A photo of a woman posing for a picture across a large crack at Birling Gap has led to fresh warnings to people to keep away from dangerous cliff edges.
In the photograph, the woman is seen next to a section of the chalk cliffs on the south coast near Eastbourne that has already broken away.
RNLI coxwain Mark Sawyer said authorities understood it was a beautiful place with stunning views.
But he said the cliffs were crumbling and could fall at any time.
Mr Sawyer said: "It does look fine from the top but what [people] can't see - as we do from the lifeboats - [is] how it's underpinned.
"They can't see the erosion underneath them. There's some huge holes underneath the earth and the grass up there.
"There's no chalk at all. It's a matter of time before those cliffs go."
He said there had been two recent cliff falls, one near the spot where the photograph was taken.
Coastguards regularly urge people to keep away from the cliff tops and also to stay away from the cliff base in case chalk falls.
Geologists have said cracks can stretch back 10m (33ft) to 15m (49ft) into the cliffs.
Safety advice from the National Trust, which owns Birling Gap, states that cliff falls and erosion are part of the landscape but visitors are advised to act sensibly and stay away from the edge.
Its website states that permanent signs are in place warning visitors of dangers.