Sub-topic 6: Erosional and Depositional Landforms by Oceans and Coastal Processes
Oceans are powerful agents of change, constantly shaping coastlines through the relentless forces of erosion and deposition. This module explores the fascinating landforms created by these dynamic coastal processes.
Coastal Erosion: Sculpting the Shoreline
Coastal erosion is the process by which sea waves, currents, and tides wear away land. The effectiveness of erosion depends on factors like wave energy, rock type, and the presence of protective features.
Wave action is the primary driver of coastal erosion.
Waves exert force on the coastline, breaking down rocks and transporting material. Different types of wave action, like hydraulic action and abrasion, contribute to this process.
Wave action is the principal force behind coastal erosion. This includes:
- Hydraulic Action: The sheer force of water entering cracks in rocks, compressing air within them. When the wave recedes, the compressed air expands, widening the cracks. Repeated cycles can break off pieces of rock.
- Abrasion (Corrasion): The grinding and scraping of rock fragments carried by waves against the coastline. This is like sandpaper smoothing a rough surface.
- Attrition: The process where rock fragments carried by waves collide with each other, becoming smaller, rounder, and smoother.
- Solution (Corrosion): The dissolving of soluble rocks, such as limestone, by the slightly acidic seawater.
Erosional Landforms
The continuous action of erosion carves out distinctive features along coastlines.
| Landform | Formation Process | Description |
|---|---|---|
| Sea Cliff | Wave undercutting and collapse | Steep, often vertical rock faces formed by wave erosion at the base of a coastline. |
| Wave-Cut Platform (Bench) | Continuous wave erosion and cliff retreat | A gently sloping surface extending from the base of a cliff towards the sea, exposed at low tide. |
| Sea Cave | Differential erosion of weak rock bands | Hollows or tunnels formed by wave erosion at the base of a cliff, often where a fault or joint is present. |
| Sea Arch | Erosion through a headland | A natural bridge of rock formed when a sea cave erodes through a headland, connecting two sides. |
| Sea Stack | Collapse of a sea arch | Isolated pillars of rock standing in the sea, formed when the roof of a sea arch collapses. |
| Stump | Further erosion of a sea stack | The remnant of a sea stack, worn down by wave action to a low-lying rock near the sea surface. |
Coastal Deposition: Building the Shoreline
Deposition occurs when the energy of the waves or currents decreases, causing them to drop the sediment they are carrying. This process builds up new landforms along the coast.
Longshore drift is a key mechanism for coastal deposition.
Waves approaching the coast at an angle, combined with the backwash returning perpendicular to the shore, create a zigzag movement of sediment along the coastline. This process is called longshore drift.
Longshore drift is the movement of sediment along a coastline. It is driven by waves that approach the shore at an angle (the swash) and then return directly down the beach (the backwash). This creates a net movement of material parallel to the coast. The sediment transported by longshore drift is then deposited in areas where wave energy is reduced, leading to the formation of various depositional landforms.
Depositional Landforms
The accumulation of transported sediment results in a variety of coastal features.
A spit is a ridge of sand or shingle that projects from the land into the sea or across the mouth of a river or bay. It forms where longshore drift is interrupted, such as by a change in the coastline or a river estuary. The spit grows outwards as sediment is deposited. A bar is similar to a spit but can connect two headlands or a headland to the mainland, or it can form offshore, parallel to the coast. A tombolo is a specific type of bar that connects an island to the mainland. A lagoon is a body of water separated from the larger body of water by a barrier island or reef, often formed behind a barrier beach or spit.
Text-based content
Library pages focus on text content
Other depositional landforms include:
- Beaches: Accumulations of sand, shingle, or pebbles deposited by waves and currents.
- Barrier Islands: Long, narrow islands of sand that run parallel to the mainland coast, often separated by a lagoon.
- Sand Dunes: Ridges of sand formed by wind action, often found behind beaches.
The collapse of a sea arch.
A tombolo.
The dynamic interplay between erosion and deposition continuously reshapes our coastlines, creating a diverse array of fascinating landforms.
Learning Resources
Provides a clear and concise overview of coastal erosion and deposition processes, including key landforms, suitable for foundational understanding.
Explains various coastal landforms created by erosion and deposition, with excellent accompanying visuals and definitions.
A university-level resource detailing the physical processes of coastal geomorphology, including wave action and sediment transport.
An informative resource from the U.S. Geological Survey explaining the science behind coastal processes and the landforms they create.
Focuses on the causes and impacts of coastal erosion, offering insights into the forces that shape shorelines.
A visual explanation of various erosional and depositional landforms found along coastlines, aiding in spatial understanding.
A blog post delving into the formation and dynamics of beaches, a common depositional coastal landform.
A clear and animated explanation of the longshore drift process, crucial for understanding depositional landforms.
A comprehensive overview of coastal geomorphology, covering both erosional and depositional processes and landforms.
Details specific depositional landforms like spits, bars, tombolos, and lagoons, explaining their formation and characteristics.