Tunabreen is a tidewater glacier in Svalbard that has recently been displaying some exciting activity. It is known as a surge-type glacier, with discrete periods where it flows markedly faster and slower. Tunabreen entered a fast-flowing phase in December 2016, which is ongoing at the time of writing. The nature of this fast-flowing phase is atypical for Tunabreen though, throwing into question whether this phase is associated with surge dynamics. What is going on at Tunabreen?!
Tunabreen is an ocean-terminating glacier on the west coast of Svalbard. This glacier is particularly special because of its unique set of dynamics. A large number of the glaciers in Svalbard are known as surge-type glaciers. A surge-type glacier undergoes periods of fast-flow followed by very slow, inactive phases. The nature of this surging pattern is due to the glacier’s inefficiency in transferring mass from its upper regions to its terminus (Sevestre and Benn, 2015). It is an internally-driven process. The trigger of this process is unrelated to external influences (i.e. changes in air temperature, ocean temperature, and precipitation).
Tunabreen is one of few glaciers in Svalbard to have been observed to undergo repeated surge cycles. It has surged in 1870, 1930, 1971, and between 2002-2005. We know these surges happened because each surge phase left a pronounced ridge on the seabed which defines the surge extent (Flink et al., 2015). As these surges have been spaced 30-60 years apart, the next surge was not expected for quite a while (at least until 2030).
Tunabreen was a very slow-moving glacier between 2005 and 2016, flowing between 0.1-0.4 metres per day (m/day). These velocities were largely derived from sequential satellite imagery. Distinct glacial features were tracked from image to image to determine surface velocities on the glacier. The highest velocities (0.4 m/day) were limited to the terminus area, with very little movement (0.1 m/day) in the upper section of the glacier tongue. It was often difficult to track glacial features from image to image because the glacier was moving so slowly.
A marked speed-up was initially observed at Tunabreen in December 2016. The entire glacier tongue suddenly flowed faster. The terminus flowed >3 m/day and velocities in the upper section increased to 0.3-2.0 m/day. This speed-up continues at the time of writing this blog post (March 2017). It is a dramatic difference from the months and years prior to this event.
So, is this a surge? is the question on everyone’s lips now. In short, we don’t know at the moment and this is a difficult question to answer with the short amount of time that we have witnessed these changes at Tunabreen. At the time of writing, there are 4 key observations that need to be considered:
- The timing of this speed-up coincides with record-high temperatures and precipitation for a winter season in Svalbard (as stated in this article by Chris Borstad, a glaciologist at UNIS). This could have had a significant influence on the presence of water at the bed of the glacier, which is understood to lubricate the interface between the ice and the underlying bedrock. This, in turn, promotes sliding and may also cause the glacier to flow faster.
- This winter, sea ice did not form in Tempelfjorden and the fjord area directly adjacent to the glacier front. Sea ice and melange is understood to provide a back-stress against the front of a glacier. This acts as an opposing force to ice flow. Without the presence of sea ice, this opposing force is absent at the front of Tunabreen. Lack of sea ice was also observed in the winter of 2015 (as noted here in a previous blog post).
- The spatial pattern of this speed-up propagated in an upward fashion i.e. an increase in velocity first occurred at the front of the glacier, with subsequent velocity changes progressing up the glacier tongue. The abundance of crevasses on the glacier surface has increased, with the crevasse field extending much further up the glacier tongue than previously. Also, the terminus has advanced roughly 400 m since December 2016, as shown from the sequence of Sentinel images tweeted by Adrian Luckman (and displayed in a post by St. Andrews Glaciology). These observations are indicative of surging dynamics, as stated by Sevestre and Benn (2015).
- This speed-up has occurred 12 years after the previous surge (2002-2005). Surges at Tunabreen have previously been spaced 30-60 years apart from one another. The next surge was not expected until at least 2030. If this speed-up is associated with surge dynamics then it has occurred much earlier than anticipated.
These observations can be used as arguments for and against this speed-up being associated with surge dynamics. Whilst the behaviour of the glacier indicates that this may be associated with surge dynamics, there have also been significant changes in external factors which could have played a crucial role in this speed-up. It is important to continue monitoring changes to better understand the processes behind the abnormal behaviour at Tunabreen. It will be interesting to see if this speed-up is sustained through the spring of 2017, and to see how much the terminus will continue to advance into Tempelfjorden. One thing is for certain: all eyes will be on Tunabreen and what it does next!
Sevestre and Benn (2015) – A comprehensive study on surge-type glaciers and their distribution around the world.
Flink et al. (2015) – Past surge extents at Tunabreen determined by topographic features on the sea bed, derived from multibeam-bathymetric surveying over Tempelfjorden.
PhD update: January 2017. Meltwater plumes are the upwelling of fresh water in front of a tidewater glacier. These are known to influence submarine melt rates, which are suggested to have a significant impact on the calving rate of glaciers that terminate in sea water. Recent work has suggested that meltwater plumes can also be used to infer the subglacial hydrology at the front of a glacier.
At land-terminating glaciers, water is evacuated via flow outlets which form large rivers on the adjacent land. It is therefore relatively straightforward to measure the amount of water leaving the glacial system. Things are a bit more complicated at glaciers which terminate in water (i.e. a fjord, sea, or ocean). Fresh water exits from the glacier at depth and interacts with the salty seawater. The fresh water moves upwards due to the density difference between freshwater and saltwater, forming a turbulent column of mixing water. This is a meltwater plume (and can also be referred to as a ‘submarine plume’, or simply just a ‘plume’).
The freshwater in a meltwater plume will continue to flow up through the water column and entrain surrounding saltwater until it is thoroughly mixed (i.e. there is no difference in the density between the plume and the surrounding water). At this point, a meltwater plume will reach its neutral buoyancy and the water will cease flowing upwards and flow horizontally away from the glacier front.
A meltwater plume can reach the sea surface if the neutral buoyancy exceeds the depth of the fjord. The surface expression of a meltwater plume is normally very distinctive, distinguished by its sediment-laden colour and turbulent flow away from the glacier. We have lovely images of meltwater plume activity at Tunabreen, a tidewater glacier in Svalbard, showing a surfacing plume which has entrained very rich red/brown sediment.
The neutral buoyancy point of a meltwater plume is influenced by a number of factors:
- The temperature/density difference between the freshwater in the plume and the surrounding saltwater
- The geometry of the fjord, such as how deep it is
- The stratification of the surrounding saltwater
- The rate at which meltwater is exiting the glacier (also referred to as discharge)
The first three of these listed influences undergo relatively little change compared to discharge over short time-scales (e.g. a summer season). Assuming this, the activity of a meltwater plume can be used as a signal for the rate at which meltwater is exiting a glacier over the course of a melt season.
Meltwater typically exits into a fjord/sea/ocean at the bed of a glacier. The meltwater can either be directed through a given number of big channels or a series of intricate, small cavities. Channels can typically accommodate large volumes of meltwater, hence they are known as an efficient drainage system. Linked cavities are not as effective at transporting meltwater and tend to hold water at the bed for much longer durations, so they are aptly referred to as an inefficient drainage system.
An efficient drainage system can quickly channel a large volume of meltwater into the adjacent sea water. It is therefore likely that the neutral buoyancy of a meltwater plume from an efficient drainage system can exceed the depth of the fjord, so the plume will surface and will be visible. An inefficient drainage system is much more limited in the rate at which it can deliver meltwater into the adjacent sea water. It is therefore likely that the neutral buoyancy of a meltwater plume from an inefficient drainage system will be at depth, so the plume will not surface and will not be visible. We can thus infer what type of drainage system is present at the front of a glacier by monitoring meltwater plume activity over short durations.
We have been monitoring meltwater plume activity at the front of Kronebreen, a fast-flowing tidewater glacier in Svalbard. Two sets of plumes were present over the 2014 melt season, on the north and south side of the terminus. It is assumed here that a meltwater plume is likely to surface in the fjord if a channel is active based on the known fjord depth (∼80 m) and modelled runoff outputs. The set of plumes on the north side of the terminus persistently surfaced throughout the melt season, whereas the plume on the south side only surfaced intermittently.
A plume may not be able to consistently surface because meltwater is not leaving the glacier through a stable efficient drainage system. This could suggest that two different drainage systems preside at the north and south side of the glacier – a stable efficient drainage system on the north side, and an unstable system that switches between efficient and inefficient drainage on the south side.
In this situation, you would expect to see other differences between the north and south side of the terminus such as surface velocity. A large amount of subglacial meltwater is in contact with the bed in an inefficient drainage system, which enhances lubrication at the bed and promotes ice sliding. In an efficient drainage system, the water is channelled through a discrete area of the glacier and thus there is less basal lubrication as a smaller amount is in contact with the bed.
Surface velocities over the 2014 melt season show a distinct difference between the north and south side of the glacier terminus – the south is much faster flowing than the north, with the south exceeding velocities of 4 metres per day whilst the north remains relatively slow (see an example velocity map above). It is likely that a difference in drainage efficiency could facilitate this difference in surface velocities. The presence of an inefficient drainage system at the south side of the glacier tongue may be promoting faster velocities.
This idea is being further explored with additional datasets to better understand glacier hydrology and dynamics. The main take-home message from this post is that meltwater plume activity could be a reliable signal for meltwater outflow. This activity can be effectively monitored using time-lapse photography. Observations of plume activity can help us to diagnose the nature of subglacial drainage beneath tidewater glaciers, which is not accessible for direct measurements at this time. Kronebreen appears to have two different drainage systems active near the glacier terminus, as reflected in the differing plume activity, and this could be facilitating fast velocities in discrete areas of the glacier.
Slater et al., 2017 – A newly-published study looked at meltwater plume activity at Kangiata Nunata Sermia (KNS) in Southwest Greenland using an in-situ time-lapse camera. They predicted from model simulations that a meltwater plume from a single channel should be able to surface in the adjacent fjord water, knowing the rate of discharge through the drainage system. However, the time-lapse imagery showed that the meltwater plume was only visible for brief periods throughout a melt season (May to September 2009). They argued that a plume was not consistently surfacing because meltwater may not leaving the glacier through a stable efficient drainage system. An efficient drainage system may not be able to persist at the front of KNS because it could be repeatedly disrupted by basal deformation, which is facilitated by the fast-flowing nature of the glacier. This paper has been neatly summarised by ice2ice.
Time-lapse sequences from Kronebreen. Note the visible plume activity seen from cameras 1 and 2 through the melt season.
At the beginning of 2016, I set myself five new year resolutions specifically relating to my PhD work. Now it is the end of the year, I thought I would review these resolutions and set new ones for 2017.
2016 PhD resolution review
1 Write more – over the course of this year I have written 25 blog posts and begun the framework for each of the chapters/papers of my thesis, including a thorough review of terrestrial time-lapse photogrammetry techniques which is currently 10,000 words long. I think I got this one in the bag.
2 Publish something – not quite, but I knew that this goal would be unlikely to achieve by the end of 2016. I am currently writing the first paper from my work on the subglacial hydrology of Kronebreen, so I hope to be submitting it early in the new year.
3 Continue our time-lapse work at Kronebreen glacier in Svalbard – I went back to Svalbard in May 2016 to install the time-lapse cameras at Kronebreen and other glaciers in the Kongsfjorden area. These successfully captured images over the summer melt season and were collected in September 2016. In addition, we installed cameras on the shoreline next to Kronebreen in August 2016 to capture high-frequency time-lapse sequences of calving events. This time-lapse work is likely to continue into 2017, but I now have plenty of data to finish my PhD!
4 Attend a big conference, along with some smaller ones – this year I attended the EGU (European Geosciences Union) General Assembly in Vienna. It was a fantastic experience and I want to do more big conferences like EGU next year (for more, see here). I also attended this year’s IGS (International Glaciological Society) Nordic Branch meeting in Tromso, Norway to present some recent work from Kronebreen. Much of the content that I presented is on my blog here and it was generally well received. I talked with a lot of people about ideas and I greatly benefited from being there.
5 Take a holiday – failed. Completely failed. Although I spent a week with my parents in their home in Derbyshire during the summer, I still did work. I don’t think a day has gone by this year where I haven’t at least thought about work. And I fear that this will continue into next year as I enter my final year as a PhD student with paper and thesis deadlines looming overhead. All I can hope for is that I find time to take a break and do not panic!
2017 PhD new year resolutions
1 DO NOT PANIC – leading directly on from the previous paragraph, I think next year will get quite stressful at times as there will be pressure to publish papers and ultimately submit a complete thesis. Exercise has largely kept my panic demons at bay thus far, so maybe one of my resolutions can be to find other ways to relieve stress and anxiety.
2 Write more… again – write, submit, publish, and repeat. I would also like to keep up on my blog posts, but this may not be manageable at certain points. Publishing papers is the priority for 2017.
3 Think about what to do post-PhD – I have begun thinking about what I want to do after a PhD and plans have been mentioned. It would be nice to have a more concrete plan by the end of 2017, possibly with a position ready to follow on directly after I’ve finished my PhD.
4 Try and enjoy it – easier said than done. Many have said to me that your PhD is the time at which you get the most freedom in your research as you have few other commitments. So I want to try and enjoy it, despite all the stresses. I have already lined up some trips to St. Andrews and Tromso to work with colleagues, and hopefully other fun opportunities will crop up to make this last year enjoyable.
Happy new year everyone!
PhD update: November 2016. Whilst preparing a talk for the Geography research seminar series at the University of Manchester, I decided to include some information on time-lapse methods in glaciology to help introduce the topic. Within this, I wanted to convey how different glacial processes were visible at specific image intervals. By constructing image sequences with various intervals, I could effectively show the processes that occur at the front of glacier and how different processes operate on different time-scales.
To begin with, we take a camera and place it in front of the glacier we wish to study. Using an external timer (or intervalometer), the camera can take photos at a set interval. We tend to use small intervals, such as every hour or 10 minutes, from which we can extract image sequences with longer intervals (e.g. one image per day). This camera can be left unattended for a period of time, accumulating images of the glacier. We normally leave our cameras for a summer melt season (May to September) because either the memory card is full or the camera system needs servicing. For more information on the elements of a time-lapse camera system and how it is powered, see here.
Once the camera has been collected, the images can be used to construct image sequences from which observations and photogrammetric measurements can be made. These images can either be selected manually to maintain consistency in illumination or based on time interval. Glacial processes are more apparent when illumination is consistent. This is especially beneficial for looking at longer-term processes such as glacier movement. By constructing a sequence using one image per day with consistent illumination, glacier movement is apparent along with changes in terminus position (see below).
Over a summer melt season, marked changes at Kronebreen glacier, Svalbard, are visible. As ice in the upper region flows into the fjord, ice breaks off at the front as if it is being ‘nibbled’ away. This is known as the rate of frontal ablation. The rate of frontal ablation is higher in the area nearer to the camera due to the presence of a submarine plume, creating a small embayment in the glacier front. The region adjacent to this embayment retreats very little, leaving a preserved pinnacle in the middle of the glacier front. Its retreat rate is likely to be the result of a low frontal ablation rate controlled by a rapid delivery of ice to the region and low calving activity. This region of the glacier front also sits on a topographic high in the sea bed, which has pinned the front in a stable location.
We can examine the processes that contribute to these long-term changes in an image sequence constructed from images at shorter intervals. The sequence below is composed from images of Kronebreen every 10 minutes, covering 4 hours (real-time) in total.
Compared to the previous image sequence, we see a different picture here. We no longer visibly see glacier movement or change in the glacier front position. Instead we see shorter-term processes such as migration of the submarine melt plume surface expression. This can be used as an arbitrary measure for the amount of meltwater leaving the glacier. We can also observe icebergs moving in the fjord which can be tracked to indicate patterns of small-scale fjord circulation. This can be especially useful for examining submarine melt, specifically how the fjord water interacts with the front of the glacier.
We can isolated events with even shorter interval image sequences. Over the past year, we have been experimenting with high-frequency time-lapse methods, capturing one image every three seconds for short periods at Kronebreen. Image sequences constructed from one image every three seconds can look similar to video, better showing processes in a high level of detail. This has been especially useful for looking at individual calving events and the study of calving mechanisms.
Above is an example of a large calving event at Kronebreen at the end of the summer melt season 2015. It is visible to distinguish that this calving event is the result of a complete failure through the ice column, with ice breaking off from above and below the waterline. Initial failure at the top of the ice face causes a rotational break-off of the ice below this, which is likely to have been encouraged by a pre-existing weakness in the ice column such as a small crack or crevasse.
Hopefully with these sequences I have illustrated that different sets of glacial processes work on different timescales. One of the main advantages of time-lapse photography and photogrammetry techniques is that we can adjust the interval rate to look at the process we wish to examine, making it much more flexible than other imagery acquisition. We hope that time-lapse techniques will continue to be used in the study of glacial environments. It is likely that with the ongoing development of camera technology, there will soon be more advantages to using time-lapse photography and photogrammetry.
I didn’t know what to expect when I picked up a popular science book about snow, especially when its tagline is ‘A search for the world’s purest, deepest snowfall’. I thought The Snow Tourist by Charlie English, a book exploring the places in the world with the most snowfall, could be quite intriguing. On reading it, I feel like this book was mis-advertised though. It wasn’t intriguing… it was much better than that. Charlie English effectively conveys an intense curiosity and obsession with snow that goes much farther than merely looking for the deepest snow. Snow is explored in the context of art, folklore, science and as a way of life. This book far surpassed my expectations. I still learnt about so many fascinating things even though my career is in the study of ice and snow. Literally anyone can pick up this book and find out something interesting about snow.
The Snow Tourist begins with author Charlie English declaring his ambitious adventure – to travel to some of the coldest places and see the best snow over the world. I felt uncertain about this endeavour at first – what constitutes the ‘best’ snow? how will the author steer away from being dry and repetitive when describing each region? is there enough to explore and discuss in relation to snow?
Over the course of each chapter, a new theme relating to snow is introduced with each region that he is exploring. He examines the portrayal of snow in art whilst he is in Vienna, for example. Stories of catastrophic avalanches and fatal snow storms are illustrated in East Sussex and New York (yes, there was actually an avalanche in East Sussex in 1836). The pioneers of skiing are reviewed in the Alps.
The tagline of the book (‘A search for the world’s purest, deepest snowfall’) somewhat misrepresents what English’s adventure amounts to. He’s not merely looking for the ‘best’ snow, instead examining snow from a variety of different perspectives that range from scientific to cultural to historic to artist and beyond. It is only in the Chapter 9 (whilst visiting Rainer, Seattle and Glacier) that English addresses the search for the deepest, ‘best’ snow. There are so many interesting aspects of snow to read about before and after that. Here are a couple of things I found fascinating to read about:
- Mary Shelley’s Frankenstein was partly inspired by her travels to Chamonix when she was just 19 years old.
- The first ski race across Greenland (a 220km race from coast to coast) was in 1884 (see image and caption for more info).
- Yuki-onna is the Japanese snow spirit that allegedly appears during heavy blizzards as a young woman with pale skin and dressed in a pure white kimono. She sometimes appears with a baby in her arms, which she asks travellers to hold for her. On taking the baby, they find that it is actually a lump of hard ice that freezes them to death.
- Monet was invited to Norway, where he painted many snowy landscapes. He would often sit outside and paint in temperatures as low as -30 degrees (Celsius) with icicles hanging off his beard.
- Given a microscope and a camera in the 1880s, a young Wilson Bentley spent most of his life photographing snowflakes up close. Whilst his family and neighbours thought he was mad, Bentley sparked massive interest among the scientific community and was generally regarded as the most dedicated observer of snow in history (see here for more on the life and works of Wilson Bentley)
To round off the book, English includes a Snow Handbook that summarises a lot of his interests surrounding snow that are discussed previously and also includes more detail such as how to build an igloo, a list of fiction books that include snow, and the legend of the abominable snowman.
Also in this is ten facts about glaciers. Now, this might be my only critique of the book – it needed more focus on glaciers. I understand that this is the bias opinion of a glaciologist, but hear me out. Glaciers and ice are an essential aspect when writing a book that is broadly exploring snow – how snow transforms into ice, how ice moves, where snow/ice is stored in the world etc. etc. By including glaciers, English could have visited many other places (such as Antarctica, Greenland, Svalbard or Iceland) to explain the scientific and cultural aspects of glaciology. Ten facts about glaciers barely scratches the surface. And in some instances, the facts are poorly explained, such as fact #9: ‘The fastest glacier whose speed has been clocked dashed 12 kilometres in three months’ – which glacier was this? when was this? how was this speed measured?
Basically, I was mesmerised by this book. English’s curiosity with snow is evident on every page. There are facts from this book that I will remember for a long time. I have already shared a lot of them with friends, beginning with ‘Fun fact! Did you know…’ (to any friend who has been on the receiving end of this, I’m sorry if you are sick of my ramblings by now). My only criticism is that I wanted more. English made snow so exciting and interesting that I wish he would do the same for glaciers, and I have no doubt that he could.
It is known that supraglacial lakes on the surface of a glacier fill and drain over the course of a summer melt season. Lake observations from time-lapse photography at Kronebreen glacier in Svalbard show possible links between their drainage and changes at the glacier bed. This month I have been further investigating these lakes using satellite imagery and other data to find that these lakes have formed and drained in similar positions for at least 30 years, indicating that the subglacial environment is relatively consistent year-on-year.
Time-lapse images at Kronebreen show lake drainage at the end of June in both 2014 and 2015. These lakes have a maximum surface area of 18,000 sq m and appear to fill and drain simultaneously, sometimes appearing to be a brown, sediment-heavy colour suggesting that they are directly connected to the glacier bed.
These lakes were tracked through time based on pixel intensity and then geo-rectified using the camera position, a three-dimensional representation of the landscape (DEM) and ground control points (GCPs) to map them in real world coordinates. For more on the details of how this method works, see an earlier post here. The three sets of lakes tracked from the 2014 sequence have an upglacier pattern of drainage – the lower lakes fill and drain first, followed by the upper glacier lakes. As it is likely that these lakes are connected to the glacier bed, it is possible that their pattern of drainage show an upglacier-propagating flushing event at the bed. A trigger causes subglacial meltwater near the glacier front to drain which subsequently draws down meltwater from further upglacier, draining the lower surface lakes before the upglacier lakes.
As we only have images of these lakes from 2014 and 2015, I had a look at archived Landsat satellite imagery of the area to see if these lakes appear in similar places in earlier years. Overall, I found that lakes consistently appear year-on-year around the same time in the same places, at least back to 1986, which is 30 years ago. From here, we are working on acquiring more satellite imagery to further investigate whether these lakes are consistent and also whether there are additional lakes in other areas on the glacier tongue. Initial assessment shows that there are other lakes nearer to the terminus that appear infrequently, suggesting that the subglacial system is dynamic and not as consistently configured as we first thought.
I presented this work at the International Glaciological Society (IGS) Nordic Branch Meeting at the end of this month, which was held at the Norsk Polarinstitutt in Tromsø. Generally the presentation went really well, probably one of the best presentations I have ever done! There were a number of people at the conference working on Kronebreen, so it was especially helpful to see what they were doing and have input from them. We also had a lot of discussions more generally about Kronebreen and the techniques that we are using to acquire data from time-lapse imagery. The conference was very well organised and a great success so I would like to say thank you to those involved in making it happen.