Fig. 1: Group photo with Mount Everest backdrop following presentations at the Sagarmatha National Park office in Namche Bazar (3,500 m a.s.l) with 60 participants (wrapped up against the cold temperatures). [Credit: Dhananjay Regmi].
The 12 day “Walk the Talk” Field Conference and Community Consultation through Sagarmatha National Park, Nepal, discussed a wide range of research outputs with local communities, tourists, and officials. Topics covered glaciers, mountains, environmental and landscape change, Sherpa livelihoods, tourism, and natural hazards. The conference, organised by Himalayan Research Expeditions, was the first of its kind, designed to receive community input into research topics and pursue applied benefits. Scott and Katie were two of the participants, presenting work from their PhDs in the Everest region and the NERC-funded EverDrill project.
Presentations and discussions
The team of international and Nepali scientists gave presentations every evening, trekking each day between six different villages along the Everest Base Camp trail. We were also joined by officials from the Nepal Department of Tourism and the Mountain Institute. The highest destination for the conference was Imja Glacial Lake, at over 5,000 m elevation, where we viewed first-hand the results of a recent $7 million project to lower the lake water level, aiming to reduce the risk of an outburst flood.
The Sagarmatha National Park has been a focus for scientists of many disciplines for decades. As well as thousands of tourists trekking to Everest Base Camp each year, it is also frequented by those hoping to summit Mount Everest (Sagarmatha). The park has therefore experienced significant change over a relatively short timescale as it copes with this huge influx of people. Presentations for the “Walk the Talk” conference ranged from impacts of tourism (for example, on local people, yak breeding and waste disposal) to natural hazards such as glacial lake outburst floods and landslides.
Katie presented ongoing work from her PhD and the “EverDrill” project (Fig. 2), for which she has conducted several field seasons on Khumbu Glacier in the Sagarmatha National Park. Fieldwork has included hot-water drilling of boreholes into the glacier and installing sensors to measure ice temperature at various depths to investigate the glacier’s thermal regime. She discussed how these measurements showed that Khumbu’s ice is warmer than expected, potentially putting the glacier at risk of more rapid melting as air temperatures rise. The warmer ice towards the terminus also allows subsurface meltwater drainage, about which very little is known. Katie has also carried out fluorescent dye tracing experiments to work out how meltwater travels through Khumbu Glacier, including storage within (englacial) and on the surface (supraglacial). As Khumbu and similar glaciers retreat in the future, meltwater storage and runoff will have implications for the downstream communities who depend on such water sources.
Fig. 2: Katie presenting measurements of Khumbu Glacier’s thermal regime and hydrology at the Sagarmatha National Park headquarters in Namche Bazar (3,500 m a.s.l.). [Credit: Dhananjay Regmi].
Scott presented results from his PhD investigating melt processes and water storage on Khumbu Glacier (Fig. 3). Areas of Khumbu Glacier have thinned by up to 80 m over the last three decades and glacier flow is slowing down, which allows meltwater to pond on the glacier surface. The rugged glacier surface is pitted with ice cliffs and ponds, which act as hot-spots of melt in areas of the glacier otherwise insulated by a thick layer of rocks and sediment (debris-cover). The rapid formation, persistence, and drainage of meltwater stored on glaciers across the Himalaya is a growing concern due to the potential for outburst floods and increased rates of glacier melt. An outburst flood event that occurred in the Everest region in 2017 destroyed trekking trails and a bridge.
Fig. 3: Scott presenting a study of glacier thinning at the Sagarmatha National Park office in Namche Bazar (3,500 m a.s.l). [Credit: Dhananjay Regmi].
After the final day of trekking, an extra night was spent in the village of Lukla, before flying back to Kathmandu. Each presentation was summarised in a few slides, and collated into a full talk that was given in Nepali by Dr. Dhananjay Regmi, organiser of the conference and head of Himalayan Research Expeditions. By presenting all our research in Nepali, more local people attended and were able to hear about and suggest new directions for research in the valley. This presentation was given again two days later, also in Nepali, at the Department of Tourism in Kathmandu, for locals who had already travelled back to the city to avoid the high-elevation winter chill.
Fig. 4: The projection augmented relief model shown after presentations in the village of Phortse. The inset shows glacier velocity data projected onto the glaciers in the Everest region. [Credit: Gu Changjun and Scott Watson].
We designed outreach activities and leaflets to enhance the PowerPoint presentations given at each village by providing interactive demonstrations of key research concepts and results. Scott used an AGU Celebrate 100 grant to design a projection augmented relief model (PARM) of the Everest region (Fig. 4). The PARM system projected research results including glacier velocity, mass loss, ice thickness, temperature, and animations of glacier flow, onto a 3D model, which stimulated discussion of the research. The 3D model allowed the local communities to easily visualise the data in the context of well-known mountain peaks and glaciers, and to observe the changing environment (such as the expansion of Imja Lake) from a projected time-lapse animation.
Fig. 5: Katie demonstrating glacier thermal regime and hydrology using a 3D model to conduct example dye tracing experiments. The lower panel is a GIF showing the dye tracing. [Credit: Scott Watson and Katie Miles].
Katie’s interactive outreach was to demonstrate dye tracing experiments on a 3D model of Khumbu Glacier (Fig. 5). Food colouring was used to “dye” the water, which was “injected” into a supraglacial stream, then “disappeared” into the glacier. The side view into the glacier showed this water flowing through and beneath the ice, before emerging back at the surface, flowing through surface ponds and exiting the glacier at its terminus. The side view also showed the approximate ice temperatures measured by the EverDrill project, which actively showed where (and why) the glacier is experiencing more melt.
The model was very well received by scientists and locals – while the water was being injected, we would explain what was happening in both English and Nepali, and there were always plenty of questions. While the dye tracing experiments didn’t work perfectly every time, surface floods offered an opportunity to talk about other hazards that have been recently observed on Khumbu Glacier.
The “Walk the Talk” Field Conference and Community Consultation was a new style of conference, aiming to communicate a wide range of research topics in the Everest region of Nepal and the Sagarmatha National Park. The combination of high-elevation trekking and presentations was sometimes tiring, but the trek facilitated discussions about the landscape we were immersed in and was a fantastic learning experience. It is hoped that the conference will travel to different locations in the future to share research and understand the priorities of other communities in Nepal.
Scott Watson is a Postdoc at the University of Arizona, USA, studying glaciers in the Everest region and the surface interactions of supraglacial ponds and ice cliffs. He also investigates natural hazards and glacial lake outburst floods. Tweets @CScottWatson. Website: www.rockyglaciers.co.uk
Katie Miles is a PhD student at the Centre for Glaciology, Aberystwyth University, UK, studying the internal structure and subsurface hydrology of high-elevation debris-covered glaciers in the Himalaya through borehole-based investigations and dye tracing experiments. Tweets @Katie_Miles_851. EverDrill website: www.EverDrill.org
Fig. 1: The view of Mount Everest and Khumbu Glacier from below Kala Patthar. The coloured tents of Base Camp can be seen stretched out alongside the glacier [Credit: Melanie Windridge].
Dr Melanie Windridge, a physicist and mountaineer, successfully summited Mount Everest earlier this year and has been working on an outreach programme to encourage young people’s interest in science and technology. Read about her summit climb, extreme temperatures, and the science supporting high-altitude mountaineering in our Image of the Week.
It’s bigger than it looks! Experiencing the majesty of Everest
In April/May this year I climbed Mount Everest. To the top. It was two months of patient toil but in surroundings so majestic, impressive and inspiring. The Western Cwm (an amphitheatre-like valley shaped by glacial erosion) is vast, the summit ridge is steep and Khumbu Glacier was fascinating in itself. Our base camp was on the glacier and it changed daily in subtle ways – the ice melted, the rocks moved, the paths morphed. And the icefall was slightly different each time I passed through – the route changing through a collapsed area, a crevasse widening, or the rope buried by ice-block debris fallen from above. It’s a wonderful, interesting place and I am grateful to have experienced it. You can read more about the climb on my personal blog.
Fig.2: The view up the Western Cwm from Camp 1. Lhotse can be seen in the distance and the summit of Everest mid-left. [Credit: Melanie Windridge].
Everest, of course, is extreme. It is steep almost everywhere, so you barely get a let-up anywhere beyond the Western Cwm. The temperature differences are extreme too – it is extremely hot or extremely cold. I took a couple of temperature loggers with me to the summit (one in a base-layer pocket under my down suit and one in an outer pocket of my rucksack). You can see from the graph of summit night (the climb from Camp 4 to the summit of Everest) (Fig. 3) how the temperature varied by tens of degrees. Since climbers dress for the coldest temperatures, this can be quite uncomfortable when the sun comes out. The temperature on summit night got down to about -25°C, but during the day it rose to 10 degrees or more so that we were sweating into our down suits.
Fig.3: Graph showing the readings from two separate temperature loggers on summit night – one in a base-layer pocket under the down suit (Down suit temperature) and one in an outer pocket of the rucksack (Air temperature). The temperature rises quickly after sunrise, which was experienced on the summit [Credit: Melanie Windridge and Scott Watson].
Sharing the Science of the Summit
It was science that really got me interested in Everest, when I realised that the main reason the British had succeeded in 1953 but hadn’t in the 1920s and 30s was because of scientific understanding and the state of technology. But so often we don’t talk about the science that supports us in these great endeavours; instead we put it all down to the strength of the human spirit. I think we need to talk about both.
As part of my climb, I have been working on an outreach project to highlight how science and technology have improved safety and performance on Everest. I have made Science of Everest videos for the Institute of Physics YouTube channel and will be giving public talks. I wanted to show how science supports us and what has improved in recent decades to contribute to the falling death rate on Everest.
In the video series I look at changes in weather forecasting, communications, oxygen, medicine and clothing. We also consider risk and preparation – videos that went out before I left for Everest – because, as a scientist, I looked into past data to see how I could give myself the best chance of reaching the summit and returning safely.
Communication has improved not only because we have a greater variety than was available to the first ascentionists or the early commercial climbers (we have satellite phones, mobile/cell-phones and WiFi now), but also because everything is a lot smaller. Electronic components have greatly reduced in size so that radios used on the mountain now are small and handheld in comparison to the bulky sets of the 1950s (see video above).
Of course, the implication of the project is wider than just Everest. I am interested in the importance of science and exploration in general. For me, Everest is an icon of exploration – the way that human curiosity, ingenuity, determination and endurance come together to drive us forward. Reaching into the unknown is good for us, on a societal level and on a personal level. I hope to give an appreciation of the value of science in our lives, give students an insight into interesting careers that use science, and show the value of doing things that scare us!
Dr Melanie Windridge is a physicist, speaker, writer… with a taste for adventure. She is Communications Consultant for fusion start-up Tokamak Energy, author of “Aurora: In Search of the Northern Lights” and is currently working on a book about Mount Everest. Website: www.melaniewindridge.co.uk (see the Science & Exploration blog to read about the Everest climb) Twitter @m_windridge, Facebook /DrMelanieWindridge, Instagram @m_windridge Science of Everest videos on the Institute of Physics YouTube channel http://bit.ly/EverestVids
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.
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].
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.
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
Fig.1: Drilling a borehole on Khumbu Glacier, Nepal Himalaya. In the foreground, the drill stem can be seen hanging off a tripod, attached to a spool of hose. Hot, pressurised water is supplied to these units from a pressure-washer in the background. [Credit: Katie Miles]
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!
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: firstname.lastname@example.org
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.
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.
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
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.
Figure 1: A schematic diagram of debris distribution on a debris-covered glacier, showing spatial variation in debris distribution with regards to rock type and layer thickness. Modelled on Baltoro Glacier, Karakoram. Surface velocity, sediment flux and debris thicknesses would vary between glaciers. Click here for a larger version. [Credit: Gibson et al., unpublished]
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 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.
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: email@example.com.
Field Site, Imja Lake, in November 2015 [Credit: D. Rounce]
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 long trek in
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]
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 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]
The glacier has melted such that the lateral moraines are now over 100 m higher
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 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]
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]
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]
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]
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]
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!
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.