The Effects of Deposition on Shoreline Features

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  • 0:05 The Beach
  • 1:07 Deposition and Longshore Drift
  • 2:50 Shoreline Features…
  • 4:48 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Shorelines constantly change due to the depositing of sand and sediment, which is a process known as deposition. Learn about shoreline features that are created by deposition, such as spits, baymouth bars, tombolos and barrier islands.

The Beach

Did you ever visit the beach and dig your toes into the sand? Did you ever wonder how the sand got there or what exactly makes up the sand that is hiding your toes? A beach is an area next to the ocean that is covered with sand or pebbles.

Beaches are made up of whatever elements are in the area. Therefore, they may be composed of minerals, such as quartz, as well as shell fragments, remains of sea creatures or coral. Each grain of sand is formed when rocks and other materials are broken down by the impact of waves.

New sand and sediment is always being added and is constantly moving under the influence of waves and being deposited in areas where wave energy is low. In this lesson, you will learn about some shoreline features that are created by deposits of sand and sediment, including spits, baymouth bars, tombolos and barrier islands.

Deposition and Longshore Drift

Waves are powerful forces that cause a constant erosion of coastal structures, such as rocky cliffs and headlands, which are narrow strips of land that project out into a body of water. Because shorelines are sloped and uneven, waves rarely strike the shore straight on.

Wave refraction is the bending of waves as they travel toward the shallow waters of the shore. When waves approach shore and the water becomes shallow, the part of the wave closest to the shore comes in contact with the bottom and is the first part of the wave to slow down. The part of the wave that is still in deep water continues on its path toward shore at full speed.

This contrast in speed causes the bending of the wave crest referred to as wave refraction. As the wave approaches the coast, it is almost parallel to the shore. Because of wave refraction, the energy carried by waves is strongest on the sides and end of shoreline protrusions, such as headlands, whereas the adjacent recessed areas along the shore, such as bays, are subjected to much less wave energy. This low wave energy allows for deposition, which is the process of depositing sand and sediment in an area over a period of time.

Deposition along the shore is the result of the longshore drift, which is the process by which sand and sediment is transported along the coast. The longshore drift is influenced by the angle of the waves hitting the shore, as well as winds and currents near the shore and can be responsible for the deposition of large amounts of sediment along the length of the shore.

Shoreline Features Caused By Deposition

The deposition of sand and sediment constantly changes beaches and affects the coastal landscape by creating some unique shoreline features. A spit is an elongated landform that extends from the coast into the mouth of an adjacent bay. It is shaped by the deposition of sand that is carried by currents of the longshore drift.

The free end of the spit often curls landward, forming a growth that resembles a hook due to the flow of the currents. A spit is a type of sandbar. If a spit grows and creates a sandbar that completely closes access to a bay, it is referred to as a baymouth bar.

A baymouth bar completely separates the bay from the ocean and is formed in much the same way that a spit is formed, through deposition caused by the longshore drift. Sand and sediment are allowed to settle in these areas because processes such as wave refraction rob the waves of their energy allowing materials to settle in the area.

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