Introduction
Coastal morphology deals with the shape and features of coastlines and coastal areas along with the natural forces that create and change them.. It encompasses a wide range of natural processes and landforms that result from interactions between the land, ocean, and various geological, climatic, and environmental factors. It combines field of geology, oceanography, geomorphology and environmental science.
Coastal Features and Zones :
• Coast: Broader geographical region which covers land and water.
• Coastline: refers to the precise boundary where the land meets the water.
• Shore: Encompasses the area along the coast influenced by tides, including land and water.
• Shoreline: The specific boundary between land and water at a particular moment, typically at high tide.
• Intertidal Zone: The area between high and low tide marks, often characterized by organisms adapted to regular submersion and exposure.
• Backshore: The area landward of the high-tide mark, typically affected by storm events and waves.
• Foreshore: The area between the high-tide mark and the low-tide mark changes with the tides each day.
• Nearshore: The area from the low-tide mark to the breaking waves, affected by wave action and currents.
• Offshore: The region located beyond the nearshore zone, where the water is deeper.
Agent of Coastal Morphology :
The main agents of coastal morphology, include:
- Waves
- Tides
- Currents
- Tsunamies
1. Waves:
Waves are oscillatory movement that travel across the surface of oceans and large water bodies. They are mainly formed when wind blows over the water, transforming energy to create surface motion. Besides winds, waves can also result from underwater disturbances such as earthquakes, volcanic eruption as well as from the gravitational influence of the moon and sun. These forces set the water in motion making waves a key factor in shaping and changing coastlines through erosion,transportation and deposition of materials.
some characteristics and aspects of sea waves:
1. Wave Generation:Most sea waves form because of wind blowing across the water. The wind creates friction with the water's surface, transferring energy and causing the water to move in a circular pattern, which formed waves.
The size and strength : depend on three main factors: the speed of the wind, duration of wind and the distances.
2. Wave Anatomy: A wave has several components, including the wave crest (the highest point of the wave), wave trough (the lowest point), wavelength (two successive crests or troughs distance) and wave height (the vertical distance of crest and the trough).
3. Wave Propagation: Waves typically travel in the direction of the wind that generated them. As they move across the ocean, they can transmit energy over long distances.
Speed of a wave : determined by its wavelength, with longer waves traveling faster than shorter ones.
4. Ocean Swell: Ocean swell refers to waves that have travelled far from their area of origin and have a more regular and uniform pattern. They often travel across the ocean for hundreds or even thousands of kilometers.
5. Wave Dissipation :
Waves loses energy and begin to dissipate as they move away from their origin. This is happens due to several reasons like friction with the sea floor, especially in shallwer waters, which slows the wave down.
6. Wave Types:
A. Destructive wave
B. Constructive wave
A. Destructive Waves:
Characteristics: Destructive waves, also known as erosional waves or plunging waves, typically have a relatively short wavelength and a high wave height. They are powerful and have a strong backwash (the water returning seaward) compared to their swash (the water rushing up the beach). Destructive waves often have a steep profile with a plunging or collapsing crest.
Effects: Destructive waves have a tendency to remove sand and sediment from the shoreline and carry it offshore.When these waves break, they create powerful backwash and currents that erode the beach surface, making it steeper and narrower over time. This process can lead to the development of coastal features such as offshore troughs, sandbars, and rip currents..
Occurrence: These waves usually appear during stormy weather or when strong winds blow toward the coast.Also more frequent during storms or when strong winds blow directly toward the shore,which can contribute to coastal erosion and the retreat of the shoreline.
B. Constructive Waves:
Characteristics: It always move in with a calm, steady rhythm, also known as surging or depositional waves. They’re low in height but stretch out with longer gaps between each wave. As they reach the shore, they push water and material up the beach more forcefully than they pull it back. This gentle push builds up layers of sand and stones, gradually forming broad, sloping beaches.
Effects: It helps to build up the coastline by depositing sand and sediment along the shore. With a strong swash and weaker backwash, they push material up the beach, gradually forming gentle slopes, wide beaches and bars etc.
Occurrence: Constructive waves are more common during calmer weather conditions when there are light to moderate onshore winds. They are associated with the accretion of beaches and the formation of sandy shorelines.
Wave Height and Impact: The height of the waves can vary widely, from small ripples to massive waves reaching heights of tens of meters during cyclone or strom. Large waves can have a significant impact on coastal erosion, shipping and coastal settelment.
Wave Forecasting: Predicting wave behaviour is crucial for various maritime activities, including navigation, fishing and offshore engineering. Using the data of wind patterns, ocean currents, and atmospheric conditions to predict wave conditions.
2. Tides:
Tides are the periodic or regular rising and falling of Earth's ocean waters, Primarily caused by tidal bulges means the gravitational pull of Moon and Sun on Earth's oceans, as well as the rotation of Earth.
Tpes of tides:
A. High Tide:
When the sea level is at its highest point. Happens twice daily, about 12 hours apart. Its timing and height vary by location and lunar phase.
B. Low Tide : Low tide is when the water level reaches its lowest point during a tidal cycle. Like high tide, low tide occurs about twice a day. When it's low tide, more of the shoreline is exposed, and in some areas, it can reveal intertidal zones or tidal flats that are normally underwater.
The daily rise and fall of tides, there are monthly variations called spring tides and neap tides:
Spring Tides: Occur during the time of around new and full moons when Sun and Moon align, causing higher tidal differences( high tides and lower low tides).
Neap Tides: Happen during the time of first and third quarters positions of the moon when the Sun and Moon are at right angles, leading to the lesser tidal differences.
3. Ocean currents:
Ocean currents are continuous, directed movements of water bodies in the oceans. These currents redistributing heat around the globe, influencing weather patterns and support marine life.
Types of ocean currents:
A. Surface Currents:
These currents are driven by winds and Earth's rotation, they flow in 100–200 meters tops of the ocean. They affect weather and navigation. Examples: Gulf Stream, California Current and Kuroshio Current.
B. Deep Ocean Currents:
Also called thermohaline currents, they are driven by differences in water temperature and salinity. These are slow-moving flows redistribute heat and nutrients worldwide. Examples: North Atlantic Deep Water (NADW), Antarctic Bottom Water (AABW).
Important effects and influences of ocean currents :
- Climate: Currents move warm water poleward and cold water toward the equator, regulating climate.
- Weather : Surface currents shift heat and moisture, which influence the local weather patterns like temperature and precipitation.
- Ecosystems: Currents distribute nutrients and plankton essential for marine food chains.
- Navigation: Used historically and today to improve travel and shipping.
- Environment: Changes in currents directions can alter spread pollutants from one place to another, also sea levels.
4.Tsunamis :
These are massive ocean waves generated due to disturbances beneath the water surface. They're often referred to as 'tidal waves".
Causes:
-Earthquakes (most common)
-Volcanic eruptions
-Landslides
-Meteorite impacts (rare)
Wave Characteristics: Tsunamis have long wavelengths and travel fast up to 800 km/h. Though not tall at ocean or deep water, As they reach shallow areas, their energy compresses, raising wave height and causing flooding.
Amplification Near Coasts: As tsunamis approach shallower coastal areas, their energy is compressed, they grow dramatically near coastlines.Which causes sudden and devastating surge of water inundating coastal regions.
Warning Systems: Many regions have systems using seismic data, buoys, and models to detect tsunamis. Early warnings help save lives.
Historical Impact: Examples include the 2004 Indian Ocean tsunami and the 2011 Japan tsunami, both causing widespread damage and loss of life.
Preparedness: Coastal communities may have evacuation plans, public education, and stronger buildings. Barriers and land-use planning also help reduce damage.
Mitigation:To reduce tsunami damage, measures such as stricter building standards for coastal areas, the creation of barriers and seawalls, and careful planning to avoid construction in vulnerable zones are often put in place
Erosional Landforms:
1. Wave-Cut Platforms:
It's a Flat or gently sloping, rocky surfaces at the base of cliffs formed by wave erosion. Also reffered as wave cut bench or shore platform.They result from abrasion, hydraulic action, and corrosion, especially in rocky coasts.
2. Sea Caves:
Formed when waves erode weak points in coastal rock, often along cliffs and headlands. Sizes and shapes vary depending on wave strength and rock type.
3. Sea Cliffs:The vertical or Steep rock faces along coastlines formed by wave erosion. Their height and structure depend on the geology of the area, which gradually wear away the base of the landmass over time.
Depositional Landforms:
Coastal depositional landforms develop when sand, gravel, or clay gradually settle and build up along the shore. It Happens through the ongoing movement of waves, the pull of currents, the rise and fall of tides, the push of wind and the flow of rivers, all working together to shape the coastline naturally.
some common types of depositional landforms:
1. Beaches:
They are gently sloping areas of sand or pebbles, sometimes clay deposition by waves and tides. Beaches differ in shape and size and are commonly used for recreation
2. Barrier Island:
Barrier islands are long, narrow, and low-lying sandy islands that run parallel to the coastline. It is located away from the landforms by lagoon, bay or tidal flat.
3.Spit: It is a thin, stretched strip of sand or gravel that grows out from the shore into the water. It takes shape as longshore currents carry and drop sediments along the edge, gradually building it outward.
4.Tombolo: It is a connection between mainland and island, when currents slows down near of these two areas and deposited sediments like a natural bridge.
5. Barrier Spit: It's a hooked shaped sand formation, which enclosed lagoon or bay. These usually take shape where mouth of the rivers meets oceans.
6. Sand Dune: Sand dunes are mounds or ridges of sand that develop along the coast in areas with sufficient sand and vegetation to trap and stabilize the sand, which formed by the wind.
7. Delta: It is forms at the river mouth where freshwater meets oceans. When flow slows, and the river begins to drop the sediment just like a triangualar or fan shaped with countless distributary channel.
8. Salt Marshes :Salt marshes are low-lying coastal areas where fine mud, silt, and clay settle in calm, shallow waters. These areas are often found behind barrier islands or along estuaries. They’re important for both wildlife and water quality.
9. Estuaries : Where rivers and sea meet also mixes frehwater and salt water of seas. It's partially enclosed water bodies ,which makes it different from the delta.
10. Lagoons: Lagoons are shallow bodies of water that develop in the calm areas situated behind spits, sandbars or barrier islands. Usually water are salty or brackish.
Conclusion :
Coastal morphology focuses on the features found where land meets the sea and the forces that shape them. These areas are constantly changing due to natural activity like waves, tides, currents, and rising sea levels, along with human influence. The result is a variety of coastal landforms—some carved away by erosion, others built up through deposition.
