Pingos: Large, ice-cored mounds that can reach heights of 90 meters. They are classified into closed-system (formed by hydrostatic pressure in continuous permafrost) and open-system (formed by hydraulic pressure in discontinuous permafrost).
Patterned Ground: Geometric shapes such as polygons, circles, and stripes formed on the surface. On flat ground, frost heave creates circles or polygons; on slopes, gravity elongates these into stone stripes.
Solifluction Lobes: Tongue-shaped deposits of debris. During summer, the saturated active layer 'slips' over the impermeable permafrost table, moving downslope under gravity.
Thermokarst: A landscape characterized by irregular hummocks and marshy hollows (subsidence) caused by the melting of ground ice or permafrost.
| Feature | Closed-System Pingo | Open-System Pingo |
|---|---|---|
| Permafrost Type | Continuous | Discontinuous |
| Water Source | Trapped lake sediments (Talik) | Groundwater from higher elevations |
| Pressure Mechanism | Hydrostatic (freezing from all sides) | Hydraulic (artesian pressure) |
| Location | Flat, lowland plains | Valley bottoms or slope bases |
Identify the Process: When describing a landform, always link it to a specific process (e.g., 'Pingos are formed by the freezing of a water body creating an ice lens').
Slope Matters: Remember that the gradient of the land determines the shape of patterned ground. Flat ground = Polygons/Circles; Sloping ground = Stripes.
Timescale Awareness: Periglacial processes are generally slow. Mention that features like ice wedges or large pingos take hundreds to thousands of years to develop.
The Role of Water: Always check if the landform requires saturated conditions (like solifluction) or thermal contraction (like ice wedges).
Glacial vs. Periglacial: A common error is assuming periglacial landforms are made by moving glaciers. They are actually formed by the absence of glaciers but the presence of intense cold and ground ice.
Active Layer vs. Permafrost: Students often confuse the two. The active layer is the only part that thaws; the permafrost remains frozen year-round. Landforms like solifluction only occur because the permafrost acts as an impermeable barrier to water.
Pingo Collapse: A pingo is not a permanent feature. If the protective sediment layer is breached, the ice core melts, leading to a collapsed hollow known as an ognip.
