August 29, 2018

Major Late July Meltdown on Lowell Glacier, Yukon

Posted by Mauri Pelto

Lowell Glacier in Landsat images from 7/4, 7/26 and 8/11 with Sentinel images from 7/22 .  The snowline is shown with purple dots. Point A-F are fixed reference locations.  The snowline migrated upglacier 20 km and 300 m in elevation.  A significant snow swamp is between the yellow and purple dots on 7/26, that was not present on 7/22. 

The Lowell Glacier drains east from the St.Elias Range on the Yukon-Alaska border.  A sequence of images from July 4-Aug. 11 indicate the rapid snowline rise, with a particularly rapid transition from July 22-July 26.  During this period weather records from Haines Junction, Yukon indicate daily high temperatures of:  7/22=29.5 C, 7/23= 28.1, 7/24=26.8, 7/25=25.5, 7/26=25.1. This equates to project freezing levels above 4200 m each day.

(NASA Post follow up to this research)

On July 4th the transient snowline on Lowell Glacier was near Point F at 1240 m.  By July 22 the transient snowline had moved 9 km upglacier to 1400 m between Point A and B. Just two days later the region from 1400-1560 m an area of 40+square kilometers was under rapid transition with the snowline rising and an area of slush developing, saturated snowpack, really a “snow swamp”.  By July 26th the slush line was at 1520 to 1560 m, with the slush indicated by a royal blue color distinguishing it from the graying blue bare ice or old firn, and the white blue snow from the previous winter than was not fully saturated with water.  It is unusual to develop such a large “snow swamp” so quickly, this was accomplished by the rapid ablation due to the high temperatures. By Aug. 11th the transient snowline had shifted above this slush zone, with all of the saturated snow having ablated away, to Point E at 1560-1600 m.  The snowline in late summer of 2010, 2015 and 2017 also reached near Point E at an elevation of 1520-1600 m.  In 2015 and 2017 a supraglacial lake developed just east of Point C.  Another good example of a large snow swamp is in Svalbard on Hinlopenbreen.

If a good image is acquired in September I will add to this post.  The consistently high late summer snowline, above 1500 m cannot sustain the Lowell Glacier, which will drive further retreat.  The retreat of this glacier be both enhanced and mitigated by surges, during the surge cylcle.  The glacier has surged five times since 1948 (Bevington and Copland, 2014).  The surge cycle has been getting shorter and will not offset the overall mass loss that will drive retreat, just as has occurred on Svalbard glaciers.

Sentinel from 7/22, 7/24 and Landsat from 7/26 indicating the change in snowline and snow swamp development, purple dots.  T indicates terminus of glacier.

Landsat image from 8/8/2017 indicating snowline near Point D and E at m on Lowell Glacier.

Landsat image from 8/3/2015 indicating snowline near Point D and E at m on Lowell Glacier.

Landsat image from 9/14/2010 indicating snowline near Point D and E at m on Lowell Glacier.