Juneau Icefield and glacier disconnections

Click to enlarge.  One of the maps from this study.  A classic example of the art of the geomorphologist. But this is a portrait of a glaciated area undergoing rapid change.

See this:

Topographic controls on ice flow and recession for Juneau Icefield (Alaska/British Columbia). 2022.
by Bethan Davies, Jacob Bendle, Jonathan Carrivick, Robert McNabb, Christopher McNeil, Mauri Pelto, Seth Campbell, Tom Holt, Jeremy Ely, Bradley Markle

Earth Surface Processes and Landforms. Research article. Volume 47, Issue 9
July 2022.  Pages 2357-2390
First published: 13 April 2022

https://doi.org/10.1002/esp.5383

This is a very detailed study in glaciology and glacial geomorphology, containing some of the most beautiful geomorphology maps I have ever seen.......

 https://onlinelibrary.wiley.com/doi/10.1002/esp.5383#.YyYOa_vX_ns.twitter

In my previous article on the catastrophic wastage of glaciers I did not distinguish sufficiently between disconnected glaciers and reconstituted glaciers.  

https://brian-mountainman.blogspot.com/2022/09/lament-for-death-of-glaciers.html

In this study the authors say that reconstitited glaciers (like Boyabreen and Supphellebreen in Norway) are supplied by a constant "feed" of ice fragments falling down a very steep cliff, whereas in many disconnected glaciers (like the ones in this study) the exposed bedrock slope is not steep enough for that to happen. The most dramatic effects are seen where the rockwall is exposed around the ELA (equilibrium line altitude). So the lower part of the glacier is entirely within the ablation zone, and wastes away very rapidly -- with the process enhanced or speeded up by torrents of descending meltwater.

Abstract

Globally, mountain glaciers and ice caps are losing dramatic volumes of ice. The resultant sea-level rise is dominated by contributions from Alaska. Plateau icefields may be especially sensitive to climate change due to the non-linear controls their topography imparts on their response to climate change. However, Alaskan plateau icefields have been subject to little structural glaciological or regional geomorphological assessment, which makes the controls on their present and former mass balance difficult to ascertain.

We inventoried 1050 glaciers and 368 lakes in the Juneau Icefield region for the year 2019. We found that 63 glaciers had disappeared since the 2005 inventory, with a reduction in glacier area of 422 km2 (10.0%). We also present the first structural glaciological and geomorphological map for an entire icefield in Alaska. Glaciological mapping of >20 800 features included crevasses, debris cover, foliation, ogives, medial moraines and, importantly, areas of glacier fragmentation, where glaciers either separated from tributaries via lateral recession (n = 59), or disconnected within areas of former icefalls (n = 281). Geomorphological mapping of >10 200 landforms included glacial moraines, glacial lakes, trimlines, flutes and cirques. These landforms were generated by a temperate icefield during the Little Ice Age (LIA) neoglaciation. These data demonstrate that the present-day outlet glaciers, which have a similar thermal and ice-flow regime, have undergone largely continuous recession since the LIA. Importantly, disconnections occurring within glaciers can separate accumulation and ablation zones, increasing rates of glacier mass loss. We show that glacier disconnections are widespread across the icefield and should be critically taken into consideration when icefield vulnerability to climate change is considered.

Since 2005 the ice-covered area has reduced by 422 km2, and 63 glaciers have disappeared from this study area alone.  In some cases the surface lowering on disconnected glaciers, below the rockwall exposures, was as high as 4m per annum.

Not good news......