flux of debris transported by ice at three alaskan tidewater glaciers the stability of tidewater terminus is controlled by glacial dynamics calving processes and sedimentary processes at the grounding line an investigation of grounding line sediment dynamics and morainal bank sediment budgets in glacier bay alaska u s a has yielded data that enable us to determine the debris fluxes of grand pacific margerie and muir glaciers debris flux ranges from 10 5 to 10 6 m 3 a 1 one to two orders of magnitude lower than the glacifluvial sediment fluxes 10 6 10 7 m 3 a 1 combined these fluxes represent the highest yields known for glacierized basins large debris fluxes reflect the combined effecrs of rapid glacier flow driven by the maritime climate of southeast alaska and highly erodible bedrock englacial debris distribution is affected by valley width and relief both of which control the availability of sediment the number of tributaries controls the distribution and volume of debris in englacial and supraglacial moraines at the terminus iceberg rafting removes up to two orders of magnitude more sediment from the ice proximal environment than is deposited by melt out or is dumped during calving events rough estimates of the sediment flux by deforming beds suggests that soft bed deformation may deliver up to an order of magnitude more sediment to the terminus than is released from within the glacier ice

climate tectonics and the morphology of the andes large scale topographic analyses show that hemisphere scale climate variations are a first order control on the morphology of the andes zonal atmospheric circulation in the southern hemisphere creates strong latitudinal precipitation gradients that when incorporated in a generalized index of erosion intensity predict strong gradients in erosion rates both along and across the andes cross range asymmetry width hypsometry and maximum elevation reflect gradients in both the erosion index and the relative dominance of fluvial glacial and tectonic processes and show that major morphologic features correlate with climatic regimes latitudinal gradients in inferred crustal thickening and structural shortening correspond to variations in predicted erosion potential indicating that like tectonics nonuniform erosion due to large scale climate patterns is a first order control on the topographic evolution of the andes

late cenozoic relief evolution under evolving climate a review abstract the present review paper is an attempt to summarize quantitative evidence of late cenozoic changes in topographic relief different meanings of the word relief as it is commonly used and detail the metrics used to quantify it we then specify methodological tools used to quantify relief change primarily low temperature thermochronometry and terrestrial cosmogenic nuclides and analyze published evidence for different regions our review first shows that relief changes and rates of changes are more important at mid than high or low latitudes and appear to be insensitive to mean precipitation rates it also show that relief change is positive relief increases in most of the reported cases 80 we subsequently define two functional relationships between relief and erosion depending on the chosen definition of relief and propose a conceptual model of landscape memory we conclude following others that erosion rates depend non linearly on relief evolution itself being a function of the spatial distribution and rates of erosion the relief increases documented in this review may be to erosion rate increases during the same timescales lastly we discuss the importance of glacial and periglacial processes on late cenozoic relief and erosion rate changes and stress the importance of frost shattering and glacial erosion at mid and high latitudes

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

laboratory measurements of elastic properties of carbonate rocks during injection of reactive co2 saturated water 1 to investigate the coupled physical and chemical effects of injecting co2 rich water into carbonate rock samples we monitor the elastic and transport properties of six carbonate rocks along with the calcium content and ph of the pore fluid under constant confining pressure carbonate samples range from calcite limestones containing dolomite to pure calcite mudstones which allow us to study how mineral composition and microstructure affect the magnitude of the observed changes the elastic properties of both the saturated and dry rock i e rock frame show a gradual loss of sstrength upon injection as testified by the continuous decrease in the dry p and s wave velocity and by proxy the bulk and shear moduli the magnitude of the observed changes in the elastic properties varies among the samples with a maximum relative change of 24 7 871 m s and 21 2 443 m s in p and s wave velocities respectively the decrease is also accompanied by a relative increase in permeability up to 495 and porosity up to 19 the observed changes likely derive from a change in microstructure which is monitored over time via scanning electron microscopy the variation in porosity results from two competing and interdependent processes the chemical dissolution of calcite and the resulting mechanical compaction under pressure the results of this study show that upon injection of fluids that are in chemical disequilibrium with the hosting rock the variation of the elastic properties cannot be described by existing rock physics models

gassmann s fluid substitution and shear modulus variability in carbonates at laboratory seismic and ultrasonic frequencies carbonates have become important targets for rock property research in recent years because they represent many of themajoroilandgasreservoirsintheworld someareundergoing enhanced oil recovery most laboratory studies to understand fluid and pressure effects on reservoir rocks have been performed on sandstones but applying relations developed for sandstones to carbonates is problematic at best we measure in the laboratory nine carbonate samples from the same reservoir at seismic 3 3000 hz and ultrasonic 0 8 mhz frequencies samples are measured dry humidified and saturated with liquid butane and brine our carbonate samples showed typical changes in moduli as a function of porosity andfluid saturation however we explore the applicability of gassmann s theory on limestone and dolomite rocks in the context of shear and bulk modulus dispersion andgassmann stheoryassumptions forourcarbonatesetat high differential pressures and seismic frequencies the bulk modulus of rocks with high aspect ratio pores and dolomite mineralogy is predicted by gassmann s relation we also explore in detail some of the assumptions of gassmann s relation especiallyrock framesensitivitytofluidsaturation our carbonate samples show rock shear modulus change from dry to brine saturation conditions and we investigate several rock fluid mechanisms responsible for this change to our knowledge these are the first controlled laboratory experimentsoncarbonatesintheseismicfrequencyrange

review of erosion dynamics along the major n s climatic gradient in chile and perspectives abstract chile is an elongated country running in a north south direction for more than 30 along a subduction zone its climate is progressively wetter and colder from north to south this particular geography has been used positively by a growing number of studies to better understand the relationships between erosion processes and climate land use slope tectonics volcanism etc here we review the erosion rates factors and dynamics over millennial to daily periods reported in the literature in addition 21 new catchment mean erosion rates suspended sediment and 10be are provided and previous suspended sediment derived erosion rates are updated a total of 485 local and catchment mean erosion rates are reported erosion rates vary between some of the smallest values on earth 10 5 mm a to moderate values 0 5 mm a compared to other active ranges this review highlights strong limitations concerning the quantification of local erosion factors because of uncertainties in sampling point location slope and rainfall data for the mean erosion rates e for the millennial and decennial catchments a model of the form e s 1 s 0 6 2 r with 0 3 0 8 accounts for 40 to 70 of the erosion variance confirming a primary role of slope s compared to precipitation rate r over this time scale over the long term this review points to the long 5 to 10 ma response time of rivers to surface uplift in north central arid chile over millennia data provide evidence for the progressive contribution of extreme erosion events to millennial averages for drier climates as well as the link between glacier erosion and glacier sliding velocity in this period of time a discrepancy exists between the long term offshore sedimentological record and continental decennial or millennial erosion data for which no single explanation appears still little information is available concerning the magnitude of variation of millennial erosion rates over centuries data show the variable role of groundwater in the dynamics of suspended load and document a decrease in erosion over hundreds of years probably associated with historical harvesting

denudation and deformation in a glaciated orogenic wedge the st elias orogen alaska apatite u th he dating from the st elias orogen in southern alaska illustrates a potential association between long term denudation and glacier sliding cooling ages as young as 0 4 ma exhumation 4 5 mm yr are concentrated in a narrow band near the glacier equilibrium line altitude ela front where mean quaternary ela intersects the windward flank of the orogen this band of denudation is not correlated with individual faults structural trends or known concentrations of precipitation and we propose that it is produced by focused glacier sliding at or near the ela front this implies that long term glacial erosion is a maximum at ela which corroborates model predictions that glaciers and climate can control the pattern of crust removal from orogens denudation rates do not covary with fluctuations in glacier size along the ela front suggesting that small glaciers are capable of keeping pace with incision by larger ones and tectonic rock uplift ice discharge may thus play a critical but complex role in excavating glaciated orogens

the relative efficacy of fluvial and glacial erosion over modern to orogenic timescales it has been debated whether rivers or glaciers are more effective agents of erosion a global compilation of erosion rates reveals that both are capable of generating rates of erosion that match or exceed the highest rates of rock uplift since the late nineteenth century it has been debated whether rivers or glaciers are more effective agents of erosion1 the dramatic landscapes associated with glaciated terrain have often led to the argument that glaciers are more erosive than rivers and recent studies have documented the topographic signature of an ice controlled limit of mountain height known as the glacial buzz saw 2 3 here we present a new global compilation of erosion rates which questions the conventional view of glaciers and erosion in regions of rapid tectonic uplift erosion rates from rivers and glaciers both range from 1 to over 10 mm yr 1 indicating that both are capable of generating erosion rates matching or exceeding the highest rates of rock uplift moreover a comparison of erosion rates over timescales ranging from 101 to 107 years indicates that glacial erosion tends to decrease by one to two orders of magnitude over glacial cycles whereas fluvial erosion rates show no apparent dependence on time we conclude that tectonics controls rates of both fluvial and glacial erosion over millennial and longer timescales and that the highest rates of erosion 10 mm yr 1 generally result from a transient response to disturbance by volcanic eruptions climate change and modern agriculture

groundwater response to the tide in wetlands observations from the gillman marshes south australia we present results from a series of piezometers installed in the foreshore flat and mangrove environments of the gillman marshes south australia in an interdisciplinary study of the propagation of the ocean tide into the coastal aquifers a unique feature of the analysis is that all water level records were harmonically analysed so that the behaviour of the four major tidal constituents could be independently examined the main findings were that 1 the decay of the groundwater tide in the coastal aquifers was greater than that predicted by the ferris solution a theoretical model has been developed and applied to the study site the model suggests that this behaviour is due to the occurrence of a time delay in the darcian response in the shelly and muddy sand substrate 2 when the tide is incident over a gently sloping bank the time delay in response gives rise to a spiked signal in which high water is confined to a small fraction of the tidal cycle and 3 at the coastal interface tidal propagation across a sloping bank causes a rise in the water table relative to mean sea level which is proportional to the variance of tidal elevation and inversely proportional to the decay constant of the groundwater tide the model developed in this study is also applicable to other coastal groundwater systems with tidal influence

sediment evacuation and glacial erosion rates at a small alpine glacier 1 glacial erosion is known to be driven by sliding which occurs in brief episodes in the melt season what is not known is how well this sliding history is reflected in the sediment output from a glacier and to what degree temporary sediment storage in the glacier smoothes the history of sediment production we document sediment evacuation rates for three seasons at bench glacier a small temperate alpine glacier in the chugach range of alaska two lines of evidence suggest that subglacial sediment storage is small strong hysteresis in the relationship between sediment and water discharge argues for sediment exhaustion from the subglacial system on seasonal and flood event timescales uplift of the glacier surface during periods of enhanced basal motion reflects intimate contact of the glacier sole with up glacier inclined stoss slopes of bedrock bumps sediment evacuation rates at bench glacier should therefore closely track glacial erosion rates over annual timescales much of the sediment emerges in a major pulse that closely follows the termination of enhanced sliding each year suggesting that the conduits and well connected cavities that allowed removal of englacial water to terminate sliding also promoted efficient transport of sediment this small glacier efficiently modifies the landscape lowering its bed by 1 2 mm yr while sliding only 1 2 m yr our sparse measurements of instantaneous bed load discharge average 41 of concurrent suspended sediment discharge assuming that half of the suspended load derives from abrasion of subglacially quarried clasts roughly two thirds of the sediment evacuated can be attributed to quarrying

glacial and tectonic control on fjord morphology and sediment deposition in the magellan region 53 s chile in the patagonian andes erosion by temperate pleistocene glaciers has produced a deeply incised fjord system in which glacial and non glacial sedimentswere deposited since the late glacial glacier retreat so far fjord bathymetry and structures in the sediment infill were widely unexplored here we report the results of an investigation of morphology and sediment characteristics of a 250 km long fjord transect across the southernmost andes 53 s using multibeam and parametric echosounder data and sediment cores subaquatic morphology reveals continuity of on land tectonic lineaments mapped using field and remote sensing data our results indicate that glacial erosion and fjord orientation are strongly controlled by three major strike slip fault zones furthermore erosion is partly controlled by older and or reactivated fracture zones as well as by differential resistance of the basement units to denudation basement morphology is regionally superimposed by late glacial and holocene subaquatic moraines which are associated to known glacier advances the moraines preferentially occur on basement highs which constrained the glacier flows this suggests that the extent of glacier advances was also controlled by basement morphology subaquatic mass flows fluid vent sites as well as distinct late glacial and holocene sediment infills have furthermore modified fjord bathymetry in the western fjord system close to the strait of magellan subaquatic terraces occur in 20 to 30 m water depth providing an important tag for proglacial lake level during the late glacial

analysis of high resolution x ray computed tomography images of bentheim sandstone under elevated confining pressures a sample of bentheim sandstone was characterized using high resolution threedimensional x ray microscopy at two different confining pressures of 1 mpa and 20 mpa the two recordings can be directly compared with each other because the same sample volume was imaged in either case after image processing a porosity reduction from 21 92 to 21 76 can be deduced from the segmented data with voxel based numerical simulation techniques we determined apparent hydraulic transport properties and effective elastic properties these results were compared with laboratory measurements using reference samples laboratory and computed volumes as well as hydraulic transport properties agree fairly well to achieve a reasonable agreement for the effective elastic properties we define pressure dependent grain contact zones in addition to mineral phases in the digital rock images from that we derive a specific digital rock physics template resulting in a very good agreement between laboratory data and simulations the digital rock physics template aims to contribute to a more standardized approach of x ray computed tomography data analysis as a tool to determine and predict elastic rock properties

rapid and synchronous ice dynamic changes in east greenland two major outlet glaciers in east greenland have suddenly begun to accelerate and retreat the speeds of kangerdlugssuaq and helheim remained steady during the 1990s despite progressive and substantial thinning but have abruptly increased within the last two years more than doubling ice flux to the ocean had it been an isolated example the comparable 1998 speed up of jakobshavn isbra in west greenland might have been explained simply by its chance retreat past a pinning point now that two further greenland outlets have exhibited similar behavior a common process seems likely a remarkable correspondence in the inter annual patterns of speed and ice front variation between kangerdlugssuaq and helheim implies a significant sensitivity to regional environmental factors the period of continued warming and thinning appears to have primed these glaciers for a step change in dynamics not included in current models we should expect further greenland outlet glaciers to follow suit copyright 2006 by the american geophysical union

changes of shear moduli in carbonate rocks implications for gassmann applicability in laboratory experiments we measured the saturation effects on the acoustic properties in carbonates and the results question some theoretical assumptions in particular these laboratory experiments under dry and wet conditions show that shear moduli do not remain constant during saturation this change in shear modulus puts gassmann s assumption of a constant shear modulus into question and also explains why velocities predicted with the gassmann equation can be lower or higher than measured velocities

pleistocene glaciation in the southern lake district of chile relative age criteria permit deposits of successive andean glacier advances in the southern lake district of chile to be divided into four mappable drift sheets the oldest two of which overlie tertiary bedrock along the eastern flank of the cordillera de la costa only the youngest drift llanquihue is datable by radiocarbon during the most extensive ice advance of the last glaciation the lago llanquihue glacier was about 95 km long and reached an estimated maximum thickness of between 1000 and 1300 m glacier equilibrium lines at that time lay about 1000 m below their present level and rose eastward with a gradient of about 5 m km successive ice advances in the lago llanquihue basin which resulted in construction of end moraines and associated outwash plains beyond the lake margin culminated sometime before about 20 000 yr ago and between 20 000 and 19 000 yr ago a later readvance inferred from the sedimentary record of lake level fluctuations in the basin had begun by about 15 000 yr ago and culminated shortly after 13 000 yr ago a comparable but less closely dated record of ice advances is found northwest of seno reloncavi and on isla chiloe deglaciation following the latest advance is likely to have been rapid for the major glacier lobes fronted on deep water bodies that would have promoted extensive calving

relationship between tidewater glacier calving velocity and water depth at the calving front an analysis of the relationship between iceberg calving rates and water depth has been completed for 22 tidewater glaciers a linear relationship provides reasonable accuracy with a correlation coefficient of 0 85 for all tidewater glaciers examined whether they be polar or temperate the polar glaciers have a slightly lower calving rate for a given water depth this relationship indicates a lower calving rate for water depths over 50 m than determined by brown and others 1982 it is based only on glaciers or ice streams and cannot be applied to ice shelves

characteristics of the bed of the lower columbia glacier alaska an unplanned but unique experiment has given an in situ measurement of the strength of deforming subglacial till under the central region of a major valley glacier we report on both planned and unplanned borehole investigations of the subglacial shear zone of columbia glacier southeast alaska basal samples coring and down hole water samples show that the fiord filling lower reach of the glacier is underlain by a thin 7 cm veneer of rock debris fluidized debris intruded at least a meter up the borehole at a higher site 13 km from the terminus and above the fiord probing samples and the bending of a drill stem which was stuck in the basal zone for 5 days showed that the basal till layer was 65 cm thick horizontal velocity of the till decreased monotonically downward from the ice till interface till at the interface moved with the ice velocity plastic deformation of the drill stem gave an estimate of the strength of the basal till which is normally described as a viscoplastic material if the till is assumed to be either perfectly plastic or newtonian viscous then the strengths are as follows the plastic yield strength of the till was 5 5 10 3 pa 0 055 bar with an upper bound of 1 3 10 4 pa 0 13 bar while the nominal viscosity was of the order of 2 10 8 pa s 2 10 9 poise with an upper bound of 5 10 8 pa s in neither case is the till strength enough to supply the bulk basal shear stress to resist the glacier flow

anomalous glacier responses to 20th century climatic changes in darwin cordillera southern chile there is an asymmetric pattern response of glaciers in darwin cordillera 54 55 s 69 71 w to the climate of the 20th century this asymmetry is suggested here as a cause of an increased wind activity which has a pronounced orographic effect although climatic records for the last 50 years show a warming trend as well as no trend in precipitation in the area some glaciers are advancing the area is characterized by strong climatic gradients with high rates of precipitation on the southwestern side of the range and dry conditions on the northern side glaciers on the northern and eastern sides show a general trend of receding fronts with a few exceptions these glaciers have gradually and uninterruptedly been shrinking since the turn of the century on the southern rim the present extents of some glaciers are similar to their 20th century maximum extents these are in turn similar or close to the holocene maximum the most extreme sites are the glaciers on either side of mount darwin which is 2469 m high the north facing glacier ventisquero marinelli has retreated several hundred metres per year over the last two decades while the south facing glaciers in the pahia pia basin have advanced during the same period in this study the frontal changes over the last 50 years of 20 glaciers have been analysed aerial photographs verticals from 1943 and 1984 have been used as well as oblique aerial photographs from 1993 the general result is that glaciers with accumulation areas facing south and west show somewhat stable fronts while glaciers facing east and north show receding fronts

estimation of rock frame weakening using time lapse crosswell the frio brine pilot project abstractco2 injection into subsurface reservoirs leads to pressure and saturation changes furthermore co2 brine minerals interaction could result in dissolution or reprecipitation of rock frame forming minerals observed time lapse seismic associated with co2 injection into poorly consolidated sandstone at the frio co2 injection site texas usa could not be predicted using classical rock physics models i e models involving elastic changes in the rock frame due to saturations and or pressures changes only and assuming no changes in the rock microstructure that and the changes in the fluid chemistry after co2 injection suggests that the assumption of a constant rock microstructure might be violated using high resolution time lapse crosswell data we have developed a methodology for estimating changes in the rock frame by quantifying the rock frame drained moduli before and after co2 injection based on rock microstructure diagnostics we found that the changes in the drained frame elastic prope

timescale dependence of glacial erosion rates a case study of marinelli glacier cordillera darwin southern patagonia 1 erosion rates have been estimated for a number of glaciated basins around the world mostly based on modern observations last few decades of sediment fluxes to fjords we use time constrained sediment volumes delivered by marinelli glacier 55 s an outlet glacier of the cordillera darwin ice cap southern patagonian andes tierra del fuego to determine erosion rates across different timescales sediment volumes are derived using a dense grid of high and low frequency single channel seismic data and swath bathymetry data along with piston and kasten cores our results show dramatic differences in erosion rates over different timescales erosion rates at marinelli glacier diminish about 80 or by factor of 5 with each ten fold increase in the time span over which erosion rates are averaged 29 3 mm yr for the last 45 years 5 3 mm yr for the last 364 years and 0 5 mm yr for the last 12 500 years these results indicate that modern sediment yields and erosion rates from temperate tidewater glaciers can exceed long term values over the time of deglaciation after the last glacial maximum centennial and millennial timescales by up to 2 orders of magnitude in view of the low exhumation rates of cordillera darwin 0 07 mm yr average for the last 30 myr modern erosion rates could be up to 3 orders of magnitude higher than rates over geological time we conclude that the pattern of erosion rate variation with time reflects the sensitivity of glaciers to climate variability

an experimental study of acoustic responses on the injection of supercritical co2 into sandstones from the otway basin quantitative knowledge of the acoustic response of rock from an injection site on supercritical co2 scco2 saturation is crucial for understanding the feasibility of time lapse seismic monitoring of co2 plume migration a suite of shaley sandstones from the injection interval of the crc 2 well otway basin australia is tested to reveal the effects of supercritical co2 injection on acoustic responses co2 is first injected into dry samples flushed out with brine and then injected again into brine saturated samples such a suite of experiments allows us to obtain acoustic velocities of the samples for a wide range of co2 brine saturations from 0 to 100 on injection of scco2 into brine saturated samples the rocks exhibit a decrease of compressional velocities by about 7 with the increase of co2 saturation from 0 to a maximum of about 50 anisotropy of the shaley sandstones from the otway basin must be taken into account as the difference in the velocities normal and parallel to bedding is comparable with the perturbation due to co2 injection and the samples of different orientations exhibit transition from gassmann hill to gassmann wood bound at different scco2 saturations changes of the dry samples before and after the co2 injection if any are not traceable by acoustic methods

magellan strait part of a neogene rift system the magellan strait joins the atlantic and pacific oceans separating tierra del fuego from southernmost continental south america the strait cuts both the andean cordillera and the magellan foreland basin other arms of the sea intrude the axial zone of the magellan basin these depressions have long been interpreted as glacial valleys on the basis of landsat images digital topography and field data we interpret the depressions as rifts or half rifts in general active rifts developed within foreland basins are unusual but in patagonia they are consistent with regional deformation and its plate tectonic setting during the neogene

velocities of compressional and shear waves in limestones carbonate rocks are important hydrocarbon reservoir rocks with complex textures and petrophysical properties porosity and permeability mainly resulting from various diagenetic processes compaction dissolution precipitation cementation etc these complexities make prediction of reservoir characteristics e g porosity and permeability from their seismic properties very difficult to explore the relationship between the seismic petrophysical and geological properties ultrasonic compressional and shear wave velocity measurements were made under a simulated in situ condition of pressure 50 mpa hydrostatic effective pressure at frequencies of approximately 0 85 mhz and 0 7 mhz respectively using a pulse echo method the measurements were made both in vacuum dry and fully saturated conditions in oolitic limestones of the great oolite formation of southern england some of the rocks were fully saturated with oil the acoustic measurements were supplemented by porosity and permeability measurements petrological and pore geometry studies of resin impregnated polished thin sections x ray diffraction analyses and scanning electron microscope studies to investigate submicroscopic textures and micropores it is shown that the compressional and shear wave velocities vp and vs respectively decrease with increasing porosity and that vp decreases approximately twice as fast as vs the systematic differences in pore structures e g the aspect ratio of the limestones produce large residuals in the velocity versus porosity relationship it is demonstrated that the velocity versus porosity relationship can be improved by removing the pore structure dependent variations from the residuals the introduction of water into the pore space decreases the shear moduli of the rocks by about 2 gpa suggesting that there exists a fluid matrix interaction at grain contacts which reduces the rigidity the predicted biot gassmann velocity values are greater than the measured velocity values due to the rock fluid interaction this is not accounted for in the biot gassmann velocity models and velocity dispersion due to a local flow mechanism the velocities predicted by the raymer and time average relationships overestimated the measured velocities even more than the biot model

observed latitudinal variations in erosion as a function of glacier dynamics erosion and velocity data from 15 outlet glaciers covering temperate to polar glacier thermal regimes from patagonia to the antarctic peninsula reveal that over the past century the basin averaged erosion rates vary by three orders of magnitude as a function of climate across this latitudinal transect glacial erosion plays an important role in shaping the earth s landscape but attempts to quantify the long term effect of the erosion of glaciers have proven inclusive and contradictory glacial erosion rates are expected to decrease towards the poles where lower temperatures limit meltwater production thereby reducing glacial sliding erosion and sediment transfer this study presents erosion and velocity data from 15 outlet glaciers covering temperate to polar glacier thermal regimes from patagonia to the antarctic peninsula the dataset reveals that during the past century the basin averaged erosion rates vary by three orders of magnitude as a function of climate across this latitudinal transect the authors suggest that climate and the glacier thermal regime exert more control over erosion rates than the extent of ice cover ice flux or sliding speeds glacial erosion is fundamental to our understanding of the role of cenozoic era climate change in the development of topography worldwide yet the factors that control the rate of erosion by ice remain poorly understood in many tectonically active mountain ranges glaciers have been inferred to be highly erosive and conditions of glaciation are used to explain both the marked relief typical of alpine settings and the limit on mountain heights above the snowline that is the glacial buzzsaw1 in other high latitude regions glacial erosion is presumed to be minimal where a mantle of cold ice effectively protects landscapes from erosion2 3 4 glacial erosion rates are expected to increase with decreasing latitude owing to the climatic control on basal temperature and the production of meltwater which promotes glacial sliding erosion and sediment transfer this relationship between climate glacier dynamics and erosion rate is the focus of recent numerical modelling5 6 7 8 yet it is qualitative and lacks an empirical database here we present a comprehensive data set that permits explicit examination of the factors controlling glacier erosion across climatic regimes we report contemporary ice fluxes sliding speeds and erosion rates inferred from sediment yields from 15 outlet glaciers spanning 19 degrees of latitude from patagonia to the antarctic peninsula although this broad region has a relatively uniform tectonic and geologic history the thermal regimes of its glaciers range from temperate to polar we find that basin averaged erosion rates vary by three orders of magnitude over this latitudinal transect our findings imply that climate and the glacier thermal regime control erosion rates more than do extent of ice cover ice flux or sliding speeds

laboratory measurements of the acoustic and transport properties of carbonate rocks and their link with the amount of microcrystalline matrix laboratory data and computer tomography ct scan image analysis of carbonate rocks were combined demonstrating a quantitative link between acoustic and transport properties the fraction of microcrystalline calcite micrite in the matrix and the grain to micrite matrix ratio samples from the monte acuto formation gargano italy a transgressive system tract tst whose microstructure ranges from basal pelagic mudstones to coarse calciturbidites were analyzed results indicate that high micrite rocks with low grain to micrite matrix ratios typical of low energy depositional settings are relatively stiffer and more impermeable in contrast lower amounts of micrite due to high energy depositional settings or its removal from intergranular macropores by progressive leaching of the matrix leads to high grain to micrite matrix ratios this process will increase porosity and reduce rock stiffness both of which reduce velocity decreasing micrite content correlates well with increasing macroporosity

holocene glacier fluctuations on the northern flank of cordillera darwin southernmost south america abstract records of past variability afford context for evaluating present day glacier behavior and for testing hypotheses of climate change here we use 69 radiocarbon dates of wood and other organic materials in association with glacial deposits to document the behavior of ventisqueros marinelli and brooks in cordillera darwin over the past 17 000 years recession from the last glacial maximum was early with most occurring prior to 17 000 yr bp any glacial resurgence during the antarctic cold reversal must have terminated within the bounds of holocene ice fluctuations by early holocene time ventisquero marinelli had retreated such that it was no more extensive than it was in ad 1992 we identify several subsequent glacier readvances but also note long periods of restricted ice extent particularly in the mid holocene there were times when holocene glaciers must have been smaller than at present our new record from marinelli shows similarities to other reconstructions of holocene glacier variation from southern south america such as at mt sarmiento and the south patagonian icefield suggesting an underlying climate signal the overall implication is of substantial early holocene deglaciation followed by repeated advances interspersed with periods of recession when ice extent was smaller than at present this general pattern of glacier behavior appears to differ from that of new zealand s southern alps and points to the value of a geographic spread of datasets to elucidate the pattern of southern hemisphere climate during the holocene

organic maturity elastic properties and textural characteristics of self resourcing reservoirs abstractorganic rich rocks have long been recognized as source rocks for clastic reservoirs but more recently they have gained importance as reservoirs however the processes of kerogen maturation and hydrocarbon transport and storage are still poorly understood some empirical relations have been developed to relate the increase in elastic modulus with increasing maturity a systematic study of the cause for this increase in elastic modulus is still lacking and information about seismic and mechanical properties of kerogen and its alteration products is scarce consequently any rock models must rely on anecdotal or extrapolated data about various types of kerogen our experiments address this paucity of data by grain scale modulus measurements coupled with careful field emission scanning electron microscopy fesem microstructural assessments on organic rich bakken formation shale samples with a range of maturities carefully acquired and detailed fesem images help to understand the microstructural c

effect of temperature and pore fluid on the strength of porous limestone the presence of pore fluid in rocks generally reduces brittle strength the role of water weakening in porous carbonate rocks and the effect of enhanced deformation on concomitant transport property evolution are poorly understood the interaction between pore fluid and deformation mechanisms in carbonate rocks is complicated by crystal plasticity and solubility in calcite at low temperatures and pressures to explore this system we perform conventional triaxial deformation experiments on indiana limestone 16 porosity over a range of temperatures 23 75 c and effective confining pressures 10 50 mpa samples are deformed with pore fluids of different saturation states with respect to calcite host rock samples tend to fail by distributed deformation sample permeability is reduced by up to an order of magnitude during deformation even in samples exhibiting dilatancy compactive yield strength associated with shear enhanced compaction is greatly reduced in saturated samples compared to dry samples dilatancy is suppressed and compaction enhanced at elevated pressures greater weakening effects are observed when pore fluid is far from equilibrium with carbonate rock observed weakening results from the interaction between microcracking mechanical twinning and pressure solution

long term glacial erosion of active mountain belts example of the chugach st elias range alaska an emerging paradigm that equates glaciers to buzz saws of exceptional erosional efficiency has been strengthened by short term 10 2 yr sediment yields from southern alaska new low temperature cooling ages from this area the glaciated chugach st elias mountains constrain long term 10 6 yr exhumation rates vertically averaged exhumation rates reach 3 mm yr but are an order of magnitude lower than rates based on short term sediment yields whereas these exhumation rates are not exceptional for oro genic belts denudation patterns are strongly correlated with the distribution of glaciers and erosion appears to keep pace with con vergence and uplift these findings imply a coupling between gla cially dominated erosion and tectonics

an experimental study of solid matrix weakening in water saturated savonnieres limestone petrophysical properties of carbonate reservoirs are less predictable than that of siliciclastic reservoirs one of the main reasons for this is the physical and chemical interactions of carbonate rocks with pore fluids such interactions can significantly change the elastic properties of the rock matrix and grains making the applicability of gassmann s fluid substitution procedure debatable this study is an attempt to understand the mechanisms of fluid rock interactions and the influence of these interactions on elastic parameters of carbonates we performed precise indentation tests on savonni eres limestone at a microscale level under dry distilled water and n decane saturated conditions our experiments display softening of the rock matrix after water saturation we have found that mainly the ooid cortices peloid nuclei and prismatic intergranular cement are affected by water flooding we also observed a shear modulus reduction in savonni eres limestone in an experiment performed at ultrasonic frequencies one of the most important results obtained in our experimental study is that the gassmann fluid substitution theory might not always be applicable to predict the elastic moduli of fluid saturated limestones

proglacial erosion rates and processes in a glacierized catchment in the swiss alps in the swiss alps climatic changes have not only caused glacier retreat but also likely increased sedimentation downstream of glaciers this material either originates from below the glacier or from periglacial environments exposed as glaciers retreat and often consist of easily erodible sediment griesgletscher s catchment in the swiss alps was examined to quantify erosion in theproglacial area possible hydrological drivers and contributions of the sub and periglacial sources digital elevation models created from annual aerial photographs were subtracted to determine annual volume changes in the proglacial area from 1986 to 2014 these data show a strong increase in proglacial erosion in the decade prior to 2012 coincident with increasing proglacial area size however examination of the gradient between discharge and sediment evacuation and the modeled sediment transport could suggest that the proglacial area began to stabilize and sediment supply is limited the large influx of sediment into the proglacial reservoir which is roughly 2 5 times greater than the amount of sediment eroded from the proglacial area demonstrates the importance of subglacial erosion to the catchment s sediment budget although far more sediment originates subglacially erosion rates in the proglacial area are over 50 times greater than the rest of the catchment in turn both sub and periglacial processes in addition to constraining sediment supply must be considered forassessing future sediment dynamics as glacier area shrinks and proglacial areas grow

forced imbibition into a limestone measuring p wave velocity and water saturation dependence on injection rate quantitative interpretation of time lapse seismic data requires knowledge of the relationship between elastic wave velocities and fluid saturation this relationship is not unique but depends on the spatial distribution of the fluid in the pore space of the rock in turn the fluid distribution depends on the injection rate to study this dependency forced imbibition experiments with variable injection rates have been performed on an air dry limestone sample water was injected into a cylindrical sample and was monitored by x ray computed tomography and ultrasonic timeof flight measurements across the sample the measurements show that the p wave velocity decreases well before the saturation front approaches the ultrasonic raypath this decrease is followed by an increase as the saturation front crosses the raypath the observed patterns of the acoustic response and water saturation as functions of the injection rate are consistent with previous observations on sandstone the results confirm that the injection rate has significant influence on fluid distribution and the corresponding acoustic response the complexity of the acoustic response that is not monotonic with changes in saturation and which at the same saturation varies between hydrostatic conditions and states of dynamic fluid flow may have implications for the interpretation of time lapse seismic responses

mechanical and hydrologic basis for the rapid motion of a large tidewater glacier 1 observations the data presented in part 1 of this paper meier et al this issue are here used to assess the role of water input output water storage and basal water pressure in the rapid movement of columbia glacier alaska consistently high basal water pressures mostly in the range from 300 kpa below to 100 kpa above the ice overburden pressure are responsible in an overall way for the high glacier flow velocities 3 5 9 m d 1 which are due mainly to rapid basal sliding caused by the high water pressure diurnal fluctuation in basal water pressure is accompanied by fluctuation in sliding velocity in what appears to be a direct causal relation at the upglacier observation site the water pressure fluctuation tracks the time integrated water input less a steady withdrawal as expected for the diurnally fluctuating storage of water in the glacier far from the terminus at the downglacier site the situation is more complex diurnal peaks in water level which are directly related to intraglacial water storage as well as to basal water pressure are shifted forward in time by 4 hours probably as a result of the effect of diurnal fluctuation in water output from the glacier which affects the local water storage fluctuations near the terminus because of the forward shift in the basal water pressure peaks which at the downglacier site lead the velocity peaks by 6 hours a mechanical connection between water pressure and sliding there would have to involve a 6 hour quarter period delay however the nearly identical nature of the diurnal fluctuations in velocity at the two sites argues for a single consistent control mechanism at both sites the velocity variations in nondiurnal speed up events caused by extra input of water on the longer timescale of several days are only obscurely if at all correlated with variations in basal water pressure but correlate well with water storage in the glacier it appears that small variations in water pressure 100 kpa sufficient to produce the observed velocity variations 15 30 are mostly masked by pressure fluctuations caused by spontaneous local reorganizations of the basal water conduit system on a spatial scale much smaller than the longitudinal coupling length over which basal water pressure is effectively averaged in determining the sliding velocity at the achieved level of observation the clearest though not complication free control variable for the sliding velocity variations is basal water storage by cavitation at the glacier bed

influence of rapid glacial retreat on the rate of erosion by tidewater glaciers glacial erosion rates inferred from total sediment budgets in recently deglaciated fjords which are the highest reported erosion rates worldwide have received considerable attention in fields as diverse as tectonics glacial sedimentation and climate these record rates however are representative only of tidewater glaciers during their extensive retreat of the post little ice age period erosion rates averaged over glacial interglacial cycles and longer periods are likely to be substantially smaller we examine the influence of retreat rate on sediment yields from tidewater glaciers by reconstructing the history of sediment output from retreating glaciers necessary to produce sediment packages observed in contemporary fjords using a simple numerical model of proglacial sedimentation in front of a retreating glacier seismic profiles of proglacial sediments and the history of terminus retreat of muir glacier glacier bay alaska we calculate the sediment flux as a function of time from this glacier between 1900 and 1979 and conclude that sediment flux scales with retreat rate the corresponding basin wide erosion rate during this 79 yr period averages 37 mm yr and exceeds long term erosion rates by a factor of 5 1 for muir glacier and by inference for other calving glaciers the general drastic retreat and the marked regional drawdown of ice since the little ice age are both linked to unusually rapid calving and fast ice motion which is conducive to rapid erosion

influence of a glacial buzzsaw on the height and morphology of the cascade range in central washington state usa abstract analysis of climatic and topographic evidence from the cascade range of washington state indicates that glacial erosion limits the height and controls the morphology of this range glacial erosion linked to long term spatial gradients in the ela created a tilted planar zone of 373 cirques across the central part of the range peaks and ridges now rise 600 m above this zone hypsometric analysis of the region shows that the proportion of land area above the cirques drops sharply and mean slopes 30 indicate that the areas above the cirques may be at or near threshold steepness the mean plus 1 relief of individual cirque basins 570 m corresponds to the 600 m envelope above which peaks rarely rise the summit altitudes are set by a combination of higher rates of glacial and paraglacial erosion above the ela and enhanced hillslope processes due to the creation of steep topography on the high precipitation western flank of the cascades the dominance of glacial and hillslope erosion at altitudes at and above the ela may explain the lack of a correspondence between stream power erosion models and measured exhumation rates from apatite u th he thermochronometry

erosion rates during rapid deglaciation in icy bay alaska 1 contemporary glacial erosion rates based on sediment yields in southeast alaska merit considerable attention because they are unsurpassed worldwide and they significantly exceed long term exhumation rates in the region two issues are likely to contribute to these high rates contemporary sediment yields in fjords 1 have generally been overestimated by failing to account for the considerable input of subaerially derived material and 2 are exceptionally high because tidewater glaciers in southeast alaska have been anomalously dynamic and erosive during the past century of rapid retreat to investigate these influences and to quantify the rate at which tyndall glacier erodes its basin we present seismic data defining the volume of sediments in taan fjord icy bay we subtract the contribution of subaerially derived sediments from the fjord sediment package to determine the sediment yield directly from tyndall glacier during the most recent period of retreat 1962 1999 using a numerical model of proglacial glacimarine sedimentation we then calculate the annual sediment yield from and the corresponding erosion rate of tyndall glacier during this period which averages 28 5 mma 1 a strong correlation emerges between glacial retreat rates and glacial sediment yields implying that most contemporary sediment yield data from retreating tidewater glaciers may correspond to contemporary erosion rates that are a factor of 3 5 1 5 higher than in the long term hence we estimate the long term erosion rate for tyndall glacier to be 9 2 mma 1

recent changes in glacier velocities and thinning at novaya zemlya abstract ice loss from the glaciers of novaya zemlya nvz is the dominant contributor to sea level for the russian arctic here we present maps of glacier elevation change rates dh dt and velocities at novaya zemlya that reveal evidence of the impact of both calving flux and surface melt on ice mass loss dh dt are calculated by applying a weighted linear regression to stacked digital elevation models dems from a 1952 map and dems created from stereo pairs of worldview images acquired between 2012 and 2014 the 60 year average mass change rate is 0 23 0 04 m w e yr 1 the recent short term 2012 2013 2014 average mass change rate is 0 40 0 09 m w e yr 1 we apply the same weighted linear regression to stacked worldview dems and icesat elevations from 2003 to 2009 as well as stacked worldview dems and aster dems from 2000 to 2013 the dh dt from both datasets confirm that thinning has been more rapid than the 60 year average since 2000 average mass loss has accelerated at the lower elevations of land terminating glaciers suggesting that recent near surface warming and increased melt have led to greater thinning marine terminating glaciers along the barents sea coast have substantially higher thinning rates near their termini in recent years than adjacent land terminating glaciers suggesting that calving flux is an important contributor to overall ice mass loss in the region flow velocities are generated by feature tracking on optical and radar image pairs marine terminating glaciers along the barents sea coast have the highest frontal velocities of any glaciers on nvz our surface velocity measurements constrain the calving flux at the two fastest retreating glaciers inostrantseva ino and vil kitskogo vis which are both on the barents sea coast we find that the calving flux is high enough to drive frontal thinning and retreat at those two glaciers summer terminus speeds at inostrantseva glacier have accelerated from a 2006 maximum of 3 m day 1 to a 2012 maximum of 9 to 10 m day 1 and the front has retreated by more than 3 km between 2006 06 27 and 2013 08 17

modern rates of glacial sediment accumulation along a 15 s n transect in fjords from the antarctic peninsula to southern chile 1 rates of glacial erosion in temperate climates rank among the highest worldwide and the sedimentary products of such erosion record climatic and tectonic signals in many glaciated settings as well as temporal changes in glacier behavior glacial sediment yields are expected to decrease with increasing latitude because decreased temperature and meltwater production reduce glacial sliding erosion and sediment transfer however this expectation lacks a solid supportive database herein we present modern 210pb derived sediment accumulation rates on decadal to century time scales for 12 fjords spanning 15 of latitude from the antarctic peninsula to southern chile and interpret the results in light of glacimarine sediment accumulation worldwide 210pb records from the antarctic peninsula show surprisingly steady sediment accumulation throughout the past century at rates of 1 7 mm yr 1 despite rapid warming and glacial retreat cores from the south shetland islands reveal accelerated sediment accumulation over the past few decades likely due to changes in the thermal state of the glaciers in this region which straddles the boundary between subpolar and temperate conditions in patagonia and tierra del fuego sediment accumulates faster 11 24 mm yr 1 and previously collected seismic profiles show that rates reach meters per year close to the glacier termini this increase in sediment accumulation rates with decreasing latitude reflects the gradient from subpolar to temperate climates and is consistent with glacial erosion being much faster in the temperate climate of southern chile than in the polar climate of the antarctic peninsula

late glacial ice margins and deglacial chronology for southeastern baffin island and hudson strait eastern canadian arctic radiocarbon dates from marine piston cores and from onshore raised marine stratigraphic sections in the hudson strait region were used to reconstruct deglacial isochrons for 9900 9500 8800 8500 and 8000 bp at the culmination of the gold cove readvance 9900 bp labrador ungava ice flowed northeastward across hudson strait and outer frobisher bay and stood for the last time on the baffin island continental shelf subsequent retreat by calving was rapid and profound opening the entire hudson strait marine trough by 9500 bp at this time ice dispersal from foxe basin labrador ungava and local ice on meta incognita peninsula supported tidewater margins along much of the coastline with the exception of northernmost ungava peninsula where the ice margin stabilized onshore this onshore margin remained in place throughout the cockburn substage while a major northeastward readvance of ungava bay ice the noble inlet readvance from 8800 to 8500 bp crossed outer hudson strait grounding on the hudson st

latitudinal variation in glacial erosion rates from patagonia and the antarctic peninsula 46 s 65 s we use extensive sedimentary and marine geophysical data to derive sediment volume based millennial time scale glacial erosion rates from glacially influenced fjords and bays across a broad latitudinal transect from central patagonia 46 s to the antarctic peninsula 65 s and to determine how glacial erosion rates change with increasing latitude and decreasing atmospheric temperatures we also calculate million year time scale erosion rates for the western antarctic peninsula cordillera and inner continental shelf from seismic stratigraphic analysis of the continental margin these results are complemented by erosion rates derived from existing thermochronology data sets apatite fission track and apatite u th he for both patagonia and the antarctic peninsula regions despite considerable regional variability our results show a clear trend of decreasing with increasing latitude millennial values span two orders of magnitude from 0 02 mm yr for illiad glacier on anvers island antarctica 64 5 s to 0 83 mm yr for san rafael glacier in northern patagonia 46 5 s regional averages are three times higher for the patagonian areas than the antarctic peninsula areas this trend is interpreted to result from a general decrease in temperature and water availability at the ice bedrock interface for the antarctic peninsula study sites erosion rates are highly clustered around 0 1 mm yr with the exception of maxwell bay for which the value is 0 36 mm yr in patagonia erosion rates are more variable than in the antarctic peninsula with ranging between 0 14 mm yr europa glacier area and 0 83 mm yr san rafael glacier area this regional variability in is interpreted as due to differences in hypsometry and bedrock resistance to erosion million year time scale values derived from thermochronology ages also decrease with latitude with maximum values decreasing from 0 9 1 1 mm yr north of 46 s to 0 1 0 2 mm yr south of 48 s in patagonia and reaching 0 2 0 3 mm yr in the antarctic peninsula the sediment based million year time scale estimates for the western antarctic peninsula cordillera indicate that glacial erosion rates increased by 25 30 after 5 3 ma from 0 09 mm yr 5 3 9 5 ma to 0 11 0 12 mm yr 5 3 ma for patagonia the decrease in long term erosion rates south of 46 s is interpreted to result from relatively long periods of slow glacial erosion associated with the ice masses having been colder subpolar on the southern patagonian cordillera and having eroded at rates comparable to those we obtained for the antarctic peninsula these long term erosion rates are 1 2 orders of magnitude lower than estimates based on recent sediment yields highlighting the transient nature of high sediment flux events however our sediment volume derived millennial time scale closely approximates the maximum values of tectonic time scale values derived from thermochronology ages our combined millennial and million year time scale glacial erosion data quantify the significant decrease in rates of glacially driven denudation at geological tectonic and millennial time scales with increasing latitude from patagonia to the antarctic peninsula highlighting the influence of climate on mountain denudation

postglacial fluctuations of cordillera darwin glaciers southernmost patagonia reconstructed from almirantazgo fjord sediments abstract most outlet glaciers of the cordillera darwin icefield cdi patagonia 54 s are currently transitioning from calving to land based conditions whether this situation is unique to the modern climate or also occurred during the holocene is entirely unknown here we investigate the holocene fluctuations of outlet glaciers from the northern flank of the cdi using a multi proxy sedimentological and geochemical analysis of a 13 5 m long sediment core from almirantazgo fjord our results demonstrate that sedimentation in almirantazgo fjord started prior to 14 300 cal yr bp with glacier proximal deposits occurring until 13 500 cal yr bp after 12 300 cal yr bp most glaciers had retreated to land locked locations and by 9800 cal yr bp almirantazgo fjord was a predominantly marine fjord environment with oceanographic conditions resembling the present day setting our sediment record shows that during the first part of the holocene cdi glaciers were almost entirely land based with a possible re advance at 7300 5700 cal yr bp this is in clear contrast with the neoglaciation during which cdi glaciers rapidly re advanced and shrank back several times mostly in phase with the eastern outlet glaciers of the southern patagonian icefield spi two significant meltwater events indicative of rapid glacier retreat were identified at 3250 2700 and 2000 1200 cal yr bp based on an increase in grain size mode and related inorganic geochemical parameters this interpretation is additionally supported by concomitant decreases in organic carbon of marine origin and in cl counts salinity reflecting higher terrestrial input to the fjord and freshening of the fjord waters overall our record suggests that cdi outlet glaciers advanced in phase with eastern spi glaciers during the neoglaciation and retreated far enough into their valleys twice to form large outwash plains our results also highlight the potential of fjord sediments to reconstruct glacier variability at high resolution on multi millennial timescales

the role of the cryosphere in source to sink systems abstract glacial erosion and sediment production are of interest to diverse scientific communities concerned with the interaction of climatic tectonic and surface processes that influence the evolution of orogens and with the climatic signals archived in glacigenic strata we review the current state of knowledge on the generation transfer and accumulation of glacigenic sediment from land to sea we draw from geomorphology marine geology geochronology numerical modeling of surface processes and landscape evolution and experimental and field observations of glacier erosion and deposition and the interaction of ice with its bed and the ocean boundary our primary goal is to examine glacial systems using a holistic source to sink approach with a focus on describing a how glacial motion produces sediment b how the sediments sink record the dynamic nature of glacial systems under different climatic thermal regimes c the challenges in using the sedimentary record to interpret these dynamics in space and time and d the approaches still needed to further our understanding of how ice and associated sediment fluxes respond to climatic and other perturbations the dynamic state of ice i e the ice flux and ice extent is defined differently between the source and sink communities reflecting the challenges of establishing a stratigraphic signal that volumetrically constrains glacigenic sediment production as a function of the ice response to climate advances in marine geophysics have greatly assisted our understanding of mass transfer pathways and of former ice extents as a measure of ice dynamics and have identified the primary depocenters and key lithofacies of glacial sinks sediment fluxes associated with the dynamic state of the ice are best constrained where sediment volumes derived from key lithofacies and seismic reflection isopachs can be temporally partitioned of which there are few examples rather than from discrete point measures of sediment flux that are subject to sediment transfer biases forward numerical modeling of sediment fluxes as a function of ice dynamics agree with observational data at the continental margin scale but finer time space scale ice dynamic models do not yet recreate observed ice extent or flowpaths future source to sink work in glaciated systems should focus on refining empirical relationships between ice velocity and sediment production and expand the application of existing methods to develop sediment volumes and fluxes in known depocenters of former and modern ice streams

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

synchronous acceleration of ice loss and glacial erosion glaciar marinelli chilean tierra del fuego to contribute to the understanding of the influence of climate on glacial erosion and on orogenic processes we report contemporary glacial erosion rates from a calving glacier in the southern andes and elucidate the influence of ice dynamics on erosion using seismic profiles of sediments collected in a proglacial fjord and a documented history of retreat we determine the time varying sediment flux of glaciar marinelli as a measure of basin wide erosion rates and compare these rates with the annual ice budget reconstructed using ncep ncar reanalysis climate data from 1950 to 2005 the rate of erosion of the largest tidewater glacier in tierra del fuego averaged 39 16 mm a 1 during the latter half of the 20th century with an annual maximum approaching 130 mm a 1 following a decade of rapid retreat a strong correlation emerges between the variable rate of ice delivery to the terminus and the erosion rate providing quantitative insight into the relationship between ice fluxes and glacial erosion rates for glaciar marinelli as for other calving glaciers for which suitable data exist the marked retreat and thinning over the past 50 years have resulted in a period of accelerated basal sliding and unusually rapid erosion

glacier surge mechanism 1982 1983 surge of variegated glacier alaska the hundredfold speedup in glacier motion in a surge of the kind the kind that took place in variegated glacier in 1982 1983 is caused by the buildup of high water pressure in the basal passageway system which is made possible by a fundamental and pervasive change in the geometry and water transport characteristics of this system the behavior of the glacier in surge has many remarkable features which can provide clues to a detailed theory of the surging process the surge mechanism is akin to a proposed mechanism of overthrust faulting

exhumation rates in the st elias mountains alaska abstract reprocessing and interpretation of seismic profiles from the gulf of alaska in the vicinity of the st elias mountains indicate that over 3000 km 3 of sediment were deposited on the ocean shelf since the end of the last glacial epoch approximately 10 000 years ago this estimate of the sediment volume does not include material moved out of the region by long shore currents transportation from the shelf to deeper waters or material trapped in fiords and basins on and near land thus an estimated sedimentation rate offshore of 7 9 mm year and the average erosion rate of 5 1 mm year from the st elias mountains derived from the estimated sedimentation rate represent minimum estimates we infer that these estimated rates are not typical of the approximately 5 m y history of mountain building in the area but rather they represent the result of efficient erosion by glaciers during this interglacial period

climatic limits on landscape development in the northwestern himalaya the interaction between tectonism and erosion produces rugged landscapes in actively deforming regions in the northwestern himalaya the form of the landscape was found to be largely independent of exhumation rates but regional trends in mean and modal elevations hypsometry frequency distribution of altitude and slope distributions were correlated with the extent of glaciation these observations imply that in mountain belts that intersect the snowline glacial and periglacial processes place an upper limit on altitude relief and the development of topography irrespective of the rate of tectonic processes operating

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

the effect of chemical and physical processes on the acoustic properties of carbonate rocks carbonate rocks have major economic significance 60 of the world s oil reserves lie in carbonate reservoirs and the potential for additional gas reserves is huge however the relationship in carbonates between measured geophysical data and rock properties is complex due to the large variety of textures that arise during postdepositional diagenesis and to the chemical processes i e dissolution and replacement by newly formed phases that characterize carbonate forming minerals most experimental and theoretical rock physics research has focused on siliciclastic and shaly rocks however applying insights gained from clastics to carbonates is rarely straightforward and thus is questioned in the literature

ultrasonic velocities of north sea chalk samples influence of porosity fluid content and texture we have studied 56 unfractured chalk samples of the upper cretaceous tor formation of the dan south arne and gorm fields danish north sea the samples have porosities of between 14 and 45 and calcite content of over 95 the ultrasonic compressional and shear wave velocities vp and vs for dry and water saturated samples were measured at up to 75 bar confining hydrostatic pressure corresponding to effective stress in the reservoir the porosity is the main control of the ultrasonic velocities and therefore of the elastic moduli the elastic moduli are slightly higher for samples from the south arne field than from the dan field for identical porosities this difference may be due to textural differences between the chalk at the two locations because we observe that large grains i e filled microfossils and fossil fragments that occur more frequently in samples from the dan field have a porosity reducing effect and that samples rich in large grains have a relatively low porosity for a given p wave modulus the clay content in the samples is low and is mainly represented by either kaolinite or smectite samples with smectite have a lower p wave modulus than samples with kaolinite at equal porosity we find that ultrasonic vp and vs of dry chalk samples can be satisfactorily estimated with gassmann s relationships from data for water saturated samples a pronounced difference between the vp vs ratios for dry and water saturated chalk samples indicates promising results for seismic amplitude versus offset analyses