Calving dynamics at Tunabreen, Svalbard, published in Annals of Glaciology

Annals of Glaciology has recently published our work examining calving dynamics at a tidewater glacier in Svalbard (click here to see article). In the study, we use time-lapse images captured every 3 seconds to document and analyse calving events at Tunabreen that occurred over a 30-hour period in August 2015.

A time-lapse camera installed at Ultunafjella, overlooking the calving front of Tunabreen (August 2015)

Our time-lapse camera installed in the field, overlooking the terminus of Tunabreen, a tidewater glacier in Svalbard. We captured images every 3 seconds over a 30-hour period in August 2015, from which we could distinguish calving events in high levels of detail.

In total, we acquired 34,117 images. Compiled together, these images produced a sequence that we distinguished 358 individual calving events from. We could also discern the style of each calving event, inferring the controls on calving at this particular glacier front.

Calving at Tunabreen was characterised by frequent events during our monitoring period, with 12.8 events occurring every hour on average. Most calving events were small in magnitude, relative to those observed at other tidewater outlets such as those in Greenland (e.g. James et al., 2014), and other tidewater glaciers in Svalbard (e.g. How, 2018).

Fig 3 from How et al. (2019)

All documented calving events and styles observed at Tunabreen, first distinguished in the image plane (left) and subsequently georectified to extract real coordinates and compare to ice velocity (right) (Figure 3 from How et al., 2019)

Five calving styles were observed – waterline events, ice-fall events, stack topples, sheet topples, and subaqueous events – based on the relative size and mechanism of failure. A high majority of calving events (97%) originated from the subaerial section of the ice cliff, despite the fact that 60–70% of the terminus is below sea level. Subaqueous calving events were very rare, with only 10 observed over our monitoring period. The rarity of subaqueous events indicates that ice loss below the waterline is dominated by submarine melting, with the only local development of projecting ‘ice feet’.

Over two-thirds of observed calving events occurred on the falling limb of the tide. suggested that tidal level plays a key role in the frequency of calving events. Calving events were also roughly twice as frequent in the vicinity of meltwater plumes compared with non-plume areas, indicating that turbulent water promotes temrinus instability. The presence of a ~ 5 m undercut at the base of the glacier further supports the idea that ice is being excavated from below the waterline. 

An example of a subaqueous calving event at Tunabreen, occurring in the plume area. The section of ice front shown is approximately 350 m, and the iceberg is 40 m wide

An example of a subaqueous calving event at Tunabreen, captured using our time-lapse camera. The section of ice front shown is approximately 350 m, and the iceberg is 40 m wide

We conclude that, based on the observations, calving rates at Tunabreen for this observation period may simply be paced by the rate of submarine melting. Similar dynamics have also been observed at other tidewater glaciers in Svalbard (e.g., Chapuis and Tetzlaff, 2014; Pȩtlicki and others, 2015), Greenland (e.g., Medrzycka et al., 2016) and Alaska (e.g., Bartholomaus et al, 2015). This being the case, the inference of calving rate from submarine melt rate would greatly simplify the challenge of incorporating the effect of melt-under-cutting in predictive numerical models; at least for this type of well-grounded, highly fractured glacier.

To read more about this research, please check out our paper published in Annals of Glaciology.

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A dummies guide to… my PhD thesis on glacier dynamics

Recently my PhD thesis was made available online through the Edinburgh Research Archive, titled ‘Dynamical change at tidewater glaciers examined using time-lapse photogrammetry’. The thesis is 342 pages long which would be a marathon to get through for anyone, so here is a short synthesis.


In a nutshell

Title: Dynamical change at tidewater glaciers examined using time-lapse photogrammetry

Goal: To understand processes linked to dynamical change at tidewater glaciers.

Three main aims:
1. Examine subglacial hydrology and its influence on glacier dynamics at Kronebreen, a fast-flowing, tidewater glacier in Svalbard
2. Investigate controls on terminus conditions and calving processes at Tunabreen, a surge-type, tidewater glacier in Svalbard
3. Develop a suite of photogrammetry tools for obtaining measurements from oblique time-lapse imagery

Techniques used: Monoscopic time-lapse photogrammetry, hot water borehole drilling, bathymetry surveying, satellite feature-tracking, passive seismic monitoring, melt/runoff modelling


Acquiring data from the field

Me at camera site 8b, Kronebreen, Svalbard (May 2015)

An example of one of our time-lapse cameras, installed at Kronebreen

High-detail monitoring of glacier termini is challenging. We decided to employ time-lapse photogrammetry as our primary technique in this study given that it can provide high-resolution data acquisition (e.g. 1 image every 3 seconds, over 24 hours) as well as appropriate acquisition rates for longer-term monitoring where needed (e.g. 1 image every hour over the course of a melt season). Therefore we can acquire different temporal frequencies depending on which aspects of the glacier system we want to examine.

Between 2014 and 2017, we deployed 7 – 14 time-lapse cameras at two glaciers in Svalbard (Kronebreen and Tunabreen) to monitor various aspects of the glacial system – ice flow, terminus retreat, supraglacial lake drainage, meltwater plumes, and local fjord circulation. We combined the findings from these images with other datasets (e.g. borehole measurements, bathymetry surveys) in order to examine dynamical change at a high level of detail.


Finding #1: Spatial variation in Kronebreen’s ice flow is primarily controlled by meltwater routing at the glacier bed

From our time-lapse images over the 2014 melt season, along with borehole data analysis, melt/runoff modelling and hydropotential modelling, we found that spatial variations in ice flow at Kronebreen were primarily controlled by the location of subglacial meltwater channels.

Efficiency in subglacial water evacuation varied between the north and south regions of the glacier tongue, with the north channel configuration draining a large proportion of the glacier catchment through persistent channels, as indicated by hydropotential modelling. Channel configurations beneath the south region of the terminus were vastly different, with rapid hydrological changes evident and cyclic ‘pulsing’ suggested from the observed meltwater plume activity.

These differences in subglacial hydrology are reflected in ice flow, with faster velocities experienced in the south region of the glacier, facilitated by enhanced basal lubrication and sliding. Two speed-up events were observed at the beginning of the 2014 melt season, the second being of significant importance given that it occurred at the end of the melt season and enabled fast flow through the winter season. It is suggested that this event was caused by an abnormal high rainfall event which overwhelmed an inefficient hydrological regime entering its winter phase. This phenomena highlights that the timing of rainfall events at tidewater glaciers is fundamental to their impact on ice flow.

The Cryosphere Kronebreen maps

Sequential velocity maps (left) and velocity change maps (right) of Kronebreen showing the first of two speed-up events experienced during the 2014 melt season.


Finding #2: Terminus stability is inherently linked to both atmospheric and oceanic variability at Tunabreen. In particular, calving activity is primarily facilitated by melt-undercutting

Terminus conditions at Tunabreen were examined on two differing temporal scales:

  1. Over a one month period in peak melt season using time-lapse images acquired every 10 minutes
  2. Over a 28-hour period in August 2015 using time-lapse images acquired every 3 seconds

Over the one-month observation period, the terminus retreated 73.3 metres, with an average retreat rate of 1.83 metres per day. The frontal ablation rate fluctuated between 0 and 8.85 metres per day, and 1820 calving events were recorded of which 115 events were simultaneously detected from passive seismic signatures recorded in Longyearbyen. Overall, strong links were found between terminus position changes and both sea surface temperature and air temperature, suggesting that atmospheric forcing plays a larger role in terminus stability than previously considered.

Calving events at Tunabreen over a 30-hour period in August 2015, captured using high-resolution time-lapse photography (one photo every three seconds). Calving events are categorised as subaerial (i.e. ice falling from the front above the waterline), subaqueous (i.e. ice breaking off from the front beneath the waterline), both (i.e. large calving events which contain both subaerial and subaqueous originating ice) and unknown (caused by concealment or poor visibility).

Calving events at Tunabreen over a 28-hour period in August 2015, captured using high-resolution time-lapse photography (one photo every three seconds). Calving events are categorised as subaerial (i.e. ice falling from the front above the waterline), subaqueous (i.e. ice breaking off from the front beneath the waterline), both (i.e. large calving events which contain both subaerial and subaqueous originating ice) and unknown (caused by concealment or poor visibility)

Calving activity at Tunabreen consists of frequent events, with 358 calving events detected from the 28-hour, high-frequency time-lapse sequence (i.e. 12.8 events per hour). The majority of these calving events (97%) occurred above the waterline despite the fact that 60-70% of the terminus is subaqueous (i.e. below the waterline). This suggests that ice loss below the waterline is dominated by submarine melting, rather than the break off of large projecting ‘ice feet’.  In addition, calving events are twice as frequent in the vicinity of the meltwater plumes, with visible undercutting (approximately 5 metres) revealed from the bathymetry side profiles. Overall, this suggests that enhanced submarine melting causes localised terminus instability at Tunabreen.


Finding #3: PyTrx is a viable Python-alternative toolbox for extracting measurements from oblique imagery of glacier environments

PyTrx velocities

An example of PyTrx’s capabilities in deriving surface velocites at Kronebreen, Svalbard. Velocities are calculated from the image using a sparse feature-tracking approach, with unique corner features identified using Shi-Tomasi corner detection and subsequently tracked using Optical Flow approximation. In this example, 50 000 points have been successfully tracked between an image pair from Kronebreen, producing a dense collection of velocity points.

Time-lapse photogrammetry is a growing method in glaciology for providing measurements from oblique sequential imagery, namely glacier velocity. When we began processing our time-lapse images, we found that there were few publicly available toolboxes for what we wanted and the range of their applications was relatively small. For this reason we decided to develop PyTrx, a Python-alternative toolbox, to process our own data and also aid the progression of glacial photogrammetry with a wider range of toolboxes.

PyTrx is an object-oriented toolbox, consisting of six scripts that can be used to obtain velocity, area and line measurements from a series of oblique images. These six scripts are:

  1. CamEnv: Handles the associated data with the camera environment, namely the Ground Control Points (GCPs), information about the camera distortion, and the camera location and pose
  2. DEM: Handles data related to the scene, or Digital Elevation Model (DEM)
  3. FileHandler: Contains functions for reading in data from files (such as image data and calibration information) and exporting output data
  4. Images: Handles the image sequence and the data associate with each individual image
  5. Measure: Handles the functionality for calculating homography, velocities, surface areas and distances from oblique imagery
  6. Utilities: Contains the functions for plotting and interpolating data

PyTrx has been used to process the data presented previously, and is freely available on GitHub with several example applications also. These examples include deriving surface velocities and meltwater plume footprints from time-lapse images of Kronebreen, and terminus profiles and calving event locations from time-lapse images of Tunabreen.


Related links

This thesis is freely available to download from the Edinburgh Research Archive

How et al. (2017) The Cryosphere – Examining the subglacial hydrology of Kronebreen and its influence on glacier dynamics 

How et al. (In Review) Annals of Glaciology – Observations of calving styles at Tunabreen and the role of submarine melting in calving dynamics

How et al. (2018) Geoscientific Instrumentation, Methods and Data Systems – Presenting the PyTrx toolbox and its capabilities with oblique imagery of glacial environments

PyTrx – PyTrx toolbox code repository, hosted on GitHub

Subglacial hydrology at Kronebreen, Svalbard, published in The Cryosphere

The Cryosphere recently published our work on Kronebreen, a fast-flowing tidewater glacier in Svalbard (click here to see the article). The study examines subglacial hydrology and its influence on basal dynamics over the 2014 melt season, with simultaneous observations of water pressure at the bed, supraglacial lake drainage, meltwater plume activity, and glacier surface velocities. In addition, melt/runoff and hydraulic potential were modelled in order to estimate surface melt production, and the routing of meltwater at the bed. This built a nice record from which we could establish a robust, theoretical picture of how water is channeled at the bed.

One of the key findings is the difference in drainage beneath the north and south regions of the glacier terminus, which is linked to spatial variations in surface velocity. The study also shows a consistently high water pressure at the glacier bed throughout the melt season. These readings were collected from a borehole that was drilled approximately 3 km upglacier of the terminus. Borehole records from tidewater glaciers are rare but the few early studies that currently exist, including this one, suggest that bed conditions at tidewater glaciers are persistently pressurised, with a high hydraulic base-level that permits fast flow.

The Cryosphere Kronebreen site map figure

Figure 1 from the TC paper: The site map of Kronebreen, along with the location of the three groups of supraglacial lakes (C1, C2 and C3) that filled and drained during the 2014 melt season. These lakes were monitored by seven time-lapse cameras, which were installed on the rock outcrops surrounding the glacier tongue (denoted by the orange numbered locations). These lakes drained sequentially in an upglacier fashion, similar to the speed-up event at the beginning of the melt season. The starred location is where the borehole was drilled and the pressure sensor was installed.

The Cryosphere Kronebreen maps

Figure 5 from the TC paper: Sequential velocity maps (left) and velocity change maps (right) of Kronebreen, derived from TerraSAR-X imagery. The south region of the glacier tongue is faster flowing than the north region throughout the melt season. We argue that this reflects a difference in drainage efficiency. An early-season speed-up event is  depicted in the velocity change maps, which originates from the terminus and propagates upglacier. Similar speed-up events occur year-on-year at Kronebreen. These may reflect changes at the terminus early in the melt season which promote longitudinal stretching, and/or reflect a seasonal hydraulic overhaul which promotes basal sliding.


Further reading

The Cryosphere paper

Other studies at Kronebreen (here and here) which show early-season speed-up events

Borehole study at a tidewater glacier in Patagonia 

 

What is going on at Tunabreen?

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).

Time-lapse at Tunabreen using one image per day

Time-lapse images from the front of Tunabreen. This glacier terminates into a large fjord called Tempelfjorden, hence it is referred to as a marine-terminating glacier. This time-lapse image sequence was constructed using one image per day between July-August 2016. This work is part of Calving Rates and Impact On Sea level (CRIOS) project at UNIS.

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. 

Speed-up at Tunabreen. Source: St Andrews Glaciology.

The speed-up at Tunabreen shown from feature-tracking through TerraSAR-X satellite images (from Adrian Luckman, Swansea University). Luckman also tweeted two images from this sequence here which nicely show the difference between 2015 and 2016. Source: St Andrews Glaciology.

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:

  1. 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.
  2. 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).
  3. 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).
  4. 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.
Tempelfjorden. This year we unfortunately could not visit Tempelfjorden and Tunabreen glacier with the students because of the lack of sea ice. Sea ice normally forms in Tempelfjorden up to the ice front over the winter, but this year it has not formed. This also happened in 2006 and 2012. For the first time ever though, there is no sea ice directly in front of Tunabreen, which will have massive repercussions for the glacier's dynamics

Tempelfjorden in March 2015. Sea ice normally forms in Tempelfjorden up to the ice front over the winter, but it did not form in 2015 and 2016. This also happened in 2006 and 2012. As well as having large implications for the dynamics of Tunabreen, this has also impacted on snow scooter routes across Svalbard. The sea ice in Tempelfjorden has previously been used as a major scooter route for tourist groups and for transporting goods.

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!

Tunabreen in March 2017

The front of Tunabreen in March 2017. I was lucky enough to visit Tunabreen earlier this month as part of the Glaciology course that runs at UNIS each year. It was incredible to see this glacier again. We have time-lapse cameras positioned on the mountain ridge (Tunafjell) that is visible in this picture. Hopefully they will give us some insight into the dynamics associated with this speed-up.


Further Reading

St. Andrews Glaciology blog: Unexpected ‘surge’ of a Svalbard tidewater glacier

UNIS post by Chris Borstad on the changes at Tunabreen

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.

Tweets by Adrian Luckman showing the speed-up from TerraSAR-X imagery and Sentinel imagery

Using meltwater plumes to infer subglacial hydrology at tidewater glaciers

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’).

An example of a meltwater plume at Tunabreen, a tidewater glacier in Svalbard

An example of a surfacing meltwater plume at Tunabreen, a tidewater glacier in Svalbard. Note the distinctive shape and the dark colour (indicating sediment content) of the surface expression.

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:

  1. The temperature/density difference between the freshwater in the plume and the surrounding saltwater
  2. The geometry of the fjord, such as how deep it is
  3. The stratification of the surrounding saltwater
  4. 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.

Kronebreen (centre) viewed from the west. Kronebreen shares its southern (right) margin with Kongsvegen, a slow-moving surge-type glacier that has been fairly inactive for the past couple of years. The glacier adjacent to Kronebreen, separated by the mountain Collethøgda (left), is called Kongsbreen. Kongsbreen has been retreating from the fjord onto land since approximately 2014 (September 2016)

A meltwater plume at the front of Kronebreen, a fast-flowing tidewater glacier in Svalbard. The surfacing plume  is situated on the north side of the plume (left side of the terminus in this image). This plume entrains sediment which gives it a red/brown colour. A plume also surfaced intermittently on the south side of the terminus during the melt season of 2014 (not pictured here). Photo taken: September 2016.

Timeline of surfacing plume activity at Kronebreen, Svalbard, monitored from time-lapse imagery. Plumes P1, P2 and P3 were present at the north side of the terminus, with P1 being active for the entire monitoring period (gaps are where there was no visibility in the images). Plume P4 surfaced at the south side of the terminus, showing intermittent activity throughout the melt season.

Timeline of surfacing plume activity at Kronebreen, Svalbard, monitored from time-lapse imagery. Activity began on the 23 June and continued through till the end of September. Plumes P1, P2 and P3 were present at the north side of the terminus. P1 (pictured in the above image) was active for the entire monitoring period (gaps are where there was no visibility in the time-lapse imagery). Plume P4 surfaced at the south side of the terminus, showing intermittent activity throughout the melt season.

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.

Velocity map of Kronebreen over an 11-day period in April 2014 (Luckman et al., 2015)

A velocity map of Kronebreen over an 11-day period in April 2014 (Luckman et al., 2015). These velocities are derived from feature tracking between image pairs, and these images are TerraSAR-X satellite images. Higher surface velocities are present at the central/south side of the terminus compared to the north side. This is possibly related to a difference in subglacial drainage beneath these two regions. Source: UNIS.

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.


Further reading

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.

PhD new year resolutions 2017

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.

Attending the EGU General Assembly in Vienna. Despite being in Vienna with glorious sunny weather, a glaciologist will always be able to find a snowman! (April 2016)

Attending the EGU General Assembly this year. Despite being in Vienna with glorious sunny weather, a glaciologist will always be able to find a snowman! (April 2016)

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.

Our camera at Kongsbreen... survived and still working! (September 2016)

Re-visiting one of our camera sites in September 2016. In total, I have spent 5 months of this year in Svalbard, making it a total of 15 months (approx.) spent in Svalbard throughout the course of my PhD!

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!

 

How time-lapse photography works in the study of glacial processes

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.
A time-lapse camera installed at Ultunafjella, overlooking the calving front of Tunabreen (August 2015)

One of our time-lapse cameras looking at the calving front of Tunabreen, a surge-type glacier in Svalbard. This camera remained here taking photos every 10 minutes between August 2015 and September 2016. This camera collected 24,136 images in total.

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).

An image sequence constructed from one photo a day at the front of Kronebreen glacier in Svalbard. This sequence spans 15 June to 26 July 2016, covering part of summer melt season. During this phase, the glacier is moving approx. 3 metres per day and calving activity is high. The muddy water in the fjord indicates that meltwater is exiting the glacier, forming a submarine plume that interacts with the saline fjord water.

An image sequence constructed from one photo a day at the front of Kronebreen glacier in Svalbard. This sequence spans 15 June to 26 July 2016, covering part of summer melt season. During this phase, the glacier is moving approx. 3 metres per day and calving activity is high. The muddy water in the fjord indicates that meltwater is exiting the glacier, forming a submarine plume that interacts with the saline fjord water.

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.

One photo every 10 minutes at Kronebreen (2-6pm 1st September 2016)

An image sequence constructed from one photo every 10 minutes at the front of Kronebreen. This sequence spans 4 hours real-time (2-6pm 1st September 2016), showing conditions at the end of the summer melt season. Here, the circulation in the fjord water can be distinguished based on the movement of icebergs, migration of the submarine melt plume is seen, and calving ice from the glacier front is visible.

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.

Large calving event at Kronebreen (September 2015), with ice originating from above and below the waterline. Iceberg approx. 100m wide, 50m high (above waterline only)

An image sequence constructed from one photo every three seconds, showing a large calving event at Kronebreen. This sequence covers two minutes real time at the end of the summer melt season 2015 (00.18 to 00.20).The iceberg that breaks off is approx. 100m wide, 50m high (above waterline only).

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.