Glacier Retreat Drives 400% Lake Expansion Southern Alps, New Zealand 1990-2020

Glaciers of the Southern Alps of New Zealand have been losing ice volume since 1978, with an increasing rate in the last decade (Pelto, 2016).  Gjermundsen et al (2011) examined glacier area change in the central Southern Alps and found a 17 percent reduction in area mainly from large valley glaciers such as Hooker, Mueller, Tasman and Murchison Glacier. The NIWA glacier monitoring program noted that 30 percent of New Zealand’s ice that was existed in the late 1970’s has been lost in the past 40 years as snowlines have been rising. The retreat has been driven by a series of  increasingly warm summers (NIWA, 2019). The NIWA and University of Wellington 2020 snowline survey indicated improvement in 2020.  Lauren Vargo and Andrew Lorrey reported there was more retained snowcover compared to the very high snowlines in 2018 and 2019, despite the presence of ash/dust from Australian fires (NIWA, 2020).

Landsat images  from 1990 and 2020 of the Mueller (M), Hooker (H), Tasman (T) and Murchison (Mn) Glacier.  Red arrows indicate the 1990 terminus location, yellow arrows the 2020 terminus location and pink arrows the upglacier extent of debris cover in 1990.

If we look back to the 1972 Mount Cook map, see below, no lakes are evident at the terminus of Hooker (H), Mueller (M), Tasman Glacier (T), or Murchison Glacier that all drain into Lake Pukaki, pink dots indicate terminus location. In 1990 four lakes had developed one in front of each retreating glacier with a combined area of 2.5 km2.  By 2020 the combined lake area is 12.9 km2.

1972 Map of region when Tasman, Mueller and Hooker Glacier lacked proglacial lakes.

Mueller Glacier has had a 2,300 meters retreat from 1990-2020, which will continue in the future as the lower 1.2 kilometer section of the glacier is stagnant. Mueller Lake area was under 0.2 square kilometers in 1990, expanding to 1.9 square kilometers by 2020. Mueller Glacier’s lower section is not a typical convex valley glacier, but a concave reach of debris covered ice with significant melt valleys and hollows indicating stagnation in the lowest 1.6 kilometer.  In 1990 a fringing discontinuous area of water along the southern glacier margin existed. By 2004 the Mueller Glacier Lake had expanded to a length of 700 meters.  Mueller Lake in 2010 had a surface area of 0.87 square kilometers and a maximum depth of 83 meters (Robertson et al, 2012). By 2015 the lake had reached 1,800 meters in length. From 2015-2020 the terminus collapsed into the lake with icebergs and other attached ice remnants.  Terminus images from 2018, taken by Jill Pelto, indicate the high turbidity of the lake, which is expected from a debris covered ablation zone.

Mueller Glacier terminus collapse in 2018, image from Jill Pelto.

Hooker Glacier retreated 1,350 m from 1990 to 2020 with the retreat enhanced by calving in Hooker Lake. The lake had an area of 0.5 square kilometers in 1990, expanding to 1.5 square kilometers by 2020. The retreat was faster during the earlier part of this period with lake area reaching 1.22 square kilometers by 2011 (Robertson et al.,2013). Hooker Glacier has a low gradient which helps reduce its overall velocity and a debris covered ablation zone reducing ablation, both factors increasing response time to climate change  (Quincey and Glasser 2009). Hooker Lake which the glacier ends in began to form around 1982 (Kirkbride, 1993). The peak lake depth is over 130 meters, with the terminus moving into shallow water after 2006 leading to declining retreat rates (Robertson et al, 2012). The debris cover now extends ~2 kilometers further upglacier than in 1990.

Tasman Glacier retreated 4,900 meters from 1990 to 2020 primarily through calving into the expanding proglacial lake. In 1990 Tasman Lake had an area of 1.7 square kilometers, expanding to 7.1 square kilometers by 2020.  Dykes et al (2011) note a maximum depth of 240 meters, and an annual growth rate of 0.34 square kilometers. The proglacial lake at the terminus continues to expand as the glacier retreats upvalley. The lake is deep with most of the lake exceeding 100 meters in depth, and the valley has little gradient, thus the retreat will continue. It has been noted by researchers at Massey University that the lake can expand in this low elevation valley another 9 kilometers, and that at the current rate this could occur over two decades. The debris cover now extends ~1.5 kilometers further upglacier than in 1990.

Canals draining from Lake Tekapo to Lake Pukaki then upriver of Lake Benmore

Murchison Glacier has retreated 2,700 meters From 1990 to 2020.  In 1990 the lake had an area of under 0.2 square kilometers, expanding to 2.5 square kilometers by 2020. The rapid retreat will continue as 2010, 2013 and 2015 imagery indicate other proglacial lakes have now developed 3.5 km above the actual terminus. The debris cover now extends ~2 kilometers further upglacier than in 1990.

For each glacier debris cover now extends further upglacier which along with rising snowlines highlights the expansion of the ablation area, that also drives volume loss, retreat and lake expansion.

Canal at Ohau hydropower, image from Jill Pelto.

Glacier runoff is a key hydropower water resource. Water from Lake Pukaki is sent through a canal into the Lake Ohau watershed and then through six hydropower plants of the Waitaki hydro scheme: Ohau A, B and C. Benmore, Aviemore and Waitaki with a combined output of 1,340 megawatts.  Meridian owns and operates all six hydro stations located from Lake Pūkaki to Waitaki.  Interestingly salmon have been introduced into the Waitaki River system for fishing near its mouth, though Lake Pukaki itself has limited fish.

This post by Mauri Pelto originally appeared on his blog From a Glacier’s Perspective, published by the American Geophysical Union.

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Kerguelen Island Glacier Retreat Expands Lake District

Eastern Outlet glaciers of Cook Ice Cap in a 2001 Landsat and 2019 Sentinel image indicating retreat from 2001 terminus positions (red arrows) to 2019 terminus location (yellow arrows) (Source: Mauri Pelto).

The east side of the Cook Ice Cap on Kerguelen Island outlet glaciers have retreated, expanding and forming a new group of lakes (Pelto, 2016). Here we examine the changes from 2001-2019, using Landsat and Sentinel imagery. Retreat of glacier in the region was examined by Berthier et al (2009) and is exemplified by the retreat of Ampere Glacier.  Verfaillie et al (2016) examined the surface mass balance using MODIS data, field data, and models.  The accelerating glacier wastage on Kerguelen Island was observed do be due to reduced net accumulation and resulting rise in the transient snowline since the 1970s, when a significant warming began.  This has led to nunatak expansion on the ice cap.

In 2001, the northern outlet glacier terminates in a wide portion of the proglacial lake #1.  The central outlet, #2, has two terminus locations the northern is in a proglacial lake that is kilometers long and the southern arm terminates on land.  The southern outlet terminates on land.  By 2011, the northern outlet has retreated into a narrow section of the proglacial lake. The center terminus has retreated with a new lake forming in front of its southern arm. The southern outlet has retreated revealing a new developing lake.  In 2014, the northern terminus has retreated from the primary proglacial lake. The central terminus is producing icebergs from both arms. The lake continues to expand at the southern outlet. The 2019 image is from early in the melt season. The northern terminus has retreated 1100m since 2001, and is no longer calving in a substantial lake. The central terminus has retreated with the northern and southern arm retreated 1500-1800m, with a new lake forming in front of the southern arm.  The southern outlet glacier has retreated the most, 2100m since 2001, leading to the formation of a new lake of the same length. Outlet glaciers of the ice cap that are not calving are also retreating indicating that the retreat has been driven by rising snowline and enhanced by calving. The central and southern outlets continue to calve and should continue retreat more rapidly than the northern outlet.

Eastern Outlet glaciers of Cook Ice Cap in a 2001 Landsat and 2019 Sentinel image indicating retreat from 2001 terminus positions (red arrows) to 2019 terminus location (yellow arrows) (Source: Mauri Pelto).
Digital Globe image of the Cook Ice Cap, with the main outlet, Ampere Glacier and the three glaciers examined here 1-3 (Source: Mauri Pelto).

This story originally appeared on the AGU blog From a Glaciers Perspective.

A Two-Century-Long Advance Reversed by Climate Change

Taku Glacier in 2016 and 2019 Sentinel 2 images. The Hole in the Wall Tributary (HW) is upper right, Taku Glacier main terminus (MT). Yellow line is the 2016 terminus location. The arrows denote locations where thinning is apparent as the area of bare recently exposed bedrock has expanded. A closeup is below. Pink and brown areas between blue ice and yellow line in 2019 indicates retreat.

The Taku Glacier is the largest outlet glacier of the Juneau Icefield in Alaska. Taku Glacier began to advance in the mid-19th century, and this continued throughout the 20th century. At first observation in the 19th century, the glacier was calving in deep water in a fjord. It advanced 5.3 kilometers between 1890 and 1948 moving out of the fjord into the Taku River Valley (See maps below (Pelto and Miller, 1990). At this time calving ceased resulting in positive mass balance without the calving losses. The glacier continued to advance 2.0 km from 1948-2013 (Pelto, 2017). The advance was paralleled by its distributary terminus, Hole in the Wall Glacier. This advance is part of the tidewater glacier cycle (Post and Motyka, 1995), updated model by Brinkerhoff et al (2017). At the minimum extent after a period of retreat the calving front typically ends at a point of constriction in fjord width or depth that limits calving. With time, sedimentation in front of the glacier reduces water depth and calving rate, allowing the glacier to begin to advance. In the case of the Taku Glacier, after a century of advance, the glacier had developed a substantial proglacial outwash and moraine complex that had filled in the fjord, and the glacier was no longer calving. Images below, from 1961 and 1981, illustrate this. This allowed the advance to continue through the rest of the 20th century and into the 21st century. The slowing of the advance in the latter half of the 20th century has been attributed to the impedance of the terminus outwash plain shoal (Post and Motyka, 1995Pelto and Miller, 1990). There is a concave feature near the terminus with an increase in crevassing where the push impacts flow dynamics as seen at black arrow in 1975 and 1998 images below. In 1980’s the Taku Glacier’s accumulation area ratio was still strong enough for Pelto and Miller (1990) to conclude that the Taku Glacier would continue to advance for the remaining decade of the 20th century, which it did.

Beginning in 1946, the Juneau Icefield Research Program began annual mass balance measurements that is the longest in North America. In conjunction with JIRP and its first director Maynard Miller, we compiled and published an annual mass balance record in 1990. From 1990 to the present, in conjunction with JIRP and Chris McNeil, we have continued to compile and publish this annual mass balance record (Pelto et al 2013).  Much of the remarkable data record of JIRP has this month been made accessible to the public, particularly through the efforts of Seth Campbell, JIRP director; Scott McGee, survey team director; and Chris McNeil, mass balance liaison with USGS.

The ELA in 2018 and 2019 in Landsat images, purple dots indicate the record high snowlines for the 1946-2019 period for each year.

Taku Glacier is one of the thickest known alpine temperate glaciers. It has a maximum measured depth of 1,480 meters, and its base is below sea level for 40-45 km above the terminus (Nolan et al 1995). Moytka et al (2006) found that the glacier base was more than 50 m below sea level within 1 km of the terminus and had deepened substantially since 1984. This suggests a very long calving retreat could occur. The glacier had a dominantly positive mass balance of +0.42 m/year from 1946-1988 and a dominantly negative balance since 1989 of  -0.34 m/year (Pelto et al 2013). This has resulted in the cessation of the long term thickening of the glacier. On Taku Glacier, the annual ELA (end of summer snowline altitude) has risen 85 m from the 1946-1988 period to the 1989-2019 period. During the 70+ year annual record the ELA had never exceeded 1,225 m until 2018, when it reached 1,425 m (Pelto, 2018).  In 2019, the ELA again has reached a new maximum of 1,450 m (see above images). Contrast the amount of the glacier above the snowline in 2018 and 2019 to other recent years that had more ordinary negative balances (see Landsat images below).

In 2008 and 2012, JIRP was at the terminus, creating the map below. There was no change at the east and west side of the margin since 2008, with 55 to 115 m of advance closer to the center. The glacier did not advance significantly after 2013 and did not retreat appreciably until 2018. The Taku Glacier cannot escape the result of three decades of mass losses, with the two most negative years of the record being 2018 and 2019. The result of the run of negative mass balances is the end of a 150+ year advance and the beginning of retreat. Sentinel images from 2016 and 2019 of the two main termini Hole in the Wall Glacier (right) and Taku Glacier (left). The yellow arrows indicate thinning and the expansion of a bare rock trimline along the margin of the glacier. The Hole in the Wall terminus has retreated more significantly with an average retreat of about 100 m.  The Taku main terminus has retreated more than 30 m along most of the front.

The retreat is driven by negative balances, mainly by increased surface melt. The equilibrium flow of the Taku Glacier near the long term ELA for the 1950-2005 period was noted by Pelto et al (2008). This occurred during a period of glacier thickening, average profile velocity was 0.5 md-1  (Pelto et al 2008). Since 1988 the glacier has not been thickening near the snowline as mass balance has declined slightly (Pelto et al 2013). The remarkable velocity consistency measured by JIRP surveyors led by Scott McGee each year at profile 4 has continued. It is below this profile that surface ablation has reduced the volume of ice headed to the terminus.

All other outlet glaciers of the Juneau Icefield have been retreating, and are thus consistent with the dominantly negative alpine glacier mass balance that has been observed globally (Pelto 2017).  Now, Taku Glacier joins the group unable to withstand the continued warming temperatures. Of the 250 glaciers I have personally worked on, it is the last one to retreat. That makes the score: climate change 250, alpine glaciers 0.

1890 United States Coast Guard map indicating deep water in the fjord in front of Taku Glacier.
Map of terminus change from Lawrence (1950)
Taku Glacier aerial photograph from US Navy in 1948. Still minor calving on right (east side
Taku Glacier in 1961, photograph indicating calving had ended
This is a view across the glacier accumulation area that until 2018 had always been snow covered at the end of summer (Credit: Pelto).

To see more photos of Taku Glacier, check out the Mauri Pelto’s original post on From a Glacier’s Perspective, a blog published by the American Geophysical Union.

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Annual Assessment of North Cascades Glaciers Finds ‘Shocking Loss’ of Volume

The summer of 2019 found the North Cascade Glacier Climate Project in the field for the 36th consecutive summer monitoring the response of North Cascade glaciers to climate change. This long term monitoring program was initiated partly in response to a challenge in 1983 from Stephen Schneider to begin monitoring glacier systems before and as climate change became a dominant variable in their behavior.

The field team was comprised of Clara Deck, Ann Hill, Abby Hudak, Jill Pelto, and myself. All of us have worked on other glaciers. The bottom line for 2019 is the shocking loss of glacier volume.

Ann Hill, University of Maine graduate student observed, “Despite having experience studying glaciers in southeast Alaska and in Svalbard, I was shocked by the amount of thinning each glacier has endured through the last two and a half decades.” 

Glaciers are typically noted as powerful moving inexorably. Clara Deck, University of Maine MS graduate, was struck by “the beauty and fragility of the alpine environment and glaciers.” Fragile indeed in the face of climate change.

Abby Hudak, a Washington State graduate student, looked at both the glacier and biologic communities as under stress, but glaciers cannot migrate, adapt, or alter their DNA.

Easton Glacier, Mount Baker. Terminus has become thin and uncrevassed as a rapid retreat of 15 meters per year continued, with 405 m of retreat since 1990.

Over the span of 16 days in the field, every night spent in the backcountry adjacent to a glacier, we examined 10 glaciers in detail. All glaciers are accessed by backpacking. The measurements completed add to the now 36-year-long database that indicate a ~30 percent volume loss of these glaciers during that period (Pelto, 2018).

Here we review preliminary results from each glacier. Each glacier will have a mass balance loss of  1.5 -2.25 m, which drives continued retreat.  Columbia and Rainbow Glacier are reference glaciers for the World Glacier Monitoring Service, with Easton Glacier joining the ranks later this year.

Below and above is the visual summary. Specific mass balance and retreat data will be published here and with WGMS after October 1.

Easton Glacier icefall at 2,200 meters typically has 1.8 m w.e. at the end of the summer, this year it will be 0 m. The overall mass balance will be ~2 m of loss.
Deming Glacier, Mount Baker has now receded over 700 m since our first visit 35 years ago.

On Lower Curtis Glacier, a key accumulation source, the NE couloir now shows bedrock. Overall by summers end ~25 percent of the glacier will retain snow cover, far short of what is needed to maintain its volume.
The Lower Curtis Glacier terminus continues to retreat at 8 meters/year, but thinning and slope reduction has been more notable.
In early August, the majority of Sholes Glacier has lost its snowpack. The thin nature of the terminus indicates the glacier is poised for continued rapid retreat that has exceeded 15 meters per year during the last 7 years.
Runoff assessment confirmed ablation stake measurement of 11 centimeters of ablation/day from 8/6-8/8 on Sholes Glacier.
High on Rainbow Glacier, there are still plenty of regions lacking snow cover instead of a thick mantle of snowpack.
Rainbow Glacier was awash in meltwater streams (see video). This area should have 1 meter of snowpack left. Rainbow Glacier has retreated 650 meters since 1984.
Just getting to each glacier does involve overcoming various miseries.

To see more photos of the 36th annual North Cascades monitoring project, check out the Mauri Pelto’s original post on From a Glacier’s Perspective, a blog published by the American Geophysical Union.

What the 2018 State of the Climate Report Says About Alpine Glaciers

For the last decade, I have written the section on alpine glaciers for the Bulletin of the American Meteorological Society‘s State of the Climate report. The 2018 report was published this week. Below is the section on alpine glaciers. 

The key data resource is the World Glacier Monitoring Service (WGMS) record of mass balance and terminus behavior (WGMS, 2017), which provides a global index for alpine glacier behavior. 

Glacier mass balance is the difference between accumulation and ablation, reported here in millimeters of water equivalence (mm). Mean annual regionalized glacier mass balance in 2017 was -921 mm for the 42 long-term reference glaciers, with an overall mean of -951 mm for all 142 monitored glaciers. Preliminary data reported from reference glaciers to the WGMS in 2018 from Argentina, Austria, China, France, Italy, Kazakhstan, Kyrgyzstan, Nepal, Norway, Russia, Sweden, Switzerland, and the United States indicate that 2018 will be the 30th consecutive year of significant negative annual balance (.-200mm); with a mean balance of -1247 mm for the 25 reporting reference glaciers, with one glacier reporting a positive mass balance (WGMS, 2018).  This rate of mass loss may result in 2018 exceeding 2003 (-1246 mm) as the year of maximum observed loss. as a mean. This WGMS mass balance record has now been regionally averaged before determining the global mean, this has not been done yet for 2018, which will reduce the magnitude of the negative balance.

Ongoing global glacier retreat is currently affecting human society by increasing the rate of sea level rise, changing seasonal stream runoff, and increasing geo-hazard potential (Huss et al, 2017).  The recent mass losses 1991-2010 are due to anthropogenic forcing (Marzeion et al. 2014).

Global Alpine glacier annual mass balance record of reference glaciers submitted to the World Glacier Monitoring Service, with a minimum of 30 reporting glaciers.

The cumulative mass balance from 1980-2018 is -21.7 m, the equivalent of cutting a 24-meter-thick slice off the top of the average glacier (Figure 1).  The trend is remarkably consistent across regions (WGMS, 2017).  WGMS mass balance from 42 reference glaciers, which have a minimum 30 years of record, is not appreciably different from that of all glaciers at -21.5 m.  Marzeion et al (2017) compared WGMS direct observations of mass balance to remote sensing mass balance calculations, and climate driven mass balance model results and found that each method yields reconcilable estimates relative to each other and fall within their respective uncertainty margins. The decadal mean annual mass balance was -228 mm in the 1980’s, -443 mm in the 1990’s, 676 mm for 2000’s and – 921 mm for 2010-2018.  Glacier retreat reflects sustained negative mass balances over the last 30 years (Zemp et al., 2015).  The increasing rate of glacier mass loss  during a period of retreat indicates alpine glaciers are not approaching equilibrium and retreat will continue to be the dominant terminus response (Pelto, 2018).

Exceptional glacier melt was noted across the European Alps, leading to high snowlines and contributing to large negative mass balance of glaciers.  In the European Alps, annual mass balance has been reported from 17 glaciers in Austria, France, Italy and Switzerland.  All 17 had negative annual balances, with 15 exceeding -1000 mm with a mean of -1640 mm.  This continues the pattern of substantial negative balances in the Alps, which will equate to further terminus retreat.  Of 81 observed glaciers in 2017 in Switzerland, 80 retreated, and 1 was stable (Huss et al, 2018).  In 2017, 83 glaciers were observed in Austria,; 82 retreated, and 1 was stable.  Mean terminus retreat was 25 m, the highest observed since 1960, when mean length change reporting began (Lieb and Kellerer-Pirklbauer, 2018).

In Norway and Sweden, mass balance surveys with completed results are available for eight glaciers; all had negative mass balances with an average loss of -1420 mm w.e. All 25 glaciers with terminus observations during the 2007-2017 period have retreated (Kjøllmoen et al, 2018).

In western North America data has been submitted from 11 glaciers in Alaska and Washington in the United States.  All eleven glaciers reported negative mass balances with a mean loss of -870 mm. The longest mass balance record in North America is from Taku Glacier in Alaska.  In 2018 the glacier had its most negative mass balance since the beginning of the record in 1946 and the highest end of summer snowline elevation at 1400 m. The North Cascade Range, Washington from 2014-2018 had the most negative five-year period for the region of the 1980-2018 WGMS record.

In the High Mountains of Asia (HMA) data was reported from ten glaciers including from China, Kazakhstan, Kyrgyzstan and Nepal. Nine of the ten had negative balances with a mean of -710 mm. This is a continuation of regional mass loss that has driven thinning and a slowdown in glacier movement in 9 of 11 regions in HMA from 2000-2017 (Dehecq et al 2018).

Taku Glacier transient snowline in Landsat 8 images from July 21, 2018  and September 16, 2018.  The July 21 snowline is at 975 m and the September 16 snowline is at 1400 m.  The average end of summer snowline from is m with the 2018 snowline being the highest observed since observations began in 1946.

References:

Huss, M., B. Bookhagen, C. Huggel, D. Jacobsen, R. Bradley, J. Clague, M. Vuille,  W. Buytaert, D. Cayan, G. Greenwood, B. Mark, A. Milner, R. Weingartner and M. Winder, 2017a: Toward mountains without permanent snow and ice. Earth’s Future5: 418–435. doi:10.1002/2016EF000514

Huss, M., A. Bauder, C. Marty and J. Nötzli, 2018: Neige, glace et pergélisol 2016/17.  Les Alpes94(8), 40-45. (http://swiss-glaciers.glaciology.ethz.ch/downloadPubs/alpen_15-16_f.pdf).

Dehecq, A., N. Gorumelon, A. Gardner, F. Brun, D. Goldberg, P. Nienow, E. Berthier, C. Vincent, P. Wagnon, and E. Trouve, 2019: Twenty-first century glacier slowdown driven by mass loss in High Mountain Asia. Nature Geoscience 12, 22–27.

Kjøllmoen B., L. Andreassen, H. Elvehøy, and M. Jackson, 2018: Glaciological investigations in Norway in 2017. NVE Report 82 2018.

Lieb, G.K. and A. Kellerer-Pirklbauer ,2018: Gletscherbericht 2016/17 Sammelbericht über die Gletschermessungen des Österreichischen Alpenvereins im Jahre 2017. Letzter Bericht: Bergauf 2/2017Jg. 72 (142), S. 18–25. (http://www.alpenverein.at/).

Marzeion, B., J. Cogley, K. Richter and D. Parkes, 2014: Attribution of global glacier mass loss to anthropogenic and natural causes. Science345(6199), 919–921, doi: 10.1126/science.1254702)

Marzeion, B., Champollion, N., Haeberli, W. et al.: Observation-Based Estimates of Global Glacier Mass Change and Its Contribution to Sea-Level ChangeSurvey of Geophys, 38: 105, doi: 10.1007/s10712-016-9394-y.

Pelto, M., 2018: How Unusual Was 2015 in the 1984–2015 Period of the North Cascade Glacier Annual Mass Balance? Water 10, 543, doi: 10.3390/w10050543.

WGMS 2017: Global Glacier Change Bulletin No. 2(2017). Zemp, M., and others(eds.), ICSU(WDS)/IUGG(IACS)/UNEP/UNESCO/WMO, World Glacier Monitoring Service, Zurich, Switzerland, 244 pp.: doi:10.5904/wgms-fog-2017-10.

WGMS 2018: Fluctuations of Glaciers Database. World Glacier Monitoring Service, Zurich, Switzerland. doi: 10.5904/wgms-fog-2018-11. http://dx.doi.org/10.5904/wgms-fog-2018-11

Zemp and others 2015: Historically unprecedented global glacier decline in the early 21st century. J. Glaciology61(228), 745-763, doi: 10.3189/2015JoG15J017.

This article originally appeared on the American Geophysical Union blog, From a Glacier’s Perspective.

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The Accumulation Zone of Alaska’s Mendenhall Glacier Is Shrinking

Mendenhall Glacier is the most visited and photographed terminus in the Juneau Icefield region. The glacier can be seen from the suburbs of Juneau.  Its ongoing retreat from the Visitor Center and the expansion of the lake it fills is well chronicled. Here we document the rise in the snowline on the glacier that indicates increased melting and reduced mass balance that has driven the retreat. The change in snowline from 1984-2018 and the associated retreat are documented. The snowline as July begins in 2019 is already in the end of summer range.

Mendenhall Lake did not exist until after 1910. In 1948 it was 2.2 kilometers across, and by 1984 the lake was 2.7 km across.  Boyce et al (2007) note the glacier had two periods of rapid retreat: one in the 1940’s and the second beginning in the 1990’s, both of which were enhanced by buoyancy-driven calving. The latter period has featured less calving, particularly in the last decade, and is a result of greater summer melting and a higher snowline by the end of the summer, which has averaged 1,250 meters since 2003 vs. 1,050 m prior to that (Pelto et al, 2016). In 2005, the base of the glacier was below the lake level for at least 500 m upglacier of the terminus (Boyce et al (2007).  This suggests the glacier is nearing the end of the calving enhanced retreat.  It is likely another lake basin would develop 0.5 km above the current terminus, where the glacier slope is quite modest.

Mendenhall Glacier in Landsat images from 1984 and 2018. Yellow arrows indicates 1984 terminus location, red arrow indicates the Suicide Basin tributary, and the purple dots indicate the snowline.

The glacier in 1984 ended at the tip of a prominent peninsula in Mendenhall Lake. The snowline is at 950 m. In 1984 with the Juneau Icefield Research Program, we completed both snowpits and crevasse stratigraphy that indicated retained snowpack at the end of summer is usually more than 2 m at 1,500-1,600 m. The red arrow indicates a tributary that joins the main glacier, where Suicide Basin currently forms. In 2014 the snowline in late August is at 1,050 m.  The terminus has retreated to a point where the lake narrows, which helps reduce calving. In 2015 the snowline is at 1,475 m. In 2017 the snowline reached 1,500 m.  There is a small lake in Suicide Basin. In September 2018 the snowline reached 1,550 m—the highest elevation the snowline has been observed to reach any year. In Suicide Basin the lake drained in early July. In 2018 Juneau Icefield Research Program snowpits indicates only 60 percent of the usual snowpack left on the upper Taku Glacier, near the divide with Mendenhall Glacier. On July 1 2019 the snowline is already as high as it was in late August of 1984.  This indicates the snowline is likely to reach near a record level again. The US Geological Survey and the National Weather Service is monitoring Suicide Basin for the drainage of this glacier melt filled lake. In 2019 the lake rapidly filled from early June until July 8—the water level increasing 40 feet. It has drained from July 8 to 16 back to it early June Level. The high melt rate has thinned the Mendenhall Glacier in the area reducing the elevation of the ice dam and hence the size of the lake in 2019 vs. 2018.

The snowline separates the accumulation zone from the ablation (melting) zone and the glacier needs to have more than 60 percent of its area in the accumulation zone. The end of summer snowline is the equilibrium line altitude where mass balance at the location is zero. With the snowline averaging 1,500 m during recent years, this leaves less than 30 percent of the glacier in the accumulation zone. This will drive continued retreat even when the glacier retreats from Mendenhall Lake. The declining mass balance is evident across the Juneau Icefield (Pelto et al 2013).  Retreat from 1984-2018 has been 1,900 m. This retreat is better known, but less than at nearby Gilkey Glacier and Field Glacier.

Mendenhall Glacier in a Landsat image from 2014. Yellow arrows indicate 1984 terminus location, and the purple dots indicate the snowline.
Mendenhall Glacier in a Landsat image from 2015. Yellow arrows indicate 1984 terminus location, and the purple dots indicate the snowline.
Mendenhall Glacier in a Landsat image from 2017. Yellow arrows indicate 1984 terminus location, and the purple dots indicate the snowline.
Mendenhall Glacier in a Landsat image from 2019. Yellow arrows indicates 1984 terminus location, and the purple dots indicate the snowline.

This article originally appeared on the American Geophysical Union blog, From a Glacier’s Perspective.

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China’s Asejiaguo Glacier Is Retreating

Asejiaguo Glacier drains east from the China-Nepal border and is at the headwaters of the Yarlung Tsangpo, which becomes the Brahmaputra River. The Yarlung Tsangpo powers the 510 megawatt Zangmu Hydropower Station.  Gardelle et al (2013) identified this glacier as part of the West Nepal region, which experienced mass loss averaging -0.32 meter/year from 1999-2011. The changes of the Asejaguo Glacier are examined for the 1993 to 2018 period using Landsat imagery. Neckel et al (2014) examined changes in the surface elevation of the glaciers and found this region lost 0.37 m/year from 2003 to 2009.

In 1993 the glacier terminated in a small proglacial lake that is ~1 kilometer long at 4,900 m. At Point 1-2 there is limited exposed bedrock at 5,400-5,600 m, which is near the snowline; the head of the glacier is at 6,000 m.  There is a prominent medial moraine that begins at 5,300 m where the north and south tributaries join.  The greater width of the southern tributary indicates this is the large contributor. In 1994, the snowline is higher, at 5,500 m, but there is still only a small outcrop of bedrock at Point 2. By 2016 the proglacial lake has expanded to a length of over 2 km. At Point 1 and 2 there is a greatly expanded area of bedrock and the separation of a former tributary near Point 1 from the main glacier. In November 2018 there is fresh snowfall obscuring the exposed bedrock at Point 1 and 2. The retreat from 1993-2018 is 1.5 km, and the expanding proglacial lake is over 2.5 km long. The expanding bedrock areas in the 5,400-5,600 m range indicate the reason rise in snowline that has generated mass loss and ongoing retreat.

Asejiaguo Glacier in Landsat images from 1993 and 2018. The yellow arrow indicates the 2018 terminus and the red arrow the 1993 terminus location. Point 1 and 2 are areas of expanding bedrock at the elevation of 5,400-5,600 meters.
Asejiaguo Glacier in Landsat images from 1994 and 2016. The yellow arrow indicates the 2016 terminus and the red arrow the 1994 terminus location. Point 1 and 2 are areas of expanding bedrock at the elevation of 5,400-5,600 meters.
Asejiaguo Glacier, blue arrows indicate flow direction. M indicates the medial moraine; the China-Nepal border is also noted.

This article originally appeared on the American Geophysical Union blog From a Glacier’s Perspective.

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Chickamin Glacier Retreat Generates Separation and Lake Expansion

Chickamin Glacier in southeast Alaska glacier drains south from an icefield near Portland Canal and straddles the border with British Columbia. The glacier ended on an outwash plain in 1955 at an elevation of 250 meters.  Shortly thereafter a lake began to form, and by 1979 a Landsat image indicates a lake that is 1,300 meters long and a retreat of ~2.5 kilometers from 1902-1979 (Molnia, 2008). The glacier at that time was fed by a substantial tributary entering from the south ~5 km above the terminus, Through Glacier, pink arrow in the image below.

Here we examine Landsat images from 1985-2018 to identify the response to climate change.

In 1985, the glacier terminated at an elbow in the lake, where the lake both narrows temporarily and turns east, red arrow. The glacier had terminated close to this location for 30 years. The snowline is at 1,150 m, and Through glacier still connects to Chickamin Glacier.  At point 1 and 2, the area of exposed bedrock is limited. In 1994, the glacier has retreated 500 m from the elbow. Through Glacier has separated from Chickamin Glacier. The snowline in 1994 is at 1,125 m. In 2013, Through Glacier has retreated 1,600 m from Chickamin Glacier. Chickamin Glacier has retreated 2 km since 1985, and the snowline is at 1,250 m.  By 2018, Chickamin Glacier has retreated 3.5 km since 1985 at a rate of just over ~100 m/year, yellow arrow.

Chickamin Glacier, Alaska in 1985 and 2018 Landsat images indicating the 3.5 kilometer retreat and associated lake expansion. Red arrow is 1985 terminus location, yellow arrow is the 2018 terminus location, pink arrow is former junction area with Through Glacier.  The purple dots indicate the snowline. Point 1 and 2 are locations of bedrock expansion above the equilibrium line altitude. 

The terminus is currently at a point where the lake narrows, which should reduce the retreat rate. In 2018, the snowline reached 1,525 m, leaving only 10-15 percent of the glacier in the accumulation zone. The exceptionally high  snowline in 2018 was also noted at Taku Glacier. The snowline from 2014-2018 has persistently been above 1,350 m, which indicates substantial negative mass balance for the glacier that will drive continued retreat. The persistent snowline elevation above 1,250 m is indicated by the expansion of bedrock areas at Point 1 and 2 from 1985 to 2018, which both are located in what was the typical accumulation zone prior to that time.

The sustained mass balance losses follow that of Lemon Creek Glacier, which has a long-term record from 1953-2018 indicating a loss of  ~-0.5 m/year (Pelto et al. 2013).  The retreat and lake expansion has become a chorus with more than 20 coastal Alaskan glaciers having at least a 2 km lake expansion due to retreat since 1984, documented individually in previous posts at this blog.

Chickamin Glacier, Alaska in 1994 and 2013 Landsat images indicating the 3.5 kilometer retreat and associated lake expansion. Red arrow is 1985 terminus location, yellow arrow is the 2018 terminus location, pink arrow is former junction area with Through Glacier. The purple dots indicate the snowline. Point 1 and 2 are locations of bedrock expansion above the equilibrium line altitude. 
US Geological Survey map of Chickamin Glacier based on 1948 aerial photographs

This story originally appeared on the AGU blog From a Glaciers Perspective.

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North Cascade 2019 Winter Accumulation Assessment

For North Cascade glaciers the accumulation season provides a layer of snow that must last through the melt season. A thin layer sets the glaciers up for a mass balance loss, much like a bear with a limited fat layer would lose more mass than ideal during hibernation.

The 2019 winter season in the North Cascade Range, Washington has been unusual. On April 1, the retained snow-water equivalent in snowpack across the range at the six long SNOTEL sites is 0.72 meters, which is ~70 percent of average. This is the fifth lowest since 1984. The unusual part is that freezing levels were well above normal in January, in the 95 percentile at 1,532 m, then were the lowest level, 372 m of any February since the freezing level record began in 1948. March returned to above normal freezing levels.

April 1 winter accumulation at the longer term North Cascade SNOTEL stations (Fish Lake, Lyman Lake, Park Creek, Rainy Pass, Stampede Pass, and Stevens Pass).

As is typical, periods of cold weather in the regions are associated with reduced snowfall in the mountains and more snowfall at low elevations. In the Seattle metropolitan area February was the snowiest month in 50 years, 0.51 m of snow fell, but in the North Cascades snowfall in the month was well below average. From Feb. 1 to April 1, snowpack SWE at Lyman Lake, the SNOTEL site closest to a North Cascade glacier, usually increases from 0.99 m to 1.47 m. This year, SWE increased from 0.83 m to 1.01 m during this period.

The Mount Baker ski area snow measurement site has the world record for most snowfall in a season: 1,140 inches (28.96 m) during the 1998-99 snow season. The average snowfall is 633 inches (16.07 m) with snowfall this year, as of April 15, at 533 inches (13.53 m). Below is a Landsat image from April 15, 2019 indicating the snowline at ~1000 m in the Nooksack River Valley and 900-1000 m in the Baker Lake valley.

Freezing levels at Mount Baker, WA from the North American Freezing Level Tracker. February was the lowest mean freezing level since 1948.

This year, for the 36th consecutive year, the North Cascade Glacier Climate Project will be in the field measuring North Cascade glaciers. The early signs point towards a seventh consecutive negative balance year.

Mount Baker cloaked in winter snow in an April 15, 2019 Landsat image. MB=Mount Baker, MS=Mount Shuksan, NR=Nooksack River

This article was originally published on the blog From a Glacier’s Perspective.

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Nevado Ausangate Glaciers, Peru Retreat, and Lake Formation

Here we examine three Ausangate Glaciers in Peru, which descend south from the Nevado Ausangate group of peaks in the Cordillera Vilcanota. A circumnavigation trek around Nevado Ausangate is a favorite for visitors to the Machu Picchu area.

Digital Globe image of the Ausangate Glaciers. Red arrows indicate 1995 terminus location and yellow dots the 2018 terminus location.

The glaciers are just west of Laguna Sibinacocha, and drain into the Rio Vilcanota. Retreat of glaciers in the Cordillera Vilcanota has been rapid since 1975, Veettil et al (2017) noted that ~80 percent of glaciated area below 5,000 meters was lost from 1975-2015, and glacier area overall area had declined 48 percent.  Henshaw and Bookhagen (2014) observed that from 1988-2010, glacial areas in the Cordillera Vilcanota declined annually by ~ 1 percent per year.

Ausangate Glaciers in 1995 Landsat and 2018 Sentinel image. Red arrows indicate 1995 terminus location and yellow arrows the 2018 terminus location. The development of three proglacial lakes at the terminus of each glacier is evident.

In 1995 the three glaciers all terminate in incipient proglacial lakes. The terminus of #3 is debris covered. By 2000 each of the glaciers is still terminating in an expanding proglacial lake. Glacier #1 and #2 have developed to a size of ~0.1 square kilometers. Glacier #3 still shows limited lake development.

By 2018 Glacier #1 has retreated 450 m and is now separated from the lake. Glacier #2 has retreated 400 m and no longer reaches the lake. Glacier #3 is still in contact with the lake which still has debris covered stagnant ice covering a portion of the basin. This lake has an area of 0.13 square kilometers, and could reach an area of ~0.2 square kilometers depending on debris cover thickness.

The terminus of each glacier has retreated above 5,000 m since 1995. The glaciers each have extensive crevassing and maintains a snow covered accumulation zone, indicating they can survive current climate. Veettil et al (2017) noted that glacier area above 5,300 m was relative stable, for Ausangate Glaciers the area above 5,200 m is in the accumulation zone and has been relatively stable.

The formation of new lakes and the retreat from proglacial lakes has been a common occurrence in recent decades for Andean glaciers in Peru such as Manon Glacier and Soranano Glacier. The key role of glaciers to runoff is illustrated by the fact that 77 percent of lakes connected to a glacier watershed have maintained the same area or expanded, while 42 percent of lakes not connected to a glacier watershed have declined in area, according to Henshaw and Bookhagen (2014). The Ausangate Glaciers supply runoff to the Machupicchu Hydroelectric Power Plant managed by EGEMSA, which has an operating capacity of 90 megawatts. The Vilcanota River becomes the Urubamba River further downstream.

Ausangate Glaciers in a 2000 Landsat image. The development of two of the three proglacial lakes at the terminus of each glacier is evident.

This article was originally published on the American Geophysical Union blog From a Glacier’s Perspective.

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Heard Island Glacier Retreat Enables Lagoon Development

The Australian Antarctic Division (AAD) manages Heard Island and has undertaken a project documenting changes in the environment on the island. One aspect noted has been the change in glaciers. The Winston, Brown, and Stephenson glaciers have all retreated substantially since 1947 when the first good maps of their terminus are available.

Fourteen Men by Arthur Scholes (1952) documents a year spent by 14 men of the Australian National Antarctic Research Expedition that documented the particularly stormy, inclement weather of the region. Their journey to the east end of the island noted that they could not skirt past the glaciers along the coast. After crossing Stephenson Glacier they visited an old seal camp and counted 16,000 seals in the area. It is a rich area for wildlife that will benefit from the lagoon formation overall. Three species of seal commonly breed on Heard Island, southern elephant seals, Antarctic fur seal, and sub-antarctic fur seals (AAD, 2019).

Stephenson Glacier (SG), Stephenson Lagoon (SL), Winston Glacier (WG), and Winston Lagoon (WL) are seen in a 2019 Sentinel Image.

Here we examine the retreat of Stephenson Glacier and Winston Glacier from 2001-2019 and the consequent lagoon expansion. As Kiernan and McConnell observed, retreat of Stephenson Glacier had begun by 1971. The glacier had retreated a kilometer from the south coast and several hundred meters from the northern side of the spit. This retreat by 1980 caused the formation of Stephenson Lagoon.

Retreat of Stephenson Glacier and Winston Glacier from 2001 (red arrows) to 2018 (yellow arrows) seen in Landsat images.

In 2001 Stephenson Glacier has two separate termini: Doppler to the south and Stephenson to the east. There are numerous icebergs in Doppler lagoon but none in Stephenson Lagoon, indicating the retreat is underway. Winston Glacier terminates where the lagoon widens.

In 2008 the two lagoons in front of Stephenson Glacier are joined with a narrow eastern channel, the lagoons are filled with icebergs as a terminus collapse is underway. Winston Glacier has retreated into a narrower inlet from the wider Winston Lagoon.

By 2010 Stephenson Glacier had retreated from the main now singular Stephenson Lagoon and, like Winston Glacier in 2001, terminates at narrow point where the glacier enters the main lagoon.

By 2018 Stephenson Glacier has retreated from the main lagoon: The northern arm of the glacier experienced a 1.8 km retreat from 2001 to 2018 and the southern arm a 3.5 km retreat. The lagoon is free of ice for the first time in several centuries if not several millennia. The period of rapid retreat due to calving of icebergs into the lagoon is over and the retreat rate will now be slower. Winston Glacier has retreated 600 meters from 2001-2018. The overall lagoon expansion has been limited as the glacier has retreated up an inlet that is 500 m wide.

The AAD has a number of images in their gallery of Heard Island glaciers including Stephenson Glacier. The climate station at Atlas Cove indicates a 1°C temperature rise in the last 60 years. The AAD will also certainly be looking at how this new lagoon impacts the local seal and penguin communities. The population of king penguins increased sharply from the 1940’s into the 21st century, while rockhopper, gentoo, and macaroni penguin numbers declined over the same period (AAD, 2019).

The map below indicates the importance of Stephenson Lagoon and Winston Lagoon for wildlife, king penguins, and cormorants are noted by AAD. The retreat of this glacier follows the pattern of glacier retreat at other glaciers on islands in the circum-Antarctic region Cook Ice Cap, Kerguelen IslandHindle Glacier, and Neumayer Galcier, South Georgia.

A map of Heard Island. (Source: Australian Antarctic Division)

Stephenson Glacier and Winston Glacier are seen in Landsat images from 2008 and 2010. The 2001 terminus locations are indicated by red arrows and terminus locations in 2018 are indicated by yellow arrows.

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Argentina’s Retreating Turbio Glacier Creates a New Lake

Turbio Glacier is at the headwaters of Argentina’s Turbio River and flows into Lago Puelo. The glacier descends east from the Chile-Argentina border at 1,500 meters, descending into a low-slope valley at 1,300-1,000 m.

From 1986-2018 this glacier like many others nearby has retreated substantially leading to development of a new lake. Wilson et al. (2018) noted a substantial growth in the number of lakes in the Central and Patagonian Andes due to the ongoing rapid retreat. Masiokas et al. (2008) reported that significant warming and decreasing precipitation over the 1912–2002 interval in the region. Harrison et al. (2018) observed the number of glacier lake outburst floods have declined despite the increase in lakes.

Turbio Glacier retreat from 1986 to 2018 in Landsat images. Red arrow is 1986 terminus location, yellow arrow 2018 terminus location, and pink arrow glacier across the border in Chile.

In 1986 the glacier terminated at the southeast end of a buttress at the junction with another valley (red arrow in the image above). The glacier was 4.3 kilometers long and was connected to a headwall segment that extends to 1,500 m. There is no evidence of a lake at the terminus of Turbio Glacier.

Across the divide in Chile, the glacier, seen with a pink arrow in the above image, has a length of 3 km. In 1998 the retreat from 1986 has been modest and no lake has formed at Turbio. Across the border in Chile the glacier has divided into two sections.

Turbio Glacier retreat from 1998 to 2017 in Landsat images. Red arrow is 1986 terminus location, yellow arrow 2018 terminus location and pink arrow glacier across the border in Chile.

By 2017 Turbio Glacier has retreated exposing a new lake. The glacier is essentially devoid of retained snowpack, illustrating the lack of a significant accumulation zone that can sustain it. Across the border in Chile the glacier has nearly disappeared with the lower section revealing a new lake and little retained snowpack indicating it cannot survive.

By 2018 Turbio Glacier has retreated 1.3 km, which is over 30 percent of its total length in 32 years. The glacier is separated from the headwall glacier, which can still shed avalanches onto the lower glacier. It is possible that with additional retreat another lake will be revealed in this valley. The substantial retreat here is comparable with that of nearby Argentina glaciers such as Pico Alto Glacier and Lago Cholila . The retreat is greater than on Tic Toc Glacier to the southwest in Chile.

Turbio Glacier in a Digital Globe image from 2013. Red arrow is 1986 terminus location, yellow arrow 2018 terminus location, blue arrows show glacier flow, and pink arrow indicates glacier across the border in Chile. The border is also indicated.

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