Coastal erosion is a gradual process where coastlines are worn down by the actions of waves. There are four primary types of erosion: hydraulic action, attrition, abrasion, and corrosion.
Factors Contributing to Coastal Erosion:
Hydraulic Action
Hydraulic Action: Coastal erosion involves complex wave processes. Destructive waves exert substantial pressure on cliffs, causing rocks to loosen. When a wave breaks, air trapped in a circular shape can be compressed into cracks and joints in the rock. The subsequent release of this pressure can explosively shatter the rock. A diagram illustrates the process, showcasing air pockets in the rock, leading to the expansion of cracks. Simultaneously, the wave crashes into the cliff face, intensifying erosion through the power of water.
Attrition
Attrition: In this process, rocks and pebbles in the breaker or surf zone collide, knocking off angular corners. This collision occurs frequently in the surf zone. For harder rocks like flint, the process is slower, eventually forming pebble beaches. Rocks break down into smaller pieces until only rounded quartz grains (sand) remain.
Abrasion
Abrasion: Abrasion is similar to attrition, but in this case, sand, pebbles, and boulders are picked up by destructive waves and thrown or scraped against the cliff face or sea bed. This process, highly effective in wave erosion, abrades or scratches the rock, wearing it away. Under stormy conditions, it can undercut cliffs at high tide, creating curved wave-cut notches and sea caves.
Corrosion
Corrosion: Corrosion occurs when seawater and salt spray react with rock minerals, actively dissolving them. The dissolved rock minerals are then carried away in solution within the seawater. Certain rock types, such as limestone, are more susceptible to corrosion.
Coastal Erosion Comparison Table
| Erosional Type | Process Description | Key Features |
|---|---|---|
| Hydraulic Action | – Destructive waves exert pressure on cliffs, loosening rocks. | – Air trapped in breaking waves compresses into rock cracks, explosively releasing pressure. |
| – Wave crashes into the cliff face, intensifying erosion with the power of water. | – Circular air pockets in the rock expand cracks. | |
| Attrition | – Rocks and pebbles in the breaker zone collide, knocking off angular corners. | – Frequent collisions in the surf zone. |
| – Process slower with harder rocks; eventually forms pebble beaches. | – Rocks break down into rounded quartz grains (sand). | |
| Abrasion | – Sand, pebbles, and boulders picked up by destructive waves, thrown or scraped against cliff face or sea bed. | – Highly effective erosion process. |
| – Abrades or scratches the rock, wearing it away. | – Undercuts cliffs at high tide, creating curved wave-cut notches and sea caves. | |
| Corrosion | – Seawater and salt spray react with rock minerals, actively dissolving them. | – Rock minerals carried away in solution within seawater. |
| – Some rock types, like limestone, are more susceptible to corrosion. |
Determinants of Erosion Effectiveness:
Several factors influence the effectiveness of erosion processes:
- The type of wave (destructive or constructive).
- The size of the wave, as larger waves carry more energy.
- Tide level, where higher tides allow waves to reach cliffs without being slowed down by the beach or cliff approach.
- The shape of the coastline, including the steepness of the approach and the presence of deflecting headlands.
- The type of rock, with different rocks eroding in unique ways.
Geological Consequences:
Coastal erosion plays a significant role in shaping landscapes. For instance, Lulworth Cove is formed as rocks erode at different speeds. Additionally, beaches are created as rocks break down, producing sand that is transported and deposited to form coastal features such as spits.
