A small part of the cliff at Petit Bot crumbled on Monday, sending large stones crashing on to the beach below.
One group of adults and children who were seeking shade by the cliff had to run for their lives and a witness reported that it was a miracle that no one was injured or killed.
The matter was reported to the Agriculture, Countryside & Land Management Services (ACLMS) which has carried out an assessment on the relative risk created by the change to the cliff face.
A spokesman for ACLMS said it was not possible to say that any coastal cliff face in Guernsey was ‘safe’, and people visiting any of the bays between Fermain and Portelet should act responsibly.
‘Soft cliffs of loose clays and small stones, such as those at Fermain, Moulin Huet, Petit Bot and Portelet, can collapse without warning, particularly after periods of heavy rain.
‘These soft cliffs may also contain large boulders, which are unseen until a fall occurs.
‘There are numerous signs warning people of the risk of rockfalls at Petit Bot placed at the entrance slipway and also attached to several rock faces.
‘This incident took place at the top of the bay and was therefore not associated with coasteering, which takes place in the mouth of the bay.’
Most rockfalls occur during winter months when the beaches are relatively quiet, but on Monday, at the beginning of the school summer holidays, the beach was teeming with people.
Cliff faces weather over a period of years through wind, rainfall and freezing conditions when ice crystals expand the cracks between rocks, and increase the risk of rockfalls.
The growth of vegetation, or small earth tremors that we do not feel, can also cause numerous small changes that over time can lead to rockfalls.
At Petit Port, immediately above the flight of access steps, there are several areas of cliff face that are heavily netted to prevent rockfalls.
The cliffs there also have regular inspection and work by contractors who operate on ropes to remove small flakes and loose stones caused by weathering, and a specialist geo-technical engineer monitors the area every year.
The work is essential to keep the access steps to open for people to enjoy Petit Port bay.
However, even with these expensive precautionary measures, ACLMS said it is never possible to entirely rule out the risk of rockfalls there.
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