The Sortebrae is a surge type tidewater calving glacier on the Geikie Peninsula of East Greenland. Surge type glaciers do not have a steady ice flow, they have non-steady ice flow where longer quiescent periods of slower flow are punctuated by short periods of faster flow. The glacier is comprised of a number of tributaries (A-D) some of which drain the main Greenland Ice Sheet (E). 
Sortebrae surged in the 1950’s and 1992-95 (Jiskoot et al, 2001). A diagnostic feature of surging glaciers is the looped or distorted medial moraines (M) that results from the changing degree of contribution of the various tributaries of a surging glacier with time. Not all tributaries surge and if they do it is not necessarily synchronous
. The 1992-1995 period featured a 5 km advance, this suggests a periodicity to surging of 4–70 years (Jiskoot et al, 2001). From 2000-2005 the retreat rate was noted as 428 m/year by Jiskoot et al (2012). Comparsion of Landsat images from 2000 (green line) and 2010 (yellow line) indicate a retreat of 5 kilometers, approximately 500 meters/year. Surging glaciers are still sensitive to climate, the surge cycle is an additional factor affecting surface elevation and terminus change. In this region the recent extensive retreat of Sortebrae mirrors that of the other glaciers, Jiskoot et al (2012) identify that just one of 113 tidewater glaciers in the region advanced, and that was during a surge. Average margin retreat rate in terms of area lost increased from 2 square kilometers per year between 1980 and 2000, to 4-5 square kilometers per year from 2001 to 2005..
Given the fact that the glacier is not due for a surge in the next couple decades, a continuation of this retreat for even one decade will lead to the separation of the terminus. With the termini entering from the southwest (red arrow) and the main termini (green arrow). The southwestern tributary does not exhibit strong surging features. It is also worth noting quite a few smaller glaciers near the coast here have very limited snowcover remaining (yellow arrow) near the end of the 2010 melt season. This is not a good sign as glacier that do not have consistent accumulation zone will not survive (Pelto, 2010). Given that 2011 also featured limited snowpack it seems to be a too frequent theme for the smaller glaciers in the region. The mass loss of smaller glacier in this region has has been particularly well observed on Mittivakkat Glacier by Mernild et al (2011). 
Category: Glacier Observations
Post detailing changes in a glacier
Kennedy Glacier Retreat, Glacier Peak Washington
At the turn of the century C.E. Rusk explored the glaciers around Glacier Peak that were retreating from their Little Ice Age maximum in the mid-19th century. The average retreat of Glacier Peak glaciers from the LIA to the 1958 map positions was 1640 m. From 1950-1955 Richard Hubley, University of Washington, completed the first aerial glacier surveys of North Cascade termini, noting the beginning of an advance on Glacier Peak that continued up through 1979. All ten glaciers on the slopes of Glacier Peak advanced ranged from 75 to 500 m and culminated in 1978. All 11 Glacier Peak glaciers that advanced during the 1950-1979 period emplaced identifiable maximum advance terminal moraines. A picture of the glacier from R.Luce during this advance shows a glacier with a strongly convex profile. 
During the 1993-1997 period the North Cascade Glacier Climate Project (NCGCP) surveyed the glaciers around the peak each summer, one century after C.E. Rusk did (Pelto and Hedlund, 2001). By 1984, all the Glacier Peak glaciers were again retreating. This peak even in summer provided some tough weather, including a 1995 August snow storm.
Two other glaciers that were a focus of this study around Glacier Peak were Milk Lake, Vista and Honeycomb Glacier.
This post focuses on Kennedy Glacier which is the main glacier draining the west side of the Peak, left glacier in image below.
Kennedy and Scimitar Glacier were joined during the LIA descending the Kennedy Creek valley to an elevation of 1315 m. Retreat from the LIA maximum of 1000 m had occurred by the turn of the century. By 1946 the glacier had retreated an additional 700 m to an elevation of 1960 m. In 1952 the glacier was advancing rapidly, as indicated by the 1955 photograph from Richard Hubley of the glacier from 1955. 
This advance continued up until 1975, the terminus having extended downslope 320 m to terminate at an altitude of 1785 m. By 1984 the terminus had begun to retreat. In 1994 the terminus had retreated 95 m and by 1997 151 m. A view of the terminus in 1993 indicates an active, crevassed terminus tongue, top image. In 1994 (miidle) and 1997 (below) the terminus is a well established vegetation and sediment line marking the 1970’s advance, burgundy arrows. 
The glacier has continued to retreat, in the 2006 and 2009 Google Earth imagery the orange line is the 1978 terminus, green line 1994, blue line 2006 and red line 2009. The left hand glacier is Kennedy the right hand Scimitar.
. The glacier is continuing too retreat, but each summer retains significant accumulation, as evident in the crevasse measurements of snow depths on the upper Kennedy Glacier at 2800 meters. This indicates a glacier that can retreat to a new point of equilibrium with current climate.
Washmawapta Glacier Retreat, British Columbia
The West Washmawapta Glacier and Washmawapta Icefield are located in the Vermillon Range in British Columbia
. They are in a basin between Limestone Peak and Helmet Peak. The West Washmawapta is a cirque glacier and has been the focus of detailed studies of its dynamics and runoff in recent years. The study of its dynamics (Sanders et al, 2010) measured velocities of 3-10 meters/year, pretty typical for a cirque glacier of this size, and had a maximum depth of 185 m, a bit deeper than usual. The runoff study (McGregor, 2007) and Dow et al (2011)examined streamflow below the glacier and found that peak flow was at 2100 hours, several hours after peak melting. They conclude that this indicates a well developed subglacial drainage system. Sanders et al (2010) noted that West Washmawapta Glacier lost 30% of its area from 1949-2007. A comparison of Google Earth imagery from 2002 (top) and 2007 (middle) and Landsat imagery from 2009(bottom) identifies changes in the two glacier in the last decade. For the West Washmawapta Glacier in 2002 the glacier ended in contact with two proglacial lakes (Point A-C) and a lake that is just forming at Point B. The retreat is from 30-50 meters in this five year span. In the 2009 Landsat the Lake at Point C is well separated from the glacier. 
For Washmawapta Icefield, does not really deserve the icefield title, has lost a lower former glacier section that was in contact with Elizajan Lake, green arrow. The purple areas point to two prominent bedrock features that indicate retreat of 30 meters over the five year time span. The problem for both glacier is the insufficient size of the accumulation area. In 2009 the image is from August 20th, a month left in the melt season and only 40% of the glaciers are snowcovered. An alpine glacier like these needs at least 55% snowcover to be in equilibrium. The 2007 imagery in from July and the accumulation area is at 65%, by September of 2007 the extent was down to 35%. 
Now if you are still not sated, the video on the West Washmawapta Glacier project illustrates the amount of hard work and good humor that is essential to complete such a field project is quite a treat.
Dzhungharia Alatau, Kazakhstan Glacier Retreat
Dzhungharia Alatau range of Kazakhstan is host to over 500 square kilometers of glacier ice. 
This amount of glacier ice declined by 1% per year from 1956 to 1990, (Severskiy, 2009: 103). This reduction in glacier area parellels that of changes in the Zailiyskiy and Kungey Alatau further south in Kazakhstan and Kyrgyzstan (Bolch, 2006). The Aksu River flows north from the Dzhungharia Alatau into Lake Balkhash.
This post focuses on several glaciers in the Aksu River Basin, Eskeldi District, Almaty Province, Kazakhstan. A 2004 Google Earth image highlights the terminus position of several glaciers (A-E) that end in small lakes that are expanding as the glaciers retreat. It is also evident in this image that the snowcovered extent is low. For a glacier to be in equilibrium 55-65% of the glacier needs to be snowcovered at the end of the melt season. In this case the percentage is below 30%. The lakes at point A and C have expanded, and the glacier at point E is no longer in contact with the glacier, in the 2009 Geoeye imagery. The 2009 imagery is after a summer snow storm, that blanketed the glaciers with a thin snowcover. 
. The amount of retreat of for the 2004-2009 period is close to 140 meters at Point A, 100 meters at Point C and E. A closeup view of the glacier ending at Point A indicates the terminus position green arrow and the outcrops of rock in upper glacier that indicate thinning of the accumulation zone. A glacier with a thinning accumulation zone will not survive (Pelto, 2010). The second image is of the glacier that ends at point C and D and indicates the lack of snowcover on the small glaciers. 
. Some on the ground photographs of the glaciers in the region from Tsvetik
Petrov Glacier Retreat, Kyrgyzstan
Petrov Glacier flows north down the slopes of Ak-Shiyrak in the Tien Shan Mountains of Kyrgyzstan. The glacier ends in Petrov Lake which continues to expand as the glacier retreats. The glacier is 12 km long has three main tributaries each beginning at 4600-4700 meters and descending to the lake at 3700 meters. 
The lake in particular has been the focus of an extensive research project by a group Czech scientists, Cerny et al (2009)and Jansky et al (2009). This research for Geomin is driven by interest in a potential outburst flood event, the water level in the Petrov Lake and the moraine-ice dam are monitored and proposals on how to decrease the water level are being developed. Petrov Glacier is the largest glacier in the Naryn River watershed, Jansky et al (2009) report that the glacier retreated at a rate of 24 meters/year from 1957-1960, 40 meters/year from 1980-1999 and 61 m year from 1999-2006. Using two satellite images from 2001 (top) and 2011 (bottom) and Google Earth imagery from 2005 (middle) here we look in detail at the current condition of the glacier. The glacier has retreated 300 meters during the 2001-2011 period. Notice the Peninsula extending from the glacier into Petrov Lake (T). 
. A snapshot of the glacier at three different locations indicate the extent of the ablation zone. For points A,B and C the red arrow indicates lateral moraines, green arrows surface wind scour features that have trapped dust, and the blue arrows surface streams. Lateral moraines and surface streams cannot exist in the accumulation zone, and the wind scour features indicate locations where accumulation is not retained. Each of these feature types at A,B and C extend to 4300 meters. A glacier such as Petrov that lacks substantial avalanching and is in a region of low annual precipitation generally needs 60% of its area in the accumulation zone to be in equilibrium. The glacier has insufficient accumulation zone size recently and will have to continue to retreat. 
Petrov Glacier reflects the trends of the region where glaciers have lost 2 cubic kilometers per year of volume from 1955-2000, as documented by Harrison and others, University of Newcastle
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Irik Glacier Retreat, Mount Elbrus, Russia
Irik Glacier flows down the southeast flank of Mount Elbrus, the highest peak in the Caucasus Mountains of Russia, red arrow on map points to current terminus of Irik Glacier, top image. The map terminus extended 1 kilometer further down the mountain. The glacier currently begins at 5000 m and descends to 2800 m, bottom image orange arrows indicate main accumulation areas, this compares to a terminus elevation of 2600 meters on the map.
A decrease of area of glaciers of the Central Caucasus by 16% in the last 40 years is reported, on Elbrus the loss has been 8 % Russian Academy of Sciences National Geophysical Committee (2011). August 1998 (Top) and 2010 image (bottom) indicate the snowline on Irik Glacier, orange arrows and the glacier terminus blue arrows. The fraction of the glacier that is snowcovered is the accumulation area ratio (AAR), typically a glacier needs an AAR of 0.5-0.65 at the end of the melt season in September to be in equilibrium. For the nearby Djankuat Glacier, where annual mass balance data is reported to the World Glacier Monitoring Service, the AAR value for equilibrium is reported as 0.55. For Irik Glacier in 1998 and 2010 the AAR is 32 and 28 respectively and this is still with several weeks of melting. By the end of the melt season both would be below 0.3.
The result of consistent negative balances is glacier retreat. For Irik Glacier the retreat from 1998 (top) to 2010 (bottom) is 600-700 meters, note blue arrows indicating terminus location and red arrow indicating a small rise on the southwest side of the glacier that the glacier used to wrap around, but no longer does. In a Google Earth image from 2009 the lower of the glacier is narrow and uncrevassed, this is a section that is quickly melting away. The orange arrows point out the lateral moraines from the Little Ice Age, the blue arrow the 1998 terminus and the red arrow the terminus in 2010. Irik Glacier must retreat to attempt to reestablish equilibrium with climate warming that has reduced the accumulation area. At present the lower 300 meters of the glacier is not crevassed and will melt away. Above that point the glacier is crevassed and vigorous in its flow.
Hailuogou Glacier Retreat, China
The Hailuogou Glacier has retreated 1.8 km during the 20th century. This glacier drains southeast from Gongga Shan beginning at 7500 m and extending to a debris covered terminus at 3000 m. The first image is a map from Li et al (2010).
The glacier has been the focus of an ongoing research program by the Laboratory of Cryospheric Sciences, Chinese Academy of Sciences, Lanzhou, China and Nagoya University, Japan. This glacier is a summer accumulation type glacier fed largely by the summer monsoon. The glacier feeds the Dadu River. which eventually joins the Yangtze River. The Dadu River has a series of hydropower plants that fed in part by the glaciers of Gongga Shan. The Pubugou Hydropower Station has a total generating capacity is 3,300 MW, Gongzui Hydropower Station 600 MW and Tongjiezi Hydropower Station 700 MW and the still under construction Dagangshan Hydropower Station 2600 MW. The main changes in the Hailuogou Glacier are the continued thinning of the ablation zone, not terminus retreat of the heavily debris covered terminus. The terminus is at 3000 meters (T), the debris cover dominates to 3400 m. The glacier continues with a low slope to the base of the icefall (I) at 3800 m. Through the icefall the elevation rises above the equilibrium line at 4900 meters (ELA). The thick debris cover insulates the underlying ice slowing the melting. Zhang et al(2010) indicate that thinning and retreat have both accelerated since 1989. The images from Google Earth below are from 2002. The glacier area has been reduced by 0.8 square kilometers over the last 44 years, but more importantly has thinned by 1.1 meters/year in the ablation zone (Pan et al, 2011). In the second image the red arrow indicates the start of the debris cover, and the blue arrow where the river emerges at the terminus. 
The beginning of the debris cover is noted (DC)(top image), the green arrow indicates where the glacier becomes stagnant and the debris cover is quite thick, the red arrow the terminus, where the glacial river emerges from below the glacier. In the closeup the blue arrows indicate the thick debris covered glacier area and red arrow the terminus where the river emerges. 
. The retreat rate was 13 meters/year from 1966-1989 and 27 m/year from 1998-2008. They also report a significant reduction in glacier velocity in the ablation zone. This is an indication of increasing stagnation of the terminus area, that will lead to continued downwasting and retreat. The glacier is responding to a temperature warming as noted at the Gongga Alpine Ecosystem Observation and Research Station of the Chinese Ecological Research Network, during 1966–2009, the mean annual temperature at the research station has been increasing by 0.15 to 0.21 C/decade. Two examples of the developing hydropower on the Dadu River fed by the glaciers of Gongga Shan are below with the Dagangshan Hydropower Station, 40 km downstream, top image and Pubugou Hydropower Station, 100 km downstream bottom image. 
Lewis Glacier Disappears, North Cascades, Washington
In 1985 during my second visit to the Lewis Glacier, was the first time I confronted the idea of a glacier disappearing. We were able to peer down several crevasses and see the bottom of the Lewis Glacier, measurements indicated a maximum depth of 12 meters over an area the size of a football field. 
This glacier had been selected for the North Cascade Glacier Climate Projects’s mass balance program(Pelto and Riedel, 2001) assessing mass balance on 10 glaciers across the glacier clad mountain range. It was a small glacier in the drier part of the range, near Rainy Pass. This size made it attractive to observe in terms of response to climate change. The USGS map indicates a significant glacier with an area of 0.12 square kilometers in the 1950’s.
By 1985 (top image) the glacier had lost half of its mapped area, there were still some significant blue ice areas, and areas of firn, snow several years old that is not yet glacier ice. Return visits each summer over the next few years chronicled the demise of the glacier. By 1988 (middle image) the glacier had shrunk dramatically even since 1985, with no area of blued ice even the size of a basketball court, the thickest ice measured was 5 meters. By 1990 the glacier was gone (bottom image), no blue ice left in the basin, the blue arrows indicate the lateral moraine above the now empty glacier basin. At the time I had not developed the model for forecasting glacier survival (Pelto, 2010). 
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. Google Earth imagery from 1998 and 2006 indicate the basin does retain snowcover late into the summer during most summers. However, the areal extent is much smaller than the glacier had been. The blue arrows in the 1998 image indicate the moraine marking the extent of the glacier during the Little Ice Age. The blue arrows in the 2006 image indicate the area where the deepest ice was measured in 1985. Runoff observation conducted below the glacier indicate a 70& drop in August streamflow after glacier loss. This is the principal impact of glacier retreat, a reduction in summer runoff, particularly acute for rivers late in the summer when all other snow in a basin has typically been gone. (Pelto, 2008)
Mueller Glacier retreat Lake Expansion, New Zealand
Volume loss in New Zealand glaciers is dominated by 12 large glaciers. The NIWA glacier monitoring program has noted that volume of ice in New Zealand’s Southern Alps has decreased 5.8 cubic kilometres, more than 10% in the past 30 years. More than 90% of this loss is from 12 of the largest glaciers in response to rising temperatures over the 20th century. Three of these glaciers are the Tasman, Mueller and Hooker Glacier. Mueller and Hooker Glacier are one valley west of the Tasman Glacier and end in the same valley ending just 3 km apart. Description of the retreat and the role of glacier lakes in accelerating the reteat of Tasman Glacier is discussed in detail in Dykes et al (2011). If we look back to the 1972 Mount Cook Map no lakes are evident at the terminus of Hooker (H), Mueller (M) or Tasman Glacier(T), pink dots indicate terminus location, top image. In 2011 the Landsat image illustrates that this has become a new lake district, bottom image.
. Mueller Glacier drains the eastern side of Mount Sefton, Mount Thompson and Mount Isabel. The lower section of the glacier is debris covered in the valley reach from the terminus at 1000 m to 1250 m. A comparison of the Mueller Glacier in a sequence of three Landsat images below from 2000 (top), 2004 (middle) and 2011 (bottom), indicates that the lake at the end of Hooker Glacier had developed by 2000. The lake at the end of the Mueller Glacier was just forming length of 400 meters. By 2004 the Mueller Glacier Lake had expanded to a length of 700 meters. By 2011 the lake had reached 1400 meters in length. The 1000 meter retreat from 2000-2011 will continue in the future as the lower section is stagnant. 
. A closer look at the lower Mueller Glacier indicates that the lower 2 km is stagnant as indicated by the formation of supraglacial lakes and considerable surface roughness (green arrow) that does not occur when a glacier is active and moving. The glacier has been fed by three different glaciers flowing off of Mount Sefton. Two of them Tuckett and Huddlesoton (pink arrow) are no longer delivering significant ice to the Mueller, only modest avalanching now spills onto the Mueller Glacier. Only the Frind Glacier (yellow arrow) is contributing to the Mueller Glacier. The result is that the end of truly active ice is at the purple arrow, this will develop into the terminus of the Mueller Glacier. In the 2011 image of the glacier the yellow-burgundy arrow indicates the snowline on the Frind Glacier is at 1900 meters, yielding too small of an accumulation zone to support the valley tongue of the Mueller Glacier. This is similar to the situation on nearby Murchison Glacier. Further the lack of ice connection from Huddleston and Tuckett Glaciers to Mueller is again evident, pink arrow. The lake will continue to expand through minor calving and downwasting. The lake has not been surveyed, but seems to lack the depth at the current terminus of Tasman Lake where calving can be more important. 
Taku Glacier Transient Snow Line Paper Published
This post examines in simpler terms and more images the paper published this week in The Cryosphere on “Utility of late summer transient snowline migration rate on Taku Glacier, Alaska”. The transient snowline (TSL) is the point of transition from snow to older glacier firn and ice. The TSL rises during the course of the summer melt season and at the end of the melt season is the equilibrium line altitude (ELA). This paper represents a concept that occurred to me while skiing and probing snow pack on the Taku Glacier in 1998 with the Juneau Icefield Research Program (JIRP), something I have spent six months doing over the years. There simply was not enough consistent satellite imagery to apply the model until recently, we also needed field data-ground truth-to quantify and verify the TSL model. This meant probing snowpack along a 5 km transect near the TSL during several summers, following my 1998 probing, Matt Beedle completed the probing in 2004 and 2005 with JIRP and Chris McNeil did so in 2010, 2011 and 2014. Below is the transient snowline in August 2014 on the Juneau Icefield. 
Landsat Image: T=Taku, G=Gilkey, H=Herbert, M=Mendenhall and N=Norris. Black arrows indicate the snowline which was quite high at over 1000 m with a month left in the melt season.
The ELA is the point at which accumulation equals melting on temperate alpine glaciers this is where snow transitions to bare glacier ice. Mass balance for non-calving glaciers is the difference between snow accumulation on a glacier and snow and ice loss from the glacier. The easiest to observe and most useful estimate of mass balance without detailed measurement is the equilibrium line altitude (ELA). Today the TSL can be observed frequently in satellite imagery. There are two ways the TSL is useful in assessing mass balance. First the rise of TSL during the melt season provides an assessment of the rate of melting. Second the TSL rate of rise can be used near the end of the melt season to determine the ELA, when imagery at that point is not available due to cloud cover. This allows widespread assessment of melt rate on glaciers. On Taku Glacier which is fairly typical we found a very consistent gradient of snowpack change with elevation from year to year. This allows determination of melt rate simply from rate of TSL rise. We use Landsat Imagery of which there are typically only two-four useful images during the melt season, barely enough and more recently MODIS imagery from GINA, which is obtained daily for the entire globe and provides the most frequent point of observation. However, the resolution of MODIS makes it inaccurate on glaciers less than 1 km wide or 1 km long. Taku Glacier is 55 km long and 5 km wide at the ELA. As the melt season begins the snow cover extent is large on Taku Glacier. The key is how rapidly the TSL rises during the melt season. On the ground the JIRP measures the snow depths and snow melt during July and August on Taku Glacier. This program was led by Maynard Miller, U Idaho for more than 50 years and is currently under the direction of Jeff Kavanaugh U Alberta. The Taku Glacier mass balance measurements allows validation of the melt rate, note snowpit locations on map below
. For example in 2004 the TSL was at 850 meters on July 15, first image below. At this time the snowpack was 1.6 meters at 1000 meters. On September 1 the snowline was at 1030 m, second image below. The TSL had risen at an average rate of 3.9 meters per day, all 1.6 m of snow had melted.
Below are images from May 26, 2006, then July 29, 2006 and then Sept. 15 2006. Indicating the rise of the snowline. 
The below images from May 26, July 29 and Sept. 15 2006 indicate the rise of the ELA during the course of the melt season, from 370 m to 800 m to 975 m. Snow depths at the the Sept. 15 ELA, where snowpack=0, was 2 m on July 22. Thus, we had 2 meters of snow melt at 975 m between July 22 and Sept. 15. In 2004 the melt rate was 0.036 meters per day and in 2006 0.038 meters per day. All of the TSL images above are from Landsat> For Sept. 14, 2009 (top), Sept. 20, 2010 (middle) and Sept. 11, 2011 (bottom) MODIS images are used, resolution not as good as with the Landsat images. Note the similarity in the end of the year snowline on Taku Glacier for those three years. 
. The next task is to apply the TSL to other glaciers and to carefully compare results from MODIS and Landsat. Through 2010 there were only four days with good coverage from both. Below is the Landsat imagery from Sept. 11, 2011, same as the MODIS date above. Noted is the TSL, in this case the ELA for Lemon Creek and Taku Glacier. 
Glaciar Gualas Retreat lake expansion, Patagonia, Chile
Glaciar Gualas drains from the northwest portion of the Northern Patagonia Icefield (NPI) into a rapidly expanding new lake Laguna Gualas. There is a spectacular icefall (I) where the glacier descends from the main NPI from 1600 m to 900 m, which is below the equilibrium line. Below this point the Gualas has a 2 km wide, 15 km long valley reach extending to the terminus which currently has a substantial calving face into Laguna Gualas (A-B). Point M inidcates an area of substantial moraine cover on the ice, that will with continued retreat be a likely location for a new lake to form, much as the periodic lake at Point C. 
Lopez and Cassasa (2011) have documented a 1.8 km retreat from 2001-2011 of this glacier, updating and expanding on the work of Rivera et al (2007). This is part of the ongoing inventory of Chilean glacier and the NPI, that is being undetaken by the Laboratory of Glaciology at the Centre for Engineering Innovation CECS (CIN), Valdivia, Chile. This project has built on initial joint work with Glacier and Cryospheric Environment Research Laboratory in Japan and now with NASA-JPL as well. The Japan Aerospace Exploration Agency with Glacier and Cryospheric Environment Research Laboratory published a comparison of selected NPI glacier retreats. Here we compare Landsat satellite images of the glacier from 1987, 2001, 2005 and 2011 illustrating the retreat that Lopez and Casassa (2011) have chronicled. They have further noted an average thinning of the valley tongue of 2.1 meters per year from 1975-2005 and a doubling in the rate of area lost, 2.8 square kilometers, from 2001-2011 versus 1975-2001. In 1987 the glacier essentially fills the lake basin, margin is indicated with pink dots. By 2001 an evident fringe of water separates the glacier from the lake margin on all but the eastern side of the lake. In 2005 the margin is hard to discern given the extensive floating icebergs in the lake. By 2011 the lake is evident and the glacier has retreated 2.2 km from its 1987 position. There is little additional change from 2011 to 2014. This retreat is like those of other NPI glaciers such as, Reichert Glacier, Steffen Glacier, Nef Glacier, and Colonia Glacier. 
1987 Landsat image
2001 Landsat image
2005 Landsat image
2014 Landsat image
The glacier surface is steep in the first kilometer behind the terminus, indicating a rising bedrock under the glacier. Then the glacier has a very modest slope for the next 14 km. As long as the glacier can calve into a lake, this will enhance retreat. The current lake may not end at the bedrock step just behind the current terminus. However, even if this occurs the low slope above that point indicates another basin that will have sufficient depth to form a second lake basin. It is unlikely that the calving retreat of this glacier will have more than a temporary interruption. In the annotated Google Earth view below the approximate elevations along the glacier are listed. What is of particular interest is the 2.1 meter per year thinning on the lower glacier has occurred while on the upper glacier there is a small amount thickening (Rivera et al;, 2007). This implies the retreat is driven by enhanced melting due to warming, since the only way to thicken the glacier in the accumulation zone is via increased snowfall. 
McAllister Glacier Retreat, North Cascades
McAllister Glacier is one of the main headwaters glaciers of Thunder Creek feeding into the Skagit River in the North Cascades of Washington. The North Cascade Glacier Climate Project has examined North Cascade glaciers each summer for 28 years and found all 47 that we visit are retreating and six have disappeared. McAllister Glacier is not a glacier we access. This glacier advanced during the 1950-1979 period. This post examines the changes in this glacier since the 1970’s. The terminus of this glacier is very hard to reach, and almost as hard to see except from the air. The glacier has an accumulation zone extending from to 2000 meters in two basins, each basin then descends an icefall to 1600 meters, the terminus tongue than extends down valley to the current terminus at 1300 meters. 
In the 1975 vertical aerial photograph from Austin Post, USGS the terminus tongue is heavily crevassed, burgundy arrow, and the glacier ends in the middle of a small lake. The terminus at that point outlined in burgundy has pulled back a bit from the advance moraine of 1972 in orange. The southern icefall, on right, is extremely active with dramatic crevassing.
. By 1998 the glacier has retreated 170 meters to the north end of the expanding lake and the terminus tongue still has less but significant crevassing. In 1998 were able to observe the glacier from nearby Snowfield Peak, the snowline on the glacier was well above the top of the icefall, first image below. By 2006 the glacier had retreated another 180 meters, the terminus tongue has even less crevassing than in 1998, middle image below. In 2009 (bottom image in sequence) the glacier has retreated another 60 meters, making a total 1975-2009 retreat of 410 meters. This retreat is very similar to the retreat observed on Mount Baker, North Cascade glaciers: Boulder Glacier, and Rainbow Glacier, Mazama Glacieras well as on nearby Boston Glacier. The terminus tongues now has very limited crevassing indicating the reduction in velocity due to less ice being contributed via the icefalls.
1998 Google Earth
2006 Google Earth
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2009 Google Earth
A more detailed look at the icefall from 1975, 1998 and 2009 indicate the changes. In 2009 the northern arm looks to almost end at the top of the icefall the southern arm is much reduced in width and crevassing. At the bottom we return to the 1975 view of the icefall when velocity and crevassing was higher transporting a greater ice volume to the valley tongue. 
From a Glaciers Perspective 