Processes in Cold Environments with Seasonal Thawing
- Cold environments are areas characterized by low temperatures, often below freezing for most of the year.
- They include polar regions, high-altitude mountains, and periglacial zones (areas near glaciers).
- In these regions, seasonal thawing plays a critical role in shaping the landscape through unique processes and landforms.
Key Processes in Cold Environments
Freeze-Thaw Weathering
- Freeze-thaw weathering is a mechanical process where water enters cracks in rocks, freezes, and expands by 10%.
- This expansion exerts pressure on the rock, causing it to fracture over repeated cycles.
- Imagine a rock with a small crack.
- During the day, meltwater seeps into the crack.
- At night, temperatures drop below freezing, causing the water to expand and widen the crack.
- Over time, the rock breaks apart into smaller pieces.
Freeze-thaw is most effective in environments with frequent temperature fluctuations around 0°C, such as periglacial zones.
Solifluction
- Solifluction refers to the slow downslope movement of water-saturated soil.
- In winter, the ground freezes, and in spring, the active layer (the top layer of soil above permafrost) thaws.
- The thawed soil becomes saturated because the underlying permafrost is impermeable, preventing drainage.
On a slope, this saturated soil slowly flows downhill, forming solifluction lobes or terracettes, small ridges or steps on the landscape.
- Think of solifluction like a slow-moving mudslide.
- The frozen ground acts as a slippery base, allowing the thawed soil to slide downhill.
Frost Heave
- Frost heave occurs when water in the soil freezes and expands, pushing soil particles or stones upward.
- As the ice melts, the soil settles unevenly, leaving stones elevated on the surface.
This process creates features like patterned ground, where stones form circles, polygons, or stripes due to repeated frost heave cycles.
Common Mistake- Don't confuse frost heave with freeze-thaw weathering.
- Frost heave affects soil and stones, while freeze-thaw breaks down rocks.
Periglacial Landforms
Permafrost
Definition
Permafrost
Ground that remains frozen for two or more consecutive years.
- It covers about 20% of the Earth's surface and can be up to 700 meters deep.
Types of Permafrost
- Continuous: Found in extremely cold regions (mean annual temperature below -5°C.
- Discontinuous: Occurs in slightly warmer areas (mean annual temperature -1.5°C to -5°C.
- Sporadic: Found in the warmest permafrost regions (mean annual temperature 0°C to -1.5°C.
- The active layer is the top layer of soil that thaws in summer and refreezes in winter.
- Its thickness varies based on temperature and location.
How might the presence of permafrost influence human activities such as construction or agriculture? Consider the ethical implications of building in these fragile environments.
