Marine Processes Wave Terminology
• Crest: The top of the wave.
Trough: The low area in between two waves.
Wavelength: The distance between two crests or two troughs.
Wave height: The distance between the crest and the trough.
Wave Frequency: The number of waves per minute.
Velocity: The speed that a wave is traveling. It is influenced by the wind, fetch (distance / open water) and depth of water.
Swash: The movement of water and load up the beach.
Backwash: The movement of water and load back down the beach. Why are there waves?
• Wind blowes over the ocean / lake … the friction causes waves to form • In deep ocean waves move up and down because water particles move in a circular motion • Waves break in shallow water because they can not move in circular motion • Some waves are strong (high / fast) because they have been driven (caused) by strong winds over a long distance (fetch).
Different types of waves
• Sediment is deposited • Sediment is taken away • I.e. construction of beach • i.e. erosion takes place Marine Erosion
• Hydraulic action • Water and rocks rub against each other causing friction • Friction breaks away particles • Corrasion / Abrasion • Rocks rub against each other causing friction • Friction breaks away particles • Corrosion / Solution • Rocks are dissolved in the water e.g. Limesone • Attrition • Rocks bang against each other causing them to break appart Erosional Landforms
• Cliffs • steep section of coast line (e.g. near Taormina) • Wave-cut platform • flat area in front of a cliff, formed through erosion by high tide vs. low tide • Cliff recession • The cliff moves in land as it gets eroded Erosional Landforms
• Headlands • Part of the land that sticks out into the ocean (e.g. headlands of Augusta and Syracusa) • Bays • Where the land curves inwards (e.g. Bay of Catania) Erosional Landforms
• Caves • Arches • Stacks Marine Transport – Longshore drift
• Waves come from South-East (bottom right), i.e. where the wind comes from the swash moves up the beach in this direction and pushes the sand up • The backwash follows gravity and moves the sand down verticaly • Results in sediment transport along the shore
Effects of groynes • Groynes are build perpendicular into the sea • they stop longshore drift / beach erosion
https://www.youtube.com/watch?v=U9EhVa4MmEs
Coastal Deposition
• Sorting of beach material Depositional Landforms
• Beach • Sand or shingle deposits between low and high water mark • Shingle forms a steep slope (San Giovanni Li Cuti) • Sand forms a gentle slope (Plaja)
Depositional Landforms
• Spit • Long, narrow, low ridge of sand or shingle deposited at bends of the coast • Grow from headland across bay or river mouth • i.e. they are attached to main land on one side
Depositional Landforms
• Bar • Like a spit but attached to the land on both sides • Encloses lagoon behind it
Depositional Landforms
• Salt Marsh • Forms behind spits and bars • Combination of mud flats and grass (salt tolerant) • Under water at high tide, exposed at low tide • Water flows along it through “tidal creeks
Depositional Landforms
• Tombolo • A bar that connects the mainland with an island
Depositional Landforms
• Barrier Island • Small islands, parallel to the coast the have a small lagoon behind it
Depositional Landforms
• Sand Dunes • Ridges of sand formed at the back of beaches and on spits by wind deposition • Ridges are moved inland because of onshore wind • New “embryo” dunes are formed near the beach • Marram grass stabelises the dunes and prevents the sand from being blown away • If the grass is desroyed “blow outs” can occur