waves and Beach Erosion The boundary between land and ocean is always changing shape. If you walk on the same beach every day, you might not notice that it is changing. From day to day, waves remove sand and bring new sand at about the same rate. But if you visit a beach just once each year, you might be startled by what you see. Waves shape a beach by eroding the shore in some places and building it up in others. As you learned in Chapter 2, erosion is the process of break ing up rock and carrying it away. At first, waves striking a rocky shoreline carve the rocks into tall cliffs and arches. Over many thousands of years, waves break the rocks into pebbles and grains of sand. A wide, sandy beach forms. Then the waves begin to eat away at the exposed beach. The shoreline slowly moves farther inland. Longshore drift carries the sand along the coast and deposits it elsewhere. Reducing Erosion any people like to live near the ocean. But over time, erosion can wear away the beach. This threatens the homes and other buildings. To avoid losing their property, people look for ways to reduce the effect of erosion Groins one method of reducing erosion along a stretch of beach is to build a wall of rocks or concrete, called a groin, out ward from the beach. The sand carried by the water piles up