Shakes Glacier Retreat-Tributary Separation, Alaska

Shakes Glacier drains the southern portion of the Stikine Icefield and terminates in Shakes Lake. It is between the more famous LeConte Glacier to the west and Great Glacier to the east. Larsen et al (2007) indicate recent thinning of 2-4 meters per year on the glaciers along the southern margin of the Stikine Icefield. Here we utilize 1985-2013 Landsat imagery to examine changes in this glacier. shakes overall

The USGS map of Shakes Glacier indicates the glacier turning the corner south along Shakes Lake. In each image the red arrow marks the 1986 terminus, the yellow arrow the 2013 terminus, the pink arrow a tributary from the east and the purple arrow a tributary from the west. shakes mapIn 1985 and 1986 the glacier has retreated onto the southeast trending arm of the lake ending at a deep gully on the west side of the lake, red arrow. The tributaries are still well connected to the glacier. By 1993 the glacier has retreated 300 m, the east tributary is still well connected, the west tributary at the purple arrow has considerably diminished. By 2003 the terminus has retreated 1.2 km from the 1985 position, the west tributary is just separating from the main glacier. The snowline is nearly at the top of the west tributary with a month left in the melt season. By 2011 a Google Earth image indicates the loss of connection with the west tributary and the disconnection on the east side which ends in a steep icefall slope. There is also a lake, green arrow just behind the terminus indicating impending rapid retreat will continue. The 2013 Landsat image the terminus has retreated 2.2 km from 1985, that is 78 meters/year. The lake is still evident behind the terminus. The continued significant retreat of Shakes Glacier matches that of other glaciers in the area Great Glacier, Baird Glacier, Patterson Glacier and Sawyer Glacier. shakes 1985
1985 Landsat image

shakes 1986
1986 Landsat image

shakes 1993
1993 Landsat image

shakes 2003
2003 Landsat image

shakes ge
2011 Google Earth image

shakes 2013
2013 Landsat image


Patterson Glacier Retreat, Southeast Alaska

Patterson Glacier is a western outlet of the Stikine Icefield in southeast Alaska. The glacier does not reach tidewater it is 23 km long and has an area of about 100 km2. At the end of the 19th century, the terminus flowed both the east and the west, and was slowly advancing. William O. Field visited the glacier in 1941 and 1948 and found a 1.3 km retreat since the late 19th century. By 1979 the USGS noted a further 1 km of retreat. I saw the glacier enroute to the Juneau Icefield in 1984 and the lake at the terminus was still rather small. I talked to William O. Field right after that field season, he was convinced that all Stikine Icefield glaciers would be retreating more and we discussed Baird Glacier just to the north because it has not retreated yet, though it is showing signs now. In this post we examine the changes between 1985 and 2011 using Landsat imagery. Since 1984 frequent satellite imagery allows identification of the equilibrium line altitude (ELA), the snowline at the end of summer where accumulation equals ablation that year. The average ELA has been 1150 m, which given that the main accumulation zone ends at 1350 m is too high to maintain equilibrium. The green arrows indicate flow directions in the Google Earth image below. The yellow arrow the 1985 terminus, the red arrow the 2011 terminus, the blue arrows the snowline and the pink arrow a peninsula where a prominent debris band is located in 2011, that is also marked by the letter D. The debris band represents an avalanche that descended onto the glacier not too long before 1985. Glacier velocity is faster in the center and this fairly round debris will quickly become drawn down glacier faster in the center than at its edge, this had not notably occurred yet in 1985. patterson glacier ge A comparison of the 1985 Landsat image of Patterson Glacier and 2011 Landsat image indicate that the debris band (D) has shifted 3000 meters down glacier in 27 years, indicating approximately 110 meters per year velocity for the north side of the Patterson Glacier valley tongue. The terminus has retreated from the yellow to the red arrow a distance of 1200 meters, a rate of 45 m/year. The terminus lake is 2 km long in 2011. The 2011 terminus is quite narrow indicating the glacier maybe reaching the eastern end of this lake basin. A close up of the terminus area in Google Earth indicates the same features, orange arrows indicate the east and west flow at the terminus that was observed in the late 19th century. This glacier is responding very similarly to Speel Glacier, Great Glacierand Norris Glacier of the Juneau Icefield
patterson galcier 1985

patterson glacier 2011

patterson terminus

Great Glacier Retreat, Stikine Icefield, BC Canada

Great Glacier is the largest outlet glacier of the Stikine Icefield terminating in Canada. The name came from the large expanse of the glacier in the lowlands of the Stikine River during the late 19th and early 20th century, that has now become a large lake. The glacier filled what is now a large lake at the terminus of the glacier pushing the Stikine River to the east side of the valley. In 1914 the glacier was easy to ascend from the banks of the Stikine River, the picture below is from the National Railroad Archive. By 1965 the new lake had formed, but the glacier still reached the far side of the lake in several places as indicated by the 1965 Canadian Topographic Map, green arrows. A comparison of 1986 Landsat, 2005 Google Earth and 2011 Landsat imagery illustrates the retreat. The yellow arrow indicates a glacier dammed lake, the violet arrows the snowline and the red arrow the northeast tributary. By 1986 the new lake had largely developed, and the glacier was beginning to retreat into the mountain valley above the lake. Retreat from the moraines of the late 19th century was 3200 m. By 2011 the glacier had retreated further into valley, 900 m retreat from 1986-2011. Great Glacier is following the pattern of behavior of other Stikine Icefield glaciers such as Sawyer Glacier There is a glacier dammed lake that has to date changed little at the yellow arrow, this lake fills and drains under the glacier periodically, top image below. A view of the glacier from across the lake today indicates the distance to the now valley confined glacier, and the trimlines of the former ice surface, yellow arrows in middle image The Great Glacier has one major tributary on the northeast tributary that is very low in elevation with a top elevation of 800 m. Given the regional snowline of 1100-1200 meters (Pelto, 1987)this is too low to retain snowcover through the summer and will lead to progressive thinning. This branch of the glacier has and will thin faster than the rest of the glacier and is doomed given its limited top elevation. The proglacial lakes on its periphery will continue to grow as this downwastes, green arrow bottom image.