Depositional Landforms Flashcards
(24 cards)
1
Q
How is a beach formed?
A
- sediment is deposited near coastline when waves lose their energy
- larger sediment, left from winter storms, remain at top of beach as backwash is weaker than swash as water quickly percolates into sand
2
Q
What are the characteristics of a beach?
A
- ridges + runnels
- storm beaches
- cusps
- ripples
3
Q
What are ridges + runnels?
A
- raised areas (ridges) + intervening depressions (runnels) on shallow, sandy beaches, formed by interaction of tides, currents, sediments + shallow beach topography
4
Q
What are storm beaches?
A
- ridge of boulders + shingle thrown to back of beach by largest waves at high tide
5
Q
What are cusps?
A
- self sustaining, semicircular depressions formed by waves breaking directly onto beach w a strong swash + backwash
6
Q
What are ripples?
A
- ridges + intervening depressions that develop on sandy beaches as a result of wave + tidal movements
7
Q
Describe how swash-aligned beaches form.
A
- when prevailing winds cause waves to break parallel to coast, LSD is limited, causing swash + backwash to move material up + down beach so sediment doesn’t travel far along beach
- this creates smoothly curved, concave beaches
- wave refraction may dec speed of high energy waves, forming a shingle beach
8
Q
Describe how drift-aligned beaches form.
A
- when prevailing winds cause waves to break at an oblique angle to coast, swash occurs at an angle + backwash runs perpendicular to beach, causing LSD to transport material far along beach
- this may lead to formation of a spit at end of beach
9
Q
Describe how a simple spit is formed.
A
- prevailing winds cause LSD to transport sediment along coastline
- when coastline suddenly changes direction, sediment is deposited out to sea
- this creates a narrow ridge of sand, that extends from land into sea
- a recurved end can form from a change in wind or wave direction
- deposition of finer sediment + plant colonisation, in sheltered, saline area w a lower speed of water flow behind spit, causes a salt marsh to form
- spit stops growing when changing currents (e.g. river currents) prevent further deposition, esp across an estuary
10
Q
What are the characteristics of a simple spit?
A
- narrow, elongated landform, made of sand or shingle
- formed from LSD transporting sediment along coast
- one end is attached to mainland + other extends out into sea
- can have a recurved end due to a change in wind or wave direction
- can form a salt marsh behind spit from deposition of fine sediment + plant colonisation
- has a single ridge w/o multiple recurved ends
11
Q
Describe how a compound spit is formed.
A
- prevailing winds cause LSD to transport sediment along coastline
- when coastline suddenly changes direction, sediment is deposited out to sea
- this creates a narrow ridge of sand, that extends from land into sea
- a recurved end forms from a change in wind or wave direction
- when direction changes again, original recurved end is abandoned + a new spit forms on top of old 1, creating multiple recurved ends over time
12
Q
What are the characteristics of a compound spit?
A
- made of sand or shingle
- formed from LSD transporting sediment along coast
- has multiple recurved ends, formed from changes in wind or wave direction
- wider + more complex than a simple spit
- can form a salt marsh behind spit from deposition of fine sediment + plant colonisation
13
Q
Describe how a tombolo is formed.
A
- prevailing winds cause LSD to transport sediment along coastline
- when coastline suddenly changes direction, sediment is deposited out to sea
- this creates a narrow ridge of sand, that extends from mainland, to an offshore island, connecting them together + forming a tombolo
- wave energy behind island is dec, allowing the sediment to be deposited in sheltered area
14
Q
What are the characteristics of a tombolo?
A
- narrow ridge of sand or shingle
- connects an offshore island to mainland
- formed by deposition from LSD
- common in low-energy envi.s w dec wave action
- forms in sheltered area behind island, where sediment is deposited
15
Q
Describe how an offshore bar/sandbar is formed.
A
- waves break before reaching shore, causing sediment to be deposited in shallow water
- over time, deposited sediment builds up parallel to coast, forming a ridge beneath or just above sea lvl
- offshore bar can absorb wave energy, dec coastal erosion
- it can also form when backwash from destructive waves remove sediment from a beach
16
Q
What are the characteristics of a offshore bar/sandbar?
A
- ridge of sand located off coast, usually submerged or just above sea lvl
- lies parallel to shoreline
- formed by wave action + deposition in shallow water
- common in low energy envi.s w an abundant sediment supply
17
Q
Describe how a barrier beach is formed.
A
- prevailing winds cause LSD to transport sediment along coastline
- a spit extends across a bay, eventually joining 2 headlands
- this traps water behind it, forming a lagoon
- over time, barrier can become wider + more stable, + sometimes supports veg
- some formed after last glacial period, as sea lvls rose, + meltwater from glaciers deposited sediment along coastlines
18
Q
What are the characteristics of a barrier beach?
A
- long, narrow ridge of sand, running parallel to coastline
- separated from mainline by a lagoon
- common in low-energy, gently sloping coastal areas w abundant sediment
- acts as a natural barrier, protecting mainland from waves + storm surges
19
Q
Describe how a costal (sand) dune is formed.
A
- prevailing winds blow dry sand, from beach, inland
- sand is trapped above high tide mark, around pioneer species (e.g. sea rocket), that are resistant + able to survive in salty sand, forming embryo dunes
- as more sand is deposited, dunes grow into foredunes, stabilised by plants like marram grass
- over time, dune becomes more stable, as decaying matter adds nutrients to soil, forming grey dunes
- dune slacks can form in low lying areas where water table reaches surface
- eventually mature dunes form when larger plants colonise area, to form a climax community
20
Q
What are the characteristics of a coastal (sand) dune?
A
- series of ridges running parallel to coast
- formed when prevailing winds blow + deposit sand above high tide line
- embryo dunes near shore are small + mobile
- foredunes + yellow dunes grow taller + wider w marram grass
- grey dunes are more stable, w deeper soils + varied veg
- biodiversity + soil quality inc inland
21
Q
Describe how tidal sedimentation occurs in estuaries.
A
- change in velocity, when freshwater from river meets saltwater from ocean, causes flocculation
- this involves clay particles in freshwater, clumping together in saltwater, to become heavier + so are deposited
- over time, layers of mud + sand build up, forming mudflats + eventually saltmarshes if sediment is trapped by colonising pioneer plants
22
Q
Describe the formation of a coastal saltmarsh.
A
- formed in low energy envi.s, often behind spits or in estuaries
- fine sediments (e.g. clay particles) clump together by flocculation, to become heavier + so are deposited
- this creates mudflats, which pioneer species colonise, trapping more sediment
- this allows salt-tolerant veg to grow + more sediment to build up, allowing stability to inc as more veg grows, leading to formation of a mature salt marsh
23
Q
What are the characteristics of a coastal saltmarsh?
A
- common in low energy envi.s (e.g. estuaries, behind spits)
- composed of fine silts + clay
- features mudflats + vegetation zones
- dominated by salt-tolerant plants
- acts as a natural flood defence + habitat for wildlife
24
Q
Describe the formation of a mangrove.
A
- form in tropical + subtropical coastal areas, in low energy envi.s
- salt-tolerant trees colonise first, which grow in saline, high T°C, + low O2 conditions
- their prop roots stabilise + trap more sediment, allowing sediment to build up over time
- this acts as a natural coastal defence, protecting areas from erosion + storms
