian arctic archipelago abstract multibeam imagery and 3 5 khz sub bottom profiles acquired from ccgs amundsen between 2003 and 2013 by arcticnet and the ocean mapping group at the university of new brunswick provide information on seafloor features geology bathymetry and morphology in eastern parry channel and the adjoining large channels in the canadian arctic archipelago together these include peel sound barrow strait lancaster sound wellington channel prince regent inlet admiralty inlet and navy board inlet those data are in part complemented by high resolution single channel seismic reflection profiles acquired by the geological survey of canada in the 1970s and 1980s and by sediment cores that provide chronological and depositional information the occurrence and pattern of streamlined mega scale ridge and groove lineations msgls indicate that these waterways were occupied by glacial ice streams in the past chronological information from marine and adjoining terrestrial areas suggests a long history of glacial events ranging in time from early pleistocene to late wisconsinan seafloor morphology and msgl trends together with terrestrial ice flow patterns indicate that ice streams flowed into barrow strait from peel sound and wellington channel and ice streams in prince regent admiralty and navy board inlets flowed northward into and eastward along lancaster sound recession of the ice stream westward along parry channel occurred 16 cal ka bp to 10 8 cal ka bp thick ice contact sediments deposited by a late ice advance from prince regent inlet constitute the seabed across a large area of western lancaster sound timing for that late ice advance appears to be bracketed between the 11 5 cal ka bp lift off of the eastern parry ice stream north of prince leopold island and the 10 0 cal ka bp deglaciation of prince regent inlet seafloor morphology and lineation trends suggest that ice delivered by the ice stream in peel sound was the westernmost tributary to the ice stream occupying lancaster sound during the late wisconsinan glaciation bathymetric data and msgls indicate that the ice stream emanating from m clintock channel flowed westward

an introduction to the global positioning system and some geological applications receivers equipped to measure dual frequency carrier phase signals from satellites of the global positioning system gps have been capable under special conditions of determining relative horizontal positions among stations separated by one to a few hundred kilometers with a precision of one to several millimeters since the early 1980s the major obstacles to making this capability routine extending it to all parts of the globe and extending it to longer station separations have been equipment cost limitations in the gps satellite constellation arduous data analysis uncertainties in satellite orbits uncertainties in propagation delays associated with variable tropospheric water vapor and difficulties in resolving carrier phase cycle ambiguities recent improvements have occurred in all these areas the increasing ease and reduced cost of gps data acquisition and analysis are having a significant impact on studies of near fault crustal deformation and earthquake processes until recently the province of conventional terrestrial geodetic techniques the enhanced satellite constellation improved models and establishment of global tracking networks have extended several millimeters horizontal positioning capability to station separations of 1000 km or more in virtually all parts of the world this enables study of new classes of tectonic problems that previously were difficult to attack with any geodetic technique examples include a complete kinematic description of ongoing crustal deformation in broad complex continental plate boundary zones and measurement of relative plate motion at convergent boundaries where global models may be poorly constrained

accumulation variability and mass budgets of the lambert glacier amery ice shelf system east antarctica at high elevations the temporal and spatial variability of the annual accumulation rate and the mass budgets of five sub basins of the lambert glacier amery ice shelf system las east antarctica at high elevations are assessed using a variety of datasets derived from field measurements and modeling the annual temporal variations of the accumulation rate for four cores from the west and east sides of the las are around 34 decadal fluctuation of the accumulation from the dt001 firn core drops to 10 and the 30 year fluctuation to 5 which is assumed to contain the information about the regional and long term trend in accumulation the 15 point running mean of the annual accumulation rate derived from stake measurements can remove most of the high frequency spatial variation so as to better represent the local accumulation model simulations show that the spatial variability of erosion deposition of snow by the wind has a noticeable impact on the surface mass balance at the higher parts of the las mass budget estimates at high elevation sub basins of the las suggest drainage 9 has a negative imbalance of 0 7 0 4 gt a 1 lambert and mellor glaciers have a positive imbalance of 3 9 2 1 and 2 1 2 4 gt a 1 respectively and fisher glacier and drainage 11 are approximately in balance the higher elevation region as a whole has a positive mass imbalance of 4 4 6 3 gt a 1 which is consistent with the most recent radar altimetry assessment that shows an overall thickening over this region

geomorphology under ice streams moving from form to process ice streams are integral components of an ice sheet s mass balance and directly impact on sea level their flow is governed by processes at the ice bed interface which create landforms that in turn modulate ice stream dynamics through their influence on bed topography and basal shear stresses thus ice stream geomorphology is critical to understanding and modelling ice streams and ice sheet dynamics this paper reviews developments in our understanding of ice stream geomorphology from an historical perspective with a focus on the extent to which studies of modern and palaeo ice streams have converged to take us from a position of near complete ignorance to a detailed understanding of their bed morphology during the 1970s and 1980s our knowledge was limited and largely gleaned from geophysical investigations of modern ice stream beds in antarctica very few palaeo ice streams had been identified with any confidence during the 1990s however glacial geomorphologists began to recognise their distinctive geomorphology which included distinct patterns of highly elongated mega scale glacial lineations ice stream shear margin moraines and major sedimentary depocentres however studying relict features could say little about the time scales over which this geomorphology evolved and under what glaciological conditions this began to be addressed in the early 2000s through continued efforts to scrutinise modern ice stream beds at higher resolution but our current understanding of how landforms relate to processes remains subject to large uncertainties particularly in relation to the mechanisms and time scales of sediment erosion transport and deposition and how these lead to the growth and decay of subglacial bedforms this represents the next key challenge and will require even closer cooperation between glaciology glacial geomorphology sedimentology and numerical modelling together with more sophisticated methods to quantify and analyse the anticipated growth of geomorphological data from beneath active ice streams

ice streams in the laurentide ice sheet identification characteristics and comparison to modern ice sheets this paper presents a comprehensive review and synthesis of ice streams in the laurentide ice sheet lis based on a new mapping inventory that includes previously hypothesised ice streams and includes a concerted effort to search for others from across the entire ice sheet bed the inventory includes 117 ice streams which have been identified based on a variety of evidence including their bedform imprint large scale geomorphology topography till properties and ice rafted debris in ocean sediment records despite uncertainty in identifying ice streams in hard bedrock areas it is unlikely that any major ice streams have been missed during the last glacial maximum laurentide ice streams formed a drainage pattern that bears close resemblance to the present day velocity patterns in modern ice sheets large ice streams had extensive onset zones and were fed by multiple tributaries and where ice drained through regions of high relief the spacing of ice streams shows a degree of spatial self organisation which has hitherto not been recognised topography exerted a primary control on the location of ice streams but there were large areas along the western and southern margin of the ice sheet where the bed was composed of weaker sedimentary bedrock and where networks of ice streams switched direction repeatedly and probably over short time scales as the ice sheet retreated onto its low relief interior several ice streams show no correspondence with topography or underlying geology perhaps facilitated by localised build up of pressurised subglacial meltwater they differed from most other ice stream tracks in having much lower length to width ratios and have no modern analogues there have been very few attempts to date the initiation and cessation of ice streams but it is clear that ice streams switched on and off during deglaciation rather than maintaining the same trajectory as the ice margin retreated we provide a first order estimate of changes in ice stream activity during deglaciation and show that around 30 of the margin was drained by ice streams at the lgm similar to that for present day antarctic ice sheets but this decreases to 15 and 12 at 12 cal ka bp and 10 cal ka bp respectively the extent to which these changes in the ice stream drainage network represent a simple and predictable readjustment to a changing mass balance driven by climate or internal ice dynamical feedbacks unrelated to climate or both is largely unknown and represents a key area for future work to address

a revised depositional setting for halton sediments in the oak ridges moraine area ontario outcrop and continuous core descriptions high resolution seismic profiling and downhole geophysical data are integrated with detailed mapping to update sedimentary and stratigraphic frameworks for halton sediment a complex mud rich lithofacies succession halton sediment has a gradational transition from underlying oak ridges moraine orm sediment and can abruptly overlie newmarket till halton strata thin and fine upwards from orm sand and gravel to graded sand silt and clay rhythmites with muddy diamicton and sand and gravel interbeds these strata fill basin lows and drape orm sediment lobes and newmarket till drumlins these distinct sedimentary units are here informally referred to as halton formation formal halton till is a proposed subunit of halton formation a clay rich diamicton mapped from niagara peninsula to orm and eastward halton till has traditionally been inferred to represent a late climatically induced readvance of grounded ice from lake ontario basin which deposited drumlini

analysis of velocity field mass balance and basal melt of the lambert glacier amery ice shelf system by incorporating radarsat sar interferometry and icesat laser altimetry measurements 1 by incorporating recently available remote sensing data we investigated the mass balance for all individual tributary glacial basins of the lambert glacier amery ice shelf system east antarctica on the basis of the ice flow information derived from sar interferometry and icesat laser altimetry we have determined the spatial configuration of eight tributary drainage basins of the lambert amery glacial system by combining the coherence information from sar interferometry and the texture information from sar and modis images we have interpreted and refined the grounding line position we calculated ice volume flux of each tributary glacial basin based on the ice velocity field derived from radarsat three pass interferometry together with ice thickness data interpolated from australian and russian airborne radio echo sounding res surveys and inferred from icesat laser altimetry data our analysis reveals that three tributary basins have a significant net positive imbalance while five other subbasins are slightly positive or close to zero balance overall in contrast to previous studies we find that the grounded ice in lambert glacier amery ice shelf system has a positive mass imbalance of 22 9 4 4 gt a 1 the net basal melting for the entire amery ice shelf is estimated to be 27 0 7 0 gt a 1 the melting rate decreases rapidly from the grounding zone to the ice shelf front significant basal refreezing is detected in the downstream section of the ice shelf the mass balance estimates for both the grounded ice sheet and the ice shelf mass differ substantially from other recent estimates

uncovering the hidden part of a large ice stream of the laurentide ice sheet northern ontario canada abstract this investigation was prompted by an enigmatic ice flow anomaly area a on the glacial map of canada which covers about 10 000 km 2 in the hearst kapuskasing area of northeastern ontario it consists of streamlined landforms and striations indicative of a major ice flow toward 130 oriented at right angle to another toward 220 both are late glacial flows but long lasting disagreement exists regarding their relative age the analysis of aerial photographs and satellite images in conjunction with a detailed survey of bedrock cross striated surfaces over an area of about 30 000 km 2 within and around area a clearly indicate that the 130 flow preceded the 220 flow the earlier conflicting interpretations within area a are attributed mainly to the sporadic occurrence of relict striated surfaces formed by older southwestward 220 240 wisconsinan ice flows that have locally escaped destruction by late glacial flows with the result that the southwestward flows are older wisconsinan at some sites and younger late glacial 220 at others relative to the 130 flow when considered with other factors such as the maximum elevation reached by the youngest late glacial flow these ice flow relationships indicate that area a is the outcropping southern part of a much larger ese ice flow system which is probably related to a large fluted belt located to the north and that was identified as the winisk ice stream the distal part of the ice stream except for area a escaped detection by remote sensing mapping methods because depositional and erosional features associated with it are masked by deposits laid down by the younger 220 cochrane ice flow and or by postglacial marine and organic deposits or were destroyed by the younger ice flow the only reliable indicators of the passage of the ice stream in this buried section are ese relict striations crossed by sw striations the advancing ice stream toward the ese not only preceded the late cochrane 220 flow but probably outlasted it as suggested by the mapping of several thousand iceberg furrows in quebec and ontario also directed toward the ese and overprinted on flutes formed by the last glacial flow if this interpretation is correct this makes the winisk ice stream the largest terrestrial ice stream in the hudson bay basin an alternative interpretation associates this fluted belt to the exposed western fringe of streamlined bedforms from a late hudson lobe buried by younger sediments

on the origin of the oak ridges moraine landscape analysis mapping sedimentology shallow geophysics and borehole data are integrated to better understand the complex landform sediment geometries and event sequences of the oak ridges moraine southern ontario a model for the origin of the oak ridges moraine is based on the recognition that the moraine is built on a high relief erosional surface unconformity consisting of drumlin uplands and a network of deep steep walled interconnected valleys tunnel channels the development of the moraine is thought to have occurred in four stages i subglacial sedimentation ii subaqueous fan sedimentation iii fan to delta sedimentation iv ice marginal sedimentation the model traces the transition from subglacial to proglacial conditions during moraine formation and examines the order and timing of sedimentation it is thought that the early stages of moraine construction are better exposed in the east in the west these stages are buried by later stages resume les etudes de paysage cartographie sedimentologie geophysique de subsurface et des carottes de trous des sondages ont ete menees conjointement pour chercher a mieux comprendre les configurations complexes des formes de relief sediments et les sequences des evenements qui ont affecte la moraine d oak ridges dans le sud de l ontario un modele interpretant l origine de la moraine d oak ridges est fonde sur le fait que cette moraine fut edifiee sur une surface d erosion discordance en terrain a topographie accentuee comprenant des drumlins sur terres elevees et des vallees a parois subverticales interconnectees chenaux tunnels le modele propose un developpement de la moraine en quatre phases i sedimentation sous glaciaire ii sedimentation d un eventail sous aquatique iii sedimentation de l eventail evoluant vers un depot deltaique iv sedimentation en bordure d un glacier le modele retrace la transition de conditions sous glaciaires a proglaciaires durant la formation de la moraine et traite de l ordre et de la chronologie du sediment il apparait que c est dans le secteur oriental que les premieres phases de l edification de la moraine sont le mieux exposees tandis que dans le secteur partie occidental elles sont enfouies sous le sediment des phases plus tardives

reply to the comment by h a j russell on converging ice streams a new paradigm for reconstructions of the laurentide ice sheet in southern ontario and deposition of the oak ridges moraine 1

predicting time lapse stress effects in seismic data time lapse changes in seismic data are commonly evaluated in terms of changes in reservoir properties such as pressure saturation or temperature traditionally the evaluation of time lapse seismic data has focused on changes of seismic signatures within the reservoir interval recent studies however have shown convincingly that time lapse seismic changes occur not only in the reservoir but also in the overburden and generally in the rock mass surrounding the reservoir these time lapse changes can be explained by production induced stress changes in the rocks surrounding the reservoir

antarctic palaeo ice streams we review the geomorphological sedimentological and chronological evidence for palaeo ice streams on the continental shelf of antarctica and use this information to investigate basal conditions and processes and to identify factors controlling grounding line retreat a comprehensive circum antarctic inventory of known palaeo ice streams their basal characteristics and minimum ages for their retreat following the last glacial maximum lgm is also provided antarctic palaeo ice streams are identified by a set of diagnostic landforms that nonetheless display considerable spatial variability due to the influence of substrate flow velocity and subglacial processes during the lgm palaeo ice streams extended via bathymetric troughs to the shelf edge of the antarctic peninsula and west antarctica and typically to the mid outer shelf of east antarctica the retreat history of the antarctic ice sheet since the lgm is characterised by considerable asynchroneity with individual ice streams exhibiting different retreat histories this variability allows antarctic palaeo ice streams to be classified into discrete retreat styles and the controls on grounding line retreat to be investigated such analysis highlights the important impact of internal factors on ice stream dynamics such as bed characteristics and slope and drainage basin size whilst grounding line retreat may be triggered and to some extent paced by external atmospheric and oceanic forcing the individual characteristics of each ice stream will modulate the precise timing and rate of retreat through time

reconciling records of ice streaming and ice margin retreat to produce a palaeogeographic reconstruction of the deglaciation of the laurentide ice sheet abstract this paper reconstructs the deglaciation of the laurentide ice sheet lis including the innuitian ice sheet from the last glacial maximum lgm with a particular focus on the spatial and temporal variations in ice streaming and the associated changes in flow patterns and ice divides we build on a recent inventory of laurentide ice streams and use an existing ice margin chronology to produce the first detailed transient reconstruction of the ice stream drainage network in the lis which we depict in a series of palaeogeographic maps results show that the drainage network at the lgm was similar to modern day antarctica the majority of the ice streams were marine terminating and topographically controlled and many of these continued to function late into the deglaciation until the ice sheet lost its marine margin ice streams with a terrestrial ice margin in the west and south were more transient and ice flow directions changed with the build up peak phase and collapse of the cordilleran laurentide ice saddle the south eastern marine margin in atlantic canada started to retreat relatively early and some of the ice streams in this region switched off at or shortly after the lgm in contrast the ice streams draining towards the north western and north eastern marine margins in the beaufort sea and in baffin bay appear to have remained stable throughout most of the late glacial and some of them continued to function until after the younger dryas yd the yd influenced the dynamics of the deglaciation but there remains uncertainty about the response of the ice sheet in several sectors we tentatively ascribe the switching on of some major ice streams during this period e g m clintock channel ice stream at the north west margin but for other large ice streams whose timing partially overlaps with the yd the drivers are less clear and ice dynamical processes rather than effects of climate and surface mass balance are viewed as more likely drivers retreat rates markedly increased after the yd and the ice sheet became limited to the canadian shield this hard bed substrate brought a change in the character of ice streaming which became less frequent but generated much broader terrestrial ice streams the final collapse of the ice sheet saw a series of small ephemeral ice streams that resulted from the rapidly changing ice sheet geometry in and around hudson bay our reconstruction indicates that the lis underwent a transition from a topographically controlled ice drainage network at the lgm to an ice drainage network characterised by less frequent broad ice streams during the later stages of deglaciation these deglacial ice streams are mostly interpreted as a reaction to localised ice dynamical forcing flotation and calving of the ice front in glacial lakes and transgressing sea basal de coupling due to large amount of meltwater reaching the bed debuttressing due to rapid changes in ice sheet geometry rather than as conveyors of excess mass from the accumulation area of the ice sheet at an ice sheet scale the ice stream drainage network became less widespread and less efficient with the decreasing size of the deglaciating ice sheet the final elimination of which was mostly driven by surface melt

causal link between quaternary paleoclimatic changes and volcanic islands evolution 1 giant landslides and resulting tsunamis represent the main geologic hazards linked to volcanic island evolution from offshore and onland studies flank failures have been identified around numerous islands in most geodynamic contexts however the triggering conditions are still poorly understood and several causes may act simultaneously to reach a critical threshold here we show that most large volume 10 km3 landslides occur at glacial stages termination and we propose that a causal relationship between flank collapse of volcanic islands and global climatic changes has existed at least since 900 kyr moreover ages reported here favour the hypothesis that major collapses occurred during the onset of glacial to interglacial transitions when sudden influx of melt water from polar ice caps causes rapid sea level rise we propose that rapid sea level rise induces enhanced coastal erosion and sudden changes of pore pressure conditions within basal layers which favour edifice failure

primary results of glaciological studies along an 1100 km transect from zhongshan station to dome a east antarctic ice sheet the chinese national antarctic research expedition ghinare carried out three traverses from zhongshan station to dome a princess elizabeth land and inaccessible area east antarctic ice sheet during the 1996 97 to 1998 99 antarctic field seasons the expeditions are part of the chinese international trans antarctic scientific expedition program in this project glaciological investigations of mass balance ice temperature ice flow stratigraphy in snow pits and snow firn ice cores as well as the glaciochemical study of surface snow and shallow ice cores have been carried out in the 1998 99 field season chinare extended the traverse route to 1128 km inland from zhongshan station the density profiles show that firnification over princess elizabeth land and inaccessible area 290 1100 km along the route is fairly slow and the accumulation rate recovered from snow pits along the initial 460 km of the route is 4 6 21 cm 46 210 kg m 2a 1 water equivalent the initial 460 km of the route can be divided into four sections based on the differences of accumulation rate this pattern approximately coincides with the study on the lambert glacier basin lgb by australian scientists during the past 50 years the trends of both air temperature and accumulation rate show a slight increase in this area in contrast to the west side of the lgb data on surface accumulation rates and their spatial and temporal variability over ice drainage areas such as the lgb are essential for precise mass balance calculation of the whole ice sheet and are important for driving ice sheet models and testing atmospheric models

neogene fjordal sedimentation on the western margin of the lambert graben east antarctica neogene glacial sedimentation east antarctica

tunnel valleys concepts and controversies a review abstract although erosion of valleys by subglacial meltwater was first proposed more than 100 years ago the processes that produced these valleys under past ice sheets have remained a topic of vigorous debate the most commonly hypothesized mechanisms have included gradual formation by sediment deformation into the incipient valleys under steady state conditions and subsequent transport by meltwater to the ice margin time transgressive formation along a retreating ice margin by drainage of surface meltwater to the bed or release of impounded meltwater behind a marginal permafrost wedge probably catastrophically and rapid erosion during widespread catastrophic basal sheetflood events recent application of new and enhanced imaging techniques has led to the identification of many new tunnel valleys both on land and offshore throughout the regions glaciated during former ice ages in addition new advances in understanding of subglacial hydrology both from modelling and field instrumentation have helped to constrain the drainage of meltwater from past ice sheet beds this work elucidates the role of subglacial groundwater flow systems in evacuating meltwater from the bed but also shows that groundwater flow alone was not enough to maintain ice bed meltwater pore pressures below the level of ice flotation both modelling and field observations indicate that subglacial conduits oriented parallel to glacial flow lines reorganize groundwater flow systems into basins containing lateral flow toward conduits cut upward into the ice or downward into the bed because of the inability of groundwater flow to account for all the meltwater produced by basal melting other drainage mechanisms involving both non channelized and channelized meltwater flow have been proposed the notion of catastrophic drainage of impounded basal meltwater is still favored by many and the discovery of hundreds of subglacial lakes beneath the antarctic ice sheet and the likelihood of similar lakes beneath pleistocene ice sheets provides a source of water for those advocating catastrophic formation for tunnel valleys proponents of catastrophic drainage consider the valleys to be channels reflecting the width and perhaps depths of flows that formed them tunnel valleys produced by the scandinavian ice sheet have been described and mapped on land as well as on the sea bed valleys and networks of valleys some of which are totally buried have been linked to 3 or more glaciations tunnel valley networks from the last weichselian glaciation in denmark can be related to specific ice margins developed during ice retreat in north america most research has focused on tunnel valleys associated with ice margins formed by the last wisconsin glaciation along the southern margin of the laurentide ice sheet

landform and sediment imprints of fast glacier flow in the southwest laurentide ice sheet evidence for former fast glacier flow ice streaming in the southwest laurentide ice sheet is identified on the basis of regional glacial geomorphology and sedimentology highlighting the depositional processes associated with the margin of a terrestrial terminating ice stream preliminary mapping from a digital elevation model of alberta identifies corridors of smoothed topography and corridor parallel streamlined landforms megaflutes to mega lineations that display high levels of spatial coherency ridges that lie transverse to the dominant streamlining patterns are interpreted as a series of minor recessional push moraines b thrust block moraines or composite ridges hill hole pairs constructed during readvances surges and c overridden moraines cupola hills apparently of thrust origin together these landforms demarcate the beds and margins of former fast ice flow trunks or ice streams that terminated as lobate forms localised cross cutting and or misalignment of flow sets indicates temporal separation and the overprinting of ice streams lobes the fast flow tracks are separated by areas of interlobate or inter stream terrain in which moraines have been constructed at the margins of neighbouring competing ice streams outlet glaciers this inter stream terrain was covered by more sluggish non streaming ice during full glacial conditions thin tills at the centres of the fast flow corridors in many places unconformably overlying stratified sediments suggest that widespread till deformation may have been subordinate to basal sliding in driving fast ice flow but the general thickening of tills towards the lobate terminal margins of ice streams outlet glaciers is consistent with subglacial deformation theory in this area of relatively low relief we speculate that fast glacier flow or streaming was highly dynamic and transitory sometimes with fast flowing trunks topographically fixed in their onset zones and with the terminus migrating laterally the occurrence of minor push moraines and flutings and associated landforms because of their similarity to modern active temperate glacial landsystems are interpreted as indicative of ice lobe marginal oscillations possibly in response to seasonal climatic forcing in locations where meltwater was more effectively drained from the glacier bed further north the occurrence of surging glacier landsystems suggests that persistent fast glacier flow gave way to more transitory surging possibly in response to the decreasing size of ice reservoir areas in dispersal centres and also locally facilitated by ice bed decoupling and drawdown initiated by the development of ice dammed lakes copyright 2008 john wiley sons ltd

quantitative estimation of compaction and velocity changes using 4d impedance and traveltime changes in some hydrocarbon reservoirs severe compaction of the reservoir rocks is observed this compaction is caused by production and it is often associated with changes in the overburden time lapse or 4d seismic data are used to monitor this compaction process since the compaction causes changes in both layer thickness and seismic velocities it is crucial to distinguish between the two effects two new seismic methods for monitoring compacting reservoirs are introduced one based on measured seismic prestack traveltime changes and the other based on poststack traveltime and amplitude changes in contrast to earlier methods these methods do not require additional empirical relationships such as for instance a velocity porosity relationship the uncertainties in estimates for compaction and velocity change are expressed in terms of errors in the traveltime and amplitude measurements these errors are directly related to the quality and repeatability of time lapse seismic data for a reservoir at 3000 m depth wit h9mo fcompaction and assuming a 4d timeshift error of 0 5 ms at near offset and 2 ms at far offset we find relative uncertainty in the compaction estimate of approximately 50 60 using traveltime information only

on the glaciological meteorological and climatological significance of antarctic blue ice areas this paper presents the current state of our knowledge about antarctic blue ice areas scattered widely over the antarctic continent yet covering only approximately 1 of its surface area blue ice areas have some peculiar characteristics that make them of particular interest for planetary geologists glaciologists meteorologists and climatologists for instance blue ice areas are subject to net ablation mainly by sublimation since any accumulation is easily swept off their smooth surfaces by winds moreover they are significantly warmer than their surroundings and the wind over them is generally more gusty an important feature of blue ice is its relatively low albedo 0 56 compared with that of snow 0 80 blue ice is probably considerably smoother than snow in the aerodynamic sense with roughness lengths as low as 3 10 6 m which indicates that blue ice is probably the only permanent natural surface over which the air flow is mainly in the aerodynamic smooth regime further since it is likely that very old ice is exposed at the surface of some blue ice areas this ice would be of great interest for paleoclimatic studies it has also been suggested that blue ice areas are sensitive to climate change this would make them useful as antarctic climate indicators because they can easily be monitored by satellite finally this paper addresses several gaps in our knowledge about blue ice areas and gives suggestions for future blue ice area research

satellite based measurements of surface deformation reveal fluid flow associated with the geological storage of carbon dioxide interferometric synthetic aperture radar insar gathered over the in salah co sub 2 storage project in algeria provides an early indication that satellite based geodetic methods can be effective in monitoring the geological storage of carbon dioxide an injected volume of 3 million tons of carbon dioxide from one of the first large scale carbon sequestration efforts produces a measurable surface displacement of approximately 5 mm year using geophysical inverse techniques we are able to infer flow within the reservoir layer and within a seismically detected fracture fault zone intersecting the reservoir we find that if we use the best available elastic earth model the fluid flow need only occur in the vicinity of the reservoir layer however flow associated with the injection of the carbon dioxide does appear to extend several kilometers laterally within the reservoir following the fracture fault zone

glacial geomorphology of terrestrial terminating fast flow lobes ice stream margins in the southwest laurentide ice sheet glacial geomorphological mapping of southern alberta canada reveals landform assemblages that are diagnostic of terrestrial terminating ice streams fast flowing outlet glaciers with lobate snouts spatial variability in features that comprise the landform assemblages reflects changes in a palaeo ice stream activity switch on off and b snout basal thermal regimes associated with climate sensitive steady state flow palaeo ice stream tracks reveal distinct inset sequences of fan shaped flowsets indicative of receding lobate ice stream margins former ice lobe margins are demarcated by a major often glacially overridden transverse moraine ridges commonly comprising glacitectonically thrust bedrock and b minor closely spaced recessional push moraines and hummocky moraine arcs details of these landform types are well exhibited around the former southern margins of the central alberta ice stream where larger scale more intensive mapping identifies a complex glacial geomorphology comprising minor transverse ridges mtr types 1 3 hummocky terrain ht types 1 3 flutings and meltwater channels spillways the mtr type 1 constitute the summit corrugation patterns of glacitectonic thrust moraines or major transverse ridges and have been glacially overrun and moderately streamlined the mtr type 2 sequences are recessional push moraines similar to those developing at modern active temperate glacier snouts the mtr type 3 document moraine construction by incremental stagnation because they occur in association with hummocky terrain the close association of hummocky terrain with push moraine assemblages indicates that they are the products of supraglacial controlled deposition on a polythermal ice sheet margin where the ht type 3 hummocks represent former ice walled lake plains the ice sheet marginal thermal regime switches indicated by the spatially variable landform assemblages in southern alberta are consistent with palaeoglaciological reconstructions proposed for other ice stream fast flow lobes of the southern laurentide ice sheet where alternate cold polythermal and temperate marginal conditions associated with climate sensitive steady state flow sequentially gave way to more dynamic streaming and surging activity

mass balance of the lambert glacier amery ice shelf system east antarctica a comparison of computed balance fluxes and measured fluxes we combine european remote sensing satellite ers 1 radar altimeter surface elevations fricker and others 2000 with six different accumulation distributions to compute balance fluxes for the lambert glacier amery ice shelf drainage system these interpolated balance fluxes are compared with fluxes derived from in situ measurements of ice thickness and velocity at 73 stations of the lambert glacier basin traverse and at 11 stations further downstream to assess the system s state of balance for the upstream line we obtain a range of imbalance estimates from 23 8 to 19 9 of the observed flux reflecting the sensitivity to the accumulation distributions for some of the accumulation distributions the imbalance estimates vary significantly between different parts of the line imbalance estimates for the downstream line range from 17 7 to 70 2 with four of the estimates exceeding 30 again reflecting the sensitivity of the result to input accumulation and strongly suggesting that the mass balance of the region between the two lines is positive our results confirm the importance of accurate estimates of accumulation in ice sheet mass balance studies furthermore they suggest that it is not possible to accurately determine the state of balance of large antarctic drainage basins on the basis of currently available accumulation distributions

past ice stream and ice sheet changes on the continental shelf off the sabrina coast east antarctica abstract our understanding of the response of the antarctic ice sheet to climate and ocean changes requires the improvement of current ice atmosphere ocean models and the accurate determination of boundary conditions such as ice thickness and extent at key time intervals so that satellite gravity observations and isostatic models can be adjusted however large portions of the antarctic margin remain understudied or lack suitable data one key area where data are lacking is the sabrina coast portion of the east antarctic ice sheet eais margin where the totten glacier which has the largest ice discharge in east antarctica is accelerating thinning and loosing mass at high rates in this work we present the results of the first geological and geophysical marine survey to the continental shelf offshore of the dalton ice tongue and moscow university ice shelf east of the totten glacier the data presented include multibeam swath bathymetry and multichannel seismic focusing on the sea floor morphology and sedimentary section above a regional angular unconformity separating pre and post miocene glacial strata sea floor scouring and iceberg keel marks on the outer shelf associated with gullies on the upper slope indicate that ice expanded in the past and grounded 5 km from the shelf edge at 450 500 mbsl extending 155 km north of the current moscow university ice shelf a nearly 1000 m deep area in the inner middle shelf oriented nw with paleo ice flow direction indicated by mega scale glacial lineations msgl and drumlins is interpreted as a cross shelf glacial trough a series of geomorphic associations on the north eastern side of the glacial trough includes glacial lobes grounding zone wedges gzw glacial lineations and transverse ridges which indicates slower ice grounding line stabilization and collapse these geomorphic associations are organized in 4 four sets representing different past ice flow configurations reflecting changes in ice flow direction grounding line position location of fast and slow ice areas and retreat pattern some of the geomorphic features identified are compatible with the presence of an organized subglacial drainage and others are with rapid grounding line collapse a well preserved series of gzws occurring at different water depths implies they were formed during different glacial stages or cycles the inferred diminishing ice thickness for consecutives gzws indicates that the margin of the antarctic ice sheet evolved to a less extensive coverage of the continental shelf through successive glacial stages or cycles the identification of different ice flow configurations evidence of subglacial water and past ice margin collapse indicates a dynamic ice sheet margin with varying glacial conditions and retreat modes we observe that some of the described morphological associations are similar to those found in the amundsen sea sector of the west antarctic ice sheet wais where they are associated with ice sheet and ice stream collapse although further studies are needed to assess the precise timing and rates of the glacial processes involved we conclude that there is enough evidence to support the hypothesis that the eais margin can behave as dynamically as the wais margin especially during glacial retreat and icesheet margin collapse

converging ice streams an unreasonable hypothesis for deposition of the oak ridges moraine southern ontario the hypothesis that oak ridges moraine orm formed between converging ice streams requires critical testing available data e g digital elevation models maps seismic profiles continuous core

dynamics of the north american ice sheet complex during its inception and build up to the last glacial maximum the north american ice sheet complex played a major role in global sea level fluctuations during the late quaternary but our knowledge of its dynamics is based mostly on its demise from the last glacial maximum lgm a period characterised by non linear behaviour in the form of punctuated ice margin recession episodic ice streaming and major shifts in the location of ice divides in comparison knowledge of the pre lgm ice complex is poorly constrained largely because of the fragmentary nature of the evidence relating to ice sheet build up in this paper we explore the inception and growth of ice 120 20 ka using a glacial systems model which has been calibrated against a large and diverse set of data relating to the deglacial interval we make use of calibration data prior to the lgm but its scarcity introduces greater uncertainty which is partly alleviated by our large ensemble analysis results suggest that following the last interglaciation oxygen isotope stage ois 5e the ice complex initiated over the north eastern canadian arctic and in the cordillera within a few thousand years it then underwent rapid growth to an ois 5 maximum at 110 ka 5d and covered 70 of the area occupied by the lgm ice cover although only 30 by volume an ois 5 minimum is modelled at 80 ka 5a before a second phase of rapid growth at the start of ois 4 which culminated in a large ice complex at 65 ka almost as large as at the lgm subsequent deglaciation was rapid maximum modelled sea level contribution of 16 cm per century and resulted in an ois 3 minimum between ca 55 60 ka thereafter the ice complex grew towards its lgm configuration interrupted by several phases of successively less significant mass loss our results support and extend previous inferences based on geological evidence and reinforce the notion of a highly dynamic pre lgm ice complex e g with episodes of 10 s m of eustatic sea level equivalent in 50 but even the thin ois 5 ice sheets exhibit fast flow features several 1000 m a 1 in major topographic troughs notwithstanding the severe limitations imposed by the use of the shallow ice approximation we note that most fast flow features generated prior to the lgm correspond to the location of known ice streams during deglaciation i e in major topographic troughs and over soft sediments at the southern and western margins moreover the modelled flux of these ice streams sensu lato appears to be non linearly scaled to ice sheet volume i e there is no evidence that decay phases were associated with significantly increased ice stream activity this hypothesis requires testing using a model with higher order physics and future modelling would also benefit from additional pre lgm constraints e g dated ice free margin positions to help reduce and quantify uncertainties

new marine evidence for a late wisconsinan ice stream in amundsen gulf arctic canada abstract amundsen gulf and adjoining dolphin and union strait and coronation gulf form the southwestern end of the northwest passage adjacent to the beaufort sea extensive high resolution multibeam sonar imagery and sub bottom profiles of the seabed have been acquired primarily in amundsen gulf by arcticnet and the ocean mapping group at the university of new brunswick these data reveal a variety of seabed landforms including mega scale glacial ridge and groove lineations drumlins moraines iceberg scours bedrock outcrops and discontinuous sediment deposits of variable thickness the lineations are widespread especially in southeastern amundsen gulf they resemble modern and paleo bedforms reported from antarctica svalbard greenland and other canadian arctic channels where they have been ascribed to ice streams the glacial sole marks on the seabed in amundsen gulf and regional data from the adjacent mainland and islands outline the configuration of a glacial ice stream from the laurentide ice sheet that occupied amundsen gulf and adjoining waterways during the late wisconsinan part of the northwestward flowing ice stream was deflected around the colville mountains on victoria island and rejoined the main ice stream in amundsen gulf by way of prince albert sound the grounded amundsen gulf ice stream extended northwestward to the outer slope in the beaufort sea where it was buttressed by arctic shelf ice maximum ice stream extent is inferred to have been coincident with the late glacial maximum multi sequence ice contact sediments and stratigraphic relations with glaciomarine sediments indicate that several ice advances and retreats occurred in the northwestern part of the gulf final retreat from the maximum position began prior to 13 000 cal yr bp and terrestrial dates indicate that the retreating ice front had reached dolphin and union strait by about 12 5 cal ka bp

the late quaternary stratigraphic record northwest of montreal regional ice sheet dynamics ice stream activity and early deglacial events the quaternary sediments of previously unstudied buried valleys and sections near montreal are analyzed and other sites are revisited to further develop the stratigraphic framework of the st lawrence lowland and to establish regional glacial and deglacial models the southwest trending buried valleys were investigated by stratigraphic drilling and high resolution seismic profiling the quaternary succession consists from base to top of proximal glaciolacustrine sediments two superposed till sheets argenteuil and oka tills of inferred late wisconsinan age and champlain sea sediments the glacial sediments of this sequence record an ice advance toward south argenteuil till followed by an abrupt ice flow shift toward the southwest oka till compositional and geomorphic data indicate that oka till is ubiquitous and is associated with a regional set of glacial landforms the analysis of a regional digital elevation model in combination with published ice flow indicators shows convergent flow pattern

ice keel seabed features in marine channels of the central canadian arctic archipelago evidence for former ice streams and iceberg scouring abstract the study area lies within the central part of the canadian arctic archipelago a region that was covered by the laurentide ice sheet during the late wisconsinan glaciation and earlier multibeam imagery from widely spaced transects indicates the presence of linear groove and ridge features on the seabed at several localities in peel sound franklin strait northern larsen sound and within m clintock channel these lineations resemble features in antarctica and in several formerly glaciated regions that have been interpreted to be sole marks emplaced beneath fast flowing ice streams based on these analogies a similar origin is inferred for the lineations on the channel floors within the study area the lineations are oriented parallel to the channel axes and margins they occur on all transects within the bathymetrically deeper area at the junction of franklin strait and peel sound northward in peel sound they occur extensively on the western and central transects and more locally on the eastern transect their north south orientation is normal to that of glacial flow features on somerset island and most of eastern prince of wales island which border peel sound to the east and west respectively the trend of the lineations is northeasterly parallel to the channel axis in franklin strait and mainly northerly in larsen sound and m clintock channel elsewhere the seabed imagery commonly displays scours of various sizes and orientations created by the keels of icebergs seabed sediments revealed by 3 5 khz sub bottom profiles are interpreted to consist primarily of ice contact sediments that in part are thinly mantled by draped water lain sediments the age of the lineations has not been established possibly their formation was coincident with an ice stream in the m clintock channel eastern victoria island region which formed an ice shelf in viscount melville sound that grounded on southern melville and byam martin islands at ca 10 4 9 6 14 c ka bp alternatively they could result from later glacial events

converging ice streams a new paradigm for reconstructions of the laurentide ice sheet in southern ontario and deposition of the oak ridges moraine geomorphometric analyses of high resolution 5 m digital elevation datasets shows that the greater toronto area and its immediate environs is built across the former till beds of two fast flowing ice streams the newly named the simcoe ice stream sis and the halton ice stream ois within the last laurentide ice sheet lis these formed during regional deglaciation sometime around 13 000 ybp and are directly analogous to fast flowing 3 km yr 1 ice streams in today s antarctic and greenland ice sheets their subglacial footprint in southern ontario consists of flow sets of highly elongated flow parallel till ridges up to 4 km in length and 100 m in width megascale glacial lineations msgls that converge on the oak ridges moraine orm from the north sis and south his orm is southern ontario s largest glacial landform extending from the niagara escarpment to kingston over some 160 km and was deposited as a series of en echelon glaciolacustrine fan deltas in a complexly evolving glaciolacustr

glacially streamlined hard and soft beds of the paleo ontario ice stream in southern ontario and new york state abstract an extensive tract of glacially streamlined terrain across a large part of southern ontario canada is recognized as the footprint of the paleo ontario ice stream ois within the easternmost great lakes sector of the last laurentide ice sheet the upstream part is a drumlinized and megagrooved hard bed underlain by cambro ordovician carbonates and sandstones subglacial plucking of jointed limestone on the lateral margins of drumlinized escarpment interfluves and rock drumlins generated a large flux of coarse debris within the ice base recorded by sporadic spreads of hummocky rubble moraine downstream the hard bed passes underneath a streamlined soft bed of till cored drift drumlins and megaridges of the classic peterborough and new york state drumlin fields the boundary between the two bed types is a 10 km wide mixed bed of isolated drift drumlins resting on drumlinized rock suggesting a common erosional origin spatial variation in the geomorphology of 2500 drift drumlins indicates that megaridges are clones resulting from the erosion and dissection of larger parent drumlins a large moraine system may mark the final collapse and melt of the ice stream accompanying abrupt flow switching of its margin

monitoring the geologic storage of carbon dioxide using multicomponent sar interferometry monitoring the geologic storage of carbon dioxide using multi component sar interferometry alessio rucci 1 d w vasco 2 and fabrizio novali 1 tele rilevamento europa milano italy berkeley laboratory university of california berkeley california 94720 summary combining interferometric synthetic aperture radar insar data from ascending and de scending orbits we estimate both quasi vertical and quasi east west displacements for a region in central algeria an area encompassing an active large scale carbon dioxide stor age project the in salah gas storage project the surface deformation associated with the injection into three horizontal wells is clearly visible in the insar estimates we find that the addition of the quasi horizontal displacement data enables us to discriminate between source models producing similar vertical displacements in particular predictions from a model consisting of a distribution of volume changes restricted to the reservoir depth interval satisfies the quasi vertical data but does not match the quasi east west displace ment data however aperture changes on sub vertical damage zones intersecting each of the injection wells give rise to displacements matching both the quasi east west and vertical components in all cases we can match the observations with the most significant volume and aperture changes in regions immediately surrounding the injection wells key words interferometry deformation inverse problem

balance velocities and measured properties of the antarctic ice sheet from a new compilation of gridded data for modelling this paper presents a new compilation of gridded data sets for three dimensional modeling of the antarctic ice sheet these are for surface elevation icethickness bedrock elevation and accumulation rate as interpolated on a 281 x 281 mesh with 20 km spacing and encompass all of the ice sheet and thesurrounding continental shelf data sources include the bamber digital elevation model from ers 1 radar altimeter data a redigitization of available ice thicknessdata the giovinetto accumulation data recent ice thickness data from british and german expeditions as well as accumulation data from german and norwegianexpeditions in particular new data were incorporated for the filchner ronne schelfeis and for dronning maud land arising from the epica pre site survey special attention was devoted to carefully match the various data sources both among themselves as across the grounding line and below the ice shelves toenable ice sheet expansion and retreat in dynamic situations as an application the balance flow is calculated over the entire ice sheet using a two dimensionalfinite difference scheme and compared with a previous assessment this brought to light the existence of ice streaming features extending well inland of the icesheet a detailed zoom over dronning maud land exhibits the general flow characteristics of interest for locating a future deep drilling site as a by product anupdated value of 26 4 x 106 km3 was obtained for the total volume of the ice sheet and ice shelves or equivalent to 61 1 m of global sea level rise after removalof the ice sheet and subsequent oceanic invasion and isostatic rebound the total accumulation over the grounded ice sheet including the antarctic peninsula is1924 gta 1 or between 5 and 20 higher than earlier estimates including all of the ice shelves the value is 2344 gta 1

palaeo ice streams in the foxe baffin sector of the laurentide ice sheet in this paper we describe mapping of palaeo ice streams in the foxe baffin sector of the laurentide ice sheet by means of geomorphological interpretation of high resolution satellite images our interpretations were guided by a glaciological inversion scheme aided by digital elevation models publicly available sonar surveys and field studies as a result we produced a map depicting the location geometry and relative temporal changes of palaeo ice streams and analysed their palaeoglaciological implications for the foxe baffin sector we conclude that in the period between the last glacial maximum and approximately 7 0 kyr bp the foxe baffin sector was largely drained by topographically controlled outlet glaciers and ice streams which were organized in a relatively stable pattern during this time large areas of melville peninsula and central baffin island were subject to cold based conditions between 7 0 and 6 0 kyr bp the foxe baffin sector collapsed catastrophically in the foxe basin after which its remnant portion became confined to baffin island during this collapse rapid successions of small transient ice streams occurred along wide loosely defined topographical corridors in two sectors of baffin island the presently available landform archive on emerged land is not sufficient to conclusively support the existence of fully scaled ice streams along the whole length of hudson strait as an alternative solution we propose that topographically controlled ice streams might have occurred along the deepest parts of hudson strait with attendant cold based ice zones on marginal areas and islands at the head of the strait

ice streams of the late wisconsin cordilleran ice sheet in western north america abstract the late wisconsin cordilleran ice sheet cis of western north america is thought to have reached its maximum extent 2 5 106 km2 as late at c 14 5 ka most 80 of the ice sheet s bed consists of high mountains but its core zone sited on plateaux of the intermontane belt of british columbia and coterminous parts of the usa shows broad swaths of subglacially streamlined rock and sediment broad scale mapping from new digital imagery data identifies three subglacial bed types 1 hard beds of variably streamlined bedrock 2 drumlinized soft beds of deformation till reworked from antecedent sediment and 3 mixed beds of variably streamlined bedrock protruding through drumlinized sediment drumlins on soft beds appear to be erosional features cut into till and antecedent sediments and identify the catchment areas of paleo ice streams expressed downglacier as flow sets of megascale glacial lineations msgls grooved and cloned drumlins appear to record the transition from drumlins to msgls the location of paleo ice streams reflects topographic funneling of ice from plateau surfaces through outlet valleys and a soft bed that sustained fast flow rock cut msgls are also present locally on the floors of outlet valleys cis disintegrated in

large scale reorganization and sedimentation of terrestrial ice streams during late wisconsinan laurentide ice sheet deglaciation glacial geomorphological mapping of shuttle radar topography mission srtm data from the western canadian prairies demonstrates that during the last late wisconsinan deglaciation of the laurentide ice sheet terrestrial ice streams underwent a major reorganization of their flow configuration this reorganization involved a 90 shift in flow direction and was accompanied by a corresponding increase in the influence of topography on streaming flow ice streams included both topographically confined and pure ice streams that flowed independent of topography streaming flow is recorded by suites of highly elongate 60 km long subglacial bedforms bounded sharply at their lateral margins by prominent moraines initial streaming flow was unconfined by topography but was replaced progressively and crosscut by younger topographically confined flows flow reorganization is inferred to have been caused by temporal and spatial variations in the interaction between frozen and thawed bed conditions with thinning and shutdown of one ice stream ultimately triggering initiation of others this highlights the role of internal glaciodynamically driven reorganization in triggering streaming flow within large ice sheets and shows that large scale flow reorganization can occur over the time scale of a single deglaciation in terrestrial ice streams

mega scale glacial lineations and cross cutting ice flow landforms landsat images reveal a previously unsuspected large scale pattern of streamlining within drift that is assumed to reflect former phases of ice flow such a glacial grain can be regarded as a landform assemblage comprised of a number of components drumlins and megaflutes form part of the pattern but in addition there are two previously undocumented ice moulded landform elements streamlined lineations of much greater proportions referred to as mega scale glacial lineations and a distinctive cross cutting topology within the grain the ice moulded landform assemblage is described and illustrated with reference to examples from canada possible modes of genesis of such landforms are discussed and their glaciological implications outlined the discovery of this pattern indicates the pervasive nature of subglacial deformation of sediment and demands a radical re interpretation of ice sheet dynamics

rock drumlins and megaflutes of the niagara escarpment ontario canada a hard bed landform assemblage cut by the saginaw huron ice stream abstract the late wisconsin c 18 000 ybp saginaw huron ice stream shis of the laurentide ice sheet was as much as 800 km long and 250 km wide in the great lakes basin of mid continent north america in its onset zone in the upper lake huron basin of ontario canada it flowed south from the high standing canadian shield to move over gently dipping ordovician and silurian dolostones devoid of glacial sediment cover the onset zone is recorded by a distinct hard bed landform assemblage across 3000 km2 of north facing escarpments niagara fossil hill and kagawong and dip slope pavements on the bruce peninsula and manitoulin island and the adjacent floor of lake huron a wide range of glacially streamlined rock landforms were carved into dolostones below fast flowing ice the largest are 30 km wide bullet shaped escarpment promontories that face upglacier superposed on these are swarms of rock drumlins up to 5 km wide with downglacier lengths of as much as 10 km promontories and drumlins record streaming of dirty basal ice around escarpment highs and create a distinct zig zag planform to the escarpments in turn down dip trailing edge dolostone pavements are corrugated by kilometre long megagrooves and megaflutes cut by basal ice flowing around resistant high standing bioherm mounds on dolostone bedding planes the geomorphology of the niagara escarpment does not primarily reflect a lengthy history of preglacial cenozoic fluvial erosion as classically argued but geologically brief episodes of accelerated abrasion and quarrying below ice streams within successive pleistocene ice sheets

catch a falling star meteorites and old ice a model for the process of meteorite concentration in blue ice regions of the antarctic ice sheet is proposed based on data from near the allan hills and the assumptions that both meteorite influx and glacial flow have been constant the meteorite influx is calculated to be 60 x 10 6 kilogram per square kilometer per year and the age of the exposed ice to be 0 to 600 000 years varying with distance from the allan hills these results are in line with other estimates of influx rate and with measurements of the terrestrial ages of the meteorites providing support for the assumption of steady flow and meteorite influx this may be the oldest sequence of ice in stratigraphic order yet discovered and the results imply that this part of the east antarctic ice sheet has been approximately steady during this time interval

evidence for large scale subglacial meltwater flood events in southern ontario and northern new york state flow line patterns constructed from the orientation of drumlin long axes are used to infer two major subglacial meltwater floods in southern ontario and northern new york state in this interpretation the flood waters of the first event the algonquin surged southward in the later ontarian event powerful floods streamed southwestward along the basins of lakes ontario and erie bedrock fluting upstream pointing noses on escarpments and tunnel channels give supporting evidence for the regional flood hypothesis regional distributions of drift thickness may be explained by this hypothesis

stratigraphic analysis of late wisconsin and holocene glaciolacustrine deposits exposed along the nottawasaga river southern ontario canada analysis of 56 outcrop exposures in cut banks along the nottawasaga river in southern simcoe county ontario canada has led to the identification of eight stratigraphic units su1 su8 that repre