CR
Cryospheric Sciences

geomorphology

Image of the Week – Vibrating Ice Shelf!

Image of the Week – Vibrating Ice Shelf!

If you listen carefully to the Ekström ice shelf in Antarctica, a strange sound can be heard! The sound of a vibrating truck sending sounds waves into the ice. These sound waves are used to “look” through the ice and create a seismic profile of what lies beneath the ice surface. Read on to find out how the technique works and for a special Cryosphere Christmas message!


What are we doing with this vibrating truck on an ice shelf?

In early December a team from the Alfred Wegener Institute (AWI) made a science traverse of the Ekström ice shelf, near the German Neumayer III Station. Their aim was to make a seismic survey of the area. The seismic source (sound source) used to make this survey was a vibrating truck, known as a Vibroseis source (Fig. 2).

Fig. 2: The Vibroseis truck. It is attached to a “poly-sled” so that it can be easily towed across the ice shelf. The vibrating plate can be seen suspended below the centre of the truck. [Credit: Judith Neunhaeuserer]

It has a round metal plate, which is lowered onto the ice-shelf surface and vibrates at a range of frequencies, sending sound waves into the ice. When the snow is soft the plate often sinks a little, leaving a rather strange “footprint” in the snow (Fig. 3).

Fig. 3: The “footprint” of the Vibroseis truck plate in the snow [Credit: Olaf Eisen].

The sound waves generated travel through the ice shelf, through the water underneath and into the rock and sediment of the sea floor, they are reflected back off these different layer and these reflections are recorded back on the ice surface by a string of recording instruments – geophones (Fig 1). There are sixty geophones in a long string, a snow streamer, which can be towed behind the truck as it moves from location to location. By analyzing how long it takes the sound waves to travel from the source to the geophones an “image” of the structures beneath the ice can be made. For example, you can see a reflection from the bottom of the ice shelf and from the sea floor as well as different layers of rock and sediment beneath the sea floor. This allows the team to look into the geological and glaciological history of the area, as well as understand current glaciology and oceanographic processes!

 

As it happens, the team from AWI consists of your very own EGU Cryosphere Division President, Olaf Eisen and ECS Rep, Emma Smith! As this is the last post before Christmas, we wanted to wish you a merry Christmas from Antarctica!

Merry Christmas! As you can see the weather is beautiful here! [Credit: Jan-Marcus Nasse]

Edited by Sophie Berger

Image of the Week – It’s all a bit erratic in Yosemite!

Image of the Week – It’s all a bit erratic in Yosemite!

When you think of California, with its sun-soaked beaches and Hollywood glamour, glaciers may not be the first thing that spring to mind – even for ice nerds like us. However, Yosemite National Park in California’s Sierra Nevada is famous for its dramatic landscape, which was created by glacial action. With our latest image of the week we show you some of the features that were left behind by ancient glaciers.


What do we see here?

Although Yosemite is now largely glacier-free the imprint of large-scale glaciation is evident everywhere you look. During the last glacial maximum (LGM), around 26,000 to 18,000 years ago, much of North America was covered in ice. Evidence of this can be seen in the strange landscape, shown in our image of the week. The bedrock surface in this area is polished and smoothed due to a huge ice mass that was moving over it, crushing anything in it’s path. When this ice mass melted rocks and stones it transported were released from the ice and left strewn on the smoothed bedrock surface. These abandoned rocks and stones are know as glacial erratics. Some of these erratics will have travelled from far-away regions to their resting place today.

During the last glacial maximum (LGM), around 26,000 to 18,000 years ago, much of North America was covered in ice.

Glaciers that still remain!

There are still two glaciers in Yosemite, Lyell and Maclure, residing in the highest peaks of the National Park. Park rangers have been monitoring them since the 1930s (Fig. 2), so there is a comprehensive record of how they have changed over this period. Sadly, as with many other glaciers around the world this means a huge amount mass has been lost – read more about it here!

Figure 2: Survey on Maclure Glacier by park rangers in the 1930s [Credit: National Parks Service]

On a more cheerful note – Here at the EGU Cryosphere Blog we think it is rather fantastic that the park rangers of the 1930s conducted fieldwork in a suit, tie and wide-brimmed hat and we are hoping some of you might be encouraged to bring this fashion back! 😀

If you do please make sure to let us know, posting it on social media an tagging us @EGU_CR! Here are a few more ideas of historical “fieldwork fashion” to wet your appetite: Danish explorers in polar bear suits, 1864-65 Belgian-Dutch Antarctic Expedition and of course Shackleton’s Endurance expedition!


Imaggeo, what is it?

You like this image of the week? Good news, you are free to re-use it in your presentation and publication because it comes from Imaggeo, the EGU open access image repository.

Image of the Week – Canyons Under The Greenland Ice Sheet!

Image of the Week – Canyons Under The Greenland Ice Sheet!

The Greenland Ice Sheet contains enough water to raise sea level by 7.36 meters (Bamber, et. al. 2013) and much of this moves from the interior of the continent into the oceans via Jakobshavn Isbræ – Greenland’s fastest flowing outlet glacier. An ancient river basin hidden beneath the Greenland Ice Sheet, discovered by researchers at the University of Bristol, may help explain the location, size and velocity of the modern Jakobshavn Isbræ. This Research also provides an insight into what past river drainage may have looked like in Greenland, and what it could look like in the future as the ice sheet retreats exposing more of the land underneath it.


Why?

The topography (i.e. shape) of the bedrock underneath the Greenland Ice Sheet exerts  a strong control on glacier ice flow , particularly  the direction  and velocity of ice flow. It also influences the  distribution of water and sediment  beneath the ice (see here for one reason why this is important). As well as this, studying the shape of the bed can provide a window into the past, to  help understand  historical  erosive processes, which allow scientists to understand the long-term evolution of the landscape, sometimes  they can even look back at what the land may have looked like before it was covered in ice. Building up this kind of picture allows researchers to  assess the interaction between the Greenland Ice Sheet and its bed and how this has evolved over great time-scales, which will further understanding of  how the ice dynamics have changed over time and what this might mean for the future.

How?

As ice is mostly transparent to radio waves at certain frequencies, scientists can use ‘ice-penetrating radar,’ either from aircraft or on the ground, to measure ice thickness as the radio waves bounce back off the bedrock. Data of this kind have been collected over several decades by research teams across the world, with more recent missions being headed by NASA (through Operation Ice Bridge). Using these data, bedrock elevation maps have been produced for both Antarctica, and Greenland allowing researchers to interpret individual features and landscapes hidden beneath the ice.

What have they found beneath the ice?

Recent research has found large channels, or ‘canyons,’ present underneath both the ice sheets of Greenland and Antarctica (e.g. Bamber, et al. 2013; Jamieson, et al. 2016), and our image of this week adds to this picture of dramatic topography underneath the Greenland Ice Sheet (Figure 1). A huge ancient basin has been discovered in southern Greenland, showing signs of being carved by ancient rivers, prior to the extensive glaciation of Greenland (i.e. before the Greenland Ice Sheet existed), rather than being carved by the movement of ice itself. The size of the drainage basin the team discovered is very large, at around 450,000 km2, and accounts for about 20% of the total land area of Greenland (including islands). This is comparable to the size of the Ohio River drainage basin, which is the largest tributary of the Mississippi – or roughly twice the size of Great Britain. The channels the team mapped could more appropriately be called ‘canyons’, with relative depths of around 1,400 metres in places, and nearly 12 km wide, all hidden underneath the ice (Figure 2).

Figure 2: Ice-penetrating radargram cross-sections of some channels within the flow network, showing the size of the features hidden beneath the ice. The bed and surface have been identified: The dashed red line, shows bedrock depth relative to the ice surface, (the solid purple line). There is an exaggeration in the vertical by a factor of 13.

Figure 2: Ice-penetrating radargram cross-sections of some channels within the flow network, showing the size of the features hidden beneath the ice. The bed and surface have been identified: The dashed red line, shows bedrock depth relative to the ice surface, (the solid purple line). There is an exaggeration in the vertical by a factor of 13.

Take Home Message

As well as the basin being an interesting discovery of great size, the channel network and basin appears to be instrumental in influencing the flow of ice from the deep interior to the margin, both now and over several glacial cycles, and in particular controlling the location and speed of the Jakobshavn ice stream, which drains a huge amount of the Greenland Ice Sheet into the oceans. This discovery helps us to better understand why this area of Greenland contains such fast flowing ice and how this might evolve in the future.

For more details of this study check out the full paper:

Cooper, M. A., K. Michaelides, M. J. Siegert, and J. L. Bamber (2016), Paleofluvial landscape inheritance for Jakobshavn Isbræ catchment, Greenland, Geophys. Res. Lett., 43, doi:10.1002/2016GL069458.

(Edited by Emma Smith)


head_shot_mikeMichael Cooper is a PhD Student at the University of Bristol, UK. He Investigates what lies beneath the Greenland ice sheet using airborne ice-penetrating radar, to help further understanding of the inter-relationship between ice and the bed with reference to both contemporary and past ice dynamics. He tweets from @macooperr

Image of the Week — Historical aerial imagery of Greenland

Image of the Week — Historical aerial imagery of Greenland

A few month ago, we were taking you on a trip back to Antarctic fieldwork 50 years ago, today we go back to Greenland during 1930s!

When geopolitics serves cryospheric sciences

The Permanent Court of International Justice in The Hague awarded Danish sovereignty over Greenland in 1933 and besides geopolitical interests, Denmark had a keen interest in searching for natural resources and new opportunities in this newly acquired colony. In the 1930s the Danish Government initiated three comprehensive expeditions; one of these, the systematic mapping of East Greenland, was set off by The Greenlandic Agency, The Marines’ air services, The Army’s Flight troops and Geodetic Institute. The Danish Marines provided pilots, mechanics, and three Heinkel seaplanes.

Danish expeditioner Lauge Koch, centre, along with his pilots all dressed in suits made from polar bear. (Credit: The Arctic Institute)

Danish expeditioner Lauge Koch, centre, along with his pilots all dressed in suits made from polar bear. (Credit: The Arctic Institute)

Aerial photography in the 1930s – practical constraints

The airplanes had three seats in an open cockpit. The pilot was seated in the front, the radio operator in the center and in the back the photographer – this seat was originally for the machine-gun operator.

At the outset, the idea was to take vertical images, but that was impossible at the time due to the height of the mountains and the limited capability of the aircraft to reach adequate heights. The airplanes couldn’t reach more than 4000 m – similar to the height of mountains in Greenland. Oblique images were therefore recorded. The reduced view of the terrain when photographing in oblique angles required many more flights than originally planned. The photographic films were processed immediately after each flight. 45,000 km were covered during the first season, which lasted about two and a half months. In the following years, each summer a flight covered parts of the Greenlandic coast. During the Second World War, the mapping was temporarily stopped due to safety reasons.

The aircraft had an open hole in the floor for the photographer, originally where the machine gunner would sit. (Credit: The Arctic Institute)

The aircraft had an open hole in the floor for the photographer, originally where the machine gunner would sit.(Credit: The Arctic Institute)

An unexplored treasure trove of climate data

The tremendous volume of aerial images obtained from several expeditions and hundreds of flights not only constitutes the cornerstone of mapping in Greenland, but is invaluable data for studying climate change in these remote regions. The 1930s survey, compared to modern imagery, provides crucial insight into coastal changes, ice sheet mass balances, and glacier movement. Glacier fluctuations in southeast Greenland have been identified, showing that many land-terminating glaciers underwent a more rapid retreat in the 1930s than in the 2000s, whereas marine-terminating glaciers retreat more rapidly during the recent warming (Bjørk et al, 2012).

An ongoing project between the University of Copenhagen, INSTAAR (Institute of Arctic and Alpine Research) in Boulder, Colorado, and Natural History Museum of Denmark is currently focusing on analysing deltaic changes in Central and Southern Greenland; linking shoreline development to climate changes – these historic aerial images are essential for detecting such coastal evolution. However, there are still many other links between the past and present climate to be discovered from these images. Interested in hearing more about the project or the aerial images? Please contact Mette Bendixen (mette.bendixen@ign.ku.dk)

Bibliography

Bjørk, A. A., Kjær, K. H., Korsgaard, N. J., Khan, S. A., Kjeldsen, K. K., Andresen, C. S., … & Funder, S. (2012). An aerial view of 80 years of climate-related glacier fluctuations in southeast Greenland. Nature Geoscience, 5(6), 427-432. http://dx.doi.org/DOI:10.1038/ngeo1481

Edited by Alistair McConnell, Sophie Berger and Emma Smith


Mette BendixenMette Bendixen is s a PhD student at the Center for Permafrost in Copenhagen. She investigates the changing geomorphology of Greenlandic coasts, where climate changes can have huge impact on the local environment.