booklet 8 - landforms

• where do beaches form? at the point where the land meets the sea and represent the accumulation of sediment between low tides and highest point reached by storm waves
• what are the main zones of the beach? upper beach - cliff face, storm beach, berms , cusps

  lower beach - runnel, ripples, ridges
• storm beach: - strong swash at spring high tide level

  - ridge composed of biggest boulders thrown by largest waves, above high tide mark
• berm: - series of ridges marking successively lower high tides as cycle goes from spring to neap

  - built up by constructive waves
• cusp: - semi circular shaped depressions which form when waves break directly on the beach

  - swash and backwash are strong

  - usually occur at junction of shingle and sandy beaches
• ripple: - developed on sand by wave action or tidal currents
• runnel: - at low water mark

  - most of swash returns as backwash, and little energy is lost

  - material carried down beach

  - ridges and runnels run parallel to shoreline and are broken by channels that drain water off the beach
• Swash Alligned Beach: - parallel to incoming wave crests

  - experience minimal longshore drift

  - found on irregular coastlines where LSD is impeded, and waves hit sections of coast head on
• Drift Alligned Beach: - parallel to direction of dominant longshore drift

  - have considerable amounts of sediment transported long distances along them

  - initially develop where section of coastline is fairly regular or where predominant wave direction is at angle to beach
• how and why do beach gradients vary? - as a result of the angle at which the waves generally approach a coastline
• why are large pebbles found further up the beach? - experience less attrition

  - swash = more powerful and has the energy to carry large material up beach

  - backwash = weaker so cant carry material back out to sea
• how does the beach profile vary in the summer and in the winter? - winter - beach is steeper and a bar forms

  - summer - beach is gentler and there are berms forming
• why are pebbles more rounded at the bottom of the beach? there's more attrition taking place
• what is a spit? - elongated narrow ridge of land that has one end joined to the mainland and projects out into the sea/ across an estuary

  - composed of sand / shingle
• where are spits found?

  along drift aligned beaches
• formation of a spit: - material transported by LSD

  - where coastline changes direction, deposition of material occurs in more sheltered water, forming spit

  - end curves due to wave refraction

  - salt marshes often form behind spit
• why don't spits extend all the way across an estuary? - as the wave refraction causes the end to curve, stopping the spit from extending across the estuary
• simple spit: - straight / recurved

  - don't have minor spits or recurved ridges
• compound spit: - have similar features to simple spit

  - have recurved ridges or minor spits
• example of a spit: -Hurst castle spit - flint pebbles

  - zlatni rat, croatia - white pebbles
• conditions needed for a sand dune: - large quantities of sand

  - constructive waves

  - large tidal range

  - dominant onshore wind

  - low gradient beach

  - human/natural obstacles to trap sand particles
• formation of sand dunes: - sand accumulates against a feature and builds upper beach height

  - wind speed drops behind accumulation resulting in more sand deposition

  - marram grass colonises embryo dunes stabilizing further dune migration

  - marram leaves further reduce wind speed and capture more blown sand

  - decaying plants add humus, makes sand darker

  - microclimate + soil conditions change allowing colonisation by additional species
• embryo dune: - disappear as fast as they form

  - extreme conditions, high ph, rapid drainage, no humus

  - reach no more than 1 metre tall
• fore dune: - beyond reach of all but the highest storm tides

  - lyme grass, sea couch grass and marram grass

  - up to 5 metres
• yellow dune: - show greater diversity of plants as conditions become more favourable

  - humus layer builds up, trapping water + nutrients

  - marram still dominates

  - 5-10 metres tall

  - 80% of sand surface now vegetated
• grey dune: - more stable

  - marram grass less common

  - red fescue, sand sedge and sea spurge dominate

  - shelter from wind

  - humus darkens and soil begins to form

  - soil is acidic

  - 10 metres tall
• dune slack: - depressions within dunes where water table is on or near the surface

  - conditions often damp
• mature dune: - several hundred metres from shore

  - develop soil that can support shrubs and trees

  - oat climax vegetation may develop
• how can humans influence the development of sand dunes? - they can cause a loss of vegetation along the dunes, which means less sand will be able to accumulate disrupting the formation

  - similarly, may provide other obstacles (sea walls) that allow the sand to accumulate
• Gibraltar point - lincolnshire: - southern pint of sediment cell

  - fastest eroding coastline so lots of sediment

  - 7 metre tidal range

  - prickly saltwart (pioneer species) gets nutrients out of dunes

  - embryo dunes, foredunes + yellow dunes known as mobile dunes

  - 1km inland theres a climax community of woodland and heathland

  - climax community is 250 years old
• conditions needed for a salt marsh: - sediment supply

  - sheltered from strong waves

  - salty conditions

  - coastal area that already has a mudflat
• what material accumulates to form a salt marsh? fine sediments
• flocculation: - fine sediments carried by slow moving river meets sea water flowing into river mouth

  - two flows meet and join together to form larger, heavier particles that sink into the bed
• formation of salt marsh: - mudflats evolve into salt marshes with colonisation by plants

  - submerged and semi submerged plants trap more sediment and reduce water velocity, increases deposition

  - new plants grow on decayed material, raising height of salt marsh

  - as height increases, saline conditions reduce and seral stages occur towards a climax community
• hydrosere


  plant succession occuring in water
• halosere: sub-set occuring in salt (as opposed to fresh) water
• how do humans influence the development of a salt marsh? introduction of pollutant in the water affect the organisms living there
• example of salt marshes

  - behind east head spit
• what is a barrier beach? - an elongated bank of sand/shingle lying parallel to the coastline
• where do barrier beaches form? - common in areas of with low tidal ranges and can be very large