What is primarily responsible for the steepening of waves in shallow waters?

The steepening of waves in shallow waters is predominantly due to bottom contour drag. As waves approach the shore and enter shallower water, the wave base interacts with the seabed, causing friction. This interaction slows down the bottom part of the wave while the wave crest continues to move at a faster speed. As a result, the wave becomes more steep as the difference in speed between the top and bottom increases, leading to a taller and steeper wave profile.

This process is essential in understanding how waves behave as they transition from deep to shallow water, impacting their shape and height. While factors like swell formation and wind action do influence wave characteristics, it is the drag from the seafloor that has the most direct effect on wave steepness in shallow environments.