Wrangell mountain glacier retreat – From a Glaciers Perspective

Mount Gordon Icefield (MG) Mesa Creek Icefield (MC) and Icefield Plateau (IP) in 2016 and 2017 Landsat imagery. The purple dots indicate the areas with retained snowcover in both years. Nabesna Glacier (N) is the largest glacier in the Wrangell Mountains, just a corner seen here.

Mount Gordon Icefield (MG) Mesa Creek Icefield (MC) and Icefield Plateau (IP) are three neighboring Icefields in the Wrangell-Saint Elias National Park and Preserve in Alaska. Each has a principal accumulation area between 2300 and 2550 m, with a limited area above . The area of Mount Gordon Icefield is ~10 square kilometers, Mesa Creek Icefield ~12 square kilometers and Icefield Plateau ~35 square kilometers. This is a region that has been experiencing significant mass loss. Das et al (2014) used repeat altimetry measurements to identify accelerated mass loss over the Wrangell Mountains, from –0.07 ± 0.19 m w.e./year during 1957–2000 to –0.24 m w.e./year during 2000–07. Larsen et al (2015) identified that the Wrangell Mountains experienced a mass balance of -0.5 to -1 m/year from 1994–2013 using laser altimetry.

On August 17, 2016 less than 10% of the Icefield Plateau is snowcovered, with the snowline at 2500 m. The snowline is at 2400 m on Mount Gordon Icefield and Mesa Creek Icefield with 30% of each icefield retaining snowcover. On August 4, 2017 there is insignificant retained snowcover on Mesa Creek Icefield. The snowline is at 2500 m on both Mount Gordon Icefield and Icefield Plateau with less than 10% overall retained snowcover. The lack of retained snowcover across most of the former accumulation area from 2300-2550 m indicates these icefields will have substantial icefield wide thinning. In addition the lack of a persistent substantial accumulation zone indicates the icefield will not survive, though a small mountain glacier may remain on the est side of Mount Gordon and the southern edge of the Icefield Plateau. In 2018 there is not a good cloud free August image from this region. The high snowline and rapid melt on nearby Lowell Glacier suggest the snowline would again have been high. This will lead to substantial retreat of the icefield margins and is indicative of the retreat of large glaciers in the range such as Nizina Glacier or Yakutat Glacier in the Saint Elias Range.

Mount Gordon Icefield (MG) Mesa Creek Icefield (MC) and Icefield Plateau (IP) in topographic map.

Mount Gordon Icefield (MG) Mesa Creek Icefield (MC) and Icefield Plateau (IP) in 1999 Landsat image. The purple dots indicate areas with retained snowcover. N=Nabesna Glacier.

Mount Gordon Icefield (MG) Mesa Creek Icefield (MC) and Icefield Plateau (IP) in 2001 Landsat image. The icefield are nearly fully covered with snow. N=Nabesna Glacier.

If you have heard of Nizina Glacier in the Wrangell Mountains of Alaska it is probably because you have contemplated a float trip down the Nizina River from Nizina Lake. In 1990 there was no lake, since 2000 the lake has provided a good location for float planes to land. In 2014 the lake has reached a new maximum in size and minimum in icebergs on its surface. Here we examine Landsat imagery form 1990-2014 to identify changes in the Nizina Glacier. The main tributary of the Nizina Glacier is Regal Glacier indicated by the dark blue flow arrows. The light blue flow arrows are from the Rohn Glacier tributary that no longer reaches the terminus area.

Google Earth image

In each image the yellow arrow marks the 1990 terminus, red arrow the 2014 terminus location and pink arrows the summer snowline. In 1990 the glacier had narrow sections of fringing lake evident, though the glacier reached the southern shore of the developing lake at yellow arrow. By 1995 the lake had developed to a width of 100-300 m fringing the shoreline around the terminus of Nizina Glacier. In 1999 the main lake has developed and is 1.6 km long and 1.3 km wide though it is still largely filled with icebergs. In 2013 there are a few icebergs left in the lake. In August, 2014 the lake is free of icebergs for the first time, which does mean more will not form. The lake is 1.4 km wide and 2.3 km long. The glacier has retreated 2.1 km from 1990 to 2014, a rate of 150 m per year, red arrow marks 2014 terminus. A close up view of the terminus in Google Earth from 2012 indicates numerous icebergs but also substantial rifts, green arrows, that will lead to further iceberg production and retreat. The snowline in this late July or early August images is typically at 1800-1900 m, pink arrow, with a month still left in the melt season. The retreat of this glacier is similar to that of glaciers in the Talkeetna Range to the west South Sheep Glacier and Sovereign Glacier and Valdez Glacier to the south.