Why do some coastlines have steep sea cliffs while others have wide sandy beaches?

The formation of distinct coastal landforms is primarily determined by the interaction between tectonic activity, sediment supply, and erosional processes.1

Erosional Coasts

Coastlines characterized by steep sea cliffs typically occur in regions dominated by erosion, often along the leading edges of lithospheric plates where tectonic forces cause crustal uplift. These areas feature exposed bedrock that resists erosion, resulting in high-relief, rugged topography. The vertical nature of these cliffs is maintained by wave-induced erosion at the base, which undercuts the slope and leads to the eventual collapse of the rock face.21345

Depositional Coasts

In contrast, wide sandy beaches and smooth plains prevail in areas of crustal subsidence where deposition is the dominant process. These coasts accumulate abundant sediment transported by streams or currents. When wave energy is relatively low, this sediment—typically sand—is deposited along the shore. The presence of these deposits can actually protect the underlying coast from direct wave attack, slowing the rate of erosion.12436

Ultimately, the specific configuration of any coastline results from the relative intensity of these forces and the structural characteristics of the underlying rock.1