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Destructive Waves• Created in storm conditions.• Big, strong waves from powerful, consistent wind• High wave energy from travelling over a long fetch.• Erode the coast.• Stronger backwash than swash.• Short wavelength and high + steep.
Constructive Waves• Calm weather + less powerful• Deposit material, building up beaches.• Swash is stronger than the backwash.• Long wavelength and are low in height.
How to spot a rip channel Head ofRip channels Rip channel (as seen from beach) Rip channel(as seen from the air) Note: a rip current is different from undertow
Coastal Deposition• When the sea loses energy, it drops the sand, rock particles and pebbles it has been carrying. – when the swash is stronger than the backwash – waves enter an area of shallow water – waves enter a sheltered area, eg a cove or bay. – there is little wind – there is a good supply of material.
Formation of Wave-Cut Platform1. Weather weakens the top of the cliff.2. The sea attacks the base of the cliff forming a wave-cut notch.3. The notch increases in size causing the cliff to collapse.4. The backwash carries the rubble towards the sea forming a wave-cut platform.5. The process repeats and the cliff continues to retreat
Refraction of Waves• Coastlines are rarely straight• Waves bend when there is a change in its speed• What changes speed of waves? – What causes a wave to slow down? • Change in depth (or shallowness)
Depositional Landforms• Beaches – Constructive waves – Larger sediments can be carried further up the beach during storms – Smallest sediments near the water
Depositional Landforms• Spit – Longshore drift moves material along the coastline. – material is deposited and extends from mainland. – grows and develops a hook if wind direction changes – creates a sheltered area where silt is deposited and mud flats or salt marshes form.
Depositional Landforms• Tombolo – a spit connecting an island to the mainland.
Types of Coastlines• It is difficult to categorize coastlines.• The form of a coast is a result of the interactions of four factors: – 1) any abrupt change in sea-level, – 2) the amount of sediment supplied to the coast by rivers, – 3) the movement of that sediment upon its arrival at the coast by oceanic processes, and – 4) whether tides or waves are most effective in moving the sediment.
Types of Coastlines• Emergent • Submergent – Raised coastline – Sunken coastline • Why? • Why? – Drop in sea level – Rise in sea level • Rias: flooded river valleys • Fjords: flooded glacial troughs • Estuaries: flooded river delta
Types of Coastlines• Concordant • Disconcordant • think “Cordillera” – Alternating ridges of – Alternating ridges of hard and soft rock hard and soft bedrock perpendicular to aligned parallel to coastline coastline – Headlands and bays – If water breaks through a weak point in the hard ridge, soft rock behind erodes to form coves – Dalmatian Coast, Croatia
Coral Reefs•Reefs are natural structures of rockformed by marine animals.•Today’s reefs are largely made bycorals, but in the geological past,have been constructed by spongesand bizarre clams.•Reef-building organisms buildskeletons of calcium carbonate inthe form of aragonite or calcite. Great Barrier Reef, Australia
Coral polyps(individual coral animals)Coral reefs are often called the “rainforests of the sea” due to thegreat diversity of creatures that form them. Note that the brilliantcolours apparent in corals are from the microscopic algae in the coraltissues (different colours absorb different wavelengths of light)
Conditions necessary for reef development•Large reefs are limited to the warm seawater areas ofthe tropics.•Calcium carbonate is easier to precipitate in warm waterthan in cold water.•Secretion of calcium carbonate is aided by microscopiccells of algae that live in the tissues of reef builders (thealgae remove carbon dioxide from the tissues, decreasingthe acidity of the water).
Conditions necessary for reef developmentReefs also tend to preferentially form in areas where:1. Little clastic sediment occurs (such sediment particles smother reef builders).2. Nutrient levels are low.3. Water is shallow
Reef zonesReef builders are zoned in a reef according to their form(encrusting forms tend to dominate the reef crest wherewave action is strongest, while more delicate branchingforms are confined to deeper water zones where water actionis more gentle) A lagoon can develop behind a reef, where it is protected from strong waves
A special kind of reef: atoll • An atoll is a special kind of reef that is ring-shaped and has a central lagoon.
How an Atoll Forms• An atoll is formed first as a reef that fringes a volcanic island.• As the island sinks (after volcanic activity has ceased and the crust has cooled, becoming denser), the reef continues to build upward, eventuallyGilligan’s Island ? as a ending up ring-shaped structure.