Sovereign Glacier is on the northeast side of the Talkeetna Mountains, Alaska and drains into the Talkeetna River. The Sovereign Glacier, red arrow, was joined by a tributary from the south in the map image, pink arrow. Molnia (2007) noted that all glaciers in the region have retreated since the early 1950’s when the area was mapped and that all the major termini were retreating and thinning in 2000. Here we examine Landsat imagery from 1986 to 2014.
In 1986 the glacier terminates at the red arrow at the valley junction. The tributary to the south, pink arrow has separated from the main glacier and ends in a proglacial lake. In 1989 retreat is evident during the last three years with an expanding proglacial lake at the pink arrow, and the glacier terminus no longer reaching the valley junction, red arrow. By 2001 the glacier has retreated most of the distance from the red arrow at the 1986 terminus location to the yellow arrow, the 2014 terminus location. The former tributary glacier has receded from the proglacial lake. In 2009 there are two new outcrops of bedrock in the upper portion of the glacier indicating glacier thinning near the equilibrium line at 2000 m, at green arrow. By 2014 the main glacier has retreated 1100 m from the 1986 position, red arrow, to the yellow arrow. The tributary glacier at the pink arrow has retreated 400 m since 1986. The green arrow indicates further thinning of the upper glacier since 2009. The thinning upglacier indicates that retreat will continue. The retreat parallels that of nearby South Sheep River Glacier. This thinning in the upper glacier is similar to that of Lemon Creek Glacier as well (Pelto et al, 2013).
1986 Landsat image
1989 Landsat image
2001 Landsat image
2009 Landsat image
2014 Landsat image
Above is a paired Landsat image from 1984 left and 2013 right indicating the 1100 m retreat during this period.
Norris Glacier began retreating before 1890 and has continuously retreated 2050 m from its 19th-20th maximum achieved around 1915. The glacier ended in a lake referred to here as Norris Lake from 1948 until 2007. By 2010 the glacier had retreated from this lake. Here we examine images from fieldwork conducted by the Juneau Icefield Research Program and overflights as part of the program from 1975 to 2010 and Google Earth imagery. I have had the chance to cross this glacier on ski a half dozen times as part of JIRP, and is was seldom an easy traverse, hence the names death valley and dead branch for portions of the glacier. Norris Glacier does not receive much attention as the program is focused on the Lemon Creek Glacier and the more famous and largerTaku Glacier, and does not garner much of our attention.
In 1948 the USGS map (top image) indicates Norris Lake was a narrow 200-500 meters wide lake and the glacier terminus was only 200 to 700 meters from Grizzly Bar, increasing with distance south along margin, an outwash plain built by the glacier beyond its advanced terminus position. By 1975 (second image; taken by Maynard Miller JIRP director for fifty years) the glacier had retreated an additional 250 meters, Norris Lake had expanded, but still had considerable ice along its western margin. The terminus was still extending a kilometer downvalley of the outlet of Glory Lake. The view of the entire glacier in Google Earth illustrates the direction of flow and accumulation sources blue arrows, typical snowline red dots and glacier boundary black line.
<In 1998 I had the opportunity to fly over the glacier at the end of the field season. A series of images indicates the trimline that had developed with the recent glacier thinning of the last 50 years. Norris Lake had expanded to a length of 1.2 km on the north shore and 1.9 km on the south shore from Grizzly Bar.
In 2010, images below, the glacier barely reached the edge of Norris Lake and the terminus was well up valley from the Glory Lake outlet, Grizzly Bar was 2.1 km from the terminus. By 2011 the glacier no longer reached the shore of Norris Lake. An examination of the icefall feeding the glacier terminus area indicates considerable melt out of crevasse features, indicating that flow is not that vigorous through the icefall above the terminus at 300 m, suggesting retreat will continue. The trimline hear has increased from 20 m to 50 m above the ice surface since 1975.
In the summer of 1998 we conducted extensive probing in the accumulation zone of the glacier, last two images in sequence below. This combined with annual identification of the snowline since 1994 indicates insufficient snowpack and continued thinning. This glacier has the majority of its area between 800 and 1200 m, with the average snowline since 1994 being 1000 m. Maximum accumulation is 1.5 m, whereas maximum ablation at the terminus exceeds 12 meters, hence you need a much larger accumulation zone to offset the higher terminus ablation. This glaciers retreat and lake expansion of the terminus follows the same pattern as all other glaciers of the Juneau Icefield except the Taku Glacier: Gilkey Glacier, Field Glacier, Eagle Glacier and Antler Glacier.
The combined Melbern and Grand Pacific Glacier with a length of 55 km and width of 2-5 km, is a large valley glacier draining from the Saint Elias Mountains near the British Columbia-Alaska boundary. The glacier separates into two distinct glacier termini at Grand Pacific Pass. One of the tongues, Melbern Glacier, flows 20 km northwest ending in . Grand Pacific Glacier flows southeast to Tarr Inlet of Glacier Bay, just across the Alaska boundary. The Melbern Glacier turns north and ends in Lake Melbern. Lake Melbern began to form around 1979 as noted by Clague and Evans (1994). By 1986 the lake had expanded greatly as the former tributary to Melbern Glacier, Konamoxt Glacier had separated, and a 7km retreat of Melbern Glacier from the Konamoxt Glacier had ensued, first image from their paper. Clague and Evansin the second image further note that the ice dam of the Konamoxt Glacier that blocks Melbern Lake had broken by 1991 and the lake level had dropped. The retreat has continued unabated up through 2009. Here we use a series of Landsat images and one Google Earth Image to illustrate the retreat up to 2013. The first is a 1986 Landsat Image, K=Konamoxt and M=Melbern. In this image Konamoxt still blocks Melbern Lake and Melbern Glacier terminates adjacent to another tributary from the south, orange marks the 1986 terminus of both glaciers. The second image is a false color Landsat image from 2001. Konamoxt Glacier extends partly across the lake but not completely. The lake to the northwest of Konamoxt is filled with icebergs. Melbern Glacier has retreated 3 km since 1986. The third image is the Google Earth image also from 2001 showing the 1986 margin as well, in orange and the 2007 terminus in purple. The fourth image is from 2007, indicating a 1.5 km retreat of Melbern Glacier in the last six years. By 2013 the retreat is 2.25 km since 2001 and 5.25 km since 1986. Konamoxt Glacier no longer reaches Lake Melbern proper and is beginning a retreat up its own valley. The lake itself has changed color and lost its fleet of icebergs. The last image is from July 2013 and Lake Melbern is now 20 km long and still expanding.
Melbern Glacier is following the same pattern as nearby Yakutat Glacier and Grand Plateau Glacier. The lower 3 km of the glacier appears stagnant. However, there is a moraine band 10m km above the terminus that has shifted down glacier 1000-1500 meters from 2001 to 2007 as seen in images from those dates below. The green line indicates the moraine position in 2007. This indicates significant flow at this point. Thus, it is evident that retreat will continue on Melbern Glacier, but should slow as either the lake basin is left behind, or the moraine band is approached
Chickamin Glacier in southeast Alaska has undergone a 3 kilometer retreat since 1955. The glacier drains south from an icefield near Portland Canal and straddling the border with British Columbia. The glacier ended on an outwash plain in 1955 at 250 meters. The Through Glacier at this time is a large tributary feeder joining Chickamin at the elbow where it turns west, (bottom image) Shortly thereafter a lake began to form, and by 1979 a Landsat image indicates a lake that is 1300 meters long. A this point the Through Glacier is just barely in contact with Chickamin Glacier. . By 2004 in an Ikonos image the glacier has retreated 1400 meters from the 1979 position, top image. This image is from the USGS and has been further annotated. In a 2009 Geoeye image the glacier has receded an additional 300 meters, 3000 meters since 1955. Just as impressive is the retreat of Through Glacier that now terminates 1500 meters from its former Junction with Chickamin Glacier. This separation and retreat has occurred during a period of higher snowlines in the region. The snowline of the glacier has averaged 1200 meters in recent years, 100 meters higher than before, and the summit of the glacier is at 2000 meters. The retreat and thinning of this glacier follow that of Sawyer Glacier, Gilkey Glacier and Lemon Creek Glacier. The current terminus region indicates considerable rifting in the lower 500 meters indicating this will be rapidly lost, note the red arrow. The blue arrow indicates a zone below which the glacier appears stagnant with no active crevasse features. The green arrow indicates the transition to a zone of active flow and crevassing. At meters kilometers above the terminus a basin has developed, orange arrow, this is filled periodically becoming a lake, which then drains beneath this glacier. This lake and basin will continue to expand.