Model Answer
0 min readIntroduction
Periglaciation refers to the processes and landforms associated with cold climates, but not necessarily covered by glaciers. The periglacial environment, characterized by permafrost and seasonally frozen ground, is found at high latitudes and altitudes. While earlier geomorphologists recognized periglacial features, it was L.J. Peltier who, in the 1950s, comprehensively proposed a cyclical model to explain their formation and evolution. Peltier’s Periglacial Cycle provides a framework for understanding the interplay of freeze-thaw action, solifluction, and nivation in shaping landscapes in these cold regions, offering a dynamic view of periglacial geomorphology.
Peltier’s Periglacial Cycle: A Detailed Explanation
Peltier’s model posits that periglacial landscapes evolve through a series of stages driven by the repeated freezing and thawing of water within the ground. The cycle isn’t strictly linear but represents a dynamic equilibrium influenced by factors like temperature, slope, and sediment availability.
1. Nivation
Nivation is the initial stage, occurring on slopes. It involves a combination of processes: frost wedging, chemical weathering enhanced by freeze-thaw cycles, and snow accumulation. These processes lead to the gradual hollowed-out formation of nivation hollows.
- Frost Wedging: Water enters cracks in rocks, freezes, expands, and exerts pressure, widening the cracks.
- Gelifluction: Slow downslope movement of saturated soil due to freeze-thaw action.
- Differential Weathering: Some rock types are more susceptible to weathering than others.
These hollows eventually deepen and widen, potentially evolving into cirques if glacial conditions develop.
2. Solifluction
Solifluction is the slow, downslope flow of saturated soil over an impermeable layer (often permafrost). It’s most active during the thaw season when the upper layer of soil becomes waterlogged.
- Active Layer: The layer of soil above the permafrost that thaws and freezes seasonally.
- Solifluction Lobes & Sheets: Characteristic landforms resulting from solifluction, often visible on slopes.
Solifluction contributes to the smoothing of slopes and the transport of material downslope, filling nivation hollows and creating terraces.
3. Patterned Ground
Patterned ground refers to the distinctive geometric patterns formed on the surface of periglacial areas. These patterns are a result of the sorting of soil particles by repeated freeze-thaw cycles.
- Circles & Polygons: Common patterned ground features, formed by the contraction and expansion of freezing and thawing ground.
- Stone Polygons: Polygons formed by the concentration of larger stones at the surface, with finer material in the interior.
- Stripes: Linear patterns often found on slopes.
The formation of patterned ground is influenced by slope angle, sediment type, and the presence of vegetation.
4. Frost Action & Landforms
Frost action encompasses a range of processes driven by the freezing and thawing of water. This includes:
- Frost Heaving: The lifting and displacement of soil and rocks due to the growth of ice lenses.
- Pingos: Ice-cored mounds formed by the freezing of groundwater. There are two types: open-system pingos (fed by groundwater) and closed-system pingos (formed by the freezing of pore water).
- Ice Wedges: Wedge-shaped masses of ice that form in cracks in the ground, expanding over time.
- Thermokarst: Irregular terrain formed by the thawing of permafrost, resulting in subsidence and the formation of lakes and wetlands.
These processes create a variety of distinctive landforms, contributing to the overall character of periglacial landscapes. The cycle then repeats, with nivation continuing to erode slopes, solifluction transporting material, and frost action shaping the surface.
| Process | Landform | Mechanism |
|---|---|---|
| Nivation | Nivation Hollows | Freeze-thaw, snow accumulation, weathering |
| Solifluction | Solifluction Lobes/Sheets | Downslope flow of saturated soil |
| Frost Action | Pingos | Ice lens growth, groundwater freezing |
| Frost Action | Ice Wedges | Expansion of ice in cracks |
Conclusion
Peltier’s Periglacial Cycle remains a foundational concept in periglacial geomorphology, providing a valuable framework for understanding the complex interplay of processes shaping these unique landscapes. While the model has been refined over time with advancements in understanding permafrost dynamics and climate change impacts, its core principles remain relevant. The increasing rate of permafrost thaw due to global warming is accelerating many of these processes, leading to significant landscape changes and posing challenges for infrastructure and communities in periglacial regions. Further research is crucial to predict and mitigate the consequences of these changes.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.