Lecture on Coastal Landforms COASTAL LANDFORMS wave length

Lecture on Coastal Landforms

COASTAL LANDFORMS wave length wave height crest trough particles in waves follow a circular pattern

At the shoreline • Water becomes shallow, wave height increases because wave length decreases • Waves become steeper, then collapse (breakers)

• Surf - sequence of breaking waves • Swash - water sliding up beach • Backwash - water flowing back down beach to sea

Wave refraction • Close to coast, water gets more shallow • Waves are slowed down • If waves arrive at an angle, one part is slower than the rest • Causes waves to bend = wave refraction

Wave refraction Bay Headland

• Waves arriving at bays are slow (deposition) • At headlands, faster (erosion)

• A sequence of features is produced as headlands are degraded • Sea cliffs • Waves erode base undercutting the cliff retreats

• Also produces sea caves • As cliffs retreat produces a wavecut platform

• Headlands may be eroded back leaving a remnant (stack) stack

Longshore drift • Waves arrive at a coast at an angle (swash) • Backwash returns at 90 degrees Sand is moved along the beach = longshore drift or longshore current

Coastal deposition • Result of longshore drift and a lot of sediment • = produces extensions of deposit from the shoreline

spit = curved extension • May grow across a bay (baymouth bar) • May link an island to the main land (tombolo)

TIDES • Daily changes in sea levels • Tides rise (FLOOD) to produce a HIGH TIDE • And fall (EBB) (LOW TIDE) • Produced by the gravitational pull that the Sun and Moon exert on the Earth’s surface (including the oceans) Moon/ Sun

This side is pulled towards the Sun and/or Moon by gravitational attraction This side bulges out because of inertia Therefore, there are two high tides on Earth at any one time

Every 24 hours 50 minutes any point on the Earth rotates through two bulges Each location experiences 2 high (FLOOD) tides and 2 low (EBB) tides

Types of Coastline Submergence and emergence changes coastlines Pocket beaches

Emergent coast • Uplifted land surface • Coastal landforms are found above present sea level a wave-cut platform when elevated uplifted marine terrace

Submergent coast • • Rise in sea level Submergent coast Landforms under water A ria coastline is an example of submergence

Submergence Shorlines • Ria coast - shorline valleys eroded by rivers are submerged – has many offshore islands – exposure to waves erodes islands and headlands • Fiord coast - shoreline valleys created by glaciers are submerged – valleys are deep and straight – because of the depth, there are few beaches

Barrier Island Coasts • Occur on low lying coasts with gentle gradients • BARRIER ISLANDS - low ridges of sand built by waves – behind the islands are lagoons – shallow water with tidal deposits • TIDAL INLETS - gaps between the islands

Delta and Volcano Coasts • DELTA - deposit by rivers entering the sea • Water slows down and spreads out as it enters • Channel divides and subdivides to create DISTRIBUTARIES • Volcano coasts develop in volcanic deposits • Low cliffs form in fresh lava

Coral reefs • Corals build up calcium deposits to produce reefs • To grow, corals need: – Clear, warm, shallow water – Wave action Corbis Digital Stock

Coral reefs • Fringing reef - directly attached to an island or coast • Barrier reef - lagoon between coast and reef • Atoll reef - circular reef surrounding a lagoon (no land in centre)

AEOLIAN (Eolian) LANDSCAPES Wind erosion, transport and deposition Occurs in dry regions, with little vegetation such as deserts and coastal landscapes

Wind Erosion • Faster the air flows, more erosion • Erodes more rapidly if wind blows constantly from one direction • 2 TYPES OF WIND EROSION – ABRASION and DEFLATION

DEFLATION HOLLOWS Removal of fine particles by wind leaves hollows behind (DEFLATION HOLLOWS) Also leaves a surface of closely packed stones (DESERT PAVEMENT)

WIND TRANSPORTATION - Very fine material may be carried in suspension in the air - But larger particles may be moved by 2 methods: SURFACE CREEP & SALTATION

1. ) SURFACE CREEP - material is rolled along the surface - accounts for 20% of wind transport

2. ) SALTATION - The asymmetrical bouncing of sand grains - Accounts for 80% of wind transport - Cause of shifting sand dunes

Aggradational land forms SAND SEAS (ERGS) = only 25% of the world's deserts surface may be covered in RIPPLES

SAND DUNES are ridges of wind deposited sand - Usually 3 to 15 metres high, but can reach 180 metres - A continuously changing dune is ACTIVE Corbis Digital Stock

The formation of dunes depends on: - amount of sand - speed and direction of wind - occurrence of vegetation Corbis Digital Stock

wind direction BACKSLOPE SLIPFACE crest t n e m e v mo d n a of s angle of repose

TYPES OF SAND DUNE 1. ) BARCHAN - most common type - crescent-shaped backslope Wind direction slip face

2. ) PARABOLIC DUNES - crescent-shaped but with the concave side on the windward side - usually elongated - may develop in associated with deflation hollows Wind direction

3. ) TRANSVERSE DUNES • low sand ridge at right angles to the wind direction • may form because of large amounts of sand wind

4. ) LONGITUDINAL DUNES • low sand ridges parallel to the wind direction • may form because of a limited amount of sand • also known as seif dunes wind

LOESS • Finely textured sediment wind-blown long distances • Wind-blown glacial debris formed large deposits