Crevasse Reduction and Retreat of Salisbury Snowfield-Almer Glacier, New Zealand

Almer Glacier is fed by the Salisbury Snowfield which also has its own terminus, and both are former tributaries to the Franz Josef Glacier.  In 2007 the Almer Glacier almost reconnected with Franz Josef Glacier.  The glaciers of the southern Alps have some of the highest recorded accumulation rates in their upper sections and highest ablation in the lower reaches. Anderson et al (2006), note accumulation rates exceeding 6 m on Franz Josef Glacier.  This combined with the steep slopes lead to higher velocity and extensive crevassing on even smaller alpine glaciers.  Purdie et al (2014)  examined modern and historic length change for Franz Josef and noted a ~ 3 km loss in length since the 1800s, with the greatest retreat from 1934 and 1983, despite two periods of advance in that 50 year period.  The retreat particularly since 1983 has been punctuated by advances 1983–1999 (1420 m) and 2004–2008 (280 m), with the current retreat up to 2014 being the fastest rate of retreat during the period of record. (Purdie et al , 2014). The annual end of summer snowline surveys by NIWA monitors the Salisbury Snowfield, the snowline was 140 m or more above the equilibrium altitude in 4 of the last six years and 20-30 m below the equilibrium line altitude in the other two.  The net result is significant mass loss in the last six years driven by exceptional melt, driving the retreat.

Salisbury snowfield

Topographic Map of Salisbury Snowfield-Almer Glacier area

Here we examine changes particularly in crevassing as well as retreat of Salisbury Snowfield and Almer Glacier from 2000-2015. In the Google Earth images from 2007 and 2013 the green arrows indicate crevassed areas and the red arrows the terminus of the Almer Glacier above and Salisbury Snowfield below.  The decrease in the amount of crevassing is evident at each location.  This indicates not just a reduction in velocity, but in glacier thickness that is driving flow.  The thinning is evident with the emergence of a bedrock knob at the pink arrow in 2013 that had been covered by crevassed ice in 2007.  The red arrow indicates the terminus where the main Almer Glacier is within 75 m of the Franz Josef Glacier.  By  2013 the terminus is much dirtier and is 200 m from Franz Josef Glacier. The icefall comparison image from 2007 and 2013 indicates the reduction in width and number of open crevasses, probably in depth too. This is something Jill Pelto (UMaine) has been measuring crevasses in the field on Easton Glacier in the North Cascades over the last few years to see how crevasses are changing as a glacier thins and slows (image below).

In 2014 New Zealand had a warm year and snowlines are high for early summer in January 2015 which will continue the retreat.  The Landsat image from January, 2015 suggests further retreat has occurred since 2013, but given the dirty terminus, it is to hard to determine a specific amount.  The retreat here follows the pattern of glaciers across the Southern Alps of New Zealand- Lyell Glacier and Tasman Glacier

salisbury 2007

2007 Google Earth image

salisbury 2013

2013 Google Earth Image.

salisbury icefall comparison

2007-2013 icefall closeup 

crevase depth
2015 Crevasse Assessment, Jill Pelto, North Cascades

salisbury 2000

 

 

 

 

 

 

 

2000 Landsat image

salisbury 2015
 

 

 

 

 

2015 Landsat image

 

Lyell Glacier retreat and separation, New Zealand

The Lyell and Ramsay Glaciers are the northernmost substantial valley glaciers in the Southern Alps of New Zealand. Their combined run-off is the chief source of the Rakaia River. The Lyell glacier was first observed by Dr.von Haast in 1862, from Mein’s Knob (M), at the time the glacier was 9 km long and ended close to Mein’s Knob. In 1949 Lyell glacier extended east from Rangiata Col some 7 km, and Lyell Lake (L) had not yet formed. (Gage, 1951). The Lyell Glacier has been the combined flow from the easterly tributary near Rangiata Col (E) and a northern tributary, Heim Plateau (H). Here we examine Google Earth Imagery and Landsat images from 2000-2013 to identify changes in the Lyell-Heim Glacier complex. lyell map

In 2000 the Heim Glacier (H) reached onto the Lyell Lake valley floor, yellow arrow. In 2001 this is evident along with the fact that Lyell Lake is a single lake. The terminus of the Lyell Glacier is obscured by thick glacier cover, and does end near Lyell Lake at the time, the end of the blue ice of the E tributary is not indicative of the terminus location. By 2013 Heim Glacier has retreated from the Lyell Valley and no longer is connected to the Lyell Glacier. A second small lake has formed as the terminus of Lyell Glacier has melted and retreated, red arrow. The terminus of Lyell Glacier does remain buried by debris, but it is stagnant and melting away. Both the Lyell Glacier and Heim Glacier have retreated 400 m from 2000-2013. The Lyell Glacier will likely experience a more rapid retreat in the near future as the debris covered tongue melts away. The 2013 austral winter featured record warmth, and the early melt season has also been warm in New Zealand, the impact on this glacier can be assessed in March or April as the melt season ends. The NIWA snowline surveys will document the impact on glaciers across New Zealand. The glaciers of New Zealand lost 15% of thier volume from 1976-2008 (Chinn et al, 2012). The retreat is like that of most all New Zealand glaciers today, Donne Glacier, Gunn Glacier, Tasman and Murchison Glacier

lyell glacier 2000
2000 Landsat image

lyell galcier 2001
2001 Landsat image

lyell glacier 2013a
2013 Landsat image

lyell glacier 2013
Landsat image 2013

lyell glacier ge
Google Earth image

lyell terminus
Google earth image of terminus

Tasman Glacier Retreat Update 2013

The New Zealand National Institute of Water and Atmospheric Research has been examining the changes in volume and snowline on New Zealand Glaciers since 1977. This survey has concluded for 2011 and 2012 that the snowline has been too high for glacier equilibrium, the glaciers are shrinking. The Tasman Glacier is evidence of this draining from the highest mountains in New Zealand. tasman glacier geFor Tasman Glacier the retreat has been ongoing, the NIWA has noted a retreat of 180 m per year on average since the 1990’s. Dykes et al (2011) note a maximum depth of 240 m, and an expansion of 0.34 square kilometers per year in area. 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 metes 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 km, and that at the current rate this will occur over two decades. This post is an update to the Tasman Glacier Retreat post of 2009 updated in 2011. Imagery of Tasman Glacier indicates the future it faces. There was no lake in 1973 and now it is more than 5.5 km long across a width of about 2 km, and 7 km long at its longest point. Here we examine four images, the 1972 topgographic map, 2000, 2012 and 2013 Landsat images and 2006 Google Earth imagery. In each image an orange and a pink arrow indicate the 2013 terminus on the east and west respectively. In the 1972 map there is no lake at the terminus of the Tasman Glacier. In 2000 the Tasman Glacier lake was 2 km long on the west side and 4.5 km along on the east side. By 2006 the lake has expanded 2.5 km on the west side and 5.5 km long in a narrow tongue on the east side. By 2013 the Lake is 5.5 km long from bank to bank. The glacier has experienced two larger calving events in recent years the first triggered by the Christchurch earthquake in February 2011 and the second on January 30, 2012. Such events can occur because the terminus has thinned to the point that the glacier terminus is more buoyant and crevasses and rifts extend through the thinner ice. tasman 1972

tasman glacier 2000
2000 Landsat Image

tasman glacier 2006
2006 Google Earth Image

tasman glacier 2013
2013 Landsat Image

The last image below is a 2012 Landsat image, the blue arrow indicates the extent to which the lake is expected to extend, the snowline in this image is at 2200 m, red arrow. The glaciers retreat is the same pattern as that of Murchison, Mueller and Hooker Glacier. tasman 20122012 Landsat Image

Douglas Neve Glacier Retreat, New Zealand

The primary portion of the Douglas Glacier was a debris covered valley tongue that is separated from the slopes feeding the terminus reach. The feeder glacier tongues, pink arrows, end on the bedrock slopes above a steep cliff and do not reach the valley glacier below, blue arrows. One section of the glacier, the furthest west portion noted by a pink arrow, the Douglas Neve flows down a steep mountains side. The bedrock slope at the base of the glacier is particularly smooth, which combined with the steep slope,, 40% grade or 22 degree slope, enhances basal sliding. On small alpine glacier the resulting high velocity leads to extensive crevassing. This crevassing can literally penetrate to the base of the glacier near the thin terminus. This leads to portions of the glacier simply separating from the rest of the glacier and avalanching down the slope or melting in place. Here we utilize Landsat images from 2000 and 2012 and Google Earth imagery from 2004 and 2009 to examine the retreat of this glacier. The sequence of images below are in order 2000, 2004, 2009 and 2012. In 2000 the terminus of the glacier terminates at a prominent bedrock fracture at 1640 meters above sea level. In 2004 the terminus still reaches this fracture. The green line in the Google Earth imagery is the 2004 terminus and the burgundy line the 2009 terminus. By 2009 the terminus has retreated 400 meters, and consists of two unsustainable narrow tongues, both less than 100 meterw side. By 2012 the two narrow tongues have been lost, resulting in a 700 m retreat from 2000 to 2012 with the terminus now at 1800 meters. As the retreat of an alpine glacier progresses crevassing typically is reduced as glacier speed declines. Here we see an increase in crevassing from 2004 above to 2009 below in the terminus area, suggesting that the retreat will continue via pieces of the glacier separating from the glacier and avalanching. This process is a much different setting, but similar in practice to ice shelf loss through rifting that reaches the critical point where the rifts lead to icebergs breaking off. At this point the terminus remains unsustainable. This retreat is similar to that of New Zealand glaciers in general as noted by the NIWA and Trevor Chinn, and examined in detail on Murchison Glacier, Mueller Glacier and Gunn Glacier

Mueller Glacier retreat Lake Expansion, New Zealand

Volume loss in New Zealand glaciers is dominated by 12 large glaciers. The NIWA glacier monitoring program has noted that volume of ice in New Zealand’s Southern Alps has decreased 5.8 cubic kilometres, more than 10% in the past 30 years. More than 90% of this loss is from 12 of the largest glaciers in response to rising temperatures over the 20th century. Three of these glaciers are the Tasman, Mueller and Hooker Glacier. Mueller and Hooker Glacier are one valley west of the Tasman Glacier and end in the same valley ending just 3 km apart. Description of the retreat and the role of glacier lakes in accelerating the reteat of Tasman Glacier is discussed in detail in Dykes et al (2011). If we look back to the 1972 Mount Cook Map no lakes are evident at the terminus of Hooker (H), Mueller (M) or Tasman Glacier(T), pink dots indicate terminus location, top image. In 2011 the Landsat image illustrates that this has become a new lake district, bottom image.. Mueller Glacier drains the eastern side of Mount Sefton, Mount Thompson and Mount Isabel. The lower section of the glacier is debris covered in the valley reach from the terminus at 1000 m to 1250 m. A comparison of the Mueller Glacier in a sequence of three Landsat images below from 2000 (top), 2004 (middle) and 2011 (bottom), indicates that the lake at the end of Hooker Glacier had developed by 2000. The lake at the end of the Mueller Glacier was just forming length of 400 meters. By 2004 the Mueller Glacier Lake had expanded to a length of 700 meters. By 2011 the lake had reached 1400 meters in length. The 1000 meter retreat from 2000-2011 will continue in the future as the lower section is stagnant. . A closer look at the lower Mueller Glacier indicates that the lower 2 km is stagnant as indicated by the formation of supraglacial lakes and considerable surface roughness (green arrow) that does not occur when a glacier is active and moving. The glacier has been fed by three different glaciers flowing off of Mount Sefton. Two of them Tuckett and Huddlesoton (pink arrow) are no longer delivering significant ice to the Mueller, only modest avalanching now spills onto the Mueller Glacier. Only the Frind Glacier (yellow arrow) is contributing to the Mueller Glacier. The result is that the end of truly active ice is at the purple arrow, this will develop into the terminus of the Mueller Glacier. In the 2011 image of the glacier the yellow-burgundy arrow indicates the snowline on the Frind Glacier is at 1900 meters, yielding too small of an accumulation zone to support the valley tongue of the Mueller Glacier. This is similar to the situation on nearby Murchison Glacier. Further the lack of ice connection from Huddleston and Tuckett Glaciers to Mueller is again evident, pink arrow. The lake will continue to expand through minor calving and downwasting. The lake has not been surveyed, but seems to lack the depth at the current terminus of Tasman Lake where calving can be more important.

Gunn Glacier Retreat, lake expansion, New Zealand

Gunn Glacier is a small cirque glacier that lies beneath Mount Gunn. A lake has formed recently and is continuing to expand. The 2000 based map of the area published in 2010, does not show a lake, but does at the terminus indicate a small water body surrounded by snow. The New Zealand NIWA has monitored the snowline of New Zealand glaciers over the last 15 years and monitored the volume and area loss of these glaciers including Tasman and Donne Glacier, other like Murchison Glacier are also retreating. On Gunn Glacier the key factor is that four of the last 11 years NIWA has observed that the glacier has lost nearly all of its snowcover indicating a glacier without a persistent accumulation zone (Pelto, 2010). The glacier area has been reduced by 40% from its 1972 mapped area. The 2006 imgery in Google Earth indicates a number of new icebergs adrift in the lake. The lake is now 300 meters across. A view of the cirque indicates a number of bare rock patches on upper sections of the glacier (bottom image), indicating a lack of a consistent accumulation zone. This glacier is thin and without a consistent accumulation it cannot survive (Pelto, 2010). The largest glacier section has an area of 0.2 square kilometers in 2006. The continued expansion of rock areas amidst the glacier and of the lake will lead to the loss of this glacier in the next two decades with a continuation of current climate.

Murchison Glacier Retreat Increasing

Murchison Glacier drains southeast from the Mount Cook region, one valley east of Tasman Glacier. The end of the glacier terminates in a lake that is rapidly developing as the glacier retreats. This retreat will become rapid as 2010 imagery indicates other proglacial lakes have now developed 3.5 km above the actual terminus. These lakes are at a higher elevation and may not endure but do help increase ablation, and in the image below show a glacier that is too narrow to provide flow to the lower 3.5 km. The increased retreat has been forecast by the NIWAand Dykes et al (2009) This lower section is debris covered, stagnant, relatively flat and will not survive long. The demise of the lower section of this glacier will parallel that of Tasman Glacier. The glacier has retreated 2200 meters from the moraines at the south end of the lake. There was not a lake in the 1972 map of the region. A comparison of 2006 and 2010 imagery indicates the decrease in glaciated area in the lake basin. The bottom image is from NASA after the Feb. 2011 earthquake near Christchurch that led to a major calving event of a portion of the rotten stagnant terminus reach of the Tasman Glacier. There is no evident calving event from Murchison Glacier. The lake on the western margin of the valley, separated from the main lake has since April 2010 expanded notably. The glacier still has a significant accumulation area above 1650 m to survive at a smaller size. The lower debris covered tongue is 6 km long and extends from the terminus at 1050 meters to 1200 meters, a very low gradient to supply healthy flow from the accumulation area. The ongoing retreat is triggered by warming and a rise in the snowline in the New Zealand Alps observed by the NIWA.

Donne Glacier Retreat New Zealand

Donne Glacier descends the spectacular east face of Mount Tutoka in southwest New Zealand. This glacier has been undergoing rapid retreat this decade creating a new alpine lake. The National Institute of Water & Atmospheric Research (NIWA) conducts an annual survey of the snowline of New Zealand glaciers. In order to thrive a glacier must have at 50-70% of its area snowcovered at the end of the summer melt season. For NZ glacier NIWA has noted 67% as the key to equilibrium conditions. If then snowline is above normal the glacier will lose mass, if the snowline is lower than normal the glacier will gain mass. Since 2000 the snowline has been above normal in nine of the ten years, only in 2005 was the snowline slightly lower than normal (NIWA, 2010). In 2009 the snowline was the highest of any of the years The result of a decade of high snowline’s is glacier mass loss and retreat. Below is a sequence of images from 2000, 2003, 2006 and 2009 of Donne Glacier the first and last images are from NIWA and the middle two are Google Earth images.
In 2000 the glacier reaches almost all the way across the newly forming unnamed lake. By 2003 the large debris covered section has detached and the lake has doubled in size. In 2006 the faint orange line indicates the 2003 terminus position. The retreat of 100 meters has led to further lake expansion. In the 2009 images the glacier is still ending in the expanding lake, and is still actively flowing. The number of crevasses and the snowcover existing even in poor snow years such as 2003, 2006 and 2009 indicate the glacier still has a persistent accumulation zone. The glacier begins near 2200 meters and descends to about 1300 meters in 2 kilometers. A persistent accumulation zone is key to survival. The retreat and formation of new alpine lakes is also occurring at two nearby glaciers that NIWA observes. Gunn Glacier (below) and Park Pass Glacier (above), in the Google Earth images. Both glaciers end in lakes still occupied by icebergs that used to be part the terminus of the glacier. The icebergs did not calve off so much as representing disintegration of the terminus. The tongue visible on Park Pass Glacier in the middle of the lake is now gone.