Jackson and Blackfoot Glacier in late August and early September Sentinel 2 false color images. Point A indicates exposed ice showing annual layers. Point B indicates exposed firn that had been retained through previous summers. The gray color of the firn indicates how dirty it is and that its albedo would enhance melting. The yellow arrow indicates the one patch of retained snow in 2021 on Blackfoot Glacier with no retained snow on Jackson Glacier.
The exceptional heat of the summer of 2021 across glaciated mountain ranges of the Pacific Northwest, reduced snowcover extent from Mount Shasta, CA north to Mount Baker, WA and west to Kokanee Glacier, BC and Bonnet Glacier, Alberta. In Glacier National Park, Montana retained snowcover by the end of summer in 2021 is the lowest observed on Blackfoot and Jackson Glacier. Snowcover extent in late summer is a good indicator of glacier mass balance, which controls changes in glacier volume/glacier area (Pelto, 2019). Here we examine the percentage of Blackfoot and Jackson Glacier that have a persistent accumulation zone from 1998-2021.
The USGS in Glacier National Park has over the last 15 years maintained an extensive glacier monitoring program including consistent mass balance observations on Sperry Glacier, and repeat mapping of the 37 named glaciers, 25 of which still qualify as glaciers. The repeat mapping indicates the area lost from 1966 to 2015, (USGS, 2017). There is considerable variation between glaciers, some have lost more than 80% of their area and others have lost less than 20% during this 50 year period. Blackfoot Glacier is the second largest glacier in Glacier National Park in Montana. Jackson Glacier the seventh largest. The USGS identified the area of Blackfoot Glacier in 2015 as 1.5 km2, a reduction of 18% from 1966-2015 (USGS, 2017). Jackson Glacier had an area of 0.8 km2, losing 40% of its area from 1966-2015. Extrapolating area loss to determine when a glacier will disappear, is typically not a useful approach. Glaciers that lack a persistent accumulation zone cannot survive current conditions (Pelto, 2010). Other glaciers may have a persistent accumulation even if small that allows them to persist.
In 2005 a year of mass balance loss in the region the retained area of accumulation in late August on Blackfoot Glacier was ~60% and Jackson Glacier ~40%. The retained area of accumulation in mid-August of 2015 was ~60%, on Blackfoot Glacier and Jackson Glacier 30-40%. In September 2019 at the end of the melt season an accumulation area covered 10-15% of Jackson and 20% of Blackfoot, the lowest observed since at least 1998. In early September 2020 as summer ended both glaciers had an accumulation area ratio of ~40%. The higher typical end of. summer snowcover extent on Blackfoot Glacier explains why area loss has been less in recent decades..
The June-August 2021 period was the warmest of the 127 period of record for the Western Montana climate division (NOAA, 2021). The result was that by the end of August 2021 0n Aug. 30 less than 5% of Jackson and ~10% of Blackfoot had retained snowcover. By September 6, 2021 Jackson Glacier had no significant snowcover and Blackfoot Glacier had less than 10% remaining. Both of these are minimum values indicating large mass balance losses for both glaciers in 2021, likely over 2 m as has been observed to the north on Kokanee Glacier, BC and to the west on Easton Glacier, Mount Baker, WA. There is considerable exposed firn on both glaciers, snow that was retained in recent years, indicative that the glacier had been stripped of more snowcover than other years. The gray color of the firn indicates it is dirty, which will enhance melting.
Jackson and Blackfoot Glacier in late early September of 2019 and 2020 Sentinel 2 false color images. Point A indicates areas of retained accumulation. layers. Point F indicates exposed firn that had been retained through previous summers.
Blackfoot Glacier (B) and Jackson (J) Glacier snowpack in 2005 and 2015.
The southwest side of Kokanee Glacier from the ridge with Cond Peak at the Right and Sawtooth Ridge at center.
By Ben Pelto, PhD, UBC Mitacs Elevate Postdoctoral Research Fellow
Since 2013 I have been working on the Kokanee Glacier. Located just outside of Nelson in southeastern British Columbia (BC), the Kokanee Glacier is due north of the Washington-Idaho border. This work began as part of a five-year study of the cryosphere in the Canadian portion of the Columbia River. This project was carried out by the Canadian Columbia River Snow and Glacier Research Network — spearheaded by the Columbia Basin Trust. The glacier research, which included the Kokanee Glacier, was led by my former PhD supervisor at the University of Northern British Columbia Dr. Brian Menounos and myself. At the culmination of the project, we published a technical report, and a plain language summary of that report. When the five-year project officially ended in 2018, I learned of a BC Parks program called Living Labs, which offers funding for climate change research in BC Parks, particularly research which documents change and guides protected area management. With Living Labs funding in 2019-2021, I have kept the annual mass balance trips going — now a continuous nine-year record — and a winter mass balance trip in 2021. In conjunction with this, Brian Menounos has secured continued funding (continued from our 5-year project) from BC Hydro for LiDAR surveys of the glacier every spring and fall. These surveys are carried out by the Airborne Coastal Observatory team from the Hakai Institute.
During the 2021 spring trip, we found that the Kokanee Glacier had an average snow depth of 4.4 meters. Using snow density measurements collected with a snow-corer, we found that the winter balance for 2021 was 1.91 meters water equivalent (m w.e.). This value was lower than the 2013-2020 average of 2.18 m w.e. (Pelto et al. 2019).
Ali Schroeder probing snow depth on the Kokanee Glacier while Joel McBurney and Drew Copeland look on.
Ben Pelto with the snow corer with Tom Hammond and Micah May on Kokanee Glacier. Photo: Jill Pelto
With a below average winter balance, 2021 would need to feature a cool summer. Instead, multiple heat waves occured, with temperature records being broken across the province. Wildfires burned all over BC and the neighboring US states of Washington and Idaho, swamping the region in smoke for weeks on end. Rather than mitigate for a slightly-below-normal snowpack on the Kokanee, summer 2021 took a blow-torch to glaciers across the region.
We hiked into the Kokanee Glacier on September 12, stopping under a boulder to wait out proximal booms of thunder and flashes in the clouds. We got pelted with bursts of both hail and graupel, and soaked in the rain, before gingerly working our way up boulder field and talus that is climbers route up the Keyhole to the Kokanee Glacier. Like the satellite imagery had shown, there was no snow in sight on the glacier — bare ice only. Instead of my usual camp on the snow, we chose a climbers bivy site to set our tent.
Camp in the Keyhole — a total lack of snow forced us to skip camping on-glacier.
The Keyhole route, a challenging scramble with 43 lb packs.
Stepping out onto the glacier, we immediately ran into difficult terrain, crevasse bridges of snow or firn had collapsed, leaving bedroom-width crevasses gaping open, necessitating an exercise in maze navigation. Our first stop was a stake at 2600 m which typically retains snow (50 to 100 cms), but this year had lost 1.6 meters. In fact, two stakes drilled at the site in 2015 and subsequently buried by snow had melted out, demonstrating that all snow/firn from the intervening years had been lost. This observation clued me in to the magnitude of melt to expect this year.
The first stake visited, showing 1.6 m of melt
Exposed layers of firn in a crevasse by the stake, showing 1.5 m-thick annual layers — now being eaten away by melt.
Travel on the glacier was more challenging in spots, but overall faster, as the total lack of snow meant that most crevasse bridges were gone, requiring less probing of crevasse bridges and roped-travel. Later, using a satellite image from the dates of our visit, I mapped the retained snow cover, limited to two tiny patches high on the glacier’s east side. The accumulation area ratio (AAR), or the ratio of snow cover to bare ice/firn was <0.01, meaning that under 1% of the glacier was covered in snow.
The upper reaches of Kokanee Glacier to Cond Peak (2800 m) with no retained snow in 2021. Bare ice is exposed on the lower half of the image, and firn, or multi-year snow above
The brown surface is multi-year firn, exposed by the loss of snow. In a typical year, the snow line would be visible here. The white surface below the brown is bare glacier ice.
Near infrared-Red-Green 30 cm resolution ortho image of Kokanee Glacier from the Hakai Geospatial/ACO team on Sept. 2, 2021. Note how badly crevassed the glacier is, most crevasses are exposed with no retained snow. The white color and mottled appearance over the upper glacier is a skiff of overnight snow just a few centimeters thick that melted off the next day. Also note bare ice patches exposed under formerly perennial snow patches that have shrunk in recent years and now are disappearing.
Visiting the toe of the glacier, our lowest stake indicated just under 5 m of ice melt, double that of 2020. In May, this location had 3 m of snow; the combined melt of snow and ice (loss of winter snow and glacier ice) is termed the summer mass balance, and at this site was -6.2 m w.e., far higher than the usual -4 m w.e. I also noticed that much of the thin ice along the margin of the toe was gone, and a little rock nunatak (rock island) that appeared in 2015 (images below) became a bite out of the glacier rather than a island. We estimated that the toe experienced 60 m of retreat. Over the past 5 years, the Kokanee has lost an average of 16 m in length annually. Expecting to see above average thinning and retreat, I was still startled to see how diminished and thin the toe looked.
2015: a small hole forms in the glacier margin above the toe, Jesse Milner in the foreground
2021: the hole is now a bite out of the glacier with two prominent rock knobs
A week prior to my field visit, the Hakai Institute ACO team flew a LiDAR survey of the Kokanee Glacier as part of their work with Brian Menounos at UNBC. Comparing this year’s glacier surface with that from last year’s survey, Brian found a whopping 2.55 m of thinning. After mapping the glacier facies (ice/firn/snow) to represent on the density of the observed thinning, this equates to a glacier mass balance of -2.16 m w.e., higher than the previous record loss of -1.20 m w.e. in 2015.
LiDAR-derived height change 2020 to 2021 from 1 m resolution DEMs from Brian Menounos and the Hakai Institue ACO team. The black line is the 2021 glacier outline, note the bite out of the glacier above the toe to the NE corner of the glacier. Small red patches off-ice are seasonal snow patches losing mass. Points represent mass balance observation locations.Kokanee Glacier terminus from 2015 to 2021. 140 meters of retreat for 23 m/yr. Data in the GIF are from Hakai Institute and Brian Menounos of UNBC ACO glacier surveys.
Back home, I crunched the numbers from our glaciological observations of mass balance (consisting of 14 ablation stakes this year) and calculated a mass balance of -1.97 m w.e. With Brian, I published a paper in 2019 (Pelto et al. 2019) comparing glaciological (field) and geodetic (LiDAR) mass balance estimates and found them to be similar — if some factors like snow and firn density were carefully considered. The small difference between estimates is likely due to timing (the LiDAR mass balance is from 8/26/2020 to 9/3/2021, while the field mass balance is 9/12/2020 to 9/13/2021), and that there was a skiff of fresh snow (likely 5-10 cms) on the glacier during the 2020 LiDAR survey.
Kokanee 2021 glacier mass balance. Blue dots are observations. The boxplots show the 100 m bins used to estimate glacier-wide mass balance (median line in black, mean dashed grey line). The grey bars depict the area of the glacier for each 100 m elevation-bandSeasonal and annual mass balance for Kokanee Glacier from LiDAR and glaciological measurements for each balance year from 2013 to 2021 with 2σ uncertainties.
In 2017, I visited the Kokanee Glacier to measure it’s ice thickness using ice-penetrating radar. I found that the glacier on average was 43 m thick using my measurements to tune a glacier model. I published these results in the Journal of Glaciology (Pelto et al. 2020). In the five years since that work, the glacier has lost over 4.8 m of total thickness. That equates to a loss of over 11% of its total volume. 2021 alone wasted away 6% of the glacier’s total volume — an eye-watering number for a single year.
Cumulative mass balance for Kokanee Glacier 2013-2021 from both field and LiDAR measurments. LiDAR-derived mass balance began in 2016.
The heat of 2021 was an outlier, but years like 2021 and 2015 take a toll on the glaciers. Currently, glaciers in western North America are losing around 0.75 m of thickness per year (according to my work in the Columbia Basin (Pelto et al. 2019) and work by Brian Menounos for all of western North America (Menounos et al. 2018)). The better years for Kokanee Glacier (2016 mass balance: +0.12 m w.e.) pale in comparison. That meager surplus was lost the very next year (2017).
Herein lies the issue, positive mass balance years in recent decades are not large enough to offset even average years; hot dry summers take years off the lifespan of glaciers across western North America.
Losing 6% of it’s total volume in 2021, the best we can hope for Kokanee Glacier is a few near-neutral or positive mass balance years to cover back up the exposed firn, to keep the glacier albedo from becoming too dark and increasing the rate at which ice can melt.
The southwest side of Kokanee Glacier from the ridge with Cond Peak at the Right and Sawtooth Ridge at center.
Since 2013 I have been working on the Kokanee Glacier. Located just outside of Nelson in southeastern British Columbia (BC), the Kokanee Glacier is due north of the Washington-Idaho border. This work began as part of a five-year study of the cryosphere in the Canadian portion of the Columbia River. This project was carried out by the Canadian Columbia River Snow and Glacier Research Network — spearheaded by the Columbia Basin Trust. The glacier research, which included the Kokanee Glacier, was led by my former PhD supervisor at the University of Northern British Columbia Dr. Brian Menounos and myself. At the culmination of the project, we published a technical report, and a plain language summary of that report. When the five-year project officially ended in 2018, I learned of a BC Parks program called Living Labs, which offers funding for climate change research in BC Parks, particularly research which documents change and guides protected area management. With Living Labs funding in 2019-2021, I have kept the annual mass balance trips going — now a continuous nine-year record — and a winter mass balance trip in 2021. In conjunction with this, Brian Menounos has secured continued funding (continued from our 5-year project) from BC Hydro for LiDAR surveys of the glacier every spring and fall. These surveys are carried out by the Airborne Coastal Observatory team from the Hakai Institute.
During the 2021 spring trip, we found that the Kokanee Glacier had an average snow depth of 4.4 meters. Using snow density measurements collected with a snow-corer, we found that the winter balance for 2021 was 1.91 meters water equivalent (m w.e.). This value was lower than the 2013-2020 average of 2.18 m w.e. (Pelto et al. 2019).
Ali Schroeder probing snow depth on the Kokanee Glacier while Joel McBurney and Drew Copeland look on.
Ben Pelto with the snow corer with Tom Hammond and Micah May on Kokanee Glacier. Photo: Jill Pelto
With a below average winter balance, 2021 would need to feature a cool summer. Instead, multiple heat waves occured, with temperature records being broken across the province. Wildfires burned all over BC and the neighboring US states of Washington and Idaho, swamping the region in smoke for weeks on end. Rather than mitigate for a slightly-below-normal snowpack on the Kokanee, summer 2021 took a blow-torch to glaciers across the region.
We hiked into the Kokanee Glacier on September 12, stopping under a boulder to wait out proximal booms of thunder and flashes in the clouds. We got pelted with bursts of both hail and graupel, and soaked in the rain, before gingerly working our way up boulder field and talus that is climbers route up the Keyhole to the Kokanee Glacier. Like the satellite imagery had shown, there was no snow in sight on the glacier — bare ice only. Instead of my usual camp on the snow, we chose a climbers bivy site to set our tent.
Camp in the Keyhole — a total lack of snow forced us to skip camping on-glacier.
The Keyhole route, a challenging scramble with 43 lb packs.
Stepping out onto the glacier, we immediately ran into difficult terrain, crevasse bridges of snow or firn had collapsed, leaving bedroom-width crevasses gaping open, necessitating an exercise in maze navigation. Our first stop was a stake at 2600 m which typically retains snow (50 to 100 cms), but this year had lost 1.6 meters. In fact, two stakes drilled at the site in 2015 and subsequently buried by snow had melted out, demonstrating that all snow/firn from the intervening years had been lost. This one observation clued me in to the magnitude of melt to expect this year.
The first stake visited, showing 1.6 m of melt
Exposed layers of firn in a crevasse by the stake, showing 1.5 m-thick annual layers — now being eaten away by melt.
Travel on the glacier was more challenging in spots, but overall faster, as the total lack of snow meant that most crevasse bridges were gone, requiring less probing of crevasse bridges and roped-travel. Later, using a satellite image from the dates of our visit, I mapped the retained snow cover, limited to two tiny patches high on the glacier’s east side. The accumulation area ratio (AAR), or the ratio of snow cover to bare ice/firn was <0.01, meaning that under 1% of the glacier was covered in snow.
The upper reaches of Kokanee Glacier to Cond Peak (2800 m) with no retained snow in 2021. Bare ice is exposed on the lower half of the image, and firn, or multi-year snow above
The brown surface is multi-year firn, exposed by the loss of snow. In a typical year, the snow line would be visible here. The white surface below the brown is bare glacier ice.
Visiting the toe of the glacier, our lowest stake indicated just under 5 m of ice melt, double that of 2020. In May, this location had 3 m of snow; the combined melt of snow and ice (loss of winter snow and glacier ice) is termed the summer mass balance, and at this site was -6.2 m w.e., far higher than the usual -4 m w.e. I also noticed that much of the thin ice along the margin of the toe was gone, and a little rock nunatak (rock island) that appeared in 2015 (images below) became a bite out of the glacier rather than a island. We estimated that the toe experienced 60 m of retreat. Over the past 5 years, the Kokanee has lost an average of 16 m in length annually. Expecting to see above average thinning and retreat, I was still startled to see how diminished and thin the toe looked.
2015: a small hole forms in the glacier margin above the toe, Jesse Milner in the foreground
2021: the hole is now a bite out of the glacier with two prominent rock knobs
A week prior to my field visit, the Hakai Institute ACO team flew a LiDAR survey of the Kokanee Glacier as part of their work with Brian Menounos at UNBC. Comparing this year’s glacier surface with that from last year’s survey, Brian found a whopping 2.55 m of thinning. After mapping the glacier facies (ice/firn/snow) to represent on the density of the observed thinning, this equates to a glacier mass balance of -2.16 m w.e., higher than the previous record loss of -1.20 m w.e. in 2015.
LiDAR-derived height change 2020 to 2021 from 1 m resolution DEMs from Brian Menounos and the Hakai Institue ACO team. The black line is the 2021 glacier outline, note the bite out of the glacier above the toe to the NE corner of the glacier. Small red patches off-ice are seasonal snow patches losing mass. Points represent mass balance observation locations.
Back home, I crunched the numbers from our glaciological observations of mass balance (consisting of 14 ablation stakes this year) and calculated a mass balance of -1.97 m w.e. With Brian, I published a paper in 2019 (Pelto et al. 2019) comparing glaciological (field) and geodetic (LiDAR) mass balance estimates and found them to be similar — if some factors like snow and firn density were carefully considered. The small difference between estimates is likely due to timing (the LiDAR mass balance is from 8/26/2020 to 9/3/2021, while the field mass balance is 9/12/2020 to 9/13/2021), and that there was a skiff of fresh snow (likely 5-10 cms) on the glacier during the 2020 LiDAR survey.
Kokanee 2021 glacier mass balance. Blue dots are observations. The boxplots show the 100 m bins used to estimate glacier-wide mass balance (median line in black, mean dashed grey line). The grey bars depict the area of the glacier for each 100 m elevation-band
In 2017, I visited the Kokanee Glacier to measure it’s ice thickness using ice-penetrating radar. I found that the glacier on average was 43 m thick using my measurements to tune a glacier model. I published these results in the Journal of Glaciology (Pelto et al. 2020). In the five years since that work, the glacier has lost over 4.8 m of total thickness. That equates to a loss of over 11% of its total volume. 2021 alone wasted away 6% of the glacier’s total volume — an eye-watering number for a single year.
Cumulative mass balance for Kokanee Glacier 2013-2021 from both field and LiDAR measurments. LiDAR-derived mass balance began in 2016.
The heat of 2021 was an outlier, but years like 2021 and 2015 take a toll on the glaciers. Currently, glaciers in western North America are losing around 0.75 m of thickness per year (according to my work in the Columbia Basin (Pelto et al. 2019) and work by Brian Menounos for all of western North America (Menounos et al. 2018)). The better years for Kokanee Glacier (2016 mass balance: +0.12 m w.e.) pale in comparison. That meager surplus was lost the very next year (2017).
Herein lies the issue, positive mass balance years in recent decades are not large enough to offset even average years; hot dry summers take years off the lifespan of glaciers across western North America.
Losing 6% of it’s total volume in 2021, the best we can hope for Kokanee Glacier is a few near-neutral or positive mass balance years to cover back up the exposed firn, to keep the glacier albedo from becoming too dark and increasing the rate at which ice can melt.
Bonnet Glacier in Sentinel 2 images indicating the emergence of bedrock due to thinning in the former accumulation zone, Point A. Note the lack of retained snowcover in both years with at least a month left in the melt season.
Bonnet Glacier, Alberta drains north from Bonnet Peak in the Sawback Range 30 km east of the Rocky Mountain Crest. It is at the headwaters of Douglas Creek that feeds into the Red Deer River. In 2017 we reported on the formation of new alpine lakes and the 900 m retreat of the glacier, 20% of its length, from 1987-2016 (Pelto, 2017). Here we examine changes from 1987-2021, including developments in the accumulation zone that provide a future forecast. An inventory 0f glaciers in the Canadian Rockies indicated area loss of 15% from 1985 to 2005 (Bolch et al, 2010), with Alberta glaciers losing area at a higher rate. Tennant et al (2012) noted that from 1919-2006 the glaciers in the central and southern Canadian Rocky Mountains lost 40% of their area. Of the 523 glaciers they observed 17 disappeared and 124 separated. Columbia Icefield, 125km northwest, lost 23 % of its area from 1919-2009 (Tennant and Menounos, 2013).
In 1987 and 1990 the accumulation zone is limited to upper periphery of Bonnet Glacier. In 2015 and 2016 the accumulation zone is restricted to the northeastern periphery. This is indicative of a glacier without a significant persistent accumulation zone. The consistent mass loss is driving the retreat and glacier thinning. In 2018 in the midst of what had been the accumulation zone a small area of bedrock has emerged at Point A. By 2021 this area has expanded substantially with the two bedrock areas poised to merge soon. This thinning in the midst of the former accumulation zone is indicative of a glacier that cannot survive (Pelto, 2010). In 2015, 2018 and 2021 the accumulation area ratio was between 10-15%, a value that typically results in glacier annual mass balance of more than -2 m. The area of main proglacial expanded 50% from 2016 to 2021 to 0.33 square kilometers.
Bonnet Glacier in Landsat images from 1987, 2016 and 2021 indicating retreat. Red arrows indicate 1987 margin, yellow arrows 2016 and the green arrow 2021. Point A indicates the emerging bedrock.
Bonnet Glacier in Landsat images from 1990, 2015 and 2021 indicating retreat. Purple arrows indicate lakes that have formed due to retreat. Point A indicates the emerging bedrock.
Southeast #3 Glacier, Devon Ice Cap in July 9, 2016 and August 29, 2021 Sentinel 2 images of the lower 10 km showing three supraglacial streams S1, S2 and S3 and the outlet plumes of each stream at Point 1-3. The yellow line is the 2016 margin.
The southeast sector of the Devon Ice Cap, Devon Island, Nunavut has three tidewater outlet glaciers Southeast Glacier #1, #2 and #3. Van Wychen et al (2017) indicate the dynamic discharge of the three at .06-.07 Gt per year, all three glaciers have been retreating during this period. Southeast #3 is between 0.01 and 0.02 Gt per year. Sharp et al (2011) note that increasing summer temperatures has led to increased mass loss on Devon Ice Cap. Here we examine retreat and the supraglacial stream networks using Landsat and Sentinel 2 imagery.
In 2002 the calving front of Southeast #3 Glacier extended north from with five distinct peninsulas of ice. The retreat by 2016 was more pronounced on the north south oriented southern portion of the front than the northwestern part. From 2016 to 2021 it is evident that the glacier front has receded, particularly at the prominent ice peninsulas evident in 2016. The retreat averages 600 m across the 5 km wide tidewater front seen above from 2016-2021. This is an addition to the 1200 m retreat from 2002-2016, while the northwestern section retreated ~500 m during the 2002-2021 period. S1, S2 and S3 indicates supraglacial stream drainages that exit the glaciers at Point 1-3 respectively. The plumes of sediment from these streams is evident in the July 24, 2020 image below from each of these surface outlet streams. The plumes are evident in the July 2016 image, but no the late August image of 2021. The lack of plumes on 8-29-2021 indicate the lower melt rates that are typical of late August. The stream network has become more prominent as melt rates have led to greater flow and more incising into the ice.
This retreat has occurred during the same period that was noted as generating three new islands in 2018 on the northeast margin of the Devon Ice Cap. Noel et al (2018) observe that this is part of a trend seen across Canadian Arctic ice caps have been losing mass for decades and that mass loss accelerated in 1996.
July 24, 2020 Sentinel 2 image of the lower 10 km of Southeast #3 Glacier showing three supraglacial streams S1,S2 and S3 and the outlet plumes of each at Point 1-3.
Southeast #3 Glacier in 2002 and 2021 Landsat images. Yellow dots indicate the 2002 margin of the glacier.
Adams Glacier in Sentinel 2 False Color image from 8-30-2021. Green dots indicate margin of the Adams Glacier and the now separated Adams Outlier section. The pink arrows indicate the top and bottom of the icefall. F=regions of exposed firn, A=areas of perennial retained accumulation.
Adams Glacier descends the north side of Mount Adams a 3743 m stratovolcano in the Cascade Range of Washington. The glacier begins from the summit plateau between 3600 m and 3700 m, before descending a steep icefall down to 2750 m and then diverging on lower slopes terminating at 2225 m. Sittts et al (2010) mapped the area change of Mount Adams glaciers from 1904 to 2006. The area was 6.93 km2 in 1904 declining to 5.16 km2 by 1969, 4.62 km2 by 1998, and 3.68 km2 in 2006. This decline since 1969 has been due largely to increased summer temperatures (Sittts et al 2010) . Here we examine the impact of the particularly warm summer of 2021 on snowpack, glacier volume and reassess the area of the glacier. The winter of 2021 had above average snowfall with 157% of the mean peak winter snowpack in April at the nearest Snotel site at Potato Hill ( 1375 m), the snowpack loss date after a dry May was the same as usual, see figure below. The mean June-August temperature at the Mount Adams Ranger Station (600 m) was the second warmest for the 1984-2021 period to 2015.
Snowpack loss from June 21 to August 25 in Sentinel images. AO=Adams Outlier, T=Terminsu Zone, I=Icefall, S= bergshrunds on upper glacier.
On June 21, 2021 nearly the entire glacier is snowcovered, which is typical. By July 1, 2021 areas of the glacier below the icefall are rapidly losing snowcover. By August 15, 50% of the glacier has retained 2021 snowcover. This rapidly diminishes to ~10% by Aug. 25, 2021. On Aug. 30, 2021 there are large areas above 10000 feet that typically retain snowcover to the end of the summer that have lost all snowcover and are particularly dirty firn, snow that fell in recent years but has not been converted to glacier ice. The retained snowcover is in five patches, the lower three are all avalanche runout zones and the upper two regions, above the icefall, of wind drift redeposition.
Adams Glacier in Sentinel 2 True Color image from 8-30-2021. Pink arrows indicate icefall top and bottom. S=summit area, A=Areas where limited pockets of 2021 snowpack has been retained through August.
Similar to Whitney Glacier on Mount Shasta , Adams Glacier will not retain snowcover in 2021. The early exposure of bare firn and ice, which melt at a faster rate than snow is causing rapid mass losses on the upper glacier this summer, as we have reported from Easton Glacier on Mount Baker. The current area of the main glacier is 1.9 km2, with the outlier have an area of 0.3 km2. The combined area of 2.2 km2 is less than 50% of the 1998 total. The loss of snowpack from the Adams Glacier is greater than in any year since 1984, exceeding 2015. The winter of 2015 had less snowfall and the mean summer temperature was warmer. The key difference is likely the excessive melt of the late June 2021 heat wave that is particularly impactful early in summer. Finn et al (2017) noted that the upper reaches of Adams Glacier ranged from ~25 to 60 m thick, while lower down on the volcano are the glacier is less than<~30m thick. This summer mass losses will be in the 2-3 m range on Adams Glacier, based on the duration of exposed ice and percentage of the glacier in the accumulation zone. This will represent a 5-10% volume loss for this glacier in 2021.
Snowpack at Potato Hill (1375 m) a Snotel site. The 2021 winter had above average peak snowpack (black line), but typical melt out date.
Sentinel 2 False and True Color images from 8-25-2021. Yellow arrows indicate where glacier is separating and purple arrows the small remanent of 2021 snowpack remaining. This remanent will not last to the end of the melt season.
The summer of 2021 is proving to be catastrophic for Whitney Glacier on Mount Shasta, California in terms of volume loss, ~15-20% this year leading to long term impacts, adding to the 50% area reduction and 1000 m retreat since 2005. The glacier will lose 100% of its 2021 snowpack and is in the process of separating into two glaciers. Here we review the glaciers behavior in recent decades and examine using Sentinel Imagery the impacts in summer of 2021.Mount Shasta is a stratovolcano home to the largest glaciers in California, Whitney Glacier on the north side is the longest. In 1981 USGS (Driedger and Kennard, 1986) mapped the area and volume of several of the glaciers, in a landmark study of glacier volume on Cascade volcanoes. Whitney Glacier had an area of 1.3 km2, a maximum depth of 38 m, and a volume of 25 million m 3. The majority of the glacier was in the 20-35 m thick range. The glacier was noted as having a length of 3.0 km ending on the USGS map at 9900 feet.
Digital Globe image indicating a area of retreat from 2005-2012 and the limited crevassing near 2012 terminus.
Tulaczyk and Howat (2008) noted that Whitney Glacier did advance during the 2000-2005 period, following a retreat in the 1980’s and 1990’s. The most recent advance was limited to the 1999-2005 period due to heavy snowfall from 1998-2002, ended with the glacier 850 m in advance of its 1951 position. There was a period of advance for many Cascade volcanoes glaciers between 1950 and 1980, followed by retreat after. On Mount Baker, Washington all of the glaciers advanced during the 1944-1979 period by an average of 480 m (Pelto and Hedlund, 2001). By 2010 Pelto and Brown (2012) observed all were retreating with an average retreat of 370 m. In 2012 the glacier is thin in its lower reaches with no crevassing. By 2014 the terminus of the glacier had retreated 700 m from 2005 and was 2.6 km in length and terminated at 10200 feet, 300 feet higher than a decade before or in the 1981 map.
Sentinel 2 True Color images from 6-16-2021, 6-28-2021 and 7-18-2021 illustrating the progressive snowcover loss on the glacier. Point A and D are on the upper Glacier, Point B is where the upper and lower glacier have joined and Point C is near the top of the lower glacier.
The summer of 2021 followed a 15 year period of overall significant mass loss and retreat on Whitney Glacier that led to a thinner glacier with a reduced velocity and consequently fewer crevasses. The stage was set with 60-75% of normal snowpack in early April 2021 at the stations in the region in the 6000-7600′ range, dropping to 20-25% of normal by early May (CDEC, 2021). This was followed by an exceptionally warm early summer, that helped strip the snowpack away early. By June 16, the snowline on Whitney Glacier had risen to 10,800 feet, near Point C, while the upper glacier extending from Point A and D to Point C was nearly all snowcovered. By June 28 the snowline had risen to 11,200 feet on the lower glacier and the upper glacier snowline was near 12,500 feet, with the west facing upper section (Point A) above 13000 feet nearly all bare. By July 18 there is a small area of snowcover near Point C on the lower glacier and Point D on the upper glacier. Most of the glacier is bare of snowcover. This underscores the particularly detrimental impact of early season heat waves that strip away winter snowpack and exposes the dirtier glacier ice and firn. The ice and firn melt ~30% faster than the snowcover for the same weather conditions. Our measurements on Mount Baker during heat waves over the last three decades indicate typical ice melt of 7-9 cm of melt per day. The average temperature over the last 70 days since much of the glacier was bare ice has been 16.8 C at Snow Bowl station at 7617 feet. Given area summer lapse rates this equates to a temperatures of ~12-13 C at the mean glacier elevation. The temperature at this station reached 29 C on June 27, 28 C on June 28 and exceeded 25 C from June 25-June 30. The rapid melt rate led to a number of areas of slushy, swampy glacier surface conditions even high on the glacier (Mount Shasta Avalanche Center ). Using the degree day formula for melt derive on Mount Baker during warm summer conditions (Pelto, 2015 and 2018) of .0053m w.e.C-1D-1, yields a cumulative melt of 4.8 m w.e., equivalent to over 5 m of ice thickness.
This given mean ice thickness in the 25-30 m range indicates that this summer ~15-20% of the glacier ice volume will be lost on Whitney Glacier. The glacier is now 2300 m long and has an area of 0.6 km 2, which is less than 50% of its area just 16 years ago. This is leading to separation of the lower and upper glacier at the yellow arrows. There is certainly still stagnant ice in this zone, but there is no longer a dynamic connection between the upper and lower Whitney Glacier.
Topographic map of Mt. Shasta.indicating the top of Whitney Glacier near the summit of Shasta and the ~1981 and 2005 terminus position.
Terminus of Columbia Glacier on left with 1984 terminus location noted. Observe the avalanche fans (A) and the relatively high snowcover on 8-2-2021. At right is Easton Glacier on 8-11-2021 with the location of the 1990 terminus indicated, 440 m of retreat to the 2021 terminus position. The glacier has only 38% snowcover at this time, which is better illustrated below.
Columbia and Easton Glacier in the North Cascade Range of Washington are two of the reference glaciers for the World Glacier Monitoring Service. We have monitored their mass balance in the field for 38 and 32 years consecutively. This year Ashley Parks, Sally Vaux, Jill Pelto and I worked on all of the glaciers with Abby Hudak, Rose McAdoo and Ben Pelto joining us for either Easton or Columbia Glacier. In 2021 a combination of an above average winter snowfall and a record summer melt has led to a different story of mass balance for the two glaciers. At Mount Baker and Stevens Pass winter snowpack on May 1 was 116% and 115% of normal (NWAC, 2021). From June 1-Aug. 17 the mean average temperature is similar to 1958 and 2015, and well above every other year. With the maximum temperature exceeding 80 F on 17 days during this period at Stevens Pass ( 3950 ft, 1200 m), each of those days represents exceptional melt conditions. Our observations indicate 11-14 cm of snowpack melt on glacier during exceptionally warm days like this. Just the melt from these 17 days would equate to half of the average summer melt for a North Cascade glacier (Pelto, 2018). The earlier summer heat wave has led to exposure of greater higher albedo and faster melting glacier ice, which is why such a heat wave is more impactful than in late summer.
Columbia Glacier occupies a deep cirque above Blanca Lake ranging in altitude from 1400 meters to 1700 meters. Kyes, Monte Cristo and Columbia Peak surround the glacier with summits 700 meters above the glacier. The glacier is the beneficiary of heavy orographic lifting over the surrounding peaks, and heavy avalanching off the same peaks. Standing on the glacier is a bit like being in the bottom of a bath tub, with avalanche slopes extending up both sides, predominantly on the west side. The last half of January 2021 was a dry period in the region, with an extensive crust forming on the snowpack. This was followed by 106 inches of dry snowfall from Feb. 4 to Feb. 20,and then 34 inches of wet snowfall and even rain through Feb. 24 This generated extreme avalanche danger and numerous climax avalanches in the Stevens Pass region.
NWAC’s avalanche forecast on 2/20 for Stevens Pass indicated that, “We haven’t seen rain above 3,500ft or so since mid-January, so one of the main concerns is that slabs 5-10′ feet thick may begin to come crashing down. The avalanche cycle(s) may last through the day Monday. In any case, very large storm slabs and wet loose avalanches are expected to continue to run from steep slopes through Monday as our once beautiful cold, dry snow becomes overloaded by wet, heavy rain and snow.”
The avalanche slopes with many pockets above Columbia Glacier in Aug. 2020, one fan can be seen bottom center. These have to filled each winter season before slides occur, in 2020 avalanching was limited.
As we headed up onto Columbia Glacier on Aug. 1, 2021 we noted a significant number of large avalanches had descended near and onto the glacier. The glacier was 87% snowcovered, including the terminus area. This is well above the recent early August average. As is the case every year we measure snow pack depth in a grid across the entire glacier. Snow depth in the three biggest west side avalanche fans averaged 4.9 m, 25% above normal. The three largest fans comprise an area of 0.14 km2, yielding a volume of 686, 000 m3 swe. The melt season ends in another month, however, due to this substantial avalanching that will keep this section of the glacier covered in snow, Columbia Glacier will have a small-moderate negative mass balance.
Ashley Parks, Jill Pelto and Sally Vaux measuring snow depth in the Columbia Glacier avalanche fans.
The three primary avalanche fans each had a slope of 23 degrees. Here we are spaced out at 50 m intervals mapping the size of the fan.
Easton Glacier on the south flank of Mount Baker does not recieve avalanche accumulation, and the regions above 2500 m, typically have significant wind scouring, that leads to little increase in mass balance with elevation above this elevation on the upper glacier. There are both basins where snow is preferetially deposited by wind and convex regions where snowpack is scoured. In 2021 enroute to the glacier terminus we observed considerable stunted alpine vegetation, that emerged and then did not grow. This was prevalent on rocky slopes that were exposed during the heat wave. The example below is of Lupine with the growth from last year now brown and flat indicating the stunted size this year.
Stunted Lupine, each patch is typically 20-30 cm high and equally broad. Here the plants are 3-5 cm high.
On Aug. 11, 2021, the glacier had only 38% snowcover, with more than 50% of the area above 2500 m having lost all winter 2021 snowcover. By summer’s end the glacier will certainly have the lowest percentage of snowcover of any year since we began monitoring in 1990. The bench at 2000 m typically has 2.75 m of snowpack on Aug. 10, and this year was 50% bare, with an average depth of 0.25 m. The icefall above also lacked snowcover as well. There are a number of pockets/basins, where wind deposition increased snow depth and this snowpack will be retained.
The observations across the range illustrated that glaciers or areas of glaciers that do not have enhanced deposition from wind drifting or avalanching are either bare already or will be by the end of August. The full extent of the loss on Columbia and Easton Glacier from this summer will be evident in a month. What is apparent is that the losses from Easton Glacier will be extraordinary. More frequent heat waves continue to plague alpine glaciers, these can even occur in winter such as on Mount Everest in January 2021 (Pelto et al. 2021)
View of the lack of snowcover in the icefall at 2000-2300 m on Easton Glacier. The lack of snowcover above this point is also evident in the upper image.
Rose McAdoo and Jill Pelto measuring the 2021 snowpack at 2350 m is alareay thinner than the 2020 or 2019 retained snowpack and will be gone by the end of the month.
In 2021, I am in front of the same serac as in 2020, down slope. The average retained accumulation at this 2600 m location in the laterally extensive layers is 2-2.2 m. This year there will no retained accumulation.
Ben and Jill Pelto amongst the seracs where snowpack should be extensive, but in 2021 they are standing on 2020 firn.
A few measures of what it takes to execute a field monitoring program of glaciers for 37 years, with no helicopter support (Illustration by Megan Pelto).
2021 Field Season: For the 38th consecutive summer we are heading into the field later this week to measure the impact of climate change on North Cascade glaciers. We will complete detailed measurements on 10 glaciers, three of which are part of the World Glacier Monitoring Service reference glacier network (42 glaciers globally) that have 30 consecutive years of mass balance observations. This field season follows both a historic heat wave at the end of June and a month long sustained period of warm weather that has extended from Late June to now. We have observed the rise of the snow line around Mount Baker from a lower than average late June ~1200 m on June 23 to ~1850 m on July 23, average in late July is 1750 m. The result is a greater exposure of bare ice on glaciers with summer only half over. For ice surfaces with a higher albedo and greater density the observed melt rates are 7-9 cm/day water equivalent during warm weather events vs 4-6 cm/day for snow surfaces. We will provide preliminary observations in three weeks when the field season is completed as we did with the 2020 Field Report.
Who we are? NCGCP was founded in 1983 to identify the response of North Cascade glaciers to regional climate change, particularly changes in mass balance, glacier runoff and terminus behavior. NCGCP is a field project that has a broader interdisciplinary scope and examines more glaciers than any other program in North America. It does so cost effectively relying on no permanent camps, helicopter support or salaries for the director. The field season includes no days off and each day is spent completing measurements on glaciers. The focus is on glacier mapping, mass balance measurement, terminus observations and glacier runoff monitoring.
Why study glaciers in the North Cascades? Glaciers are one of the world’s best climate monitors and are a critical water resource to many populated glaciated regions. This is particularly true in the North Cascades where 700 glaciers yield 200 billion gallons of summer runoff and glaciers have lost 30 % of their area in the last century. This has reduced glacier runoff in late summer in the region as the reduction in glacier area has been exceeded the increase in melt rate (Pelto, 2011) .
Field Team 2021:
Jill Pelto is an artist and scientist from New England who grew up loving winter sports and trips to the mountains. She incorporates scientific research and data into paintings and prints to communicate environmental changes. Her multi-disciplinary work weaves visual narratives that reveal the reality of human impacts on this planet. She completed both her B.A. degrees in Studio Art and Earth and Climate Science and her M.S. focused on studying the stability of the Antarctic Ice Sheet at the University of Maine, spending two field seasons at a remote camp in the southern Transantarctic Mountains. Jill will be joining the project for her 13th field season. She is excited to continue documenting North Cascade Glacier changes that she has witnessed each of the last 12 years—through science and art.
Jill Pelto sketch of Easton Glacier Icefall
Mauri Pelto has directed the project since its founding in 1984, spending more than 700 nights camped out adjacent to these glaciers. He is the United States representative to the World Glacier Monitoring Service, author of the AGU blog “From a Glacier’s Perspective”, and associate editor for three science journals. His primary job is Dean of Academic Affairs at Nichols College, where he has been a professor since 1989.
Mauri Pelto probing on Easton Glacier
Sally Vaux (she/her) is an incoming MS student in Environmental Science at Western Washington University. Her research interests include the impacts of aerosol deposition on snow and ice melt and equitable K-12 science education. While obtaining her BS in Environmental Science from WWU, Sally began a water quality monitoring project focused on dissolved organic carbon in the Nooksack River. This summer, she is working on a NASA Space Grant project to understand how climate-driven increases in frequency and intensity of wildfires in the Arctic lead to light-absorbing aerosol deposition on sea ice and how these deposits impact ice albedo. She will also be working to adapt polar and alpine snow science into lessons for elementary and middle school students in Whatcom County, WA. Outside of school and work, Sally likes to run, ski, bike, and read.
Ashley Parks is a recent Huxley graduate from Western Washington University, Environmental Science. Growing up in Bellingham and being an avid fan of winter sports, she has been able to become familiar with the North Cascade Mountain Range, inspiring her to become interested in the glaciology of her region. As glaciers enter a period of trouble due to the climate crisis, she hopes to connect our understanding of climate change effects on local glaciers, and what that means for local communities. Ashley will also be collecting pink snow for The Living Snow project which is run out of Western Washington University in order to characterize the biodiversity of the algae in the snow and its impact on snowmelt dynamics. This summer’s goal is to be able to communicate her findings through an artistic medium that she can share with others, and to be able to gain experience with field data collection.
Field Partners 2021
Alia Khan’s, research team including grad students Sally Vaux and Shannon Healy focus on environmental chemistry in the cryosphere, including black carbon and snow algae to document global change of glacier and snow melt in mountainous and polar regions.
Rose McAdoo, is a visual artist using desserts to communicate science and make big ideas digestible. Her work pulls her between New York City, Alaska, and Antarctica — where she works as the sous chef for NASA’s Long Duration Balloon atmospheric research camp and as a member of the winter Search and Rescue team. In 2019, her edible documentation of the U.S. Antarctic Program’s field season won the attention of NPR, Forbes, and — most recently — as the featured cover artist for the American Polar Society. She’s currently working as an ice climbing and glacier helicopter guide in Seward, Alaska, and is eager to further visualize the extensive research of the North Cascades Glacier Climate Project.
Cassidy Randall, is a freelance writer covering stories that push the boundaries on how we think about environment, adventure and people exploring the bounds of human potential https://www.cassidyrandall.com/ . She’s on assignment with NCGCP for National Geographic.
Nooksack Indian Tribe, for the 10th consecutive year we will be conducting field work aimed at providing field validation and streamflow calibration data below Sholes Glacier for the ongoing work of the tribe.
Measuring streamflow below Sholes Glacier. Forest fire haze obscuring sky
2021 Schedule
Jul 31: Hike in Columbia Glacier
Aug. 1: Columbia Glacier
Aug. 2: Columbia Glacier
Aug. 3: Hike Out Columbia, Hike in Ptarmigan Ridge
Aug. 4: Sholes Glacier
Aug. 5: Rainbow Glacier
Aug. 6: Rainbow Glacier
Aug.7: Hike out, Hike In Lower Curtis Glacier
Aug. 8: Lower Curtis Glacier
Aug. 9: Hike out, Hike in Easton Glacier
Aug. 10: Easton Glacier
Aug. 11: Easton Glacier
Aug. 12: Hike out Easton/Hike in Daniel
Aug. 13: Ice Worm Glacier Survey
Aug. 14: Daniel and Lynch Glacier Survey
Aug. 15: Hike out
Aug. 16: Arrive home
Landsat images of Tulsequah Glacier on June 22 and July 5, 2021. Lake No Lake is between the yellow arrows with the margin of glacier extending upvally on June 22nd. By July it has receded back to main valley and lake has largely drained. The former location of Tulsequah glacier dammed lake is at red arrow.
Tulsequah Glacier, British Columbia drains east from the Juneau Icefield and is best known for its Jökulhlaups or glacier lake outburst floods (GLOF) from Tulsequah Lake and Lake No Lake dammed by Tulsequah Glacier in northwestern British Columbia, Canada (Neal, 2007). The floods pose a hazard to the Tulsequah Chief mining further downstream. This glacier feeds the Taku River which has seen a significant decline in salmon in the last decade (Juneau Empire, 2017).The continued retreat of the main glacier at a faster rate than its subsidiary glaciers raises the potential for an additional glacier dammed lakes to form. The main terminus has disintegrated in a proglacial lake. Pelto (2017) noted that by 2017 the terminus has retreated 2900 m since 1984, with a new 3 km long proglacial occupying the former glacier terminus. The USGS has a stream gage measuring a range of parameters including turbidity and discharge which can identify a GLOF. Neal (2007) examined the 1988-2004 period identifying 41 outburst floods from 1987-2004. Here we examine Landsat images and USGS records of Taku River to quantify the 2021 GLOF event between June 25 and July 3.
USGS records of turbidity and discharge on Taku River that indicate the onset on glacial lake drainage and of the GLOF event on July 3, note purple arrows.
On June 22, 2021 the region between the yellow arrows is an iceberg choked lake. The red arrow indicates the location where Tulsequah Lake used to expand, it is limited. The terminus of the glacier reaching upvalley 600 m from the main glacier. Discharge is at 60,000 cfs and the turbidity is at ~100 FNU. Starting on the June 25th through the 27th turbidity rises to 400 FNU, while discharge rises to 90,000 cfs. This is during a protracted dry period and is the result of the beginning of increased glacier discharge from the lake. On July 27th-June 30th it is evident that the margin of the distributary glacier tongue has receded ~500 m back to the main glacier margin, representing a terminus collapse generating icebergs likely resulting from a fall in water level. There is no change in the small Tulsequah Lake at the red arrow. On July 3rd turbidity rises above 500 FNU and discharge exceeds 130,000 cfs, this is at the high end of the typical peak GLOF events from Lake No Lake as noted by Neal (2007) from 90,000-130,000 cfs. This is the main event and was reported by the USGS. By July 5 Landsat imagery indicates the water level has dropped between the yellow arrows, resulting in more prominent icebergs. The Sentinel image illustrates the zone of iceberg stranding as well. The icebergs continue to melt away by July 20. No change at the red arrow. If we look back to Sept. 2020 we see what Lake No Lake will appear like by the end of summer and that the distributary terminus margin does not extend upvalley at that time. The large proglacial lake that has formed after 1984 due to retreat helps spread out the discharge from ice dammed lake GLOF’s of Tulsequah Glacier. This lake will continue to expand and the damming ability of the glacier will continue to decline, which will eventually lead to less of a GLOF threat from Lake No Lake.
Sentinel images from June 22, July 5 and July 20 of the area of the lake and then the area of stranded icebergs. Note how almost the entire width of a the northern tributary flows into this valley.
Landsat images of Tulsequah Glacier on June 27 and June 30. Lake No Lake is between the yellow arrows. The former location of Tulsequah glacier dammed lake is at red arrow. Tulsequah Glacier in 1984 and 2017 Landsat images. The 1984 terminus location is noted with red arrows for the main and northern distributary tongue, southern distributary red arrow indicates lake margin. The yellow arrows indicate the 2017 glacier terminus locations. The retreat of 2900 m since 1984 led to a lake of the same size forming. Purple dots indicate the snowline.
Landsat images of Tulsequah Glacier on Sept. 15, 2020. Lake No Lake now drained fills between the yellow arrows. The former location of Tulsequah glacier dammed lake is at red arrow.
Sheridan Glacier in 2002 and 2020 Landsat images illustrating retreat of the margin and expansion of the lake. Red arrow is 2002 margin on small island, yellow arrow is 2020 terminus location just north of Sherman Glacier stream and purple dots are the snowline.
Sheridan Glacier in the Chugach Mountains of Alaska begins at 1500 m and flow southwest out of the mountains with the terminus spreading out in a lake basin on the low slope coastal plain. Sheridan Lake is a proglacial lake at the terminus that drains into the Sheridan River which 12 km later reaches tidewater. From 1950 to 2000 Sheridan Glacier experienced modest retreat, with the terminus, with a fringing proglacial Sheridan Lake persisting, followed by a terminus disintegration from2000-2016. (Shugar et al 2018). Here we examine Landsat imagery from 2002-2020 to identify the retreat and resultant lake expansion.
In 2002 the proglacial lake has an area of 3.8 km2, with the terminus crossing one small island in the lake. The snowline is at 750 m. In 2013 there is a 4 km2 terminus area that has disintegrated, the terminus has retreated off of the island. The snowline is at 850 m. By 2016 the terminus has retreated north of the glacier stream from Sherman Glacier entering from the east, though much of the lake is still filled with an iceberg melange. The snowline is at 925 m. In 2020 the Sheridan Lake area has expanded to 11.2 km2, representing a retreat of 7.4 km2 since 2002. The snowline in 202o is at 970 m. In June 2021 there are a significant number of new icebergs indicating ongoing lake expansion during 2021. Sheridan Lake is not a large glacial lake by Alaskan standards, but is bigger than any glacial lake in most alpine regions such as the Himalaya. The ability to be so large is in large part due to the ability to develop larger basin on low sloped terrain near the coastline.
The amount of terminus retreat here is less than that at Excelsior Glacier or Yakutat Glacier, but the lake expansion rate is comparable to Excelsior Glacier.
Sheridan Glacier in 2013 and 2016 Landsat images illustrating the breakup of a large terminus region generating a melange of icebergs. Red arrow is 2002 margin on small island, yellow arrow is 2020 terminus location just north of Sherman Glacier stream and purple dots are the snowline.
June 2021 Sentinel Image indicating considerable new iceberg activity leading to ongoing lake expansion in 2021.
Porcupine Glacier, British Columbia in a July 4, 2021 Sentinel image illustrating the retreat from 2015-2021 and new iceberg breakup (B). Red arrow is 2015 terminus location and yellow arrows 2021 terminus locations of both branches.
Porcupine Glacier is a 20 km long outlet glacier of an icefield in the Hoodoo Mountains of Northern British Columbia that terminates in an expanding proglacial lake. During 2016 the glacier had an unusually large 1.2 km2iceberg break off (A) the iceberg is still present. NASA generated better imagery to illustrate this observation. The southern branch of the glacier has a tongue poised to breakup at that time (B). Menounos et al (2018) identified a mass loss for glaciers in this region of ~0.6 m year from 2000-2018 which is driving retreat. Here we examine the change in terminus position and iceberg deterioration from 2015-2021 using Landsat and Sentinel images.
In 2015 the glacier had retreated 3.1 km from the 1988 location (Pelto, 2016). In 2015 there are two tongues of the glacier vulnerable to calving at Point A and B. In 2016 Iceberg A has calved generating an immediate retreat of 1.7 km. In June of 2017 the iceberg size has been reduced 10-15%, with little change in position. The iceberg is plugging smaller icebergs from moving down the lake. In August 2018 the iceberg because of its size has still drifted little and at 0.6 km2 has lost half of its area in the two years. This has enabled smaller icebergs to move past the iceberg down the lake. In July of 2019 the iceberg has diminished further to 0.45 km2, but is enmeshed in a melange of other icebergs as well. The glacier has continued to retreat from 2016 to 2019 as expected, ~500 m. The glacier tongue at Point B narrowed considerably from 2015 to 2019 and is poised to separate. The narrowness and potentially shallower depth of this inlet may make it difficult for a single iceberg to emerge from the collapse of this glacier tongue. Iceberg B calved in the summer of 2020 and by July of 2021 is in four main pieces. The retreat of the main terminus from 2015-2021 is 2000 m and for the southern branch it has been 1600 m.
The retreat rate is greater than that at Dawes Glacier to the west in Alaska or Jacobsen Glacier to the south in British Columbia.
Porcupine Glacier in Landsat images from 2015 and 2020. Ice tongue A and B are indicated for 2015 and then Iceberg A and B for 2020.
Porcupine Glacier in Landsat images from 2016 and 2018 and 2019 Sentinel Image. Iceberg A and Ice tongue B are indicated on each. The haziness in 2019 is forest fire smoke. The yellow arrows mark the 2019 terminus location.
Topographic map of Mt. Shasta.indicating the top of Whitney Glacier near the summit of Shasta and the ~1981 and 2005 terminus position.
From a Glaciers Perspective 