Ground-penetrating radar (GPR) and satellite ERS-2 synthetic aperture radar (SAR) are used to map the thickness and extent of the superimposed ice (SI) zone on the surge-type glacier Kongsvegen, Svalbard. GPR imagery shows sub-horizontal SI layers lying unconformably above a discrete boundary. Below this boundary, the ice has a GPR signature similar to that of ice further down-glacier in the ablation zone. This boundary is posited to represent the closing of crevasses that were created during the last surge of Kongsvegen in ∼1948. Open crevasses would have interrupted the formation of sheet layers of SI due to efficient vertical drainage of the snowpack. Aerial photographs suggest that the crevasses closed sometime in the period 1956–66. A classified SAR image from 2003 is used to delineate the extent of the SI zone. The SI extent in the SAR image agrees well with the SI zone mapped by GPR. Using the SI spatial depth distribution, we estimate the mean annual accumulation of superimposed ice to be 0.16 ± 0.06 m w.e. a−1 (locally up to 0.43 m a−1 w.e.). This corresponds to ∼15–33% of the local winter balance and ∼5–10% of the total winter balance measured since 1987.

For more than 30 years the quantitative method of evaluating stability (e.g. Roch, 1966; Föhn, 1987; Jamieson, 1995; Jamieson and Johnston, 1998a) has been focused on calculation of a strength-to-load ratio (or stability index): when the shear stress applied to the weak layer reaches the shear strength, failure is imminent. However, field observations combined with experience and measurements indicate that snow-slab temperatures and slab hardness can have a strong influence on dry-snow slab stability. In this paper, we present a simple static analysis of the stability index, and discuss the importance of slab temperatures and hardness and macroscopic size effects (factors not contained in the stability index) on snow-slab stability. Our conclusion is that the traditional method lacks some elements which are very important in snow-slab stability, particularly when skier triggering is involved.

El Niño and La Niña affect global climate and atmospheric circulation to determine winter temperature and precipitation patterns. Both winter temperatures and the associated precipitation patterns have effects on mountain snow deposition and snow avalanche occurrences. Approximately 25 000 slab avalanches from 30 winters were analyzed in relation to snowfall patterns contrasted for El Niño and La Niña winters for two avalanche areas with different snow climates in British Columbia (BC), Canada. La Niña winters were shown to produce more snow, more avalanches and a higher percentage of dry avalanches than wet avalanches. The data and analysis show that the avalanche patterns depend on the altitude and snow climate. Analysis of snowfall and accident data from the Andes of Chile suggests behavior opposite to BC. El Niño winters in central Chile produced the most snow and, by inference, the most avalanches. This paper is the first to show the links of El Niño and La Niña to snow avalanche activity.

Accurate quantification of rates of glacier mass loss is critical for managing water resources and for assessing hazards at ice-clad volcanoes, especially in arid regions like southern Peru. In these regions, glacier and snow melt are crucial dry season water resources. In order to verify previously reported rates of ice area decline at Nevado Coropuna in Peru, which are anomalously rapid for tropical glaciers, we measured changes in ice cap area using 259 Landsat images acquired from 1980 to 2014. We find that Coropuna Ice Cap is presently the most extensive ice mass in the tropics, with an area of 44.1 km2, and has been shrinking at an average area loss rate of 0.409 km2 a−1 (~0.71% a−1) since 1980. Our estimated rate of change is considerably lower than previous studies (1.4 km2 a−1 or ~2.43% a−1), but is consistent with other tropical regions, such as the Cordillera Blanca located ~850 km to the NW (~0.68% a−1). Thus, if glacier recession continues at its present rate, our results suggest that Coropuna Ice Cap will likely continue to contribute to water supply for agricultural and domestic uses until ~2120, which is nearly 100 years longer than previously predicted.

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 than 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% 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% 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% of a 1 m tide dynamics, a physical shift of the grounding line of 0.3 km per metre of tide can lever misplacements of >2 km. Examples of real interferometric profiles from West Antarctic ice shelves corroborate our results.

Karst topography may occur on stagnant, drift-covered parts of glaciers such as the Martin River Glacier in south-central Alaska. Glacial karst features there include ice sink-holes, tunnels, caves, sinking streams, blind valleys, large springs, natural bridges, lapiés, hums, and residual “soils” or ablation till. The glacial karst cycle is essentially the same as the limestone karat cycle. Glacial karst is rare today but was widespread on stagnant glaciers in areas such as the northern Great Plains of North America in late Wisconsin time.

Understanding the climate response of the Antarctic Peninsula ice sheet is vital for accurate predictions of sea-level rise. However, since climate models are typically too coarse to capture spatial variability in local scale meteorological processes, our ability to study specific sectors has been limited by the local fidelity of such models and the (often sparse) availability of observations. We show that a high-resolution (5.5 km × 5.5 km) version of a regional climate model (RACMO2.3) can reproduce observed interannual variability in the Larsen B embayment sufficiently to enable its use in investigating long-term changes in this sector. Using the model, together with automatic weather station data, we confirm previous findings that the year of the Larsen B ice shelf collapse (2001/02) was a strong melt year, but discover that total annual melt production was in fact ~30% lower than 2 years prior. While the year before collapse exhibited the lowest melting and highest snowfall during 1980–2014, the ice shelf was likely pre-conditioned for collapse by a series of strong melt years in the 1990s. Melt energy has since returned to pre-1990s levels, which likely explains the lack of further significant collapse in the region (e.g. of SCAR Inlet).

We present novel results of pollen analyses performed on a 10 m firn core retrieved from Alto dell’Ortles glacier (3840 m a.s.l.), Eastern Italian Alps, in 2009. The objective was to identify and quantify pollen grains retained in the ice to detect annual and interannual variations in the pollen spectra, thus enabling construction of an accurate pollen-based timescale. Up to now, this has been achieved by pollen diagram interpretation. Here we present a statistical approach developed to extract the seasonal/annual signal contained in the pollen spectra of an ice core. The method is based on principal component analyses of pollen assemblages obtained by high-level taxonomical identification. We apply this approach to the Ortles samples, demonstrating that seasonal and yearly variations of the pollen spectra are easily detectable and provide valuable information that can help improve the chronological model of the firn core. This approach can potentially be used for deeper cores as well as other types of archives (e.g. varved sediments), allowing faster, more objective estimation of yearly and seasonal variations than with classical percentage pollen diagrams.

We examine the ability of synthetic aperture radar (SAR) to detect the equilibrium line on the glacier Austre Okstindbreen, Norway, using multipolarization SAR images in C- and L-band acquired with the Electromagnetic Institute of the Technical University of Denmark’s airborne EMISAR sensor during the European Multisensor Airborne Campaign EMAC ’95. The late-summer snowline, approximating the equilibrium line, cannot be seen on the SAR images. Instead, photographs from Austre Okstind-breen show that a distinct boundary visible on the C-band SAR images corresponds to the firn line created by old snow from many previous years. This is better seen on the cross-polarized SAR images (HV and VH), which in general reveal more detail than the HH- and VV-polarized images. We model the stratigraphy from net balance and glacier velocity data to calculate the firn-line altitude (FLA). Modelled FLA and the observed boundary are separated by 50 m in elevation, but considering errors during co-registration and modelling we conclude that the observed boundary on Austre Okstindbreen is the firn line. Monitoring FLA rather than equilibrium-line altitude (ELA) for mass-balance studies with remote sensing is therefore suggested.

Measurements of ice thickness and surface elevation are prerequisite to many glaciological investigations. A variety of techniques has been developed for interpretation of these data, including means of constructing regularly gridded digital elevation models (DEMs) for use in numerical studies. Here we present a simple yet statistically sound method for processing ice-penetrating radar data and describe a technique for interpolating these data onto a regular grid. DEMs generated for Trapridge Glacier, Yukon Territory, Canada, are used to derive geometric quantities that give preliminary insights into the underlying basin-scale hydrological system. This simple geometric analysis suggests that at low water pressures a dendritic drainage network exists that evolves into a uniaxial morphology as water pressure approaches flotation. These predictions are compared to hydraulic connection probabilities based on borehole drilling.

In August 1978 “Hazard Lake” released 19.62 × 106 m3 of water through a subglacial tunnel beneath Steele Glacier, Yukon Territory, Canada. The discharge during the outburst flood was measured by recording lake level changes with time, and a peak discharge of approximately 640 m3 s–1 was estimated from the data. We have attempted to model the 1978 flood from “Hazard Lake” using an adaptation of Nye’s (1976) theoretical model for jökulhlaups from Grimsvötn. Our aim has been to calibrate the Nye model as a first step toward using it as a peak discharge estimator for other glacier–dammed basins. The agreement between our measured and simulated hydrographs is good, and we find that creep closure, though included in our analysis, appears to play an insignificant role in limiting the discharge of “Hazard Lake”. Release of thermal energy from the relatively warm lake water is the dominant factor contributing to tunnel enlargement.

The Manning roughness of outlet channels from glacier–dammed lakes is not known a priori and must either be assumed or estimated after the fact from the flood hydrograph. For “Hazard Lake” our fit implies Manning roughness in the range n′ = 0.105 m–1⁄3 s, consistent with Nye’s estimate of n′ = 0.12 ml⁄3s for the 1972 Grimsvötn flood and our estimate of n′ = 0.12 m 1/3 s for the 1967 Summit Lake flood. If the Manning roughness for flood conduits can be shown to lie within a narrow range, this would constrain one of the least certain variables of the Nye model.

By making several simplifying assumptions, we have succeeded in reducing our adapted version of Nye’s model to a simple mathematical description involving dimensionless numbers characterizing reservoir geometry and the relative magnitudes of creep closure and tunnel enlargement by melting. In this simplified form, the influence of lake temperature, reservoir geometry, and creep closure on the character of flood hydrographs can be conveniently studied.

Puncak Jaya, Irian Jaya, Indonesia, contains the only remaining tropical glaciers in East Asia. The extent of the ice masses on Puncak Jaya has been mapped from high-resolution IKONOS satellite images acquired on 8 June 2000 and 11 June 2002. Exclusive of Southwall Hanging Glacier, the ice extent on Puncak Jaya was 2.326 km2 and 2.152 km2 in 2000 and 2002, respectively. From 2000 to 2002, the Puncak Jaya glaciers lost a surface area of 0.174 km2 or 7.48% of their 2000 ice extent. Comparison of the IKONOS-based glacier extents with previous glacier extents demonstrates a continuing reduction of ice area on Puncak Jaya. By 2000, ice extent on Puncak Jaya had reduced by 88% of its maximum neoglacial extent. Between 1992 and 2000 Meren Glacier disappeared entirely. All remaining ice masses on Puncak Jaya continue their retreat from their neoglacial maxima. Comparison of 2000/2002 ice extents with previous extents suggests that these glaciers have not experienced accelerating rates of retreat during the last half of the 20th century. If the recession rates observed from 2000 to 2002 continue, the remaining ice masses on Puncak Jaya will melt within 50 years.

The pattern of elevation change along the length of glaciers caused by retreat from Neoglacial maximum to present is investigated and described in terms of a profile-shape factor f defined as the ratio of the average thickness change to the local thickness change at the present terminus. The factor f is relevant to estimation of the change in volume of a glacier in relation to its change in length and the response time to a change in climate. Thickness-change profiles on a selection of 15 mountain valley glaciers give f in the range 0.1–0.4 with an average of 0.28. The elevation changes are in all cases largest near the terminus and decrease headward more rapidly than a linear variation with distance that would correspond to f of 0.50, a value assumed to be characteristic in the past. The smaller values of f indicate reduced estimates of changes in volume versus change in lengths and smaller response times for glaciers. Total volume change for glaciers and ice caps (excluding ice sheets in Greenland and Antarctica) as estimated roughly by these means, is consistent with previous estimates from mass-balance measurements and supports the view that melting of these ice masses has made a significant contribution to sea-level change over the last century. The observed values of f do not explain an apparent discrepancy between alternative theoretical methods for estimating the response time of glaciers based on length and terminus velocity or based on the thickness and terminus-ablation rate. The discrepancy may be caused in part by the relationship between terminus velocity and ablation rate associated with strongly non-steady-state conditions during advance or retreat. The patterns of elevation change measured for short time intervals of a few decades or less correspond to a wide spread of profile-shape factor f from less than 0.1 to more than 1.2 indicative of transients in the short time-scale response.

This paper is the second (Paper II) in a set of studies concerning the errors involved in the estimate of ice thickness and ice volume. Here we present a detailed analysis of the errors involved in the generation of ice-thickness DEMs constructed, most often, from GPR data, complemented by boundary data and sometimes, additional synthetic data arising from estimates based on theoretical considerations supported by independent data. We describe a complete methodology of error analysis that, starting from the errors in the data, propagates them to the grid nodes. In turn, the interpolation error at the grid nodes is calculated using a novel procedure that also provides an estimate of the bias introduced by the interpolation process. Finally, both errors are combined at the grid nodes to produce a gridpoint-dependent error estimate, which is complemented by an overall error estimate providing an assessment of the quality of the DEM. This methodology is illustrated with the case study of Werenskioldbreen, a land-terminating polythermal glacier in Svalbard.

We infer the horizontal velocity fields of the ice caps Langjökull and Hofsjökull, central Iceland, using repeat-pass interferometric synthetic aperture radar (InSAR). NASA’s uninhabited aerial vehicle synthetic aperture radar (UAVSAR) acquired airborne InSAR data from multiple vantage points during the early melt season in June 2012. We develop a Bayesian approach for inferring three-dimensional velocity fields from multiple InSAR acquisitions. The horizontal components generally agree with available GPS measurements wherever ice motion is well constrained by InSAR observations. We provide evidence that changes in volumetric moisture content near the glacier surface induce phase offsets that obfuscate the vertical component of the surface velocity fields, an effect that could manifest itself on any glacier that experiences surface melt. Spatial patterns in the InSAR-derived horizontal speeds are broadly consistent with the results of a simple viscous flow model, and the directionality of the InSAR-derived horizontal flow field is nearly everywhere consistent with the ice surface gradient. Significant differences between the InSAR-derived horizontal speed and the speed predicted by the viscous flow model suggest that basal slip accounts for more than half the observed outlet glacier flow.

A scheme for katabatic turbulent heat transfer proposed by Oerlemans and Grisogono (2002), here referred to as the OG parameterization, is compared with bulk heat-transfer estimates on Peyto Glacier, Alberta, Canada. Automatic weather stations (AWSs) provide off-glacier data to drive the parameterization and glacier data for bulk estimates. Micrometeorological datasets are used to assess two schemes that employ the Monin-Obukhov stability parameter, z/L, to modify logarithmic, or neutral, bulk heat-transfer equations to allow for stability. Both schemes fail at >1 m above the surface, where the AWS sensors are located, unless a modified approach is used in which the stability correction is constant for z/L ≥1/3. Then the bulk sensible-heat-flux density falls to ≈0.93 of its neutral estimate at all measurement levels, thus providing a basis for comparison with the parameterization. The results of the comparison are very good, indicating that a one-to-one relationship between bulk and parameterized values can be achieved by optimizing the fit with a background exchange coefficient and, because there is only one off-glacier AWS, using a sinusoidal function to model the diurnal variation of the potential temperature lapse rate.

An instrument is described that automatically records ice ablation while eliminating the need for ablation stakes. A pressure transducer placed at the bottom of a hole drilled into the ice is connected by a hose to a bladder lying on the surface. Ice ablation is detected as a reduction in the hydrostatic pressure measured by the transducer.

The conductive heat flux through the snow cover (Fa) is used as a proxy to examine the hypothesis that there is a significant heat flow from the Alaskan North Slope to the atmosphere because of the large number of lakes in the region. Fa is estimated from measurements of snow depth, temperature and density on tundra, grounded ice and floating ice in mid-April 1997 at six lakes near Barrow, northwestern Alaska. The mean Fa values from tundra, grounded ice and floating ice are 1.5, 5.4 and 18.6 W m2, respectively. A numerical model of the coupled snow/ice/water/soil system is used to simulate Fa and there is good agreement between the simulated and measured fluxes. The flux from the tundra is low because the soils have a relatively low thermal conductivity and the active layer cools significantly after freezing completely the previous autumn. The flux from the floating ice is high because the ice has a relatively high thermal conductivity, and a body of relatively warm water remains below the growing ice at the end of winter. The flux from the grounded ice is intermediate between that from the tundra and that from the floating ice, and depends on the timing of the contact between the growing ice and the lake sediments, and whether or not those sediments freeze completely. Using the estimated Fa values combined with the areal fractions of tundra, grounded ice and floating ice derived from synthetic aperture radar images, area-weighted Fa values are calculated for six areas. Fa values for the ice vary between 9.8 and 13.8 W m−2, and those from the ice plus tundra vary between 3.9 and 5.3 W m−2. The Fa values are similar to those observed in the sea-ice-covered regions of the south and north polar oceans in winter. The North Slope of Alaska may thus make a significant contribution to the regional energy budget in winter.

The only complete inventory of New Zealand glaciers was based on aerial photography starting in 1978. While there have been partial updates using 2002 and 2009 satellite data, most glaciers are still represented by the 1978 outlines in contemporary global glacier databases. The objective of this project is to establish an updated glacier inventory for New Zealand. We have used Landsat 8 OLI satellite imagery from February and March 2016 for delineating clean glaciers using a semi-automatic band ratio method and debris-covered glaciers using a maximum likelihood classification. The outlines have been checked against Sentinel-2 MSI data, which have a higher resolution. Manual post processing was necessary due to misclassifications (e.g. lakes, clouds), mapping in shadowed areas, and combining the clean and debris-covered parts into single glaciers. New Zealand glaciers cover an area of 794 ± 34 km2 in 2016 with a debris-covered area of 10%. Of the 2918 glaciers, seven glaciers are >10 km2 while 71% is <0.1 km2. The debris cover on those largest glaciers is >40%. Only 15 glaciers are located on the North Island. For a selection of glaciers, we were able to calculate the area reduction between the 1978 and 2016 inventories.

The decay of a lake-ice cover in the Canadian High Arctic was studied for 2 years. Melt at the upper surface accounted for 75% of the decrease in ice thickness, while 25% occurred at the ice–water interface. An energy-balance model, incorporating density reduction due to internal ice melt, was used to simulate the decay of the ice cover. The overall performance of the model was satisfactory despite periods when computed results differed from the observed ice decay. Energy-balance calculations indicated that the absorption of shortwave radiation within the ice provided 52% of the melt energy while 33 and 15% came from the surface-energy balance and heat flux from the water.