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WHAT IS A WAVE?. This is the movement of water surface caused by the energy of the wind moving over open stretch of water. WHAT ARE THE PARTS OF A WAVE?. Crest-This is the curved part of the wave. Trough( Trof )-This is the bottom of the wave, the lowest part of the wave.
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WHAT IS A WAVE? • This is the movement of water surface caused by the energy of the wind moving over open stretch of water.
WHAT ARE THE PARTS OF A WAVE? • Crest-This is the curved part of the wave. • Trough(Trof)-This is the bottom of the wave, the lowest part of the wave. • Wave height-This is the distance from the crest to the trough. • Wave length-This is the length from one crest to the other crest.
Features of a coast • The coast line-this is where the land meets the sea. • The Coast-is a zone or strip of land extending from the coastline, which borders the sea to where the land rises inland. Its limit is marked by the level of high water. • The shore-the area which lies in between the low watermark and the high watermark. • The back shore-the zone of land between the mean high tide level and the coastline • The foreshore-the zone of land between the low and high watermark
Wave Processes • Attrition-is the process by which rock fragments are broken up along the coast by impact or by striking against each other. • Hydraulic Action-this occurs when the waves smash against the bases of cliffs or headlands(pieces of land which extend out to the sea) . The small pockets or crevices are filled with air which becomes compressed. When the wave retreats the air pockets expand. This process of repeated compression and expansion of the air causes the rock to eventually break up and shatter. • Corrasion or Abrasion –where materials in the water, such as rocks, pebbles and sand are hurled against the coast, eroding its surface.
TYPES OF WAVES • Destructive waves are waves which approach the shore between 12-14 times per minute. They have short wave lengths, as the swash of one meets the backwash of the previous wave causing a vertical movement of water. The backwash is strong and the swash is weak. Materials are swept towards the sea in the process. Waves move forward with a steep plunge on top of the beach. Sediments(small pieces of rocks) are scoured and pulled away.
Features formed by destructive waves. • Some features formed by destructive waves: • Cliffs , Arches , Stacks , Stumps • Blowholes • Caves
Constructive waves are waves which approach the shore 7 times per minute or 10 seconds per wave. The waves are widely spaced. Swash is strong where as the backwash is weak. The slower-moving backwash completes its retreating movement without interference from the up rushing swash. Materials are transported up the beach. Depositional features are formed as sediments are pushed up the beach. Constructive waves form beaches.
Features formed by constructive waves • Features formed by constructive waves are: • Beaches • Spits • Bars • Mudflats • Tombolos • Sand dunes (not commonly found in Grenada )
FEATURES FORMED BY MARINE DEPOSITION • Marine deposition forms different features which include beaches, spits and bars, mud flats and tombolos. Waves deposit materials such as sand and pebbles along the beach. These are continuously moved sideways up the beach by the swash and deposited on the shore.
FEATURES FORMED BY MARINE DEPOSITION • A BEACH-is an accumulation of materials such as boulders, pebbles, shingle, sand and mud on a sloping or shelving ground. The waves which break offshore result in its erosive power decreasing.
FEATURES FORMED BY MARINE DEPOSITION • A Spit-is a long narrow projection of sand and shingle or pebbles connecting the land at one end with the other terminating in the sea. There is a special type of spit called a tombolo. This is where sand from the coast links an offshore island to the mainland.
FEATURES FORMED BY MARINE DEPOSITION • A bar-is a ridge of sand, mud or shingle deposited by waves and currents. A bar is formed by longshore drift, which is the movement of the swash and backwash.
FEATURES FORMED BY MARINE DEPOSITION • Mudflats-are low-lying parts of the coast which are submerged at high tide and visible at low tide. They are normally located behind a bar or sandpit, or beside estuaries and are made of slit or clay. They are found in sheltered areas such as bays and lagoons.
FEATURES FORMED BY MARINE DEPOSITION • Sand dunes-some sea shores consist of ridges of sand deposited by waves and shaped by the wind. These are termed sand dunes. They are confined to coastal areas which are low-lying and are above high tide level.
Cliffs are formed by corrasion and hydraulic action which assist in cliff formation. Erosion is confined between high and low tide and is influenced by the rock layers and joints, and the strength of the waves. The cliff is undercut by wave action, causing it to recede until, eventually, it collapses. Landslips occur when the rocks dip seaward, and overhanging cliffs are formed when the rocks dip landwards.
Headlands are alternating beds of hard and soft rocks, the hard rocks offer a greater degree of resistance to erosion. They eventually stand out as headlands, an extension of land with steep cliff sides projecting out into the sea. A cape is also a headland which juts out into the sea. The softer rocks are easily eroded as they are less resistant to marine erosion. In due course a curve is then formed and is called a bay.
Coves are where waves attack weaknesses in rocks, breaching them by cutting inlets( a narrow body of water between islands or leading inland from a larger body of water).They erode further inland into the less resistant rock strata to form a circular bay with a narrow entrance. This is known as a cove.
Wave-cut shore or platform are slopes which descend into deep water and a notch or niche is cut between the high and low tide level. The base is undermined, often resulting in the upper part collapsing. It slopes gently on its seaward side. Shingles form the main abrasive agent.
Blow holes are lines of weakness at the base of cliffs such as joints or fissures which are opened up through the process of corrosion and the hydraulic action of breaking waves. A cave or long narrow tunnel or cavern is thus formed. It extends inland due to continuous wave erosion. These grow inwards and upwards into narrow vertical shafts and expose themselves towards the surface as a blow hole.
Stack is a resistant pillar of rock from the arch left standing in the sea, it was formerly part of a headland.
Arches are formed when caves on both sides of a narrow headland are eroded or tunnelled through.
Process of coastal deposition. • Longshore drift: This is the movement the wave.Waves deposit material such as sand and pebbles along the beach. The materials are continuously moved sideways up the beach by the wave and deposited. The materials are then dragged back down at right angles to the shore by the wave. • Groynes are put in place to reduce the effect of longshore drift by and slowing down the movement of longshore drift
