February 29, 2020

Ålfotbreen, Norway Mass Balance Large Loss in 2019

Posted by Mauri Pelto

Ålfotbreen (A) in August 2003 and 2019 Landsat images.  The yellow line marks the divide between Ålfotbreen and Hansebreen (H). Pink dots indicate the 2003 margin.  There is no retained snowpack in 2003.  In 2019 there are two small patches near the divide  on Aug. 26 that melt away by the end of the summer.

The Ålfotbreen Ice Cap , Norway (61°45’N, 5°40’E; area=17 km2) is the westernmost and most maritime glacier in Norway. Mass balance studies have been carried out on one of the glaciers of the ice cap since 1963, Ålfotbreen and since 1986 on Hansebreen, by the Norwegian Water Resources and Energy Directorate. Both of these glaciers supply runoff to the Askara Kraftwerk an 85 MW hydropower plant completed in 1973.  Ålfotbreen is a reference glacier for the World Glacier Monitoring Service (WGMS). From 1963-2000 the mean annual mass balance of Ålfotbreen was -0.9 m/year (see below).  From 2001-2019 the mean annual mass balance has been -1.7 m/year.  From 2001-2019 there have been seven years where the mass loss has been greater than 2 m.  This only occurs when all of the retained accumulation from the previous winter is lost.

To be in equilibrium Ålfotbreen must have at least 55% of its area still covered by snow at the end of the summer.  In On August 3, 2003 the glacier had lost all of its snowcover, with more than a month left in the melt season.  The majority of the glacier surface is firn that is several years old, but not fully transformed to glacier ice.  The mass balance in 2003 was  very negative at -3.03 m.  The winter mass balance measured in early May was 2.26 m with a summer balance of -5.29 m.  Glacier runoff during the melt season of 2003 from Ålfotbreen is the product of its area at that time 4.4 km2 and summer balance, which yields 23 million m3. On Aug. 26, 2019 the glacier has two small areas of retained snowpack near the divide, light blue. There is a substantial area of darker blue-glacier ice exposed and medium blue firn exposed. The accumulation area ratio is 15% on Aug. 26, 2019 and was 0% by the end of the melt season.  The final mass balance in 2019 was -2.4 m with a winter balance of 2.38 m and a summer balance of -4.82 m.  The glacier area in 2019 is ~3.8 km2, yielding melt season glacier runoff of 18 million m3. This is 20-25% less runoff than in 2020 due to 10% lower melt per unit area and a ~15% reduction in glacier area. In 7 of the last 19 summers no snowcover remained at the end the melt season, this indicates the accumulation zone is not persistent, suggesting this glacier cannot survive current climate. This glacier has no slopes to deliver avalanche accumulation and is dependent on direct snowfall and wind drifted snowfall.

In contrast snowcover was 100% on July 17, 2017 and August 3, 1999, both years ended the melt season with smaller negative balances of -0.75 m and -0.37 m respectively. This illustrates the vast difference in exposed glacier ice between large negative balance years such as 2003 and 2019 and years with a smal negative or postiive balance.

The loss in glacier area has been due to a retreat of the broad terminus of the glacier, pink dots, ~150 m from 2003-2019. This retreat is less than at Harbardsbreen or Tunsbergdalsbreen.  Continued reductions in glacier area, will lead to a continued decline in glacier runoff and available water resources for summer hydropower production.

Ålfotbreen (A) in August 1999 and July 2017 Landsat images.  The yellow line marks the divide between Ålfotbreen and Hansebreen (H).

Map of the Ålfotbreen ice Cap form the Norway Glacier Atlas 

Mass balance record of the Alfotbreen from the WGMS.