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Coastal Processes and Landforms

This document discusses various coastal landforms and processes. It describes how waves, currents, erosion and deposition shape coastlines. Key points include: - Waves erode cliffs and platforms while deposition builds beaches, spits and bars. - Longshore drift transports sediment parallel to the shore, while rip currents carry it seaward. - Refraction of waves around headlands forms bays. Erosion of headlands produces arches, stacks and tunnels. - Coral reefs develop in warm, tropical waters where calcium carbonate precipitation exceeds dissolution. Atolls form as islands submerge, leaving ring-shaped reef structures.

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Coastal Processes and Landforms
Wind and Waves • Fetch – the amount of open water influenced by wind • Swell – larger waves caused by storms out to sea
Evidence of the power of wind
Trees learn to grow with the wind
Coastal Zones • A beach is part of a coastal system, which includes several zones defined by their proximity to shore and the dominant processes that occur within them.
Features of Waves • Crest • Trough • Wavelength
Speed of a wave • Speed = Wavelength Period • Period: time it takes a wavelength to pass a given location
Formation of Breakers
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.
Swash • Water moving up the beach
Backwash • Water running back down the beach under the next wave • Gravity • Strong = undertow
Destructive wave action Patong Beach, Thailand Berm formed after intense rain storm.
Surf Zone
Bigger Surf Zone
4 Coastal Erosion Processes
How is sediment transported along a coastline ? • Most waves move toward the shore at a slight angle. • Water (swash) from each breaking wave is oblique.
Shoreline Currents • Most waves strike shorelines at angles • Swash washes ashore diagonally • Backwash go straight back down • Sediments are carried by longshore drift
Rip Currents • Strong surface currents that flow away from the beach • Too much water converges at the shore • 2 longshore currents meet
La Jolla, San Diego, USA
Wickaninnish Beach, Tofino, BC
Rip Currents and Longshore Drift
How to spot a rip channel Head of Rip 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 Platform 1. 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)
Headlands and Bays
El Arco
El Arco, Cabo San Lucas, Mexico
Arches from wave erosion • Headland is attacked by waves • Hydraulic pressure and abrasion
Early stage of an arch in Oregon
Sea Stacks
Haystack Rock, Cannon Beach, OR
Headlands and Sea Stacks
Arch
Ocean Geyser
Spouting Horn
Lagoon
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.
Crescent Beach, White Rock, BC
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
Sydney, Australia
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
Dalmatian Coast, Croatia
Duddle Door, Dorset, England
Coral Reefs •Reefs are natural structures of rock formed by marine animals. •Today’s reefs are largely made by corals, but in the geological past, have been constructed by sponges and bizarre clams. •Reef-building organisms build skeletons of calcium carbonate in the 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 the great diversity of creatures that form them. Note that the brilliant colours apparent in corals are from the microscopic algae in the coral tissues (different colours absorb different wavelengths of light)
Conditions necessary for reef development •Large reefs are limited to the warm seawater areas of the tropics. •Calcium carbonate is easier to precipitate in warm water than in cold water. •Secretion of calcium carbonate is aided by microscopic cells of algae that live in the tissues of reef builders (the algae remove carbon dioxide from the tissues, decreasing the acidity of the water).
Conditions necessary for reef development Reefs 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 zones Reef builders are zoned in a reef according to their form (encrusting forms tend to dominate the reef crest where wave action is strongest, while more delicate branching forms are confined to deeper water zones where water action is 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.
Coastal Processes and Landforms