Glacial Budgets

AIM: To understand the concept of glacial budgets and the inputs and outputs of glacial material

So now we know what a glacier is and how it is formed - but what we havent covered is where the materials come from!

Sources of glacier ice are:

Direct - From water of the glacier itself.

Indirect - From snow or ice crystals in the atmopshere.

A Glacier can be viewed as a system with inputs, stores, transfers and outputs ( as shown in figure 1) :

 Figure 1: Image illustrating the glacer mass budget showing major mass inputs and ouputs. (Source: Glaciers)

These Include:

• Inputs: precipitation in the form of snow and ice, and avalanches which add snow, ice and debris from the valley side.
• Storage: represented by the glacier itself.
• Transfer (throughput): this is the way ice moves.
• Outputs: This is water vapour from evaporation of water on the ice surface and water in liquid form from ablation (melting). The debris deposited at the snout can also be considered an output.

Glacial Budget:

• The upper part of the glacier is where inputs exceeds outputs = zone of accumulation.
• The lower part is where outputs exceeds inputs = zone of ablation.
• Between the two zones is the line of equilibrium - this seperates net loss from net gain.
• Net Balance = difference between the total accumulation and the total ablation during 1 year.

REFERENCES:

Portland State University (Undated) "Glacier Change in the Upper Skagit River Basin" Available at http://www.glaciers.pdx.edu/Projects/LearnAboutGlaciers/Skagit/Basics00.html#top [Accessed 01/08/2011]

Professor Tweed, F (2011) "Glaciers & Ice Sheets - Formation" Lecture from The Geography Department, Staffordshire University. 

Redfern, D & Skinner, M (2005) Advanced Geography. 2nd Edition. Philip Allan Updates, Oxfordshire

How is a Glacier Formed?

Aim: To be able to understand the way a glacier is formed .

First watch this video, if nothing it is a simplistic version of how a glacier is formed.

Student Made Glacier Video 

• A glacier is formed in an area where the climate never rises enough to melt ice/snow.

• Snow initially falls as flakes which trap air, melting as they come into contact with the warmer surface temperatures.

• When the air temperatures drop, the melted snow refreezes turning into a more compact form known as FIRN or NEVE.

• Meltwater seeps into the gaps within the snow, freezing and compacting the mass further.

• As more snow falls, air is progressively squeezed out of the lower snow by the weight of the upper layers.

• When the accumulation reaches 150 feet the weight  after approx 20-40 years and pressure ensures the snow is crystalised into solid ice.

• During this time the ice may take a bluish olour, indicating that most of the air has been expelled.

• As more snow accumulates and the ice mass grows thicker it becomes too large to sit still and gravity pulls the ice downhill.

• This is the ice that begins to flow downhill as a glacier.
  

Dr Iain Stewart provides a video version of this process.

How Glaciers Are Formed - Iain Stewart 

IN PRACTICE: The video above is the perfect idea for group work for students. By combining IT and the fun of music and animation, videos like this one can prove as a successful self learning activity for students.

REFERENCES:

Redfern, D & Skinner, M (2005) Advanced Geography. 2nd Edition. Philip Allan Updates, Oxfordshire.

Stewart, I (2007) Video clip “How Form” from Episode “Ice” from Series “Earth: The Power of the Planet”