Journal of Glaciology

Published by International Glaciological Society
Online ISSN: 1727-5652
Publications
Conference Paper
Azimuth modulation of the normalized radar cross-section in satellite data sets over Greenland is investigated. Data sets from the NASA Scatterometer (NSCAT) and from the European Remote Sensing Advanced Microwave Instrument (ERS) are employed. Azimuth dependence is clearly observed. The largest azimuth dependence occurs in the C-band ERS data with peak-to-peak azimuth modulations up to 3.0 dB. The Kuband NSCAT data exhibits slightly smaller modulations of up to 2.0 dB. Azimuth modulation is largest in the lower dry snow zone for ERS and in the dry to percolation transition zone for NSCAT. The incidence angle dependence of the azimuth modulation is parameterized over the ice sheet. In general, the azimuth modulation is found to either decrease with increasing incidence angles, or be relatively independent of incidence angle. Regions of large incidence angle dependence for the azimuth modulation include the western dry snow zone for ERS and the northeast dry snow to percolation transition zone for NSCAT. The second order azimuth modulation orientation is highly correlated with wind direction. A new simple surface model is introduced to relate azimuth modulation to surface properties. Using this model, the size and orientation of surface sastrugi are estimated.
 
Article
This paper presents radar-altimeter scattering models for each of the diagenetic zones of the Greenland ice sheet. AAFE radar-altimeter waveforms obtained during the 1991 and 1993 NASA multi-sensor airborne altimetry experiments over Greenland reveal that the Ku-band return pulse changes significantly with the different diagenetic zones. These changes are due to varying amounts of surface and volume scattering in the return waveform. In the ablation and soaked zones, where surface scattering dominates the AAFE return, geophysical parameters such as rms surface height and rms surface slope are obtained by fitting the waveforms to a surface-scattering model. Waveforms from the percolation zone show that sub-sruface ice features have a much more significant effect on the return pulse than the surrounding snowpack. Model percolation waveforms, created using a combined surface- and volume-scattering model and an ice-feature distribution obtained during the 1993 field season, agree well with actual AAFE waveforms taken in the same time period. Using a combined surface- and volume-scattering model for the dry-snow-zone return waveforms, the rms surface height and slope and the attenuation coefficient of the snowpack are obtained. These scattering models not only allow geophysical parameters of the ice sheet to he measured but also help in the understanding of satellite radar-altimeter data.
 
Article
The two-dimensional surface velocity of Thwaites Glacier, West Antarctica, was mapped with 23 ascending- and 22 descending-orbit European Remote-sensing Satellite synthetic aperture radar (ERS SAR) interferograms (time range 1995-2000). The velocity map covers 175 500 km 2 from the Amundsen Coast to the southern turning point of the satellite orbit and comprises >80% of the Thwaites catchment. Relative velocity errors are <10% except for rare regions (about 5% of the total area) of unfavorable look geometry. Six individual tributaries were identified; their center-line velocities increase from 0 at the catchment boundary to similar to0.3 km a(-1) when they join the main glacier trunk. On the main trunk, velocity increases to similar to1.8 km a(-1) at the grounding line and 3.6 km a(-1) on the floating tongue. As at neighboring Pine Island Glacier, no strong longitudinal velocity gradients are found except near the grounding line. Within expected error bounds, the flow pattern appears temporally stationary, i.e. flowlines agree with the delineation of flow suggested by the pattern of velocity magnitude. A potential temporal shift of tributary boundaries must consequently be <4.4 m a(-1).
 
Article
Surface strain rate is best observed by fitting a strain-rate ellipsoid to the measured movement of a stake network or other collection of surface features, using a least squares procedure. Error of the resulting fit varies as 1/(L delta t square root of N), where L is the stake separation, delta is the time period between initial and final stake survey, and n is the number of stakes in the network. This relation suggests that if n is sufficiently high, the traditional practice of revisiting stake-network sites on successive field seasons may be replaced by a less costly single year operation. A demonstration using Ross Ice Shelf data shows that reasonably accurate measurements are obtained from 12 stakes after only 4 days of deformation. It is possible for the least squares procedure to aid airborne photogrammetric surveys because reducing the time interval between survey and re-survey permits better surface feature recognition.
 
Top: The received voltage in a 50 Ω receiver as a function of time with the log-periodic antennas buried in the snow, pointed downward. A large reflection is evident at 36.1 μ s (highlighted in red), consistent with a depth of 3014 +48 − 50 m. Bottom: 
The power spectral density of the received ground bounce signal compared to the noise level in the trace. 
The measured electric field attenuation length as a function of temperature for the Summit Station site, shown with the blue line. We have assumed that the relationship between attenuation length and temperature is consistent with the measured attenuation length vs. temperature from Bogorodsky and others (1985), also shown on this plot (red and green lines). The dashed lines denote ± 1 σ . 
The measured electric field attenuation length profile as a function of depth for the Summit Station site at 75 MHz. We have combined our measurements with the temperature profile measured for the GRIP borehole (Greenland Ice Core Project, 1994; Johnsen and others, 1995) and the measured attenuation length vs. temperature from Bogorodsky and others (1985). The shaded region denotes ± 1 σ . 
Article
We report an in situ measurement of the electric field attenuation length at radio frequencies for the bulk ice at Summit Station, Greenland, made by broadcasting radio-frequency signals vertically through the ice and measuring the relative power in the return ground bounce signal. We find the depth-averaged field attenuation length to be 947 +92/-85 meters at 75 MHz. While this measurement has clear radioglaciological applications, the radio clarity of the ice also has implications for the detection of ultra-high energy (UHE) astrophysical particles via their radio emission in dielectric media such as ice. The measured attenuation length at Summit Station is comparable to previously measured radio-frequency attenuation lengths at candidate particle detector sites around the world, and strengthens the case for Summit Station as the most promising northern site for UHE neutrino detection.
 
Article
A hanging glacier at the east face of Weisshorn (Switzerland) broke off in 2005. We were able to monitor and measure surface motion and icequake activity for 25 days up to three days prior to the break-off. The analysis of seismic waves generated by the glacier during the rupture maturation process revealed four types of precursory signals of the imminent catastrophic rupture: (i) an increase in seismic activity within the glacier, (ii) a decrease in the waiting time between two successive icequakes, (iii) a change in the size-frequency distribution of icequake energy, and (iv) a modification in the structure of the waiting time distributions between two successive icequakes. Morevover, it was possible to demonstrate the existence of a correlation between the seismic activity and the log-periodic oscillations of the surface velocities superimposed on the global acceleration of the glacier during the rupture maturation. Analysis of the seismic activity led us to the identification of two regimes: a stable phase with diffuse damage, and an unstable and dangerous phase characterized by a hierarchical cascade of rupture instabilities where large icequakes are triggered. Comment: 16 pages, 7 figures
 
Article
The microwave emission from a half-space medium characterized by coordinate dependent scattering and absorbing centers was calculated by numerically solving the radiative transfer equation by the method of invariant imbedding. A Mie scattering phase function and surface polarization was included in the calculation. Also included are the physical temperature profile and the temperature variation of the index of refraction for ice. Using published values of grain size and temperature profile data of polar firn, the brightness temperature was calculated for the 1.55 cm and 0.8 cm wavelengths. For selected regions in Greenland and Antarctica, the results are in reasonable agreement with the observed Nimbus-5 and Nimbus-6 ESMR data.
 
Article
Interferometric radar observations of Glaciar San Rafael, Chile, were collected in October 1994 by NASA's Spaceborne Imaging Radar C (SIR-C) at both L- (24cm) and C-band frequency (5.6cm), with vertical transmit and receive polarization. The C-band data did not yield good geophysical products, because the temporal coherence of the signal was significantly reduced after 24h. The L-band data were, however, successfully employed to map the surface topography of the icefield with a 10m uncertainty in height, and measure ice velocity with a precision of 4 mm/d or 1.4 m/a. The corresponding error in strain rates is 0.05/a at a 30 m horizontal spacing. The one-dimensional interferometric velocities were subsequently converted to horizontal displacements by assuming a flow direction and complemented by feature-tracking results near the calving front. The results provide a comprehensive view of the ice-flow dynamics of Glaciar San Rafael. The glacier has a core of rapid flow, 4.5 km in width and 3.5 degrees in average slope,surrounded by slower moving ice, not by rock. Ice velocity is 2.6 m/d or 0.95 km/a near the equilibrium line altitude (1200m), increasing rapidly before the glacier enters the narrower terminal valley, to reach 17.5 m/d or 6.4 km/a at the calving front. Strain rates are dominated by lateral shearing at the glacier margins (0.4-0.7/a), except for the terminal-valley section, where longitudinal strain rates average close to 1/a. This spectacular longitudinal increase in ice velocity in the last few kilometers may be a fundamental feature of tidewater glaciers.
 
Article
The first four strings of phototubes for the AMANDA high-energy neutrino observatory are now frozen in place at a depth of 800 to 1000 m in ice at the South Pole. During the 1995-96 season an additional six strings will be deployed at greater depths. Provided absorption, scattering, and refraction of visible light are sufficiently small, the trajectory of a muon into which a neutrino converts can be determined by using the array of phototubes to measure the arrival times of \v{C}erenkov light emitted by the muon. To help in deciding on the depth for implantation of the six new strings, we discuss models of age vs depth for South Pole ice, we estimate mean free paths for scattering from bubbles and dust as a function of depth, and we assess distortion of light paths due to refraction at crystal boundaries and interfaces between air-hydrate inclusions and normal ice. We conclude that the depth interval 1600 to 1800 m will be suitably transparent for the next six AMANDA strings and, moreover, that the interval 1600 to 2100 m will be suitably transparent for a future 1-km$^3$ observatory except possibly in a region a few tens of meters thick at a depth corresponding to a peak in the dust concentration at 60 kyr BP.
 
An image of a 10 x 10 cm 2 vertical thin section of ice from the depth 115 m. The section is viewed between two crossed linear polarizers and the different colors represent almost 3000 individual crystals with various orientations of the crystal optical c-axes.
Distributions of ice crystal sizes at depths 115m, 165m, 220m, 330m, 440m and 605m.
The mean vertical size of the ice crystals shown versus their age in years B.P. The smooth line shows the best fit predicted from our dynamical description of ice crystal growth. From the fit we read off the diffusion constant, D ≈ 1.4 · 10 −3 mm 2 ·yr −1 , and fragmentation rate, f ≈ 5.2 · 10 −4 yr −1 ·mm −1. The time scale is taken from ref. (Johnsen and others, 2001).
The figure shows a "data collapse" of the size distributions as a consequence of a rescaling, ˜ x = (log x − log x)/σ(log(x)), i.e. the shown distributions have zero mean and unit standard deviation. The lines correspond to the eight data points in Fig. 3 of the oldest samples (t > 2500 years) and the black line on top is the steady-state solution of eq.(1). We use the rescaling˜xrescaling˜ rescaling˜x in order to improve the resolution around the smallest crystal sizes and note that the steady-state solution is transformed accordingly.
Article
The North Greenland Ice Core Project (NorthGRIP) provides paleoclimatic information back to at about 120 kyr before present (Dahl-Jensen and others, 2002). Each year, precipitation on the ice sheet covers it with a new layer of snow, which gradually transforms into ice crystals as the layer sinks into the ice sheet. The size distribution of ice crystals has been measured at selected depths in the upper 880 m of the NorthGRIP ice core (Svensson and others, 2003b), which covers a time span of 5300 years. The distributions change with time toward a universal curve, indicating a common underlying physical process in the formation of crystals. We identify this process as an interplay between fragmentation of the crystals and diffusion of their grain boundaries. The process is described by a two-parameter differential equation to which we obtain the exact solution. The solution is in excellent agreement with the experimentally observed distributions.
 
Trend sur/ace in three-dimensional space illustrating changes of (J with time over the range 0-90 ° of incidence angles at a frequency of /3 CHz.  
Trend sur/ace in three-dimensional space illustrating changes of (J with time over the range 0-90 ° of  
Article
Observations of the physical properties of the snow cover and underlying young fast ice in Resolute Passage, Canada, were made during the winter of 1982. Detailed measurements of snow density and ice and snow temperatures, salinities, and brine volumes were made over a period of 46 d, beginning when the ice was 0.4 m thick and about 9 d old. The recorded values are used in a theoretical mixture model to predict the dielectric properties of the snow cover over the microwave frequency range. The results of this analysis are then used to investigate the effects of the snow properties on the radar backscatter signatures of young sea ice. The results show that backscatter is a function of the incidence angle and can change significantly over short periods of time during the early evolutionary phase of ice and snow-cover development. This has important consequences for the identification of young ice forms from SAR or SLAR images.
 
Article
The remote sensing of snow-pack characteristics with surface installations or an airborne system could have important applications in water-resource management and flood prediction. To derive some insight into such applications, the electromagnetic response of multilayered snow models is analyzed in this paper. Normally incident plane waves at frequencies ranging from 1 MHz to 10 GHz are assumed, and amplitude reflection coefficients are calculated for models having various snow-layer combinations, including ice layers. Layers are defined by thickness, permittivity, and conductivity; the electrical parameters are constant or prescribed functions of frequency. To illustrate the effect of various layering combinations, results are given in the form of curves of amplitude reflection coefficients versus frequency for a variety of models. Under simplifying assumptions, the snow thickness and effective dielectric constant can be estimated from the variations of reflection coefficient as a function of frequency.
 
Article
This paper presents an overview of recent remote-sensing techniques as applied to geophysical studies of floating ice. The current increase in scientific interest in floating ice has occurred during a time of rapid evolution of both remote-sensing platforms and sensors. Mesoscale and macroscale studies of floating ice are discussed under three sensor categories: visual, passive microwave, and active microwave. The specific studies that are reviewed primarily investigate ice drift and deformation, and ice type and ice roughness identification and distribution.
 
Article
The possibility that the variation in areal extent of the snow cover may be related by empirical means to the average monthly run-off in a given watershed was demonstrated by comparing run-off records from the Indus River Basin in south-east Asia with a series of snow-cover maps obtained from Nimbus-3 and 4 imagery. Similar studies using the higher spatial resolution available with ERTS-1 imagery were carried out for the Wind River Mountains watersheds in Wyoming, where it was found that the empirical relationship varied with mean elevation of the watershed. In addition, digital image enhancement techniques are shown to be useful for identifying glacier features thought to be related to extent of snow cover, moraine characteristics, debris coverage, and the like. Finally, longer wavelength observations using sensors on board the Nimbus-5 satellite are shown to be useful for indicating crystal size distributions and onset of melting on glacier snow cover.
 
Article
A previously developed method for the reconstruction of surface radar backscatter characteristics is applied to Seasat scatterometer (SASS) data for the study of Greenland's ice sheet. A time series of the radar backscatter images provides an island-wide view of the ice sheet which shows the extent of the summer melt. Medium-scale scatterometer images provide frequent island-wide observations permitting precise measurements of the seasonal extent of the summer melt.
 
Article
We investigate limitations of the one-dimensional elastic beam model to detect grounding line and thickness of an ice shelf from a differential interferogram. Spatial limitations due to grounding line curvature and variable ice thickness are analyzed by comparison with two-dimensional plate flexure. Temporal limitations from the tide-dependent shift of the grounding line are analyzed by superpositions of four tidal flexure profiles representing differential interferograms. (i) At scales greater one ice thickness seaward protrusions of the grounding line are well represented by the elastic beam model, while landward embayments of the same scale produce significant misplacements >10 per cent of the ice thickness. (ii) For reasonable spatial variations of shelf thickness the elastic beam model gives reliable estimates of grounding line position and unfractured mean ice thickness near the grounding line. (iii) For about 20 per cent of superpositions of four tidal flexure profiles the resulting grounding line misplacements exceed the physical tidal shift of the grounding line by factors >2. For differential tide levels <10 per cent of a 1 m tide dynamics, a physical shift of the grounding line of 0.3 km per meter of tide can lever misplacements of >2 km. Examples of real interferometric profiles from West Antarctic ice shelves corroborate our results.
 
Article
We have investigated the formation of 10-50 mm long ``ice spikes'' that sometimes appear on the free surface of water when it solidifies. By freezing water under different conditions, we measured the probability of ice spike formation as a function of: 1) the air temperature in the freezing chamber, 2) air motion in the freezing chamber (which promotes evaporative cooling), 3) the quantity of dissolved salts in the water, and 4) the size, shape, and composing material of the freezing vessel. We found that the probability of ice spike formation is greatest when the air temperature is near -7 C, the water is pure, and the air in the freezing chamber is moving. Even small quantities of dissolved solids greatly reduce the probability of ice spike formation. Under optimal conditions, approximately half the ice cubes in an ordinary ice cube tray will form ice spikes. Guided by these observations, we have examined the Bally-Dorsey model for the formation of ice spikes. In this model, the density change during solidification forces supercooled water up through a hollow ice tube, where it freezes around the rim to lengthen the tube. We propose that any dissolved solids in the water will tend to concentrate at the tip of a growing ice spike and inhibit its growth. This can qualitatively explain the observation that ice spikes do not readily form using water containing even small quantities of dissolved solids.
 
Article
The form drag of large bedrock bumps sticking into the base of an ice stream can produce effective 'sticky spots' supporting large basal shear stress. Bedrock regions surrounded by lubricating till at the same topographic level can cause sticky spots, but tend to collect lubricating water and thus are unlikely to support a shear stress of more than a few tenths of a bar unless they contain abundant large bumps. Raised regions on the ice-air surface also can cause moderate increases in the shear stress supported on the bed beneath. Surveys of large-scale bedrock roughness, strain grids across the margins of ice-surface highs, and possibly, water-pressure measurements in regions of thin or zero till would help identify and characterize sticky spots.
 
Article
. A finite-element solution of the time-dependent mass-continuity equation for column-averaged ice sheet flow and sliding is applied to the Antarctic Ice Sheet. First a calibration of the model to the steady-state present ice sheet configuration is presented. With fitted values of the parameters describing the regions of sliding, the degree of bed coupling, and the ice hardness, a change in the mean annual sea-level temperature is used to simulate variation of the climatic conditions over Antarctica for both warming and cooling of the climate. Paradoxically a climate warming of up to 9 degrees leads to an increase in ice volume, while cooling leads to decreasing ice volume as long as the present margins of Antarctica are maintained. Some extreme simulations of the Antarctic Ice Sheet for "maximum over-riding" and "minimum warm-climate" are shown for situations where the present bed conditions are altered. Finally a time-dependent simulation shows the response of the ice sheet system to...
 
Article
. Jakobshavns Isbrae (69 o 10'N, 49 o 59'W) drains about 6.5 percent of the Greenland Ice Sheet and is the fastest ice stream known. The Jakobshavns Isbrae basin of about 10,000 km 2 was mapped photogrammetrically from four sets of aerial photography, two taken in July 1985 and two in July 1986. Positions and elevations of several hundred natural features on the ice surface were determined for each epoch by photogrammetric block aerial triangulation, and surface velocity vectors were computed from the positions. The two flights in 1985 yielded the best results and provided the most common points (716) for velocity determinations and are therefore used in the modeling studies. The data at these irregularly spaced points were used to calculate ice elevations and velocity vectors at uniformly spaced gridpoints 3 km apart by interpolation. The field of surface strain rates was then calculated from this gridded data and used to compute the field of surface deviatoric stresses, using t...
 
Article
. A finite-element method solution of the continuity equation is used to investigate complex features of the Younger Dryas period. By comparing results of the model with field evidence, we conclude that the climatic event responsible for the Younger Dryas stillstand was probably short (less than 500 years). The assumption of a general sliding condition for elevations below 100 m, with an enhanced sliding zone through the center of the Baltic and Gulf of Bothnia, yields broad agreement for marginal positions in Sweden and Finland during a simulated termination. A stillstand near the Younger Dryas moraine position is attained with a climatic equilibrium line altitude (ELA) depression of 600 m for a time period of 500 years. Agreement of simulated behavior with observed behavior is less consistent in the more maritime western Sweden and western Norway. INTRODUCTION The most prominent event of the deglaciation of Scandinavia occurred during the period called the Younger Dryas (11000-10200...
 
Article
A large portion of the recent increase in the rate of mass loss from the Greenland ice sheet is from increased outlet glacier discharge along its southeastern margin. While previous investigations of the region's two largest glaciers suggest that acceleration is a dynamic response to thinning and retreat of the calving front, it is unknown whether this mechanism can explain regional acceleration and what forcing is responsible for initiating rapid thinning and retreat. We examine seasonal and interannual changes in ice-front position, surface elevation and flow speed for 32 glaciers along the southeastern coast between 2000 and 2006. While substantial seasonality in front position and speed is apparent, nearly all the observed glaciers show net retreat, thinning and acceleration, with speed-up corresponding to retreat. The ratio of retreat to the along-flow stress-coupling length is proportional to the relative increase in speed, consistent with typical ice-flow and sliding laws. This affirms that speed-up results from loss of resistive stress at the front during retreat, which leads to along-flow stress transfer. Large retreats were often preceded by the formation of a flat or reverse-sloped surface near the front, indicating that subsequent retreats were influenced by the reversed bed slope. Many retreats began with an increase in thinning rates near the front in the summer of 2003, a year of record high coastal-air and sea-surface temperatures. This anomaly was driven in part by recent warming, suggesting that episodes of speed-up and retreat may become more common in a warmer climate.
 
Article
We derive mass changes of the Greenland ice sheet (GIS) for 2003-07 from ICESat laser altimetry and compare them with results for 1992-2002 from ERS radar and airborne laser altimetry. The GIS continued to grow inland and thin at the margins during 2003-07, but surface melting and accelerated flow significantly increased the marginal thinning compared with the 1990s. The net balance changed from a small loss of 7 ± 3 Gt a-1 in the 1990s to 171 ± 4 Gt a-1 for 2003-07, contributing 0.5 mm a-1 to recent global sea-level rise. We divide the derived mass changes into two components: (1) from changes in melting and ice dynamics and (2) from changes in precipitation and accumulation rate. We use our firn compaction model to calculate the elevation changes driven by changes in both temperature and accumulation rate and to calculate the appropriate density to convert the accumulation-driven changes to mass changes. Increased losses from melting and ice dynamics (17-206 Gt a-1) are over seven times larger than increased gains from precipitation (10-35 Gt a-1) during a warming period of ∼2 K (10 a)-1 over the GIS. Above 2000 m elevation, the rate of gain decreased from 44 to 28 Gt a-1, while below 2000 m the rate of loss increased from 51 to 198 Gt a-1. Enhanced thinning below the equilibrium line on outlet glaciers indicates that increased melting has a significant impact on outlet glaciers, as well as accelerating ice flow. Increased thinning at higher elevations appears to be induced by dynamic coupling to thinning at the margins on decadal timescales.
 
Article
Current trends show a rise in Arctic surface and air temperatures, including over the Greenland ice sheet where rising temperatures will contribute to increased sea-level rise through increased melt. We aim to establish the uncertainties in using satellite-derived surface temperature for measuring Arctic surface temperature, as satellite data are increasingly being used to assess temperature trends. To accomplish this, satellite-derived surface temperature, or land-surface temperature (LST), must be validated and limitations of the satellite data must be assessed quantitatively. During the 2008/09 boreal winter at Summit, Greenland, we employed data from standard US National Oceanic and Atmospheric Administration (NOAA) air-temperature instruments, button-sized temperature sensors called thermochrons and the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite instrument to (1) assess the accuracy and utility of thermochrons in an ice-sheet environment and (2) compare MODIS-derived LSTs with thermochron-derived surface and air temperatures. The thermochron-derived air temperatures were very accurate, within 0.1±0.3°C of the NOAA-derived air temperature, but thermochron-derived surface temperatures were ∼3°C higher than MODIS-derived LSTs. Though surface temperature is largely determined by air temperature, these variables can differ significantly. Furthermore, we show that the winter-time mean air temperature, adjusted to surface temperature, was ∼11°C higher than the winter-time mean MODIS-derived LST. This marked difference occurs largely because satellite-derived LSTs cannot be measured through cloud cover, so caution must be exercised in using time series of satellite LST data to study seasonal temperature trends.
 
Article
We have tested the ability of a 1.12-1.76 GHz bandwidth airborne Frequency Modulation-Continuous Wave (FM-CW) radar with an effective pulse duration of 3 ns to penetrate temperate ice of the ablation zone of Black Rapids Glacier, central Alaska, U.S.A. We used high-gain horn antennas to suppress clutter, and tested over cold and nearly ideal surface conditions. Englacial horizons dipping to at least 60 m depth were found along three sections of one axial profile. More narrow-band (1.21-1.29 GHz), low-resolution (24 ns pulse duration) profiles from a fourth section detected events at about 100-150 m depth. Comparative profiles recorded with a 100 MHz short-pulse-type radar reproduce the horizons of two of the sections, and verify the penetration in all cases. All horizons are composed of diffractions. We interpret voids from the phase of the 100 MHz diffractions within one of the horizons. The diffraction nature of the horizons, the void interpretation and the proximity to a nearby and up-glacier pothole field lead us to conclude that the horizons within two of the sections are meandering drainage channels. A more complex, branching structure with near-surface horizons profiled within the third section much farther down-glacier may also be a complex drainage system fed by near-surface melting. The FM-CWsignal-to-clutter-noise ratios of some of the targets predict that they could be detected at 200 m depth in the 1-2 GHz range. Significant performance improvements at maximum vertical resolution could be achieved with higher-gain antennas.
 
Article
This paper presents an overview of firn accumulation in Dronning Maud Land (DML), Antarctica, over the past 1000 years. It is based on a chronology established with dated volcanogenic horizons detected by dielectric profiling of six medium-length firn cores. In 1998 the British Antarctic Survey retrieved a medium-length firn core from western DML. During the Nordic EPICA (European Project for Ice Coring in Antarctica) traverse of 2000/01, a 160 m long firn core was drilled in easternDML. Together with previously published data from four other medium-length ice cores from the area, these cores yield 50 possible volcanogenic horizons. All six firn cores cover a mutual time record until the 29th eruption. This overlapping period represents a period of approximately 1000 years, with mean values ranging between 43 and 71 mm w. e. The cores revealed no significant trend in snow accumulation. Running averages over 50 years, averaged over the six cores, indicate temporal variations of 5%. All cores display evidence of a minimum in the mean annual firn accumulation rate around AD 1500 and maxima around AD 1400 and 1800. The mean increase over the early 20th century was the strongest increase, but the absolute accumulation rate was not much higher than around AD 1400. In eastern DML a 13% increase is observed for the second half of the 20th century.
 
Article
During the summer field seasons of 1987-91, studies of central East Antarctica by airborne radio-echo sounding commenced. This scientific work continued in the 1990s in the Vostok Subglacial Lake area and along the traverse route from Mirny, and led to the discovery of 16 new subglacial water cavities in the areas of Domes Fuji and Argus and the Prince Charles Mountains. Twenty-nine subglacial water cavities were revealed in the area near Vostok, along with a feature we believe to be a subglacial river. Two subglacial lakes were discovered along the Mirny-Vostok traverse route. These are located 50 km north of Komsomolskaya station and under Pionerskaya station. We find high geothermal heat flux in the vicinity of the largest of the subglacial lakes, and suggest this may be due to their location over deep faults where additional mantle heat is available.
 
Article
Glaciar Chacaltaya is an easily accessible glacier located close to La Paz, Bolivia. Since 1991, information has been collected about the evolution of this glacier since the Little Ice Age, with a focus on the last six decades. The data considered in this study are monthly mass-balance measurements, yearly mappings of the surface topography and a map of the glacier bed given by ground-penetrating radar survey. A drastic shrinkage of ice has been observed since the early 1980s, with a mean deficit about 1m a-1 w.e. From 1992 to 1998, the glacier lost 40% of its average thickness and two-thirds of its total volume, and the surface area was reduced by >40%. With a mean estimated equilibrium-line altitude lying above its upper reach, the glacier has been continuously exposed to a dominant ablation on the whole surface area. If the recent climatic conditions continue, a complete extinction of this glacier in the next 15 years can be expected. Glaciar Chacaltaya is representative of the glaciers of the Bolivian eastern cordilleras, 80% of which are small glaciers (<0.5 km2). A probable extinction of these glaciers in the near future could seriously affect the hydrological regime and the water resources of the high-elevation basins.
 
Article
Ice salinity and 18O/16O ratios were measured on 12 ice cores drilled from thick, multi-year land-fast sea ice (MLSI) off the north coast of Ellesmere Island, Canada. Fresh, brackish, and sea ice were identified in the ice cores using the 18O/16O ratios. Two cases are considered: case I, which assumes that no isotopic fractionation occurs on freezing; and, case 2, which assumes that a maximum isotopic fractionation factor (a) of 1.003 applies. The amount of each ice type is variable among the cores, but overall the 12 cores comprise 29.6% brackish ice, 70.0% sea ice, and 0.4% fresh ice in case I, and 42.3% brackish ice, 57.3% sea ice, and 0.4% fresh ice in case 2. The data suggest that time-dependent brackish sea-water stratification below the ice is Quite common and is often associated with the inverted bottom topography. However, the stratification is not always confined to small, areally limited under-ice melt pools in inverted depressions, and neither is it a summer-only phenomenon. Brackish ice growth apparently occurs in a brackish water layer that in some instances underlies the ice sheet year-round. For both case I and case 2 the salinity distribution in brackish ice is positively skewed, with 50% of salinity values occurring in the range 0−0.49%. Sea-ice salinity values are more evenly distributed. In case I, brackish ice has mean salinity and mean δ18O values of 0.66 and −19.9%, respectively, compared to mean values of 1.88 and −6.5%0 for the sea ice. In case 2, brackish ice has mean salinity and mean δ18O values of 0.75 and −18.1% compared to mean values of 2.03 and −5.2% for the sea ice. The salinity of brackish ice and sea ice, ice-growth mechanisms, and the inclusion of brine in the sub-structure are discussed briefly.
 
Article
A history of the fluctuations of the Nisqually Glacier on the southern slope of Mt. Rainier, Washington, including the period of increased glacial activity during the last ten years, indicates that a number of minor advances have occurred since the maximum extension of the ice about 1750. These new data on glacial activity in the United States of America should be useful in examining the idea of synchronism in glacial behavior in different regions of the world. In addition, photographs of the changes in the Nisqually Glacier during the last four years indicate the magnitude of the recent increase in glacial activity in this country.ZUSAMMENFASSUNG. Die Geschichte der Schwankungen des Nisqually Glacier auf dem südlichen Hang des Mt. Rainier, Washington, einschliesslich der Periode der verstärkten Gletschertätigkeit während der letzten zehn Jahre, zeigt dass eine Anzahl geringerer Vorstösse seit der maximalen Ausbreitung des Eises um 1750 erfolgt sind. Diese neuen Angaben über Gletschertätigkeit in den Vereinigten Staaten von Amerika sollten beim Studium des Gedankens der Synchronisierung im Verhalten der Gletscher in verschiedenen Regionen der Welt nützlich sein. Noch dazu zeigen Photographien der Veränderungen im Nisqually Glacier während der letzten vier Jahre die Grösse des jüngst statthabenden Anwachsens der Gletschertätigkeit in diesem Lande an.
 
Article
Brittle structures exposed in the ablation area of Pasterzenkees, Austria, were interpreted using aerial photographs and maps covering a period of 100 years. The most common structural features observed in aerial photographs are: (1) normal faults, which are particularly well developed along the lateral margins of the glacier and at the terminus; (2) large-scale tension gashes and Riedel shears that develop along the northeastern lateral margin of the glacier and between ice-flow units; (3) thrust faults, which develop at the terminus and cross-cut the full width of the glacier; and (4) band ogives. Longitudinal and transverse topographic profiles are available for the period covered in this study, and ice-flow velocity data are available from 1927. These data provide a means for interpreting the variations of observed structures in terms of ice-flow velocity. Thrust faults predominantly develop during periods of glacier retreat, when the glacier snout becomes an obstacle. Normal faults typically develop in areas of high glacier surface relief and are interpreted as gravity collapse structures. The orientation of sub-vertical, wide open crevasses along the lateral margin of Pasterzenkees varied. These variations are interpreted as reflecting changes of the flow regime and indicate a transition from simple shearing to transtension during a period of ice-flow deceleration.
 
Three-year running mean of positive degree-days (solid black curve) and solid precipitation (dashed curve) between 1870 and 1895 at 3000 m a.s.l. at the location of the 1895 Altels break-off. Annual values are also indicated (circles for PDD and crosses for solid precipitation) .  
Illustration of the model consisting of springs and blocks resting on an inclined plane. The blocks lie on an inclined curved surface and gravity is the driving force. Only a small subset of the spring?block system is shown here.  
Distribution of the slope of the bedrock at the position of the blocks.  
DEM of the Altels.  
Time of rupture, t i , as a function of ??/?t . The dotted line plots the equation: t i S 0.78 ? 116(??/?t ) ?0.82 .  
Article
The Altels hanging glacier in Switzerland broke off on 11 September 1895. The ice volume of this catastrophic rupture was estimated as 4 × 106 m3, the largest icefall event ever observed in the Alps. However, the causes of this collapse are not entirely clear. Based on previous studies, we reanalyzed this break-off event, with the help of a new numerical model, initially developed by Faillettaz and others (2010) for gravity-driven instabilities. The simulations indicate that a break-off event is only possible when the basal friction at the bedrock is reduced in a restricted area, possibly induced by the storage of infiltrated water within the glacier. Further, our simulations reveal a two-step behavior: (1) a first quiescent phase, without visible changes, with a duration depending on the rate of change in basal friction; (2) an active phase with a rapid increase of basal motion over a few days. The general lesson obtained from the comparison between the simulations and available observations is that detectable precursors (crevasse formation and velocity increase) of the destabilization process of a hanging glacier, resulting from a progressive warming of the ice/bed interface towards a temperate regime, will appear only a few days prior to the break-off.
 
Article
Precipitation at 2050 m on Blue Glacier, U.S.A., was measured daily from August 1957 through July 1958. Its correlation with a nearby lowland station with a good, long-term (1914-96) record is used to estimate precipitation on the glacier over that entire period. Average annual precipitation on Blue Glacier is 4500 mm w.e. Snowfall depends on the joint distribution of precipitation and temperature. Over the period 1948-96, for which twice-daily radiosonde observations are available, temperature at any elevation on the glacier is interpolated in the radiosonde profile to partition the precipitation as either rain or snow. Daily partitioning is preferred, especially during spring and autumn storms when averaging over longer periods may substantially under- or overestimate snowfall on the glacier. Prior to 1948, snowfall is estimated from the mean over 1948-96, in a particular month and elevation, of the fraction of the precipitation falling as snow. The standard error in the October-May snowfall at 2100 m is estimated to be 250 mm w.e. during the radiosonde era (1948-96) and 350 mm prior to that. For the first 10 years or so after mass-balance measurements began at Blue Glacier (1957), precipitation increased and winter temperature at 850 mbar (about 1450 m) decreased, but since then the trends have reversed. The combined effect, increasing snowfall until 1965 and decreasing since, closely parallels measured mass changes of Blue Glacier. When the average vertical profile of total annual snowfall is subjected to a hypothetical 1K warming, the resulting reduction in snowfall is greatest at the glacier terminus and decreases up-glacier; the average over the entire glacier is 300 mm w.e.
 
Article
Glacier responses to tephra deposition are shown to be highly variable where wind-transported eruption plumes produce narrow distal fallout zones with steep lateral thickness gradients. Significant but short-lived advances of faster-flowing glaciers can be triggered by deposition from modest eruptions. The 1947 eruption of Hekla, south Iceland, covered nearby glaciers with variable thicknesses of tephra, causing dramatic spatial variations in ablation rate. Relative snowablation increased by an estimated >80% at the eastern margin of Eyjafjallajo¨kull, but decreased by >54% at the western margin. Relative ice ablation increased by only 4% in the eastbut decreased by >75% atthe western margin, only 15km distant.The effect on mass balance therefore depends on tephra distribution as well as on the nature of the glacier surface. On Gı´gjo¨kull, retardation of ablation was greatest at the terminus, associated with an anomalous advance of ≥328 m between 1947 and 1954. Other glaciers in the fallout zone show either no recognizable response, or accelerated retreat. Advances will be short-lived due to the rapid redistribution of supraglacial tephra in a maritime climate, and the potential for discriminating between volcanically and climatically forced advances in the glacio-geomorphological record is low.The long-term glaciological effect of volcanism is to create thin, low-albedo covers after reworking, which make conditions less favourable for glaciation.
 
Article
We have constructed a new digital elevation model (DEM) of the 1995 surface of Black Rapids Glacier, a surge-type glacier in the central Alaska Range, using ERS-1/-2 repeat-pass interferometry. We isolated the topographic phase from three interferograms with contrasting perpendicular baselines. Numerous phase-unwrapping errors caused by areas of poor coherence were corrected in all three interferograms, using a novel, iterative, semi-automated approach that capitalizes on the multi-baseline nature of the dataset. Comparison of our DEM with a 1949 US Geological Survey DEM and with 1973-95 ground survey data shows the gradual return of Black Rapids Glacier to a presurge hypsometry following a surge in 1936/37. Maximum elevation changes along the glacier center line in the ablation and accumulation areas are, respectively, −249 and +63 m (−5.4 and +1.4 m a−1). Maximum elevation changes of survey points at nearby locations are −4.9 m a−1 (1975-84) and +0.5 m a−1 (1975-85). Center-line thickening of +62 m between 1949 and 1995 (+1.4 m a−1), just above the Loket tributary in the upper part of the ablation zone, indicates dynamic thickening following the 1936/37 surge.
 
Article
Glaciological studies during the British Ruwenzori Expedition, 1952, included assessment of the extent of Pleistocene glaciation and detailed study of the late-glacial and post-glacial fluctuations of two of the glaciers originating in the Stanley Plateau. Correlation between photographs taken by earlier expeditions, the stratigraphy of lake site excavations and lichen re-colonization provide a good preliminary basis for assessing the climatic fluctuations. Stratification in existing glaciers appears to link up satisfactorily with meteorological observations to indicate two ablation phases annually.ZUSAMMENFASSUNG. Die glaziologischen Forschungen “der British Ruwenzori Expedition 1952” umfasste unter anderem Schätzungen vom Umfang der Pleistozäner Vereisung sowie eingehendes Studium der spätglazialen und postglazialen Schwankungen von zweien der Gletscher, die auf dem Stanley Plateau ihren Ursprung haben. Wechselbeziehungen zwischen Photographien, die von früheren Expeditionen aufgenommen worden waren, die Stratigraphie von Aushöhlungen am See, und das Wiederbewachsen von Flechten liefern eine gute einleitende Grundlage zur Begutachtung der klimatischen Schwankungen. Die Schichtung in bestehenden Gletschern scheint beftiedigenstellend mit meteorologischen Beobachtungen im Einklang zu stehen, wonach zwei Ablationsphasen jährlich angezeigt sind.
 
Article
Firn and ice thickness measurements were carried out by seismic refraction and reflection methods on a flat col of the highland snowfields of the Penny Ice Cap and on a medium-sized valley glacier (Highway Glacier). The longitudinal wave velocities were found to vary from some 1000 m./sec. (3280 ft./sec.) in firn to 3810 m.,/sec. (12,500 ft./sec.) in ice and approximately 6000 m.% sec. (20,000 ft./sec.) in the bedrock (gneiss). The thickness of firn and ice at the firn col was found to be 254 m. (834 ft.). On Highway Glacier some 80 reflections were evaluated, giving position, dip and strike of the bedrock surface. A longitudinal profile of Highway Glacier from the junction of three main tributary glaciers to the tongue is given; the ice thickness slowly decreases. At the junction, the bedrock is 400 m. (1310 ft.) deep, there is no deep basin as might be expected from the surface features. The mean slope of the glacier surface is about 3° of arc and of the bed about 1°.
 
Article
The horizontal and vertical motions of eight points on the surface of Highway Glacier, Baffin Island are reported. The average horizontal speed below the lowest tributary glacier is 56 metres/year. The major part of this motion arises from the glacier sliding on its bed. The mean shear stress on the bed is practically constant and equal to about 0.9 bars, but it is much smaller beneath the retreating tongue. A measure of the retreat in the lower part of the glacier is obtained from the difference between the ice discharge and the net ablation.RÉSUMÉ. Cette communication décrit Ie mouvement, en direction horizontale et verticale, de huit points situés á la surface du “Highway Glacier” sur I'ite de Baffin. La vitesse de déplacement en dessous du dernier glacier tributaire est en moyenne de 56 métres par an. Ce mouvement est d û en grande partie au glissement du glacier sur son lit. L'effort tranchant moyen á la surface du lit du glacier est pratiquement constant et d'environ 0.9 bars, mais il est beaucoup moindre en dessous de la langue en retrait. La différence entre Ie débit annuel et la perte annuelle de glace donne une mesure du retrait ou de la perte en volume dans la partie inférieure du glacier.
 
Article
The construction and use of some portable ice-boring equipment are described. The total weight of equipment for boring to a depth of 20 m. is about 36 kg. The weight increases by 1 kg. for each extra metre of depth.Résumé. On a décrit la construction et l'usage des appareils portatifs pour sonder la glace. Le poids total des appareils pour un sondage de 20 m est 36 kg environ. Le poids augmente d'un kilogramme pour chaque metre en profondeur.
 
Article
Accumulation and ablation measurements on Morsárjökull are described and a tentative glacier budget for the three seasons 1951-52, 1952-53 and 1953-54 is presented. Observations of glacier flow on Morsärjökull, Svinafellsjökull and Skaftafellsjökull are considered. The recent fluctuations of the snouts of Skaftafellsjökull and Svlnafellsjökull are discussed and related to variations in the height of the accumulation zones of the glaciers; recent glacier thinning is also mentioned.ZUSAMMENFASSUNG. Anhäufungs- und Ablationsmessungen auf dem Morsárjökull werden beschrieben, und ein vorläufiges Gletscher-Budget für die drei Saisons 1951-52, 1952-53 und 1953-54 ist aufgestellt.Beobachtungen der Gletscherströmung auf dem Morsárjökull, dem Svínafellsjökull und dem Skaftafellsjökull werden in Betracht gezogen. Die jüngsten Schwankungen der Stromenden des Skaftafellsjökull und des Svínafellsjökull werden besprochen und auf Unterschiede in der Höhe der Anhäufungszonen der Gletscher bezogen; jüngster Gletscherschwund wird auch erwähnt.
 
Article
Observations and measurements of ogives on Morsárjökull, Svínafellsjökull and Falljökull are given and discussed. The problems associated with the smaller ogives on Svínafellsjökull and the ridges below the ice falls are considered.ZUSAMMENFASSUNG. Beobachtungen und Messungen det Ogiven auf Morsárjökull, Svínafellsjökull und Falljökull sind angegeben und besprochen. Die mit den kleineren Ogiven auf Svínafellsjökull verknöpften Probleme und die Grate unter den Gletscherbröchen werden erwogen.
 
Article
Mass-balance and dynamic measurements carried out on glacier de Saint Sorlin since 1957 provide a good opportunity to study the dynamics of this glacier. Ice-flow analysis shows that dynamic changes have been important over the last 40 years and that these changes are not consistent with the concepts usually used in glacier modelling. Present velocities are larger than the 1960 velocities, although the thickness decreased everywhere (10-30 m in the ablation zone). A simple numerical ice-flow model which does not include longitudinal stress gradients has been used to investigate these phenomena. This model allows us to infer the sliding velocity from observed surface and calculated deformation velocities. We conclude that: (1) the sliding velocity cannot be described by Weertman analysis or empirical relations which link the sliding to the thickness and surface slope; (2) the inferred sliding velocity is uniform over at least half of the glacier; and (3) there is no clear link between the sliding process and the quantity of water coming from surface ablation. Furthermore, it may not be reasonable to calibrate model flow parameters from geometry changes because the surface geometry is relatively insensitive to velocity changes over some decades.
 
Article
Stake surveys on Glacier de Saint-Sorlin, French Alps, during the period 1957-76 show that annual surface velocities fit a linear vectorial model, with a term depending on the site, another on the year, and an important random component. Strain rates, viscosities and stresses at shallow depth are computed using strain triangles of hectometric (102m) size. Between 1961/62 and 1972/73 the isotropic point, where streamlines cease to converge, moved downstream about 200 m. This trend may explain increasing velocities. Crevasses appear where annual strain is > 1.2%. Faults limit the effective shear stress at the surface to about 0.38 bar. Ten modes of flow are distinguished, instead of only two for the two-dimensional model (compressive and extensive). The gradients of shallow stresses, which ensure extra driving forces, are computed with another mosaic of triangles of similar size (stress triangles). There are also important extra driving forces at the bottom, which force the flow to deviate from the direction of the steepest surface slope. Two criteria allow elimination of stress triangles where these unknown basal extra driving forces are important. Even so, no sliding law in terms of mean annual values can be obtained. This study shows that the classical perturbation theory, which explains advances and retreats by the arrival of kinematic waves, is unsuitable for glaciers of kilometric size.
 
Location of the study area and the distribution of glaciers within it during 1958. 
Number of glaciers against area for 1958. Glaciers are grouped into 0.1 km 2 intervals. 
Individual glacier FAC against area. Open circles represent individual glaciers and the solid lines represent the error envelope about the axis. 
Comparison of glacier change by size class for the Swiss Glacier Inventory (SGI; Paul and others, 2004) and the North Cascades National Park Complex (NOCA). The period for the SGI is 1973-98, while the period for NOCA is 1958-98
Volume errors (%) using the 'empirical' topographically derived volume change as the standard. The glacier names define the columns and AVG is the average error for the five glaciers
Article
The spatial characteristics for all glaciers in the North Cascades National Park Complex, USA, were estimated in 1958 and again in 1998. The total glacier area in 1958 was 117.3 ± 1.1 km2; by 1998 the glacier area had decreased to 109.1 ± 1.1 km2, a reduction of 8.2 ± 0.1 km2 (7%). Estimated volume loss during the 40 year period was 0.8 ± 0.1 km3 of ice. This volume loss contributes up to 6% of the August-September stream-flow and equals 16% of the August-September precipitation. No significant correlations were found between magnitude of glacier shrinkage and topographic characteristics of elevation, aspect or slope. However, the smaller glaciers lost proportionally more area than the larger glaciers and had a greater variability in fractional change than larger glaciers. Most of the well-studied alpine glaciers are much larger than the population median, so global estimates of glacier shrinkage, based on these well-studied glaciers, probably underestimate the true magnitude of regional glacier change.
 
Article
The retreat of Laika Glacier (4.4 km2), part of a small ice cap situated on Coburg Island, Canadian Arctic Archipelago, is analyzed using field data, satellite remote sensing and mass-balance modelling. We present a methodology for merging various data types and numerical models and investigate the temporal and spatial changes of a remote glacier during the past five decades. A glacier mass-balance and surface-evolution model is run for the period 1959-2006, forced with in situ weather observations and climate re-analysis data (ERA-40, NARR). The model is calibrated using the ice-volume change observed between 1959 and 1971, and measured seasonal mass balances. Calculated glacier surface elevation is validated against ICESat GLAS altimeter data and ASTER-derived elevation. Landsat-derived glacier outlines are used to validate calculated ice extent. The piedmont tongue of Laika Glacier has retreated considerably and is in a state of disintegration. The modelled glacier mass balance between 1959 and 2006 was −0.41 m w.e.a−1, on average. Model results indicate a significant trend towards higher mass-balance gradients. A complete wastage of Laika Glacier by 2100 is predicted by model runs based on climate scenarios.
 
Article
Using Geographical Information System (GIS) and remote-sensing technologies, we describe quantitative measurements of glacier variations in the Geladandong mountain region of central Tibet. Data from Landsat images at three different times, 1973-76, 1992 and 2002, are compared with glacier areas digitized from a topographic map based on aerial photographs taken in 1969. We find that while some glaciers have advanced during the past 30 years, others have retreated. The area of retreat is much larger than that of advance. The total glacier area has decreased from 889 km2 in 1969 to 847 km2 in 2002, a reduction of almost 43 km2 (i.e. 4.8% decrease, or an average of 1.29 km2 a−1). The variation of glacier area in the Geladandong mountain region is not as large as in other regions within the Tibetan Plateau. Glacier areas decreased 4.7 km2 (i.e. an average of 0.68 km2 a−1) during 1969-76, 15.4 km2 (0.96 km2 a−1) during 1976-92, and 22.4 km2 (2.24 km2 a−1) during 1992-2002, suggesting accelerated glacier retreat in recent years. The recession rates of glacier termini also increased. It is likely that the increase in summer air temperature is the major reason for glacier shrinkage in the Geladandong mountain region.
 
Article
Glacier area changes in the Pumqu river basin, Tibetan Plateau, between the 1970s and 2001 are analyzed, based on the Chinese Glacier Inventory and ASTER images. A new glacier inventory is obtained by visually interpreting the remote-sensing images and the digital elevation model. By comparing the two inventories, glacier area changes over the past 30 years are revealed. The results show that the area loss is about 9.0% % and the shrinkage trend continues according to the meteorological data.
 
Article
Using airborne and spaceborne high-resolution digital elevation models and laser altimetry, we present estimates of interannual and multi-decadal surface elevation changes on the Bering Glacier system, Alaska, USA, and Yukon, Canada, from 1972 to 2006. We find: (1) the rate of lowering during 1972-95 was 0.9±0.1 m a−1; (2) this rate accelerated to 3.0±0.7 m a−1 during 1995-2000; and (3) during 2000-03 the lowering rate was 1.5±0.4 m a−1. From 1972 to 2003, 70% of the area of the system experienced a volume loss of 191±17 km3, which was an area-average surface elevation lowering of 1.7±0.2 m a−1. From November 2004 to November 2006, surface elevations across Bering Glacier, from McIntosh Peak on the south to Waxell Ridge on the north, rose as much as 53 m. Up-glacier on Bagley Ice Valley about 10 km east of Juniper Island nunatak, surface elevations lowered as much as 28 m from October 2003 to October 2006. NASA Terra/MODIS observations from May to September 2006 indicated muddy outburst floods from the Bering terminus into Vitus Lake. This suggests basal-englacial hydrologic storage changes were a contributing factor in the surface elevation changes in the fall of 2006.
 
Article
Near-concurrent surges and multi-decadal surface-elevation changes on the Malaspina Glacier system Alaska, USA, and Yukon, Canada, were investigated using digital elevation models and laser altimetry from airborne and space-borne sensors. Surface-elevation changes on Seward Lobe in two time periods support a hypothesis of moraine folding by a mechanism of sequential surges alternating from southeast to south-southwest. The near-concurrent surges of Agassiz, Lower Seward and Marvine glaciers support a hypothesis of englacial water storage being a critical factor of surging. Acceleration of area-average surface lowering on the piedmont glaciers occurred, from 1.5 ± 0.1 m a−1 between 1972 and 1999 to 2.3 ± 0.3 m a−1 between 1999 and 2002. On the western half of Upper Seward Glacier, above 1600 m, acceleration of surface lowering occurred from 2000 to 2003 relative to that from 1976 to 2000, indicating an effect from the surge of Lower Seward Glacier. From 2003 to 2006, the rate of surface lowering on Upper Seward Glacier has moderated back to the pre-2000 rate, indicating a recovery of surface elevation following the surge. From 1972 to 2002, the Malaspina Glacier system lost 156 ± 19 km3 (ice equivalent) on an area of 3661 km2.
 
Article
We have measured the glacier area changes in the central Southern Alps, New Zealand, between 1978 and 2002 and have compiled the 2002 glacier outlines using an image scene from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). Three automated classification methods were tested: (1) band ratio, (2) normalized-difference snow index and (3) supervised classification. The results were compared with the glacier outlines photo-interpreted from the ASTER data, and were further validated using GPS-aided field mapping of selected test glaciers. The ASTER 3/4 band ratio provided the best results. However, all the classification methods failed to extract extensive debris-covered parts of the glaciers. Therefore, the photo-interpreted 2002 outlines were used when comparing with the existing 1978 glacier inventory derived from aerial photographs. Our results show a ∼17% reduction of glacier area, mainly driven by the retreat of the large valley glaciers. Despite the large climatic gradient from west to east, glaciers on both sides of the Main Divide lost similar percentages of area, except Franz Josef and Fox Glaciers which advanced. Smaller glaciers were found to have changed very little in the study period.
 
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John Frederick Nye
  • University of Bristol
Roger LeB. Hooke
  • University of Maine
Wilfried Haeberli
  • University of Zurich
Matthew Sturm
  • University of Alaska
Roger Braithwaite
  • The University of Manchester