When the seabed rises

Raise the seabed

This time you can raise the seabed yourself. Use the “Water depth” slider to change how deep the sea is. Once the seabed is closer than half the crest-to-crest distance, the circles are squashed from above and below into flat ovals. Dots near the bottom move almost only back and forth. And the wave slows down.

Why?Water cannot move down through the seabed. So water near the bottom has less room to move up and down, and is only pushed forward and back. That is why the circles flatten.

Learn moreAn 8-second wave travels at 45 km/h in water 60 m deep, but at 32 km/h in water 10 m deep. At 60 m the surface circle is 100% as tall as it is wide — almost round — but at 10 m it is 71%, clearly flatter. Wave height on screen is drawn 2× larger.

Crest speed at this depth

32 km/h

60 m deep

45 km/h · circle 100%

10 m deep

32 km/h · circle 71%

calculated from the textbook equations for water waves (linear wave theory)