little ice age subsidence and post little ice age uplift at juneau alaska inferred from dendrochronology and geomorphology abstract application of dendrochronology and geomorphology to a recently emerged coastal area near juneau alaska has documented a little ice age lia sea level transgression to 6 2 m above current sea level the rise in relative sea level is attributed to regional subsidence and appears to have stabilized by the mid 16th century based on a sea cliff eroded into late pleistocene glaciomarine sediments land began emerging between a d 1770 and 1790 coincident with retreat of regional glaciers from their lia maximums this emergence has continued since then paralleling regional glacier retreat total juneau uplift since the late 18th century is estimated to be 3 2 m the rate of downward colonization of newly emergent coastline by sitka spruce during the 20th century closely parallels the rate of sea level fall documented by analysis of local tide gauge records 1 3 cm yr regional and glacier bay lia loading and unloading are inferred to be the primary mechanisms driving subsidence and uplift in the juneau area climate change rather then regional tectonics has forced relative sea level change over the last several hundred years

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

history and isostatic effects of the last ice sheet in southern british columbia abstract the late wisconsinan cordilleran ice sheet covered british columbia southern yukon territory and parts of alaska washington idaho and montana its major source areas were the high mountain ranges of the canadian cordillera and flow was strongly controlled by topography the last ice sheet began to develop about 30 000 25 000 14c yr ago but it did not achieve its maximum extent until 15 000 14 000 14c yr bp ice sheet growth was interrupted locally by stillstands and retreat ice sheet decay was rapid and was characterized by complex frontal retreat at the periphery accompanied locally by brief readvances and by downwasting and stagnation by 10 000 14c yr bp

crustal deformation associated with glacial fluctuations in the eastern chugach mountains alaska the changes of the solid earth in south central alaska in response to two major glacial fluctuations on different temporal and spatial scales have been estimated and we evaluated their influence on the stress state and ongoing tectonic deformation of the region during the recent 1993 1995 bering glacier surge a large transfer of ice from the bagley ice field to the bering glacier terminus region occurred we estimated the elastic displacement of the solid earth due to ice mass redistribution from global positioning system gps measurements at sites near the surging glacier we can account for these displacements by transfer of an ice volume of about 14 km3 from the surge reservoir area to the terminus region we examined the background seismicity ml 2 5 before during and after the surge we found that the occurrence of small earthquakes ml 4 0 in the surge reservoir region increased during the surge time interval possibly in response to a decrease in ice mass this suggests that a small decrease in the vertical stress 3 could be enough to modulate the occurrence of small shallow earthquakes in this dominantly thrust fault setting during this century the southern alaska coastal glaciers have been undergoing an overall decrease in volume based on our compilation of changes in the extent and thickness of the coastal glaciers between the malaspina and bering we calculated surface displacements due to the earth s viscoelastic response to annual thinning and to the cumulative retreat over the last 100 years the uplift of the region due to an average annual thinning rate of 1 6 m yr in the ablation region is 1 12 mm yr for our reference model with a viscosity of 5 1019 pa s for depths between 40 and 200 km the total viscoelastic response due to the retreat over the last century may be as much as a couple of meters within the coastal ablation zone near icy bay the maximum decrease in v between 0 and 10 km was 1 0 mpa which is significant in relation to the stress drops in recent earthquakes 2 to 10 mpa but small in relation to the estimated tectonic stress magnitude therefore the occurrence of an earthquake such as the st elias 1979 ms 7 2 may have been advanced in time however most of the ongoing stress accumulation would be primarily due to tectonic forces

tide gauge records of uplift along the northern pacific north american plate boundary 1937 to 2001 1 vertical crustal motions at 15 sites along the northern pacific north america plate boundary are determined using relative sea level changes from tide gauge records our analysis is based on monthly mean sea levels from which barometric pressure and seasonal effects are removed the records are corrected for common mode oceanographic variations these records are statistically examined for non linear behavior related to glacial isostatic tectonic and postseismic effects to estimate land uplift rates the local effect of global sea level rise is removed from the relative sea level rates slow rates of vertical motion are observed along the southern strike slip plate boundary the extremely rapid uplift of the northern strike slip boundary can be attributed entirely to viscoelastic postglacial rebound associated with tidewater glacier retreat in glacier bay and regional post little ice age deglaciation isostatic modeling indicates a mantle viscosity of 2 1019 5 1019 pa s similar to that found elsewhere along the pacific north america plate margin at yakutat near the transition of plate motion from strike slip to subduction complex non linear behavior is evident with a significant change in uplift rate following the 1979 st elias earthquake non linear uplift rates are predominant within the 1964 great alaskan earthquake near field rapid uplift at kodiak during a 3 5 year period starting mid 1964 totaled 47 8 cm anchorage seward and seldovia exhibited oscillatory uplift in the period immediately following the earthquake until mid 1972 since mid 1972 uplift rates have increased steadily at anchorage seward cordova and valdez during this period nikiski and kodiak show decreasing uplift rates

a complete formalism for the inversion of post glacial rebound data resolving power analysis summary a formal inverse theory for mantle viscosity based upon the data of glacial isostatic adjustment is here formulated and applied to synthetic data in this theory full account has been taken of the normal mode nature of the forward problem for realistic viscoelastic maxwell models of the planet since it is impossible to accurately infer the excitation and decay constants of the individual normal modes from the observations the formalism is cast in terms of the observed gross earth data in the time domain in this analysis expressions are required for the first order perturbations in both the modal amplitudes and relaxation times that are induced by an arbitrary radial perturbation to the starting viscosity profile a numerical technique is developed which enables us to accurately determine differential kernels for the modal amplitudes the analogous kernels for the modal decay times are derived analytically peltier 1976 and the complete set of kernels is shown to satisfy the physical constraint imposed by the uniqueness of the state of isostatic equilibrium for the viscously incompressible maxwell models that we employ when the problem is parametrized in terms of the logarithm of viscosity the kernels are capable of accurately predicting shifts in the normal mode characteristics for at least an order of magnitude variation in mantle viscosity using bayesian statistics a formal inversion is applied to a set of synthetically generated data these data chosen to reproduce the space time coverage of the actual observables include a subset related to the global gravity field and a large sequence of idealized relative sea level rsl curves it is found that even very weak a priori constraints can provide a stable and accurate inversion a resolving power analysis indicates a spatial resolution of approximately 1200km near the core mantle boundary cmb with a gradual improvement to better than 350km in the middle of the upper mantle subsets of the synthetic data are inverted in order to examine conditions on stability and accuracy and to determine their relative contributions to the spatial resolution data from progressively older beaches are shown to contribute most to the spatial resolution at all depths though the improvement in lower mantle resolution converges for data obtained from beaches formed within the last 5000 yr furthermore the rsl curves in the vicinity of the peripheral bulge of the ancient laurentide ice sheet are significant contributors to lower mantle resolution as demonstrated in previous analyses of the forward problem the inversion of this subset of the data also appears to be encouragingly stable

gravity measurements in southeastern alaska reveal negative gravity rate of change caused by glacial isostatic adjustment 1 for the past 300 years southeastern alaska has undergone rapid ice melting and land uplift attributable to global warming corresponding crustal deformation 3 cm yr caused by the little ice age retreat is detectable with modern geodetic techniques such as gps and tidal gauge measurements geodetic deformation provides useful information for assessing ice melting rates global warming effects and subcrustal viscosity nevertheless integrated geodetic observations including gravity measurements are important to detect crustal deformation caused by glacial isostatic adjustment and to elucidate the viscosity structure in southeastern alaska japanese and u s researchers began a joint 3 year project in 2006 using gps earth tide and absolute gravity measurements a new absolute gravity network was established comprising five sites around glacier bay near juneau alaska this paper reports the network s gravity measurements during 2006 2008 the bad ocean model in this area hindered ocean loading correction large tidal residuals remain in the observations accurate tidal correction necessitated on site tidal observation results show high observation precision for all five stations 1 gal the gravity rate of change was found to be 3 5 to 5 6 gal yr in the gravity network furthermore gravity results obtained during the 3 years indicate a similar gravity change rate these gravity data are anticipated for application in geophysical studies of southeastern alaska using gravity and vertical displacement data we constructed a quantity to remove viscoelastic effects the observations are thus useful to constrain present day ice thickness changes a gravity bias of about 13 2 0 1 mgal exists between the potsdam and current fg5 gravity data

active tectonics of the st elias orogen alaska observed with gps measurements 1 we use data from campaign and continuous gps sites in southeast and south central alaska to constrain a regional tectonic block model for the st elias orogen active tectonic deformation in the orogen is dominated by the effects of the collision of the yakutat block with southern alaska our results indicate that 37 mm yr of convergence is accommodated along a relatively narrow belt of n nw dipping thrust faults in the eastern half of the orogen with the present day deformation front running through icy bay and beneath the malaspina glacier near the bering glacier the collisional thrust fault regime transitions into a broad northwest dipping decollement as the yakutat block basement begins to subduct beneath the counterclockwise rotating elias block the location of this transition aligns with the gulf of alaska shear zone implying that the pacific plate is fragmenting in response to the yakutat collision our model indicates that the bering glacier region is undergoing internal deformation and could correspond to the final stage of offscraping and accretion of sediments from the yakutat block prior to subduction predicted block motions at the western edge of the orogen suggest that the crust is laterally escaping along the aleutian fore arc

fjords as temporary sediment traps history of glacial erosion and deposition in muir inlet glacier bay national park southeastern alaska glacimarine sedimentary deposits within the basins of muir inlet a 48 km long silled fjord are interpreted from complimentary sets of high resolution seismic reflection profiles using known glacial advance and retreat history two prominent glacial erosion surfaces are identified the lowest attributed to the last glacial maximum lgm advance and the upper coincident with the little ice age lia advance the lgm ice sheet which advanced onto the continental shelf was 1700 m thick in muir inlet and eroded bedrock whereas the thinner lia ice did not lgm deposits 300 m thick occur beneath the lia erosion surface in the deepest basins evidence for earlier neoglacial advances is present in subaerial deposits however neoglacial sediments preserved within the marine record are restricted to one depositional package on the entrance sill volumes of lia retreat sediments were calculated within basins an average annual sediment flux was calculated by modeling the duration of sediment contributed from muir glacier and from tributary glaciers and side entry sources the annual sediment flux ranged from 1 3 10 6 m 3 yr to 4 6 10 7 m 3 yr and increases logarithmically with increasing drainage basin area similar to fluvial systems this sediment flux does not only represent bedrock erosion additional sediment is contributed from persistent tributary glaciers and from lgm sediment stored within deeper basins basin wide reflections characterize the most common seismic facies and indicate that strata are horizontal and continuous across each basin confirming the importance of sediment gravity flows originating from sills and sloping fjord walls

lithospheric thickness inferred from australian post glacial sea level change the influence of a ductile crustal zone 1 we investigate the influence of a crustal low viscosity zone clvz on numerical predictions of post glacial late holocene sea level variations in the australian region specifically we compare predictions from a model with a 15 km thick clvz within an otherwise elastic plate to results from a suite of models in which the thickness of a purely elastic crust lithosphere is varied we conclude that previous inferences of lithospheric thickness based on differential highstands from the region represent approximately the thickness of the elastic layer above the clvz and thus if a clvz exists these inferences may be significantly underestimating the total depth extent of the crust lithosphere system

new constraints on the motion of the fairweather fault alaska from gps observations 1 gps velocities from sites near to the fairweather fault in southern alaska are combined with line length data from geodetic surveys by the u s geological survey usgs to estimate the slip rate and locking depth of the fairweather fault using dislocation theory we perform a weighted least squares inversion of the geodetic data and obtain a best fitting slip rate of 45 6 2 0 mm yr and locking depth of 9 0 0 8 km the slip rate we estimate is one of the highest observed across any strike slip fault we also include the dalton creek segment of the denali fault in our model and estimate a slip rate of 3 8 1 4 mm yr for this section of the fault this is substantially lower than the rate observed for the denali fault segment to the northwest which ruptured in the november 3 2002 mw 7 9 denali fault earthquake

tectonic block motion and glacial isostatic adjustment in southeast alaska and adjacent canada constrained by gps measurements 1 we use data from campaign and continuous gps sites in southeast alaska and the neighboring region of canada to constrain a regional tectonic block model that estimates block angular velocities and derives a self consistent set of fault slip rates from the block motions present day tectonics in southeast alaska is strongly influenced by the collision of the yakutat block our model predicts a velocity of 50 3 0 8 mm a toward n22 9 0 6 w for that block our results suggest that the eastern edge of the yakutat block is deforming along this edge the fairweather fault accommodates a large portion of the pacific north america relative plate motion through 42 9 0 9 mm a of dextral slip further south along the queen charlotte fault our model predicts an average of 43 9 0 6 mm a of dextral slip and a southward increasing amount of transpression strain from the yakutat collision is transferred far to the east of the strike slip system this strain transfer causes the region north of glacier bay to undergo a clockwise rotation south of glacier bay and inboard of the queen charlotte fault a smaller but clearly defined clockwise rotation is observed the heterogeneous block motion north and south of glacier bay may indicate the area is undergoing internal deformation and could explain regional patterns of diffuse seismicity the northern cordillera of canada displays a small northeasterly motion our block model suggests that the entire southeastern alaska northwestern canada margin is mobile

land motion estimates from gps at tide gauges a geophysical evaluation summary space geodesy applications have mainly been limited to horizontal deformations due to a number of restrictions on the vertical component accuracy monitoring vertical land motion is nonetheless of crucial interest in observations of long term sea level change or postglacial rebound measurements here we present a global vertical velocity field obtained with more than 200 permanent gps stations most of them colocated with tide gauges tgs we used a state of the art homogeneous processing strategy to ensure that the reference frame was stable throughout the observation period of almost 10 yr we associate realistic uncertainties to our vertical rates taking into account the time correlation noise in the time series the results are compared with two independent geophysical vertical velocity fields 1 vertical velocity estimates using long term tg records and 2 postglacial model predictions from the ice 5g vm2 adjustment the quantitative agreement of the gps vertical velocities with the internal estimates of vertical displacements using the tg record is very good with a mean difference of 0 13 1 64 mm yr 1 on more than 100 sites for 84 per cent of the gps stations considered the vertical velocity is confirmed by the tg estimate to within 2 mm yr 1 the overall agreement with the glacial isostatic adjustment gia model is good with discrepancy patterns related either to a local misfit of the model or to active tectonics for 72 per cent of the sites considered the predictions of the gia model agree with the gps results to within two standard deviations most of the gps velocities showing discrepancies with respect to the predictions of the gia model are however consistent with previously published space geodesy results we in turn confirm the value of 1 8 0 5 mm yr 1 for the 20th century average global sea level rise and conclude that gps is now a robust tool for vertical land motion monitoring which is accurate at least at 1 mm yr 1

mantle flow beneath a continental strike slip fault postseismic deformation after the 1999 hector mine earthquake two recent large earthquakes in the mojave desert california the magnitude 7 3 1992 landers and magnitude 7 1 1999 hector mine earthquakes have each been followed by elevated crustal strain rates over periods of months and years geodetic data collected after the hector mine earthquake exhibit a temporally decaying horizontal velocity field and a quadrant uplift pattern opposite to that expected for localized shear beneath the earthquake rupture we interpret the origin of this accelerated crustal deformation to be vigorous flow in the upper mantle in response to the stress changes generated by the earthquake our results suggest that transient flow in the upper mantle is a fundamental component of the earthquake cycle and that the lower crust is a coherent stress guide coupling the upper crust with the upper mantle

contemporary deformation and stressing rates in southern alaska summary the subduction of the pacific plate beneath north america induces broad scale stressing of the alaskan crust that has led to the development of the highest mountains in north america the highest slip rates along some of the longest strike slip faults on earth and widespread seismicity that includes the 1964 m9 2 alaska earthquake the second largest ever recorded these features are a consequence of deformation associated with three primary processes interseismic loading due to relative plate motions large earthquakes and postseismic processes how these mechanisms contribute to the evolution of stress in the alaskan crust is not well understood here we use observed contemporary surface velocities to constrain 2 d and 3 d viscoelastic numerical models of relative pacific north american plate motions coseismic slip associated with the 1964 m9 2 megathrust event and strike slip earthquakes on the transform boundary in 1949 m8 1 1958 m7 8 and 1972 m7 6 the four largest events prior to the 2002 m7 9 denali quake viscoelastic relaxation following these events and afterslip to gain insight into how these processes are shaping alaska today results suggest that interseismic deformation and on going post seismic deformation following the 1964 earthquake both contribute significantly to the gps measured contemporary velocity field viscoelastic relaxation associated with a mantle with a viscosity of 10 19 pa s is required to explain southerly directed velocities that are observed in the cook inlet region to well north of the denali fault results also suggest that subduction of the pacific plate leads to a broad zone of deformation with high stressing rates concentrated in a band that lies several hundred kilometres from the plate boundary coeval with the inboard location of the maximum locking depth of the megathrust interseismic deformation and stressing rates remain high further inland across the yakutat microplate where flat subduction extends the width of the locked plate interface calculations show that post seismic relaxation following the large strike slip events serves to reload these rupture surfaces while relieving stress on the eastern denali fault post seismic relaxation following the 1964 earthquake combined with coseismic stress changes promoted the triggering of the 2002 denali quake calculations also suggest that over the past 50 years high stress has accumulated on part of the thrust interface to the west and east of the 1964 rupture surface and along the queen charlotte fault to the south of the 1949 rupture surface

exhumation along the fairweather fault southeastern alaska based on low temperature thermochronometry 1 the southern alaskan syntaxis marks the spectacular junction between the 1000 km long pacific north america transform margin and the chugach st elias belt where subduction and terrane accretion drive rapid convergent deformation and rock uplift new low temperature thermochronometry reveals that intense orogenic deformation is not restricted to one side of the syntaxis but extends nearly 300 km south along the dextral fairweather fault apatite and zircon u th he ages as young as 0 9 and 2 0 ma suggest maximum exhumation rates of nearly 2 mm a in close proximity 0 5 mm a along the entire plate margin we estimate that long term rock uplift accommodates 3 mm a of fault normal convergence in this area this suggests that the fairweather fault is slightly transpressive and highly partitioned analogous to the central san andreas fault this convergence only accounts for 1 5 of the obliquity between pacific plate motion and the continental margin however implying the deficit is taken up by 1 2 cm a thrust sinistral motion along the offshore transition fault additionally thermochronometry shows a marked increase in bedrock cooling coincident with onset of heavy glaciation similar to what has been observed in other parts of the pacific northwest the tectonically active fairweather corridor is distinguished however by the magnitude of the acceleration and the depth of exhumation since pliocene climate change

post 10 ma uplift and exhumation of the northern coast mountains british columbia apatite u th he ages reveal three distinct periods in the exhumation history of the northern coast mountains 54 n a well developed helium partial retention zone indicates little or no exhumation between ca 30 and 10 ma beginning at 10 ma and extending to at least 4 ma the range underwent steady but slow exhumation of 0 22 mm yr after which the exhumation rate increased by at least 70 an 85 km long he age traverse across the orogen at sea level shows that vertical offsets on post 10 ma faults are minor furthermore the sea level he ages 14 2 8 ma inversely correlate with local mean elevation along the traverse these data suggest that the coast mountains first appeared as a significant topographic feature only within the past few million years this history is not consistent with suggestions that uplift of the range resulted from formation of the queen charlotte basin in early middle miocene time we speculate that intense erosion by alpine and continental glaciation after 2 5 ma triggered isostatic uplift and creation of the modern topography of the coast mountains

radial profile of mantle viscosity results from the joint inversion of convection and postglacial rebound observables we present new inferences of the radial profile of mantle viscosity that simultaneously fit long wavelength free air gravity harmonics associated with mantle convection and a large set of decay times estimated from the postglacial uplift of sites within previously glaciated regions hudson bay arctic canada and fennoscandia the relative sea level variation at these latter sites is constrained by age height pairs obtained by geological survey rather than the subjective trends which are commonly used in glacial isostatic adjustment gia studies our viscosity inferences are generated using two approaches first we adopt a relative viscosity profile which is known to provide a good fit to the free air gravity harmonics and determine an absolute scaling which yields a best fit to the gia decay time constraints second we perform an iterative nonlinear joint inversion of the two data sets in both cases our inferred profiles are characterized by a significant increase of viscosity 2 orders of magnitude with depth to values of 1022 pa s in the bottom half of the lower mantle the new viscosity profiles are shown to satisfy constraints based on the postglacial uplift of both fennoscandia the classic haskell 1935 number and hudson bay which have commonly been invoked to argue for an isoviscous mantle furthermore the models are used to predict a set of long wavelength signatures of the gia process these include predictions of gia induced variations in 1 the length of day over the late holocene period 2 the earth s precession constant and obliquity over the last 2 6 myr and 3 the present day zonal harmonics of the geopotential jl l 7 the predictions 1 and 3 bound the late holocene and ongoing mass flux between the large polar ice sheets greenland and antarctic and the global oceans to small values 0 4 mm yr equivalent eustatic sea level rise

historic retreat of grand pacific and melbern glaciers saint elias mountains canada an analogue for decay of the cordilleran ice sheet at the end of the pleistocene

reevaluation of the viscoelastic and elastic responses to the past and present day ice changes in southeast alaska abstract we have reevaluated the viscoelastic and elastic responses to the past and present day ice changes in southeast alaska se ak based on a gps data set by combining the data previously published in 2005 with additional uplift rates compiled recently there are 22 new gps sites yielding a total of 91 sites the mean observation epoch of the data sets is the middle of 2003 here we considered three ice unloading effects due to the last glacial maximum lgm the little ice age lia and the present day ice melting pdim we also examined the dependency of the estimated lithospheric thickness and the asthenospheric viscosity on pdim models for this test two pdim models were used one is a model called here the uaf05 ice model whose mean epoch is the mid 1970s and the other is a model called here the uaf07 model whose mean epoch is the mid 1980s statistical examinations of the misfits between observations and model predictions indicate that uaf07 gives much more consistent results than uaf05 based on the magnitude of the minimum 2 and the agreement of the residual distribution with a gaussian function we have tested two different kinds of mantle viscosity structure a 2 layer model similar to the model used the paper previously published in 2005 and a 4 layer model for the 2 layer model at the 95 confidence level the optimum values for the lithospheric thickness and the asthenospheric viscosity with a thickness of 110 km are 54 45 65 km and 5 58 4 0 12 0 in unit of 10 18 pa s respectively on the other hand for the 4 layer model the best values were 60 42 63 km and 10 0 3 0 13 in unit of 10 18 pa s respectively the comparison between the analysis results for gps data and the model computations indicates that the observations detect not only the uplift rates in se ak but also their time variations which are considered to be due to the glacier changes after the 1990s

sea level change glacial rebound and mantle viscosity fornorthern europe northwestern europe remains a key region for testing models of glacial isostasy because of the good geological record of crustal response to the glacial unloading since the time of the last glacial maximum models for this rebound and associated sea level change require a detailed knowledge of the ice sheet geometry including the ice thickness through time existing ice sheet reconstructions are strongly model dependent and inversions of sea level data for the mantle response may be a function of the model assumptions thus inverse solutions for the sea level data are sought that include both ice and earth model parameters as unknowns sea level data from fennoscandia the north sea the british isles and the atlantic and english channel coasts have been evaluated and incorporated into the solutions the starting ice sheet for fennoscandia is based on a reconstruction of a model by denton hughes 1981 that is characterized by quasi parabolic cross sections and symmetry about the load centre both global northwestern europe as a whole and regional subsets of the data solutions have been made for earth model parameters and ice height scaling parameters the key results are as follows 1 the response of the upper mantle to the changing ice and water loads is spatially relatively homogenous across scandinavia the north sea and the british isles 2 this response can be adequately modelled by an effective elastic lithosphere of thickness 65 85 km and by an effective upper mantle viscosity from the base of the lithosphere to the 670 km depth seismic discontinuity of about 3 4 1020 pa s the effective lower mantle viscosity is at least an order of magnitude greater 3 the ice thickness over scandinavia at the time of maximum glaciation was only about 2000 m much less than the 3400 m assumed in the denton hughes model 4 the ice profiles are asymmetric about the centre of the ice sheet with those over the western part being consistent with quasi parabolic functions whereas the ice heights over the eastern and southern regions increase much more slowly with distance inwards from the ice margin

spatial variations in present day deformation kenai peninsula alaska and their implications from four years of global positioning system gps measurements we find significant spatial variations in present day deformation between the eastern and western kenai peninsula alaska sites in the eastern kenai peninsula and prince william sound move to the nnw relative to north america in the direction of pacific north america relative plate motion velocities decrease in magnitude from nearly the full plate rate in southern prince william sound to about 30 mm yr at seward and to about 5 mm yr near anchorage in contrast sites in the western kenai peninsula move to the sw in a nearly trenchward direction with a velocity of about 20 mm yr the data are consistent with the shallow plate interface offshore and beneath the eastern kenai and prince william sound being completely locked or nearly so with elastic strain accumulation resulting in rapid motion in the direction of relative plate motion of sites in the overriding plate the velocities of sites in the western kenai along strike to the southwest are opposite in sign with those predicted from elastic strain accumulation these data are incompatible with a significant locked region in this segment of the plate boundary trenchward velocities are found also for some sites in the anchorage area we interpret the trenchward velocities as being caused by a continuing postseismic transient from the 1964 great alaska earthquake there may be significant along strike differences in the long term behavior of the plate interface between the western and eastern kenai based on roughly coincident boundaries in the coseismic slip distribution cumulative postseismic uplift present day plate coupling and stress field the present postseismic response appears to generate purely trenchward motion suggesting a creep process that is purely dip slip our observations suggest that postseismic processes after the largest earthquakes can influence patterns of deformation for decades after the event

gravity and uplift rates observed in southeast alaska and their comparison with gia model predictions gravity change rates unit mgal yr 1 mgal 10 8 ms 2 over the 6 sites are estimated to be 4 50 0 76 and 4 30 0 92 by only using our data and also using the 1987 data respectively we computed the uplift and gravity rates predicted by ice load models for three different time intervals last glacial maximum lgm little ice age lia and present day pd except for 1 2 examples the predictions recover the observed rates within the observation errors we also estimated the viscous portion of the ratio unit mgal mm of the observed gravity rate to the uplift rate by correcting for the effects of the present day ice mass change pdimc two pdimc models are compared which are called here as uaf05 and uaf07 mean ratios are estimated to be 0 205 0 089 and 0 183 0 052 for the cases using uaf05 and uaf07 respectively the predicted mean ratios are 0 166 0 001 and 0 171 0 002 for the cases using both the lga and lia ice models and only using the lia ice model respectively we have confirmed that our ag and gps observations detect the rates and ratios reflecting an early stage of viscoelastic relaxation mainly due to the unloading effects after the lia

simple models for late holocene and present day patagonian glacier fluctuations and predictions of a geodetically detectable isostatic response summary the late holocene glacial moraine chronology in the southernmost south american andes includes four 14c dated neoglacial advances and retreats these are used as proxy information to characterize mass fluctuation of the patagonian icefields during the last 5000 years modelled ice loads force a phase lagged viscoelastic gravitational deformation of the solid earth the ancient glacier fluctuations may therefore drive present day crustal motion even in the absence of present day ice mass imbalance numerical models show that such rates of present day uplift and subsidence are larger than those driven by the viscous memory of late pleistocene deglaciation both spherical and flat earth models are employed the latter being used to study exhaustively the evects of glacial load history on the predicted vertical crustal velocity recent assessment of net mass balance from 1944 to 1985 indicates that the southern patagonian icefield has significantly deteriorated due to snout retreat and thinning volume loss rates are estimated at about 3 4 9 3 km3 yr 1 the predicted vertical isostatic response to this recession and to the modelled holocene neoglaciations is at a marginally detectable level 1m m yr 1 if the mantle asthenosphere beneath patagonia has a viscosity of about 1021 pa s however for reduced mantle viscosities the younger holocene glacial load histories predict larger signatures in fact if the viscosity is about 2 1020 pa s or lower then geodetically detectable vertical motion may be driven by a regional little ice age lia 1400 1750 ad glacier advance and subsequent 20th century retreat although this value for mantle viscosity is lower than thought typical of continental shield mantle 1021 pa s it is consistent with inversions for post seismic relaxation time constants in island arc environments and in regions with significant neogene continental tectonism in the viscosity regime of 5 1018 2 1019 pa s the predicted rates of vertical crustal motion are similar to those presently occurring in fennoscandia and hudson bay 5 10 mm yr 1 geodetic data may be sensitive to the time integrated growth and subsequent retreat of patagonian glacier ice mass over the last 600 years

a macroscopic approach to glacier dynamics a simple approach to glacier dynamics is explored in which there is postulated to be a relationship between area and volume with three parameters the time for area to respond to changes in volume a thickness scale and an area characterizing the condition of the initial stale this approach gives a good fit to the measurements of cumulative balance and area on south cascade glacier from 1970 97 the area time scale is roughly 8 years the thickness scale about 123 m and the 1970 area roughly 4 larger than required for adjustment with volume combining this relationship with a version of mass continuity expressed in terms of area and volume produces a theory of glacier area and volume response to climate in which another time constant the volume time scale appears area and volume both respond like a damped spring and mass system the damping of the south cascade response is approximately critical and the volume time scale is roughly 48 vexes six times the area time scale the critically damped spring and mass analogy reproduces the time dependence predicted by the more complicated traditional theory of nyc

rapid uplift of southern alaska caused by recent ice loss summary extreme uplift rates and sea level changes in southern alaska have been documented by global positioning system gps surveys tide gauge measurements and studies of raised shorelines the movements detected in a network of 45 gps survey points describe a broad pattern of rapid regional uplift the majority of the study area is uplifting at a rate faster than 10 mm yr 1 with several sites uplifting more rapidly than 25 mm yr 1 new tide gauge data presented here consist of repeat occupations of 18 temporary gauge sites sea level rates at these sites agree with similar measurements in southern alaska taken 50 yr earlier and also with the pattern of uplift derived from the gps data raised shoreline studies at 14 sites document total sea level change with a maximum change in sea level of 5 7 m found in upper lynn canal the start of the ongoing uplift episode that raised these shorelines has been dated with dendrochronology and found to be coincident with the start of the collapse of the glacier bay icefield at ca 1750 ad the pattern of total sea level change is in general agreement with upliftrate measurements with greater sea level change found at the sites closest to the peak uplift rates in upper glacier bay we use a viscoelastic earth model subjected to an ice load history built upon observations of glacial change to predict uplift rates at the tide gauge and gps sites as well as the total uplift at the raised shoreline sites our modelling exercises are limited to an ice load model based on independent studies of the region s glacial history over the past 1 7 kyr to evaluate whether the uplift observations can be explained by simple earth models subjected to this load history two layer earth models consisting of an elastic crust and a low viscosity upper mantle half space can be adjusted to fit either the raised shoreline data or the combined gps and tide gauge uplift rate data but cannot fit all the data with a single set of earth model parameters however all three data sets are consistent with an approximated three layer earth model the combined model is constrained by a total of 77 uplift measurements which at the 95 per cent confidence level require a low viscosity asthenosphere a 1 4 0 3 10 19 pa s and thickness 110 20

a method for detecting rapid mass flux of small glaciers using local sea level variations there is increasing evidence that the global reservoir of small or mountain glaciers is presently experiencing an accelerated phase of net melting perhaps linked to climatic warming we argue that relative sea level and sea surface fingerprints local to such events provide a potentially powerful integrated diagnostic for the mass imbalance for example we demonstrate using an inference of glacier mass balance near alaska over the last 50 years that the present day relative sea level fall at nearby sites can reach amplitudes that are 2 orders of magnitude greater than the ongoing eustatic sea level rise associated with the melting the peak sea surface subsidence is a factor of 15 greater than the eustatic amplitude we find that the predicted present day sea surface change arising from the 50 year loading history is sensitive only to the ongoing rate of accelerated melting in contrast the present day relative sea level fingerprint becomes increasingly sensitive to the history of the recent loading when the viscosity of the asthenosphere adopted in the prediction is progressively reduced below 1020 pa s specifically the relative sea level fingerprint becomes more localized and reaches higher amplitudes close to the glacier system as viscous effects become active our results have application in efforts to constrain small glacier mass balance using tide gauge records of relative sea level change or satellite derived constraints on sea surface geoid rates

impacts of post glacial rebound on landslide spatial distribution at a regional scale in northern iceland skagafjorður in de glaciated areas para glaciation i e the conditioning of landscapes by prior glaciation has often been considered a major predisposing factor in landslide occurrence its consequences have been particularly well identified at a fine scale especially on bedrock jointing hitherto the relative impacts of para glaciation on hillslope dynamics at a regional scale had nevertheless not been quantified statistically we examine skagafjor ur area northern iceland where landslides are widespread at least 108 were mapped in an area of c 3000km2 we compare the role of para glaciation debuttressing influence of post glacial rebound with that of classic factors topography lithology etc in landslide occurrence and location using a spatial analysis based on a chi square test on the one hand the results highlight that landslides are over represented in areas where post glacial rebound was at its maximum with a stronger concentration of landslides in the northern part of the fjord on the other hand the distribution of landslides did not show any clear relationship with the pattern of glacial debuttressing tschuprow coefficient highlights that the influence of post glacial rebound on landslide location is higher than the combined influence of slope gradient curvature or geological structure this result is supported by our initial evidence for the timing of landslides in the area most landslides occurred during the first half of the holocene and a period of hillslope instability was initiated when the post glacial uplift was at its maximum finally the mechanisms that link post glacial rebound and landsliding as well as the geomorphic impacts of landslides are discussed

fluid overpressure in subduction plate boundary caused by mantle derived fluids abstract subduction plate boundaries are commonly weak owing to fluid overpressure the generation of fluid overpressure has been invoked for compaction disequilibrium and mineral dehydration in subducting sediments and altered oceanic crust the subduction melange in the shimanto accretionary complex southwest japan preserves the quartz calcite filled shear veins and sigmoidal extension veins formed under fluid overpressure near the downdip limit of the thermally controlled seismogenic zone the shear veins record the repeated low angle brittle thrusting under fluid overpressure while the extension veins constitute the riedel shear zones developed during subduction under vertical maximum principle stress to examine the origin of overpressured fluids we conducted fluid inclusion and noble gas analyses on the shear and extension veins the result of fluid inclusion analysis shows various fluid pressures between lithostatic to hydrostatic pressures during the vein formation which were associated with warm fluid infiltration 3he 4he values of shear veins and extension veins range 1 6 2 5 ra and 1 6 2 3 ra respectively indicating the presence of mantle helium 40ar 36ar values and 84kr 36ar and 130xe 36ar ratios of the veins are similar to those of serpentinized mantle suggesting that mantle helium originated from serpentinized mantle because the mantle derived rocks such as peridotite and serpentinite are absent in the melange the results of noble gas analyses represent the infiltration of fluids from the serpentinized mantle into the melange shear zone our results show that an infiltration of fluids derived from serpentinized mantle contributed the fluid overpressure in the melange shear zone near the downdip limit of the seismogenic zone

tree ring dated little ice age histories of maritime glaciers from western prince william sound alaska tree ring studies at 13 glacier forefields in western prince william sound show little ice age glacial fluctuations were strongly synchronous on decadal timescales cross dated glacially overrun trees at eight sites indicate ice margins advanced in the early late twelfth through thirteenth centuries and middle seventeenth to early eighteenth centuries little ice age tree ring dates of 22 moraines at 13 glaciers show two main periods of stabilization the earlier of these in the first decades of the eighteenth century overlaps with the second period of glaciers overrunning trees and marks culmination of this middle little ice age expansion stabilization of moraines on nine of the study forefields in the latter part of the nineteenth century delineates a third interval of little ice age glacial advance the detailed little ice age record from land terminating glaciers in western prince william sound is consistent on a timescale of decades with four other tree ring dated glacial histories from across the northern gulf of alaska this coastal northeastern pacific glacial record reveals the structure of the little ice age in the region and provides a strong basis for comparison with other proxy climate records spanning the past 1000 years

rapid viscoelastic uplift in southeast alaska caused by post little ice age glacial retreat our observations show that extreme uplift in southeast alaska began about 1770 ad with relative sea level rsl change to 5 7 m and current uplift rates to 32 mm yr this region experienced widespread glacial melting following the little ice age lia with the collapse of the glacier bay icefield alone equivalent to 8 mm of global sea level rise geodynamic modelling links the uplift to post lia isostatic rebound with the extreme uplift signal and a priori knowledge of ice load changes requiring the presence of a low viscosity asthenosphere 3 710 18 pa s these crustal deformations are triggered by climate change

where glaciers meet water subaqueous melt and its relevance to glaciers in various settings glacier change is ubiquitous but the fastest and largest magnitude changes occur in glaciers that terminate in water this includes the most rapidly retreating glaciers and also several advancing ones often in similar regional climate settings furthermore water terminating glaciers show a large range in morphology particularly when ice flow into ocean water is compared to that into freshwater lakes all water terminating glaciers share the ability to lose significant volume of ice at the front either through mechanical calving or direct melt from the water in contact here we present a review of the subaqueous melt process we discuss the relevant physics and show how different physical settings can lead to different glacial responses we find that subaqueous melt can be an important trigger for glacier change it can explain many of the morphological differences such as the existence or absence of floating tongues subaqueous melting is influenced by glacial runoff which is largely a function of atmospheric conditions this shows a tight connection between atmosphere oceans and lakes and glaciers subaqueous melt rates even if shown to be large should always be discussed in the context of ice supply to the glacier front to assess its overall relevance we find that melt is often relevant to explain seasonal evolution can be instrumental in shifting a glacier into a different dynamical regime and often forms a large part of a glacier s mass loss on the other hand in some cases melt is a small component of mass loss and does not significantly affect glacier response

mining induced crustal deformation in northwest germany modelling the rheological structure of the lithosphere abstract large scale coal mining in germany causes deloading of the crust by the removal of weight the crust responds by regional uplift while locally in the mining areas proper the surface subsides by sagging above extracted coal seams and removed groundwater in this study only the regional uplift is addressed the deloading consists of the total annual mass of coal and ground water removal since the 19th century for all significant mines the uplift data are from repeated levellings between about 1950 and 1980 reduced to mean annual rates of elevation change these observations are interpreted as the visco elastic response of the crust and uppermost mantle but alone they cannot discriminate layering from a homogeneous viscous half space or an elastic layer above such a half space if the seismically determined layered structure of upper and lower crust lithosphere mantle and asthenosphere is assumed to constrain the rheological structure a plausible model can be found by inversion only the lower crustal and asthenospheric effective maxwell viscosities are subjected to inversion a model consistent with the observations has the following properties 15 km of elastic upper crust 15 20 km thick lower crust of surprisingly low viscosity of 6 10 17 0 3 pas 30 50 km visco elastic mantle lithosphere with an assumed average viscosity of about 10 22 pas a visco elastic asthenosphere assumed bottomless with 5 10 19 0 6 pas the low viscosity values are consistent with active rifting and above average heat flow in the region the very low effective viscosity of the lower crust in this model it could be even lower if the thickness is smaller may be explained by elevated stresses quartz rheology and water content as suggested by xenoliths from the lower crust below the eifel region as a by product the tectonic subsidence in the lower rhine embayment filled with tertiary and quaternary sediments can be better defined by taking the anthropogenic effect into account

computer simulations of alaskan neotectonics ongoing deformation and fault slip neotectonics in the alaskan bering sea region were modeled with thin plate finite element methods by computing anelastic strain rate stress and velocity fields which represent time averages over several seismic cycles models included variable crust and lithosphere thickness heat flow and elevation and incorporated all faults known or thought to be active three sets of experiments totaling 46 models were computed with systematic variations of shear traction on the megathrust fault friction within north america internal friction of lithospheric blocks and mantle creep strength model quality was scored by comparing predictions to geologic data on fault slip rates the most compressive horizontal principal stress direction and geodimeter and very long baseline interferometry vlbi baseline rates best results were obtained with a driving traction of only 10 15 mpa on the aleutian megathrust and fault friction of only 0 17 within north america this is clearly a low stress model the fanning of away from the syntaxis was reproduced but does not imply high deviatoric stress magnitudes within the north american plate the aleutian forearc west of kodiak island moves westward along strike at rates which increase to 65 mm yr 1 in the komandorsky region however no crust is presently escaping westward from the alaskan syntaxis instead it is shortened and stacked by thrusting principally in the vicinity of the chugach and wrangell mountains because stresses in this model are low and are delicately balanced against topography it is likely that the present regime represents a transient response to plio pleistocene glacial mass redistribution and differs from typical tectonic flow in the tertiary

global geoid and sea level changes due to present day ice mass fluctuations we predict gravitationally self consistent global geoid and relative sea level rsl perturbations due to present day melting of ice complexes including the antarctic and greenland ice sheets and a suite of mountain glaciers and ice sheets classic analyses of sea level change indicate that these perturbations will depart significantly from eustatic i e geographically uniform trends e g woodward 1888 farrell and clark 1976 although this result has not always been appreciated in modern analyses mass flux of individual ice reservoirs will produce unique geometries of sea level change and this distinctiveness admits the possibility of using global geoid sea surface and rsl signatures of recent climate change to infer the ongoing mass balance of each reservoir rather than simply the net mass flux as an example we show that perturbations to the geoid arising from noneustatic water loads associated with each ice reservoir are sufficiently large at low degrees to be theoretically measurable within 5 years by the grace satellite mission we complete the study by reanalyzing tide gauge data at 23 sites selected by douglas 1997 in a recent analysis of global rsl rise traditionally estimates of global sea level rise are generated by taking the mean of a set of secular tide gauge trends that have been corrected for the influence of ongoing glacial isostatic adjustment gia related to the late pleistocene glacial cycles the common assumption in such studies is that the geographic scatter in the residual gia corrected trends is due to errors in the gia model or unmodeled processes e g tectonics we consider a large suite of gia model predictions and apply a least squares approach to the gia corrected tide gauge trends to estimate the weighting of various present day sea level signatures we find that the fit to the residual rsl trends is significantly improved and that the procedure is able to resolve a long standing observation of anomalously low sea level rates in europe this preliminary analysis which is relatively insensitive to changes in the assumed geometry of the present day mass balance assumes that ocean thermal expansion is globally uniform however the procedure can be easily extended to incorporate a realistic steric contribution once the geometry of the process is sufficiently well constrained

reservoir induced deformation and continental rheology in vicinity of lake mead nevada lake mead is a large reservoir in nevada formed by the construction of the 221 m high hoover dam in the black canyon of the colorado river the lake encompasses an area of 635 km2 and the total volume of the reservoir is 35 5 km3 filling started in february 1935 on the basis of a first order leveling in 1935 several levelings were carried out to measure the deformation induced by the load of the reservoir subsidence in the central parts of the lake relative to the first leveling was around 120 mm 1941 218 mm 1950 and 200 mm 1963 the subsidence pattern clearly shows relaxation of the underlying basement due to the water load of the lake which ceased after 1950 modeling of the relaxation process by means of layered viscoelastic compressible flat earth models with a detailed representation of the spatial and temporal distribution of the water load shows that the thickness of the elastic crust underneath lake mead is 30 3 km the data are also consistent with a 10 km thick elastic upper crust and a 20 km thick viscoelastic lower crust with 1020 pa s as a lower bound for its viscosity the subcrust has an average viscosity of 1018 0 2 pa s a surprisingly low value the leveling data constrain the viscosity profile down to 200 km depth

viscoelastic perturbations of the earth significance of the incremental gravitational force in models of glacial isostasy summary the incremental gravitational force igf arises from perturbations of the earth s gravitational potential in glacial isostasy its sources are the surjicial and internal mass redistributions associated with the growth and decay of the continental ice sheets we examine the errors caused by the neglect of the igf using closed form solutions of the equations governing surface load induced perturbations of two types of incompressible spherical earth models 1 maxwellian viscoelastic mantle enclosed by elastic lithosphere and 2 maxwellian viscoelustic mantle enclosing inviscid core calculations in the legendre domain of the radial surface displacement for these models show that neglecting the igf causes enhancement of the elastic response and acceleration of the viscous relaxation in the space domain these changes entail corresponding modifications of the calculated land adjustment the magnitude of the error caused by the neglect of the igf strongly depends on the deglaciation history and load radius adopted assuming a typical deglaciation history the error reaches a maximum of less than 20 m at the end of the deglaciation phase for loads comparable in size to the canadian or the fennoscandian ice sheets we also compare sphericul earth models with igf and plane earth models without igf calculations of the radial surface displacement show that the errors due to the neglect of sphericity and the igf partially compensate each other taking the uncertainties of the observational data into account we conclude that the majority of the canadian and fennoscandian glacial isostatic adjustment data can be modelled with sufficient accuracy using a plane earth model without igf

late pleistocene to holocene marine transgression and thermohaline control on sediment transport in the western magellanes fjord system of chile 53 s abstract in the western strait of magellan in southernmost chile marine transgression occurred between 14 500 and 13 500 cal bp this is indicated by strongly increased accumulation of biogenic carbonate and first appearance of foraminifers in sediment records from that time until 11 500 cal bp sedimentation in the western fjords became predominant autochthonous due to higher salinity and clay flocculation and late glacial glacier retreat present day thermohaline zonation pattern extensively representative for the holocene and sedimentation rates indicate that westerlies hampered westward outflow of superficial 0 30 m water depth glacial clay rich freshwater from glaciated areas during the holocene isostatic uplift of the andes overcompensated sea level rise in areas with high glacial glacier loading this led to shallowing fjord sills and restricted exchange with marine water especially since high freshwater inflow produced strong pycnoclines and preserved old saline water in fjord bottoms to the east of the climate divide the seno skyring fjord system shows a year round stable stratification despite a strong wind induced eastward superficial current in the upper 30 50 m of the water column such currents enabled significant late glacial eastward transport of glacial clay sediment cores from this area indicate that east ward sediment flux slowed down during the holocene probably due to less intense westerlies investigated present day thermohaline characteristics of the fjord system across the superhumid climate divide of the southern andes indicate details of the exchange between marine and freshwater which are fundamental for evaluation of sediment transport pathways biogenic productivity and interpretation of paleoclimate records in this area

ice 3g a new global model of late pleistocene deglaciation based upon geophysical predictions of post glacial relative sea level change a new high resolution global model of late pleistocene deglaciation is inferred on the basis of geophysical predictions of postglacial relative sea level variations in which the ice ocean solid earth interaction is treated in a gravitationally self consistent fashion for the purpose of these analyses the radial viscoelastic structure of the planet is assumed known on the basis of previously published sensitivity tests on solutions of the forward problem only radiocarbon controlled relative sea level histories from sites that were actually ice covered with one or two additions are employed to constrain the model leaving relative sea level rsl data from sites that were not ice covered to be employed to confirm its consistency results for these confirmatory analyses are reported elsewhere here the new deglaciation model referred to as ice 3g is compared to previous models derived by several independent means and tested against a number of additional observations other than sea level histories including geologically controlled retreat isochrones oxygen isotope data from deep sea sedimentary cores and coral terrace elevations the latter two observations strongly constrain the net sea level rise that has occurred since the onset of deglaciation and therefore the mass of ice that melted during the last glacial interglacial transition

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

rapid wastage of alaska glaciers and their contribution to rising sea level we have used airborne laser altimetry to estimate volume changes of 67 glaciers in alaska from the mid 1950s to the mid 1990s the average rate of thickness change of these glaciers was 0 52 m year extrapolation to all glaciers in alaska yields an estimated total annual volume change of 52 15 km 3 year water equivalent equivalent to a rise in sea level sle of 0 14 0 04 mm year repeat measurements of 28 glaciers from the mid 1990s to 2000 2001 suggest an increased average rate of thinning 1 8 m year this leads to an extrapolated annual volume loss from alaska glaciers equal to 96 35 km 3 year or 0 27 0 10 mm year sle during the past decade these recent losses are nearly double the estimated annual loss from the entire greenland ice sheet during the same time period and are much higher than previously published loss estimates for alaska glaciers they form the largest glaciological contribution to rising sea level yet measured

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

constraints on regional drivers of relative sea level change around cordova alaska abstract new records of paleoenvironmental change from two lakes near cordova south central alaska combined with analysis of previously reported sediment sequences from the adjacent copper river delta provide quantitative constraints on a range of earth system processes through their expression in relative sea level change basal sediment ages from upper whitshed lake indicate ice free conditions by at least 14 140 15 040 cal yr bp while upper and lower whitshed lakes provide only upper limits to relative sea level change interbedded layers of freshwater peat and intertidal silt extending more than 11 m below present sea level in copper river delta indicate net submergence over the last 6000 years and multiple earthquake deformation cycles in contrast lower whitshed lake situated just above present high tide level records only one episode of marine sedimentation commencing ad 1120 1500 that we interpret as the result of isostatic subsidence due to little ice age mass accumulation of the chugach mountain glaciers lower whitshed lake also records isostatic uplift at the end of the little ice age before the end of marine sedimentation caused by 1 5 m coseismic uplift in the great alaska earthquake of ad 1964 we successfully explain the records of relative sea level change from both copper river delta and the whitshed lakes by integrating the effects of eustatic sea level rise glacial isostasy earthquake deformation cycles sediment loading sediment compaction and late holocene changes in glacier mass into a single model this approach provides initial quantitative constraints on the individual contributions of these processes taking reasonable estimates of eustasy post last glacial maximum and neoglacial glacial isostatic adjustment and a simple earthquake deformation cycle we demonstrate that sediment loading and sediment compaction are both contributors to relative sea level rise at copper river delta together producing subsidence averaging approximately 1 2 mm yr 1 over the mid to late holocene further isolation basin studies have the potential to greatly improve our understanding of the individual contributions of these processes in this highly dynamic region

post glacial rebound and asthenosphere viscosity in iceland during the weichselian glaciation iceland was covered with an ice cap which caused downward flexure of the earth s surface the post glacial rebound in iceland was very rapid being completed in about 1 000 years the length of this time interval constrains the maximum value of asthenosphere viscosity in iceland to be 1 times 10 sup 19 pa s or less further clarification of the ice retreat and uplift history may reveal lower viscosity current changes in the mass balance of icelandic glaciers must lead to measurable elevation changes considering this low viscosity expected current elevation changes around the vatnajoekull ice cap are of the order of 1 cm per year due to mass balance change in this century

the thermochronological record of tectonic and surface process interaction at the yakutat north american collision zone in southeast alaska we investigate the material fluxes in space and time as a result of exhumation and erosion processes at the ongoing yakutat north american collision in southeast alaska many thermochronologic studies using a variety of sampling strategies are challenged by the widespread ice cover that limit field observations and accessibility this paper reviews new and published low temperature thermochronological data from southeast alaska to give a comprehensive interpretation of the exhumation patterns through time and how they are influenced by surface processes and climate change we find that the southeastern margin of alaska was exhumed and eroded long before the late miocene pliocene yakutat collision but since the beginning of the subduction of the yakutat lithosphere in the oligocene early miocene today there is a distinct pattern of exhumation in southeast alaska with a localized very rapid and deep seated exhumation at the yakutat plate corner st elias syntaxis where strike slip motion changes to convergence exhumation is also rapid but less deep along the dextral fairweather fault and in the evolving fold and thrust belt we present a re interpretation of the exhumation pattern in the fold and thrust belt and suggest that mass transport by exhumation is parallel to the observed active thrust faults and oblique to the suture zone and orogenic strike the locus of most rapid exhumation migrated from northwest to southeast with recent exhumation occurring near the st elias syntaxis exhumation of the chugach terrane rocks is still active however to a lesser degree than on the south side of the orogen where precipitation rates are much higher the wrangellia terrane to the north has experienced little exhumation and has essentially formed the backstop for terrane accretion in southeast alaska since the early cretaceous apatite u th he ages give the first evidence that rocks of the wrangell range have only been recently uplifted and eroded as a consequence of the continuing yakutat collision in general the thermochronology in southeast alaska reveals that climate variations across the region as well as changes through time have a limited influence on the pattern of erosion and that the location of deep exhumation is primarily influenced by tectonic processes

viscosity estimates for the crust and upper mantle from patterns of lacustrine shoreline deformation in the eastern great basin the deformed shorelines of lake bonneville constitute a classic source of information on lithospheric elastic thickness and upper mantle viscosity we describe and apply a new model to a recently augmented data set new data better constrain both the complex spatio temporal pattern of the lake load and the crustal deformation response to that load the history of lake level fluctuations has been significantly refined and somewhat modified this is due to both more radiocarbon dates from within the bonneville basin and to an improved calibration of the radiocarbon timescale itself the data which constrain the crustal deformation pattern consist of ages and shoreline elevations from several hundred points which sample three major levels of lake bonneville and corresponding elevations from the high stands of three smaller lakes situated to the west of lake bonneville the data from the smaller lakes help elucidate the pattern of deflection which occurred beyond the edge of the big lake the geometry of the earth model incorporates an arbitrary number of layers overlying a half space and the rheology of each level can accommodate an arbitrary number of maxwell viscoelastic elements in parallel the inverse modeling comprises three complementary approaches for the simplest configurations we performed a direct search of the parameter space and delineated the irregular boundary of the subspace of acceptable models for more complex configurations we constrained the elastic parameters to their seismically determined values and then solved for viscosity versus depth profiles by either expressing the log viscosity versus log depth profile as a series of specially constructed orthogonal polynomials or by allowing each of 8 10 layers plus the half space to have an independently determined viscosity we found that the data do not strongly support nor can they conclusively exclude a more complex rheology than simple maxwell viscoelasticity the orthogonal polynomial solution exhibits an essentially monotonic decrease in viscosity with depth the most rapid change occurs at shallow depths decreasing from 1023 pa s at 3 km to 102o pa s at 30 km the decrease is much more gradual below with only another factor of 5 decrease between 30 and 300 km depth the unconstrained solution exhibits a rapid decrease in viscosity with depth from 2x 10 24 pa s in the top 10 km to 4x 1017 pa s at a depth of 40 km a nearly isoviscous asthenospheric region extends from 40 to 150 km and is underlain by a mantle lithospheric region with increased viscosity 2x 102o pa s extending from 150 to 300 km depth and by a uniform viscosity 1019 pa s half space below

assessing the impact of vertical land motion on twentieth century global mean sea level estimates near global and continuous measurements from satellite altimetry have provided accurate estimates of global mean sea level in the past two decades extending these estimates further into the past is a challenge using the historical tide gauge records not only is sampling nonuniform in both space and time but tide gauges are also affected by vertical land motion vlm that creates a relative sea level change not representative of ocean variability to allow for comparisons to the satellite altimetry estimated global mean sea level gmsl typically the tide gauges are corrected using glacial isostatic adjustment gia models this approach however does not correct other sources of vlm that remain in the tide gauge record here we compare global positioning system gps vlm estimates at the tide gauge locations to vlm estimates from gia models and assess the influence of non gia related vlm on gmsl estimates we find that the tide gauges on average are experiencing positive vlm i e uplift after removing the known effect of gia resulting in an increase of 0 24 0 08 mm yr 1 in gmsl trend estimates from 1900 to present when using gps based corrections while this result is likely dependent on the subset of tide gauges used and the actual corrections used it does suggest that non gia vlm plays a significant role in twentieth century estimates of gmsl given the relatively short gps records used to obtain these vlm estimates we also estimate the uncertainty in the gmsl trend that results from limited knowledge of non gia related vlm