CR
Cryospheric Sciences

debris covered glacier

Image of the Week – Making waves: assessing supraglacial water storage for debris-covered glaciers

Fig. 1: Deriving the bathymetry and temperature of a large supraglacial pond on Khumbu Glacier, Everest region of Nepal. The sonar-equipped unmanned surface vessel nicknamed ‘BathyBot’ (left), and kayak retrieval of temperature loggers (right) [Credit: Scott Watson].

A creeping flux of ice descends Everest, creating the dynamic environment of Khumbu Glacier. Ice and snow tumble, debris slumps, ice cliffs melt, englacial cavities collapse, ponds form and drain, all responding to a variable energy balance. Indeed, Khumbu Glacier is a debris-covered glacier, meaning it features a layer of sediment, rocks and house-sized boulders that covers the ice beneath. Recent advances in understanding debris-covered glacier hydrology come from combining in situ surveys with remotely sensed satellite data.


Khumbu Glacier

The dramatic beauty of Nepal’s Everest region attracts a mix of trekkers, climbers, and scientists. Flowing down from the slopes of Mount Everest, the debris-covered Khumbu Glacier has drawn scientists from the mid-1900s, and offers temporary residence for research teams and a myriad of climbers. In some locations, Khumbu Glacier has thinned by up to 80 m in the last three decades, leading to moraines overlooking the glacier with impressive topographic relief and providing an instant visualisation of glacier mass loss for trekkers heading to Everest Base Camp.

Melt at the surface of this glacier is moderated by an undulating debris layer, which insulates the ice beneath,   and enhanced locally by dynamic surface features such as supraglacial ponds and ice cliffs thinly veiled by debris. These features contribute disproportionately to melt and lead to the development of hummocky, pitted surface topography. The resulting variable surface topography and melt rates complicate meltwater runoff and flow routing across the glacier. To better understand them, in situ surveying (Fig. 1) is increasingly combined with fine spatial-temporal resolution satellite imagery to reveal the hydrological evolution of debris-covered glaciers, which is closely linked to their mass loss.

Hydrology of Khumbu Glacier

As with debris-free glaciers, water may be routed through supraglacial, englacial, and subglacial pathways, which are conceptually distinct but physically link to one another.

At Khumbu Glacier, surface channels collect and rapidly convey meltwater generated in the upper ablation area (Fig. 2), just below the treacherous Khumbu Icefall, incising at a faster rate than the surface melt. In the middle of the debris-covered area, such streams disappear into the glacier’s interior through cut-and-closure and/or hydrofracture.

Fig.2: The upper ablation area of Khumbu is drained by supraglacial channels which enter the glacier’s interior through hydrofracture and cut-and-closure, while the lower portion is characterised by pitted surface depressions and an increasing density of ponds. Right panel looking east to west shows the hummocky topography and ponding on Khumbu Glacier. [Credit: Evan Miles (left), Ann Rowan (right)].

In areas of low surface gradient , and particularly throughout the hummocky lower reaches of the glacier, supraglacial ponds collect water in surface depressions. These features haveregulate the runoff of debris-covered glaciers by seasonally storing meltwater. The annual melt cycle thus leads to pond expansion and contraction, or their disappearance when the protecting debris layer thaws and relict meltwater conduits become avenues for drainage (Fig 3). The areal fluctuation of ponds can be quantified using  satellite images at different times, but cloud cover during the summer monsoon season limits useable imagery at a time when the ponds are most dynamic. Therefore, field-instrumented ponds provide valuable insights into their active melt season behaviour.

Fig. 3: A small 4.5 m deep pond that drained over the course of a year [Credit: Watson et al., 2017a].

Turbid ponds associated with debris influx from ice cliffs are often ephemeral but some can grow to hold vast quantities of water (Fig. 1). Stored water absorbs and transmits solar energy to melt adjacent ice, which generates additional meltwater and leads to pond expansion. The ponds also thermally undercut ice cliffs, leading to both subaqueous and subaerial  retreat (Fig. 4). Khumbu Glacier has been developing a growing network of ponds in recent years, which means meltwater is increasingly stored on the surface of the glacier before contributing to downstream river discharge. Ponds that coalesce into larger and more persistent lakes behind unstable deposits of sediment can in some cases pose a hazard  to downstream communities. Field and satellite-based techniques are therefore used simultaneously to monitor lake development.

 

Fig. 4. Supraglacial ponds often exist alongside ice cliffs. These ‘hot spots’ of melt can be observed with repeat point cloud differencing [Credit: Watson et al., 2017b]. An interactive view of the drained pond basin (right) is available here.

What lies beneath?

Ephemeral ponds drain into the ‘black box’ glacier interior, where relatively little is known about the internal structure and hydrology. Scientists have occasionally ventured into the subsurfac e realm through networks of englacial conduits that become exposed as the glacier thins (Fig. 5); such conduits often re-emerge at the glacier surface but may also lead to the bed. The conduits carry meltwater through the glacier but can become dormant if blocked by falling debris or creeping ice, or when the meltwater that sustains them finds a route of lesser resistance. Whilst satellite data can be used to infer the presence of conduits, field-based methods are required for hydrological budgeting and quantifying meltwater transit times. For example, dye tracing can detect the subsurface passage of meltwater where strategically placed fluorometers measure the receipt and dilution of the dye upon re-emergence. Such methods are crucial for developing an improved understanding of the links between, for example, flow in the supraglacial channels up-glacier and discharge at the outlet.

Fig. 5: An exposed conduit on Lirung Glacier (left) [Credit: Miles et al., 2017] and researchers inside a conduit on Ngozumpa Glacier (right) [Credit: Benn et al., 2017].

 

Outlook

Multiple teams working across the Himalaya are advancing our understanding of debris-covered glacier hydrology, which is essential to forecast their future and quantify their downstream impact. With the ready availability of increasingly high temporal resolution satellite imagery (e.g. Sentinel-2, Planet Labs), the link between field and spacebourne observations will become increasingly complementary. Developing these links is crucial to upscale observations from specific sites more broadly across the Himalaya.

Further reading

Edited by Violaine Coulon and Sophie Berger


Scott Watson is a Postdoc at the University of Arizona, USA. He studies glaciers in the Everest region and the surface interactions of supraglacial ponds and ice cliffs. He also investigates natural hazards and the implications of glacial lake outburst floods.
Tweets @CScottWatson. Website: www.rockyglaciers.co.uk

 

 

Evan Miles is a Research Fellow at the University of Leeds, UK, where he is a part of the EverDrill project’s hot-water drilling at Khumbu Glacier. His recent work has examined the seasonal hydrology and dynamics of debris-covered glaciers, with a focus on the melt associated with dynamic surface features such as supraglacial ice cliffs and ponds.
Tweets @Miles_of_Ice

EverDrill website: www.EverDrill.org

Image of the Week – Drilling into a Himalayan glacier

Image of the Week – Drilling into a Himalayan glacier

How water travels through and beneath the interior of debris-covered glaciers is poorly understood, partly because it can be difficult to access these glaciers at all, never mind explore their interiors. In this Image of the Week, find out how these aspects can be investigated by drilling holes all the way through the ice…


Hydrological features of debris-covered glaciers

Debris-covered glaciers can have a range of hydrological features that do not usually appear on clean-ice valley glaciers, such as surface (supraglacial) ponds. These features are produced as a result of the variable melting that occurs across the glacier surface, depending on the thickness of the debris layer on the surface. Melting is reduced where the debris layer is thick (e.g. near the terminus), which leads to mass loss primarily by thinning, rather than terminus retreat like clean-ice glaciers (read more about this process in this previous blog post). This produces a low-gradient surface covered by hummocks and depressions in which ponds can form, often with steep bare ice faces (ice cliffs) surrounding them. The occurrence of ice cliffs and ponds also affects the surface melt rate, as glacier ice in/on/under these features melts considerably faster (up to 10 and 7 times more, respectively) than that of the debris-covered areas surrounding them (Sakai et al., 2000). Consequently, these hydrological features are an important contributing factor to the general trend of surface lowering of debris-covered glaciers (Bolch et al., 2012).

As a result, most hydrological research on debris-covered glaciers to date has focused on the (more accessible) supraglacial hydrological environment, as well as measuring the proglacial discharge of meltwater from these glaciers, which is a vital water resource for millions of people (Pritchard, 2017). Below the debris-covered surface of these glaciers, next-to-nothing is known about their hydrology; do drainage networks exist within (englacial) or beneath (subglacial) these glaciers, can they exist, and how can they be observed in such challenging environments?

A limited amount of direct research has been carried out in attempt to answer some of these questions, such as speleological techniques to investigate shallow englacial systems on a few glaciers (e.g. Gulley and Benn, 2007; Narama et al., 2017). However, all other inferences of subsurface drainage through debris-covered glaciers have come from hydrogeochemical analyses of water samples taken from the proglacial environment (e.g. Hasnain and Thayyen, 1994) or interpretation of observed glacier dynamics from satellite imagery (e.g. Quincey et al., 2009). While relict englacial features can be observed on the surface of many debris-covered glaciers (Figure 2), studying these systems while they are still active is more difficult.

Fig. 2: A relict englacial feature in the centre of an ice cliff on Khumbu Glacier (looking downglacier), through which the associated supraglacial pond is thought to have drained in the past. Following the drainage event, the pond water-level would have dropped, exposing the ice cliffs around its edge and resulting in the pond water-level being too low to sustain a water flow through the channel. The inset shows the same feature from the far side (looking upglacier): on this side, a vast amount of surface lowering of the ice surface has occurred and the previously englacial channel is now visible from the surface. For scale, the feature is approximately 10 metres in height. [Large image credit: Evan Miles; Inset image credit: Katie Miles]

Hot-water drilling to investigate subsurface hydrology

One way in which potential hydrological systems beneath the surface of debris-covered glaciers can be investigated is through the use of hot-water drilling, as was carried out on Khumbu Glacier, Nepal Himalaya this year by the EverDrill team. A converted car pressure-washer was used to produce a small jet of hot, pressurised water, which was sent through a spool of hose into the drill stem to melt the ice below as it was slowly lowered into the glacier (our Image of the Week). The result (if all went well!) was a borehole 10-15 cm in width, that penetrated the ice all the way to the glacier bed (Figure 3). During the field campaign, we managed to drill 13 boreholes at 3 different drill sites across Khumbu Glacier, ranging in length from 12 to 155 metres.

Once the borehole has been drilled, it can be used to investigate the hydrology of the glacier in a number of ways. If the water level suddenly drops while drilling is in progress, it is possible that the borehole has cut through an englacial conduit, through which the excess drill water has drained. If it drops at the base of a borehole drilled to the bed, it can be assumed that some form of subglacial drainage network exists at the base of the glacier, and the excess water drained through this system. Such features can be examined further through the use of an optical televiewer (360° camera that is lowered slowly through the length of the borehole, taking hundreds of images to give a complete picture of the internal surface of the borehole), or by installing a variety of sensors along the hole’s length to collect various types of data.

Fig. 3: A borehole drilled into Khumbu Glacier during the EverDrill field season in Spring 2017. The borehole was approximately 10 cm in width. A small channel (to the left of the borehole) was formed during the drilling process to drain away the excess water as the borehole was drilled. [Credit: Katie Miles]


During the EverDrill fieldwork in Spring 2017, we televiewed three of the drilled boreholes. These boreholes were then instrumented with sensors to measure the temperature of the ice and, where the boreholes reached the bed, a subglacial probe to measure electrical conductivity, temperature, water pressure and suspended sediment concentration (turbidity). We have left these probes in the boreholes, so that we have measurements both through our field season and additionally through the monsoon summer months. This will allow us to see whether any subsurface hydrological drainage systems develop when there is an additional source of water contributing to the melting of these glaciers. We will return in October to collect this data, and hopefully find out a little more about the englacial and subglacial drainage systems of this debris-covered glacier!

Further reading

Edited by Morgan Gibson, Clara Burgard and Emma Smith


Katie Miles is a PhD student in the Centre for Glaciology, Aberystwyth University, UK, studying the internal structure and subsurface hydrology of high-elevation debris-covered glaciers in the Himalaya by investigating boreholes and measurements that can be made within them. She is also interested in the potential of Sentinel-1 SAR imagery in detecting lakes on the surface of the Greenland Ice Sheet. Katie tweets at @Katie_Miles_851, contact email: kam64@aber.ac.uk

Image of the Week – Far-reaching implications of Everest’s thinning glaciers

Fig. 1: Surface lowering on the debris-covered Khumbu Glacier, Nepal derived from differencing two digital elevation models. (a) The debris-covered surface looking down-glacier. (b-d) Surface elevation change 1984−2015. [Credit: Scott Watson and Owen King]

From 1984 to 2015, approximately 71,000 Olympic size swimming pools worth of water were released from the melting Khumbu Glacier in Nepal, which is home to Everest Basecamp. Find out how Himalayan glaciers are changing and the implications for downstream communities in this Image of the Week.


Himalayan glaciers supply freshwater

Himalayan glaciers supply meltwater for ~800 million people, including for agricultural, domestic, and hydropower use (Pritchard, 2017). They also alleviate seasonal variations in water supply by providing meltwater during the dry season. This freshwater resource is rapidly depleting as glaciers thin and glacial lakes begin to form (Bolch et al., 2008; Watson et al., 2016; King et al., 2017). Additionally, outburst floods from these lakes (see those previous posts on the topic) threaten downstream impacts for communities and infrastructure (Rounce et al., 2016).

Debris-covered glaciers thin, rather than retreat

Erosion in the rugged mountain topography leads to high quantities of rocky debris accumulating on the glacier surface, which changes the glacial response to climatic warming. The debris-layer (which can be several metres thick at the lower terminus) insulates the ice beneath, leading to highest melt rates up-glacier of the terminus. Therefore these debris-covered glacier thin, rather than retreat up-valley.

This thinning is actually a complex process of sub-debris melt, and mass loss associated with supraglacial ponds and ice cliffs, which form pits on the glacier surface and are ‘hot-spots’ of mass loss. Since the highest rates of surface lowering are up-glacier from the terminus, the surface slope of the glacier reduces and meltwater increasingly ponds on the surface, which can ultimately form a large glacial lake.

Khumbu Glacier

Fig 2 : Khumbu Icefall viewed from Kala Patthar. [Credit: Scott Watson]

The image of this week (Fig 1) shows surface elevation change on Khumbu Glacier, which flows down from Everest and is home to Everest Base Camp in Nepal. Parts of the glacier surface have thinned by up to 80 m 1984−2015 and over 197,600,000 m³ of ice melted over study period, which is approximately 71,000 Olympic size swimming pools worth of water! The thinning is clearly visible in the vertical offset between the contemporary glacier surface and the Little Ice Age moraines (a) and is highest in the mid-section of the glacier (b).

Mountaineers ascending Mount Everest climb the Khumbu icefall (Fig 2) and camp on the glacier surface. Additionally, popular trekking routes also run alongside and across the glacier, which are used by thousands of tourists every year. The accessibility of both these mountaineering and trekking routes is changing in response to glacier mass loss.

Stagnating glaciers are unhealthy glaciers

Accumulation of snowfall in the highest reaches of the glacier would typically compress to form new ice and replenish mass loss on the lower glacier as the glacier flows downstream. However, trends of reduced precipitation (Salerno et al., 2015) and decreasing glacier surface slopes promote a reduction in glacier velocity. Figure 3 shows glaciers stagnating in their lower reaches, where water is also visibly ponding on the glacier surface. For Khumbu and Ngozumpa glaciers, this contributes to the development of large glacial lakes. If these lakes continue to grow, once fully established they can rapidly increase glacier mass loss as a calving front develops (e.g. at Imja Lake).

Fig. 3: Surface velocity of glaciers in the Everest region derived from feature tracking on ASTER satellite imagery. [Credit: Scott Watson]

Edited by Sophie Berger

References/further reading

  • Bolch, T Buchroithner, MF Peters, J Baessler, M and Bajracharya, S. 2008. Identification of glacier motion and potentially dangerous glacial lakes in the Mt. Everest region/Nepal using spaceborne imagery. Nat. Hazards Earth Syst. Sci. 8: 1329-1340. 10.5194/nhess-8-1329-2008
  • King, O Quincey, DJ Carrivick, JL and Rowan, AV. 2017. Spatial variability in mass loss of glaciers in the Everest region, central Himalayas, between 2000 and 2015. The Cryosphere 11: 407-426. 10.5194/tc-11-407-2017
  • Pritchard, HD. 2017. Asia’s glaciers are a regionally important buffer against drought. Nature 545: 169-174. 10.1038/nature22062
  • Rounce, DR McKinney, DC Lala, JM Byers, AC and Watson, CS. 2016. A new remote hazard and risk assessment framework for glacial lakes in the Nepal Himalaya. Hydrol. Earth Syst. Sci. 20: 3455-3475. 10.5194/hess-20-3455-2016
  • Salerno, F Guyennon, N Thakuri, S Viviano, G Romano, E Vuillermoz, E Cristofanelli, P Stocchi, P Agrillo, G Ma, Y and Tartari, G. 2015. Weak precipitation, warm winters and springs impact glaciers of south slopes of Mt. Everest (central Himalaya) in the last 2 decades (1994–2013). The Cryosphere 9: 1229-1247. 10.5194/tc-9-1229-2015
  • Watson, CS Quincey, DJ Carrivick, JL and Smith, MW. 2016. The dynamics of supraglacial ponds in the Everest region, central Himalaya. Global and Planetary Change 142: 14-27. http://dx.doi.org/10.1016/j.gloplacha.2016.04.008

Scott Watson is a PhD student at the University of Leeds, UK. He studies glaciers in the Everest region and specifically the surface interactions of supraglacial ponds and ice cliffs, which act as positive feedback mechanisms to increase glacier mass loss. He also investigates glacial lake hazards and the implications of glacial lake outburst floods.

Tweets @CScottWatson. Outreach: www.rockyglaciers.co.uk

Image of the Week – Supraglacial debris variations in space and time!

Image of the Week – Supraglacial debris variations in space and time!

There is still a huge amount we don’t know about how glaciers respond to climate change. One of the most challenging areas is determining the response of debris-covered glaciers. Previously, we have reported on a number of fieldwork expeditions to debris-covered glaciers but with this Image of The Week we want to show you another way to investigate these complex glaciers – numerical modelling!


Debris-covered glaciers

Debris-covered glaciers occur globally, with a great many being found in the Himalaya-Karakoram mountain range. For example, in the Everest Region of Nepal 33% of glacier area is debris covered (Thakuri et al., 2014). The response of debris-covered glaciers to future climate change in such regions has huge implications for water resources, with one fifth of the world’s population relying on water from the Himalayan region for their survival (Immerzeel et al., 2010).

Debris-covered glaciers respond to climate change differently to debris-free glaciers as the supraglacial debris layer acts as a barrier between the atmosphere and glacier (Reznichenko et al., 2010). The supraglacial debris layer has several key influences on the glacier dynamics:

  • Glacier ablation (loss of mass from the ice surface) is enhanced or inhibited depending on debris layer thickness and properties – see our previous post.
  • Supraglacial debris causes glaciers to reduce in volume through surface lowering rather than terminus retreat (typical of debris free mountain glaciers).

Understanding the influence of a supraglacial debris layer on mass loss or gain is, therefore, key in determining the future of these glaciers. The properties of supraglacial debris layers can vary in time and space both in debris layer thickness and distribution, as well as properties of the rocks which make up the debris (e.g. albedo, surface roughness, porosity, size and moisture content). It is these characteristics of the debris-cover which control the heat transfer through the debris and therefore the amount of thermal energy that reaches the underlying ice causing melting (Nicholson and Benn, 2006). In order to better predict the future of debris-covered glaciers we needs to be able to numerically model their behaviour. This means we need a better understanding of the variations in debris cover and how this affects the ice dynamics.

How does a supraglacial debris layer vary in time and space?

Our Image of the Week (Fig. 1) shows a schematic of how debris distribution can vary spatially across a glacier surface and also this can change through time. The main inputs of debris are:

  • Upper regions: snow and ice avalanches in the upper reaches of the glacier.
  • Mid and Lower regions: rock avalanches and rock falls (Mihalcea et al., 2006).

These irregular mass movement events vary in frequency and magnitude, and therefore affect debris distribution across the glacier surface but also through time. The irregularity of them makes it really hard to predict and simulate! Luckily, debris transport is a little more predictable.

Figure 2: An ice cliff emerging out of the supraglacial debris layer on Khumbu Glacier, Nepal, with Nuptse in the background. [Credit: M. Gibson]

Debris is initially transported along medial moraines (glacially transported debris)  in the upper and mid-sections of the glacier, this is known as entrained debris. The various sources of entrained debris combine to form a continuous debris cover in the lower reaches of the glacier (Fig. 1). As a supraglacial debris layer is forming, such as for Baltoro glacier (Fig. 1), the boundary between the continuous debris layer and entrained debris sections progresses further upglacier over time.

Eventually transported debris will reach the terminus of the glacier and be deposited (Fig. 1), mainly due to a decrease in surface velocity of the glacier towards the terminus. However, once debris is deposited it doesn’t just sit there; debris is constantly being shifted around as ablation (surface melting) occurs. As ablation occurs the debris surface ablates unevenly, as the thickness of the debris layer is spatially variable. Uneven ablation, otherwise known as differential surface lowering, causes the glacier surface to be made up of topographic highs and lows, the latter of which sometimes become filled with water, forming supraglacial ponds (Fig. 1) . Another product of debris shifting is that ice cliffs, such as the one seen in Fig. 2, are exposed. These features are initially formed when englacial channels collapse  or debris layers slide (Kirkbride, 1993). All this movement and shifting means that not only do glacier models have to consider variation in debris layers across the glacier and through time, but also the presence of ice cliffs and supraglacial ponds. They are important as they have a very different surface energy balance to debris-covered ice. To complicate things further the frequency and area of ice cliffs and supraglacial ponds also vary through time! You see the complexity of the problem…

Modelling spatially and temporally varying debris layers

Numerical modelling is key to understanding how supraglacial debris layers affect glacier mass balance. However, current numerical modelling often either omits the presence of a supraglacial debris layer entirely, or a debris layer that is static in time and/or space (e.g. Collier et al., 2013; Rowan et al., 2015; Shea et al., 2014). However, as outlined earlier, these supraglacial debris layers are not static in time or space. Understanding the extent to which spatiotemporal variations in supraglacial debris distribution occur could aid identification of when glaciers became debris-covered, glaciers that will become debris-covered glaciers in the future, and the timescales over which supraglacial debris layers vary. The latter is particularly relevant to numerical modelling as it would result in total glacier ablation being calculated more precisely throughout the modelling time period. Understanding the interaction between glacier dynamics and debris distribution is therefore key to reconstructing debris-covered glacier systems as accurately as possible.

Edited by Emma Smith


Morgan Gibson is a PhD student at Aberystwyth University, UK, and is researching the role of supraglacial debris in ablation of Himalaya-Karakoram debris-covered glaciers. Morgan’s work focuses on: the extent to which supraglacial debris properties vary spatially; how glacier dynamics control supraglacial debris distribution; and the importance of spatial and temporal variations in debris properties on ablation of Himalaya-Karakoram debris-covered glaciers. Morgan tweets at @morgan_gibson, contact email address: mog2@aber.ac.uk.

Katabatic winds – A load of hot (or cold) air?

Katabatic winds – A load of hot (or cold) air?

It might seem obvious that a warming world will lead to a reduction in glacial ice cover, but predicting the response of glaciers to climatic change is no simple task (even within the short term). One way to approach this problem is to come up with relationships which describe how glaciers interact with the world around them, for example, how the ice interacts with the air above it. Our post today delves into the world of ice-air interaction and describes some of the problems encountered by those who are investigating it, in particular the problem of modelling katabatic winds! Not sure what we are talking about…then read on to find out more! 


What are katabatic winds?

Anyone who has stood on, or in front of a glacier on a clear, sunny day has no doubt felt the bitter chill of a katabatic wind, forcing them to don a warm jacket and lose their chance at that lovely “glacier tan”. Katabatic winds (derived from the Greek word katabasis, meaning ‘downhill’) develop over snow and ice surfaces because the 0°C ice surface cools the air just above it. This cold, dense air then flows downhill under the force of gravity (Fig. 1 and Fig. 2). This is not recent news and such wind chill has no doubt punished glaciologists and explorers for the last century or more –  Mawson’s Description of the 1911-1914 Australian Antarctica Expedition is aptly named “The Home of the Blizzard“. However, despite being well known, this phenomenon still causes much uncertainty when it comes to modelling the melting of glacier ice surfaces around the world.

Soon gusts swept the tops of the rocky ridges, gradually descending to throw up the snow at a lower level. Then a volley raked the Hut, and within a few minutes we were once more enveloped in a sea of drifting snow, and the wind blew stronger than ever. – Mawson, 1915, The Home of the Blizzard

Figure 2: The view from the upper reaches of Tsanteleina Glacier in the western Italian Alps (Val d’Rhemes, Aosta). Katabatic winds generally flow in a down-glacier direction – here, from right to left [Credit: T Shaw].

Challenges for modelling

Air temperature is really important in determining how much a glacier melts and we need to know as much about it as possible to provide accurate predictions now and into the future. This is particularly relevant because the warmer it gets, the more energy is available to melt ice and seasonal snow. Unfortunately though, we don’t have an infinite supply of meteorological observations (e.g. air temperature, wind speed etc) at many locations we are interested in. As a result, we have to make simple assumptions about what the weather is doing at a remote, far away glacier. One such simple assumption is based upon the fact that air temperature typically decreases with increasing elevation, and so if we know the elevation of a location we are interested in, we can assume a ‘likely’ temperature. The rate of change in temperature with elevation is known as a ‘lapse rate’.

Air temperature is really important in determining how much a glacier melts…the warmer it gets, the more energy is available to melt ice and seasonal snow.

When predicting glacier melt, it is common practice to use a lapse rate which stays constant in time and space. This is convenient as we often don’t know the actual lapse rate at a given location, but this often ignores things happening at the surface of the Earth. An important example of this is when we have katabatic winds over glaciers!

When conditions are warm, and skies are clear, the cooling of the air above the ice surface, means that the application of a lapse rate is fairly useless, or close to it [Greuell and Böhm, 1998]! That is because the cooling from the surface continues as air flows down the glacier, typically creating colder temperatures at lower elevations, the opposite of the typical lapse rate assumption that models will apply.

‘Bow-shaped’ temperature vs. elevation relationships

To complicate matters for people trying to model the air temperature over glaciers, the effect of surface cooling is not just dependent on the amount of time an air parcel is in contact with the ice surface but also the characteristics of the ice surface it has been in contact with. In fact, after cooling on their descent down-glacier, air parcels have been documented to warm again, leaving interesting slightly “bow-shaped” curves to the temperature-elevation relationship. This effect has been found for the Swiss Haut Glacier d’Arolla and the Italian Tsanteleina Glacier (Fig. 3c,d). A new model approach to tackling this bow-shaped problem has been presented by recent research [Ayala et al., 2015] and offers a means of accounting for katabatic winds in glacier models. Nevertheless, more data and more work are still needed to generalise these models [Shaw et al., in review].

Figure 3: Relationship between elevation and air temperature on three different glaciers in the western Alps. Miage (Italy), Tsanteleina (Italy) and Arolla (Switzerland). Glaciers are represented using the mean of all data available (green), the top 10% of off-glacier temperatures (P90 – red) and the bottom 10% of off-glacier temperatures (P10 – blue), plus one standard deviation. The debris-covered Miage Glacier does not demonstrate a classic katabatic flow regime and therefore temperature corresponds well to elevation even under warm conditions [Credit: T Shaw, unpublished].

after cooling on their descent down-glacier, air parcels have been documented to warm again, leaving interesting slightly “bow-shaped” curves to the temperature-elevation relationship.

Air temperatures across debris-covered glaciers

As you may have read in our previous post on the topic, debris-covered glaciers behave in a different way to those with a clean ice surface. Detailed observations of air temperature across a debris-covered glacier show that the glacier responds to the heating of surface debris in the sunlight and a consequent warming of the lower atmosphere [Shaw et al., 2016]. Because of this, air temperature conforms very strongly to the elevation dependency that is assumed when using a lapse rate. Although very local variations of air temperature on other debris-covered glaciers cannot be well estimated by a lapse rate [Steiner and Pellicciotti, 2016], the insulating effect of thick debris cover means that the current approach to using simple lapse rates for estimating air temperature over debris-covered glaciers could be suitable.

Nevertheless, challenges for accurately representing air temperature above glaciers without debris cover remain. The fact that globally averaged temperatures are expected to rise over the current century (areas at high latitudes have shown a stronger warming trend) [Collins et al, 2013], the applicability of using lapse rates could further diminish. Recent patterns of warmer-than-average temperatures also suggest a difficulty of accurately estimating on-glacier temperatures in the short-term. For example, for the period of May 2015 – August 2016, every month beat the previously held record for warmest globally average temperature (GISTEMP). Imagine the bow-shaped problem to that!

Edited by Matt Westoby and Emma Smith


Thomas Shaw is a PhD student in the Department of Geography at Northumbria University, UK. His research is focused on the spatial and temporal variance in near-surface air temperature across debris-covered and debris-free glaciers in the western Italian Alps. As well as conducting research in the Alps, he is also very interested in glaciers and their processes on Svalbard (Norwegian Arctic) and has spent plenty of time studying above, or within (!), ice at high latitudes. Contact e-mail: thomas.shaw@northumbria.ac.uk

Image of the Week – Hidden Beauty on a Himalayan Glacier

Image of the Week –  Hidden Beauty on a Himalayan Glacier

Today’s image of the week comes from stunning setting of Chhota Shigri Glacier in the Pir Panjal Range of northern India. The range is part of the Hindu-Kush Karakorum Himalaya region which is a notoriously challenging place to work as it is very remote and completely inaccessible during the winter months. However, when have these challenges ever stopped a hardy glaciologist?! 

Our image this week was taken during a field expedition as part of an ongoing long term monitoring program in the area and today we are going to tell you why the region is so important (other than being the source of some rather good photos!)


Why is monitoring glaciers in the Himalaya so important?

Location of Chhota Shigri Glacier taken from Wagon et al., 2007

The Hindu-Kush Karakorum Himalaya region is made up of the biggest mountain ranges on Earth which contain the largest ice mass outside of the polar regions. This region provides water to 50-60% of the world’s population (Wagon et al., 2007), some of which comes from glacial melt water, therefore it is critical to understand how the glaciers in this region may respond to ongoing climate change and predict the impact this may have for the future. As glaciers are very sensitive to changing climate they are also used to understand climate variations at annual and decadal timescales in the region.

Chhota Shigri Glacier is representative of many glaciers in this region and was chosen as the site for a long-term monitoring program in 2002. It was chosen for a number of reasons including previous field studies on the glacier in the 1980s,  glacier geometry, accessibility and its dynamic environment; with areas of partial debris cover and supraglacial lakes (as seen in the image above). The data record on this glacier now continuously spans 13 years and the program has become a benchmark for studying Himalayan glaciers.

What do we see on the picture

The beautiful shot shows a supraglacial lake, a pond of liquid water, on the top of the Chhota Shigri Glacier. This supraglacial lake is an ephemeral lake, forming immediately after winter season. Supraglacial lakes form due to the melting of snow/ice and their presence helps to determine surface melt rates. When the lake water drains it also allows the distribution of subsurface hydrological conduits to be investigated. If the lake does not drain and exists long term there may be glacial lake outburst floods. These are a natural hazard and must be monitored and better understood. This is just one of the aspects of Chhota Shigri Glacier that is being investigated by the long term monitoring program.

Chhota Shigri Glacier has the longest monitoring record

The long term monitoring program, initiated on Chhota Shigri Glacier in 2002, has recorded the evolution of mass balance, ice velocity, ice thickness, stream runoff and melt water quality. The program is a joint collaboration between India and France under the frame work of DST/CEFIPRA programme at School of Environmental Science, Jawaharlal Nehru University, New Delhi. Presently, the annual and seasonal mass balance series (13 years) of Chhota Shigri glacier since 2002 is the longest continuous record in the entire Hindu-Kush Karakorum Himalaya region and represents a benchmark for climate change studies in this region. To measure the annual and seasonal mass balance, we survey the glacier at the end of winter season (May/June) for winter balance measurements and end of summer (September end/October) for annual measurements. We monitor a network of ablation stakes distributed throughout the entire ablation zone (including debris-covered area) to estimate the glacier-wide ablation. To estimate the accumulation we drill snow cores or dig snow pits at representative locations within the accumulation zone (>5150 m) of Chhota Shigri Glacier. For more detailed information and the results of this monitoring see Azam et al. (2016) and Ramanathan (2012).

Long term monitoring on Chhota Shigri Glacier (a) accumulation zone at the end of summer (area is largely covered in dust with clearly visible medial moraine . (b) accumulation zone at the end of winter (fresh snow cover), (c) ablation stake (bamboo) installation in a partly debris covered region during the summer and, (d) drilling of snow core at top of the glacier during winter (Credit: Arindan Mandal/JNU).

Long term monitoring on Chhota Shigri Glacier (a) accumulation zone at the end of summer (area is largely covered in dust with clearly visible medial moraine . (b) accumulation zone at the end of winter (fresh snow cover). (c) ablation stake (bamboo) installation in a partly debris covered region during the summe. (d) drilling of snow core at top of the glacier during winter (Credit: Arindan Mandal).

 

Acknowledgements

Thanks to Department of Science and Technology, Govt. of India, SAC-ISRO, CEFIPRA, INDICE, GLACINDIA and CHARIS for funding our research. Special thanks to Emma and Sophie for help in putting together this post.

Edited by Emma Smith and Sophie Berger


Arindan_PhotoArindan Mandal is a PhD student at the School of Environmental Science, Jawaharlal Nehru university, New Delhi, India under the supervision of Prof. AL. Ramanathan. His current work is focused on Chhota Shigri Glacier where he is working to analyse the past and present state of mass balance in the changing climate scenario and also to understand the complex local scale meteorological processes that drive the mass balance of the glacier. He is working to develop a coupled distributed surface energy-balance model combined with various glaciological and hydrological aspect using in-situ dataset to understand the processes that govern and runoff at Chhota Shigri glacier pro-glacial stream and its sensitivity to the future climate. He tweets as @141Arindan.
Contact Email: arindan.141@gmail.com,

Fieldwork at 5,000 meters in altitude

Fieldwork at 5,000 meters in altitude

Imja Lake is one of the largest glacial lakes in the Nepal Himalaya and has received a great deal of attention in the last couple decades due to the potential for a glacial lake outburst flood. In response to these concerns, the UNDP has funded a project that is currently lowering the level of the lake by 3 m to reduce the flood hazard. The aim of our research efforts is to understand how quickly the glacier is melting and how rapidly the lake is expanding such that we can model the flood hazard in the future. The focus of this research expedition was to install an automatic weather station, measure the thickness of the ice behind the calving front of Imja Lake, and measure the bathymetry of Imja Lake amongst other smaller tasks.

However, before any work could be done, we had to get there first.

The 8-day trek from Lukla to Imja Lake [Credit: GoogleEarth]

The 8-day trek from Lukla to Imja Lake [Credit: GoogleEarth]

The long trek in

Tenzing-Hillary Airport in Lukla, at an altitude of 2,845 m [Credit: D. Rounce]

Tenzing-Hillary Airport in Lukla, at an altitude of 2,845 m [Credit: D. Rounce]

The launch point for our expedition was Kathmandu, Nepal, where we met with our trekking agency, Himalayan Research Expedition, purchased any last minute supplies, and took a day to kick our jet lag. Then the real trip began with a flight from Kathmandu to Lukla. Depending on the weather, this flight can be smooth and showcase the splendor of the Himalaya or it can be nerve-wracking flying through turbulence and clouds. Unfortunately, we had the latter and spent most of the 30-minute class flying through white clouds. Once our feet touched the ground at Tenzing-Hillary Airport, we were all excited and ready to start trekking.

Located at 5010 m above sea level (a.s.l) in the Everest region of the Himalaya, Imja Lake required 8 days of trekking to reach our base camp. The first 6 days followed the route to Everest Base Camp and provided the first glimpses of Everest, Lhotse, and Ama Dablam among many others. Due to the late start of our trek on May 29th, the monsoon clouds often blocked most of these peaks, so whenever the skies did clear we enjoyed them thoroughly. The 8-day trek also included two rest days (one in Namche and one in Dingboche) that were critical to be properly acclimated. The general rule of thumb that we follow is an acclimatization day for every 1,000 m of elevation gain. After the first rest day at Namche, at 3,400 m.a.s.l., the effects of altitude began to set in. The trekking slowed down as oxygen was a bit harder to come by. By the time we reached Imja Lake, there was about half as much oxygen as there is at sea level.

At 5,000 meters in altitude there is about half as much oxygen as there is at sea level

Imja Lake looked…different

The team at our base camp at Imja Lake [Credit: D. Rounce]

The team at our base camp at Imja Lake [Credit: D. Rounce]

I was beyond excited to be back at Imja Lake. This was my 5th time at the lake and this time I was accompanied by a great team of colleagues. This project is funded by the NSF’s Dynamics of Coupled Natural and Human Systems (CNH) program and is led by Daene McKinney (University of Texas), Alton Byers (University of Colorado Boulder), and Milan Shrestha (Arizona State University). One of the great aspects of this trip was we were all able to be in the field at the same time providing an excellent mix of fieldwork on the glacier and social science work with the communities downstream. My group consisted of myself, Greta Wells from the University of Texas, Jonathan Burton from Brigham Young University, Alina Karki from Tribhuvan University, and eight hard-working individuals from our trekking agency (unfortunately, Daene was with us, but had to leave the expedition early).

The first drastic change that we saw when we got to Imja Lake was the large camp set up by the Army to work on the lake-lowering project. Usually, the only people that we see up here are people at Island Peak base camp, but now the location where were typically set up camp was packed with tents for the workers. The next surprise was seeing a backhoe operating on the terminal moraine (the natural dam comprising sand, rocks, and boulders). Typically, once you get off the plane in Lukla, you don’t see any motorized transportation besides the occasional helicopter flying to Everest Base Camp, so seeing this large piece of construction machinery was quite surprising! The lake lowering project was fascinating to see in progress. A cougher dam has been established to divert the outlet stream such that the typical outlet can be dredged and an outlet gate established, which will reduce the lake level by 3 m. This is a large undertaking due to the difficulty of working at 5,000 m (for both the workers and the machinery), but is an excellent step forward for Nepal in addressing the hazards associated with their glacial lakes.

The lowering project at Imja Lake in progress [Credit: D. Rounce]

The lowering project in progress at Imja Lake, with a backhoe working on a terminal moraine [Credit: D. Rounce]

Seeing this large piece of construction machinery [at that altitude] was quite surprising!

Let the work begin

On June 6th, we woke up at 6:00 a.m. to pure fog and limited visibility – not the weather you hope for on your first day of fieldwork. Fortunately, the fog burned off as the sun came up giving us a nice partly cloudy day to perform our reconnaissance of the glacier for the upcoming work. The first task was figuring out how to get onto the glacier from the lateral moraines (the sides of the glacier). This may sound trivial, but the glacier has melted such that the lateral moraines are now over 100 m higher than the debris-covered glacier surface and their slopes are very steep, which makes descending down them quite difficult. Fortunately, we found a good spot near Island Peak base camp, where Laxmi (our guide) set a rope and cleared the path of loose rocks and boulders.

Arduous descent onto the glacier [Credit: D. Rounce]

Arduous descent onto the glacier [Credit: D. Rounce]

The glacier has melted such that the lateral moraines are now over 100 m higher

utomatic Weather Station on Imja-Lhotse Shar Glacier [Credit: D. Rounce]

Automatic Weather Station on Imja-Lhotse Shar Glacier [Credit: D. Rounce]

Once on the glacier, we were tasked with determining the location of the weather station and wind tower in addition to finding potential routes for our Ground Penetrating Radar transects. The problem with Imja-Lhotse Shar Glacier is there are very few suitable flat spots. The debris cover on the glacier consists of fine sands, gravel, and boulders with melt ponds and bare ice faces scattered over the surface. The thickness of the debris can range from these bare ice faces to a thin cover of a few centimetres to many meters thick. Needless to say, the heterogeneous terrain can make walking on its surface quite difficult. My initial thought was to use a location where we had installed temperature sensors and ablation stakes two years ago; however, this site had turned into a melt pond ! Hence, we need to select a spot that seems relatively stable such that it won’t be in the middle of a pond when we return!

After many hours of trekking on the glacier, we returned to camp fatigued. The altitude wears you down quickly, especially in the first couple of days, so it’s crucial to stay hydrated, warm, and well rested such that we can work hard for all of the 16 scheduled days that we were out here. I find the first couple days to be the most difficult as my body adjusts to the limited supply of oxygen and for the first 2-3 days I typically have a mild headache in the afternoon. A good meal of dal baht (rice, lentil soup, and typically a meat or vegetable curry) along with a good night’s sleep and a little ibuprofen does the trick to have me feeling refreshed the next day though.

The fieldwork

The first task was to set up the weather station and wind tower. The weather station will record meteorological data every 30 minutes that is important for energy balance modelling. This will allow us to model melt rates that can be applied to the entire glacier such that we can understand the evolution of the debris-covered glacier – crucial for future hazard modelling! The wind tower allows us to measure the surface roughness of the topography, which influences the turbulent heat flux transfers, i.e., the transfer of heat and moisture between the surface of the debris and the air – an important debris property to measure for energy balance modelling as well. Additionally, beneath the weather station, we installed temperature and relative humidity sensors within the debris such that we can understand how heat is transferred through the debris. Each piece of equipment has an essential role in the energy balance modelling.

The other large undertaking in the first week was performing ground penetrating radar (GPR) transects on Imja-Lhotse Shar Glacier. GPR is a geophysical technique that is used to measure and detect objects beneath the surface. In our case, we’ll be trying to measure the ice thickness of the glacier.

Ground Penetrating Radar in short

Ground Penetrating Radar survey in action [Credit: D. Rounce]

Ground Penetrating Radar survey in action [Credit: D. Rounce]

The quick and dirty of GPR is you have a transmitter and a receiver. The transmitter sends a great deal of energy into the ground, which then reflects off various surface, e.g., we should see a strong reflection at the ice/rock interface, and this reflected signal is then picked up by the receiver. Sounds easy right?
Things become a bit more difficult when you get on the debris-covered glacier and everything must be carried or dragged across the surface. This requires a lot of people such that the antennas don’t get stuck on the boulders, requires everyone to be walking at the same speed, and requires that all the electrical connections, batteries, etc. are secure and operating.
In a nutshell, it is a great deal of work, but provides an excellent dataset to understand the extent to which glacial lakes may grow in the future.
When this ice thickness is paired with lake expansion rates, one can predict the evolution of the glacial lake, which is critical for understanding the future hazard associated with Imja Lake. Two full days were spent climbing over the glacier, around bare ice faces and melt ponds, and attempting to collect transects that provide a good picture of the ice thickness behind the calving front of Imja Lake. During these days, we completed half of our planned transects and were ready for our first day of rest.

A flood and a community meeting

After 6 days of hard work, I was exhausted. The plan was to hike down to Chukung at 4700 m.a.s.l., where we would stay for two nights. A change in 300 m may not sound like a lot, but at altitude, this can provide a great boost in energy. During our “rest day” in Chukung, we were planning to hike down to Dingboche (4400 m.a.s.l.) to help out with a focus group session with the community led by Milan. What happened next was completely unexpected… we witnessed a glacier flood!

We witnessed a glacier flood!

A glacier flood threatened the village of Chukung [Credit: D. Rounce]

A glacier flood threatened the village of Chukung [Credit: D. Rounce]

Our colleagues Alton and Elizabeth Byers were heading down to Dingboche before us. Along the way, they heard the sound of a landslide and when they checked to see what it was they were surprised to witness the start of a glacier flood. These floods appeared to have originated from the drainage of supraglacial lakes on Lhotse Glacier and appeared to have discharged through a series of englacial conduits. This englacial conduit flood grew rapidly as the initial flood continued to melt the surrounding ice. The videos that Elizabeth took were absolutely remarkable and fortunately everyone in Chukung was safe. By the time we arrived at the typical crossing point around 3:00 p.m., the flood had supposedly diminished by quite a bit, but was still very powerful. We ended up having to an hour detour over an ice bridge (literally a place on the glacier where the flood had carved into the ice and was going underneath the glacier such that we could walk above the flood on the debris-covered surface). It was truly fascinating to witness a flood from a glacier. When we arrived at Chukung, we made the decision to continue hiking to Dingboche such that we were safely out of the potential flooded area.

The energy in Dingboche was electric. Our entire NSF group was in the lodge and eager to talk to one another. The flood had also sparked a great deal of interest with community members as they witnessed the flood coming downstream and were fortunately able to contact members in Chukung to learn that this was not a larger glacial lake outburst flood (GLOF) from Imja Lake, which alleviated a great deal of concern. After a good meal and great conversation, we were all exhausted and went to bed early (not to mention that for the first time in over a week we were able to reconnect and update family and friends on the internet, which was a wonderful treat as well). The next day we were able to sit in on Milan’s focus group session with the members of Dingboche. From my background in engineering, I was fascinated to see first-hand the important work that Milan was conducting with the community. The community member’s interest and questions were very inspiring. For many years, these communities have seen researchers come to Imja Lake and not share any of their results. This has led to a great deal of skepticism and also led to unnecessary fear and/or panic, so every opportunity that we have to share our results and have a dialogue with the community is crucial. It is wonderful to be working with Milan as his work is a wonderful vessel for us to learn about the community’s concerns and vice versa, for us to share our work with them as well. I’m incredibly excited to see how this work progresses and see the field science and the social science come together.

The community of Dingboche [Credit: D. Rounce]

The community of Dingboche [Credit: D. Rounce]

Every opportunity that we have to share our results and have a dialogue with the [local] community is crucial

Finishing off the fieldwork

After a day of “rest” in Dingboche, our team was ready to get back to work at Imja Lake. The first task was more GPR transects on the glacier. The benefit was that we were all feeling rejuvenated from our days at lower elevations and now that this was our 3rd day of GPR things were running smoothly.

The other benefit was that after almost 10 days at 5000 m.a.s.l. our bodies were feeling well adjusted to the limited supply of oxygen. The headaches that came and went over the first couple days were non-existent. The only downfall was we were now getting into the heart of the monsoon season, where clouds came up the valley every morning and it rained almost every afternoon. The work had to go on though, so we simply shifted our wake-up time an hour earlier in an attempt to avoid the rain.

Greta Wells and Jonathan Burton conducting a bathymetric survey on Imja Lake [Credit: G. Wells]

Greta Wells and Jonathan Burton conducting a bathymetric survey on Imja Lake [Credit: G. Wells]

As our days were winding down, it was time to start splitting up the group. Jonathan and Greta became our kayaking experts and quickly became adept at working the sonar system to conduct a bathymetric survey of Imja Lake. The bathymetric survey is a remarkable experience and one that Jonathan and Greta seemed to thoroughly enjoy. The calving front of Imja Lake is ~10-20 m tall, which seems huge from the view of a kayak on the water. Furthermore, the calving front is quite active each year, so there are icebergs floating on the surface that provide some fun obstacles during the survey. They did a wonderful job and I am incredibly thankful for their support.

While the bathymetric survey was being conducted, Alina and I worked on the Structure from Motion (SfM) survey and the operation of the differential GPS (dGPS). Structure from Motion is a technique that allows us to take hundreds of pictures of the debris-covered surface and transform these pictures into a digital elevation model using the software PhotoScan Pro.

differential GPS measurement of a ground control point [Credit: D. Rounce]

differential GPS measurement of a ground control point [Credit: D. Rounce]

This technique requires ground control points, which is where the dGPS comes into play. The differential GPS provides centimetric accuracy of specific points on the glacier (in our case spray painted boulders), which provide the spatial scale for the digital elevation model. We had ~40 ground control points and each point took approximately 10 minutes to measure… hence, the dGPS survey was a great deal of work. Once again, I have to thank my wonderful colleague, Alina, for her hardwork operating the dGPS with me.

The bathymetric survey, SfM, dGPS, and GPR transects occupied all of our remaining time on the glacier. Two days before I left the glacier, I sent our team members off to visit Everest Base Camp and Kala Patthar as the only activities left were finishing off the dGPS survey and downloading the last bit of meteorological data from the weather station. The trek to Everest Base Camp takes about 2 days from our site and I was glad that they would have an opportunity to go visit – they certainly deserved it. Perhaps one of the best surprises of the trip was the day that Jonathan, Greta, and Alina went to Kala Patthar, they had a couple hours of clear skies in the morning such that they were able to see Everest! What a better way to end the trip for them. On my side, the last couple days went very smoothly and I was ecstatic with all the work that we had accomplished. 16 days of hard work paid off and I am anxiously waiting for us to return and collect all the remaining data next year!

Acknowledgements

A special thanks to the NSF-CNH program for funding this research. Also a big thanks to my colleagues Daene McKinney, Alton Byers, Elizabeth Byers, Milan Shrestha, Greta Wells, Jonathan Burton, and Alina Karki among the countless others who were with Alton and Milan’s groups. Lastly, this work would not be possible without the tremendous effort and support provided by Himalayan Research Expedition and our team of guides, porters, and cooks.

For more details on the trip, see: http://davidrounce.weebly.com/imja-lake-live-2016

Edited by Sophie Berger

Image of The Week – A Game of Drones (Part 1: A Debris-Covered Glacier)

Image of The Week – A Game of Drones (Part 1: A Debris-Covered Glacier)

What are debris-covered glaciers?

Many alpine glaciers are covered with a layer of surface debris (rock and sediment), which is sourced primarily from glacier headwalls and valley flanks. So-called ‘debris-covered glaciers’ are found in most glacierized regions, with concentrations in the European Alps, the Caucasus, Hindu-Kush-Himalaya, Karakoram and Tien Shan, the Andes, and Alaska and the western Cordillera of North America. Debris cover is important for ice dynamics for several reasons:

  • A layer of surface debris thicker than a few centimetres suppresses ice ablation (Brock et al., 2010), as it insulates the underlying ice from atmospheric heat and insolation.
  • In contrast, a thin layer of debris serves to enhance melt rates through reduced albedo (reflectance) and enhanced heat transfer to underlying ice.
  • A continuous or near-continuous layer of debris can result in debris-covered glaciers persisting at lower elevations than, and attaining lengths which exceed those of their ‘clean ice’ counterparts (Anderson and Anderson, 2016).

Miage Glacier – the largest debris-covered glacier in the European Alps

The Ghiacciaio del Miage, or Miage Glacier, is Italy’s longest glacier and is the largest debris-covered glacier in the European Alps. It is situated in the Aosta Valley, on the southwest flank of the Mont Blanc/Monte Bianco massif. The glacier descends from ~3800 m to ~1700 m above sea level (a.s.l.) across a distance of around 10 km, and is fed by four tributary glaciers. The glacier surface is extensively debris-covered below ~2400 m a.s.l., and the average surface debris thickness is 0.25 m across the lower 5 km of the glacier (Foster et al., 2012).

 

Figure 2: Up-glacier view of Miage Glacier, in which three of the glacier’s four tributaries are visible – from upper centre-left: Tête Carée Glacier, Bionnassay Glacier, Dome Glacier.

Figure 2: Up-glacier view of Miage Glacier, in which three of the glacier’s four tributaries are visible – from upper centre-left: Tête Carée Glacier, Bionnassay Glacier, Dome Glacier.

Glacier surveying using Unmanned Aerial Vehicles

Researchers from Northumbria University, UK, acquired these images of the glacier using a lightweight unmanned aerial vehicle (UAV) during a recent field visit to Miage Glacier. During the visit the team carried out a range of activities including the installation and maintenance of a network of weather stations and temperature loggers across the glacier and geomorphological surveying of the glacier and its catchment, whilst undergraduate students collected data for their final-year research projects. The UAV imagery reveals the emergence of surface debris cover from beneath winter snow cover and the persistence of a channelized hydrological network in the snowpack, characterised as a cascade of streams and storage ponds. A recent study by Fyffe et al. (2015) found that high early-season melt rates and runoff concentration in intermoraine troughs promotes the development of a channelized subglacial hydrological system in mid-glacier areas, whilst the drainage system beneath continuously debris-covered areas down-glacier is largely inefficient due to lower melt inputs and hummocky topography.

(Edited by Emma Smith and Sophie Berger)


Matt Westoby is a postdoctoral researcher at Northumbria University, UK. He is a quantitative geomorphologist, and uses novel high-resolution surveying technologies including repeat UAV-based Structure-from-Motion to quantify surface processes and landscape evolution in glacial and ice-marginal environments. Fieldwork on the Miage Glacier in June 2016 was supported in part by an Early Career Researcher Grant from the British Society for Geomorphology. He tweets as @MattWestoby Contact e-mail: mjwestoby@gmail.com