What is the difference between solifluction and gelifluction?

Solifluction is a general term for the slow downslope flow of saturated soil. Gelifluction is a specific type of solifluction that occurs specifically over a permafrost layer, which acts as the sliding plane.

How does a closed-system pingo differ from an open-system pingo?

Closed-system pingos form in drained lake beds where trapped pore water is pressurized by advancing permafrost. Open-system pingos form on slopes where groundwater from higher elevations moves under hydraulic pressure to a site where it freezes.

What is the distinction between continuous and discontinuous permafrost?

Continuous permafrost occurs in the coldest regions where the ground is frozen everywhere except under large lakes. Discontinuous permafrost occurs in slightly warmer areas where frozen ground exists in patches separated by unfrozen 'taliks'.

Why is it a mistake to assume permafrost is defined by the presence of ice?

Permafrost is defined strictly by temperature (remaining at or below $0^{\circ}C$ for 2+ years). While it often contains ice, 'dry permafrost' exists where the ground is frozen but lacks sufficient moisture to form ice.

What error occurs when confusing periglacial features with glacial features?

Periglacial features are formed by freeze-thaw cycles in the ground, whereas glacial features are formed by the movement of massive ice bodies. Confusing them leads to incorrect reconstructions of past climate and moisture levels.

Why is it incorrect to think that frost wedging only happens at the surface?

Frost wedging can occur deep within rock fractures as long as water can penetrate and the temperature fluctuates around the freezing point. However, it is most intense near the surface where temperature swings are most frequent.

Define the 'Active Layer' in a periglacial context.

The active layer is the uppermost portion of the ground that thaws during the summer and refreezes in the winter. It is the zone where almost all geomorphic and biological activity in permafrost regions takes place.

What is 'Cryoturbation'?

Cryoturbation, or frost churning, is the process where soil layers are mixed and heaved by repeated freeze-thaw cycles. This process is responsible for the formation of patterned ground and the vertical movement of stones.

A talik is a layer or body of unfrozen ground within a permafrost region. They often exist beneath deep lakes that do not freeze to the bottom, acting as conduits for groundwater movement.

How does frost heave lead to the sorting of stones in patterned ground?

Stones have higher thermal conductivity than soil, so the ground beneath a stone freezes faster, forming an ice lens that pushes the stone upward. Over many cycles, stones migrate to the surface and are eventually nudged to the edges of the heave mounds.

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Glacial Systems & Landscapes

Periglacial Features

Summary

Periglacial geomorphology focuses on landforms and processes in cold climates where freezing and thawing are the primary drivers of landscape evolution. These environments, often adjacent to glacial margins or in high-latitude/altitude regions, are characterized by permafrost and a seasonally thawing active layer that facilitates unique mass wasting and ground-sorting phenomena.

1. Definition & Core Concepts

Periglacial Environment: These are regions where the average annual temperature is near or below $0^{\circ}C$ , leading to the dominance of frost-related processes rather than glacial ice movement.
Permafrost: Ground that remains at or below $0^{\circ}C$ for at least two consecutive years, acting as an impermeable layer that prevents water drainage.
Active Layer: The top layer of soil above the permafrost that thaws during the summer and refreezes in winter, serving as the site for most geomorphic activity.
Talik: An unfrozen patch of ground within or below the permafrost, often found beneath water bodies that retain heat throughout the winter.

Cross-section of a pingo showing the central ice core, the overlying active layer, and the surrounding permafrost.

2. Underlying Principles of Frost Action

Frost Wedging (Gelifraction): The mechanical breakdown of rocks caused by the expansion of water as it freezes in cracks, exerting pressures up to $2100 \text{ kg/cm}^2$ .
Frost Heaving: The upward displacement of soil and rocks caused by the formation of ice lenses; as water migrates toward the freezing front, it expands and pushes the surface upward.
Cryoturbation (Frost Churning): The mixing of soil layers due to repeated freeze-thaw cycles, which can move larger stones toward the surface while smaller particles settle.
Thermal Contraction: In extremely cold temperatures, the ground contracts and cracks, forming polygonal patterns that can later be filled with ice or sediment.

3. Classification of Periglacial Landforms

4. Methods of Mass Movement

5. Key Distinctions

6. Exam Strategy & Tips