The mass balance of Langenferner / Vedretta Lunga
About the study site
Langenferner is a small valley glacier in the Eastern European Alps. The glacier is located at the head of Martell-Valley in the Ortles-Cevedale Group in the Autonomous Province of Bozen, northern Italy (46.47° North / 10.60° East). Langenferner is one of several glaciers flowing down from the Cevedale-Massive. The glacier covers an area of about 1.6 km² (2013) extending from its highest point at 3370 m a.s.l. down to 2711 m a.s.l. at the terminus. The median altitude is 3143 m a.s.l. The upper glacier section is mainly exposed to the north, while the tongue is flowing eastwards. The glacier is part of the catchment of Plima River which comprises an area of 162 km² and contributes to the river Etsch, the main water resource for the intensive agriculture in the Vinschgau (Galos et al., 2015). The current (2017) glacier volume estimated based on ground penetrating radar measurements carried out by the ACINN in spring 2010 and ever since measured mass balance is approximately 0.07 km³ with a maximum thickness of more than 100 m in the plateau east of Casati Hut.
Direct glaciological measurements at Langenferner were initiated by the University of Innsbruck on behalf of the Hydrological Service of the Autonomous Province of Bozen/Südtirol in the hydrological year 2004. The program was established as a supplement to the mass balance program at Weißbrunnferner/Fontana Bianca, which was (i) considered as potentially threatened by rapid glacier retreat and (ii) deemed to be not representative for the region due to the specific setting of the glacier.
The mass balance program
Mass balance measurements at Langenferner are performed applying the direct glaciological method. Since the year 2014 the analyses follow the fixed date convention (e.g. Cogley et al., 2011) which implies that measurements are carried out exactly at the beginning / end of the hydrological year (or seasons) or are subject to corrections in case of delayed field campaigns (Galos et al., 2017).
Measurements of winter balance are performed annually at the beginning of May. The depth of the winter snow pack is measured by probings performed at about 80 to 100 selected points including the positions of ablation stakes. Snow depth is converted into mass using bulk snow density values recorded in four snow pits distributed over the glacier surface.
The annual balance is calculated based on measurements at about 25 to 30 ablation stakes which are commonly read once to six times a year - depending on the location and local conditions at the individual position. In years with larger accumulation areas data from one to four end-of-summer snow pits are combined with a number of firn depth probings to calculate the amount of accumulation.
To obtain the glacier wide mean specific mass balance the measured point values are extrapolated using the contour line method (e.g. Cogley et al., 2011). The manual generation of contour lines at Langenferner incorporates the integration of further observational information such as the position of the snow line, date of ice emergence at individual locations, meteorological conditions on the glacier and other expert knowledge such as typical spatial mass balance patterns. The hand-drawn and digitized contour lines and the set of point balance values are interpolated using the Esri ArcGIS interpolation tool “topo to raster”. This results in mass balance rasters with a 1x1m resolution which are subsequently spatially integrated to obtain the glacier wide mean specific mass balance.
Glacier outlines are frequently updated using orthophotos from aerial or satellite imagery or other remote sensing data such as airborne laser-scans to reduce the effect of outdated glacier outlines on the mass balance record. Since such data often only become available after several years the mass balances of recent years require a reanalysis which is currently in progress for the years 2015 to 2017 while the respective work for the period 2004 to 2013 has been recently accomplished.
As on most glaciers in the Alps strong mass loss was recorded at Langenferner during the observation period 2004 to 2017. Except for the year 2014 when an extraordinarily humid winter combined with a relatively cool summer lead to a positive mass balance, all annual balances were negative. The glacier area at the same time was reduced from 1.94 km² to about 1.5 km². Despite the strong glacier retreat and the consequent loss of large fractions of the main ablation area, the most negative glacier wide specific mass balances were recorded in 2015 and 2017.
Annual and seasonal mass balances at Langenferner for the period 2004 to 2017. The plot shows the reanalyzed balance values for the period 2004 to 2013. For recent years a reanalysis is in progress. However, the expected impacts on values for individual years or seasons are in the order of 100 kg/m² or less.
Reference area (Sref), annual mean specific balance (Ba), winter balance (Bw), summer balance (Bs), equilibrium line altitude (ELA) and accumulation area ratio (AAR) at Langenferner for the period 2004 to 2017. Note that a reanalysis for the years 2015 to 2017 is required to account for uncaptured changes in Sref in this period.
Mass balance reanalysis
The record of annual and seasonal mass balances at Langenferner for the first ten measurement years has undergone a detailed reanalysis which has become necessary due to a number of inconsistencies and shortcomings in the original record. Those were mainly related to a provisional measurement set-up and the limited knowledge on spatial mass balance patterns combined with an insufficient consideration of snow line data during the early measurement years. A detailed description of the applied reanalysis is presented by Galos et al. (2017).
Besides the creation of a consistent mass balance series and a thorough uncertainty assessment the reanalysis included a cross check of directly measured mass balances to geodetically derived mass change. This showed that at least for the period 2005 to 2013 no significant differences between the two methods are detectable at Langenferner.
A Comparison between geodetic and glaciological mass balances for three periods (upper three subplots) and cumulative series of annual mass balance calculated using a set of different extrapolation methods as described in Galos et al. (2017). The comparison shows that significant differences between the two mass balance methods are not detectable at Langenferner.
Due to the rapidly shrinking glacier area a reanalysis is also required for the years 2015 to 2017. In absence of any data on current the glacier outline and topography the mass balance for these years was calculated using the glacier outlines of 2013 which results in an expected negative bias of about 50 to 80 kg/m² for the annual balance 2017. Orthophotos from satellite and aerial imagery are meanwhile available for 2014, 2015 and 2016 providing the basis for a respective reanalysis.
Data on annual and seasonal mass balance of original and reanalyzed records are available through the world glacier monitoring service. These data include point mass balance, as well as glacier wide and altitude-band-based analyses. Meta-data and mass balance reports for selected years are available on Pangea.de while annual short reports are published by the Hydrographic Office Bozen: http://wetter.provinz.bz.it/publikationen.asp .
All other data is available on request at the ACINN.
Note that original as well as reanalyzed mass balance values for Langenferner are available. If you intend to use these data for scientific applications be sure to benefit from the data-set which is best suited for the individual purpose.