Nivation: This process occurs beneath and around the edges of snow patches. It involves a combination of freeze-thaw weathering and meltwater erosion, which gradually deepens a depression into a nivation hollow.
Solifluction (Gelifluction): During summer, the active layer becomes saturated because meltwater cannot drain through the impermeable permafrost below. This saturated soil loses internal friction and flows slowly downslope under gravity, forming solifluction lobes.
Frost Heaving and Sorting: Repeated freeze-thaw cycles push larger stones to the surface and move them laterally. This natural sorting creates patterned ground, such as stone polygons on flat surfaces or stone stripes on slopes.
Thermokarst: This refers to the subsidence of the ground caused by the melting of ground ice. It results in an irregular landscape of pits, hummocks, and thaw lakes (also known as alas).
| Feature | Solifluction | Gelifluction |
|---|---|---|
| Definition | General term for slow downslope flow of saturated soil. | Specific type of solifluction occurring over permafrost. |
| Mechanism | High pore water pressure reduces shear strength. | Impermeable permafrost prevents drainage, saturating the active layer. |
| Climate | Can occur in various cold climates. | Restricted to periglacial/permafrost regions. |
Continuous vs. Discontinuous Permafrost: Continuous permafrost exists as a solid sheet across the landscape (except under deep lakes), whereas discontinuous permafrost contains gaps of unfrozen ground (talik) where the climate is slightly warmer or vegetation provides insulation.
Frost Heave vs. Frost Shattering: Heave is the vertical displacement of soil due to ice growth, while shattering (or wedging) is the mechanical disintegration of solid rock into angular fragments.
Identify the Driver: When analyzing a periglacial landform, always identify the role of the active layer and the permafrost table. Most movement and weathering occur because the permafrost acts as an impermeable barrier to water.
Cyclical Nature: Emphasize that these landforms are rarely the result of a single event. They require hundreds or thousands of freeze-thaw cycles to develop features like large pingos or sorted polygons.
Slope Influence: Remember that the same process can produce different landforms based on gradient. For example, frost sorting produces polygons on flat ground but stripes on slopes due to the added influence of gravity.
Scale Awareness: Be able to distinguish between micro-scale features (ice needles, small stones) and macro-scale features (pingos, blockfields).
Glacial vs. Periglacial: A common error is assuming periglacial landforms are created by moving glaciers. In reality, they are created by the action of ground ice and seasonal temperature fluctuations in ice-free areas.
Permafrost is Not Just Ice: Students often think permafrost is a solid block of ice. It is actually soil, rock, or sediment that is frozen; it may contain varying amounts of ice, from thin films to massive lenses.
Static Landscape: There is a misconception that frozen ground is static. The active layer is one of the most geomorphically active environments on Earth due to its high water content and seasonal mobility.
