coasts
Created | Updated Feb 12, 2004
The coast is the area influenced by maritime processes and by humans in pursuit of a livelihood.
waves
· waves are responsible for most of the erosion along coasts.
· waves can move material along the shore by longshore drift.
· the amount of energy in waves depends on their height and length, which are affected by: wind speed, wind duration and fetch (distance the wave has travelled across the sea).
waves can be constructive or destructive:
constructive: they operate in calm weather and are about a metre high. The swash is strong and erosion is limited. They are involved with the transport and deposition of material creating landforms.
destructive: they operate in storm conditions and are high in proportion to their length, 5-6 metres. The backwash is strong and there is a lot of erosion.
Processes of Coastal Erosion:
· Hydraulic Action- wave pounding, greatest effect under storm conditions. Remember, one cubic metre of water weighs one tonne.
· Abrasion- sand and pebbles break off pieces of rock and cause undercutting.
· Attrition- rock fragments grind each other down into small pebbles, which are easily carried away by waves and later deposited on beaches.
· Solution- chemical action on rocks by sea water.
Coastal Transport
· Traction- large boulders rolled along the seabed.
· Saltation- smaller boulders bounced along.
· Sand grains are carried in suspension.
· Limestone and lime from chalk is dissolved and carried in solution.
Coastal Landforms from Deposition
Spits are long beaches formed by longshore drift.
· Longshore drift happens when waves break at an oblique angle to the coast due to a prevailing wind. Thus, each wave pushes material up the beach a bit more.
· Spits are sand or pebble beaches sticking out to sea, but joined to the land at one end.
· Spits tend to be formed across river mouths; where the coast suddenly changes direction; where tides meet calmer waters of a bay or inlet.
· At the spit end are usually some hooks or recurves formed by occasional strong winds from another direction.
· Waves can’t reach the sea areas behind the spit, so they’re often mud flats and salt marshes.
· A spit that joins an island to the mainland is a tombolo, e.g. Chesil Beach, joining the Isle of Portland to the south coast.
· A spit that extends right across a bay is called a barrier beach.
Beaches are formed by deposition.
· Beaches are found on coastlines where eroded material in the sea has been deposited.
· Beach fragment size depends on local rock type and wave energy e.g. fine sand at Blackpool, or pebbles at Hastings.
Coastal Landforms from Erosion
Rock Erosion forms Cliffs.
· Waves erode rocks along the shoreline by hydraulic action, solution and abrasion
· A notch forms at the high water mark, which then becomes a cave.
· Rock above the notch becomes weak and unstable and collapses.
· The coastline begins to retreat, and over many years, a wave cut platform is formed.
Eroded hard and soft rock form Headlands.
· If there are alternate bands of hard and soft rock in the coastline, the harder rocks take longer to erode, because the sea has less effect.
· The hard rock will be left jutting out forming one or more headlands.
· The softer rock will be eroded to form bays, creating room for a beach to form.
· The local geology will affect the shape and size of the features formed.
Caves, Arches, Stacks and Stumps.
· There must be a weakness in the rock for this process to operate, which is then eroded to form a cave.
· Further erosion enlarges the cave and it breaks through the headland forming an arch.
· The roof of the arch is often unstable and collapses, leaving a stack, or a series of stacks.
· When a stack is weathered, or eroded, it collapses and becomes much shorter, a stump.
coastal management
· paths- popular to walk on so they have to be managed. If paths are eroded, people won't walk on them, but will walk on grass, thus causing erosion of the soil.
· beaches- sand constantly deposited and washed away by waves. Any interruption in the replenishing of sand caused by human features such as rock groynes (which stop the process of sand moving up the coastline to build up beaches), threaten the existence of beaches further down the coast.
waves
· waves are responsible for most of the erosion along coasts.
· waves can move material along the shore by longshore drift.
· the amount of energy in waves depends on their height and length, which are affected by: wind speed, wind duration and fetch (distance the wave has travelled across the sea).
waves can be constructive or destructive:
constructive: they operate in calm weather and are about a metre high. The swash is strong and erosion is limited. They are involved with the transport and deposition of material creating landforms.
destructive: they operate in storm conditions and are high in proportion to their length, 5-6 metres. The backwash is strong and there is a lot of erosion.
Processes of Coastal Erosion:
· Hydraulic Action- wave pounding, greatest effect under storm conditions. Remember, one cubic metre of water weighs one tonne.
· Abrasion- sand and pebbles break off pieces of rock and cause undercutting.
· Attrition- rock fragments grind each other down into small pebbles, which are easily carried away by waves and later deposited on beaches.
· Solution- chemical action on rocks by sea water.
Coastal Transport
· Traction- large boulders rolled along the seabed.
· Saltation- smaller boulders bounced along.
· Sand grains are carried in suspension.
· Limestone and lime from chalk is dissolved and carried in solution.
Coastal Landforms from Deposition
Spits are long beaches formed by longshore drift.
· Longshore drift happens when waves break at an oblique angle to the coast due to a prevailing wind. Thus, each wave pushes material up the beach a bit more.
· Spits are sand or pebble beaches sticking out to sea, but joined to the land at one end.
· Spits tend to be formed across river mouths; where the coast suddenly changes direction; where tides meet calmer waters of a bay or inlet.
· At the spit end are usually some hooks or recurves formed by occasional strong winds from another direction.
· Waves can’t reach the sea areas behind the spit, so they’re often mud flats and salt marshes.
· A spit that joins an island to the mainland is a tombolo, e.g. Chesil Beach, joining the Isle of Portland to the south coast.
· A spit that extends right across a bay is called a barrier beach.
Beaches are formed by deposition.
· Beaches are found on coastlines where eroded material in the sea has been deposited.
· Beach fragment size depends on local rock type and wave energy e.g. fine sand at Blackpool, or pebbles at Hastings.
Coastal Landforms from Erosion
Rock Erosion forms Cliffs.
· Waves erode rocks along the shoreline by hydraulic action, solution and abrasion
· A notch forms at the high water mark, which then becomes a cave.
· Rock above the notch becomes weak and unstable and collapses.
· The coastline begins to retreat, and over many years, a wave cut platform is formed.
Eroded hard and soft rock form Headlands.
· If there are alternate bands of hard and soft rock in the coastline, the harder rocks take longer to erode, because the sea has less effect.
· The hard rock will be left jutting out forming one or more headlands.
· The softer rock will be eroded to form bays, creating room for a beach to form.
· The local geology will affect the shape and size of the features formed.
Caves, Arches, Stacks and Stumps.
· There must be a weakness in the rock for this process to operate, which is then eroded to form a cave.
· Further erosion enlarges the cave and it breaks through the headland forming an arch.
· The roof of the arch is often unstable and collapses, leaving a stack, or a series of stacks.
· When a stack is weathered, or eroded, it collapses and becomes much shorter, a stump.
coastal management
· paths- popular to walk on so they have to be managed. If paths are eroded, people won't walk on them, but will walk on grass, thus causing erosion of the soil.
· beaches- sand constantly deposited and washed away by waves. Any interruption in the replenishing of sand caused by human features such as rock groynes (which stop the process of sand moving up the coastline to build up beaches), threaten the existence of beaches further down the coast.
