Coastal Erosion at Birling Gap

Rob Wassell

The chalk cliffs at the Seven Sisters and Beachy Head are kept white due to the constant effect of coastal erosion – the process where the fragile chalk is slowly eaten away by wind and rain causing fissures and cracks which inevitably lead to a cliff fall – and the process starts all over again.

Most cliff falls occur in the winter months due to the effect of water expansion in the cracks of the cliffs. Over time cracks form which turn into fissures. The wind and rain that lash the cliffs drives water into the cracks which freeze and expand, which turn into fissures. These weaken the cliff further until an eventual fall.

Cliff falls are also common around April and May. As the cliffs dry out from the spring rains, the cliffs become dry and brittle which in turn make the cliffs even more fragile and prone to falls.

When a cliff fall occurs this is referred to as an Active period of erosion. The newly fallen chalk boulders form a breakwater which protects the cliffs. The new chalk is pristine and clean and much tougher than the weakened rock which replaced it. This is the Passive period of erosion. Over time, due to the force of the wind, the lashing of rain and the constant bombardment of high tide at the base of the cliffs twice a day, the cycle starts all over again. 

It is this process that helps keep the chalk cliffs white. 

Whilst some cliff falls are large, some cliff falls are smaller, yet the average rate of coastal erosion over time is 60cm per year.

The rate of erosion at Birling Gap is actually much quicker than elsewhere and this is due to Birling Gap being situated on an ancient river bed. Instead of chalk, it is Coombe Rock, which is a gravel mixture of chalk, flint and clay silt. As this is much softer than chalk, the effects of coastal erosion at Birling Gap are more dramatic, which has resulted into the loss of buildings, including a number of the coastguard cottages.

Sea defences are costly and also unnatural and this is why they will not be considered at Birling Gap. Coastal erosion is a natural process and one that has to be accepted, regardless of what is lost as a result.

Due to the unpredictable nature of coastal erosion, a cliff fall could happen at any time and it is always wise to stay as far away from the cliff edge as possible. When walking under the cliffs, also stay as far away as safely possible due to falling rocks.

Many thanks to @robwassell for writing this article for us. Please take a look at his compelling website at for more information about this beautiful location.

Back to the blog

Book Now