South Sheep River Glacier Retreat, Alaska

On November 23, 2014November 28, 2014 By mspeltoIn Glacier Observations1 Comment

South Sheep River Glacier is the informal name of the longest glacier in the Talkeetna Mountains of Alaska. This glacier is the headwaters of the Sheep River and is comprised of two major glacier branches from the east and west meeting and turning north down the Sheep River valley. Molnia (2007) noted that all glaciers in the region have retreated since the early 1950’s when the area was mapped. Molnia (2007) noted that all the major termini were retreating and thinning in 2000. Here we examine Landsat imagery from 1986 to 2014. In the early 1950’s the glacier extended 5.5 km north down the Sheep River Valley from the main glacier junction, red arrow.

USGS Map
In each image the red arrow indicates the early 1950 terminus position, the yellow arrow the 1986 terminus and the pink arrow the 2014 terminus position. In 1986 the glacier had retreated 2.5 km from the 1950’s position. The terminus is at the mouth of the first significant glacier valley draining into the Sheep River from the west. The medial moraine extending to the terminus from the glacier junction is quite prominent. There is a small tributary at Point A that joins the eastern branch of the glacier. In 1989 the snowline on the glacier is at 1700 m. By 2001 the glacier has retreated substantially from the yellow arrow and side valley from the west. In 2009 the snowline is quite high at 2000 m. Th eastern tributary is quite thin beyond the junction, and adds little ice to the now short northward flowing segment. The late Sept. 2014 Landsat image is after a fall snowstorm and the snowline has lowered. The terminus is now at the pink arrow a 4.5 km retreat since the early 1950’s. The glacier has retreated 2 kilometers since 1986. The tributary at Point A now terminates 600 meters from the eastern branch. The glacier flows just 1 km north from the main junction versus 5.5 km in 1950. The terminus remains thin, and the narrow eastern tributary appears ready to separate from the west flowing tributary. This is not an imminent change, but is inevitable. The retreat is the same as that of nearby Sovereign Glacier and glaciers to the south, Pedersen Glacier and Fourpeaked Glacier

1986 Landsat image

1989 Landsat image

2001 Landsat image

2009 Landsat image

2014 Landsat image

Ferebee Glacier Rapid Retreat, Alaska 1986-2014

On October 12, 2014October 13, 2014 By mspeltoIn Glacier Observations1 Comment

Ferebee Glacier is in the Coast Range of Alaska 15 km northeast of Skagway. The Ferebee River that drains the glacier flows into the Chilkoot Inlet. The glacier begins at 1800 m in the Klukwah Mountains and flowed south and terminated on an outwash plain at 200 m in the USGS map of the region from 1955. Little change in the terminus occurred prior to 1981. I observed the glacier from the air in 1981 and there was no lake at the terminus and only a minor several hundred meter wide devegatated zone from recent retreat. Here we examine Landsat imagery from 1986-2014 to identify recent change. A landslide occurred onto Ferebee Glacier in 2014, that will add debris cover to the surface that is limited today.

Google Earth image

USGS map of area

In each image the red arrow marks the 1986 terminus, the yellow arrow the 2014 terminus and the purple dots the snowline. In 1986 the glacier still terminated on the outwash plain at the south end of what is a newly forming lake small pockets of open water are evident on the lateral margins. The snowline is at the base of the lower icefall at 900 m. By 1999 a lake has formed at the terminus, that is 1.2 km long, a retreat of nearly 100 meters per year. The snowline is at 1000 m in 1999. A 2004 Google Earth image of the terminus area indicates two regions of concentric crevassing upglacier of the terminus, one adjacent to the yellow arrow, this indicates ice that has been lifted and then dropped by water, which only happens if the ice is thin enough for flotation. By 2013 the lake has more than doubled in length and the snowline is near the top of a pair of icefalls at 1300 m. In 2014 the lake is 2.7 km long on the eastern shore and 2.5 km long on the western shore. The glacier has retreated 2.6 km in 28 years, still nearly 100 m/year. The lake is not becoming narrower and there is no elevation step on the glacier, to suggest the end of the developing lake is near. The snowline in 2014 even in early August is at 1400 m. This glacier will continue to retreat as long as the snowline is above the top of the icefalls at 1250 m. The retreat of this glacier is like the Meade Glacier across Chilkoot Inlet, LeBlondeau Glacier just to the west and Gilkey Glacier to the south.

1986 Landsat image

1999 Landsat image

2004 Google Earth image

2013 Landsat image

2014 Landsat image

Meade Glacier Rapid Retreat 1986-2014, Alaska

On October 9, 2014October 9, 2014 By mspeltoIn Glacier Observations1 Comment

Meade Glacier drains the northwest portion of the Juneau Icefield, with meltwater entering the Katzehin River and then Chilkoot Inlet. The glacier begins in British Columbia and ends in Alaska. Here we use Landsat imagery to examine changes in the glacier from 1984 to 2014. The glacier experienced a slow continuous retreat from 1948 to 1986 of 400 m, the glacier ended on an outwash plain. From 1991-2006 JAXA’s EROC program noted a retreat of 570 m, retreating into a lake basin. In 2007 the lower 2.5 km of the glacier was stagnant and heavily crevasses, poised for collapse in a developing proglacial lake. The 1948 map of the glacier indicates no proglacial lake with the glacier terminating on an outwash plain.

USGS Topographic map from 1948 aerial photographs

In 1986 the terminus is indicated by an orange arrow, the 2014 terminus by a red arrow, two tributaries that connect to the Meade Glacier are indicated by yellow arrows and the snowline at is indicated by purple dots. The snowline is at 1250 m in 1986, there is no evident lake at the terminus of glacier just an expanding outwash plain. Both tributaries are 750 m+ wide where they join Meade Glacier. By 2004 a 400 m long proglacial lake has formed at the terminus. The two tributaries from the south at the yellow arrows no longer are connected to the glacier. The snowline is at 1450-1500 m, which is much higher than in 2004 on Taku Glacier or Brady Glacier. In 2009 the snowline is at 1400 m, the proglacial lake has expanded to 600 m in length. In 2014 the proglacial lake is 3.5 km long, the entire lower 2.5 km of the glacier has collapsed since 2007. There is still considerable relict ice floating in the lake. There is a substantial lake along the southern margin of the glacier where a tributary streams enters the main valley. This indicates the glacier will quickly retreat to this point by further collapse into the lake. The snowline in 2013 and 2014 was quite high and the summer’s quite warm which aided in the lake expansion. The snowline in 2014 is at 1400 m on Aug. 2, the date of the imagery, the high snowlines ensure continued mass loss and glacier retreat. There was still six week of summer melting remaining on the date of the imagery. The Meade Glacier is poised to continue a rapid retreat in the near future its retreat parallels that of most Juneau Icefield glaciers including the next glaciers to the south Field Glacier and Gilkey Glacier.

1986 Landsat image

2004 Landsat image

2009 Landsat image

2014 Landsat Image

Spotted Glacier Retreat, Katmai Region, Alaska

On July 31, 2014 By mspeltoIn Glacier Observations

Spotted Glacier flows north from Mount Douglas and terminates in a developing proglacial lake. In the USGS map from 1951 the lake is not evident. Giffen et al (2008) noted that the glacier retreated ~1200 m from 1951-1986, a rate of 33 m/year.

Here we examine 1985 to 2013 Landsat imagery to identify the terminus change of this glacier since 1985. In each image the red arrow indicates the 2013 east side of the terminus, the pink arrow a rock knob adjacent to the 1985 terminus, and the yellow arrow a peninsula that should become an island as the further retreat occurs. In 1985 there is no evidence of the peninsula, the lake is relatively round, and has a north-south length of 1250 m. By 2000 the glacier has retreated sufficiently to expose the peninsula at the yellow arrow. The lake is now 1450 m from north to south. Neither of the images indicates many icebergs suggesting this is currently not a main mechanism of ice loss. By 2013 the peninsula is 450 m long, the north-south length of the lake is 1700 m. The retreat of 450 m in the 28 year period is nearly 30 m/year, a similar rate to the 1951-2000 period. The 2012 Google Earth image indicates a few small icebergs in the lake, again suggesting that despite some calving this is not a main glacier volume loss. The glacier front remains active and crevassed, suggesting that retreat will remain slower than for nearby Fourpeaked, Excelsior or Bear Glacier.

1985 Landsat image

2000 Landsat image

2013 Landsat image

2012 Google Earth image

Fourpeaked Glacier Retreat, Katmai area, Alaska

On July 27, 2014July 27, 2014 By mspeltoIn Glacier Observations2 Comments

Fourpeaked Glacier drains east from the volcano of the same name in the Katmai region of southern Alaksa. The Park Service in a report (Giffen et al 2008) noted that the glacier retreated 3.4 km across a broad proglacial lake that the glacier terminates in from 1951-2986, a rate of 95 m/year. From 1986-2000 they noted a retreat of 163 m, or 13 m/year. In a more recent report with the Park Service Arendt and Larsen (2012) provide a map of the change in glacier extent from 1956-2009, Figure 4, but note the poor data overall on historic changes of Fourpeaked. Here we utilize Landsat imagery to examine retreat from 1981 to July 2014.

Google Earth image
A Landsat 2 image from 1981 with relatively low resolution indicates much of the proglacial lake still occupied by ice, but much of this is floating icebergs detached from glacier, which is hard to distinguish in this image. In each image the red arrow is the 1985 terminus and the yellow arrow is 2013-2014 terminus. In 1985 the terminus is at the red arrow, with considerable floating ice still evident that is not part of the glacier. The snowline, purple dots, is at 750-800 m though this is not near the end of the summer. By 2000 the floating ice is gone, and the terminus has retreated into a narrower inlet. The snowline is at 850 m. By 2013 the glacier has receded further up this inlet and the width of the lower glacier is less. This is a July image and the snowline is still relatively low. In the July 2014 image the snowline is quite high at 700 m, given that this is mid-summer. It is not apparent in the Landsat image, but the large local forest fires in the spring could reduce albedo and enhance melt this summer. The terminus has retreated 1.9 km from 1986 to 2014 a rate of 68 m/year. The retreat from 1981-2000 was fed by calving in a broad proglacial lake. From 2000-2014 the retreat has continued despite the narrowing of the calving front. That the glacier has narrowed even more and thinned in the lower reach is indicative of a retreat that will continue. This glacier is behaving like other Katmai area glaciers, Giffen et al (2008) noted that 19 of 20 are retreating. The glacier retreat has led to formation and expansion of a large lake much like other glaciers in the region; Bear Glacier, Excelsior Glacier and Pedersen Glacier. The last image is an animated gif created by Espen Olsen illustrating the change in the glacier.
1981 Landsat image

1985 Landsat image

2000 Landsat image

2013 Landsat image

2014 Landsat image

Espen Olsen animated gif of Landsat images

Wright Glacier Retreat, Southeast Alaska

On July 2, 2014July 2, 2014 By mspeltoIn Glacier Observations2 Comments

Wright Glacier is the main glacier draining a small icefield just south of the Taku River and the larger Juneau Icefield. Wright Glacier is 60 km east of Juneau and has ended in a lake since 1948. A picture of the glacier in 1948 from the NSIDC collection indicates the terminus mainly filling the lake, but breaking up. The glacier drains the same icefield as the retreating West Speel and Speel Glacier. The dark blue arrows indicate the flow vectors of Wright Glacier, light blue arrows flow vectors for adjacent glaciers. Despite being 30 km long this glacier has been given very little attention, maybe because it does not reach tidewater.

NSIDC Glacier Photograph Collection Photographer unknown.

Google Earth view

In 1984 the glacier ended at a peninsula in the lake where the lake turns east. This was my view of this glacier during the summers of 1981-1984 from the Juneau Icefield with the Juneau Icefield Research Program. Our bad weather came from that direction so keeping an eye on that region during intervals between whiteout weather events, the norm, was prudent. Here we examine Landsat imagery from 1984-2013 to document the retreat of Wright Glacier and the elevation of the snowline on the glacier. The red arrow indicates the 2013 terminus, the red arrow the terminus at the time of the image and the red dots the snowline on the date of the imagery. In 1984 the lake had a length of 3.1 km extending northwest from the glacier terminus. The snowline in mid-August with a month left in the melt season was at 1150 m. By 1993 the glacier had retreated little on the north side of the lake and 200 m on the south side. The snowline in mid-September close to the end of the melt season was at 1150 m. In 1997 the fourth in a five year run of extensive mass balance losses and high equilibrium lines in the region, noted on the Juneau Icefield (Pelto et al, 2013), the snowline had risen to 1450 m. The terminus had retreated 200 m on the north side since 1984 and 600 m on the south side. In 2003 the snowline was at 1250 m with a month left in the melt season. The terminus retreat on the north side and south side since 1984 had now evened out with 900 m of retreat. In 2013 the snowline was at 1150 m in mid-August and 1350 m by the end of the melt season. The terminus had retreated 1300 m since 1984 and the lake is now 4.5 km long. The lower 2 km of the glacier has many stagnation features on it, suggesting continue retreat. It is unclear how far the basin that will be filled by the lake upon retreat extends, but it is not more than 2 km from the current terminus, as a small icefall reflecting a bedrock step occurs there. This glaciers retreat has accelerated since 1984. To be in equilibrium the glacier needs a minimum of 60% of its area to above the snowline at the end of the melt season. This is to offset the 10-12 m of melt that occurs at the terminus. This requires a snowline no higher than 1150 m. The snowline has been above this level in 1994-1998, 2003-2006 2009-2011 and in 2013, which suggest the glacier cannot maintain its current size and will continue to retreat. The glacier has a larger high elevation than the West Speel and Speel Glacier that originate from the same mountains. The glacier is following the pattern of retreat of all but one of the glaciers of the Juneau Icefield.

1984 Landsat image

1993 Landsat image

1997 Landsat image

2003 Landsat image

2013 Landsat image

Long Peak Glacier, Southeast Alaska

On June 26, 2014June 26, 2014 By mspeltoIn Glacier Observations

“Long Peak” Glacier is an unnamed glacier southeast of Juneau, Alaska. The glacier occupies a narrow northeast oriented avalanche fed valley, light blue arrows indicate the avalanche feeding regions around the glacier. In 1948, as indicated in the USGS map,the glacier extended from 1600 m to 500 m, a small lake is shown at the terminus, with an overall length of 3.8 km. The glacier is a short distance southwest of the retreating Speel Glacier, and it does drain into the Speel River. Here we examine Landsat imagery of changes in this glacier from 1984 to 2013. This is a small, remote glacier that receives that has not attracted attention. It is close to the Long Lake Snotel snowpack measurement station operated by the USDA. I observed the glacier in 1998 from a helicopter and thought it did not look poised to survive our warming climate for long.
Here we examine Landsat imagery from 1984-2013 to observe glacier retreat and lake expansion. By 1984 the lake had expanded to 750 m in length, with a glacier retreat of 500 m from the mapped terminus. The snowline is marked with purple dots, the 2013 terminus with a red arrow, and the orange arrow indicates a debris covered region of the glacier. Only 20% of the glacier is snowcovered and the melt season is not yet over in the 1984 image. This same pattern of snowcover remaining is seen in 1993, 1995, 1996, 1997 and 1998 for example. By 1999 the glacier has retreated an additional 300-350 m, the snowcovered area is greater but this is an August image. In 2013 a late June and a Late July image depict the loss of snowcover during a month. The overall length of the glacier is now 2.6 km, indicating a retreat of 1200 m since and a retreat of 700 m from 1984-2013. The glacier is still terminating in the lake that has expanded by the same amount. This glacier has not only retreated but also thinned and the slopes above the glacier have greened a bit particularly on the north side. This glacier cannot survive with the level of retained snowcover it has (Pelto, 2010). Ongoing mass balance work on the Lemon Creek Glacier of the Juneau Icefield, where the Juneau Icefield Research Program is beginning measurements next week, has thinned by 29 m during the 1955-2013 period (Pelto et al, 2013). In 2014 the Long Lake Snotel site at an elevation of 850 feet, lost its snowpack on June 11, a bit earlier than normal, indicating this glacier will lose most of its snowpack in 2014.

1984 Landsat image

1997 Landsat image

1999 Landsat image

June 2013 Landsat image

July 2013 Landsat image

Shakes Glacier Retreat-Tributary Separation, Alaska

On June 11, 2014 By mspeltoIn alaska glacier retreat, Glacier Observations2 Comments

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.

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. In 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.
1985 Landsat image

1986 Landsat image

1993 Landsat image

2003 Landsat image

2011 Google Earth image

2013 Landsat image

Walker Glacier Retreat and Lake Development, Alaska

On January 26, 2014March 13, 2014 By mspeltoIn Glacier Observations1 Comment

Walker Glacier terminates adjacent to the Alsek River, a popular rafting river route. Many rafting trips visit Walker Glacier since it is close to river, has a low slope and few crevasses.

Google Earth Image

In 1984 the glacier ended as a piedmont lobe separated from the river by meters. Today the terminus has retreated into a lake basin at the terminus. Here we examine Landsat imagery from 1984, 2011 and 2013 to identify retreat and lake development. In 1984 there is no lake at the terminus, red dots indicate glacier margin. The terminus particularly on the northwest side is debris covered. The yellow and red arrows indicate locations where the terminus is in 2013 and where new lakes have developed. The pink arrow indicates the end of a tributary that has fed the Walker Glacier. By 2004 the Google Earth imagery indicates a lake that is 400 m wide and 1500 m long. By 2011 the lake on the north side of the terminus is well developed, yellow arrow, but on the west side of the terminus no lake exists, red arrow. By 2013 the new lake is 750 m wide and 1800 m long. The glacier has retreated 800 m since 1984 on the north side, yellow arrow. A narrow lake has now developed on the west side. The combination of lakes indicates that the entire terminus lobe in the lake basin will soon be lost. The terminus remains quite debris covered, has a gentle slope and is relatively uncrevassed; hence, it is stagnant and will collapse-melt away. The last image is from Colorado River & Trail Expeditions , that shows low glacier slope looking north across new lake. This is similar to the collapse of glacier termini in proglacial lakes such as nearby East Novatak Glacier, Grand Plateau Glacier and Yakutat Glacier.
1984 Landsat image

2011 Landsat image

2013 Landsat image

Google Earth image from 2004

Colorado River & Trail Expeditions image-note low glacier slope looking north across new lake.

East Novatak Glacier Retreat, Alaska

On January 12, 2014January 13, 2014 By mspeltoIn Glacier Observations3 Comments

Novatak Glacier and a large unnamed south-flowing glacier to the east, here designated as East Novatak Glacier, were connected when first mapped by the International Border Commission in the 1906-08 period. By the 1950’s maps indicated the Novatak and East Novatak Glacier have separated, with a lake (A) developing between them. Here we examined 1984-2013 Landsat images to determined changes over the last 30 years.

Map of East Novatak Glacier area.

Google Earth image

East Novatak Glacier ended in a lake (B) in 1984, this lake then drained a short distance south to the Alsek River. The glacier was separated from the main Novatak Glacier by 3.5 km. In each image the 1984 terminus is marked by red arrow and 2013 image by yellow arrow, N marks the location of a nunatak that develops after 1984. In 1987 glacier retreat has connected the northern and southern half of B Lake. Lake A is still getting glacier runoff leading to a lighter blue color. By 2010 A Lake is no longer getting much glacier runoff and the water color is much darker than B Lake. A nunatak has emerged as well due to thinning ice. East Novatak Glacier has retreated out of the lake basin on the low lying plain, and into the mountain valley. In 2013 the terminus has narrowed and has retreated 2.5 to 3 km since 1984. The glacier is now separated from the retreating Novatak Glacier by 6 km. The tributary that used to connect to the main glacier and is partly obscured by the red arrow, now ends well short of the East Novatak Glacier. Most of the East Novatak Glacier is below 1000 m in elevation, which has been the recent snowline elevation. The retreat of this glacier like that of nearby Yakutat Glacier, indicates how suscpetible the Alaskan glaciers in the region with lower elevation accumulation zones are to our warming climate (Truessel et al, 2013). The retreat is similar to Grand Plateau Glacier, but that glacier does have high elevation accumulation areas, that will allow that glacier to survive.

Juneau Icefield Glacier Terminus Change from Landsat 5 1984 to Landsat 8 2013

On July 1, 2013July 13, 2013 By mspeltoIn Glacier Observations

The Juneau Icefield Research Program (JIRP) has been examining the glaciers of the Juneau Icefield since 1946. Until the NASA Landsat program began field measurements and aerial observations were the only means to observe the glaciers of the icefield. For more than 40 years it was Maynard Miller, U of Idaho, who led this expedition that has trained so many of today’s glaciologists, today it is Jeff Kavanaugh, U of Alberta. Given the difficult weather conditions that produce the 4000+ square kilometers of glaciers, this was not a task that could be done comprehensively. Here we examine the changes from the August 17, 1984 Landsat 5 image to the June 21, 2013 image from newly launched Landsat 8. Landsat 5 was launched in 1984, Landsat 8 launched in 2013. The Landsat images have become a key resource in the examination of the mass balance of these glaciers (Pelto, 2011). The August 17th 1984 image is the oldest Landsat image that I consider of top quality. I was on the Llewellyn Glacier with JIRP on the east side of the icefield the day this image was taken. On June 21, 2013 JIRP’s annual program had not begun, but the field season is now underway once again observing fin and reporting from the field across this icefield.
Post reblogged at NASA

First we have the two reference images of the entire icefield that indicate the location of the 12 main glaciers we focus on here. Followed by a chart indicating the amount of terminus change, 14 glaciers have retreated and one has advanced.
This is followed by 12 closeup glacier by glacier comparisons of the terminus, with the 1984 image always on the left and 2013 on the right, the 1984 margin is marked with red dots and the 2013 with yellow dots. This is an update to an examination of the Juneau Icefield terminus changes from 1948 to 2005. There are also links to more detailed discussions for each glacier, as the focus here is on the 1984 to 2013 changes visible in the images here. The images were first overlain in ArcGIS and the terminus change based on three measurements one at the glacier terminus midpoint, one each halfway to the margin from the mid-point. The exception is the Taku Glacier which is based on the JIRP field measurement mean and the Llewellyn where three measurements are made on each of the two termini, the average is then rounded to the nearest 100 m. The ongoing retreats reflects the long term negative mass balance of the glaciers with the exception of the Taku Glacier. The ongoing warming of our globe will continue to lead to retreat. The glaciers are all fed from the central portion of the icefield that always has a large snow covered area even at the end of recent warm summers.

August 17, 1984 Landsat 5 image: N=Norris, L=Lemon Creek, M=Mendenall, H=Herbert, E=Eagle, G=Gilkey, A=Antler, F=Field, LL=Llewellyn, Tu=Tulsequah, TW=Twin and T=Taku.

June 21, 2013 Landsat 8 image

1984-2013 chart of terminus change of individual glaciers from 1984 to 2013, see individual images below for the observed changes.

From 1984 to 2011 Norris Glacier has retreated 1100 m. The glacier terminus that has been ending in a proglacial lake for the last 40 years is now mostly grounded. Since 1984 the northern half of this lake has formed and the long term lake development is discussed in a more detailed discussion on Norris Glacier.

In 1984 Lemon Creek Glacier (L) has pulled back 300 m from a small lake it reached in 1984. Lemon Creek Glacier has a long term mass balance record that indicates more than 15 m of thinning from 1984 to 2012. This thinning is more dramatic than the 300 m retreat that has occurred. The yellow arrow indicates a tributary that no longer connects to the glacier.

Mendenhall Glacier is the most visited and photographed terminus in the region. The glacier in 1984 ended at the tip of a prominent peninsula in Mendenhall Lake. By 2013 the terminus has retreated 1200 m, with an equal expansion of the lake. The red arrows indicate a tributary that decreased dramatically in width and contribution to the main glacier. This is the location of Suicide Basin, where a lake has formed the last two summers and then rapidly drained. A nice set of images of the glacier are provided by Matt Beedle.

Herbert Glacier has retreated 600 m since 1984. The width of the terminus has also declined. The red arrow indicates a tributary that no longer feeds the main glacier.

Eagle Glacier has retreated from the edge of a lake in 1984. The retreat of 1100 m is rivaled by the width reduction of the glacier in the lower 3 km. Eagle Glacier‘s ongoing retreat is examined in more detail.

Gilkey Glacier had begun to retreat into a proglacial lake by 1984, the lake was still just 1 km long. A short distance above the terminus the Gilkey was joined by the sizable tributaries of the Thiel and Battle Glacier. By 2013 the glacier has retreated 3200 m, the lake is now 4 km long. Thiel and Battle Glacier have separated from the Gilkey Glacier and from each other. Thiel Glacier retreated 2600 m from its junction with Gilkey Glacier from 1984-2013 and Battle Glacier 1400 m from its junction with Thiel Glacier

Antler Glacier is actually a distributary glacier of the Bucher Glacier, which in turns joins the Gilkey Glacier. As this glacier has thinned, less ice has overtopped the lip of the valley that Antler occupies. In 1984 Antler Glacier was 3 km long descending the valley to end near a proglacial lake, that it had recently occupied. By 2013 the glacier was just 400 m long, having lost 2600 m of its length.

Field Glacier in 1984 ended at the edge of an outwash plain with a few glimpses of a lake developing near its margin. By 2013 a substantial lake has formed at the terminus and the glacier has retreated 2300 m. A lake has also developed at the first terminus joining from the east, most of the width of this glacier has been lost. It is clear that the two lakes will merge as the retreat continues.

The second largest glacier of the icefield is the Llewellyn Glacier which is in British Columbia. The glacier has several termini, here we examine two of them that have retreated 900 m from 1984-2013. Hoboe Glacier is another terminus that has been examined, but not in this post. This has led to formation of new lakes, and water level changes in existing lakes. Matt Beedle has examined the recent changes at the terminus.

Tulsequah Glacier in 1984 ended at an outwash plain with a small marginal lake beginning to develop, red arrow. By 2013 a large proglacial lake has developed due to the 2500 m retreat. A side valley down which a distributary tongue of the glacier flowed in 1984 has retreated out of the valley by 2013, pink arrow.

The East and West Twin Glacier are receding up separate fjords, though they are fed from a joint accumulation zone. The East Twin is a narrower glacier and has retreated 900 m. The West Twin has retreated 600 m, at an elbow in the fjord. Elbows like this are often good pinning points that are a more stable setting, once the glacier retreats out of the Elbow retreat should speed up.

Taku Glacier is the largest glacier of the icefield and unlike all the others it has been advancing non-stop over the last century. The sustained positive mass balance from 1946-2012 has driven this advance (Pelto, 2011), this led to the glacier thickenning along its entire length. Since 1950 observations of velocity near the snowline of the glacier by JIRP indicates that the glacier has had a remarkably steady flow over the past 50 years (Pelto et al, 2008). Since 1988 the glacier has not been thickening near the snowline as mass balance has declined. We have been able to observe the snowline movement in satellite images to help determine the mass balance. The changes at the glacier front are quite variable as the glacier advances. JIRP measurements of the terminus indicate this from 2001-2008 with an interactive map from Scott McGee, indicating advances in some area, minor retreat in others and back and forth in others. In 2012 JIRP was back at the terminus creating the map below. There is no change at the east and west side of the margin since 2008 and 55 to 115 m of advance closer to the center.

Riggs Glacier Retreat from the Sea, Alaska

On January 16, 2013 By mspeltoIn Glacier Observations5 Comments

Riggs Glacier for most of the 20th century was a tributary to the Muir Glacier in Glacier Bay Alaska. The two glaciers separated between 1960 and 1963 as noted by the USGS in their detailed research led by Bruce Molnia . The USGS chronicled the changes of this glacier from 1940 to 2004 with pictures from the same location by Bruce Molnia. The Muir and Riggs are still joined in 1950 and the Riggs Glacier is retreating out of sight into its own valley by 2004.

Dan Lawson in a 2004 National Park Service brochure noted that Riggs Glacier was about 1.2 km wide at the terminus, had a 40 to 90 feet high ice face and was 15 miles long. The terminus that had been calving into Muir Inlet for the entire 20th century became mostly terrestrial during the mid-1980,s as an outwash delta built at the southern margin. In 2004 tidewater only reached the terminus during higher tides on either side of the bedrock knob that separates the glacier into two ice tongues. Riggs Glacier has been thinning progressively over the past two decades and is expected to continue thinning and slowly receding. Ice recession has been averaging about 20 to 30 feet per year for the last 5 years. This post examines changes as seen in Landsat images from 1990 to 2011.

In 1990 the two terminus tongues are still connected at the black arrow, and a prominent knob is just being exposed by retreat of the western terminus, red arrow. The terminus still reaches tidewater on the very northern margin. There is no vegetation evident on the knob separating the ice tongues. A tributary from the east at the orange arrow just reaches the Riggs Glacier. By 1999 the termini are separated the prominent knob is now fully exposed by retreat of the western terminus and the glacier is no longer tidewater except briefly at high tide. Vegetation has become to develop on the rock knob that separates the two ice tongues. By 2009 the glacier has retreated well back from tidewater. The delta building in front of the eastern terminus has expanded into the inlet some. Vegetation has spread over most of the rock knob that separates the two ice tongues. In 2010 in a late summer images the snowline of the glacier is at 975 m. The tributary from the east at the orange arrow has retreated 1 km from the Riggs Glacier. By 2011 the western terminus has retreated 600 meters since 1990 and the eastern terminus has retreated 800 meters from the black arrow where it used to connect to the main glacier. Examination of the snowline elevation on Riggs Glacier indicates that it now typically it is typically between 950 and 1050 m. This recent increase in the snowline is similar to the increase seen on Brady Glacier. This has led to the glacier retreat and it no longer reaching the sea.