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

• I.e. construction of beach

• Sediment is taken away

• 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