The cryosphere is the portion of water in a solid state on Earth, i.e. frozen water. It comes from the Greek words "kruos" and "sphaira", which mean cold and spherical object. The cryosphere therefore includes ice floes, glaciers, but also snowfields, permafrost (permanently frozen subsoil) and frozen waters such as lakes and rivers.
All components of the cryosphere have differences in their composition and impact on their melting, including glaciers and sea ice. Here is a simple experiment to demonstrate this difference, followed by an explanation.
Experiment: the difference between a glacier and an ice pack
In order to carry out an experiment on the difference between glaciers (which correspond to ice on continents) and ice floes (which correspond to a large mass of ice floating on water), you need :
- Ice cubes ;
- 2 salad bowls ;
- Pebbles ;
With all this material, you will :
- Fill the two bowls with water to a quarter of their height.
- Use a felt-tip pen to mark the height of the water on the left-hand bowl, or dip something in the water that will help you spot it, such as a toy soldier. If you choose this option, put enough pebbles in the water so that the figure is not in contact with the water.
- For the right-hand bowl, place all the pebbles so that they are above the water level.
Now you will perform two different manipulations on the salad bowls:
- In the left-hand bowl, place the ice cubes on top of the water without touching the bottom of the bowl, to form an ice pack (you can add a few pebbles to the bottom if necessary).
- On the right-hand bowl, place the ice cubes on the pebbles to form a glacier.
- Let the ice cubes melt.
When everything is melted, ask yourself these questions:
- What happened to the left-hand bowl representing the ice floe?
- What happened to the bowl on the right representing the glacier?
- Is the water level the same in both bowls after melting?
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Glacier and pack ice: different characteristics, different consequences
If you performed the experiment correctly, you should have noticed that the water level in the left-hand bowl, which is the ice pack, did not rise, or at least not as much as the glacier. This is the case in extreme cold, where the difference in characteristics and constitution means that the glaciers cause the water to rise due to melting as a result of global warming.
The ice pack is a vast sheet of ice that floats on the water. It is present in the oceans near the poles, where the salt water in these oceans will freeze, and form this ice pack when it becomes so thick that the waves can no longer break the ice. In this sense, the size of the pack ice varies according to the time of year. In September, only permanent pack ice is present, then it is extended by fast ice in February, which disappears when summer arrives in the Arctic for example. As the pack ice is already on the water, it has already caused the water to rise, displacing an amount of water equal to its weight.
On the other hand, Glaciers are areas of continental ice. These are snow masses that compact and form glaciers. It is fresh water, not salt water. Different types of glaciers exist, including ice caps, which are very large glaciers, and smaller ones formed according to the relief present, such as in mountain hollows, at the foot of mountains, or framed in valleys.
Ice caps can break off when they reach the oceans and form icebergs. Icebergs are huge blocks of ice that float on the water at a low height, while most of it is submerged. Their fate is to melt within several months or years depending on their size and climatic conditions.
As you will have understood, glaciers are continental ice, whereas pack ice is formed by the freezing of salt water in the oceans. Their melting by global warming Therefore, the consequences of the melting of the sea ice are not the same as the consequences of the rising sea level. Unfortunately, this is not the only impact and their melting creates other unfortunate impacts such as the disruption of ecosystems, habitats, ocean circulation, etc.