Does Debris Cover Offset Glacier Retreat In The Greater Caucasus?

Figure 1: Supra-glacial debris cover (SDC) change on the Elbrus Massif from 1986 to 2014. A SPOT-7 image is used as the background. Blue shows retreat of clean-ice parts. Clean ice in 1986 consists of the clean ice in 2014 (grey, transparent) plus clean-ice area that retreated between 1986 and 2014 (dark blue). Credit: Tielidze et al., 2020

In this week’s blog, Levan Tielidze tells us about supra-glacial debris cover change for the Greater Caucasus. His recent study indicates more than a doubling in the area of supra-glacial debris cover for the Elbrus Massif‘s glaciers from 1986 to 2014, the largest glacierized massif in the whole region. Glaciers on the western slope of the Elbrus Massif are affected by avalanches and thus are partially debris-covered. But the most significant increase of supra-glacial debris cover occurred on the eastern oriented glaciers. Overall, supra-glacial debris cover increased from ~2% to ~4.5% on the Elbrus Massif between 1986 and 2014.

The Greater Caucasus

The Greater Caucasus is one of the world’s highest mountain systems, and the major mountain range of the Caucasus region. The Greater Caucasus contains over 2,000 glaciers, adding up to a total area of about 1,200 square kilometers, with many more glaciers located on the northern slopes than on the southern slopes (Tielidze and Wheate, 2018). To give you an idea of size, the glaciers of the Greater Caucasus are about four times the size of the Republic of Malta. The melting of the ice and snow contained in the Greater Caucasus’ glaciers represents a major source of fresh water for populated places in many parts of the Caucasus region.

Supra-glacial Debris

Supra-glacial debris is the general term for the rocks, soil and dust found on the surface of glaciers, which come from rockfalls and avalanches (see a previous blog on features of supra-glacial debris covered glaciers here). Supra-glacial debris cover is an important control on the ice loss rate of glaciers, and therefore an important component of the glacier mass balance in this region (mass balance is the total net gain or net loss of mass of a glacier). Therefore, correctly estimating supra-glacial debris cover is important to correctly model future glacier evolution in the Greater Caucasus. Until now, studies had been restricted to smaller regions or individual glaciers in the Greater Caucasus, so there was a clear need to provide improved estimates of supra-glacial debris cover and its evolution for this region.

Satellite Imagery

A total of nine Landsat images were used in our study, in order to select nearly 700 glaciers, adding up to a total area of ~590 square kilometers. We also used the Shuttle Radar Topography Mission Digital Elevation Model (SRTM DEM) over our study area to evaluate the debris cover in 500 m altitude bands. The Landsat images were used to make an initial assessment of the supra-glacial debris cover and the SPOT-7 image was then used to correct supra-glacial debris cover over the Elbrus Massif specifically.

Debris Cover Change From 1986 to 2014

The largest glacier in the Greater Caucasus is the Bezingi Glacier. The area covered by supra-glacial debris for the Bezingi Glacier increased from ~11% to ~ 20% between 1986 and 2014. In contrast, there was a reduction in the total glacier area by ~6% during the same period, and the glacier tongue became ~374 m shorter (Fig.2). In comparison, the debris-free Karaugom Glacier (third largest glacier of the Greater Caucasus), located in the same region, shrank in length by ~18% (i.e. 1366 m shorter, Fig.2). This suggests that the debris-covered glaciers in the Greater Caucasus are not shrinking as quickly as the debris-free glaciers.

Figure 2: Debris-covered Bezingi and debris-free Karaugom glacier retreat in 1986-2014. Blue color corresponds to the glacier. White and yellow lines correspond to the glacier terminus in 1986 and 2014. A Landsat 5 image for 6/08/1986 and a Landsat 8 image for 03/08/2014 are used as background. Credit: Levan Tielidze.

The Elbrus Massif contained the smallest percentage of supra-glacial debris cover in our entire study region back in 1986. Since then, the debris-covered area more than doubled between 1986 and 2014. Between 1986 and 2014, the supra-glacial debris cover area was highest on the eastern slope of the Elbrus, while it was lowest on its western slopes. Over that same period, we observed that the glaciers located on the eastern slopes showed the strongest decrease in surface area while the glaciers on the western slope showed the weakest decrease in surface area (Fig.3). This confirms the importance of debris cover for reducing glacier loss.

Figure 3: Total glacier area and supra-glacial debris cover area (in yellow) change on the Elbrus Massif between 1986 and 2014. A Landsat 5 image for 26/08/1986 and a SPOT-7 image for 20/08/2016 are used as background. Credit: Tielidze et al., 2020

Overall, we found an increase in supra-glacial debris cover for all investigated glaciers from ~7% in 1986 to ~13% in 2014. For all regions investigated in the Greater Caucasus, the area of supra-glacial debris cover increased, although the rate of increase varied between the western, central and eastern sections of the mountain range (Fig.4). The cause for this increase in supra-glacial debris cover is still being studied. It could be controlled by climate, lithology of the relief (i.e. the types of rock the relief is made of), as well as the different tectonic and ongoing mountain building (uplifting) processes.

Figure 4: Study area with percentage change of supra-glacial debris cover in the Greater Caucasus by region. The SRTM DEM is used as background. Credit: Tielidze et al., 2020

The glaciers in the Greater Caucasus have retreated continuously since 1960, suggesting that the shielding effect of increased supra-glacial debris cover may only partially offset the glacier loss. Other glaciers in the world also show a similar behavior, such as the Zmuttgletscher, in the Swiss Alps (see this study) or the debris-covered and debris-free glaciers in the Himalayas (see this study).

Given the increasing supra-glacial debris cover in the Greater Caucasus region, and its effect on glacier response to climate change, close monitoring of the glaciers in this part of the world should continue. The recent observed increase in the supra-glacial debris cover area in this region may alter the mass balance of the glaciers, depending on debris thickness and properties. Feedbacks between the ice and the debris overlying it will certainly affect the future evolution of these glaciers and should be considered when modelling these glaciers in general.

This post was written by Levan Tielidze originally published on the blogs of the European Geosciences Union.

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Progress Made Toward Understanding Glacier Surge Motion

Previous studies of glacial surges neglected to account for till mechanics––the unsorted glacial sediments underlying glacier beds. A new study submitted to Proceedings of the Royal Society A in January 2020 accounts for the hydromechanical properties of those sediments.

From the abstract: “Glacier surges are quasi-periodic episodes of rapid ice flow that arise from increases in slip-rate at the ice-bed interface. The mechanisms that trigger and sustain surges are not well-understood. Here, we develop a new model of incipient surge motion for glaciers underlain by sediments to explore how surges may arise from slip instabilities within this thin layer of saturated, deforming subglacial till. Our model represents the evolution of internal friction, porosity, and pore water pressure within the sediments as functions of the rate and history of shearing. Changes in pore water pressure govern incipient surge motion, with less-permeable till facilitating surging because dilation-driven reductions in pore-water pressure slow the rate at which till tends toward a new steady state, thereby allowing time for the glacier to thin dynamically. The reduction of overburden pressure at the bed caused by dynamic thinning of the glacier sustains surge acceleration in our model. The need for changes in both the hydromechanical properties of the till and thickness of the glacier creates restrictive conditions for surge motion that are consistent with the rarity of surge-type glaciers and their geographic clustering.”

Read the full study here.

Storstrømmen and L. Bistrup Bræ in east Greenland probably are the largest surge‐type glaciers in the world (Source: WikiCommons).

Supra-glacial Debris Cover Changes in the Greater Caucasus from 1986 to 2014

New research on debris atop glaciers in the Caucasus––an important and understudied region––spans nearly three decades of change for nearly 700 of the area’s glaciers. While some debris accelerates melt; a lot can protect against it. A new study exploring the pattern was published on February 14 in The Cryosphere.

From the abstract: “Knowledge of supra-glacial debris cover and its changes remain incomplete in the Greater Caucasus, in spite of recent glacier studies. Here we present data of supra-glacial debris cover for 659 glaciers across the Greater Caucasus based on Landsat and SPOT images from the years 1986, 2000 and 2014. We combined semi-automated methods for mapping the clean ice with manual digitization of debris-covered glacier parts and calculated supra-glacial debris-covered area as the residual between these two maps.”

Read the full study here.

Supra-glacial debris cover increase on the Elbrus Massif from 1986 to 2014. SPOT-7 image from 20 August 2016 is used as the background. Blue shows retreat of clean-ice parts. Clean ice in 1986 consists of the clean ice in 2014 (light blue, transparent) plus clean-ice area that retreated between 1986 and 2014 (dark blue) (Source: Tielidze et al)

Glacier Retreat Could Allow Expansion of Mining in Greenland

As Greenland’s glaciers retreat, mining companies are prospecting the exposed mineral riches. One Canadian company is going after molybdenum, an important metal for electronics and communication. According to Live Science, small amounts of molybdenum can be found in a wide variety of products: missiles, engine parts, drills, saw blades, electric heater filaments, lubricant additives, ink for circuit boards and protective coatings in boilers. It is also used as a catalyst in the petroleum industry.

Greenland Resources Inc is a Canadian reporting issuer regulated by the Ontario Securities Commission, focused on the acquisition, exploration and development of mineral properties in Greenland. Yahoo Finance reports that the The Greenland Mineral Authority has provided comments on environmental and social impact assessments and is working with the Geological Survey of Denmark and Greenland on three deliverables:

  1. A high-resolution satellite study to forecast glacial ablation at Malmbjerg during the years 2028-2048 to better understand how the Malmbjerg molybdenum surface mineable mineral resource estimate may increase with the current accelerated glacial ablation that could positively impact project economics;
  2. An updated Digital Elevation Model that will show the magnitude and spatial distribution of recent changes in glacier thickness; and
  3. A time-series of annual surface mass balance on Malmbjerg, to understand the site-specific increase in ice melt over the past four decades.

Will other rapidly de-glaciating regions of the world, like Antarctica, be next?

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