Here's why:

* Water depth and wave speed: Waves slow down as they approach shallower water. The shallower the water, the slower the wave travels.

* Wave height: As the wave slows down, the energy it carries has to go somewhere. This causes the wave to build up in height, leading to larger, more powerful waves.

* Steep slope: A steep slope means the water depth changes rapidly. This rapid change in depth causes the wave to slow down and build up in height more quickly, resulting in a breaking wave.

Types of breaking waves:

* Plunging waves: These occur when the wave's crest curls over and collapses dramatically, typically forming on steep slopes.

* Spilling waves: These occur when the wave crest breaks gradually, spilling down the face of the wave. They are more common on gentler slopes.

* Surging waves: These are waves that don't fully break but surge up the beach. They occur on very steep slopes.

Important Note: While steep slopes are a contributing factor, other factors like the strength of the wind, the distance the wave has traveled, and the underlying seabed can also influence wave types.