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coastal depositional landforms (Beaches (beach zones (Backhore: …
coastal depositional landforms
Beaches
beach zones
Backhore:
consists of the storm beach
made up of large sediment, that is pushed to the top of the
beach by storm waves
Berms are formed fortnightly by the
spring tide
Nearshore
Also known as the
Breaker zone
Between the normal low tide mark and the spring low tide mark
On beaches with a low tidal range, they often form a point where waves break known as
breaker bars
Foreshore:
The zones between the the normal high and low tide mark
The width is dependent on the greadent of the beach and the
tidal zones
Low ridges running parallel to the coastline (fulls) are often
formed by constructive waves.
The amount of sediment on the foreshore is depend on the
sources of sediment and LSD
Offshore:
This zone is always underwater
Longshore bars can also be found within this area
These bars can grow to be quite substantial and can contribute to the formation of
barrier beaches
and
barrier Islands
Beach morphology
There are many landforms that can be found on beaches, these include:
Berms
Bars
Fulls
Swales
Ripples
Beach cusps:
semi circular deprestion cut into the lower edge of the storm
beach.
There formation has not been found out but once they have
been formed they self-sustain due to the cusp causing the
backwash to take away the sediment .
swash and drift-aligned beaches
swash-aligned:
The costs are aligned parallel to the crests of the prevailing
waves
swash and backwash occur straight up and down the beaches
therefore LSD does not occur
beach cusps
and
cuspate tombolos
can form along these
beaches due to the waves being refracted
Drift-aligned:
The costs are aligned at an angle to the crests of the precaling
waves
on these beaches the swash waves up the beach at an angle
and the backwash runs straight down the beach and therefore
LSD will occur
spits, bars, tombolos
and
cuspate Forelands
can form at this type of coastline
Formation of a beach:
Beaches are the most common coastal landform, normally made from sand and/or shangle. Beaches have a pebble line a the top of the beach followed by the high water mark and the low water mark, in between these two marks is the
intertidal range
Longshore drift moves the sediment across the beach and therefore the beach is a
dynamic
landforms and the sediment is moving along it, as if on a conveyor belt
simple and compound spits
Simple spits:
A simple spit is the most common spit
They can be straight but are usually curved due to the wave refraction or the prevailing wind
They accumulate to form a long, narrow spit which can grow over time due to the waves carrying sediment along
Compound spits:
They have a narrow base that attaches to the mainland and then this widens into a broad re-curved end
these consist of a series of ridges which have grown over time
Formation of a spit:
Spits are formed when LSD extends past the beach section of the coastline and makes its way across an estuary,bay or inlet.
sand
spits are formed by constructive waves
shingle
spits are formed by destructive waves
A spit will never reach the other side of an estuary due to the river currant and depth of main river channel
Bars
Bars are formed when a spit exceeds all the way across an inlet. this will happen when the river current is not powerful enough to stop the growth of the spit.
Behind the bar a lagoon will form between the bar and the original coastline. A lagon can also form when a
offshore bar
migrates inwards
Tombolos
Tombolos are formed when a beach extends outwards to join an offshore island.
Formation theories:
Longshore drift is extended on the beach along the coastline and out to an island
The beach was an offshore bar driven onto the modern shoreline by rising sea levels at the end of the glacial period
Offshore bars, barrier beaches and barrier islands
Barrier beaches:
Long sandy beaches, detached from but parallel to the coastline
A tidal lagoon will form behind the beach and will stretch to the original coastline
salt marshes and mangrove swamps can also form with in this lagoon
Offshore bars:
offshore bars form before a Barrier beach
they bild up above the low tide mark by the action of storm waves
They can also form a low wau out to sea and then when the sea level rose, they migrated landwads
offshore bars can also be found farther out to sea but are only undercovered during low tide
Barrier Islands:
A barrier island is formed from a barrier beach
once the bearer beach has started to form vegetation and sand dunes it is a barrier island
they are typically 200-400m wide but can be very long
