The landform that results from waves eroding the soft rock at the base of a steep coast is called a sea cliff.

Here's how it happens:

1. Wave action: Waves constantly pound against the base of the coast, especially during storms.

2. Erosion: The waves erode the softer rock, creating a notch at the base of the cliff.

3. Undercutting: As the notch gets bigger, the cliff above becomes unsupported and starts to overhang.

4. Collapse: Eventually, the unsupported rock collapses, causing the cliff to retreat inland.

This process continues, resulting in a steep, vertical cliff face that is constantly being eroded by the waves.