Debris-covered glacier landsystems

Debris-covered glaciers are valley glaciers that have a layer of rocks and sediment on top of the ice surface. While this can range from a thin smattering of rocks to a thick layer several meters deep (even on the same glacier surface), we typically define a debris-covered glacier as one with a mostly continuous layer of supraglacial debris over the ablation area, usually increasing in thickness towards the terminus1,2.

Debris-covered glacier landsystems are therefore generally similar to those of clean-ice valley glaciers, but with a few key differences and unique features.

The debris-covered Chola Glacier, Nepal. The width of the image is ~1.5 km (across the glacier terminus and glacier-dammed lake).

Where are debris-covered glaciers found?

There is no geographical limitation on debris-covered glaciers3 – they are found everywhere you might find clean-ice glaciers. There are even counterparts on Mars4! The most important control on whether a glacier surface is clean or debris-covered is the supply of debris from the surrounding topography. This means that you can have different glacier surfaces even in neighbouring valleys (e.g. Glaciers Noir and Blanc, French Alps).

The debris-covered Khumbu Glacier, Nepal. The glacier is clean in the upper ablation area (mid-left of the image), with the debris cover appearing and increasing in thickness towards the terminus (ice flow is towards the bottom right of the image).

Developing debris covers

Debris can be supplied to the ablation area in a number of ways, for example:

  • Rockfalls or avalanches from surrounding hillslopes, directly onto the ablation area;
  • Slumping from lateral moraines (usually spatially limited5);
  • Melt-out of englacial debris6.

Debris can be trapped in the ice through rockfalls in the accumulation area (becoming englacial when it is buried with the annual snowfall), falling into crevasses, or being entrained at the bed and later elevated to an englacial position by differential glacier motion. The debris is transported with the ice to the ablation area, and as the glacier surface melts, the debris melts out with it and adds to the amount of debris in the surface layer.

Folded englacial debris layers, approximately parallel with the ice surface, exposed in an ice cliff on Khumbu Glacier, Nepal.

Dynamics of debris-covered glaciers

The surface melt rates of debris-covered glaciers are dependent on the supraglacial debris layer thickness and thus vary spatially. Where debris layers are thick, particularly at the terminus, the ice surface is insulated, and heat has to be transferred through the debris layer before it reaches the ice surface.

This means that debris-covered glaciers are slower to respond to shifts in climate than clean-ice glaciers, and may persist for longer in the current warming climate – making them increasingly important and valuable water resources7,8.

Melt rates are greatest when the debris layer is only a few millimetres to centimetres thick9, so mass loss tends not to occur by terminus fluctuations, as for clean-ice glaciers. Instead, mass loss occurs primarily through surface lowering (thinning), with greatest rates often in the middle of the ablation area10. This difference produces some unique surface features that are not typically found on clean-ice valley glaciers.

Looking across the surface of Khumbu Glacier, Nepal. The different melt rates according to the local debris thickness results in a “hummocky topography” punctuated by ice cliffs and supraglacial ponds.

Unique features of debris-covered glaciers

Ice cliffs are steep faces of bare, exposed ice. These might be the only way you know you’re walking on a debris-covered glacier’s ablation area!

Ice cliffs on Khumbu Glacier, Nepal. Where melt rates are high, the clean-ice faces can become covered in a thin layer of sediment by meltwater transport.

Supraglacial ponds are pools of water, ranging in diameter from centimetres to kilometres. While not typically found on clean-ice valley glaciers, they are increasingly common on low-gradient areas of ice sheets and shelves. Ponds store meltwater and delay its transport downstream11.

A supraglacial pond on Khumbu Glacier, Nepal. The pond surface is partly frozen.

The bare ice faces and warm water of these features both act to further enhance glacier melt rates, resulting in a positive feedback cycle. Ponds and cliffs are commonly found together and referred to as “hotspots” of debris-covered glacier ablation.

An ice cliff adjacent to a (frozen) supraglacial pond on Khumbu Glacier, Nepal.

As the ponds expand, they can merge, storing more water and contributing even more to glacier ablation. In some cases, this can result in one large proglacial lake12 – either at the terminus (dammed by the terminal moraine) or further upglacier where melt rates were highest and the most ponds produced.

Such a lake is then dammed by the “dead” glacier ice below, which has been cut off from the main active glacier as the lake has expanded. This ice-cored moraine can be eroded over time by the warmer lake water, potentially making the dam unstable.

The terminus and calving front of Imja Glacier into its proglacial lake, Imja Tsho. The width of the glacier front is ~0.75 km and has retreated rapidly since the formation of the proglacial lake, which measured ~2.7 km in length in 2018, filling the basin between the lateral and terminal moraines. Some recently calved icebergs are floating just in front of the glacier terminus.

Unstable proglacial lake dams, whether moraine- or ice-dammed, can occasionally produce a risk of a Glacial Lake Outburst Flood (GLOF). GLOFs can present considerable hazards to communities living downstream, though mitigation strategies are increasingly being implemented.

For example, damage from the 2016 Lhotse Glacier GLOF, Nepal, was minimal due to the construction of gabions around the downvalley village of Chukhung13. However, many proglacial lakes are stable because water leaves through an outlet channel, and in some regions of the world (such as the Karakoram), the number of these lakes is actually decreasing14.

About the Author

This article was contributed by Katie Miles from Aberystwyth University. Katie is a PhD candidate and lecturer at Aberystwyth University, specialising in glaciers and glacial hydrology. She’s interested in what happens beneath the ice surface, and her PhD research investigated this for Khumbu Glacier, a high-elevation debris-covered glacier in Nepal. You can follow Katie on Twitter @Katie_Miles_851. She has had two field seasons on Khumbu during 2017 and 2018 with the EverDrill research project.

Katie Miles


1.        Kirkbride, M. P. Debris-Covered Glaciers. in Encyclopedia of Snow, Ice and Glaciers (eds. Singh, V., Singh, P. & Haritashya, U.) 180–182 (Springer Netherlands, 2011). doi:10.1007/978-90-481-2642-2_622.

2.        Miles, K. E. et al. Hydrology of debris-covered glaciers in High Mountain Asia. Earth-Science Rev. 207, 103212 (2020).

3.        Scherler, D., Wulf, H. & Gorelick, N. Global Assessment of Supraglacial Debris-Cover Extents. Geophys. Res. Lett. 45, 11,798-11,805 (2018).

4.        Hubbard, B., Souness, C. & Brough, S. Glacier-like forms on Mars. Cryosph. 8, 2047–2061 (2014).

5.        van Woerkom, T., Steiner, J. F., Kraaijenbrink, P. D. A., Miles, E. S. & Immerzeel, W. W. Sediment supply from lateral moraines to a debris-covered glacier in the Himalaya. Earth Surf. Dyn. 7, 411–427 (2019).

6.        Kirkbride, M. P. & Deline, P. The formation of supraglacial debris covers by primary dispersal from transverse englacial debris bands. Earth Surf. Process. Landforms 38, 1779–1792 (2013).

7.        Anderson, L. S. & Anderson, R. S. Modeling debris-covered glaciers: Response to steady debris deposition. Cryosph. 10, 1105–1124 (2016).

8.        Immerzeel, W. W. et al. Importance and vulnerability of the world’s water towers. Nature 577, 364–369 (2020).

9.        Østrem, G. Ice Melting under a Thin Layer of Moraine, and the Existence of Ice Cores in Moraine Ridges. Geogr. Ann. 41, 228–230 (1959).

10.      Watson, C. S. & King, O. Everest’s thinning glaciers: implications for tourism and mountaineering. Geol. Today 34, 18–25 (2018).

11.      Irvine-Fynn, T. D. L. et al. Supraglacial Ponds Regulate Runoff From Himalayan Debris-Covered Glaciers. Geophys. Res. Lett. 44, 11,894-11,904 (2017).

12.      Benn, D. I. et al. Response of debris-covered glaciers in the Mount Everest region to recent warming, and implications for outburst flood hazards. Earth-Science Rev. 114, 156–174 (2012).

13.      Rounce, D. R., Byers, A. C., Byers, E. A. & McKinney, D. C. Brief Communications: Observations of a glacier outburst flood from Lhotse Glacier, Everest area, Nepal. Cryosph. 11, 443–449 (2017).

14.      Gardelle, J., Arnaud, Y. & Berthier, E. Contrasted evolution of glacial lakes along the Hindu Kush Himalaya mountain range between 1990 and 2009. Glob. Planet. Change 75, 47–55 (2011).

Shelf-edge margins of the British-Irish Ice Sheet

What is the shelf-edge margin of the British-Irish Ice Sheet? | How do we know the British-Irish Ice Sheet reached the shelf edge? | How did the British-Irish Ice Sheet retreat from the shelf edge? | Why do we study shelf-edge margins of the British-Irish Ice Sheet?

What is the shelf-edge margin of the British-Irish Ice Sheet?

At its maximum extent, around 27,000 years ago1, the British-Irish Ice Sheet covered most of Britain, all of Ireland, and extended all the way to the edge of the continental shelf2. The continental shelf is the shallow part of the ocean that surrounds most land, before the continental slope drops into the deep oceans. Around Britain and Ireland, this continental shelf extends 100-150 km from the present-day coastline. It is generally shallower than 120 m below present-day sea level. The maximum extent of the British-Irish Ice Sheet, crossing over the continental shelf, is shown in Figure 1.

Figure 1. The maximum extent of the British-Irish Ice Sheet, extending over the continental shelf (green) to reach the ocean at the shelf edge (blue). Trough-mouth fans are shown in yellow outlines, taken from the BRITICE v2 dataset7. Bathymetry data are from the GEBCO 2016 dataset ( and land elevation from the European Environment Agency EU-DEM (

Figure 2 shows a cross-section that runs from the northwest to the southeast from the deep ocean of the Rockall Trough through to the Cairngorm mountains of Scotland. The ice sheet margin is located at the shelf edge because in deeper water, the ice floats and becomes an ice shelf. Thick ice, which built up in the accumulation zones of the Outer Hebrides and Scottish domes1, spread out across the flat topography of the continental shelf to reach the margin when the ice sheet was at its greatest volume.

Figure 2. A cross-section from the deep ocean to the mountains, showing the relationship of the British-Irish Ice Sheet to the continental shelf. Bathymetry data are from the GEBCO 2016 dataset ( and land elevation from the European Environment Agency EU-DEM (

How do we know the British-Irish Ice Sheet reached the shelf edge?

Evidence for the ice sheet reaching the shelf edge comes from marine geological surveys. These geophysical surveys tell us the shape of the seabed, and the pattern of sediment layers under the seabed. Such surveys reveal glacial geomorphology all over the continental shelf, right out to the shelf edge3. At the shelf edge, large trough-mouth fans are present (Figure 3), which tell us that large volumes of sediment were carried to the shelf edge by ice, then tipped over the side and down the continental slope. The style of these fans, the type of glacial geomorphology, and the depth of the shelf edge, tell us that the British-Irish Ice Sheet ended in the ocean. This means the British-Irish Ice Sheet was marine-based, much like the West Antarctic Ice Sheet is today.

Figure 3. Trough-mouth fans formed at the margin of the British-Irish Ice Sheet. Trough-mouth fans are shown in yellow outlines, taken from the BRITICE v2 dataset7. Bathymetry data are from the GEBCO 2016 dataset ( and land elevation from the European Environment Agency EU-DEM (

How did the British-Irish Ice Sheet retreat from the shelf edge?

Figure 4. Ice streams of the British-Irish Ice Sheet and their relation to trough-mouth fans and the shelf-edge margin. Background image from Gandy et al., 20196.

Along the shelf edge, the British-Irish Ice Sheet had numerous ice streams (Figure 4). These ice streams moved vast amounts of ice rapidly from the accumulation zone of the ice sheet out to the shelf edge. Ice streams are vulnerable to rapid retreat when they are marine-terminating, a process known as marine ice sheet instability. This instability can cause rapid, irreversible retreat, and is suggested to have caused the demise of the Minch Ice Stream4. The removal of ice shelves and retreat of ice streams can cause a debuttressing effect5, which caused the retreat of the ice sheet between the ice streams. De Geer moraines are moraines that form underwater, and are present on the continental shelf north of Scotland (Figure 5). These moraines tell us that the sectors of ice between the ice streams, known as interstreams, retreated more slowly as sea level rose3, as ice from the accumulation zones flowed more slowly out to an ice margin, which was calving icebergs straight into the sea1.

Figure 5. Glacial geomorphology offshore Orkney, showing retreat moraines and De Geer moraines, based on Bradwell et al. (2008)3 and Bradwell and Stoker (2015)8. Bathymetry data are from the GEBCO 2016 dataset ( and land elevation from the OS Terrain 5 dataset (

Why do we study shelf-edge margins of the British-Irish Ice Sheet?

The marine ice sheet instability theory could mean that present day, marine-based ice sheets, such as the West Antarctic Ice Sheet, may retreat rapidly4. That means studying past marine-based ice sheets, such as the British-Irish Ice Sheet, becomes important to understand what may happen in the future. Theories on the effect of marine ice sheet instability can be tested using models based on actual ice sheet data, such as in the Minch Ice Stream4. These models tell us that ice streams may be vulnerable to marine ice sheet instability6, but interstream areas may be more dependent on calving, and topography beneath the ice sheet, and less susceptible to runaway retreat1,3.


1.          Clark, C. D., Hughes, A. L. C., Greenwood, S. L., Jordan, C. & Sejrup, H. P. Pattern and timing of retreat of the last British-Irish Ice Sheet. Quat. Sci. Rev. 44, 112–146 (2012).

2.          Hughes, A. L. C., Gyllencreutz, R., Lohne, Ø. S., Mangerud, J. & Svendsen, J. I. The last Eurasian ice sheets – a chronological database and time-slice reconstruction, DATED-1. Boreas 45, 1–45 (2016).

3.          Bradwell, T. et al. The northern sector of the last British Ice Sheet: Maximum extent and demise. Earth-Science Rev. 88, 207–226 (2008).

4.          Gandy, N. et al. Marine ice sheet instability and ice shelf buttressing of the Minch Ice Stream, northwest Scotland. Cryosph. 12, 3635–3651 (2018).

5.          Sejrup, H. P., Clark, C. D. & Hjelstuen, B. O. Rapid ice sheet retreat triggered by ice stream debuttressing: Evidence from the North Sea. Geology 44, 355–358 (2016).

6.          Gandy, N. et al. Exploring the ingredients required to successfully model the placement, generation, and evolution of ice streams in the British-Irish Ice Sheet. Quat. Sci. Rev. 223, 105915 (2019).

7.          Clark, C. D. et al. BRITICE Glacial Map, version 2: a map and GIS database of glacial landforms of the last British-Irish Ice Sheet. Boreas 47, 11-e8 (2018).

8.          Bradwell, T. & Stoker, M. S. Asymmetric ice-sheet retreat pattern around northern Scotland revealed by marine geophysical surveys. Earth Environ. Sci. Trans. R. Soc. Edinburgh 105, 297–322 (2015).

Global SRTM digital elevation model

If you’re introducing the idea of GIS and digital elevation models, then check out this Earth Engine tool for the global SRTM.

This Earth Engine App visualises the SRTM, a global 30 m digital elevation model (a DEM). The colour ramp is linked to the elevation range on the screen; as you zoom in and out, the colours change automatically.

This app visualizes the global SRTM 30m DEM.

Students can visualise how the land changes with elevation near their hometown, or varies across different mountain ranges and river valleys.

As you zoom and pan, there wil be a delay for the DEM to load.

By default, the map is centered on the confluence of the Wisconsin and Mississippi rivers in the USA.

If you wish to take things further, the app allows you to easily download the data in the viewport as a GeoTiff format, which could be integrated into an ArcGIS lesson.

This Earth Engine app was made by Kai Hu from the University of Wisconsin-Madison.

Water resources

Mountains around the world provide water for downstream communities. Glaciers and snowpacks store the water, and release it in dry seasons as the snow and ice melts. Glaciers are therefore a water resource, but this water resource is threatened by glacier recession.

Water is essential for life on Earth. Human societies use water to irrigate their fields, generate hydropower, for domestic consumption, and for boiodiversity and wildlife.

Perpetual Planet: Water Towers

The World’s Water Towers were ranked and listed by Immerzeel et al. (2020), with the supply and the demand on each mountain water tower being characterised.

For the study, scientists assessed the water towers’ importance, not only by looking at how much water they store and provide, but also how much mountain water is needed downstream and how vulnerable these systems and communities are to a number of likely changes over the next few decades.

By analysing these various factors of the 78 mountain water towers worldwide, scientists have identified the five most relied-upon systems by continent that should be on the top of regional and global political agendas:

  • Asia: Indus, Tarim, Amu Darya, Syr Darya, Ganges-Brahmaputra
  • Europe: Rhône, Po, Rhine, Black Sea North Coast, Caspian Sea Coast
  • North America: Fraser, Columbia and Northwest United States, Pacific and Arctic Coast, Saskatchewan-Nelson, North America-Colorado
  • South America: South Chile, South Argentina, Negro, La Puna region, North Chile

To explore the data in more detail and compare water tower rankings, visit

Explore the Water Towers with National Geographic

Water Balance App

The Water Balance App could be useful as a front-of-class tool. It shows soil moisture, snow pack, precipitation, evapotranspiration, runoff and change in storage globally and over time. The Water Balance App presents data on the different inputs, outputs and stores of water around the world over the last 20 years.

Students may be able to work through exploring the app on their own, or in a classroom environment. This is an ArcGIS Online app.

There is a ready-made storymap and guide to maximising success at A-Level here.

Water Balance App

Further reading

Films and video resources

Time for Geography

This excellent website has a number of videos explaining key processes and geomorphic features of Britain. It is produced by academics at a wide range of universities, and includes “knowledge boosters” on a range of subjects, including Glaciation, Waterfalls, Coasts and much more.

There are a number of videos about glaciation, with “knowledge booster” and “grade booster” videos.

Films about Climate Change and Glaciers

There are a number of excellent climate change documentaries and films publicly available for little investment.

  • Thin Ice talks about climate change from the scientists’ perspectives. The website has many resources, including extra clips and information. The film can be rented and watched online for NZ$5 and downloaded for NZ$10.
  • Chasing Ice uses stunning repeat photography to characterise glacial recession over several years. The film is available to download from iTunes.
  • Operation Iceberg is a BBC documentary that follows the exploits of scientists in Greenland. Stunning visuals are combined with exciting feats of bravery for compelling viewing.


YouTube is an outstanding teaching resource, with thousands of videos explaining all aspects of glaciology. Here are some of my favourites:

Interactive apps and models

Interactive glacier models

Get the students playing with one of these simple, browser-based interactive glacier models, and understanding concepts such as ablation, accumulation, glacier advance and recession and glacier mass balance.

You can also explore the OGGM-edu (see separate page on this).

NASA JPL Virtual Earth System Laboratory

The folks at NASA Jet Propulsion Laboratory have developed a suite of simulations of glaciers, ice sheets and sea level that you can explore at the Virtual Earth System Laboratory. These simulations use real model physics to calculate changes in the ice mass over time.

Preview of Columbia Glacier simulation
Columbia Glacier model from the NASA JPL Virtual Earth System Laboratory

Things to think about: How does changing the surface mass balance (SMB) affect glacier thickness and length? How long does it take to reach a new equilibrium (i.e. what’s the response time?). How does changing the SMB affect melting across the glacier?

IceFlows game

The new IceFlows game (Exeter University) allows students to experiment with ice flow of an ice shelf in Antarctica, and learn about the Antarctic ice sheet.

The Iceflows Game uses real ice physics to demonstrate how ice shelves flow and melt.

Sea level rise

There are a number of interactive student resources on sea level rise.

Exploring present-day glaciers in a GIS


This is a free GIS app that you can use to explore the glaciers and sea ice around Antarctica. Quantarctica is easy to use ,and includes base maps, satellite imagery, glaciology and geophysics data from data centres around the world, prepared for viewing in QGIS.


Google Earth

Google Earth has fabulous satellite images of Antarctica, Iceland, Patagonia, the UK and everywhere else in the world. It lets you explore the continent from the comfort of your sofa. There are fabulous images of crevasses, glaciers, moraines and more.  Google Earth pro allows you to map directly in Google Earth, so you could set a task identifying and mapping moraines, for example.

Drumlins around lago Viedma, South Patagonian Icefield. The background image is Landsat 7 ETM+ from 2001. Mapped in Google Earth Pro.

Explore Scott’s hut through the Google World Wonders project.

WGMS Fluctuations of Glaciers

The World Glacier Monitoring Service has created, in association with ESRI ArcGIS, a browser for investigating the fluctuations of glaciers.

The data are overlain on Google Earth imagery, but you can also choose Bing roads, OpenStreetMap and a variety of other basemaps.

When you zoom into an area, you see circles with numbers in. Clicking on these circles brings up a popup with information about the glacier, including glacier length change over time. Clicking on the graph opens it fully in another tab. This is a really interactive way of learning all about glacier length fluctuations and glacier recession over time. How fast are glaciers receding? Where are they receding fastest? Get the students to think about how the data are created, how reliable the data are, and how consistent the story of glacier recession is.

Randolph Glacier Inventory

From the Randolph Glacier Inventory you can download GIS shapefiles for all the glaciers in the world. Set a practical exploring the glaciers of different parts of the world, or compare the glaciers to the LGM mapped in the Quaternary Glaciations: extent and chronology book.

Overlay the glaciers on satellite images (e.g. Landsat images are freely available from NASA) for a wonderfully immersive practical for the students.

You can also explore the data and select glaciers to download using the GLIMS Viewer.

GLIMS/RGI Glaciers showing current worldwide glacier extent.

Glacial Geomorphology and GIS resources

There are several resources available for teaching about glacial geomorphology using a GIS.


BRITICE is a brand new (published late 2017) database of all the glacial landforms in Britain. It includes all you need to know about the last glaciation of Britain. There’s an accompanying paper that explains the landforms, maps you can buy or download and print yourself, and best of all, a huge GIS database that you can download and explore for free.  If you don’t use a GIS, you can use the free ArcGIS Online app to explore the landforms near where you live.

BRITICE V2 (Clark et al., 2017)


Resources on the glacial geomorphology of Patagonia, including a freely available map on ArcGIS Online, are available on this very website.

The GIS data are freely available from ArcGIS Online, and you can use the resources available on this website to learn in more detail about the differnet landforms.

PATICE: A new reconstruction of the last Patagonian Ice Sheet.

You can explore the geomorphological and chronological data for the reconstruction of the Patagonian Ice Sheet in the ArcGIS online map.

PATICE interactive map on ArcGIS Online.

Journal of Maps

There are a number of papers on Journal of Maps which are of excellent use in teaching glaciology.

Hughes et al. 2010a provide an excellent map of subglacial bedforms of the last British Ice Sheet (included in the BRITICE V2 database) and a downloadable database of all the published ages constraining the deglaciation of Britain (Hughes et al 2010b).

The Glacial Map of Southern South America (Glasser and Jansson, 2008) is freely accessible and shows all the glacial features in southern South America.

DATED-1 Database

This open-access publication, again led by Anna Hughes (Hughes et al. 2016), provides the most up-to-date and comprehensive reconstruction yet of the last British and European ice sheets. The authors also provide GIS shapefiles of the reconstruction for you to peruse.

DATED Database, by Hughes et al. 2016
DATED-1 Database (Hughes et al. 2016). Click to view animation.

Digital Elevation Models

Get the students doing interactive practicals using the glaciers downloaded from the RGI overlain on a Landsat image or an ASTER GDEM.

This is a free, global DEM that gives high-quality digital elevation data.

The Shuttle Radar Topography Mission (SRTM) also provides free global digital elevation data.

Field Trips

As a Geography Teacher, you may want to lead field trips for your students. If you are looking for inspiration, then the Quaternary Research Association has a series of field guides available for purchase from their website. They are affordable and cover many areas of the UK.

The QRA is the UK organisation for the study of the Quaternary. It is a friendly association of academics, graduate students and interested members of the public. There are many school teacher members, and school teachers are very welcome to join.

The QRA field guides contain information about the Quaternary history of the site, including glaciation. Want to lead a field trip to Gower or Norfolk? There’s a guide for that. Want to visit Teesdale or the Pennines? There’s a guide for that. These excellent resources provide all the information you need to run a field trip. Members get a discount on the list price.

QRA Fieldtrip to Teesdale, May 2017

Annual membership is just £20.  Members are able to participate in the two or three annual fieldtrips to different parts of the UK, attend the QRA conferences and short discussion meetings, and receive the Quaternary Newsletter journal and the QRA Circular.