Water Erosion

Beaches

Baymouth bars are somewhat like barrier islands. Baymouth bars large bars of sand that are ahead of the shore but are somehow connected to the land.

A barrier island is just like a baymouth bar in the sense that it sits in front of the shore, but it's not connected to the land.

Another type of erosion that longshore currents cause are called spits. Spits are similar to baymouth bars but instead of forming the shape of a mouth, it sticks straight out like a long walkway. In Martha's Vineyard, Massachusetts, there is a baymouth bar and a spit right next to each other.

Sand on beaches is a mix of what has eroded around it. For example, Hawaii's black sands are made of basalt from the volcanoes and white sand from the sea. Beaches can be made of anything. Mostly though, beaches are deposits of sand from the sea.

Beaches are temporary. Just like barrier islands, beaches don't last forever. It's impossible for a beach to last forever because they are sitting right next to a large mass of moving water.

Barrier Islands

Spits

Baymouth Bars

Beaches

Barrier Islands are sand deposits that are separated from the mainland, but are still even with it. The small islands start out as underwater sand ridges. They are formed by breaking waves. Sediments are added through hurricanes and storms. This raises the underwater island to sea level. Loose sand is blown into dunes once the barriers are exposed. This keeps the island above sea level. Barrier islands are short term like most seashore features. They only last a few years to a few centuries. The picture of the light house to the left is located in North Carolina on a barrier island called Cape Hatteras. The Cape Hatteras Lighthouse had to be moved a mile from its original spot because the barrier island changed. Barrier Islands are the outcome of sand erosion and deposition. Once a barrier island is formed, it starts to erode as well.

Sometimes a beach will be eroded by longshore currents. Longshore currents move sand up and down the shore. They also create baymouth bars.

Longshore Currents

By the ThinkQuest Team of Grant School

Photos courtesy of USGS

Photo courtesy of National Park Service, Cape Hatteras National Seashore