Above is a pair of Landsat images from 1984 and 2013 indicating the 2600 m retreat of Antler Glacier in that period. Below is a detailed analysis of the glacier.
The Antler Glacier is an outlet glacier of the Juneau Icefield. It is actually a distributary glacier of the Bucher Glacier. It splits from the Bucher Glacier 8.5 km above where the Bucher Glacier joins the Gilkey Glacer as a tributary. In 1948 it spilled over the lip of the Antler River valley from the Bucher Glacier and flowed 6 kilometers downvalley to end in a proglacial lake. The glacier was 6200 m long in 1948. Note the comparison of the USGS map based on 1948 photographs and the 2005 satellite image below. My only chance to see this glacier in person was in August, 1981 scouting the geology along the Bucher Glacier. Antler Glacier disappeared downvalley into the fog and light snow flurries. The terminus not in site, and icefall to daunting to wish to descend. By 2005 the glacier has retreated almost to the lip of the valley, a 5400 m retreat which is 85-90% of it total length. The Lake -Antler Lake- has expanded from a length of 1.6 km to 4.2 km. The lake is a gorgeous sight, and the valley once filled by the glacier is now nearly devoid of glacier input. The retreat is largely a result of reduced flow from the thinning Bucher Glacier which no longer spills over the valley lip significantly. As the Bucher Glacier continues to thin, the Antler Glacier will cease to exist. This thinning is due to increased melting (ablation) of the glacier. The neighboring glaciers Field and Gilkey Glacier have also thinned and retreated considerably.
The Jakobshavn Isbrae (glacier) has captured our attention over the last 30 years because it has the highest long term average velocity of any glacier in the world. At the ice front the velocity has remained above 16 meters per day for all measurements completed over the last 50 years. The ability of this glacier which is 10 km wide at its front and 800 m thick at the calving front to drain 6.5 % of the Greenland Ice Sheet is its importance. The annual volume of discharge is 40 cubic kilometers. This prompted the University of Maine’s Terry Hughes to take a close look at the glacier in 1985. I participated in that project and one key conclusion we reached was that the Jakobshavn Isbrae was in approximate equilibrium (Pelto and others, 1989). The terminus had not shifted significantly in the past 30 years and no thinning was evident either. The image below of terminus change The top image above is from Jason Box, Byrd Polar Research Center, Ohio State University, and is a mosaic of Landsat and ASTER images indicates a substantial retreat from 1850-1964 of about 30 km. The first image is from the fall of 2009 and the second a Modis image from June 2010. The third from July 2010,from NASA. The last two in the sequence are Landat 8 imagery from May 9 and June 1, 2014 indicate an early summer retreat that was first noticed by the ongoing sharp observations of Espen Olsen. The retreat follows the typical winter advance, and is not back to the 2013 furthest retreat also identified by Espen Olsen. Notes on these latest images below the sequence.
From 1964 to 2001 the glacier terminus did not recede significantly and observations of terminus velocity remained relatively constant at 16 to 20 m year at the glacier front. Then in 1997 an acceleration began. The velocity reached 34 m per day by 2003, twice its normal speed, the glacier thinned by up to 15 m year and retreated 10 km, from 2001 to 2003. From 2004-2007 an additional retreat of 5 km occurred.
The pink arrow notes a prominent lateral rift, the yellow arrow a reference point. Red dot is a transverse rift near the ice front. No large rifts are apparent in the area of the main calving on May 9.[/caption] A bedrock high beneath the glacier is reflected by the sudden increase in slope below point A. What is fascinating is the speed at which the glacier surface below A at Point C was transformed from an ordinary set of transverse crevasses to the chaotic scene typically indicative of an area of rapid acceleration and failure of seracs, those walls betweens crevasses. The glacier has had a profound response to the rifting-calving retreat of the previous day. The area of crevasse transformation is an indication of the connection of this area of the glacier to action at the terminus, the crevassed areas response was so swift that it was effectively involved in the calving retreat incident. The area around C is a zone of weakness to watch for further appearance of rifting. The area in front of the bedrock high is clearly not a place for the terminus to stabilize. The bedrock high itself could well be a point of greater stability for the terminus. Upglacier 2010 is not a good year for the glacier either the snowline is high for June exposing larger areas of bare glacier ice with higher albedo for melting, see image at bottom.
On Jakobshavn the acceleration began at the calving front and spread up-glacier 20 km in 1997 and up to 55 km inland by 2003 (Joughin et al., 2004). Luckman et. al., (2006) observed…“The most plausible sequence of events is that the thinning eventually reached a threshold, ungrounded the glacier tongues and subsequently allowed acceleration, retreat and further thinning. It is reasonable to believe that the 1998 Jakobshavn speed-up, also following a long period of stability, was triggered by the same processes of thinning but occurred earlier and after a shorter period of thinning because the tongue was already afloat.”
On Jakobshavn the acceleration was not restricted to the summer, persisting through the winter when surface meltwater is absent. This indicates that it is the change in conditions at the calving front where the backforce on the glacier was reduced that allowed acceleration and retreat. This is typical for Greenland marine terminating outlet glaciers, they have accelerated most at the calving front and the acceleration is not seasonal. The acceleration is not significantly due to meltwater enhanced lubrication. Below is the acceleration of the last decade compared to before, illustrating that the greatest acceleration is at the calving front (Thomas et al., 2009).
The Jakobshavn is of particular importance as it has a bed below sea level for at least 80 km inland from the terminus. In this reach there are no significant pinning points, or abrupt changes in slope or width (Clarke and Echelmeyer, 1996) that would help stabilize the glacier during retreat. In particular the bed becomes deeper from 24-40 km behind the calving front, which should reinforce calving acceleration (Thomas et al., 2009). Images of Jakobshavn Isbrae in 2001 indicate substantial rifts on the north side of the glacier near the 2005 terminus position, suggesting the glacier had been preconditioned for retreat. In the image below from June 17, 2010 the snowline is evident on the north side of Jakobshavn as the transition to the much lighter blue tone, in this Landsat image. The red line is the June 2009 snowline and the green line the 2008 June snowline.
A comparison of April 2010 (top image below) and April 2011 Landsat image (middle image) indicates a somewhat lower snowline on the Jakboshavn in 2011. The zoomed in version indicates the amount o the ice that is actually icebergs.
The Peridido Glacier, Pyrenees Mountains, Spain has lost 92% of its area since 1894. The glacier lost 50% of its area declining from 90 hectares to 44 hectares from 1991 to 2001. Pyrenees Glacier report, written by a group of scientists including Enrique Serrano from the Universidad de Valladolid and Eduardo Martínez de Pisón from the Autónoma de Madrid has noted the loss of 50-60% of the entire area of Pyrenees Glaciers since 1990. The images of Peridido Glacier from 1898 and 1910 were provided by Eduardo Blanchard. In 1910 as seen in the picture below right, the glacier has three sections each connected. The upper section connected with the mid section by a narrow crevassed icefall, the crevasses indicate active movement. The middle section is connected to the lower avalanche fed section by a wide crevassed icefall. The lower section is not heavily crevassed and has thinned and pulled back from the terminus moraine of the Little Ice Age. This moraine is the sediment ridge in the foreground. By 1998 there is no connection between the three sections, the lower section is nearly gone, with just a bit or relict ice. There are very few crevasses indicating a lack of active movement. The glacier is melting more or less in place. The Pyrenees have experienced a 0.9 C degree warming since 1910.
Peridido Glacier is rapidly disappearing, at the current rate of area loss it cannot survive to 2050, and more likely not until 2030. It is not alone in the Pyrenees, at least three glaciers have disappeared in the last 15 years, Balaitus, La Munia and Perdigurero.
This blog will focus glacier by glacier on the changes that are resulting from climate changes. Each has a unique story, yet there will be a recognizable refrain. Lyman Glacier, North Cascades, Washington retreated 1300 m from 1907 to 2008. Below is the glacier viewed from near Cloudy Pass in 1921 on a Mountaineers expedition and in 2005.
This 76% loss in length has been accompanied by a 88% loss in area and a 91% loss in glacier volume. I first visited the glacier in 1985, and have since been to the glacier on 15 occasions, twice with Bill Long, who first visited the glacier in 1940, measuring its terminus position then. The glacier currently ends in a beautiful expanding glacier lake, with an impressive ice cliff that is 40 meters high, 26 meters above the water. This aids in the retreat as the glacier does calve icebergs occassionally. The rate of retreat is 11 meters per year, for a glacier that is 440 m long, this gives the glacier 40 years at the current retreat rate. The glacier is losing area at a rate of 4% per year, giving it 25 years to survive. Volume loss is between 4 and 5% per year, giving the glacier 20-25 years to survive. By any measure with current climate Lyman Glacier will not survive to 2050. For this glacier the warmer summers since 1977 and the reduced snowpack due to more winter rain events has hastened its decline. The glacier is near a snow measurement station of the US Dept. of Agriculture, which indicates an 18% decline in mean April 1 snowpack since 1945, despite a small rise in precipitation. The glacier is no longer large, but still has considerable thickness, up to 50 m. This particular glacier has not approached equilibrium since the end of the Little Ice Age. Its loss has been hurried along by the recent warming. Even small glaciers take a long time to fully melt away.[url=http://www.youtube.com/watch?v=SiJzgiKReZI]