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

Paulabreen

This month I have been in Svalbard, demonstrating on the Glaciology course (AG-325/825) at the University Centre in Svalbard (UNIS). The course is aimed at Masters and PhD students who want a taste of the Arctic. The course consists of four weeks of glaciology lectures  and weekly excursions to glaciers in the local area. I have been supporting the logistical side of the weekly excursions, with the odd bit of teaching here and there. This week we have been to Paulabreen, a surge-type glacier, which has some impressive ice exposures.

Map of Paulabreen, which flows into Rindersbukta, along with Skobreen and Bakaninbreen. The camera labelled on the map is the location of a time-lapse camera installed by researchers at UNIS, which captured the 2003-05 surge of Paulabreen-Skobreen. Source: Kristensen and Benn (2012)

Map of Paulabreen, which flows into Rindersbukta, along with Skobreen and Bakaninbreen. The camera labelled on the map is the location of a time-lapse camera installed by researchers at UNIS, which captured the 2003-05 surge of Paulabreen-Skobreen. Source: Kristensen and Benn (2012)

Paulabreen is a tidewater glacier that calves into Rindersbukta, a sheltered embayment that is situated close to the small mining settlement called Svea. Bakaninbreen and Skobreen are tributary glaciers of Paulabreen. All three of these are a special type of glacier called surging glaciers. A surge-type glacier is classified by its inability to transfer its mass from the upper accumulation region to the lower ablation region in a steady way. In the quiescent phase of a surge,  ice accumulates over time with slow throughput to the front (i.e. low velocities). At a given threshold, the glacier switches and rapidly transfers this large reservoir of accumulated ice, surging forward with velocities up to ten times faster than its slower, inactive phase. To find out more about surging glaciers, why they surge and where they can be found, I recommend reading a series of papers by Heidi Sevestre, whose PhD was specifically looking at surging glaciers – cataloging where they are, and producing a new concept that explains the processes behind surging dynamics.

Paulabreen and Skobreen last experienced a surge from 2003-2005, which was beautifully captured in this time-lapse sequence. The surge initiated at Skobreen, dragging Paulabreen with it as it propagated down into Rindersbukta. Over its surge period, these two glaciers advanced 2800m, with an average velocity of 3.2 m per day. For more information on the Paulabreen-Skobreen surge, click here.

Currently Paulabreen is very slow-moving and experiencing a steady retreat. The position of the glacier front is similar to its position in the 1980s, having advanced and retreated between then and now. Observations from the time-lapse sequence of the surge shows that the ice experienced thrusting and severe ice deformation, which is still seen in the ice today. By examining the ice exposures at the front of Paulabreen, we can get up close and personal to the processes that occurred during its surge phase. There are several features of interest that we could see…

Paulabreen in 1982 Photo credit: Simon Collins @RGSweather

Paulabreen in 1982. Photo credit: Simon Collins @RGSweather

Map of Paulabreen in 1982. Credit: Simon Collins @RGSweather

Map of Paulabreen in 1982. Credit: Simon Collins @RGSweather

Summary of the survey of Paulabreen in 1982. Credit: Simon Collins @RGSweather

Summary of the survey of Paulabreen in 1982. Credit: Simon Collins @RGSweather

Many thanks to Simon Collins (@RGSweather) for sharing his amazing photos and information about Paulabreen in the 1980s. Simon was part of an expedition who surveyed Paulabreen and Vallakrabreen, also taking sediment samples, weather readings and collecting information on the flowering species Alpine Bistort. The expedition consisted of a week-long hike from Longyearbyen to Svea, and then taking small boats across Rindersbukta to the study area. They spent six weeks there in total. 

Check out RGSweather for information on the Reigate Grammar School Weather Station, an automated weather station which collects high-resolution data on temperature, rainfall, barometric pressure, humidity, wind speed, wind direction and sunshine hours in the south of the UK. RGSweather are particularly dedicated to stimulating interest in the weather, with regular blog posts and information. 

The front of Paulabreen, with glaciology students on snow scooters for scale (March 2016)

A section of Paulabreen’s calving front with glaciology students on snow scooters for scale (March 2016)

Glaciology students examining the ice exposure at Paulabreen (March 2016)

Glaciology students examining the ice exposure at west side of Paulabreen (March 2016)

Glaciology students studying a section of the ice exposure at Paulabreen. The section here is approximately 6 m high (March 2016)

Glaciology students studying a section of the ice exposure at Paulabreen. The section here is approximately 6 m high (March 2016)

 

Wind pockets. High-winds exploit small indentations in the ice, creating hollows in the ice face. This process is not associated with the surge at Paulabreen, but is commonly seen at ice faces all over the world.

Wind pockets at Paulabreen (March 2016)

Wind pockets at Paulabreen (March 2016)

Wind pockets at Paulabreen (March 2016)

Wind pockets at Paulabreen. This picture shows approx. 15m ice face (March 2016)

 

‘Wormy’ ice. When ice is warmed by rapid motion, it partially melts. This allows air to move around the ice. It often travels towards ice crystal grain boundaries. This creates the ‘worm’-like veins in the ice. .

Wormy ice at Paulabreen (March 2016)

Wormy ice at Paulabreen. The section shown here is approx. 0.5 x 0.3 m (March 2016)

 

Regelation ice. Ice under a high amount of pressure, squeezing all air out of it to create very clear ice. Regelation ice can form at the bed of a glacier (in a high-pressure environment) or can form when exerted under high pressure. This changes the melting point of the ice and allows it to be partly liquid. During the surge at Paulabreen, sections of ice were pushed on top of one another, creating high amounts of pressure  and liberating the air from the ice.

Regelation ice and glacier ice separated by a debris layer at Paulabreen (March 2016)

Regelation ice (left) and meteoric ice (right) separated by a layer of debris at Paulabreen. Meteoric ice refers to ice derived from precipitation. Regelation ice is modified meteoric ice, transformed in a high-pressure environment. The section here is approx. 2 x 1.5 m (March 2016)

 

Debris entrainment features. Debris (i.e. fine-grained sediment, small pebbles, rocks) is often found in glaciers. This can be inputted on the glacier surface via rock fall and washed into surface meltwater channels. It can also be introduced at the base, entrained as the glacier ice flows over the bed. The size, texture and orientation of the debris entrainment can tell us about its origin and entrainment mechanism.  At Paulabreen, we see a lot of angular debris bands, with small pebbles orientated in the same direction. In this case, the debris has been entrained from the bed as one ice section has thrust over an adjacent stationary section during the 2003-05 surge.

Entrained sediment at Paulabreen (March 2016)

Entrained debris at Paulabreen. This debris band extends to the top of the ice face, with small angular pebbles all orientated in the same direction. This was formed during the surge phase of Paulabreen (March 2016)

Sediment squeezing at Paulabreen (March 2016)

Debris squeeze feature at Paulabreen. The debris here is rounded and sorted, with finer sediment at the top of the feature and larger pebbles and rocks at the bottom. In this case, crevasses and cracks appear at the base of the glacier as it surges rapidly. A slurry of wet mud and stones is then forced into these under the pressure exerted by the weight of the glacier. The debris squeeze feature shown in this image is approx. 3 x 0.5 m  (March 2016)

 

Debris – Regelation ice – Meteoric ice patterns. During the surge of Paulabreen, multiple sections of ice were thrust over each other as the ice was being pushed down Rindersbukta. This created a distinct pattern of debris band, regelation ice and meteoric ice. There is a gradual transition from the regelation ice to meteoric ice, from less bubbly to more bubbly ice. Where the debris passes over the ice, there is a sharp transition from meteoric ice to debris. As a section of ice is thrust over another, debris is entrained from the bed. This creates the debris band. The process of thrusting generates a large amount of pressure that transforms the ice immediately adjacent to the bed into regelation ice. This creates the seciton of regelation ice. On top of this regelation ice is normal unmodified meteoric ice, which has not been subjected to high pressure conditions. Over the period of the surge, multiple ice thrusting events create multiple lines of debris, regelated ice and meteoric ice.

Debris-Regelation ice-glacier ice patterns seen at Paulabreen (March 2016)

Debris-Regelation ice-glacier ice patterns seen at Paulabreen. The section here is approx. 3 x 2 m (March 2016)

Debris-Regelation ice-glacier ice patterns seen at Paulabreen (March 2016)

Debris-Regelation ice-glacier ice patterns seen at Paulabreen (March 2016)

 

Internal ice fractures. Cracks or faults in the ice that relate to cooling of the ice as it meets relatively cold winter air temperatures, and strong pressure gradients near the free ice face. These features are not directly related to the surge of Paulabreen.

Ice fracturing at Paulabreen (March 2016)

Ice fracturing at Paulabreen. Image here shows 1 x 0.6 m section of the ice exposure (March 2016)