Coastal landforms, management and sea level change

what are landforms of erosion

• cliffs and wave cut platforms

• headlands and bays

• caves, arches and stacks

how do cliffs form

as the sea erodes the land due to the action of waves and erosional processes

process of cliffs forming

weathering and wave erosion cause a notch to form at the high water mark

this eventually develops into a cave

rock above the cave becomes unstable due to lack of support and collapses to form a cliff face

wave cut platform left behind

how do headlands and bays form

through differential erosion

process of headlands and bays forming

alternating bands of soft and hard rock

soft rock is eroded quickly forming a bay

harder rock eroded less and sticks out as a headland

what are caves found in cliffs called

cliff profile features

how do caves, arches and stacks form

weak areas in the cliff like joints eroded to form caves

what is concordant coastline

coastline where layers of rock run parallel to the shore so experience fewer bays and headlands

what is discordant coastline

where bands of differing rock run perpendicular to the shore which leads to differential erosion and landforms like headlands and bays

example of a concordant coastline in the uk

Lulworth Cove in Dorset where the sea has breached the outer hard portland limestone and eroded the softer clays behind to form a cove

example of a discordant coast

the Isle of Purbeck, where harder rocks create prominent headlands and softer rocks form bays.

Describe the sequence of landform development from a crack in a headland to a stump.

• Crack – Hydraulic action and abrasion widen a small crack in a headland.

• Cave – Continued erosion deepens the crack into a cave.

• Arch – The cave is eroded through the headland to form an arch.

• Stack – The arch collapses due to gravity and erosion, leaving a stack.

• Stump – The stack is eroded down to a stump, often only visible at low tide.

landforms of deposition (6)

beaches

spits

offshore bars and tombolos

barrier islands

sand dunes

estuarine mudflats and saltmarshes

how do beaches form

beaches form when constructive waves deposit sediment on the shore

characteristics of shingle beaches

steep and narrow and made up of larger particles which pile up at steep angles

features of beaches

berms, runnels, cusps

what are berms

ridges of sand and pebbles about 1-2m high found at high tide marks

what are runnels

grooves in the sand that run parallel to the shore formed by backwash draining to the sea

what are cusps

crescent shaped indentations that form on beaches of mixed sand and shingle

where do spits tend to form

where the coast suddenly changes direction like across river mouths

three types of spits

simple spit, spit with recurved end and compound spit

What is a spit and how does it form

A spit is a long, narrow ridge of sand or shingle that extends from the coastline into the sea, formed by longshore drift depositing material across a river mouth or bay.

What process moves sediment along the coast to form a spit?

Longshore drift transports sediment along the coast. When the coastline changes direction (e.g., at a river mouth), material is deposited, creating a spit

What is a simple spit?

A simple spit is a straight spit that extends into the sea, growing roughly parallel to the coast without recurved ends.

Why do spits sometimes have recurved ends?

Changes in the dominant wind or wave direction can cause the tip of the spit to curve inland, creating a recurved end.

What is a compound spit?

A compound spit has multiple recurved ends, formed by several periods of growth as wind and wave directions change over time.

What forms in the sheltered area behind a spit?

The sheltered area behind a spit often develops into mudflats and saltmarshes due to reduced wave energy and sediment accumulation.

what is a bar

a landform made when a spit joins two headlands together usually across a bay or river mouth

what can form behind a bar

a lagoon

What is a lagoon in relation to a bar?

A lagoon is a shallow body of water that forms behind a bar, sheltered from the sea.

What is an offshore bar and how does it form?

Ridges of sand or shingle running parallel to the coast in the offshore zone formed by sediment eroded by destructive waves being carried seawards by backwash and deposited wave movement no longer touches the floor

What is a tombolo?

A tombolo is a type of bar that joins the mainland to an island, often a stack. It's formed by the deposition of sediment.

Give an example of a tombolo.

St Ninian’s Isle, Shetland Islands – joined to the mainland by a tombolo.

what are barrier islands

long, narrow islands of sand or gravel that run parallel to the shore and are detached from it

where does a barrier island form

in areas where there is a good supply of sediment, a gentle slope offshore, powerful waves and a small tidal range

what is tidal range

Tidal range is the vertical difference in height between the high tide and the low tide at a particular place.

how are barrier islands formed (main theory)

not entirely clear but scientists think after the last ice age ended and the sea rose so much that rising waters flooded land behind beaches and transported the sediment offshore where it was deposited in shallow water

second theory about the formation of barrier islands

were originally bars which were eroded in sections causing it to breach

what is found behind barrier islands

lagoons or marshes as it is sheltered from wave action

example of a barrier island

lots on the east coast of USA like Horn Island in Mississippi

what is barrier beach a general term for

for any beach that shelters the coast like barrier islands, spits and bars

what are sand dunes

Sand dunes are mounds or ridges of sand formed when sand from longshore drift is blown inland by the wind and trapped by obstacles like vegetation or driftwood, typically forming at the back of a beach.

what happens to the sand blown up the beach

it is trapped by driftwood or berms and colonised by plants and grasses

example of vegetation that grows on sand dunes

marram grass

what does vegetation growth do to sand dunes

it stabilises dunes and encourages more sand to accumulate there and from embryo dunes

key features of a sand dune

gentle slopes on the windward side

steep slip face

crest up to 15m high

What conditions are required for sand dune formation?

(5 points)

• large supply of sand

• wide, flat beach

• time to dry (wide tidal range)

• onshore wind

• an obstacle like driftwood

How does wind build up a sand dune?

Wind transports sand up the dune. As sand builds up, it reaches a steep crest, then collapses down the leeward side, stabilising at 30–34°.

Why do dunes get taller further inland?

Stronger winds and vegetation (like marram grass) help trap and stabilise sand, creating mature dunes up to 15m high.

How does vegetation succession affect dune development?

Over time, plants colonise dunes, stabilising them. Dunes turn from yellow to grey as humus and bacteria build up.

What is a slack in a sand dune system?

A slack is the dip between dunes, formed by erosion. If deep enough to reach the water table, it may become a salty wetland.

where do mudflats and saltmarshes from

in sheltered low energy environments like river estuaries or behind spits

how do mudflats form

silt and mud are deposited by the river or tide and begins to accumulate, vegetation resistant to salinity and submergence colonise the mud and in turn trap more silt and mud which gradually builds upwards to create an area that remains exposed for longer and longer between tides

what can form in mudflats and saltmarshes

channels on the surface caused by erosion from tidal currents which can become permanently flooded or dry at low tide

example of saltmarsh

there is a saltmarsh behind Spurn point at the holderness coast

what is eustatic sea level change

sea level change caused by a change in the volume of water in the sea or by a change in the shape of ocean basins

what is isostatic sea level change

sea level change caused by the vertical movement of the land relative to the sea, a downward movement of land causes a sea level rise locally and an upward movement causes a local sea level fall

at what scale are the effects of eustatic sea level change felt

globally

at what scale are the effects of isostatic sea level change felt

locally

what are the 2 main causes of eustatic sea level change

climate change and tectonic movements

how can climate change cause eustatic sea level rise

• temperature increase causes melting of ice sheets which increases sea level due to a greater volume of water

• temperature increase causes thermal expansion of sea water

how can climate change cause eustatic sea level decrease

decrease in temperature causes more precipitation to fall as snow which increases volume of water held in glaciers and thus decreases the volume of water held in the sea

how can tectonic movements cause eustatic sea level change

tectonic movements can alter the shape and so the volume of ocean basins

example of a specific tectonic movement causing eustatic sea level change

sea floor spreading increases the volume of the basin and so decreases sea levels

what are the main causes of isostatic sea level change

• uplift or depression of earth’s crust due to accumulation or melting of ice sheets

• subsidence of land due to shrinkage

• tectonic processes

how does uplift or depression of earth’s crust cause isostatic sea level rise

uplift or depression of crust occurs due to either accumulation or melting of ice sheets, slow uplift can continue for thousands of years after a retreating glacier has gone and accumulation of sediment mostly at the mouths of major rivers can cause depression

how can subsidence cause isostatic sea level rise

subsidence due to shrinkage after over abstraction of groundwater can cause land to sink and sea levels to increase

how can tectonic processes cause isostatic sea level change

if one place is forced beneath another at a plate margin , the displaced material causes local changes in sea level. For example, subduction can lead to increased pressure and subsequent uplift in surrounding areas.

what has happened to sea levels in the last 10,000 years

they have risen

how does sea level vary on a daily basis

the tidal cycle, onshore winds and low atmospheric systems

what was sea level like at the last glacial maximum

about 130m lower than present

when did sea level reach its present level

about 4000 years ago

when was the last glacial period

110,000 years ago- 12,000 years

what has happened to sea level over the last 4000 years

it has fluctuated around its current level

since when have sea levels been consistently rising

1930s

how have global average temperatures changed

1.08 degrees between 1900-2016

how does climate change cause changes in sea level

it has caused global warming

what do greenhouse gasses do

absorb outgoing long wave radiation so less is lost to space and more heat energy is trapped and the planet warms up

how much are global sea levels rising currently

2mm a year

if greenhouse gas emissions remain high what is predicted to happen to global sea levels

an increase of 8-16mm a year by 2100

how do temperature increases cause eustatic sea level change

ice sheets and glaciers melting as well as thermal expansion

how does sea level rise affect coastal areas (5 points)

• more frequent and severe coastal flooding

• submergence of low lying islands

• changes in the coastline

• Increased coastal erosion

• contamination of water sources and farmland

sea level change and storms

storms are likely to become more frequent and intense due to changes in ocean circulation and wind patterns which would cause damage to ocean ecosystems and habitats

sea level rise and coastal flooding

flooding of low lying areas has increased with sea level rise and will only increase further like in Kings Point NY

how many times did kings point new york flood between 1994-2004

around 80 times

how many times did kings point in new york flood from 2005-2014

nearly 160 times

sea level change and islands

likely to cause submergence of low lying islands which are at risk of disappearing

sea level rise and the maldives

will be submerged if sea levels rise by just 0.5m

sea level rise and changes to coastlines

as sea levels rise changes like the creation of islands and area of land decreases happen

Bangladesh and sea level rise

if sea levels rise 0.3m from current level, 8000km2 of land in Bangladesh will be lost

contamination and sea level rise

flooding caused by sea level rise might cause the contamination of freshwater sources and agricultural land meaning nothing can be grown

what are coastlines of emergence

coastal areas formed when the sea level falls

coastlines of submergence

coastal areas formed when sea level rises

types of landforms on coastlines of emergence

• wave cut platforms/marine platforms

• raised beaches

• relict cliffs

raised beaches

form when fall in sea level leaves beaches above the high tide mark and are vegetated over time and turn into soil

wave cut/marine platforms

are exposed when sea levels fall and they are above the high tide mark

relict cliffs

cliffs above raised beaches that are no longer eroded by wave action so get covered by vegetation

what can happen to relict cliffs

they can have caves, wave cut notches, arches and stacks within them which are eventually weathered over time

landforms of submergence

rias

fjords

dalmatian coasts

rias

formed where river valleys are partially submerged, also known as drowned river valleys