Storms wash away Braunton Burrows dunes
Up to 10m (33ft) of sand dunes at a United Nations site are believed to have been washed away by recent storms.
Braunton Burrows, Britain's first Unesco biosphere reserve, has one of the UK's largest sand dune systems.
The sea has punched its way through the dunes in places, leaving a nearby estuary behind them more exposed to the open sea.
Natural England said it was working with the Environment Agency to find a way to restore them.
The Christie Devon Estate Trusts, which owns the beach, said it was essential to restore the dunes because of flood risks inland in the direction of Braunton.