The major landforms of advancing (depositional) coastlines Advancing coasts – depositional coasts that are growing as a consequence of sediment deposit and/or the infill of coastal marshes. Advancing coasts may also arise from a negative change in sea level (sea level fall or uplift of land)

Which of these are erosional & depositional coastal landforms?

Depositional processes at the coast Occurs where the accumulation of sand and shingle exceeds its depletion In sheltered areas with low energy waves Where rapid coastal erosion further along coast provides abundant supply of material (in terms of a system, deposition takes place as inputs exceed outputs therefore beach is a store)

Sources of beach sediment Rivers: account for 90% (sand and shingle transported as bedload) Cliff erosion: 5% Sea bed (18,000BP northern Europe in Ice age and sea level 100m lower, therefore continental shelf was dry land, as climates warmed and sea rose push these sediments on shore to form modern beaches) Rivers: sand and shingle transported as bedload Cliff erosion: although very active in places Sea bed: 18,000BP northern Europe in Ice age and sea level 100m lower, therefore continental shelf was dry land, as climates warmed and sea rose push these sediments on shore to form modern beaches

What is longshore Drift?

Depositional landforms You need to be able to recognize and explain each of these… Beach Spit On-shore and off-shore bars Tombolo Lagoon

Landforms of coastal deposition Beach “buffer zone between the waves and the coast” In dynamic equilibrium with its environment - composed of loose material it can rapidly adapt its shape to changes in wave energy 4 sections to a beach: Dynamic equilibrium: because composed of loose material it can rapidly adapt its shape to changes in wave energy

Maximum spring tide High water mark Low water mark Storm beach Offshore Beyond the influence of waves Near shore Breaker zone Foreshore Inter-tidal or surf zone Backshore Usually above the influence of the waves Maximum spring tide High water mark Cliffs or dunes Low water mark Sand shingle pebbles Storm beach

Beach profiles (way it looks depends on) Wave Energy *spearman rank correlation for phase difference and beach gradient Landmark AS geog p88*

Beach profiles (way it looks depends on) Particle Size Wave energy: constructive waves (surging breakers) low-energy have a net transfer of sediment onshore so profile becomes steep, with a prominent beach face and berms Destructive waves (surfing breakers) high-energy flatten beaches. They erode sediment from beaches and transport is offshore to form breakpoint bar However, beaches are systems in equilibrium so, if gradient is gentle then constructive waves are dominant. These move material up the beach which will steepen the gradient, shorten the wave length and increase the wave steepness until they are eventually replaces by destructive waves. Negative feedback as the original process or landform is reversed. In GB more storms in winter therefore beaches degraded and built up again in summer. Particle size: shingle normally steeper and narrower than sand, because higher percolation rate of shingle compared to sand. On shingle percolation is so rapid that swash is short and the backwash is insignificant. So, while swash piles up shingle, there is no backwash to drag the shingle back to the sea. Therefore, the net sediment movement is in one direction, this produces a steep beach (up to 10 degrees. Sand beaches with lower percolation rates, have a longer swash and more powerful backwash, which drag the sand back - a beach with a lower slope angle. *spearman rank correlation for phase difference and beach gradient Landmark AS geog p88*

Beach profiles Summary: Destructive waves carry material down beach Constructive waves carry material up beach Material is carried upwards on shingle Material is carried downwards on sandy Therefore as destructive waves occur on shingle beaches the movement of beach material will, under normal conditions be evened out. The beach system is in long term equilibrium Wave energy: constructive waves (surging breakers) low-energy have a net transfer of sediment onshore so profile becomes steep, with a prominent beach face and berms Destructive waves (surfing breakers) high-energy flatten beaches. They erode sediment from beaches and transport is offshore to form breakpoint bar However, beaches are systems in equilibrium so, if gradient is gentle then constructive waves are dominant. These move material up the beach which will steepen the gradient, shorten the wave length and increase the wave steepness until they are eventually replaces by destructive waves. Negative feedback as the original process or landform is reversed. In GB more storms in winter therefore beaches degraded and built up again in summer. Particle size: shingle normally steeper and narrower than sand, because higher percolation rate of shingle compared to sand. On shingle percolation is so rapid that swash is short and the backwash is insignificant. So, while swash piles up shingle, there is no backwash to drag the shingle back to the sea. Therefore, the net sediment movement is in one direction, this produces a steep beach (up to 10 degrees. Sand beaches with lower percolation rates, have a longer swash and more powerful backwash, which drag the sand back - a beach with a lower slope angle. *spearman rank correlation for phase difference and beach gradient Landmark AS geog p88*

Formation of a spit

Explain formation of a spit..

Formation of a Bar 3. Bars e.g. “when a spit extends across a bay linking two headlands, straightening the coastline” Deben estuary, Suffolk Off-shore bar: accumulates below the low tide mark and moves progressively inland How does it differ to a spit? The relatively shallow water generates constructive waves which transport material landwards creating a long smooth coastal feature topped by sand dunes

Tombola? Explain it.. Chesil beach: 30km long, 14m high to the prevailing winds in the English Channel, linkingIsle of Portland to the mainland

Lagoon? Explain it… Lagoon - A shallow body of salt water close to the sea but separated from it by a narrow strip of land, such as a barrier island, or by a coral reef.

Suggest how a tombolo is formed 4 2. Outline how marine processes contribute to the formation of beaches 3 3. Outline how marine processes contribute to the formation of off-shore bars 4 Could you do these?

Depositional landforms - task – draw and explain how each forms.. Beach Spit On-shore and off-shore bars Tombolo Lagoon