September 2015
Overview
0 minutes – Introduction
3:30 minutes – Lecture begins
7:50 minutes – Extent of glacial retreat
11.30 minutes – Glaciers as conveyor belts
25:15 minutes – Expedition to the Russell Glacier
48:50 minutes – On location with the Store Glacier
View the Lecture here (24th June 2015)
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Introduction – How is Greenland under threat?
Since the mid-1990s Greenland, the world’s largest island has been topographically changing at an alarming rate. Sitting in largely within the Arctic Circle, the autonomous country has traditionally represented one of the most extreme cold environments that human beings have been able to colonise but most recently the warming of Greenland has been a large cause for concern amongst glacial scientists. In just one year a section of western Greenland of over 260km2 has melted (ablated) into the sea, and similar patterns of glacial melting have been witnessed all over the southern extent of the island. In July 2012 Greenland recorded record levels of melting at the same time as record high temperatures were seen across Northern Europe and North America. This melting has been shown to have a direct effect on sea level rise: Greenland alone is thought to contribute to rises of 0.7mm a year.
Location of prominent research glaciers in Greenland
How do glaciers work?
At a simplistic level, glaciers systems act in a similar way to river systems. These large floes of ice act as conveyor belts, carrying rock material from higher altitudes down to the sea. They move as a result of gravity with their own weight exerting enormous pressure on the landscape, increasing friction and slowing their movement to a barely noticeable pace.
This pressure and friction means that, like a river, glaciers erode the rock either side of the floe, as well as underneath it. The debris created is known as scree and can be deposited on the land after the glacial period has passed or moved into the sea in the case of Greenland.
The Russell Glacier, Greenland. (Flickr Source: destinationarcticcircle)
How is glacial melting being exacerbated?
It is easy to think about glacial movement and melting in relatively simple terms. Increased temperature increases the rate of ablation and the glacier, through reduced weight and density the glacier moves more rapidly towards the sea. In actual fact the glacial system is highly complex and contains a number of dynamic responses whereby one part of the system has secondary effects on another.
Russell Glacier in central west Greenland and is a well observed glacier by both scientists and tourists due to its ease of access. Advancing at a rate of twenty five metres a year, the glacier is moving relatively rapidly and so it has become of interest to glaciologists whom wish to see and test these dynamic responses more closely.
Meltwater generated by glacial ablation in large parts pools on top of large glaciers like Russell Glacier. As the water accumulates, lakes can appear on the surface of the glacier and in extreme cool periods these can solidify in parts, creating seasonal ice accumulation. However in warmer periods, such as the one we are now entering with the effects of climate change being felt more widely, the lakes remain in a liquid form throughout the year, growing in size and exerting a downward pressure on the ice sheet on which they sit. The weight of the water can cause ice collapse and enormous moulins can develop: large crevasses that run vertically down from the ice surface and can be over a kilometre deep. Such moulins can drain these glacial lakes within hours, sending water cascading through the heart of the glacier’s beds and internal structures. This movement can in turn trigger the creation of other moulins to develop under other glacial lakes and hundreds of gallons of water, which has a higher temperature than the ice it flows through, can run through the centre of a glacier in an instant.
A moulin in a glacier in Indiana, USA. (Flickr Source: Pete Burzynski)
What happens to this water and the effect it has on higher rates of ablation forms a body of recent research work. It has long been thought that this water, in its pursuit of running as directly into the sea as possible has acted as a lubricant under the glacier, increasing the seaward speed of the ice sheet itself. Though this has been found to be true, further, and more complex, processes have been found to be acting under the glacier too. The movement of the water generates large amounts of energy which through friction actually starts to melt the ice at the bed of the glacier. In many cases, and especially with large glaciers, pipeline-like channels are created through the bed and act as small rivers under the glacier; transporting the water to the sea and dissipating the energy the flow contains.
If the glacial ice is very thick (such as those over 1.5km depth), the glacial bed can experience very high pressures and the channels of water do not have the chance to form in the more conventional way. Instead these channels link together and form one large reservoir under the glacier; an under-ice glacial lake where the volume of water is often increasing year on year. It is these lakes that create a more lubricious slip plane and speed the rate at which glaciers move and enter the sea, where permanent melting occurs.
The impact of these under-ice reservoirs and their connected moulins can be seen at Store Glacier in north west Greenland. Around four hundred metres of the glacier is known to sit below the sea surface but recent exploration has shown that the bottom of the glacier has been undercut by roughly 150m. It is thought that this is linked to the exit point of the under-ice reservoirs and as glaciers retreat, the undercutting could be indicative of moulins themselves slowly becoming exposed at the glacial snout.
Conclusion
It is becoming increasingly important to understand the processes that are taking place within Greenland and other places with glacial systems. Greenland’s ice is now flowing at twice the speed of flow in 1995 and the melting of its glaciers is the largest contributor to global sea level rise. It is important for all of us to understand the impact of this despite its seeming geographical and sociological distance from our lives. The Gulf Stream, into which this melted freshwater feeds, through thermohaline circulation produces temperate weather patterns for the UK and in a climatic zone that allows farming to be possible. If this were to change it would have an impact directly on the lives of people living in the northern Atlantic zone but may also on those further afield as warm and cool currents around the globe seem likely to change. Understanding the glacial processes at work allows scientists to work towards predicting ablation levels and the extent to which climate change will affect our lives.
References
Unless otherwise stated, all data in the above piece relates to figures taken from Alun’s lecture.
Key Words
Ablation
The erosion of snow or ice, especially by melting.
Glacier
A river of ice that moves down a gradient towards the sea
Moulin
A vertical crevasse that extends from the glacier surface towards the bed, carrying meltwater.
Lesson Ideas
In one corner of a landscape A4 page students can write ‘increased climatic temperatures’ and in the opposite corner ‘rising sea level’. Using the processes highlighted in the lecture, students can try to draw a flow diagram that uses the dynamic glacial processes as an explanation for the effects of climate change.
If you wanted to prove that a moulin led directly to a glacier bed and an outlet to the sea, how else might you prove it? The video gives some ideas, but given no budget restraints what else could be done? Students can research the use of ice cores to show age within an ice sheet and hypothesise how this could be used.
Using plasticine, students can try to model a glacier and include ‘flags’ to show areas of ablation, accumulation, erosion and scree deposits, as well as moulin and glacial lakes/reservoirs.
Articles
Glacial Retreat: Historical Evidence of Climate Change
Ask the Experts
Glacial Change
Resources