Report Abuse. As the wave approaches the shoreline the bottom part of the wave comes in contact with the bottom (ground) which causes friction and slows the water at the bottom of the wave causing the top of the wave to break as there is no longer the volume of water under it.Lee. Easygo · 6 years ago.Thumbs up.est Answer: The bottom of the wave slows down because it is hitting into the slope of the beach. The top of the wave continues on at the same speed and this causes it to roll over the bottom, hence the break. Source(s): Lozza_07 · 6 years ago.