Periglacial Cycle of Erosion

Let’s again imagine yourself standing in a vast, icy wilderness where the land is constantly being shaped by frost, ice, and gravity. Unlike warm, humid regions where rivers and vegetation drive erosion, in periglacial areas, it’s the freeze-thaw cycles that carve out landscapes over time. The Periglacial Cycle of Erosion, proposed by L.C. Peltier in 1950, follows a systematic sequence similar to Davis’ Geographical Cycle, progressing through Youth, Maturity, and Old Age. However, here, the key forces at play are cryoplanation—a combination of frost weathering (Congelifraction) and mass movement (Cryoturbation).

Let’s take a journey through this icy transformation.

1. Youth Stage: The Birth of a Frozen Landscape

The periglacial cycle kicks off as the climate turns icy and permafrost establishes itself. The initial landscape undergoes dramatic changes:

• Frost Weathering (Congelifraction) Becomes Dominant
  • Water seeps into cracks, freezes, and expands, causing rock disintegration.
  • The result? Steep, bare rock slopes with angles between 25° to 30°, gradually eroding backward.
• Formation of Frost-Riven Cliffs
  • These vertical rock faces develop due to the repeated breaking of rock by frost action.
• Cryoplanation Surfaces Begin to Form
  • At the base of these cliffs, flat or gently sloping surfaces emerge—similar to pediments in deserts.
  • Weathered material collects here but is not fully carried away, as seasonal rivers lack the strength to transport all debris.
• Mass Movement via Congelifluction
  • The debris on cryoplanation surfaces slowly moves downslope due to thawing and refreezing.
  • Valleys start filling up with this deposited material.

2. Mature Stage: Expansion of Cryoplanation Surfaces

As time progresses, frost action continues reshaping the terrain:

• Parallel Retreat of Frost-Riven Slopes
  • The steep cliffs waste away, reducing the number of scattered rock remnants.
• Uplands Become More Rounded
  • Sharp features erode, leaving behind smoother, rolling landscapes.
• Cryoplanation Surfaces Expand
  • These flat surfaces dominate, while valleys continue accumulating eroded debris.
  • By this stage, much of the landscape is now shaped by periglacial forces rather than original landforms.

3. Old Stage: The Frozen Plains Take Over

At the final stage of the periglacial cycle, the landscape transforms into an almost featureless plain:

• Hills Shrink & Slopes Flatten
  • The last remnants of elevated terrain are gradually lowered by frost weathering and mass movement.
  • Slopes reduce to angles of 5° or less.
• Wind Erosion Gains Prominence
  • With finer sediments forming, wind becomes a key player, creating sand dunes and ventifacts (wind-shaped stones).
• Cryoplanation Surface Becomes the End Product
  • This vast, eroded plain resembles Davis’ Peneplain, but instead of rivers, it is frost that has leveled the land.

Final Thoughts

The Periglacial Cycle of Erosion is a cold-climate counterpart to the classic cycle of erosion. While water shapes landscapes elsewhere, here, it’s ice and temperature fluctuations that dominate. Over thousands of years, the once rugged, frost-riven cliffs give way to expansive, windswept plains—an ultimate testament to the power of freezing and thawing in shaping the Earth’s surface.