Please check tide times as the cliffs may not be accessible during high tides. You can tide times check here.
Please take care as the cliffs are actively eroding and rocks can fall at any time.
Coastal Erosion
Coastal erosion is the wearing away of rock along the coastline. This wearing away is caused by destructive waves in various ways:
- Hydraulic action: Air can become trapped in crevices cracks on the cliff face. When waves breaks, this trapped air becomes compressed and subsequently weakens the cliff, causing erosion.
- Abrasion: Fragments of rock and sand found in waves can grind down cliff surfaces like sandpaper.
- Attrition: Waves throw rocks and pebbles on the shore into each other, and they break and become smoother
- Solution: Acids found in seawater can dissolve some types of rock such as chalk or limestone.
Factors Affecting Erosion Rates
The biggest factor affecting coastal erosion is the strength of the breaking waves. A wave’s strength is controlled by its fetch (its length along the water) as well as the wind speed. Longer fetches & stronger winds create bigger, more powerful waves that subsequently have more erosive power. As waves approach the coastline they will lose energy as friction with the seabed increases. As a result, the bathymetry (the underwater elevation) of the sea bed also impacts the strength of waves.
Particular landforms can further reduce wave’s erosive power. Beaches increase the distance a wave has to travel before it reaches the cliffs and reduces its energy. Headlands refract waves around them, thereby reducing their erosive power in one spot while increasing it at another.
Weathering also plays a role in the rate of erosion by creating weaknesses in rocks that are exploited by the processes of erosion.
Humans also have an impact on coastal erosion. Human activities have a variety of effects on coastal erosion but most commonly the activities increase the strength of waves.
Rock Types Prone to Erosion
Hard rocks such as granite and basalt are more resistant to coastal erosion. Softer rocks such as sand or clay are mmore susceptible to erosion.
Formation of Cliffs at Shanganagh
The Shanganagh Cliffs were formed as a result of glacial deposits. The cliffs are made up of glacial till which was deposited from glacial ice. Till includes a mix of undifferentiated material ranging from clay size to boulders, the usual composition of a moraine.
When a glacier's size shrinks below a critical point, its flow stops and it becomes stationary. Meanwhile, meltwater inside and beneath the ice leaves stratified alluvial deposits. These deposits remain after the glacier melts and are known as "glacial deposits".
Till is unsorted glacial sediment. Till is classified into primary deposits, laid down directly by glaciers, and secondary deposits, reworked by fluvial transport and other processes.
Remains of Disused Dump
Unfortunately, glacial deposits are not the only thing being eroded at this beach. The disused landfill north of Bray, which stopped taking in waste at least 25 years ago, is being worn away by advancing waves from the Irish Sea washing out the clay walls.
Approximately 200m of the face of the tip has been exposed by the weather and rusted metal, heavy plastics, bricks and bags can be seen at the foot of eroded cliffs. This issue has been debated by local authorities but nothing is happening to date to resolve the issue.
To log this earthcache as a find, please message me answers to the following questions:
1. How many layers can you see in the cliff face?
2. What do you think the layers are composed of?
3. Estimate the height of each layer.
4. Based on your observations, which of the four types of erosion described above is occuring here?
5. OPTIONAL: Take a photo of you/your GPSr on the beach
Happy earthcaching!
