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11.0. The Sea. 11.1. Ireland’s Coastline. The more sheltered east coast. The west coast , exposed to the full force of the Atlantic Ocean. Ireland has a varied coastline. A basic difference can be seen between:. 11.2. Coastal Processes.
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11.0 The Sea
11.1 Ireland’s Coastline The more sheltered east coast. The west coast, exposed to the full force of the Atlantic Ocean Ireland has a varied coastline. A basic difference can be seen between:
11.2 Coastal Processes The sea is constantly shaping our coastline. Waves are eroding, depositing and transporting material along the coast. Hydraulic action Waves erode by: The power of water as it crashes against the coast.
11.2 Coastal Processes The sea is constantly shaping our coastline. Waves are eroding, depositing and transporting material along the coast. Abrasion Waves erode by: Waves pick up stones and throw them against the coast. These stones abrade the coast.
11.2 Coastal Processes The sea is constantly shaping our coastline. Waves are eroding, depositing and transporting material along the coast. Compressed air Waves erode by: Air in rocks becomes trapped by the incoming waves. The trapped air puts pressure on the rocks. When the water retreats, the air expands and the pressure drops. This repeated process causes the rock to shatter.
11.2 Coastal Processes The sea is constantly shaping our coastline. Waves are eroding, depositing and transporting material along the coast. Attrition Waves erode by: Stones carried by the waves hit off each other. Over time they are worn down and smoothed.
11.2 Coastal Processes The sea is constantly shaping our coastline. Waves are eroding, depositing and transporting material along the coast. Solution Waves erode by: Certain rocks, such as limestone, are dissolved by the water.
11.3 Features of Sea Erosion Headlands and Bays Hard rock Soft rock Differential erosion Headland Bay 1 2 3 Wave attack Bays and headlands are formed on coastlines where an area of soft rock is eroded more quickly than the hard rock in the headland. This is known as differentialerosion. 1
11.3 Features of Sea Erosion Headlands and Bays Hard rock Soft rock Differential erosion Headland Bay 1 2 3 Wave attack Soft rock, such as sandstone, is more easily eroded and begins to form a hollow in the coast known as a bay. 2
11.3 Features of Sea Erosion Headlands and Bays Hard rock Soft rock Differential erosion Headland Bay 1 2 3 Wave attack The area of hard rock, such as granite, is left jutting out on either side into the sea. This is called the headland. 3
11.3 Features of Sea Erosion Sea Cliff Cliffs of Moher Examples can be seen at the Cliffs of Moher,Co. Clare, and at Howth Head, Co. Dublin.
11.3 Features of Sea Erosion Sea Cliff – Formation Waves erode a notch at the base of the cliff by hydraulic action, abrasion and compressed air. 1
11.3 Features of Sea Erosion Sea Cliff – Formation When the notch becomes large enough, the overhanging rock collapses under its own weight. 2
11.3 Features of Sea Erosion Sea Cliff – Formation 3 A sea cliff has then been formed.
11.3 Features of Sea Erosion Sea Cliff – Formation The notch continues to erode; so, the cliff continues to retreat slowly into the coast. As the cliff retreats, an almost flat, rocky area is created on the shore. This is called a wave-cut platform. The wave-cut platform is usually visible at low tide. 4
11.3 Features of Sea Erosion Sea Cave, Arch, Stack and Stump Strong waves attack cracks and weakness in the base of a cliff. Through hydraulic action, abrasion and compressed air, they erode a large hole at the foot of the cliff. 1
11.3 Features of Sea Erosion Sea Cave, Arch, Stack and Stump 2 This continues over thousands of years. The hole is known as a sea cave.
11.3 Features of Sea Erosion Sea Cave, Arch, Stack and Stump If a sea cave erodes all the way through the headland (or if two caves erode back to back), a sea arch will form. This is an archway straight through the headland. 3
11.3 Features of Sea Erosion Sea Cave, Arch, Stack and Stump If the roof of the arch collapses, a pillar of rock will remain standing alone in the sea. This pillar is known as a sea stack. 4
11.3 Features of Sea Erosion Sea Cave, Arch, Stack and Stump If over time the sea stack collapse into the sea, all that remains is a small stump of rock. This is known as a sea stump. 5
11.3 Features of Sea Erosion Blowhole A blowhole is a passage that goes through the roof of a cave to the land surface above. Blowholes are formed when waves compress air that breaks a hole through the roof of the cave.
11.4 Transport by the Sea Material carried by the sea (sand, silt, mud, pebbles) is known as its load. 1 Waves approach the shore from the side.
11.4 Transport by the Sea Material carried by the sea (sand, silt, mud, pebbles) is known as its load. 2 The swash pushes the material up the beach at an angle.
11.4 Transport by the Sea Material carried by the sea (sand, silt, mud, pebbles) is known as its load. 3 The backwash drags the material back down the beach at a right angle.
11.4 Transport by the Sea Material carried by the sea (sand, silt, mud, pebbles) is known as its load. 4 As the processes repeat, the material is moved in a zig-zag pattern along the shore.
11.5 Features of Sea Deposition Beach A beach is a gently sloping area of sand, shingle or stones that is found between the high and low tide levels. It is formed by the swash and backwash movements of the waves.
11.5 Features of Sea Deposition Beach – Formation 1 When waves break, they lose their energy and drop the load they were carrying. The swash carries this material up the shore and deposits it.
11.5 Features of Sea Deposition Beach – Formation 2 Backwash is weaker than swash; so, it is unable to carry all of the deposited material back out.
11.5 Features of Sea Deposition Beach – Formation 3 The heaviest material is deposited first. The finer material is carried closer to the shoreline.
11.5 Features of Sea Deposition Beach – Formation 4 Over time, this material builds up to form a beach.
11.5 Features of Sea Deposition Beach – Formation 5 In times of storm, the waves are stronger and are able to carry heavier material further up the shoreline to the high-tide mark. This material is then deposited and creates a storm beach.
11.5 Features of Sea Deposition Sand Dunes Sand dunes are mounds of sand that build up on the shore beyond the high-tide mark at the back of the beach. 1 Sand on the beach is dried by the wind.
11.5 Features of Sea Deposition Sand Dunes Sand dunes are mounds of sand that build up on the shore beyond the high-tide mark at the back of the beach. 2 Dry sand is lighter; so, the wind can then blow it inland.
11.5 Features of Sea Deposition Sand Dunes Sand dunes are mounds of sand that build up on the shore beyond the high-tide mark at the back of the beach. 3 The sand becomes trapped by vegetation or other barriers.
11.5 Features of Sea Deposition Sand Dunes Sand dunes are mounds of sand that build up on the shore beyond the high-tide mark at the back of the beach. 4 It then builds up to form sand dunes.
11.5 Features of Sea Deposition Sand Dunes Sand dunes are mounds of sand that build up on the shore beyond the high-tide mark at the back of the beach. Marram grass is sometimes planted on sand dunes to stop the sand blowing further inland. Marram grass has deep roots and is a thick, coarse grass that is resistant to salt. 5
11.5 Features of Sea Deposition Sand Spit A sand spit is a narrow ridge of sand or shingle that is connected to the land on one end and juts out to sea at the other. Sand spit Attribution: Roger Cornfoot
11.5 Features of Sea Deposition Sand Spit – Formation 1 Longshore drift loses energy when it is interrupted by a sheltered bay.
11.5 Features of Sea Deposition Sand Spit – Formation 2 The material carried by longshore drift is then deposited.
11.5 Features of Sea Deposition Sand Spit – Formation 3 These deposits build up over time to gradually form a spit.
11.5 Features of Sea Deposition Sand Spit – Formation 4 The spit extends across the bay. As it increases in size, vegetation grows on it.
11.5 Features of Sea Deposition Sand Bar A sand bar is a narrow ridge of sand or shingle that seals off the mouth of a bay. A spit can grow in size until it completely seals off a bay. A lagoon is a small lake that is formed behind the sand bar.
11.5 Features of Sea Deposition Tombolo A tombolo is a narrow ridge of sand or shingle that joins an offshore island to the mainland. A spit can grow in length until it reaches a nearby island. The spit is then known as a tombolo. Tombolo
11.6 People and the Sea Humans have put measures in place to protect their coasts from the powerful processes of sea erosion. Groyne Gabion Sea wall
11.6 People and the Sea Groynes are concrete or wooden walls or fences that are built out into the sea at right angles to the coast. They reduce longshore drift by trapping the sediment carried by waves. They trap the sand, which then builds up the level of the beach. Groyne
11.6 People and the Sea Sea walls are built to break the power of the incoming waves. They are curved at the top to push the waves back out to sea. Sea wall
11.6 People and the Sea Gabions are steel wire cages filled with stones. They are then stacked on top of each other where they act like a sea wall. They are used to slow down or prevent erosion by breaking the power of the waves. An example can be seen at Lahinch, Co. Clare. Gabion
11.7 Coastal Management Case Study: North Bull Island, Co. Dublin North Bull Island is located in Dublin Bay. It exists as a result of coastal decisions made over 200 years ago. In the early nineteenth century, longshore drift was carrying large amounts of sand and silt into Dublin Bay. The deposits were partially blocking the mouth of the harbour, making it difficult for ships to enter.
11.7 Coastal Management Case Study: North Bull Island, Co. Dublin After a survey, it was decided that walls would be built on both sides of Dublin Harbour. The north wall was completed in 1821. Longshore drift now deposited material behind the North Bull wall. This helped to build a large sand spit, which developed into North Bull Island.
