Landforms change over time through erosion. Cracks and weaknesses in resistant rock are widened by hydraulic action and air, forming wave-cut notches and caves. Cliffs made of resistant rock like chalk steeply face coastlines. As cliffs collapse, wave-cut platforms of smooth, eroded rock are left behind on beaches. This process of cliff retreat and wave-cut platform formation is demonstrated in a diagram. Students are asked to identify specific landforms like headlands, bays, arches, and stacks on a map of the south coast.