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Accretion (English)
堆積 (日本語)
Acreción (Español)
Accumulation (Français)
Sand dune.jpg

Deposition of sediment, usually sand, which is evident by the seaward advance of a shoreline indicator, such as the high water line, berm crest, or vegetation line. Accretion causes the beach to become wider. Opposite of Erosion.

Accretion begins with sand deposition on shore, from the movement of the waves, tides and longshore current. Some sand is then dried out by the wind and sunlight, allowing it to be blown to other areas of the beach by the prevailing winds. Sand is the major component in accretion/erosion cycles. Sand is sourced from weathered or eroded material along the shore or from inland areas, carried to the shore by rivers. Sand can also come from corals or shellfish.

Wave action plays a significant role in the formation of a beach. Waves can assist in both the deposition (accretion) and erosion of a beach. In calmer weather, the wash of the waves deposits sand onto the shore while the backwash removes small amounts of material. The amount deposited is typically greater during this time. During more unsettled conditions, such as storms and periods of large waves, removal of material is much higher.