Coastal Morphology

Coastal morphology

Coastal morphology refers to geomorphology of the coast. It is often shortened to morphology. The study of the interaction of waves and currents with the coast. The coast is shaped by tectonic and structural features, the nature of the rock forming the coast and depositional and erosive activity. The basic type of coast is determined by tectonic and structural factors that have been imprinted during formation of the continents.

Coastal Process: Mainly there are three coastal processes. They are

1.       Erosion

2.       Transportation, and

3.       Deposition

Coastal Landform:

1.       Erosional landforms

2.       Depositional landforms

Erosional landform: the landform which is created due to the erosional process is called erosional landform. There are many types of erosional landforms. They are follows:

a.       Cliff

b.      Notch

c.       Cove

d.      Cave

e.      Stack/chimney rock/Needle/Columns/Pillar/Scalp

f.        Arch

g.       Inlet

h.      Wave cut platform.   Etc.

Cliff: A cliff is a vertical, or near vertical, rock exposure. Cliffs are formed as erosion landforms due to the processes of erosion and weathering that produce them. Cliffs are common on coasts, in mountainous areas, escarpments and along rivers. Cliffs are usually formed by rock that is resistant to erosion and weathering. Sedimentary rocks most likely to form cliffs include sandstone, limestone, chalk, and dolomite. Igneous rocks such as granite and basalt also often form cliffs. A cliff is a vertical, near vertical or sloping wall of rock or sediment that borders the sea.  They generally differ in their angle of slope because of their rock structure and geology, but the processes involved in their formation are the same. The sea cliff is the most widespread landform of coastal erosion.

Notch/Wave cut: It forms after destructive waves hit against the cliff face, causing undercutting between the high and low water marks, mainly as a result of corrosion and hydraulic power, creating a wave-cut notch. By the wave processes such as hydraulic power and abrasion, the waves undercut the face forming a wave-cut notch. The rock above hangs over the notch.

Cove: A cove is a small type of bay or coastal inlet. Coves usually have narrow, restricted entrances, are often circular or oval, and are often situated within a larger bay. Small, narrow, sheltered bays, inlets, creeks, or recesses in a coast are often considered coves. Colloquially, the term can be used to describe a sheltered bay. Coves form where rock runs in bands horizontal to the direction of wave attack. There is a band of resistant rock closest to the sea and a band of less resistant rock inland.

Cave: A cave or cavern is a natural underground space large enough for a human to enter. Caves form naturally by the weathering of rock and often extend deep underground. The word "cave" can also refer to much smaller openings such as sea caves,  

Rock, shelters and grottos. Waves attack vertical lines of weakness in the rock known as Faults. Processes such as hydraulic action and abrasion widen these faults into cracks and eventually the waves will penetrate deeply enough to create caves. Waves are particularly good at exploiting any weakness in a rock, such as a joint. By the same processes of erosion, and particularly by hydraulic power and abrasion, any vertical line of weakness may be increased in size into a cave. However, the rock needs to be relatively hard or resistant otherwise it will collapse before the cave is formed. Once a cave has formed, when a wave breaks, it blocks off the face of the cave and traps the air within it. This compresses the air trapped inside the cave, which increases the pressure on the roof, back and sides.

Stack: A stack is a geological landform consisting of a steep and often vertical column or columns of rock in the sea near a coast, isolated by erosion. Stacks are formed by time, wind, and water, processes of coastal geomorphology. They are formed when part of a headland is eroded by hydraulic action, which is the force of the sea or water crashing against the rock. The force of the water weakens cracks in the headland, causing them to later collapse, forming free-standing stacks and even a small island. Without the constant presence of water, stacks also form when a natural arch collapses under gravity, due to sub-aerial processes like wind erosion. Stacks can provide important nesting locations for seabirds, and many are popular for rock climbing.

Stack is a vertical column of rock.

Arch: Once a cave has formed, when a wave breaks, it blocks off the face of the cave and traps the air within it. This compresses the air trapped inside the cave, which increases the pressure on the roof, back and sides. Where the rock has vertical lines of weakness, a blowhole can be formed extending through the roof of the cave and opening onto the cliff top. When the tide is high enough water can be forced through natural part to give a spectacular release of water and the cliff top. If the cave forms part of a narrow headland, the pressures from the waves may result in the back of the cave being pushed through to the other side so that it is open at both sides. The cave then becomes a natural arch. A natural arch or natural bridge is a natural rock formation where a rock arch forms, with an opening underneath. Most natural arches form as a narrow bridge.

Inlet: An inlet often leads to an enclosed body of water, such as a sound, bay, lagoon, or marsh. In sea coasts, an inlet usually refers to the actual connection between a bay and the ocean and is often called an "entrance" or a recession in the shore of a sea, lake, or river. A certain kind of inlet created by glaciation is a fjord, typically but not always in mountainous coastlines and also in mountain lakes.

Wave cut platform: A wave-cut platform, coastal benches, wave-cut benches or shore platform is the narrow flat area often found at the base of a sea cliff or along the shoreline of a lake, bay, or sea that was created by the action of waves. Wave-cut platforms are often most obvious at low tide when they become visible as huge areas of flat rock. Sometimes the landward side of the platform is covered by sand, forming the beach, and then the platform can only be identified at low tides or when storms move the sand. It forms after destructive waves hit against the cliff face, causing undercutting between the high and low water marks, mainly as a result of corrosion and hydraulic power, creating a wave-cut notch. This notch then enlarges into a cave. The waves undermine this portion until the roof of the cave cannot hold due to the pressure and freeze-thaw weathering acting on it, and collapse, resulting in the cliff retreating landward. The base of the cave forms the wave-cut platform as attrition causes the collapsed material to be broken down into smaller pieces, while some cliff material may be washed into the sea. This may be deposited at the end of the platform, forming an off-shore terrace.

Depositional landform: Coastal deposition is the laying down of material on the coast by the sea. It occurs when waves lose energy or when large inputs of sediment are made into the coastal system - perhaps due to the arrival of fluvial sediment at a river estuary. Wave refraction in bays also encourages deposition due to the dispersal of wave energy. Lower-frequency constructive waves often contribute to deposition due to their strong swash, moving beach material inland. Depositional coasts are generally found along coast lines of gentle relief, where sediments from various sources are available. The depositional coasts are found along the Atlantic and Gulf coasts of the United States. Such coasts are influenced by the erosional processes and inundation during storms. The following are the depositional landform.

a.       Sea beach

b.      Bar

c.       Off shore and long shore bar

d.      Spit

e.      Hook

f.        Head land

g.       Loop

h.      Connecting bar

i.         Looped bar

j.        Tombolo

k.       Wing head land

l.         Lagoon.

Sea beach:

A beach is a deposit of loose sediment adjacent to a body of water. Though sand is common to most beaches, a remarkable diversity of sediment size, from boulders to fine silt is found on beaches around the world. Larger particles and steeper slopes are found where wave action is high. Fine particles and gentle slopes are characteristic of beaches exposed to low wave action. A beach is a landform along the shoreline of an ocean, sea, lake, or river. It usually consists of loose particles, which are often composed of rock, such as sand, gravel, shingle, pebbles, or cobblestones. The particles comprising the beach are occasionally biological in origin, such as mollusk shells or coralline algae.

Bar: A bar is a somewhat linear landform within or extending into a body of water, typically composed of sand, silt or small pebbles. A bar may separate a lake from the sea, as in the case of an ayre. They are typically composed of sand, although could be of any granular matter that the moving water has access to and is capable of shifting around.

Offshore and long shore bar: the simplest coastal accumulative relief form, formed by the action of sweeping breakers. The bar has the form of a low ridge (bar), extending along the shoreline. Bars can reach hundreds of m or several km in length and 1–4 m in height; they are defined by the energy of the surf. Such bars are made of sand, gravel, pebbles, and shells. Ancient offshore bars are relicts of the old shoreline. A ridge of sand, gravel, or mud built on the seashore by waves and currents, generally parallel to the shore and submerged by high tides.

Spit: A spit or sand spit is a deposition landform found off coasts. At one end, spits connect to a head, and extend into the nose.  A spit is a type of bar or beach that develops where a re-entrant occurs, such as at cove's headlands, by the process of longshore drift. Longshore drift (also called littoral drift) occurs due to waves meeting the beach at an oblique angle, and backwashing perpendicular to the shore, moving sediment down the beach in a zigzag pattern. Longshore drifting is complemented by longshore currents, which transport sediment through the water alongside the beach. These currents are set in motion by the same oblique angle of entering waves that causes littoral drift and transport sediment in a similar process. Spits are created by the process of Long shore drift. Some eroded material ends up caught up within the waves and is carried by the sea along the coastline in cells known as littoral cells. Material is carried along the shore in a zigzag fashion by waves as they swash material up the beach at an angle and backwash material down the beach at a right angle. The angle of swash is determined by the prevailing wind (the dominant or main direction in which the wind blows).

Hook: Hook is created mainly by the ocean current due to giving pressure from one side to a spit. Hook is created from the spit due to giving pressure. Once a spit forms, wave action remains strong on the seaward side of the spit, and the longshore drift continues to transport sediment to the end of the spit, where it is deposited. The spit protects the bay from ocean waves, creating a shadow zone of calm water on its landward side. Deposition in the shadow zone at the end of the spit can cause the spit to turn landward and form a hook.

Head land: A headland is a point of land, usually high and often with a sheer drop that extends out into a body of water. The word is often used as a synonym for promontory; a headland of considerable size often being called a cape.  A headland is often referred to as simply a head, either in context or in names such as Beachy Head.

Tombolo: Away from the mouths of rivers, deposition also occurs wherever wave activity is weak. For example, a small island close to shore shelters the mainland shoreline from strong ocean waves, thus diminishing wave activity between the island and the mainland. This region is called a wave shadow zone. The longshore drift cannot pass through this quiet region because wave motion is needed to maintain longshore drift. Therefore, any sediment carried by longshore drift into such an area is deposited there. The deposition of sediment eventually builds up a sand bridge that connects the island to the mainland. The sand bridge is called a tombolo. Wave energy also dissipates in the lee of large sea stacks or islets. Wave refraction sweeps sediment behind the obstruction from two directions, depositing it as a slender finger called a tombolo.

Lagoon: Spits can extend across the mouth of a bay, but wave action is usually strong enough to wash sand out to sea or be deposited in the embayment. They may curve into the bay or stretch across connecting to the other side as a bay mouth bar. When the bay is closed off by a bar it becomes a lagoon.

Connecting bars:

Sometimes a spit is built across any stretch of water and joins Is-lands, headlands, islands and headlands. Such a spit is called a connecting bar.

Loops:

Under special conditions opposing currents may encounter littoral currents in such a way that it leads to the landward growth of hooks until they connect with the coastline forming loops.