Model Answer
0 min readIntroduction
Pediplanation, a significant concept in geomorphology, describes the formation of vast, gently sloping plains (pediplains) through the prolonged erosion of mountainous regions. It posits that landscapes evolve through cycles of uplift, erosion, and base level adjustment. Lester Charles King, a South African geomorphologist, developed this theory in the mid-20th century, but it wasn’t created in isolation. King explicitly acknowledged his debt to earlier geomorphological thinkers, notably William Morris Davis, Albrecht Penck, and John Wood, integrating their ideas while simultaneously addressing their shortcomings to present a more comprehensive model of landscape evolution. This answer will elaborate on how King combined these pre-existing concepts to formulate his theory of pediplanation.
The Precursors: Davis, Penck, and Wood
Understanding King’s pediplanation requires first understanding the foundations laid by his predecessors.
William Morris Davis and the Geographic Cycle
Davis, a prominent American geomorphologist, proposed the ‘Geographic Cycle’ or ‘Cycle of Erosion’. This model described landscape evolution through stages of youth, maturity, and old age, driven by uplift and erosion. He emphasized the role of rivers in shaping landscapes and believed that landscapes progressed through predictable stages. However, Davis’s cycle was criticized for its rigid, deterministic nature and its limited applicability to complex landscapes, particularly those with varied lithology and tectonic activity. He largely focused on humid temperate regions.
Albrecht Penck and the Monoclinal Ridge System
Albrecht Penck, a German geomorphologist, focused on the influence of climate and tectonic activity on landscape evolution. He proposed a classification of landforms based on their relationship to tectonic movements and erosion. Penck identified two main types of landscapes: those shaped by uplift and erosion (monoclinal ridge systems) and those shaped by deposition. His work highlighted the importance of considering tectonic history, but his model was criticized for being overly focused on structural control and neglecting the role of fluvial processes in arid and semi-arid regions.
John Wood and the Plains as Erosional Surfaces
John Wood, a British geomorphologist, argued that plains were primarily erosional surfaces, formed by the prolonged removal of material from upland areas. He emphasized the role of sheetwash and pedimentation in the formation of plains. Wood’s work was significant in shifting the focus from river valleys to the broader landscape, but his explanation of the processes involved in plain formation was somewhat vague and lacked a comprehensive framework.
King’s Synthesis: Pediplanation
King synthesized the ideas of Davis, Penck, and Wood, addressing their limitations to develop the concept of pediplanation. He agreed with Davis that landscapes evolve through cycles, but rejected the rigid, deterministic nature of the Davisian cycle. He incorporated Penck’s emphasis on tectonic control but broadened the scope to include the influence of climate and lithology. Crucially, he built upon Wood’s idea of plains as erosional surfaces, providing a detailed explanation of the processes involved.
Key Elements of King’s Pediplanation Theory
- Pediplains: King defined pediplains as gently sloping, extensive plains formed by the prolonged erosion of mountainous regions.
- Pedimentation: He emphasized the role of pedimentation – the formation of gently sloping erosional surfaces at the base of mountains – as a key process in pediplanation.
- Sheetwash: King recognized the importance of sheetwash (unconfined overland flow) in transporting eroded material from upland areas to the pediplains.
- Lateral Erosion: He highlighted the significance of lateral erosion by streams and rivers in widening valleys and contributing to the overall lowering of the landscape.
- Cyclic History: King proposed that pediplanation occurs in cycles, with periods of uplift followed by periods of erosion.
How King Addressed the Limitations of his Predecessors
King’s theory differed from Davis’s in its emphasis on arid and semi-arid environments, where pediplanation is most prevalent. Unlike Davis, King didn’t see the landscape evolving towards a single, inevitable end-state. He acknowledged the influence of Penck’s tectonic control but argued that climate and lithology played equally important roles. He provided a more detailed and mechanistic explanation of plain formation than Wood, emphasizing the interplay of pedimentation, sheetwash, and lateral erosion.
| Concept | Davis’s Geographic Cycle | Penck’s Monoclinal Ridge System | Wood’s Erosional Plains | King’s Pediplanation |
|---|---|---|---|---|
| Dominant Process | River Erosion | Tectonic Uplift & Erosion | Sheetwash & Pedimentation | Pedimentation, Sheetwash, Lateral Erosion |
| Landscape Focus | Humid Temperate Regions | Structurally Controlled Landscapes | Plains | Arid & Semi-Arid Regions, Pediplains |
| Cyclicity | Rigid, Deterministic Cycle | Less Emphasis on Cyclicity | Limited Cyclical Framework | Cyclic History of Uplift & Erosion |
Conclusion
In conclusion, King’s theory of pediplanation represents a significant advancement in geomorphological thought. By skillfully integrating the ideas of Davis, Penck, and Wood, while simultaneously addressing their limitations, he developed a more comprehensive and nuanced model of landscape evolution, particularly applicable to arid and semi-arid regions. Pediplanation remains a crucial concept for understanding the formation of plains and the long-term evolution of landscapes, and continues to be refined with modern geomorphological techniques.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.