How does deposition form

On coasts that are dominated by depositional processes, most of the sediment being deposited typically comes from large rivers. There are no large rivers bringing sandy sediments to the west coast of Vancouver Island, but there are still long and wide sandy beaches there. In this area, most of the sand comes from glaciofluvial sand deposits situated along the shore behind the beach, and some comes from the erosion of the rocks on the headlands.

The components of a typical beach are shown in Figure On a sandy marine beach, the beach face is the area between the low and high tide levels. A berm is a flatter region beyond the reach of high tides; this area stays dry except during large storms.

Most beaches go through a seasonal cycle because conditions change from summer to winter. In summer, sea conditions are relatively calm with long-wavelength, low-amplitude waves generated by distant winds. Winter conditions are rougher, with shorter-wavelength, higher-amplitude waves caused by strong local winds. As shown in Figure The gentler waves of summer gradually push this sand back toward the shore, creating a wider and flatter beach.

The evolution of sandy depositional features on sea coasts is primarily influenced by waves and currents, especially longshore currents. Waves follow a zigzag fashion while carrying the material along the shore as they swash material up to the beach at an angle and backwash material down the beach at a right angle. The direction of prevailing wind determines the angle of swash. Eventually, this material builds up, out into the sea and creates a spit.

Spit mostly curves inwards towards the land due to the prevailing wind that directs waves pushing the sediment in towards the shore. A break in the coastline also causes the materials to get deposited closest to the shore. It is mainly due to counter currents and a loss in velocity that drop or collect the materials. Waves also deposit sediment in areas offshore that build up to be sandbars and dunes. These formations usually occur when it crashes down in shallow waters and draw some of the sediment from the bottom back out towards the ocean.

Sometimes when sand deposits are blown off the beach and dried in the intertidal zone, then a dune is created. Usually, the rate of sand deposition, in this case, is higher than the erosion that formed a dune.

Debris such as rocks and pebbles trap the dried sand at the top of the beach. When the dune is colonized by plants or increase in size, it tends to trap more sand. Dunes are formed as embryo dunes in the starting and then gradually get developed into dune ridges. When a spit links two headlands, a bar is formed.

At low tides, bars are more pronounced because they cause the water to be shallow and break the water waves. A lagoon may be formed by a bar within a bay. Besides, a tombolo is formed when the mainland and an island get linked by the spit. A sandy beach generally has a more gentle profile compared to a pebble beach which has a steep, stepped profile. Sea defences also affect the profile of a beach.

Where there are defences such as groynes, where the material is trapped, a beach tends to have a steeper profile. A profile for a beach at Hornsea, Holderness Coast.

Ridge and runnels are common on wide sandy beaches with a large tidal range big difference between high and low tide. Ridges are areas of the beach that are raised. The dips are water-filled troughs called runnels. The cross-section is similar to that of hills and valleys but at a much smaller scale. Ridge and runnels on Harlech beach, North Wales. A spit is a landform of coastal deposition.

It is an extended stretch of beach material that sticks out to sea and is joined to the mainland at one end.

Longshore drift moves material along a coastline. Where the coastline changes direction or the power of the waves is reduced material being transported by the sea is deposited. Where rivers or estuaries meet the sea deposition often occurs. The sediment which is deposited usually builds up over the years to form a long ridge of material usually sand or shingle. Such a ridge is called a spit. A spit is an unstable landform.

It will continue to grow until the water becomes too deep or until the material is removed faster than it is deposited. Spurn Point was breached by a storm surge in December Sand dunes were destroyed and the spit was breached by sea water. Spits often have salt marshes build up behind them because the spit offers protection from the stronger waves and the wind, allowing salt tolerant plants to grow.

If a spit extends from headland to headland then a bar will be created. You can see this process on an animation at this link. Deposition Landforms Characteristics and formation of beaches, spits and bars. Spits by rgamesby If rocks and cliffs are being continually weathered, eroded and moved then it stands to reason that this will generate a lot of material that will need to be deposited or laid down somewhere else along the coastline.

Think about it!