Background:
Layers of perennially frozen ground known as permafrost exist under about 20% of the Earth’s surface. Permafrost occurs on land in both the Arctic and Antarctic, as well as beneath the ocean around the Arctic coast and in many high mountain areas. Seasonal thawing and freezing of the soil forms a shallow active layer that overlies the permafrost. In contrast, deep permafrost, frozen to depths of 500 to 1000 meters, may have existed in a frozen state for thousands of years. Frozen soils have greater mechanical stability than unfrozen soils. Permafrost degradation can cause problems for roads, pipelines or buildings on the surface.
Permafrost Demonstration
Materials:
Two clear, wide-mouthed plastic containers or jars (approximately 500 mL each)
Ice cubes
Sand and local soil (enough to fill one jar with each)
Toothpicks and modelling clay
Water
Preparing the permafrost:
Put layers of wet sand in one jar and of wet soil in the other, filling each 1/3 full.
Place 3-5 ice cubes on top of the sand or soil, filling the jar to the 2/3 mark. This represents ‘ice wedges’ that form in cracks in the frozen soil as the permafrost expands and contracts with seasonal temperature changes. (See http://arctic.fws.gov/permcycl.htm for more.)
Cover the ice with a second layer of sand or soil.
Moisten the entire sample with water and freeze for at least 24 hours.
Activity:
Construct two small sturctures from clay and toothpicks and place them on top of the frozen samples. Use the toothpicks to hold the sturctures in place.
Predict what you think will happen as the permafrost thaws? What will happen to the ice? …the soil? …the structures?
Allow the samples to thaw and note what happens.
Discussion questions:
How did the thawing of the permafrost affect your structures?
Did the type of soil make a difference?
What happened to the surface of the ground when the permafrost thawed? How might this affect vegetation or animals in permafrost regions?
Permafrost contains large quantities of stored organic carbon. How might the thawing of permafrost affect levels of atmospheric greenhouse gases such as carbon dioxide and methane?
Thanks to Jenny Baeseman, Jerry Brown, Louise Huffman and Sandy zicus for developing the activity and providing the images.
Additional variations of the activity: