Periglacial: Meaning, Processes and Landforms

Periglacial is referred to the areas at the periphery/edge of the glacier. It is characterized by low temperature. Its annual mean temperature is around Zero Degrees Celsius. It’s the summer season, and the surface is free from ice but subsurface water is found in the frozen state.

The landscape is the surface of the earth, as we observe while being in the field. It is basically the appearance of the land. Many agents of erosion sculpture the land itself. Depending upon the processes of sculpturing, the landscapes are different. Periglacial landscapes refer to the land features developed due to the process of peri-glaciation.

Periglacial Conditions

A periglacial condition exists in the peripheral areas of the glaciated regions. In this zone, the annual average temperature is around zero degrees Celsius. In winter, there is a thin layer of ice and snow accumulation, but it is not the same during summer days. Even during summer days, the subsurface moisture content is found to be in a frozen condition.

In the soil zone, the temperature is less than zero degree Celsius. Freezing and thawing are normal conditions which is the main cause of weathering here. Both glacial and periglacial conditions are quite different from each other.

Periglacial Landforms

Periglacial refers to the area in the periphery of the glaciated region. During summer, the region is almost free from ice on the surface, but the subsoil is still frozen throughout the year. This is very clearly seen in Figure, and a thin layer of snow and ice accumulation in Figure No. 22B.

The seasonal freezing and thawing of the subsoil is a regular feature of the region. During winter, the surface witnesses heavy snowfall and ice accumulation.

In other words, the area is almost permanently frozen but without permanent surface ice cover. The mean monthly temperature is between minus one degree to minus 15 degrees Celsius. The periglacial areas change with the change in the climatic condition prevailing on the planet.

Based on the extent of the freezing conditions, the permafrost areas are classified into three groups – continuous permafrost, discontinuously permafrost, sporadic permafrost and isolated permafrost. The surface layer, where freezing and thawing are seen, is known as an active layer.

Periglacial Processes

The periglacial areas witness several important processes: frost action, frost heave, and frost shattering, indirectly leading to rock fall, earthflow and debris flow.

Frost Action: It is obvious that the ice volume is greater than that of water. Freezing and thawing are natural processes. The water laying in the pores/ cracks or openings expands and breaks the rocks when it turns into ice. Therefore, weathering process is amplified by this process.

Frost Heave: When the subsoil water freezes, it leads to upward swelling of the top soil. This process is repeated time and again with changing seasons. Upper soil is loosened and subject to removal easily.

Frost Shattering: The freezing and thawing process is known as frost shattering. The water laying in the cracks of exposed rocks in cold climates leads to breaking them.

Rock Fall: Rock-fall is a type of mass movement in which the fragmented rocks tumble down almost freely. In cold climates, the exposed rocks are fragmented by freezing and thawing action, and hence, the credit of rock-fall is credited to permafrost action.

Earthflow and Debris Flow: The availability of water content liquefies the soil, and if it is on the slope, it flows quickly. This action is seen in the periglacial areas as the meltwater of ice triggers it. Debris flow includes unconsolidated soil, rock fragments, remnants of biotic life, and water. When these are associated with the slope, it leads to debris flow, and it is also triggered by water made available by snow melt in periglacial areas.

Periglacial Landforms

Several types of landforms are found in the periglacial areas. Some of them are:

Patterned Ground

Patterned ground is termed to that ground surface when the laying materials are distributed in a certain pattern. The pattern may be of any kind like stripes, ovals, circles, or polygons, particularly in the periglacial areas. They are made by frost heave action (Figure).

Ice Wedges

The wedges are pieces or slices or blocks. When the rocks are broken into pieces due to ice action, it is termed ice wedges. In this situation, the water or ice penetrates vertically into the surface for several meters.

In cold climates (periglacial areas), the seasonal freezing and thawing cause the rock to break and penetrate further down during summer. In winter, it freezes, and further, the space is widened, leading to rock breaking.

Blockfields

Blockfields are areas of huge expanse constituting the freeze-thaw weathered angular rock blocks in periglacial areas. Rock blocks get disintegrated into smaller pieces, and thus, angular rocks are seen on the surface (Figure).

Pingos

Pingos are hills of earth and gravel in dome-shaped formed in the periglacial areas under which the subsoil water freezes and tends to push the upper part upward. Its height may vary from 5 meters to 70 meters, and the diameter from 30 meters to one km. Most of the pingos are circular in shape.

Read More in Geomorphology

1. Earth Movements: Meaning and Types
2. Epeirogenic Earth Movements
3. Orogenic Earth Movements
4. Cymatogenic Earth Movements
5. Concept of Stress and Strain in Rocks
6. Folds in Geography
7. Fault in Geography
8. Mountain Building Process
9. Morphogenetic Regions
10. Isostasy: Concept of Airy, Pratt, Hayford & Bowie and Jolly
11. Continental Drift Theory of Alfred Lothar Wegener (1912)
12. Plate Tectonics: Assumptions, Evidences, Plate Boundaries and Features Formed
13. Volcanoes: Process, Products, Types, Landforms and Distribution
14. Earthquakes: Processes, Causes and Measurement
15. Plate Tectonics and Earthquakes
16. Composition and Structure of Earth’s Interior
17. Artificial Sources to Study Earth’s Interior
18. Natural Sources to Study Earth’s Interior
19. Internal Structure of Earth
20. Chemical Composition and Layering of Earth
21. Weathering: Definition and Types
22. Mass Wasting: Concept, Factors and Types
23. Models of Slope Development: Davis, Penck, King, Wood and Strahler
24. Davis Model of Cycle of Erosion
25. Penck’s Model of Slope Development
26. King’s Model of Slope Development
27. Alan Wood’s Model of Slope Evolution
28. Strahler’s Model of Slope Development
29. Development of Slope
30. Elements of Slope
31. Interruptions to Normal Cycle of Erosion
32. Channel Morphology and Classification
33. Drainage System and Drainage Pattern
34. River Capture or Stream Capture
35. Stream Channel Pattern
36. Fluvial Processes and Landforms: Erosional & Depositional
37. Delta: Definition, Formation and Types
38. Aeolian Processes and Landforms: Erosional & Depositional
39. Desertification: Definition, Problem and Prevention
40. Glacier: Definition, Types and Glaciated Areas
41. Glacial Landforms: Erosional and Depositional
42. Periglacial: Meaning, Processes and Landforms
43. Karst Landforms: Erosional and Depositional
44. Karst Cycle of Erosion
45. Coastal Processes: Waves, Tides, Currents and Winds
46. Coastal Landforms: Erosional and Depositional
47. Rocks: Types, Formation and Rock Cycle
48. Igneous Rocks: Meaning, Types and Formation
49. Sedimentary Rocks: Meaning, Types and Formation
50. Metamorphic Rocks: Types, Formation and Metamorphism
51. Morphometric Analysis of River Basins
52. Soil Erosion: Meaning, Types and Factors
53. Urban Geomorphology: Concept and Significance
54. Hydrogeomorphology: Concept, Fundamentals and Applications
55. Economic Geomorphology: Concept and Significance
56. Geomorphic Hazard- Earthquake: Concept, Causes and Measurement
57. Geomorphic Hazard- Tsunami: Meaning and Causes
58. Geomorphic Hazard- Landslides: Concept, Types and Causes
59. Geomorphic Hazard- Avalanches: Definition, Types and Factors
60. Integrated Coastal Zone Management: Concept, Objectives, Principles and Issues
61. Watershed: Definition, Delineation and Characteristics
62. Watershed Management: Objective, Practice and Monitoring
63. Applied Geomorphology: Concept and Applications