The raw power of Storm Eleanor has shifted tonnes of sand to create new landscapes on beaches.
New "sand cliffs" have developed along the coast of north Cornwall, causing one beach to be closed by the council.
Gusts of up to 100mph (161km/h) hit parts of the UK on Wednesday morning, combining with powerful tides to make a significant impact on the coastline.
The RNLI is advising people to "stay well clear" of the features.
A sheer cliff of sand has formed in the middle of Perranporth beach, and two bridges on to the beach have been flattened.
Crantock beach has been significantly eroded, with the lifeguard hut being undermined, and 10m (32ft) sand cliffs have formed in some sections of the dunes above the beach.
One popular beach in Bude, Summerleaze, has been closed by Cornwall Council for safety reasons after significant sand erosion.
The RNLI's area lifesaving manager Dickon Berriman said: "We strongly advise visitors to beaches to stay well clear of the sand cliffs that have been formed by the recent high tides and stormy weather.
"They contain huge quantities of heavy sand and are extremely unstable."
In the village of Portreath, a 20m (65ft) chunk of sea wall was destroyed just metres from several homes.