stereo radargrammetry with radarsat 2 in the canadian arctic a digital elevation model dem is generated using a radarsat 2 r 2 high resolution stereo pair acquired over challenging icefields and fjords site in the canadian arctic 80 of ice covered areas and almost 50 of 40 circ slopes the stereo dem was produced using a new hybrid radargrammetric model which did not need any reference cartographic data the accuracy of the stereo dem was quantified with a topographic 1959 dem and ice cloud and land elevation satellite icesat data over and outside the icefields and as a function of slope the method could be applied to ice covered areas with 1 sigma 25 or 18 m accuracy over less than 30 circ or 5 circ slopes respectively in addition a systematic elevation lowering of around 10 m computed between 1959 dem and recent elevation data r 2 and icesat could be due to icefield wastage over the last 50 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

glacier changes in southeast alaska and northwest british columbia and contribution to sea level rise 1 the digital elevation model dem from the 2000 shuttle radar topography mission srtm was differenced from a composite dem based on air photos dating from 1948 to 1987 to determine glacier volume changes in southeast alaska and adjoining canada srtm accuracy was assessed at 5 m through comparison with airborne laser altimetry and control locations measured with gps glacier surface elevations lowered over 95 of the 14 580 km2 glacier covered area analyzed with some glaciers thinning as much as 640 m a combination of factors have contributed to this wastage including calving retreats of tidewater and lacustrine glaciers and climate change many glaciers in this region are particularly sensitive to climate change as they have large areas at low elevations however several tidewater glaciers that had historically undergone calving retreats are now expanding and appear to be in the advancing stage of the tidewater glacier cycle the net average rate of ice loss is estimated at 16 7 4 4 km3 yr equivalent to a global sea level rise contribution of 0 04 0 01 mm yr

recent volume and area changes of kaskawulsh glacier yukon canada recent surface elevation changes of kaskawulsh glacier yukon canada are quantified by comparing an air photo derived dem from 1977 and airborne lidar measurements from 1995 2000 and 2007 surface area changes are assessed using historical aerial photography from 1956 and satellite imagery from 1977 to 2007 combined these measurements provide some of the first detailed records of volume change of a large yukon glacier between 1977 and 2007 kaskawulsh glacier underwent a decrease in area of 1 53 and a decrease in volume of 3 27 5 94 km 3 w e the terminus also retreated by 655 m over the period 1956 2007 there was relatively minor volume change over the period 1977 95 0 01 km 3 w e a 1 while over the periods 1995 2000 and 2000 07 volume losses occurred at a relatively constant rate of 0 51 and 0 50 km 3 a 1 w e respectively since 1995 thinning has been prominent throughout the ablation zone while relative stability and even slight thickening has occurred in the accumulation zone these findings are similar to those recently observed at other nearby alaskan glaciers

seasonal fluctuations in the advance of a tidewater glacier and potential causes hubbard glacier alaska usa satellite imagery has been used to acquire seasonal terminus positions of tidewater hubbard glacier alaska usa from 1992 to 2006 during this 15 year time period the width averaged advance of the entire terminus has been 620 m at a mean rate of 35 m a 1 seasonal fluctuation of the terminus ranges from 150 to 200 m on average and varies spatially a section of the terminus near a narrow gap where the glacier has now twice closed off 40 km long russell fiord exhibited little to no mean advance during this time period but displayed seasonal fluctuations of 300 500 m seasonal variability in surface ice speeds and surface sea water temperatures was also observed both are potential forcing mechanisms for terminus fluctuations seasonal changes in sea water temperature of 10 128c as well as seasonal changes in subglacial freshwater discharge are inferred to influence calving and submarine melting at the terminus driving seasonal variations displacements of the medial moraine separating hubbard and valerie glaciers at the terminus suggest surge like pulses of the latter with a periodicity of several years the timing of these pulses suggests they may influence the hubbard terminus near gilbert point and have implications for future closures of russell fiord

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

recent glacier mass changes in the gulf of alaska region from grace mascon solutions the mass changes of the gulf of alaska goa glaciers are computed from the gravity recovery and climate experiment grace inter satellite range rate data for the period april 2003 september 2007 through the application of unique processing techniques and a surface mass concentration mascon parameterization the mass variations in the goa glacier regions have been estimated at high temporal 10 day and spatial 2 2 arc degrees resolution the mascon solutions are directly estimated from a reduction of the grace k band inter satellite range rate data and unlike previous grace solutions for the goa glaciers do not exhibit contamination by leakage from mass change occurring outside the region of interest the mascon solutions reveal considerable temporal and spatial variation within the goa glacier region with the largest negative mass balances observed in the st elias mountains including the yakutat and glacier bay regions the most rapid losses occurred during the 2004 melt season due to record temperatures in alaska during that year the total mass balance of the goa glacier region was 84 5 gt a 1 contributing 0 23 0 01 mm a 1 to global sea level rise from april 2003 through march 2007 highlighting the large seasonal and interannual variability of the goa glaciers the rate determined over the period april 2003 march 2006 is 102 5 gt a 1 which includes the anomalously high temperatures of 2004 and does not include the large 2007 winter balance year snowfall the mascon solutions agree well with regional patterns of glacier mass loss determined from aircraft altimetry and in situ measurements

identification and characterization of alpine subglacial lakes using interferometric synthetic aperture radar insar brady glacier alaska usa the temporary storage and subsequent release of water at glacial margins can cause severe flooding in downstream areas and substantially impact glacier dynamics alpine subglacial lakes may not be identified until they become subaerially exposed or release a jokulhlaup we use interferometric synthetic aperture radar insar to identify and characterize three dynamic alpine subglacial lakes of brady glacier alaska usa we quantify changes in vertical displacement of the glacier surface and lake volumes from september 1995 through march 1996 using european remote sensing satellite 1 2 ers 1 2 tandem data in the autumn subsidence ranged from 4 to 26 cm d 1 and the volume of water discharged ranged from 22 000 2000 to 243 000 14 000 m 3 d 1 subsidence and discharge rates declined significantly during the winter and continued at a lesser rate through march application of this technique may allow researchers to locate alpine subglacial lakes years or decades before they begin to release hazardous outburst floods and substantially impact glacier dynamics

paleomagnetic data from the precordillera of northern chile a multiphase rotation history related to a multiphase deformational history abstract one of the most conspicuous features of the andean chain is the change in its trajectory from nw se to n s at 18 s known as the bolivian orocline although the central andes rotation pattern carp agrees roughly with the geometry of the orocline large variations and greater than expected rotation magnitudes cannot be explained by a progressive oroclinal bending history alone in this work 621 oriented samples from mesozoic and cenozoic rocks in three different areas in the precordillera of northern chile north of calama were analyzed the samples were subjected to different demagnetization processes to isolate the characteristic magnetic remanence and calculate the tectonic rotations by sampling pretectonic syntectonic and post tectonic units the rotation history of different structural blocks was determined and related to specific deformational events the results obtained from lower cretaceous units intruded or overlain by upper cretaceous units not rotated or recording smaller rotations indicate the existence of 20 clockwise and 20 counterclockwise rotated sites related to the late cretaceous peruvian orogenic event data obtained from upper cretaceous lowermost paleocene rocks show areas slightly clockwise rotated 10 15 and not rotated during the early paleocene k t deformation event remanence data from upper cretaceous eocene units across the area indicate as much as 20 clockwise rotation in the hanging wall of the eocene chintoraste quetena rabonas jaspe reverse fault system whereas the footwall was unaffected this eocene rotation occurred during the early stages of the eocene oligocene incaic orogenic phase prior to emplacement of the 40 37 ma fortuna granodiorite complex current models propose that rotations in carp were entirely cenozoic and largely accomplished in a single paleogene event our data indicate that each of the peruvian k t and incaic deformation events contributed to carp with each event generating a non uniform pattern of rotations which was superimposed on prior rotations in a non uniform manner

climatic and morphometric controls on the altitudinal range of glaciers british columbia canada to examine the relation between climate and glacier extent we compared gridded monthly temperature and precipitation data to the altitudinal range of glaciers in british columbia canada we related glacier relief to ablation season temperature june august accumulation season precipitation september march and morphometric variables that included slope glacier order and a shape index for 523 alpine glaciers that ranged from 5 to 15 km2 in surface area a 1 c increase in mean june august temperature equates to a 109 to 182 m decrease in glacier relief and a 1 mm increase in mean monthly september march precipitation equates to a 0 78 to 2 20 m increase in glacier relief the most important morphometric controls on this glacier climate relation include average surface slope glacier order analogous to stream order and the ratio of upper accumulation area to lower ablation area width all of which are positively related to glacier relief we note strong relations between glacier relief and cli

use of historical elevation data to calculate surface elevation and volume changes of ha iltzuk icefield southwest british columbia canada 1970 to mid 1980s investigations into glacial changes including understanding variations in the rates of glacial volume and surface elevation changes have increased over the past decade this study uses historical glacier elevation data in the form of topographic maps from 1970 and a digital elevation model from the mid 1980s to calculate surface elevation and volume changes for ha iltzuk icefield southwest british columbia canada results indicate that the icefield thinned at an average rate of 0 76 0 25 m a 1 during this period a previous study of ha iltzuk icefield also using the geodetic method found a thinning rate of 1 0 0 20 m a 1 between the mid 1980s and 1999 indicating a slight increase in the amount of icefield thinning within the ablation zone thinning increased with decreasing elevation at a rate of 1 9 0 68 m a 1 km 1 between these two periods 1970 to mid 1980s versus mid 1980s to 1999 analysis of meteorological data suggests that increases in both temperature and rainfall as well as decreases in snowfall likely contributed to the increased thinning rate

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

penetration depth of interferometric synthetic aperture radar signals in snow and ice digital elevation models of glaciated terrain produced by the nasa jet propulsion laboratory jpl airborne interferometric synthetic aperture radar insar instrument in greenland and alaska at the c 5 6 cm wave length and l band 24 cm frequencies were compared with surface elevation measured from airborne laser altimetry to estimate the phase center of the interferometric depth or penetration depth p on cold polar firn at greenland summit p 9 2m at c and 14 4m at l band on the exposed ice surface of jakobshavn isbrae west greenland p 1 2 m at c and 3 3 m at l band except on smooth marginal ice where p 15 5 m on colder marginal ice of northeast greenland p reaches 60 to 120 m at l band on the temperate ice of brady glacier alaska p is 4 2 m at c and 12 6 m at l band with little dependence on snow ice conditions the implications of the results on the scientific use of insar data over snow ice terrain is discussed

short term flow dynamics of a retreating tidewater glacier leconte glacier alaska u s a an analysis of motion in the terminus region of leconte glacier alaska u s a delineates mechanisms that are important to tidewater glacier stability this glacier is undergoing rapid retreat since 1995 it has retreated 2 km and thinned 125 m at the present location of the terminus ice velocities in this region are quite high at the terminus they exceed 27 m d 1 our analysis reveals that fluctuations in speed and surface elevation are forced by ocean tides surface melt and precipitation the near terminus ice speed is 180 out of phase with the tide such that high tide corresponds to low speed smaller melt forced diurnal variations in speed are present throughout the lowermost 7 km speed ups in excess of 10 of the mean often occur after rainstorms as a result of increased basal water pressure and storage but the relation is not simple the velocity does not vary over the spring and summer seasons

glacier changes in alaska can mass balance models explain grace mascon trends temperature and precipitation data from three weather stations in the st elias mountains of alaska and northwestern canada were used to drive one dimensional 1 d elevation dependent and 0 d degree day mass balance models model outputs were optimized against a 10 day resolution time series of mass variability during 2003 07 obtained from gravity recovery and climate experiment grace mass concentration mascon solutions the models explained 52 60 of the variance in the grace time series modelled mass variations matched the phase of the grace observations and all optimized model parameters were within the range of values determined from conventional mass balance and meteorological observations we describe a framework for selecting appropriate weather stations and mass balance models to represent glacier variations of large regions there is potential for extending these calibrated mass balance models forwards or backwards in time to construct mass balance time series outside of the grace measurement window

elevation and volume changes on the harding icefield alaska airborne surface elevation profiles of the harding icefield south central alaska were made in 1994 and 1996 thirteen glaciers were profiled along with the upper region of the icefield the profiles were compared to u s geological survey topographic maps made in the 1950s to obtain elevation and volume changes comparison of the changes for the different glaciers shows no significant correlation between volume change and the type of glacier or characteristics such as location aspect size slope or terminus changes estimated total volume change for this 43 year period is about 34 km 3 which corresponds to an area average elevation change of 21 m the estimated error in this elevation change of 5 m is mainly due to errors in the maps at higher elevations our measurements provide an accurate baseline against which future determinations of volume change can be made

recent volume loss of british columbian glaciers canada 1 we use the shuttle radar topography mission srtm data and digital terrain models from aerial photography to quantify the change of glacier volume in british columbia bc canada for the period 1985 1999 we note substantial elevation bias in the srtm elevations typically on the order of 12 m km 1 the bias corrected thinning rate is 0 78 0 19 m a 1 which yields an annual volume loss of 22 48 5 53 km 3a 1 this rate of glacier volume loss is 65 of the estimate uncorrected for elevation bias 34 7 km 3a 1 and cautions against the use of uncorrected srtm data for glacier change studies glacier recession in bc could account for ca 0 67 0 12 mm of sea level rise over the period 1985 1999 0 05 0 009 mm yr 1 or about 8 3 of the contribution from mountain glaciers and ice caps the recent rate of glacier loss in the coast mountains 17 0 km 3a 1 is approximately double that observed for the previous two decades

effect of large eddies on atmospheric surface layer turbulence and the underlying wave field to improve existing models for air sea interaction a better understanding of the energy transfer across the boundary layer and in particular of the coupling of large atmospheric eddies with the air sea interface is needed recent investigations have already shown a possible coupling of large structures in atmospheric turbulence and surface ripples this was done using synthetic aperture radar sar imagery of ocean surface and almost simultaneous advanced very high resolution radiometer avhrr imagery of cloud streets at a cold air outbreak the intent of our study is to further validate this hypothesis in a general case of coastal circulation for this purpose we analyze a suite of collocated simultaneous records of airflow radar return and surface elevations from a coastal platform we investigate the influence of large eddies 20 60 min on the turbulent properties of the airflow in the first 2 m above the ocean surface the analysis shows very prominent peaks in the magnitude of 12 to 16 min fluctuations which are further modulated in 20 to 40 min intervals these scales and modulations are characteristic for all variables of interest here the detected scales and their modulation suggest significant interaction of surface layer within the first 1 2 m with large eddies of scales of o 1 and o 10 km the intermittent structure of turbulence responds by alternating contributions from bursts and sweeps the frequency of occurrence of bursts and sweeps also reveals the influence of large structures the instantaneous cross correlation between the shorter scales of momentum flux and radar return corresponding to the individual burst events can be 4 times as strong as the overall cross correlation

the surges of variegated glacier alaska u s a and their connection to climate and mass balance one of the questions still unanswered concerning the surge behavior of glaciers concerns their quasi periodic occurrence some results on the phenomenological connection between local cumulative balance and surge initiation of variegated glacier alaska u s a are discussed here based on climate data from neighboring weather stations an empirical relation between precipitation temperature and local mass balance is established and used to reconstruct the annual balance at a location in the accumulation area back to 1905 between the last four surges in 1946 47 1964 65 1982 83 and 1994 95 the ice equivalent cumulative balance was 43 5 m on average with a 1 error of 1 2 m although the existence of a surge level cannot be directly interpreted in physical terms it explains the variable length of the quiescent periods of variegated glacier by variations in the accumulation rate prior to the surge we use the surge level to hindcast former unobserved surges to compare the results with other surge datings obtained from photographs and to establish a complete surge history for variegated glacier for the 20th century

contribution of the patagonia icefields of south america to sea level rise digital elevation models of the northern and southern patagonia icefields of south america generated from the 2000 shuttle radar topography mission were compared with earlier cartography to estimate the volume change of the largest 63 glaciers during the period 1968 1975 2000 these glaciers lost ice at a rate equivalent to a sea level rise of 0 042 0 002 millimeters per year in the more recent years 1995 2000 average ice thinning rates have more than doubled to an equivalent sea level rise of 0 105 0 011 millimeters per year the glaciers are thinning more quickly than can be explained by warmer air temperatures and decreased precipitation and their contribution to sea level per unit area is larger than that of alaska glaciers

flotation and retreat of a lake calving terminus mendenhall glacier southeast alaska usa mendenhall glacier is a lake calving glacier in southeastern alaska usa that is experiencing substantial thinning and increasingly rapid recession long term mass wastage linked to climatic trends is responsible for thinning of the lower glacier and leaving the terminus vulnerable to buoyancy driven calving and accelerated retreat bedrock topography has played a major role in stabilizing the terminus between periods of rapid calving and retreat lake terminating glaciers form a population distinct from both tidewater glaciers and polar ice tongues with some similarities to both groups lacustrine termini experience fewer perturbations e g tidal flexure high subaqueous melt rates and are therefore inherently more stable than tidewater termini at mendenhall rapid thinning and simultaneous retreat into a deeper basin led to flotation conditions along approximately 50 of the calving front this unstable terminus geometry lasted for approximately 2 years and culminated in large scale calving and terminus collapse during summer 2004 buoyancy driven calving events and terminus break up can result from small rapidly applied perturbations in lake level

using stereo satellite imagery to account for ablation entrainment and compaction in volume calculations for rock avalanches on glaciers application to the 2016 lamplugh rock avalanche in glacier bay national park alaska

seasonal hydrological loading in southern alaska observed by gps and grace 1 we compare vertical seasonal loading deformation observed by continuous gps stations in southern alaska and modeled vertical displacements due to seasonal hydrological loading inferred from grace seasonal displacements are significant and gps observed and grace modeled seasonal displacements are highly correlated we define a measure called the wrms reduction ratio to measure the fraction of the position variations at seasonal periods removed by correcting the gps time series using a seasonal model based on grace the median wrms reduction ratio is 0 82 and the mean is 0 73 0 26 with a value of 1 0 indicating perfect agreement of gps and grace the effects of atmosphere and non tidal ocean loading are important we add the aod1b de aliasing model to the grace solutions because the displacements due to these loads are present in the gps data and this improves the correlations between these two geodetic measurements we find weak correlations for some stations located in areas where the magnitude of the load changes over a short distance due to grace s limited spatial resolution grace models can correct seasonal displacements for campaign gps measurements as well

does calving matter evidence for significant submarine melt abstract during the summer in the northeast pacific ocean the alaska coastal current sweeps water with temperatures in excess of 12 c past the mouths of glacierized fjords and bays the extent to which these warm waters affect the mass balance of alaskan tidewater glaciers is uncertain here we report hydrographic measurements made within icy bay alaska and calculate rates of submarine melt at yahtse glacier a tidewater glacier terminating in icy bay we find strongly stratified water properties consistent with estuarine circulation and evidence that warm gulf of alaska water reaches the head of 40 km long icy bay largely unaltered a 10 20 m layer of cold fresh glacially modified water overlies warm saline water the saline water is observed to reach up to 10 4 c within 1 5 km of the terminus of yahtse glacier by quantifying the heat and salt deficit within the glacially modified water we place bounds on the rate of submarine melt the submarine melt rate is estimated at 9 m d 1 at least half the rate at which ice flows into the terminus region and can plausibly account for all of the submarine terminus mass loss our measurements suggest that summer and fall subaerial calving is a direct response to thermal undercutting of the terminus further demonstrating the critical role of the ocean in modulating tidewater glacier dynamics

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

map based methods for estimating glacier equilibrium line altitudes we examine the validity of two methods for estimating glacier equilib rium line altitudes elas from topographic maps the ela determined by contour inflection the kinematic ela andthe mean elevation of the glacier correlate extremely well with the ela determined from mass balance data observed ela however the range inglacierelevations above sea level is much larger thanthe variation in ela mak ing this correlation unhelpful the data were normalized and a reasonable correlation r 2 0 59 was found between observed and kinematic ela the average of the normal ized kinematic elas was consistently located down glacier fromthe observed ela con sistent withtheory thenormalized mean elevationoftheglacierexhibitedno correlation and suggests that the toe headwall altitude ratio is not a good approximation for the ela kinematic waves had no effect on the position of the kinematic ela therefore topographic maps of glacier surfaces can be used to infer the position of the ela and provide a method for estimating past elas from historic topographic maps

rapid submarine melting driven by subglacial discharge leconte glacier alaska 1 we show that subglacial freshwater discharge is the principal process driving high rates of submarine melting at tidewater glaciers this buoyant discharge draws in warm seawater entraining it in a turbulent upwelling flow along the submarine face that melts glacier ice to capture the effects of subglacial discharge on submarine melting we conducted 4 days of hydrographic transects during late summer 2012 at leconte glacier alaska a major rainstorm allowed us to document the influence of large changes in subglacial discharge we found strong submarine melt fluxes that increased from 9 1 1 0 to 16 8 1 3 m d 1 ice face equivalent frontal ablation as a result of the rainstorm with projected continued global warming and increased glacial runoff our results highlight the direct impact that increases in subglacial discharge will have on tidewater outlet systems these effects must be considered when modeling glacier response to future warming and increased runoff

mass balance in the glacier bay area of alaska usa and british columbia canada 1995 2011 using airborne laser altimetry the glacier bay region of southeast alaska usa and british columbia canada has undergone major glacier retreat since the little ice age lia we used airborne laser altimetry elevation data acquired between 1995 and 2011 to estimate the mass loss of the glacier bay region over four time periods 1995 2000 2000 05 2005 09 2009 11 for each glacier we extrapolated from center line profiles to the entire glacier to estimate glacier wide mass balance and then averaged these results over the entire region using three difference methods normalized elevation area weighted method and simple average we found that there was large interannual variability of the mass loss since 1995 compared with the long term post lia average for the full period 1995 2011 the average mass loss was 3 93 0 89 gt a 1 0 6 0 1 m w e a 1 compared with 17 8 gt a 1 for the post lia 1770 1948 rate our mass loss rate is consistent with grace gravity signal changes for the 2003 10 period our results also show that there is a lower bias due to center line profiling than was previously found by a digital elevation model difference method

contribution of alaskan glaciers to sea level rise derived from satellite imagery over the last 50 years retreating glaciers and ice caps gic contributed 0 5 mm yr to sea level rises slr and one third is believed to originate from ice masses bordering the gulf of alaska however these estimates of ice wastage in alaska are based on methods that measure a limited number of glaciers and extrapolate the results to estimate ice loss for the many thousands of others how these methods capture the complex pattern of decadal elevation changes at the scale of individual glacier and mountain range is unclear here combining a comprehensive glacier inventory with elevation changes derived from sequential digital elevation models dems we found that between 1962 and 2006 alaskan glaciers lost 41 9 8 6 km 3 yr water equivalent w e and contributed 0 12 0 02 mm yr to slr our ice loss is 34 lower than previous estimates reasons for our lower values include the higher spatial resolution of our glacier inventory and the reduction of ice thinning under debris and at the glacier margins which were not resolved in earlier work estimates of mass loss from gic in other mountain regions could be subject to similar revisions

glacier change in western north america influences on hydrology geomorphic hazards and water quality the glaciers of western canada and the conterminous united states have dominantly retreated since the end of the little ice age lia in the nineteenth century although average rates of retreat varied from strong in the first half of the twentieth century with glaciers stabilizing or even advancing until 1980 and then resuming consistent recession this retreat has been accompanied by statistically detectable declines in late summer streamflow from glacier fed catchments over much of the study area although there is some geographical variation over recent decades glaciers in northwest bc and southwest yukon have lost mass dominantly by thinning with relatively low rates of terminal retreat and glacier fed streams in that region have experienced increasing flows in many valleys glacier retreat has produced geomorphic hazards including outburst floods from moraine dammed lakes mass failures from oversteepened valley walls and debris flows generated on moraines in addition to these hydrologic and geomorphic changes evidence is presented that glacier retreat will result in higher stream temperatures possibly transient increases in suspended sediment fluxes and concentrations and changes in water chemistry with climate projected to continue warming over the twenty first century current trends in hydrology geomorphology and water quality should continue with a range of implications for water resources availability and management and hydroecology particularly for cool and cold water species such as salmonids copyright 2008 john wiley sons ltd

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

how do glaciers surge a review the quasi periodic oscillations between normal and fast motion exhibited by surge type glaciers provide the best observational opportunity to determine limiting conditions that allow fast motion the measurements from variegated glacier prove that its surge motion is caused by rapid sliding induced by high water pressure this arises from a major restructuring of the basal hydraulic system which impedes water discharge prior to and during surge although the evolving glacier geometry and stress distribution play a principal enabling role the seasonal timing of two distinct surge pulses each initiated in winter and terminated in summer indicates a major influence from variable external water inputs this influence is not considered in existing surge models and should promote caution in the use of data from temperate and subpolar surge type glaciers to deduce surge potential in polar ice masses the spatial spreading of surge motion from a zone of local initiation occurs by stress redistribution which may spread the surging zone rapidly upglacier or downglacier inside a region of active ice and by mass redistribution with compressional thickening at the surge front which enables down glacier propagation into less active ice the data from other surge type glaciers including the extensive data from medvezhiy glacier are not inconsistent with the above processes but are inadequate to establish whether completely different mechanisms operate in some surges the way by which water accumulates and produces fast sliding is not established in detail for any surge type glacier and may be different on different glaciers depending for example on the presence or absence of unconsolidated debris between the ice and rock

evolution of glacier dammed lakes through space and time brady glacier alaska usa abstract glacier dammed lakes and their associated jokulhlaups cause severe flooding in downstream areas and substantially influence glacier dynamics brady glacier in southeast alaska is well suited for a study of these phenomena because it presently dams 10 large 1 km 2 lakes our objectives are to demonstrate how brady glacier and its lakes have co evolved in the past and to apply this knowledge to predict how the glacier and its lakes will likely evolve in the future to accomplish these objectives we georeferenced a variety of maps airphotos and optical satellite imagery to characterize the evolution of the glacier and lakes we also collected bathymetry data and created bathymetric maps of select lakes despite small advances and retreats the main terminus of brady glacier has changed little since 1880 however it downwasted at rates of 2 3 m y between 1948 and 2000 more than the regional average the most dramatic retreat 2 km and downwasting 120 m have occurred adjacent to glacier dammed lakes and are primarily the result of calving brady glacier is a former tidewater glacier with continued downwasting brady glacier may return to a tidewater regime and enter into a phase of catastrophic retreat the situation at brady glacier is not unique and the lessons learned here can be applied elsewhere to identify future glacier dammed lakes jokulhlaups and glacier instability

rapid sea level rise abstract several global and regional factors contribute to observed sea level change along any particular coast global processes include changes in ocean mass glacio eustasy from ice melt ocean volume steric effects viscoelastic land movements glacioisostatic adjustment gia and changes in terrestrial water storage regional processes often connected to steric and glacial changes include changes in ocean circulation meridional overturning circulation moc glacial melting local gia regional subsidence and others paleoclimate instrumental and modeling studies show that combinations of these factors can cause relatively rapid rates of sea level rise exceeding 3 mm yr 1 over various timescales along particular coasts this paper discusses patterns and causes of sea level rise with emphasis on paleoclimatological records it then addresses the hypothesis of late holocene pre 20th century sea level stability in light of paleoclimatic evidence notably from reconstructions of sea surface temperature and glacial activity for significant climate and sea level variability during this time the practical difficulties of assessing regional sea level sl patterns at submillennial timescales will be discussed using an example from the eastern united states

holocene glacial history of the lituya district southeast alaska radiocarbon dates from the lituya district of southeast alaska indicate the occurrence of at least four glacial periods during the past 10 000 years further detail is added to the record by a relative age chronology for moraines based on cross cutting relationships as well as soil vegetation and boulder weathering characteristics the most recent deglaciation occurred approximately 350 500 years bp ending advances begun shortly after 1500 years bp the relative age chronology for moraines indicates that at least three episodes of moraine building occurred during this period dates on logs in outwash and organic deposits in a moraine pond indicate glacial recession 1500 1900 years bp this recession was preceded by advances beginning sometime after 3600 years bp and including several periods of moraine construction radiocarbon dated basal organics in moraine ponds buried soils and overridden forest beds delimit a mid holocene advance ending before 5000 years bp and probably starting around 6000 yea

spatial variability of glacier elevation changes in the swiss alps obtained from two digital elevation models 1 massive glacier thinning in the alps during the past 20 years is documented by direct mass balance measurements on nine regularly observed glaciers how representative this limited sample of glaciers is for the entire alps however remained uncertain the near global digital terrain model from the srtm enables a closer analysis of this question which is of fundamental importance to assess overall glacier volume change here we present elevation changes from 1985 to 1999 for about 1050 glaciers in the swiss alps the analysis reveals extreme thickness losses 80 m for flat low lying glacier tongues and a strong overall surface lowering the mean cumulative mass balance of the nine glaciers with direct measurements 10 8 m w e agrees well with the mean change of the entire region from dem differencing 11 m w e and can thus be considered to be representative mean thickness change of individual glaciers is correlated with their size elevation and exposure to solar irradiation this implies that mass losses of large glaciers can be underestimated when they are directly inferred from values measured at much smaller glaciers

quantifying the effects of climate and surface change on glacier mass balance when a mass balance is computed using an outdated map that computation does not reveal the actual mass change but older maps often must be used for practical reasons we present a method by which with a few additional measurements each year a mass balance computed with an outdated map can be transformed into an actual mass change this is done by taking into account the influence of changes in areal extent and changes in the surface elevation of the glacier since the map was made this method is applied to south cascade glacier washington u s a as an example the computed cumulative mass balance from 1970 to 1997 would have been 16 too negative if the 1970 map had not been updated while the actual volume change of a glacier is relevant to hydrological studies the change that would have occurred on a constant or static surface is more relevant to certain glacier dynamics problems and most climate problems we term this the reference surface balance and propose that such a balance which deliberately omits the influence of changes in area and surface elevation is better correlated to climatic variations than the conventional one which incorporates those influences

a passive probe for subsurface oceans and liquid water in jupiter s icy moons abstract we describe an interferometric reflectometer method for passive detection of subsurface oceans and liquid water in jovian icy moons using jupiter s decametric radio emission dam the dam flux density exceeds 3000 times the galactic background in the neighborhood of the jovian icy moons providing a signal that could be used for passive radio sounding an instrument located between the icy moon and jupiter could sample the dam emission along with its echoes reflected in the ice layer of the target moon cross correlating the direct emission with the echoes would provide a measurement of the ice shell thickness along with its dielectric properties the interferometric reflectometer provides a simple solution to sub jovian radio sounding of ice shells that is complementary to ice penetrating radar measurements better suited to measurements in the anti jovian hemisphere that shadows jupiter s strong decametric emission the passive nature of this technique also serves as risk reduction in case of radar transmitter failure the interferometric reflectometer could operate with electrically short antennas thus extending ice depth measurements to lower frequencies and potentially providing a deeper view into the ice shells of jovian moons

the environments of deposition of the triassic main buntsandstein formation in the p and q quadrants offshore the netherlands interpretations of core and log data within the p and q quadrants were used to quantify the relative change in the distribution of environments of deposition within each of the five members of the main buntsandstein formation this triassic formation was deposited in a semi arid continental basin sediments reached the p and q quadrants in braided stream complexes from a hinterland to the southeast the braided stream complexes were flanked by aeolian interdune flood plain and crevasse splay environments and terminated in playa lakes the distribution and systematic arrangement of environments of deposition migrated subtly across the study area this is attributed to slight fluctuations in climatic conditions rainfall and windstrength or direction

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

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

rapid disintegration of alpine glaciers observed with satellite data analyses of multispectral satellite data indicate accelerated glacier decline around the globe since the 1980s by using digitized glacier outlines inferred from the 1973 inventory and landsat thematic mapper tm satellite data from 1985 to 1999 we obtained area changes of about 930 alpine glaciers the 18 area reduction as observed for the period 1985 to 1999 1 3 a corresponds to a seven times higher loss rate compared to the 1850 1973 decadal mean extrapolation of area change rates and cumulative mass balances to all alpine glaciers yields a corresponding volume loss of about 25 km since 1973 highly individual and non uniform changes in glacier geometry disintegration indicate a massive down wasting rather than a dynamic response to a changed climate our results imply stronger ongoing glacier retreat than assumed so far and a probable further enhancement of glacier disintegration by positive feedbacks

airborne surface profiling of glaciers a case study in alaska a relatively lightweight and simple airborne system for surface elevation profiling of glaciers in narrow mountain valleys has been developed and tested the aircraft position is determined by kinematic global positioning system gps methods the distance to the glacier surface is determined with a laser ranger the accuracy is about 0 3 m sufficient to permit future changes to be observed over short time intervals long term changes can be estimated by comparison of profiles with existing maps elevation profiles obtained in 1993 94 from three glaciers in central and south central alaska are compared with maps made about 1950 the resulting area averaged seasonally corrected thickness changes during the interval are gulkana glacier central alaska range 11 m worthington glacier central chugach mountains 7 m and bear lake glacier kenai mountains 12 m all three glaciers retreated during the interval of comparison the estimated uncertainty in the average thickness change is 5 m which is mainly due to errors in the existing maps constraints on the accuracy of the maps are obtained by profiling in proglacial areas

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

polyphase tectonic history of the southern peninsula haiti from folding and thrusting to transpressive strike slip abstract the southern peninsula of haiti is a seismically active east west trending transpressive mountain range with elevations over 2 km present day deformation is mainly partitioned along the left lateral enriquillo plantain garden fault zone epgfz and associated oblique reverse faults and or folds the configuration of these faults their respective timing and the role of structural heritage on their development is poorly understood to address these questions we present the results of extensive field campaigns combined with satellite imagery interpretation and published data which allows us to constrain the cenozoic evolution of the southern peninsula our results show a polyphase tectonic history consisting of three major tectonic events 1 maastrichtian to early paleocene crustal scale folding that developed coevally with predominantly north to northeast dipping thrusts resulting in uplift and erosion of the cretaceous sedimentary cover in large parts of the southern peninsula 2 early miocene uplift and erosion which was strongest in the southwestern part of the peninsula and decreased eastwards did not affect the massif de la selle uplift is most likely unrelated to strike slip activity but resulted from folding in response to ne sw shortening that possibly reactivated older predominantly n to ne dipping thrusts 3 late miocene to present day deformation and uplift spatially distributed strike slip started during the late miocene and became progressively focused along the epgfz in the latest miocene oblique and thrust faults locally post date strike slip activity from the pliocene onward increase in compressional deformation from west to east is reflected by a change in structural style with predominantly strike slip faults in the west and transpressional faults in the east the latter possibly rooted on the epgfz at depth paleo stresses associated with a strike slip regime are at a significantly high angle to the trace of the epgfz indicating that the epgfz is a mechanically weak fault

modeling the evolution of the juneau icefield between 1971 and 2100 using the parallel ice sheet model pism we study the evolution of the juneau icefield one of the largest icefields in north america 3700 km 2 using the parallel ice sheet model pism we test two climate datasets 20 km weather research and forecasting model wrf output and data from the scenarios network for alaska planning snap derived from spatial interpolation of observations good agreement between simulated and observed surface mass balance was achieved only after substantially adjusting wrf precipitation to account for unresolved orographic effects while snap s climate pattern is incompatible with observations of surface mass balance using the wrf data forced with the rcp6 0 emission scenario the model projects a decrease in ice volume by 58 68 and a 57 63 area loss by 2099 compared with 2010 if the modeled 2070 99 climate is held constant beyond 2099 the icefield is eliminated by 2200 with constant 1971 2010 climate the icefield stabilizes at 86 of its present day volume experiments started from an ice free state indicate that steady state volumes are largely independent of the initial ice volume when forced by identical scenarios of climate stabilization despite large projected volume losses the complex high mountain topography makes the juneau icefield less susceptible to climate warming than low lying alaskan icefields

how much do we really know about glacier surging some of the ideas about glacier surging are considered mainly but not entirely in the light of observations of temperate glaciers in alaska u s a made within the last 15 years climate has an influence on surge recurrence interval climate and weather also affect surge initiation termination and magnitude regional studies lead to the speculation that subglacial till plays a key role in surging and it has been found under all surge type glaciers studied so far including black rapids and variegated glaciers alaska in most of the glaciers studied till deformation processes dominate the motion in quiescence the linked cavity model of surge triggering and rapid motion is not consistent with these observations but the limited coverage of the observations does not rule it out under parts of the glaciers studied the till observations in alaska raise old questions about the interaction between till and the hydraulic systems of temperate glaciers the role of stored water which observations show to be active even in winter on black rapids glacier is noted

the importance of the inelastic and elastic structures of the crust in constraining glacial density mass change and isostatic adjustment from geodetic observations in southeast alaska

impact of resolution and radar penetration on glacier elevation changes computed from dem differencing regional glacier mass balances can be measured by subtracting multi temporal digital elevation models dems however dems are often biased with altitude and it remains unclear whether the elevation differences observed on the ice free terrain can be used to correct biases on ice covered areas iwe investigate such altitude related biases using dems from three different sensors spot5 srtm c band and srtm x band the bias due to different original resolutions can be corrected using a relationship between curvature and elevation difference calculated on ice free terrain the impact of c band radar penetration into snow and ice can be evaluated for a specific region by comparing srtm c band and srtm x band dems in our test area karakoram the resolution related bias has a minor influence on region averaged elevation change conversely not accounting for c band penetration would significantly biased the mean elevation change

biases of srtm in high mountain areas implications for the monitoring of glacier volume changes because of its nearly global coverage the shuttle radar topographic mission srtm topography is a promising data set for estimating mountain glacier volume changes but first its absolute accuracy must be thoroughly investigated in a glacial environment we use topographic data available in the french alps to assess the usefulness of srtm for the monitoring of glacier volume variations we observe clear biases with altitude both on ice free and glacier covered areas at high altitudes srtm elevations are underestimated by up to 10 m these biases can have a significant impact on any estimate of glacier volume changes if srtm is the most recent of the two compared topographies the volume loss is overestimated and vice versa we cannot conclude definitively on the origin of these biases and whether they affect all high mountain areas but our findings invite reconsideration of previous estimates of glacier wastage based on srtm

recent rapid thinning of the mer de glace glacier derived from satellite optical images the rapid wastage of mountain glaciers and their contribution to sea level rise require worldwide monitoring of their mass balance in this paper we show that changes in glacier thickness can be accurately measured from satellite images we use spot image pairs to build digital elevation models dems of the mont blanc area french alps for different years to register the dems we adjust their longitude latitude and altitude over motionless areas the uncertainty of the thickness change measurement is greatly reduced by averaging over areas covering altitude intervals of 50 m comparisons with topographic profiles and a differential dem from aerial photographs obtained on the mer de glace indicate an overall accuracy of 1 m for the thickness change measurement below 2100 m satellite dems show an evolution of the thinning rate from 1 0 4 m a years 1979 1994 to 4 1 1 7 m a 2000 2003

global sea level contribution from the patagonian icefields since the little ice age maximum the melting of mountain glaciers and ice caps is expected to contribute significantly to sea level rise in the twenty first century 1 3 although the magnitude of this contribution is not fully constrained glaciers in the patagonian icefields of south america are thought to have contributed about 10 of the total sea level rise attributable to mountain glaciers in the past 50 years 3 however it is unclear whether recent rates of glacier recession in patagonia are unusual relative to the past few centuries here we reconstruct the recession of these glaciers using remote sensing and field determinations of trimline and terminal moraine location we estimate that the north patagonian icefield has lost 103 20 7 km 3 of ice since its late holocene peak extent in ad 1870 and that the south patagonian icefield has lost 503 101 1 km 3 since its peak in ad 1650 this equates to a sea level contribution of 0 0018 0 0004 mm yr 1 since 1870 from the north and 0 0034 0 0007 mm yr 1 since 1650 from the south the centennial rates of sea level contribution we derive are one order of magnitude lower than estimates of melting over the past 50 years 3 even when we account for possible thinning above the trimline we conclude that the melt rate and sea level contribution of the patagonian icefields increased markedly in the twentieth century

rising ela and expanding proglacial lakes indicate impending rapid retreat of brady glacier alaska brady glacier is a large alaskan tidewater glacier that is beginning a period of substantial retreat examination of 27 landsat and modis images from the period 2003 to 2011 indicates that brady glacier has a mean equilibrium line altitude ela of 745 m and accumulation area ratio aar of 0 40 the zero balance ela is 600 m and equilibrium aar 0 65 the negative mass balance associated with the increased ela has triggered thinning of 20 100 m over most of the glacier below the ela from 1948 to 2010 the thinning has caused substantial retreat of seven calving distributary termini of the glacier thinning and retreat have led to an increase in the width of and water depth at the calving fronts in contrast the main terminus has undergone only minor retreat since 1948 in 2010 several small proglacial lakes were evident at the terminus by 2000 a permanent outlet river issuing from trick lake had developed along the western glacier margin initial lake development at the terminus combined with continued mass losses will lead to expansion of the lakes at the main terminus and retreat by calving the glacier bed is likely below sea level along the main axis of brady glacier to the glacier divide retreat of the main terminus in the lake will likely lead to a rapid calving retreat similar to bear excelsior norris portage and yakutat glaciers copyright 2013 john wiley sons ltd

changes in the ablation zones of glaciers in the western himalaya and the karakoram between 1972 and 2015 abstract observed estimates of changes in the himalayan and karakoram glaciers remain ambiguous because of limited knowledge regarding complex glacier behaviour low quality of remote sensing data and sparse ground based monitoring remote sensing has indicated anomalous behaviour of glaciers in the karakoram during the past two decades attracting scientists attention to the region in this context this study has made detailed estimates of changes in thickness and area of two glaciers the sachen in the western himalaya and the burche in the karakoram to facilitate understanding of recent glacier changes and their potential impacts on water resources this study used several datasets including landsat the shuttle radar topographic mission srtm the ice cloud and land elevation satellite icesat and differential global positioning system dgps in situ measurements from the period 1972 through 2015 the extent of debris cover increased significantly between 1972 and 2014 while the total glacierized area decreased slightly further our study estimated thickness changes after removing recognizable biases and seasonal variations computed through comparisons of icesat data with dgps a thinning trend occurred between 2000 and 2015 suggesting that the glaciers in the western part of the karakoram and himalaya regions have not recently gained mass this study also found non uniform variations within different zones of the glaciers avalanches have fed most of the karakoram glaciers providing spatially heterogeneous thickness changes the frequency of observations data quality acquisition time and local weather affect our observations of temporal changes careful assessment of regularly acquired remote sensing and ground based observations should reduce uncertainty regarding estimates of glacier changes for management of water resources and associated hazards

ice wastage on the kerguelen islands 49 s 69 e between 1963 and 2006 1 we observed the wastage of ice masses on the kerguelen islands indian ocean 49 s 69 e using historical information and recent satellite data overall the total ice covered area on the islands declined from 703 to 552 km2 between 1963 and 2001 a reduction of 21 the area of cook ice cap the main ice body decreased asymmetrically from 501 to 403 km2 west flowing glaciers lost 11 of their area while east flowing glaciers lost 28 after 1991 the retreat rate accelerated from 1 9 km2 a 1963 1991 to 3 8 km2 a 1991 2003 between 1963 and 2000 the ice volume loss was 25 30 km3 equivalent to an area average ice thinning rate of 1 4 1 7 m a the glacial retreat took place in the climatic context of a relatively low level of precipitation compared to the 1950s and a 1 c warming that occurred between 1964 and 1982 the acceleration of the ice losses since at least the 1990s indicates that the state of the ice bodies on the kerguelen islands is still far from balanced together with other studies in patagonia south georgia and heard island our analysis is consistent with a pattern of strong and accelerated wastage of ice masses influenced by the southern ocean

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

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

ice thickness measurements of taku glacier alaska u s a and their relevance to its recent behavior using radio echo soundings and seismic reflections we measured cross sections of taku glacier near juneau alaska to resolve inconsistencies in previous measurements and to understand better the glacier s dynamics the maximum thickness is about 1477 m and the minimum bed elevation is about 600 m below sea level which establishes taku glacier as the thickest and deepest temperate glacier yet measured our data indicate that during the 19th century the terminus of taku glacier may have begun its rapid advance at a position where the ice bed was greater than 300 m below sea level and more than 25 km from the inland end of its submarine trough this behavior is uncharacteristic of temperate tide water glaciers the glacier which no longer calves has eroded a sediment layer 100 m thick since 1890 at an average rate of about 3 m a 1 since 1948 this high erosion rate retards advance by entrenching the glacier into the terminal moraine calculations based on ice deformation theory indicate significant basal ice motion near the terminus and high basal shear stress 140 220 kpa along much of its length estimated differences between ice flux and balance flux are consistent with observed thickening and positive net mass balance these data indicate that ice volume is increasing and that further advance is likely

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

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 crustal structure of the continental margin east of the falkland islands abstract the 1500 km long falkland plateau is the most prominent morphological structure in the southern south atlantic ocean which crustal composition and development is mainly unknown at the westernmost boundary of the plateau the falkland islands precambrian geology provides the only insight into basement structure and age the question of whether continental basement of a similar age and origin underlies the falkland plateau further east is strongly disputed we present new high quality constraints on the crustal fabric of the plateau east of the falkland islands based on wide angle seismic and potential field data acquired in 2013 the p wave velocity model supported by amplitude and density modelling shows that the falkland plateau basin is filled with 8 km of sediments continental crust of 34 km thickness underlies the falkland islands the eastern continental margin of the falkland islands can be classified as a volcanic rifted margin the falkland plateau basin is floored by up to 20 km thick oceanic crust the exceptionally thick igneous crust and its high lower crustal velocities up to 7 4 km s indicate the influence of a regional thermal mantle anomaly during its formation which provided extra melt material the wide angle model revises published crustal models which predicted thin oceanic or thick extended continental crust below the falkland plateau basin our results provide a sound basis for future tectonic interpretations of the area

taku glacier alaska u s a on the move again active deformation of proglacial sediments taku glacier is one of the few glaciers in alaska u s a that has advanced over the last century 7 km since 1890 this advance slowed substantially during the past decade but in summer 2001 the glacier terminus began to readvance at a rate of 30 cm d 1 the advance produced dramatic proglacial sediment deformation up to 200 m in from of the terminus two to three large bulges and several secondary bulges developed in the proglacial sediments as a result of glacial compression along a 1 km wide portion of the terminus the bulge nearest the terminus was 10 m high and 65 m wide the middle bulge 7 m high advanced at 15 cm d 1 and the distal bulge 3 m high and 50 m wide at 9 cm d 1 crenulations and prominent fractures developed in the overlying vegetation layer the frontal lobes of the bulges were steep and overlaid a shear zonc where sediments were being thrust up and over the ground surface ice proximal push moraines 1 10 m high formed along much of the 9 km wide terminus although deformation was minimal at some locations

constraining attenuation uncertainty in common midpoint radar surveys of ice sheets for common offset radar data there is no clear way to disentangle path effects from reflector characteristics so efforts to determine the physical properties at the bed using reflection amplitude are inherently limited by the constraints on englacial attenuation in this study we identify the theoretical considerations required for interpreting bistatic radar surveys and use data collected on the northeast greenland ice stream negis and kamb ice stream to compute local attenuation profiles we found that failing to correct for angle dependent controls on return power including antenna directivity the reflection coefficient and refractive focusing can bias the computed attenuation rates as much as 30 db km for reflectors at 1 km depth because the radiation characteristics are the dominant source of uncertainty in our data we recommend either a simplified survey design for the future where the antennae are decoupled from the ice surface or additional data collection to constrain the near field permittivity and its effect on the radiation pattern depth averaged attenuation rates computed using cmp methods for deep reflectors yield values 10 db km higher than attenuation rates computed using common offset techniques with the same data we attribute these anomolously high attenuation rates to additional wavenumber and therefore angle dependent interferences between sub wavelength reflectors

elevation changes measured during 1966 2010 on the monsoonal temperate glaciers ablation region gongga mountains china abstract temperate glaciers are more sensitive to climate change than are polar or continental glaciers and can drive remarkable runoff variation in local water catchments changes in the glacier area and surface elevation of the three monsoonal temperate glaciers in the gongga mountains china were analyzed using series of remote sensing images and digital elevation model dem data all possible sources of uncertainty were considered in detail the results showed that the total glacier area decreased by 4 3 km 2 6 7 between 1966 and 2010 a comparison of glacier surface elevations using dems derived from dual frequency differential gps dgps surveys in 2010 and from 1966 to 1989 from topographic maps the three glaciers underwent significant mass loss from 1966 to 2010 and the mean surface elevation changes were 0 90 0 45 m y 1 06 0 45 m y and 1 12 0 45 m y for hailuogou hlg dagongba dgb and yanzigou yzg glaciers respectively from 1966 to 2010 analysis of the meteorological data showed that the mean annual air temperature increase was the main reason for the thinning and volume loss thinning of the glacier tongue and volume loss was more intense in the period 1989 2010 than in 1966 89 debris thickness and other factors are also believed to play important roles in differential thinning among different areas and periods

holocene history of hubbard glacier in yakutat bay and russell fiord southern alaska stratigraphic and geomorphic data defined by radiocarbon ages tree ring dates and historical observations provide evidence of three major holocene expansions of hubbard glacier early in each advance the hubbard glacier margin blocked russell fiord to create russell lake raising base level and causing stream beds and fan deltas throughout the russell drainage basin to aggrade each hubbard glacier expansion continued with an ice lobe advancing through disenchantment and yakutat bays in the west and an eastern lobe advancing into russell fiord the earlier two holocene expansions were respectively under way at 7690 and 5600 calibrated yr b p and each advance culminated more than 1 k y later the late holocene advance was under way by 3100 yr ago and reached 13 km farther south in russell fiord than the preceding two expansions late holocene deglaciation of yakutat and disenchantment bays was complete before a d 1791 nunatak glacier flowing from neves east of russell fiord became the primary ice source to the russell fiord lobe at or before this date ice retreat from the southern end of russell fiord began in the late eighteenth century and the penultimate russell lake drained ca a d 1860 the relatively slow advances and more rapid retreats of hubbard glacier are consistent with the model of the iceberg calving glacier cycle hubbard glacier is currently advancing and will likely reestablish russell lake in the near future affecting local fisheries however glacier lobes are unlikely to reach the area of the town of yakutat built on late holocene glacial deposits in the next 1 k y