What does hydraulic action involve in coastal erosion?

Hydraulic action is a significant process in coastal erosion that involves the force of water exerting pressure against the coastline. When waves crash against rocks and cliffs, they create a powerful force that can compress air trapped in any cracks or fissures on the surface. This rapid increase in pressure can lead to the cracks widening and eventually breaking the rock apart.

This process distinguishes hydraulic action from other forms of erosion. For example, options such as the collision of rocks and pebbles pertain more to abrasion, while the gradual wear by sand particle movement involves a different mechanism. Additionally, the dissolution refers to chemical weathering rather than physical erosion. Thus, the correct answer highlights the unique physical force at play in hydraulic action specifically.