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Geodetic mass balance of the western Svartisen ice cap, Norway, in the periods 1968-1985 and 1985-2002
Abstract
The geodetic mass balance of the western Svartisen ice cap in northern Norway is determined, in this work, from photogrammetry on vertical aerial photographs taken in 1968, 1985 and 2002. The existing 1968 digital terrain model (DTM) was generated using analogue photogrammetry, and the 1985 and 2002 DTMs are newly generated using digital photogrammetry. The geodetic mass balance for 1968-85 is −2.6 ± 0.8 m w.e., and for 1985-2002 it is −2.0 ± 1.6 m w.e. The area of western Svartisen decreased from 190 km2 in 1968, to 187 km2 in 1985 and to 184 km2 in 2002. The outlet glacier Flatisen in the southeast retreated 1700 m over the two periods. The geodetic mass balance is also determined for Engabreen drainage basin, as −2.1 ± 0.9 m w.e. for the first period, and −0.3 ± 2.4 m w.e. for the second. The results for Engabreen are compared to traditional mass balances, and the large deviations cannot be explained from uncertainties determined for the geodetic method. The assessed errors contributing to the uncertainty in the geodetic mass balance are elevation errors, uncertainties from the applied melt correction, and the use of Sorge's law, assuming constant snow thickness and density.
... In the 1960s and 1970s measurements began at many other glaciers in Scandinavia (e.g., Holmlund andJansson 1999, Andreassen et al. 2005). In addition to the field observations, aerial photographs have been taken in about decadal intervals and are used for comparison of the glaciological and the geodetic mass balances (e.g., Andreassen 1999, Østrem and Haakensen 1999, Haug et al. 2009, Zemp et al. 2010. Results reveal cumulative mass surplus at the maritime glaciers (e.g., Hardangerjøkulen, Nigardsbreen, Ålfotbreen, Engabreen), whereas the more continental glaciers (e.g. ...
... Whereas glaciers in the Svartisen region in northern Norway showed an area reduction close to zero from 1968 to 1999 (Paul and Andreassen 2009), the glacier area reduced by 10% from about 1980 to 2003 in Jotunheimen, southern Norway (Andreassen et al. 2008). Analysis of aerial photographs from 1968 1985, and 2002 of the western Svartisen Ice Cap confirmed the limited glacier area reduction in that region and suggest a volume loss for the drainage basin of Engabreen (Haug et al. 2009). The latter is in contrast to mass gain over the same periods reported from direct glaciological measurements at Engabreen and might be caused by changing ice divides of the ice cap . ...
... In the 1960s and 1970s measurements began at many other glaciers in Scandinavia (e.g., Holmlund andJansson 1999, Andreassen et al. 2005). In addition to the field observations, aerial photographs have been taken in about decadal intervals and are used for comparison of the glaciological and the geodetic mass balances (e.g., Andreassen 1999, Østrem and Haakensen 1999, Haug et al. 2009, Zemp et al. 2010. Results reveal cumulative mass surplus at the maritime glaciers (e.g., Hardangerjøkulen, Nigardsbreen, Ålfotbreen, Engabreen), whereas the more continental glaciers (e.g. ...
... Whereas glaciers in the Svartisen region in northern Norway showed an area reduction close to zero from 1968 to 1999 (Paul and Andreassen 2009), the glacier area reduced by 10% from about 1980 to 2003 in Jotunheimen, southern Norway (Andreassen et al. 2008). Analysis of aerial photographs from 1968 1985, and 2002 of the western Svartisen Ice Cap confirmed the limited glacier area reduction in that region and suggest a volume loss for the drainage basin of Engabreen (Haug et al. 2009). The latter is in contrast to mass gain over the same periods reported from direct glaciological measurements at Engabreen and might be caused by changing ice divides of the ice cap . ...
... In the 1960s and 1970s measurements began at many other glaciers in Scandinavia (e.g., Holmlund andJansson 1999, Andreassen et al. 2005). In addition to the field observations, aerial photographs have been taken in about decadal intervals and are used for comparison of the glaciological and the geodetic mass balances (e.g., Andreassen 1999, Østrem and Haakensen 1999, Haug et al. 2009, Zemp et al. 2010. Results reveal cumulative mass surplus at the maritime glaciers (e.g., Hardangerjøkulen, Nigardsbreen, Ålfotbreen, Engabreen), whereas the more continental glaciers (e.g. ...
... Whereas glaciers in the Svartisen region in northern Norway showed an area reduction close to zero from 1968 to 1999 (Paul and Andreassen 2009), the glacier area reduced by 10% from about 1980 to 2003 in Jotunheimen, southern Norway (Andreassen et al. 2008). Analysis of aerial photographs from 1968 1985, and 2002 of the western Svartisen Ice Cap confirmed the limited glacier area reduction in that region and suggest a volume loss for the drainage basin of Engabreen (Haug et al. 2009). The latter is in contrast to mass gain over the same periods reported from direct glaciological measurements at Engabreen and might be caused by changing ice divides of the ice cap . ...
This paper was elaborated by more than 50 scientists from three dozen research institutions and agencies all over Europe. It provides key messages and graphs supported by thorough and more technical reviews of the corresponding scientific state of knowledge. The paper can help to address the information needs of a wide audience, including policy-makers at the European, national and sub-national level, non-governmental organizations, and the wider public.
The analysis of the state of the cryosphere in Europe is based on in-situ and remote sensing observations, and modelling. The paper covers Svalbard, Iceland, Scandinavia, the European Alps, the Tatra Mountains, the Pyrenees, as well as the Baltic Sea. It assesses the primary impact of climate change on the cryospheric components such as snow cover, glaciers and ice caps, permafrost, lake and river ice, and sea ice; as well as related secondary impacts on avalanches, landslides and rock slope failures, and glacier floods.
... Especially if the absolute signal in elevation change is small such as observed for Gourdon Glacier, the resulting uncertainty in yearly mass balance estimates remains high. Large differences are also observed for a comparison of geodetic glacier mass balances with values from direct glaciological field measurements (e.g., Krimmel, 1999;Østrem and Haakensen, 1999;Cogley, 2009;Haug et al., 2009). In addition to the above mentioned impediments in geodetic mass balance estimates, glaciological measurement are also prone to errors in the ablation stakes/snow pits measurements, for example, due to the sampling, the sinking of stakes in the firn area or neglected internal refreezing and ablation processes (Krimmel, 1999;Rolstad et al., 2009). ...
The Antarctic Ice Sheet is the largest reservoir of frozen freshwater, with an ice mass equivalent to ~58 m sea-level rise in the case of a complete melt. One of the strongest temperature increases on Earth was reported for the northern Antarctic Peninsula over the second half of the 20th century. Thus, accurate mass balance estimates of glaciers located in this region are necessary for projections of the future sea-level. Despite advances in the length of observation periods, the number of measurements, and the reduction of errors, the intercomparison of mass balance estimates derived from various methods still reveals considerable differences. This holds true even if the results are averaged over large spatial extents. This considerable uncertainty was visible, for example, in the recent review of the role of melt caused by the ocean or the stability of the East Antarctic Ice Sheet. In order to contribute to the improvement of glacier mass balance estimates, this study compares estimates by applying the input-output method, as well as the geodetic method on a local scale. The study site, James Ross Island, is located at the eastern side of the northern Antarctic Peninsula. It consists of a complex topography with a ~300 to 500 m high, almost vertical cliff separating the catchment areas from the marine-terminating outlets of many glaciers on the island. A special focus of this thesis is on the influence of the individual input variables propagated onto the error of the final mass balance estimate. Due to the harsh environmental conditions, many mass balance estimates in Antarctica rely only on remotely sensed data, such as that used in the geodetic method, which has the drawback of propagating potential errors if no validation data are available. In the scope of this thesis, in-situ measurements from several expeditions in Antarctica, which are necessary, especially for accurate estimates of the input-output method, are conducted. These in-situ data such as the ice thickness or meteorological variables conducted by automatic weather stations provide the unique opportunity of a much higher accuracy without, for example, interpolating or downscaling simulated data. A high spatial variability in glacier mass loss was observed on James Ross Island. This was related to the occurrence of Föhn events and the collapse of the ice shelf in the Röhss Bay. Previously published area estimates for the time steps 1988 and 2009 revealed strong glacier retreat on James Ross Island. In this thesis, the observation period of comparable frontal area changes is extended by exploiting glacier calving fronts starting from 1945 with a common-box approach. For almost all investigated glaciers the frontal area change rates before 1988 are lower than the retreat rates in the period 1988-2008/2009 with an overall rate on James Ross Island of -1.646 km^2 a^−1. Afterwards, the annual recession rates decrease to -0.093 km^2 a^−1 in 2008/2009-2014 and -0.039 km^2 a^−1 in 2014-2018. A continuous data set of glacier surface velocities derived by TerraSAR-X/TanDEM-X satellite acquisitions is validated with the in-situ measurements and used to analyse the temporal and spatial variability in ice dynamics between 2014 and 2018. Meteorological and oceanic data from the in-situ measurements and regional climate models are additionally used to determine potential atmospheric and oceanographic forcing factors. Sporadic acceleration events in surface velocity are observed for single glaciers, but the temporal patterns in velocity and area changes differ also for glaciers in immediate proximity. The analysis of the atmospheric conditions fails to explain the different patterns. Therefore, it is suggested that the bathymetry controls the local impact of oceanic forcing and partially over-modulates the atmospheric influence. These new results for James Ross Island suggest a stronger oceanic influence also in regions influenced by the Weddell Sea. In-situ ice thickness measurements are rare in Antarctica, but accurate estimates are an important input variable in the input-output method. Differences in ice thickness and their influence on ice discharge between published simulated data and in-situ measurements derived with ground penetrating radar are compared for the cliff-separated glacier type of Gourdon Glacier. A comparison of the measurements from 2018 with older in-situ data from the 1990s reveals differences mostly smaller than the estimated errors. The application of three interpolation and reconstruction approaches reveals a minor impact of ice thickness differences on the ice discharge estimation, if the used flux gates are in areas with a good spatial coverage of in-situ measurements. A much stronger influence is observed for uncertainties in the glacier velocities derived from remote sensing, especially in proximity to the ice cliff. Errors in ice discharge are estimated at the frontal part of Gourdon Glacier with ~0.8 Mt a^-1 for higher velocities in 2015 and ~0.3 Mt a^-1 for lower velocities in 2017. The results have a high significance for the scientific community because the in-situ ice thickness measurements show that the published simulated data strongly overestimate the ice thickness at the outlet of Gourdon Glacier, resulting in an overassessment of the ice discharge of up to 30 Mt a^-1. The in-situ ice discharge measurements can be used with high confidence as the "output" part for the input-output method in this thesis. In the case of the "input" part, the resolution of the regional climate models is too low to represent the topography of Gourdon Glacier. Thus, measurements from ablation stakes as well as the installed weather stations are used as input variables in a degree-day model. Additional mass input from the catchment area on the plateau, calculated by ice thickness and surface velocity measurements, is included in the model to generate a new surface mass balance model for the outlet part of Gourdon Glacier. Together with the ice discharge at a validated grounding line on the glacier frontal area, the mass balance could be calculated using the input-output method. Whereas the ice discharge estimation at the frontal part of the outlet derives reliable results with errors smaller than 1 Mt a^-1, the errors from the simulated SMB and the ice discharge from the plateau raise the error to ~4-6 Mt a^-1. For the geodetic approach it is not possible to establish altimetry data as a suitable candidate for serving as a reference ground truth on James Ross Island, which would be a valuable product for calibration and validation in this study area. Differences in surface elevation up to several metres are observed for different data sets using optical imagery and SAR interferometry. This can be largely attributed to high uncertainties in the co-registration of distinct elevation products due to the limited amount of stable ground. A detailed error estimation is conducted for mass balance estimates using SAR interferometry with TanDEM-X satellite acquisitions under the assumption of a successful co-registration, and under the assumption of uncorrected systematic biases in the data. The occurrence of systematic biases would raise the error from several Mt a^-1 up to ~100 Mt a^-1, and could at least partially explain the large differences in mass balance rates between the input-output and the geodetic method. The application of several "control" areas supports the assumption that the error is underestimated if systematic errors are not considered. The different results between the input-output and the geodetic method together with the high uncertainties in the error estimates lead to the conclusion that the complex topography of James Ross Island hampers the mass balance estimates. The inhomogeneous distribution of stable ground results in a limited co-registration, strong elevation differences for distinct products, as well as higher errors in the case of uncorrected systematic biases. Moreover, it was observed that the complex topography on James Ross Island is not resolved in many published simulated input data such as the SMB or the ice thickness, which are both necessary for the input-output method. This underlines the demand of in-situ measurements in the future. Nevertheless, the comparison of the influence of the error of each single variable on the final error provides novel insights into the error of small-scale glacier mass balance estimates.
... Alternative approaches can rely on modelling techniques derived from climatic records (Oerlemans, 2001), chemical and isotopic records extracted from ice cores (Ginot et al., 2006;Matsuoka and Naruse, 1999;Shiraiwa et al., 2002), the hydrological method (Tangborn et al., 1975), the flux component method (Allison et al., 2009) and indirect methods derived from the glaciological method Dumont et al., 2012;Kaser et al., 2003;Khalsa et al., 2004;Rabatel et al., 2005). These options each have advantages and disadvantages, but are also considered complementary Cogley, 2009;Haug et al., 2009;Ostrem and Haakensen, 1999;Tangborn et al., 1975Tangborn et al., , 1977. In the following section, the glaciological as well as the geodetic method for glacier mass balance are described. ...
The Tasman Glacier is New Zealand’s largest body of ice comprising several tributary glaciers. Since the early 1990s it has undergone a rapid frontal retreat associated with the expansion of a proglacial lake. In this study, digital photogrammetric processing of vertical aerial photographs were used to derive two high-resolution Digital Elevation Models (DEM) of the Tasman Glacier. Additionally, in order to account for the volume loss due to lake expansion, the subaqueous lake topography was generated from a recent bathymetric survey and appended to the latest DEM. Detailed analysis of the multitemporal DEM enabled the quantification of geodetic surface elevation and mass balance changes. Calculations show that the main Tasman Glacier and its tributaries have lost 19.72 ± 0.05 × 10^8 m^3 of ice between 1986 and 2008. The proglacial Tasman Lake occupied ca. 28% of this volume loss. The glacier-wide volume loss corresponds to a geodetic balance of 0.87 ± 0.002 m w. eq. yr^-1. Differential DEM analysis revealed diverse spatial patterns of thickness and volume change, varying between the tributaries and within and between elevation bins. Furthermore, reworked and transported material from recent rockfall deposits produced localised areas of apparent positive elevation changes. Previous ice volume change estimates may have underestimated mass loss from the Tasman Glacier, partly due to a lack of bathymetric data to account for the glacier-wide volume variation and omission of the tributary glaciers. The methods developed in this study offer a potential way forward for glacier monitoring in New Zealand, where old aerial photographs are available but have not previously been processed in this manner to obtain accurate assessment of geodetic mass balance.
... iamdonovan/dem_voids (last access: 8 March 2019). Ordinarily, using DEMs derived from radar of different bands, especially those acquired in different seasons such as the SRTM (February) and IfSAR (typically AugustSeptember), would require a consideration of the effects of differential radar penetration in snow and ice, as well as a temporal correction accounting for the difference in season, before converting elevation changes to a mass balance value ( Haug et al., 2009;Kronenberg et al., 2016). In this region, the SRTM is known to have particularly high levels of penetration that cause significant biases when used in geodetic mass balance calculations ). ...
Glacier mass balance has been estimated on individual glacier and regional scales using repeat digital elevation models (DEMs). DEMs often have gaps in coverage (“voids”), the properties of which depend on the nature of the sensor used and the surface being measured. The way that these voids are accounted for has a direct impact on the estimate of geodetic glacier mass balance, though a systematic comparison of different proposed methods has been heretofore lacking. In this study, we determine the impact and sensitivity of void interpolation methods on estimates of volume change. Using two spatially complete, high-resolution DEMs over southeast Alaska, USA, we artificially generate voids in one of the DEMs using correlation values derived from photogrammetric processing of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) scenes. We then compare 11 different void interpolation methods on a glacier-by-glacier and regional basis. We find that a few methods introduce biases of up to 20 % in the regional results, while other methods give results very close (<1 % difference) to the true, non-voided volume change estimates. By comparing results from a few of the best-performing methods, an estimate of the uncertainty introduced by interpolating voids can be obtained. Finally, by increasing the number of voids, we show that with these best-performing methods, reliable estimates of glacier-wide volume change can be obtained, even with sparse DEM coverage.
... However, there is a hypothesis that the increased activity around the Svartisen glacier could be related to the glacier itself (i.e., yearly variations of ice growth or melting). Studies of the Svartisen glacier (Nesje & Dahl, 2000) showed several kilometres of glacier advancement of its western margin during the Little Ice Age in the 18 th and 19 th centuries, whereas the major retreats of its western border have been reported during the 20 th century (Paul & Andreassen, 2009;Haug et al., 2009). The fact that the earthquake swarm started in April and peaked in early and in late-2015 there was a burst of seismicity around Steigen following a period of silence. ...
A temporary network of 27 seismic stations was deployed from August 2013 to May 2016 along the coast of Nordland, northern Norway, where northwestern Europe’s largest earthquake of magnitude 5.8 over the last two centuries has occurred. The NEONOR2 project aimed to improve our understanding of neotectonic movements, stress regime and the overall seismicity pattern in Nordland and the adjacent offshore areas. From the data retrieved from the temporary NEONOR2 deployment and the permanent stations of the Norwegian National Seismic Network, nearly 1250 earthquakes were located in the study area. During the monitoring period, the seismic activity in Nordland was mostly sporadic, but in some areas it was clearly episodic, especially to the west of the Svartisen glacier where an earthquake swarm with several hundred small seismic events was recorded from April 2015 until March 2016. The shallow swarm activity could possibly be partly related to the changes in the glacier mass and groundwater conditions. During the monitoring period, no earthquakes were recorded along the prominent Bivrost transfer zone, on the Trøndelag Platform and in the larger Vestfjorden Basin area, and it could therefore be concluded that these areas are aseismic; however, only three years of monitoring in such areas of low deformation rates is not enough to make strict conclusions. The observed lack of seismicity in the area generally confirmed earlier observations, though in this case with much more improved new data. The observations onshore provided clear indications of seismic activity along several previously unknown structures and well-defined lineaments trending NE–SW and NNW–SSE to the southwest of Svartisen, while a migration of the seismicity on some of these features was also recorded.
... Several studies assume that density in the accumulation area is constant over time and, hence, use glacier ice density for the conversion (e.g. Andreassen, 1999;Haug et al., 2009). As long as snow or firn is present, the density of ice (ρ ice =900 kg m −3 ) causes an overestimation of the mass 245 change. ...
This study presents a reanalysis of the glaciologically obtained 2001–11 annual glacier mass balances record at Hintereisferner, Ötztal Alps, Austria. The reanalysis is accomplished through a comparison with geodetically derived mass 15 changes, using annual high-resolution airborne laser scanning (ALS). The grid based adjustments for the method-inherent differences are discussed along with associated uncertainties and discrepancies of the two forms of mass balance measurements. A statistical comparison of the two datasets shows no significant difference for seven annual as well as the cumulative mass changes over the ten years record. Yet, the statistical view hides significant differences in the mass balance years 2002/03 (glaciological minus geodetic records = +0.92 m w.e.), 2005/06 (+0.60 m w.e.) and 2006/07 (–0.45 m w.e.). 20 The validity of the results is critically assessed and concludes that exceptional atmospheric circumstances can render the usual glaciological observational network inadequate. Furthermore, we consider that ALS data reliably reproduce the annual mass balance and can be seen as calibration tools of or, under certain circumstances, even as a substitute for the glaciological method.
... Traditionally, these DEMs have been derived from multi-angular passive optical imagery using photogrammetric methods (e.g. Haug et al., 2009;Koblet et al., 2010). More recently, multitemporal lidar has been used to monitor changes of glaciers and ice caps over time (Geist, 2005;Hopkinson and Demuth, 2006;Larsen et al., 2015). ...
Capturing and quantifying the world in three dimensions (x,y,z) using light detection and ranging (lidar) technology drives fundamental advances in the Earth and Ecological Sciences (EES). However, additional lidar dimensions offer the possibility to transcend basic 3-D mapping capabilities, including i) the physical time (t) dimension from repeat lidar acquisition and ii) laser return intensity (LRIλ) data dimension based on the brightness of single- or multi-wavelength (λ) laser returns. The additional dimensions thus add to the x,y, and z dimensions to constitute the five dimensions of lidar (x,y,z, t, LRIλ1… λn). This broader spectrum of lidar dimensionality has already revealed new insights across multiple EES topics, and will enable a wide range of new research and applications. Here, we review recent advances based on repeat lidar collections and analysis of LRI data to highlight novel applications of lidar remote sensing beyond 3-D. Our review outlines the potential and current challenges of time and LRI information from lidar sensors to expand the scope of research applications and insights across the full range of EES applications.
... Glacier elevation changes in Himalayas and its surroundings are of major concerns (Bolch et al., 2012). Quantification of these changes are often based on the " geodetic " method (Finsterwalder, 1954; Krimmel et al., 1999; Cox et al., 2004; Haug et al., 2009; Zemp et al., 2010; Fischer et al., 2011) by comparing two maps or DEMs (Digital Elevation Models) of the same 5 area from different years (Arendt et al., 2002; Abdalati et al., 2004; Rivera et al., 2005; DeBeer and Sharp, 2007; Berthier and Toutin, 2008). ICESat (Ice, Cloud and land Elevation Satellite), GRACE (Gravity Recovery and Climate Experiment) combined with Shuttle Radar Topography Mission (SRTM) has been used to estimate glacier thickness changes in the early 21st century (e.g., Zhang et al., 2011; Kääb et al., 2012; Phan et al., 2012; Gardner et al., 2013). ...
"Pamir–Karakoram–Western-Kunlun-Mountain (northwestern Tibetan Plateau) Glacier Anomaly" has been a topic of debate due to the balanced, or even slightly positive glacier mass budgets in the early 21st century. Here we focus on the evolution of glaciers on the western Kunlun Mountain and its comparison with those from other regions of the Tibetan Plateau. The possible driver for the glacier evolution is also discussed. Western Kunlun Mountain glaciers reduce in area by 0.12 % yr−1 from 1970s to 2007–2011. However, there is no significant area change after 1999. Averaged glacier thickness loss is 0.08 ± 0.09 m yr−1 from 1970s to 2000, which is in accordance with elevation change during the period 2003–2008 estimated by the ICESat laser altimetry measurements. These further confirm the anomaly of glaciers in this region. Slight glacier reduction over the northwestern Tibetan Plateau may result from more accumulation from increased precipitation in winter which to great extent protects it from mass reductions under climate warming during 1961–2000. Warming slowdown since 2000 happening at this region may further mitigate glacier mass reduction, especially for the early 21st century.
... Often an ice density of 900 kg m −3 has been used to convert volume to mass (e.g. Andreassen, 1999;Haug et al., 2009); other studies have used values of 917 kg m −3 (Nuth et al., 2010) or 860 ± 60 kg m −3 . Huss (2013) showed that a density conversion factor, f V , of 850 ± 60 kg m −3 is appropriate to convert volume change to mass change for a wide range of conditions. ...
Glaciological and geodetic methods provide independent observations of glacier mass balance. The glaciological method measures the surface mass balance, on a seasonal or annual basis, whereas the geodetic method measures surface, internal, and basal mass balances, over a period of years or decades. In this paper, we reanalyse the 10 glaciers with long-term mass-balance series in Norway. The reanalysis includes (i) homogenisation of both glaciological and geodetic observation series, (ii) uncertainty assessment, (iii) estimates of generic differences including estimates of internal and basal melt, (iv) validation, and, if needed, (v) calibration of mass-balance series. This study comprises an extensive set of data (484 mass-balance years, 34 geodetic surveys, and large volumes of supporting data, such as metadata and field notes). In total, 21 periods of data were compared and the results show discrepancies between the glaciological and geodetic methods for some glaciers, which are attributed in part to internal and basal ablation and in part to inhomogeneity in the data processing. Deviations were smaller than 0.2 m w.e. a-1 for 12 out of 21 periods. Calibration was applied to 7 out of 21 periods, as the deviations were larger than the uncertainty. The reanalysed glaciological series shows a more consistent signal of glacier change over the period of observations than previously reported: six glaciers had a significant mass loss (14-22 m w.e.) and four glaciers were nearly in balance. All glaciers have lost mass after the year 2000. More research is needed on the sources of uncertainty to reduce uncertainties and adjust the observation programmes accordingly. The study confirms the value of carrying out independent high-quality geodetic surveys to check and correct field observations.
... Les glaciers de l'Antisana ont une taille réduite (inférieure à 3,5 km²) et l'analyse de leur bilan de masse est parfaitement envisageable par la méthode géodésique, méthode qui est souvent adaptée aux grands glaciers (e.g. Cox et March, 2004, Berthier et al., 2007Haug et al., 2009). Toutefois, celle-ci exige une certaine précision qui peut seulement être obtenue par l'utilisation des clichés aériens (Soruco et al., 2009b) 1949-19531963-1998INAMHI 4 Cuyuja 1982-1990-2013 Cosanga ...
Le climat des régions tropicales joue un rôle important dans l'équilibre du système climatique mondial. De ce fait, il apparaît essentiel d'en comprendre le fonctionnement et la variabilité pour appréhender au mieux les effets du changement climatique. Dans les régions tropicales où les projections climatiques montrent un réchauffement important à haute altitude, les glaciers sont les premières victimes de l'augmentation des températures. Mais ils apparaissent également comme des indicateurs précis des variations du climat. Jusqu'à présent, les observations glaciologiques réalisées dans les tropiques internes sur le glacier Antisana 15 ont été utilisées dans de multiples études qui nous ont permis de comprendre les processus physiques qui régissent la fonte des glaciers dans cette région. Cependant ces études n'ont pas pris en compte la représentativité spatiale et temporelle de ces processus à l'échelle de toute la calotte glaciaire. A partir d'observations géodésiques, la présente étude montre l'évaluation spatiale et temporelle de neufs glaciers sur quatre périodes échelonnées durant les cinquante dernières années (1956-2014). Situés sur le cône volcanique de l'Antisana, ces glaciers ont été choisis pour leur orientation et leurs caractéristiques morphologiques. Dans un premier temps, nous avons évalué les observations glaciologiques existantes sur le glacier Antisana15α entre 1995 et 2012. Nos résultats suggèrent la surestimation d'au moins 5 m éq. eau dans le bilan de masse cumulé de ce glacier. Cet excès dans les taux d'ablation est causé par une sous-estimation dans la mesure d'accumulation annuelle, liée à la difficulté à déterminer la couche qui sépare deux années hydrologiques. Dans une deuxième étape, nous analysons les fluctuations géométriques des glaciers : de manière générale il existe une tendance négative avec un taux de perte de -0.5 m éq. eau par an, occasionnant un recul de 38% de la superficie de la calotte glaciaire. Cependant, cette tendance n'est pas régulière. Nous avons mis en évidence un comportement contrasté d'une période à l'autre : certaines caractéristiques attirent l'attention, comme le fait que le bilan de masse soit très déficitaire entre 1956 et 1964 (-1,3 m éq. eau par an) alors que dans une période plus récente (1998 et 2009) les glaciers se trouvent presque en équilibre (-0.2 m éq. eau par an). Durant la période globale, ces glaciers montrent une réponse commune à un signal climatique régional, tandis qu'à l'échelle locale l'exposition aux flux humides combinés aux caractéristiques morpho-topographiques confère un comportement spécifique à chaque glacier. Ce travail est le premier dans les tropiques internes qui détaille la réponse des glaciers face à la variabilité du climat sur plusieurs décennies et qui prend en considération l'influence des facteurs morphologiques sur ce comportement. Cette thèse s'inscrit dans les objectifs scientifiques de l'équipe Great Ice de l'IRD (LMI Great Ice), et participe aux avancées du service de surveillance glaciologique SOERE GLACIOCLIM.
... A density of 900 kg m −3 is commonly used (e.g. Krimmel, 1999;Cogley, 2009;Haug et al., 2009;Scambos et al., 2014). From the similarity of the radar backscatter coefficients in the 2011 and 2013 SAR images and the rather short time span of two years we can exclude any significant change in the structure and mean density of the snow/firn medium. ...
... In this study, we estimate the mass balance by geodetic means. In general, the geodetic mass balance is calculated by subtracting data sets of glacier surface elevation acquired at different times (e.g., Rignot et al., 2003;Kääb, 2008;Haug et al., 2009;Bolch et al., 2011). For the PIC two such data sets are available. ...
Due to their remoteness, altitude and harsh climatic conditions, little is known about the glaciological parameters of ice caps on the Tibetan Plateau (TP). This study presents an interferometrical approach aiming at surface elevation changes of Purogangri ice cap, located on the central TP. Purogangri ice cap covers an area of 397 ± 9.7 km2 and is the largest ice cap on the TP. Its behavior is determined by dry and cold continental climate suggesting a polar-type glacier regime. We employed data from the actual TerraSAR-X mission and its add-on for Digital Elevation Measurements (TanDEM-X) and compare it
with elevation data from the Shuttle Radar Topography Mission (SRTM).
These datasets are ideal for this approach as both datasets feature the same wavelength of 3.1 cm and are available at a fine grid spacing. Similar snow conditions can be assumed since the data were acquired in early February 2000 and late January 2012. The trend in glacier extend was extracted using a time series of Landsat data. Our results show a balanced mass budget for the studied time period which is in agreement with previous studies. Additionally, we detected an exceptional fast advance of one glacier tongue in the eastern part of the ice cap between 1999 and 2011.
... The geodetic method obtains the mass change by evaluating the elevation change of the entire glacier surface between two discrete times. A comparison of the stake and the geodetic methods (Haug et al. 2009; Huss et al. 2009) sometimes yields large differences, which helps finding errors efficiently in one or both of the measurements. This method is of increasing importance with the satellite data especially for larger glaciers. ...
Glacier mass balance and secular changes in mountain glaciers and ice caps are evaluated from the annual net balance of 137
glaciers from 17 glacierized regions of the world. Further, the winter and summer balances for 35 glaciers in 11 glacierized
regions are analyzed. The global means are calculated by weighting glacier and regional surface areas. The area-weighted global
mean net balance for the period 1960–2000 is −270±34mma−1w.e. (water equivalent, in mm per year) or (−149±19km3a−1w.e.), with a winter balance of 890±24mma−1w.e. (490±13km3a−1w.e.) and a summer balance of −1,175±24mma−1w.e. (−647±13km3a−1w.e.). The linear-fitted global net balance is accelerating at a rate of −9±2.1 mm a−2. The main driving force behind this change is the summer balance with an acceleration of −10±2.0mm a−2. The decadal balance, however, shows significant fluctuations: summer melt reached its peak around 1945, followed by a decrease.
The negative trend in the annual net balance is interrupted by a period of stagnation from 1960s to 1980s. Some regions experienced
a period of positive net balance during this time, for example, Europe. The balance has become strongly negative since the
early 1990s. These decadal fluctuations correspond to periods of global dimming (for smaller melt) and global brightening
(for larger melt). The total radiation at the surface changed as a result of an imbalance between steadily increasing greenhouse
gases and fluctuating aerosol emissions. The mass balance of the Greenland ice sheet and the surrounding small glaciers, averaged
for the period of 1950–2000, is negative at −74±10 mma−1w.e. (−128±18km3a−1w.e.) with an accumulation of 297±33mma−1w.e. (519±58km3a−1w.e.), melt ablation −169±18mma−1w.e. (−296±31km3a−1w.e.), calving ablation −181±19mma−1w.e. (−316±33km3a−1w.e.) and the bottom melt-21±2mma−1w.e. (−35±4km3a−1w.e.). Almost half (−60±3km3a−1) of the net mass loss comes from mountain glaciers and ice caps around the ice sheet. At present, it is difficult to detect
any statistically significant trends for these components. The total mass balance of the Antarctic ice sheet is considered
to be too premature to evaluate. The estimated sea-level contributions in the twentieth Century are 5.7±0.5cm by mountain
glaciers and ice caps outside Antarctica, 1.9±0.5cm by the Greenland ice sheet, and 2cm by ocean thermal expansion. The
difference of 7cm between these components and the estimated value with tide-gage networks (17cm) must result from other
sources such as the mass balance of glaciers of Antarctica, especially small glaciers separated from the ice sheet.
KeywordsMass balance–Greenland–Mountain glaciers–Trends
... Thibert et al., 2008; Huss et al., 2009). Over the past decades, it has become a standard procedure to check the (annual) glaciological with (decadal) volumetric mass balance methods, utilizing techniques such as topographic map comparison (e.g., Andreassen 1999; Conway et al. 1999; Kuhn et al. 1999; Hagg et al., 2004; Østrem and Haakensen, 1999), photogrammetry (e.g., Krimmel, 1999; Cox and March, 2005; Thibert et al., 2008; Haug et al., 2009; Huss et al., 2009; Fischer, 2010), global positioning systems (e.g., Hagen et al. 1999, Miller and Pelto 1999), or laser altimetry (e.g., Conway et al., 1999; Fischer, 2010; Echelmeyer et al., 1996; Sapiano et al., 1998; Geist and Stötter, 2007 ), the latter three references without direct comparison . It has become evident that a sound validation ideally is based on consistent data and procedures, and includes a sound assessment of stochastic and systematic uncertainties . ...
Seasonal glaciological mass balances have been measured on Storglaciären without interruption since 1945/46. In addition, aerial surveys have been carried out on a decadal basis since the beginning of the observation program. Early studies had used the resulting aerial photographs to produce topographic glacier maps with which the in-situ observations could be verified. However, these maps as well as the derived volume changes are subject to errors which resulted in major differences between the derived volumetric and the glaciological mass balance. As a consequence, the original photographs were re-processed using uniform photogrammetric methods, which resulted in new volumetric mass balances for 1959–69, 1969–80, 1980–90, and 1990–99. We compared these new volumetric mass balances with mass balances obtained by standard glaciological methods including an uncertainty assessment considering all related previous studies. The absolute differences between volumetric and the glaciological mass balances are 0.8 m w.e. for the period of 1959–69 and 0.3 m w.e. or less for the other survey periods. These deviations are slightly reduced when considering corrections for systematic uncertainties due to differences in survey dates, reference areas, and internal ablation, whereas internal accumulation systematically increases the mismatch. However, the mean annual differences between glaciological and volumetric mass balance are less than the uncertainty of the in-situ stake reading and stochastic error bars of both data series overlap. Hence, no adjustment of the glaciological data series to the volumetric one is required.
In this paper, we give an overview of changes in area, length, surface elevation and mass balance of glaciers in mainland Norway since the 1960s. Frontal advances have been recorded in all regions except the northernmost glaciers in Troms and Finnmark (Storsteinsfjellbreen, Lyngen and Langfjordjøkelen). More than half of the observed glaciers, 27 of 49, had marked advances in the 1990s. The glaciological mass-balance values for the period 1962–2018, where 43 glaciers have been measured, show great inter-annual variability. The results reveal accelerated deficit since 2000, the most negative decade being 2001–2010. Some years with a positive mass balance (or less negative) after 2010s can be attributed to variations in large-scale atmospheric circulation. A surface elevation change and geodetic mass balance were calculated for a sample of 131 glaciers covering 817 km ² in the ‘1960s’ and 734 km ² in the ‘2010s’, giving an area reduction of 84 km ² , or 10%. The sample covers many of the largest glaciers in Norway, and they had an overall change in surface elevation of −15.5 m for the ~50 year period. Converted to a geodetic mass balance this gives a mean mass balance of −0.27 ± 0.05 m w.e. a ⁻¹ .
This study presents a reanalysis of the glaciologically obtained annual
glacier mass balances at Hintereisferner, Ötztal Alps, Austria, for the
period 2001–2011. The reanalysis is accomplished through a comparison with
geodetically derived mass changes, using annual high-resolution airborne
laser scanning (ALS). The grid-based adjustments for the method-inherent
differences are discussed along with associated uncertainties and
discrepancies of the two methods of mass balance measurements. A statistical
comparison of the two datasets shows no significant difference for seven
annual, as well as the cumulative, mass changes over the 10-year record.
Yet, the statistical view hides significant differences in the mass balance
years 2002/03 (glaciological minus geodetic records = +0.92 m w.e.), 2005/06
(+0.60 m w.e.), and 2006/07 (−0.45 m w.e.). We conclude that exceptional
meteorological conditions can render the usual glaciological observational
network inadequate. Furthermore, we consider that ALS data reliably reproduce
the annual mass balance and can be seen as validation or calibration tools
for the glaciological method.
Due to their remoteness, altitude and harsh climatic conditions, little is known about the glaciological parameters of ice caps on the Tibetan Plateau (TP). This study presents an interferometrical approach aiming at surface elevation changes of Purogangri ice cap, located on the central TP. Purogangri ice cap covers an area of 397 ± 9.7 km2 and is the largest ice cap on the TP. Its behavior is determined by dry and cold continental climate suggesting a polar-type glacier regime. We employed data from the actual TerraSAR-X mission and its add-on for Digital Elevation Measurements (TanDEM-X) and compare it with elevation data from the Shuttle Radar Topography Mission (SRTM). These datasets are ideal for this approach as both datasets feature the same wavelength of 3.1 cm and are available at a fine grid spacing. Similar snow conditions can be assumed since the data were acquired in early February 2000 and late January 2012. The trend in glacier extend was extracted using a time series of Landsat data. Our results show a balanced mass budget for the studied time period which is in agreement with previous studies. Additionally, we detected an exceptional fast advance of one glacier tongue in the eastern part of the ice cap between 1999 and 2011.
Close-range photo-based surface reconstruction from the ground is rapidly emerging as an alternative to lidar (light detection and ranging), which today represents the main survey technique in many fields of geoscience. The recent evolution of photogrammetry, incorporating computer vision algorithms such as Structure from Motion (SfM) and dense image matching such as Multi-View Stereo (MVS), allows the reconstruction of dense 3-D point clouds for the photographed object from a sequence of overlapping images taken with a digital consumer camera. The objective of our work was to test the accuracy of the ground-based SfM-MVS approach in calculating the geodetic mass balance of a 2.1 km2 glacier in the Ortles-Cevedale Group, Eastern Italian Alps. In addition, we investigated the feasibility of using the image-based approach for the detection of the surface displacement rate of a neighbouring active rock glacier. Airborne laser scanning (ALS) data were used as benchmarks to estimate the accuracy of the photogrammetric DTMs and the reliability of the method in this specific application. The glacial and periglacial analyses were performed using both range and image-based surveying techniques, and the results were then compared. The results were encouraging because the SfM-MVS approach enables the reconstruction of high-quality DTMs which provided estimates of glacial and periglacial processes similar to those achievable by ALS. Different resolutions and accuracies were obtained for the glacier and the rock glacier, given the different survey geometries, surface characteristics and areal extents. The analysis of the SfM-MVS DTM quality allowed us to highlight the limitations of the adopted expeditious method in the studied alpine terrain and the potential of this method in the multitemporal study of glacial and periglacial areas.
The glaciological and geodetic methods provide independent observations of glacier mass balance. The glaciological method measures the surface mass balance, on a seasonal or annual basis, whereas the geodetic method measures surface, internal and basal mass balances, over a period of years or decades. In this paper, we reanalyse the 10 glaciers with long-term mass balance series in Norway. The reanalysis includes (i) homogenisation of both glaciological and geodetic observation series, (ii) uncertainty assessment, (iii) estimates of generic differences including estimates of internal and basal melt, (iv) validation, and (v) partly calibration of mass balance series. This study comprises an extensive set of data (454 mass balance years, 34 geodetic surveys and large volumes of supporting data, such as metadata and field notes). In total, 21 periods of data were compared and the results show discrepancies between the glaciological and geodetic methods for some glaciers, which in part are attributed to internal and basal ablation and in part to inhomogeneity in the data processing. Deviations were smaller than 0.2 m w.e. a−1 for 12 out of 21 periods. Calibration was applied to seven out of 21 periods, as the deviations were larger than the uncertainty. The reanalysed glaciological series shows a more consistent signal of glacier change over the period of observations than previously reported: six glaciers had a significant mass loss (14–22 m w.e.) and four glaciers were nearly in balance. All glaciers have lost mass after year 2000. More research is needed on the sources of uncertainty, to reduce uncertainties and adjust the observation programmes accordingly. The study confirms the value of carrying out independent high-quality geodetic surveys to check and correct field observations.
This study evaluates sensitivities of glacier mass balance and runoff to both annual and monthly perturbations in air temperature and precipitation at four highly glacierized catchments: Engabreen in northern Norway and Ålfotbreen, Nigardsbreen and Storbreen, which are aligned along a west–east profile in southern Norway. The glacier mass-balance sensitivities to changes in annual air temperature range from 1.74 m w.e. K À 1 for Ålfotbreen to 0.55 m w.e. K À 1 for Storbreen, the most maritime and the most continental glaciers in this study, respectively. The runoff sensitivities of all catchments are 20–25% per degree temperature change and 6–18% for a 30% precipitation change. A seasonality of the sensitivities becomes apparent. With increasing continentality, the sensitivity of mass balance and runoff to temperature perturbations during summer increases, and the sensitivity of annual runoff to both temperature and precipitation perturbations is constricted towards changes during the ablation period. Comparing sensitivities in northern and southern Norway, as well as the variability across southern Norway, reveals that continentality influences sensitivities more than latitude does.
Glaciological and geodetic measurements are two methods to determine glacier mass balances. The mass balance of Urumqi Glacier No. 1 has been measured since 1959 by the glaciological method using ablation stakes and snowpits, except during the period 1967–1979 when the observations were interrupted. Moreover, topographic surveys have been carried out at various time intervals since the beginning of the glacier observations. Therefore, glacier volume changes are calculated by comparing topographic maps of different periods during nearly 50 years. Between 1962 and 2009, Urumqi Glacier No. 1 lost an ice volume of 29.51 × 106 m3, which corresponds to a cumulative ice thickness loss of 8.9 m and a mean annual loss of 0.2 m. The results are compared with glaciological mass balances over the same time intervals. The differences are 2.3%, 2.8%, 4.6%, 4.7% and 5.9% for the period 1981–86, 1986–94, 1994–2001, 2001–06 and 2006–09, respectively. For the mass balance measured with the glaciological method, the systematic errors accumulate linearly with time, whereas the errors are random for the geodetic mass balance. The geodetic balance is within the estimated error of the glaciological balance. In conclusion, the geodetic and glaciological mass balances are of high quality and therefore, there is no need to calibrate the mass balance series of Urumqi Glacier No. 1.
Icelandic glaciers cover ∼11 000 km2 in area and store ∼3600 km3 of ice. Starting in 2008 during the International Polar Year, accurate digital elevation models (DEMs) of the glaciers are being produced with airborne lidar. More than 90% of the glaciers have been surveyed in this effort, including Vatnajökull, Hofsjökull, Mýrdalsjökull, Drangajökull, Eyjafjallajökull and several smaller glaciers. The publicly available DEMs are useful for glaciological and geological research, including studies of ice-volume changes, estimation of bias in mass-balance measurements, studies of jökulhlaups and subglacial lakes formed by subglacial geothermal areas, and for mapping of crevasses. The lidar mapping includes a 500–1000 m wide ice-free buffer zone around the ice margins which contains many glacio-geomorphological features, and therefore the new DEMs have proved useful in geological investigations of proglacial areas. Comparison of the lidar DEMs with older maps confirms the rapid ongoing volume changes of the Icelandic ice caps which have been shown by mass-balance measurements since 1995/96. In some cases, ice-volume changes derived by comparing the lidar measurements with older DEMs are in good agreement with accumulated ice-volume changes derived from traditional mass-balance measurements, but in other cases such a comparison indicates substantial biases in the traditional mass-balance records.
The continuation of valuable, long-term glacier observation series is
threatened by the accelerated mass loss which currently affects a large
portion of so-called "benchmark" glaciers. In this work we present the
evolution of the Careser Glacier, from the beginning of systematic
observation at the end of the 19th century to its current condition in
2012. In addition to having one of the longest and richest observation
records among the Italian glaciers, Careser is unique in the Italian Alps for
its 46 yr mass balance series that started in 1967. In the present study,
variations in the length, area and volume of the glacier since 1897 are
examined, updating and validating the series of direct mass balance
observations and adding to the mass balance record into the past using the
geodetic method. The glacier is currently strongly out of balance and in
rapid decay; its average mass loss rate over the last 3 decades was
1.5 m water equivalent per year, increasing to 2.0 m water equivalent per
year in the last decade. Although these rates are not representative at a
regional scale, year-to-year variations in mass balance show an unexpected
increase in correlation with other glaciers in the Alps, during the last
3 decades. If mass loss continues at this pace, the glacier will
disappear within a few decades, putting an end to this unique observation
series.
Glacier-wide mass balance has been measured for more than sixty years
and is widely used as an indicator of climate change and to assess the
glacier contribution to runoff and sea level rise. Until present,
comprehensive uncertainty assessments have rarely been carried out and
mass balance data have often been applied using rough error estimation
or without error considerations. In this study, we propose a framework
for re-analyzing glacier mass balance series including conceptual and
statistical toolsets for assessment of random and systematic errors as
well as for validation and calibration (if necessary) of the
glaciological with the geodetic balance results. We demonstrate the
usefulness and limitations of the proposed scheme drawing on an analysis
that comprises over 50 recording periods for a dozen glaciers and we
make recommendations to investigators and users of glacier mass balance
data. Reanalysis of glacier mass balance series needs to become a
standard procedure for every monitoring programme to improve data
quality and provide thorough uncertainty estimates.
In this paper we document changes of Langfjordjøkelen, a small ice cap in northern Norway. Surface mass-balance measurements have been carried out on an east-facing part (3.2 km2) of the ice cap since 1989. Measurements reveal a strong thinning; the balance year 2008/09 was the 13th successive year with significant negative annual balance (≤–0.30 m w.e.). The average annual deficit was 0.9 m w.e. over 1989–2009. The recent thinning of Langfjordjøkelen is stronger than observed for any other glacier in mainland Norway. Maps from 1966, 1994 and 2008 show that the whole ice cap is shrinking. The total volume loss over 1966–2008 was 0.264 km3. The east-facing part has been greatly reduced in volume (46%), area (38%) and length (20%). For this part over 1994–2008, the cumulative direct mass balance (–14.5 m w.e.) is less negative than the geodetic mass balance (–17.7 m w.e.). A surface mass-balance model using upper-air meteorological data was used to reconstruct annual balances back to 1948 and to reconstruct unmeasured years 1994 and 1995. Sensitivity of annual balance to 1°C warming is –0.76 m w.e. and to 10% increase in precipitation is +0.20 m w.e.
Glacier mass balance in Norway is only observed over a small portion (<15%) of the glacierized surface and only for short time periods (<10 years) for most sites. To provide a comprehensive overview of the temporal mass-balance evolution, we modeled surface mass balance for the glacierized area of mainland Norway from 1961 to 2010. The model is forced by operationallygridded daily temperature and precipitation fields which are available at 1km horizontal resolutionfrom 1957 until the present. The applied mass-balance model accounts for melting of snow and ice by using a distributed temperature-index approach. The precipitation input is corrected to obtain agreement between modeled and observed winter mass balance, and a melt factor and two radiation coefficients are optimized to the corresponding summer balance. The model results show positive trends of winter balance between 1961 and 2000 followed by a remarkable decrease in both summer and winter balances which resulted in an average annual balance of –0.86+-0.15 m w.e. a–1 between 2000 and 2010 after four decades of zero to slightly positive annual mass balances.
In glaciology, volumetric changes from multi-temporal digital elevation models (DEMs) serve to validate and calibrate glacier mass balances from traditional in situ measurements. In this study, we provide a thorough uncertainty assessment of multi-temporal airborne laser scanning DEMs based on: (a) applying a statistical error model, (b) comparing laser echoes to reference points and surfaces, and (c) developing a physical error propagation model. The latter model takes into account the measurement platform characteristics, components of the measurement process, and the surface properties. Such a model allows the estimation of systematic and stochastic uncertainties for single laser echoes, as well as for distributed surfaces in every part of the study site, independent of the reference surfaces. The full error propagation framework is applied to multi-temporal DEMs covering the highly undulating terrain in the Findelengletscher catchment in Canton Valais, Switzerland. This physical error propagation model is able to reproduce stochastic uncertainties in accordance with measurements from reference surfaces. The high laser point density in the study site reduces the stochastic uncertainties over the whole glacier area to negligibly small values. However, systematic uncertainties greatly influence the calculation of mass changes and lead to corrections of the thickness change of up to 35%.
A widespread loss of glacier area and volume has been observed in the European Alps since the 1980s. In addition to differences among various regions of the Alps, different responses to climate change characterize neighboring glaciers within the same region. In this study we describe the glacier changes in the Ortles-Cevedale group, the largest glacierized area in the Italian Alps. We analyze the spatial variability, the drivers, and the main factors controlling the current loss of ice in this region, by comparing mean elevation changes derived from two digital terrain models (DTMs), along with glacier extents and snow-covered areas derived from Landsat images acquired in 1987 and 2009, to various topographic factors. Glacier outlines were obtained using the band ratio method with manual corrections. Snow was classified from a near-infrared image after topographic correction. The total glacierized area shrank by 23.4 ± 3% in this period, with no significant changes in the mean altitude of the glaciers. In 2009 the snowline was 240 m higher than in the 1960s and 1970s. From the snow-covered area at the end of summer 2009, which fairly represents the extent and local variability of the accumulation areas in the 2000s, we estimate that approximately 50% of the remaining glacier surfaces have to melt away to re-establish balanced mass budgets with present climatic conditions. The average geodetic mass budget rate, calculated for 112 ice bodies by differencing two DTMs, ranged from −0.18 ± 0.04 to −1.43 ± 0.09 m w.e. a−1, averaging −0.69 ± 0.12 m w.e. a−1. The correlation analysis of mass budgets vs. topographic variables emphasized the important role of hypsometry in controlling the area and volume loss of larger glaciers, whereas a higher variability characterizes smaller glaciers, which is likely due to the higher importance of local topo-climatic conditions.
Glacier-wide mass balance has been measured for more than sixty years and is widely used as an indicator of climate change and to assess the glacier contribution to runoff and sea level rise. Until recently, comprehensive uncertainty assessments have rarely been carried out and mass balance data have often been applied using rough error estimation or without consideration of errors. In this study, we propose a framework for reanalysing glacier mass balance series that includes conceptual and statistical toolsets for assessment of random and systematic errors, as well as for validation and calibration (if necessary) of the glaciological with the geodetic balance results. We demonstrate the usefulness and limitations of the proposed scheme, drawing on an analysis that comprises over 50 recording periods for a dozen glaciers, and we make recommendations to investigators and users of glacier mass balance data. Reanalysing glacier mass balance series needs to become a standard procedure for every monitoring programme to improve data quality, including reliable uncertainty estimates.
The continuation of valuable, long-term glacier observation series is threatened by the accelerated mass loss which currently affects a large portion of so-called "benchmark" glaciers. In this work we present the evolution of the Careser glacier, from the beginning of systematic observation at the end of the nineteenth century to its current condition in 2012. In addition to having one of the longest and richest observation record among the Italian glaciers, Careser is unique in the Italian Alps for its 45 yr mass balance series started in 1967. In the present study, variations in the length, area and volume of the glacier since 1897 are examined, updating the series of direct mass balance observations and extending it into the past using the geodetic method. The glacier is currently strongly out of balance and in rapid decay; its average mass loss rate over the last three decades was −1.5 m water equivalent per year, increasing to −2.0 m water equivalent per year in the last decade. If mass loss continues at this pace, the glacier will disappear within a few decades, putting an end to this unique observation series.
A widespread loss of glacier area and volume was observed in the
European Alps since the 1980s. Besides differences among various regions
of the Alps, different responses characterize neighboring glaciers
within the same region. In this study we describe the glacier changes in
the Ortles-Cevedale group, the largest glacierized area in the Italian
Alps. We characterize the drivers, the spatial variability and the main
factors controlling the current loss of ice in this region by comparing
glacier extents and snow covered areas derived from Landsat images
acquired in 1987 and 2009. Glacier outlines were obtained from a band
ratio with manual corrections and snow was classified from a near
infrared image after topographic correction. The total glacierized area
shrank by 23% in this period, with no significant changes in the mean
altitude of the glaciers. The snowline is now 240 m higher than in the
1960s and 1970s. From the snow covered area of 2009, which fairly
represents the extent of the accumulation areas over the last decade, we
estimate that about 50% of the remaining glacier surfaces have to melt
away to re-establish equilibrium with present climatic conditions. The
average geodetic mass budget rate, calculated for 112 ice bodies by
differencing two Digital Terrain Models (DTMs), ranged from -0.15 to
-1.50 m w.e. a-1, averaging -0.68 m w.e. a-1. A
correlation analysis of mass budgets vs. topographic variables confirmed
the important role of the hypsometry in controlling area and volume loss
of larger glaciers, while a higher variability characterizes smaller
glaciers and glacierets, likely due to the increasing importance of
local topo-climatic conditions.
Estimates of glacier mass balance using geodetic methods can differ significantly from estimates using direct glaciological field-based measurements. To determine if such differences are real or methodological, there is a need to improve uncertainty estimates in both methods. In this paper, we focus on the uncertainty of geodetic methods and describe a geostatistical technique that takes into account the spatial correlation of the elevation differences when calculating spatially averaged elevation changes. We apply this method to the western Svartisen ice cap, Norway, using elevation differences from the surrounding bedrock derived from stereophotogrammetry. We show that the uncertainty is not only dependent on the standard error of the individual elevation differences but is also dependent on the size of the averaging area and the scale of the spatial correlation. To assess if the geostatistical analysis made over bedrock is applicable to glacier surfaces, we use concurrent photogrammetrical and laser scanning data from bedrock and a range of glacier surfaces to evaluate the dependency of the geostatistical analysis on the surface type. The estimated geodetic mass balance, and its uncertainty, is -2.6±0.9 m w.e. for the period 1968-85, and -2.0±2.2 m w.e. for 1985-2002.
The two ice caps of Svartisen, at the latitude of the Arctic Circle in Norway, supply 60 glaciers, ranging in size from >50
to <1 km2. Until the last two decades of the 19th century, the glaciers remained close to their maximum recent (Little Ice Age) size.
In response to the prevailing 20th century climate, they have become smaller, but the changes have varied between glaciers.
Climatic factors have not been the sole control of the variations. The response times of small, steep glaciers are shorter
than those of the longer, more gently sloping outlet glaciers. Topographic factors may moderate the response of individual
glaciers to climate. The 20th century mass balance of several of the larger glaciers was dominated by calving into marginal
lakes. The mass balance of Engabreen, the largest outlet of the western ice cap, has been measured every year since 1970 and
the cumulative balance to 2008 was a gain of 22.7 m water equivalent. Although the pattern of annual variations probably applies
to the other glaciers of Svartisen, it does not indicate their actual changes (gain or loss). Thus, the Engabreen record is
of little utility in water resource planning for the whole area.
Key WordsSvartisen-climatic change-glacier variation-calving-mass balance
Seasonal glaciological mass balances have been measured on Storglaciären without interruption since 1945/46. In addition, aerial surveys have been carried out on a decadal basis since the beginning of the observation program. Early studies used the resulting aerial photographs to produce glaciological maps with which the in-situ observations could be verified. However, these maps as well as the derived volume changes are subject to errors which resulted in major differences between the derived volumetric and the glaciological mass balance. As a consequence, the original photographs were re-processed using uniform photogrammetric methods, which resulted in new volumetric mass balances for 1959–1969, 1969–1980, 1980–1990, and 1990–1999. We compare these new volumetric mass balances with mass balances obtained by standard glaciological methods including an uncertainty assessment considering all related previous studies. The absolute differences between volumetric and the glaciological mass balances are 0.9 m w.e. for the period of 1959–1969 and 0.3 m w.e. or less for the other survey periods. These deviations are slightly reduced when considering corrections for systematic uncertainties due to differences in survey dates, reference areas, and internal ablation, whereas internal accumulation systematically increases the mismatch. However, the mean annual differences between glaciological and volumetric mass balance are less than the uncertainty of the in-situ stake reading and, hence, do not require an adjustment of the glaciological data series.
Assessing the impact of possible climate change on the water resources of glacierized areas requires a reliable model of the climate-glacier-mass-balance relationship. In this study, we simulate the mass-balance evolution of Engabreen, Norway, using a simple mass-balance model based on daily temperature and precipitation data from a nearby climate station. Ablation is calculated using a distributed temperature-index method including potential direct solar radiation, while accumulation is distributed linearly with elevation. The model was run for the period 1974/75-2001/02, for which annual mass-balance measurements and meteorological data are available. Parameter values were determined by a multi-criteria validation including point measurements of mass balance, mass-balance gradients and specific mass balance. The modelled results fit the observed mass balance well. Simple sensitivity experiments indicate a high sensitivity of the mass balance to temperature changes, as expected for maritime glaciers. The results suggest, further, that the mass balance of Engabreen is more sensitive to warming during summer than during winter, while precipitation changes affect almost exclusively the winter balance.
Key issues of glacier monitoring are changes in glacier geometry and glacier mass. As accurate direct measurements are costly and time-consuming, the use of various remote-sensing data for glacier monitoring is explored. One technology used and described here is airborne laser scanning. The method enables the derivation of high-quality digital elevation models (DEMs) with a vertical and horizontal accuracy in the sub-metre range. Between September 2001 and August 2002, three laser scanner data acquisition flights were carried out, covering the whole area of Engabreen, Norway, and corresponding well to the measurement dates for the mass-balance year 2001/02. The data quality of the DEMs is assessed (e.g. by comparing the values with a control area which has been surveyed independently or GPS ground profiles measured during the flights). For the whole glacier, surface elevation change and consequently volume change is calculated, quantified and compared with traditional mass-balance data for the same time interval. For the winter term, emergence/submergence velocity is determined from laser scanner data and snow-depth data and is compared with velocity measurements at stakes. The investigations reveal the high potential of airborne laser scanning for measuring the extent and the topography of glaciers as well as changes in geometry (Δarea, Δvolume).
The net mass balance on Gulkana Glacier, Alaska, U.S.A., has been measured since 1966 by the glaciological method, in which seasonal balances are measured at three index sites and extrapolated over large areas of the glacier. Systematic errors can accumulate linearly with time in this method. Therefore, the geodetic balance, in which errors are less time-dependent, was calculated for comparison with the glaciological method. Digital elevation models of the glacier in 1974, 1993 and 1999 were prepared using aerial photographs, and geodetic balances were computed, giving −6.0 ± 0.7 m w.e. from 1974 to 1993 and −11.8 ± 0.7 m w.e. from 1974 to 1999. These balances are compared with the glaciological balances over the same intervals, which were −5.8 ± 0.9 and −11.2 ± 1.0 m w.e. respectively; both balances show that the thinning rate tripled in the 1990s. These cumulative balances differ by <6%. For this close agreement, the glaciologically measured mass balance of Gulkana Glacier must be largely free of systematic errors and be based on a time-variable area-altitude distribution, and the photography used in the geodetic method must have enough contrast to enable accurate photogrammetry.
The Norwegian Water Resources and Energy Administration has photographed glacial areas in Norway for several decades. Detailed maps or digital terrain models have been made for selected glaciers from vertical aerial photographs. Multiple models of seven glaciers have been used here to calculate glacier volume change during the time between mappings using the geodetic method. Analyses and results are presented and compared with traditional mass-balance measurements. We estimated uncertainties of ±1.3-2.7 m w.e. for the geodetic method, and ±1.3-3.5 m w.e. for the traditional method. The discrepancies between the methods varied between 0.4 and 4.7 m w.e. All glaciers decreased in volume from the 1960s/70s to the 1990s, except Hardangerjøkulen. This glacier experienced a significant increase in volume: the geodetic and traditional methods showed net balance values of +6.8 m and +9.4 m w.e., respectively. Trollbergdalsbreen had the largest total volume loss: the geodetic and traditional methods showed net balance values of -12.3 and -16.8 m w.e.
The response of grounded ice sheets to a changing climate critically influences possible future changes in sea level. Recent satellite surveys over southern Greenland show little overall elevation change at higher elevations, but large spatial variability. Using satellite studies alone, it is not possible to determine the geophysical processes responsible for the observed elevation changes and to decide if recent rates of change exceed the natural variability. Here we derive changes in ice-sheet elevation in southern Greenland, for the years 1978-88, using a physically based model of firn densification and records of annual snow accumulation reconstructed from 12 ice cores at high elevation. Our patterns of accumulation-driven elevation change agree closely with contemporaneous satellite measurements of ice-sheet elevation change, and we therefore attribute the changes observed in 1978-88 to variability in snow accumulation. Similar analyses of longer ice-core records show that in this decade the Greenland ice sheet exhibited typical variability at high elevations, well within the long-term natural variability. Our results indicate that a better understanding of ice-sheet mass changes will require long-term measurements of both surface elevation and snow accumulation.
Hourly melt and discharge of Storglaciaren, a small glacier in Sweden, were computed for two melt seasons, applying temperature-index methods to a 30 m resolution grid for the melt component. The classical degree-day method yielded a good simulation of the seasonal pattern of discharge, but the pronounced melt-induced daily discharge cycles were not captured. Modelled degree-day factors calculated for every hour and each gridcell from melt obtained from a distributed energy-balance model varied substantially, both diurnally and spatially. A new distributed temperature-index model is suggested, attempting to capture both the pronounced diurnal melt cycles and the spatial variations in melt due to the effects of surrounding topography. This is accomplished by including a radiation index in terms of potential clear-sky direct solar radiation, and thus, without the need for other data besides air temperature. This approach improved considerably the simulation of diurnal discharge fluctuations and yielded a more realistic spatial distribution of melt rates. The incorporation of measured global radiation to account for the reduction in direct solar radiation due to cloudiness did not lead to additional improvement in model performance.
Ernst Sorge, a member of Wegener’s Greenland Expedition 1930–31, discovered an important law on the densification of snow in high polar glaciers. It is here given a simple mathematical form and some of its implications are formulated and discussed. Apart from its significance to glaciology and snow mechanics, Sorge’s law should also be useful in the study of consolidation of accumulating fine-grained lacustrian and oceanic sediments.
This study uses older topographic maps made from high-oblique aerial photographs for glacier elevation change studies. We compare the 1936/38 topographic map series of Svalbard (Norwegian Polar Institute) to a modern digital elevation model from 1990. Both systematic and random components of elevation error are examined by analyzing non-glacier elevation difference points. The 1936/38 photographic aerial survey is examined to identify areas with poor data coverage over glaciers. Elevation changes are analyzed for seven regions in Svalbard (∼5000 km2), where significant thinning was found at glacier fronts, and elevation increases in the upper parts of the accumulation areas. All regions experience volume losses and negative geodetic balances, although regional variability exists relating to both climate and topography. Many surges are apparent within the elevation change maps. Estimated volume change for the regions is −1.59±0.07 km3 a−1 (ice equivalent) for a geodetic annual balance of −0.30 ma−1 w.e., and the glaciated area has decreased by 16% in the 54 year time interval. The 1936-90 data are compared to modern elevation change estimates in the southern regions, to show that the rate of thinning has increased dramatically since 1990.
The Svartisen Hydropower Scheme is Norway's most recent hydropower development. Most of the runoff from West Svartisen (221 km2, Fig. 1) is delivered to the power station via 60 intakes around the western and eastern ice-caps, including one subglacial intake located beneath the Engabreen outlet glacier. Estimates of water input to each intake are important for management of the power station. Average water inputs are obtained by integrating area-specific runoff over the intake catchment area. Previous calculations of the positions of catchment divides on Svartisen have been based upon ice surface topography alone and are thus a mapping of ice divides. However, meltwater flow along the glacier bed is driven by a gradient in hydraulic head, which is dependent on bed topography as well as ice surface topography. Calculations on other glaciers (Bjornsson 1988, Kennett 1990) show that the positions of water divides can differ significantly from ice divides.
A number of Norwegian glaciers were selected in the 1960s for long-term mass-balance measurements, to produce necessary hydrological information for hydropower exploitation. Special large-scale glacier maps were produced for field work and data processing, and some glaciers have been mapped more than once. Thus, comparison of glacier maps can be used to calculate changes in glacier volume for some of the glaciers, provided they are of sufficient accuracy.
Conventional mass-balance measurements were carried out on all the selected glaciers. A cumulative calculation of net balances for a series of years is used to indicate the change in a glacier's volume during that period. However, various errors originate in the field, some of which are systematic, particularly on glaciers with large winter accumulation.
The present study indicates that certain errors are difficult to define and determine, For the maritime glacier Ålfotbreen, a cumulative mass-balance calculation gives a positive total balance (+3.4 m water equivalent in the period 1968–88), whereas the map comparison indicates a total negative balance (−5.8 m water equivalent). This indicates a discrepancy between the methods, which must be accounted for.
Determination of errors in mass-balance measurements is difficult. Sinking of stakes in the accumulation area and the use of sounding sticks (steel probes) in heavy snowlayers cause problems.
Storbreen glacier is situated in the western part of Jotunheimen, a mountain area in central southern Norway. Annual mass balance data have been recorded since 1949. In addition, detailed topographical maps at the scale 1:10,000 exist from the years 1940, 1951, 1968, 1984 and 1997. In this paper, volume change calculated from maps is compared with annual mass balance data. The volume change was in reasonable agreement with the measured cumulative mass balance for the periods 1940–1951 and 1968–1984; however, for the periods 1951–1968 and 1984–1997, the mass balance measurements showed larger negative values than obtained from map comparisons. One obvious reason for this is the inaccuracy of the contour lines in the upper areas of the glacier on maps from 1940 and 1951. Other factors influencing the result are tested, and also suggestions are given for improving the techniques for mapping glacier volume changes.
Net mass balance has been measured since 1958 at South Cascade Glacier using the ‘direct method,’ e.g. area averages of snow gain and firn and ice loss at stakes. Analysis of cartographic vertical photography has allowed measurement of mass balance using the ‘geodetic method’ in 1970, 1975, 1977, 1979–80, and 1985–97. Water equivalent change as measured by these nearly independent methods should give similar results. During 1970–97, the direct method shows a cumulative balance of about −15 m, and the geodetic method shows a cumulative balance of about −22 m. The deviation between the two methods is fairly consistent, suggesting no gross errors in either, but rather a cumulative systematic error. It is suspected that the cumulative error is in the direct method because the geodetic method is based on a non-changing reference, the bedrock control, whereas the direct method is measured with reference to only the previous year's summer surface. Possible sources of mass loss that are missing from the direct method are basal melt, internal melt, and ablation on crevasse walls. Possible systematic measurement errors include under-estimation of the density of lost material, sinking stakes, or poorly represented areas.
A one-dimensional, numerical model of time-evolving firn densification was used to simulate the response of the density profile through an ice sheet to changes in the temperature, density and accumulation rate at the surface. The equilibrium response of the model was compared with ice-core density profiles from Byrd, Antarctica and Site 2, Greenland, and the model predicted the density to within 10% of both cores. The response of the model to step-wise changes and random fluctuations in the surface boundary conditions was investigated. The standard deviation of elevation changes as a function of observation interval was computed. These changes were found to be small in comparison with the magnitude of present uncertainties in the mass balances of the Antarctic and Greenland Ice Sheets. It was concluded that, in the dry snow zones, natural variability in the densification will not prevent the geodetic determination of ice sheet mass balance from improving upon current estimates. Uncertainty in the constitutive equation for snow and firn is the dominant source of error in the calculations.
Forprosjekt - Opplegg for forvaltning, drift og vedlikehold av terrengdata
- O C Kjekshus
- A Edvardsen
- S Kristensen
- S Jaren
- Ø Olafsen
- J Tallhaug
Glaciological investigations in Norway in 2002
- Kjøllmoen