EQ 2: how are coastal landforms developed?

what is weathering?

the breakdown of rock in situ at or near the surface of the Earth

what are the three types of weathering?

physical, biological, chemical

what are three examples of physical weathering?

freeze-thaw, thermal expansion, salt crystallisation

what is freeze-thaw weathering?

water enters cracks/joints and expands by nearly 10% when it freezes
this exerts pressure on the rock, causing it to split or pieces to break off

what is thermal expansion weathering?

rocks expand when heated and contract when cooled
if they are subject to frequent cycles of temperature change, then the outer layers may crack and flake off

what is salt crystallisation weathering?

solutions of salt can seep into the pore spaces of porous rocks
the salts precipitate, forming crystals which puts stress in the rock, causing it to disintegrate
(e.g. sodium sulphate and sodium carbonate)

what are two examples of chemical weathering?

oxidation and carbonation

what is oxidation weathering?

some minerals in rocks react with oxygen, especially iron which produces iron oxides and increases volume, contributing to physical breakdown

what is carbonation weathering?

rainwater combines with dissolved CO2 from the atmosphere to produce a weak carbonic acid
this reacts with calcium carbonate in rocks to produce soluble calcium bicarbonate which causes new minerals to dissolve into the solution

what are two types of biological weathering?

tree roots and organic acids

what is tree root weathering?

tree roots grow in cracks or joints in rocks and exert outwards pressure, significant on cliff tops and cliff faces

what is organic acid weathering?

organic acids produced during decomposition of plant and animal litter cause soil water to become more acidic and react with some minerals in a process called chelation

what is mass movement?

the downhill movement of weathered material under the force of gravity

what are the three forms of mass movement?

rock fall, slides, slumps

what is rock fall?

rocks become detached from the slope by physical weathering which fall to the foot of the cliff under gravity

what are slides?

a large block of soil or rock moves rapidly down a slop along a flat surface

what are slumps?

rainwater saturates permeable clay which causes it to slump downwards in a rotational motion along a curved slip plane

what are four examples of erosional landforms?

cliff and shore platforms, bays and headlands, geos and blowholes, caves, arches, stacks and stumps

how are cliff and shore platforms formed?

destructive waves break repeatedly on steeply sloping coastlines
undercutting occurs between the high and low tide levels which forms a wave-cut notch
continued undercutting weakens supports for the rock strata above, which collapses
collapse and retreat continues, forming a high cliff and a wide platforms which produces shallow water and small waves
friction from platforms slows down approaching waves, causing them to break at the platform
wave erosion greatest at high and low tide → forming ramp at high tide level and small cliff at low tide level (tidal range less than 4m)

how are bays and headlands formed?

bays (softer rock → more erosion) and headlands (more resistant rock → slower erosion) form adjacent to each other - discordant coastline = perpendicular to coast, concordant coastline = parallel to coast
waves slows down by friction of shallower water at headland, wave bends around headland and orthogonals converge, wave energy focused on headland → erosion
orthogonals diverge in bays → deposition

how is a geo formed?

geos are steep sided narrow inlets in the cliff, formed due to a weakness in the cliff (joints or faults) which are eroded more quickly than the more resistant rock by wave action
hydraulic action forces air and water into cracks and joints, weakening rock strata (e.g. huntsman’s leap in pemobrokeshire, south wales - 35m deep)

how is a blowhole formed?

if parts of the roof of a tunnel like cave (initial formation of a geo) collapses along a master joint, it may form a vertical shaft that reaches the cliff top → blow hole
large waves can force spray out of blowholes as plumes of white, aerated water (e.g. trevone bay round hall, cornwall - 25m deep)

how are caves, arches, stacks, and stumps formed?

energy is concentrated on sides of headlands due to wave refraction
weaknesses are exploited by erosion processes and a cave forms, which can enlarge to extent to other side of headland to form an arch
continued erosion widens arch and weakens its support, and weathering on top of arch may cause it to collapse → isolated stack
erosion via hydraulic action at base of stack causes further collapse to leave a stump (e.g. Harry Rocks, Dorset)

what are six examples of depositional landforms?

beaches, spits, onshore bars, tombolos, salt marshes, deltas

how are spits formed?

spits are long narrow beaches of sand or shingle that extend across a coastline
beach material is transported across beach in direction of longshore drift and prevailing wind, continuing out into sea when there is a change in the direction of the coastline
secondary wave direction and wave refraction around the end of a spit causes it to become hooked
salt marshes are formed in the sheltered area behind a spit as low energy environment allows deposition (e.g. Farewell Spit, new Zealand - 16 miles long)

what are two theories for the development of an onshore bar?

depositional landforms that run parallel to the coast, formed in low energy environment
formed where a spit grows across a bay to join two headlands (describe formation of spit)
inward movement of sediment during inter-glacial periods - Flandrian Transgression, sea levels rose, caused sediment (till) to move onshore, forming berm ridges
e.g. Slapton Sands in Devon - 9km long

what are two theories for the development of tombolos?

a beach which forms between the mainland and a nearby island
describe formation of a spit BUT offshore island causes wave refraction to occur around island → wave shadow behind island → low energy conditions → deposition
Chesil Beach, Dorset - onshore movement of glacial outwash, where glacial sediment during the Wurm glacial accumulated in Lyme Bay
Flandrian Transgression → material eroded from deposits and carried north east where sediment attached to isle of Portland + Abbotsbury mainland

how are salt marshes formed?

formed in low energy environment behind spits
tidal currents deposit fine grain material → mud flats
mud flats colonised by pioneer plant species (halophytes) and develop over mud to form large areas of vegetation
vegetation creates friction to slow tidal currents even more → more deposition → salt marsh
vegetation waste builds up sediment level - combined effect of these processes increase level of salt marsh between 1mm-30mm per year

how are deltas formed?

large areas of sediment found at mouths of rivers (cuspate, arcuate, bird’s foot)
formed when rivers entering sea are carrying large sediment loads, tidal ranges are low, low energy environments exist in coastal area
consist of upper delta plain (composed entirely of river deposits), lower delta plain (composed of both river and marine deposits), submerged delta plain (composed mainly of marine sediments)