Which description best explains the formation of surf?

Which description best explains the formation of surf?

• A. Waves energy, rebounding from its impact with shore, crashes into oncoming waves, causing them to break.
• B. Entering shallow water forces wave energy upward, making the wave crest unstable and causing it to break.
• C. A wave encountering shallow water begins to slow at its bottom, while the top of the wave continues at its previous speed. This causes the wave to break.
• D. As waves enter shallow water, the distance between wave crests shortens, increasing the tendency to break.

Answer: (C)

Surf forms as a wave moves into shallower water. The seabed slows the lower part of the wave through friction while the upper part continues at its original speed, causing the wave to steepen until the crest can no longer balance the front and breaks forward. This process, called shoaling, also involves a shortening of wavelength as depth decreases, which contributes to the increasing height of the wave until breaking occurs. The other descriptions don’t capture the main mechanism: breaking isn’t caused by energy rebounding from the shore, nor by energy being forced upward in shallow water; and while crest spacing shortening happens as waves slow, it’s the bottom friction and resulting steepening that trigger the break.

Surf forms as a wave moves into shallower water. The seabed slows the lower part of the wave through friction while the upper part continues at its original speed, causing the wave to steepen until the crest can no longer balance the front and breaks forward. This process, called shoaling, also involves a shortening of wavelength as depth decreases, which contributes to the increasing height of the wave until breaking occurs. The other descriptions don’t capture the main mechanism: breaking isn’t caused by energy rebounding from the shore, nor by energy being forced upward in shallow water; and while crest spacing shortening happens as waves slow, it’s the bottom friction and resulting steepening that trigger the break.