Northam Burrows in Devon features a remarkable natural coastal defense in the form of a limestone cobble bank stretching nearly two miles and rising over two meters above high tide. This formation, known locally as the Pebble Ridge, is the product of centuries of wave action rather than human construction.

The ridge exemplifies a type of coastal boulder deposit formed by longshore drift, where material eroded from nearby cliffs is transported eastward along the shoreline. During storms, powerful waves carry a mixture of stones, pebbles, gravel, and sand up the beach. As the waves retreat, the backwash pulls smaller particles and sand back toward the sea, but it lacks the strength to retrieve the larger cobbles, leaving them deposited higher on the shore.

A key factor in the ridge's formation is a process called percolation, where water draining through the gaps between the larger pebbles reduces the force of the backwash. This reduction helps retain more sizable stones on the beach. As the ridge grows and becomes more pronounced, percolation intensifies, stabilizing the bank and transforming it into a long-lasting natural barrier.

Beyond its geological significance, the Pebble Ridge functions as an effective defense against flooding and coastal erosion, safeguarding the land beyond Northam Burrows. While shingle banks are relatively common along the UK coastline, this kind of extensive cobble barrier is rare, with Chesil Beach in Dorset being one of the few comparable examples.

The Pebble Ridge thus serves as a visible record of past storm activity and highlights the dynamic natural processes that shape coastal landscapes over time.