Which statement about waves breaking is true?

Which statement about waves breaking is true?

• A. A wave encountering shallow water slows at the bottom while the top continues at its previous speed, causing the wave to break.
• B. A wave speeds up as it enters shallower water, making the crest offshore.
• C. Waves break only when wind overpowers gravity.
• D. Waves break due to moon phase and not water depth.

Answer: (A)

Waves break when the water depth can’t support the wave’s tall, steep shape any longer. As a wave travels from deep water into shallower water, the bottom part of the wave is slowed by friction with the seabed while the crest above it keeps moving at nearly its previous speed. This mismatch causes the wave to steepen and shorten in wavelength. When the crest becomes too tall and unstable for the shallower depth, it spills forward and breaks. This shoaling effect—slowing at the bottom and faster movement of the upper part—is the key reason waves break near shore. The other ideas don’t fit because a wave does not speed up as it enters shallower water; it slows. Breaking isn’t caused solely by wind overpowering gravity, but by the interaction of wave height, steepness, and bottom depth. The phase of the moon has no direct effect on breaking; it’s water depth and seabed interaction that matters.

Waves break when the water depth can’t support the wave’s tall, steep shape any longer. As a wave travels from deep water into shallower water, the bottom part of the wave is slowed by friction with the seabed while the crest above it keeps moving at nearly its previous speed. This mismatch causes the wave to steepen and shorten in wavelength. When the crest becomes too tall and unstable for the shallower depth, it spills forward and breaks. This shoaling effect—slowing at the bottom and faster movement of the upper part—is the key reason waves break near shore.

The other ideas don’t fit because a wave does not speed up as it enters shallower water; it slows. Breaking isn’t caused solely by wind overpowering gravity, but by the interaction of wave height, steepness, and bottom depth. The phase of the moon has no direct effect on breaking; it’s water depth and seabed interaction that matters.