2. Transportation of Snow Behind Mountains

Objective: creation of models and a small experimental fan for understanding the depositing or non-depositing of snow behind a mountain.

At the interior of the Antarctic, the environment is above all characterised by ubiquitous snow and wind, which never stops blowing. Under the action of the wind, the snow is therefore continually carried away to be deposited elsewhere.

Behind a mountain or an obstacle, which is downstream of the airflow, the snow is carried in whirlwinds. As the wind blows in a fairly constant direction, one can at times observe particular phenomena such as an over-deposit of snow (a snowdrift), or on the other hand a deficit of snow, which creates a ditch.

This experiment consists in visualising these manifestations. It is divided into two levels.

2.1 Different forms of mountains

The first level consists of trying to understand how mountains can disrupt the movement of the wind and the snow that it is carrying. For that we propose that the class constructs several model mountains, creates a small experimental fan and visualises the movement of the air behind them.

Experimental fan 1

Necessary equipment

  • Papier-mâché or model paste
  • A wooden or strong cardboard tray
  • A fan or a hairdryer
  • Strips of light paper or a means of making smoke

Steps to be followed :
  • Imagine different mountain shapes by referring for example to books on mountaineering or the Antarctic. It is interesting to conceive them sufficiently differently.
  • These mountains must then be built in model paste or in papier-mâché, the models should be fairly large and should be fixed to the wooden or strong cardboard tray.
  • Place one of the models on the ground or on a large table. Place a fan or a hairdryer upstream. Turn it on, and the air will blow around the mountain.
  • To visualise the movement of the air behind the mountain, the most standard method is to produce smoke (cigarette smoke, incense, fumigating spray…). Another solution is to hold strips of light paper vertically behind the model (one can imagine a small portico with several strips). In the wind, the strips incline and show the direction of the movement of the air.
  • For each model, visualise the movements of the air behind the mountain, in particular the whirlwinds, and then distinguish the areas where the snow can be deposited and those where it will inevitably be carried away by the wind.

The visualisation of these physics is certainly not self-evident, the comparison of the influence of each shape of model is therefore important because it could be a principle tool for the understanding of the disruptions that mountains represent for wind. One can also vary the direction in which the fan sends the air.

At the end of the experiment, the children should share their results with other classes participating in the project.

2.2 Work on a real case

For classes of a sufficiently high level, the experiment conducted previously can lead to work on a real case. This is the second level of this experiment, the chronology of which is the following:

  1. The field team chooses an interesting site where one can observe a particular phenomenon in the depositing of snow. They put on the network the geographical characteristics of the mountain or obstacle, the local topography, the wind direction, and photographs of the way in which the snow deposits itself.
  2. Each class interested in the experiment creates a model of the mountain, to recreate experimentally around it the movement of the air and the snow (an experimental fan) and to propose a solution to the following problem: how is this particular phenomenon created?
  3. A laboratory of mechanical digital model of fluids (the MASTER of Bordeaux University) creates a model of the airflow in the selected site. This will allow the provision of a possible solution to the problem once all the classes have offered their solutions.
  4. All the results will be put on the Network and a forum, between the classes and the scientists associated with the project, will be set up to solve the problem.

Experimental fan 2

For the creation of this second experimental fan, certain solutions "to make it work" have to be found by the children, as in a genuine scientific experiment.

Necessary material

  • Papier-mâché or model paste
  • A wooden or strong cardboard tray
  • A fan or a hairdryer
  • Strips of light paper or a means of making smoke
  • polystyrene particles

 

Steps to be followed :

  • On the tray, with the help of the papier-mâché or model paste, reconstitute the general topography of the icecap and the mountain. Try to maintain the scale. Enough space must also be left downstream of the mountain.
  • Place a fan upstream at a certain distance from the model, oriented in accordance with the direction of the wind. The distance and speed of the fan are to be established by trial and error.
  • Switch the fan on and the air blows around the mountain.
  • As for the first level, visualise the movements of the air with the use of smoke (cigarette smoke, incense, fumigation spray…). Then report on a card of the model the movements of the smoke at ground level. Draw the vertical and three-dimensional movements on separate pages..
  • This work is made in several manipulations, by sending the smoke into different areas without altering the arrival of the air.
  • The other solution for visualisation is to use strips of light paper on a portico or on the end of a ruler. Report on a card the local declination of the strips that is to say the direction of the wind, and then start again by positioning them differently. Little by little, the form of the flow will appear.
  • After this stage, one can try to represent the snow in the experiment.
  • Spread the polystyrene particles on the ground upstream of the mountain. Polystyrene is not necessarily the best material, children could imagine others and each try to find the most suitable.
  • Switch on the fan and observe the movement of the particles.

The problem with this experiment derives from the fact that the particles will be dispersed into the room. Vertical panels along three sides on the floor could limit this phenomenon, but it should be known that this will falsify the results in relation to reality, especially if they are too close to the model.

In all these experiments, deduce the movements of the air and the snow and explain the phenomenon observed in the photographs.

The school will then send its solution of the problem to the Activity Manager of the educational site, and the original means that they might have used and the difficulties encountered. The various classes will then be able to talk to each other to compare the results and the methods.