Cliffs, Headlands, and Coastal Erosion

Rocky coasts are shaped by four principal mechanisms of marine erosion, often acting together during the same storm. Hydraulic action is the sheer, repeated force of water and compressed air driven into cracks and joints in a cliff face by breaking waves, which can fracture rock directly through pressure alone; abrasion, sometimes called corrasion, occurs as waves hurl sand, pebbles, and rock fragments against the cliff, scouring and wearing it down much like sandpaper; attrition wears down the fragments themselves as they collide with one another and the seabed, progressively rounding and reducing their size; and corrosion, or solution, dissolves soluble rock, particularly limestone and chalk, through the mildly acidic action of seawater. Acting together at the base of a cliff, these processes typically cut a notch that undermines the rock above it, producing periodic collapse and a gently sloping, wave-cut platform exposed at low tide in front of the retreating cliff line, a visible record of how far the coast has already retreated.