Model Answer
0 min readIntroduction
Coastal geomorphology is a dynamic field, shaped by the interplay of tectonic forces, sea-level changes, and erosional processes. Shepard’s classification provides a foundational framework for understanding the diverse types of coastlines found globally. The marine cycle of erosion, particularly evident along submergent coastlines, demonstrates how sea level rise sculpts the landscape, creating characteristic features like rias, fjords, and estuaries. Understanding these processes is crucial, especially in the context of accelerating sea-level rise due to climate change. This answer will detail Shepard’s classification and then focus on the erosional cycle along a submergent shoreline.
Shepard’s Classification of Coasts
Shepard (1963) classified coasts based on their relationship to the geological structure and the prevailing processes shaping them. The classification is broadly divided into primary and secondary coasts.
- Primary Coasts: These coasts are directly influenced by landmasses and are shaped by subaerial processes like river action, glacial activity, volcanic activity, and tectonic movements.
- Ria Coasts: Formed by the submergence of river valleys, resulting in a dendritic coastline with long, narrow inlets. Example: The coast of Brittany, France.
- Fjord Coasts: Created by the submergence of glaciated valleys. Characterized by steep-sided, U-shaped valleys with deep water. Example: Norwegian Fjords.
- Volcanic Coasts: Formed by volcanic activity, often exhibiting steep cliffs, black sand beaches, and lava platforms. Example: Hawaiian Islands.
- Tectonic Coasts: Result from land uplift or subsidence due to tectonic forces. Often characterized by fault lines and raised beaches. Example: San Francisco Bay Area, California.
- Secondary Coasts: These coasts are shaped by the action of waves and currents on primary coasts. They are modified by depositional and erosional processes.
- Cliff Coasts: Dominated by steep cliffs formed by wave erosion.
- Beach Coasts: Characterized by extensive sandy or gravel beaches.
- Barrier Beach Coasts: Feature offshore barrier islands or spits protecting the mainland.
- Estuarine Coasts: Dominated by estuaries formed where rivers meet the sea.
Marine Cycle of Erosion along a Shoreline of Submergence
A shoreline of submergence is formed when sea level rises relative to the land, flooding existing river valleys or glacial troughs. The marine cycle of erosion in such areas involves a distinct sequence of processes and landform development.
Stage 1: Initial Submergence & Drowning of Valleys
The initial stage involves the flooding of river valleys or glacial troughs. This creates features like rias (drowned river valleys) and fjords (drowned glacial valleys). Wave refraction begins to act on the headlands, concentrating erosive energy.
Stage 2: Wave Refraction and Headland Erosion
Wave refraction causes waves to bend around headlands, concentrating energy on the bays. This leads to differential erosion, with headlands eroding and bays becoming wider. Longshore drift transports sediment along the coast, contributing to beach formation in bays and erosion of headlands.
Stage 3: Formation of Bays and Beaches
As headlands erode, bays become more pronounced. Sediment transported by longshore drift accumulates in bays, forming beaches. The sheltered nature of bays reduces wave energy, promoting deposition. Estuaries develop where rivers enter the sea, often becoming brackish water bodies.
Stage 4: Development of Offshore Features
Continued erosion and sediment transport can lead to the formation of offshore features like barrier islands and spits. These features are formed by longshore drift and are often separated from the mainland by lagoons. Submerged platforms may also develop due to wave abrasion.
Diagrammatic Representation: (Imagine a diagram here showing a cross-section of a submergent coastline, illustrating the stages of erosion, formation of rias/fjords, bays, beaches, and offshore features. This would be included in a handwritten exam.)
| Feature | Process of Formation | Example |
|---|---|---|
| Ria | Submergence of river valley | Coast of Galicia, Spain |
| Fjord | Submergence of glacial valley | Sognefjord, Norway |
| Estuary | River meets sea, sediment deposition | Thames Estuary, UK |
| Barrier Island | Longshore drift, sediment accumulation | Outer Banks, North Carolina, USA |
Conclusion
Shepard’s classification provides a valuable framework for understanding the origin and evolution of coastlines. The marine cycle of erosion along submergent coastlines demonstrates the powerful role of sea level rise and wave action in shaping coastal landscapes. Recognizing these processes is increasingly important in the face of climate change and its associated impacts on coastal communities and ecosystems. Effective coastal management strategies must consider these dynamic processes to mitigate erosion and protect vulnerable areas.
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.