Lesson 9- What are the depositional landforms at the coast? (PART 1)

Question 1

What acctually are beaches?

Answer 1

A depositional landform between the highest high tide and the lowest low tide marks.

Question 2

What is beach accretion and beach excavation?

Answer 2

• Beach accretion occurs during prolonged periods of constructive waves where sediment is deposited
  -Beach excavation occurs during prolonged periods of destructive waves where sediment is removed from the beach

Question 3

Swash alligned beach vs Drift alligned beach

Answer 3

-Swash alligned> Waves approach at a 90 degree angle to the coast so there is no sideways transport
-Drift alligned> Wind+Waves alligned with the coast at a 45 degree angle that causes longshore drift

Question 4

What is the relationship between sediment and distance up the beach?

Answer 4

Found towards the cliffs as its too heavy for the backwash to take right back down the beach so is just deposited on the beach.
-pebbles also get more angular away from the shoreline as they arent eroded by the waves as much
-Scree also explains this as it falls off of a cliff face

Question 5

How constructive waves effect sediment deposition?

Answer 5

-They carry sediment up a beach due to strong swash.

-However, as the water percolates into the beach the backwash will only be able to drag smaller pebbles back.

-This leads to smaller sediments being towards the bottom and large at the top

Question 6

What is beach morphology?

Answer 6

Beach profiles are steeper in the summer when waves are more constructive than destructive

-these waves are less frequent and have a longer wavelength (6-9 per min) so wave energy dissipated and deposits over a wide area

-winter have have a higher frequency of 11-16 per minute therefore berms may be eroded by these waves
>these waves drag lots of sediment off of the beach leading to offshore bars

Question 7

Key characteristics and features of beaches-Berm

Answer 7

• Ridge marks at the high tide
  -after several berms on a beach that represent different tidal levels)
  -these may be a storm berm at the highest point on the beach
  -berms can be made of sand or pebbles and are built by constructive waves

Question 8

Key characteriostics and features of a beach-Ridges

Answer 8

• A raised area where waves slow down and deposit material to more friction

Question 9

Key characteristics anfd features of a beach-Runnel

Answer 9

• Area of the beach between two ridges

Question 10

Key characteristics and features of as beach-Cusp

Answer 10

• Semi-circular depressions
  -created where the swash interacts with waves coming from a different direction (maybe reflected off of a headland)
  -produces two wave directions which interact creating cusps

Question 11

What are spits and how do they form?

Answer 11

• Is a long shingle or sand land jutting into sea
  1) Longshore drift transports sand along the beach
  2) Change in orientation of coastline
  3) Spit grows out into sea
  4) Spit is now exposed to changes in wind/wave direction
  5) Saltmarsh forms in sheltered water behind the spit

Question 12

Proximal point of a spit

Answer 12

• Where the spit joins the mainland

Question 13

Distal point of a spit

Answer 13

• Furthest point of the spit that extends outwards

Question 14

Simple spit definition

Answer 14

• Stereotyped/textbook spit as it only has one spur where the dominant current slows and weakens to produce an extended finger of deposited material, often with a ercurved end

Question 15

Compound spit definition

Answer 15

• These have a number of recurved ‘spurs’ along their length as each curvature represents a ‘break in coastline orientation’

-requires consistent longshore drift and a varied wind direction

Question 16

What would happen to a spit of the prevailing winds changed direction?

Answer 16

1) Could just get eroded away
2) Could become a compound spit
3) Could create a spit ion the opposite direction

Question 17

Esturine mudflat definition

Answer 17

• River estuaries are important sediment stores where lots of river sediment is deposited close to the edges of the river (away from the faster tidal currents that scour the channels).

-Rising tides create a buffer to the river flow, slowing velocity and leading to considerable deposition.

-Most of the sediment that accumulates here is mud

Question 18

Salt marshes

Answer 18

• Saltmarshes are areas of flat, silty sediment that accumulate around estuaries or lagoons. They develop in:
  -In sheltered areas where deposition occurs (e.g. the lee of a spit)
  -Where there are no strong tides or currents to prevent sediment deposition and accumulation

Question 19

How are saltmarshes formed?

Answer 19

1)Mud is deposited close to the high-tide line, dropping out of the water by flocculation

2)Pioneer plants colonise the transition between high and low tide(EG eelgrass and cordgrass).
-As these are halophytes they can tolerate inundation by salty water so help trap more sediment

3) Mud level rises above high tide and a lower saltmarsh develops with a wider range of plants that no longer need to be so well adapted to salty conditions.

4)Soil conditions improve and the vegetation succession continues to form a meadow.

5)Shrubs and trees colonise the area as the succession leads to climatic climax community.

Question 20

What is the positive feeback loop that links plants, deposition and salt marshes?

Answer 20

-Initial deposition occurs
-Plants take root and start growing
-Plants trap more sediment and cause more deposition
-Water velocity reduces and even more deposition occurs-means that salt tolerant plants can grow

Question 21

How do plants cause vegetation succession?

Answer 21

1) Plants grow and die and drop organic material
2)Raises height of ..
3) Less saline as its harder for sea water to flood higher up- means less salt tolerant plants can grow

Question 22

What is hydrosere?

Answer 22

-Plant succession occuring in conditions of water is termed as hydrosere
- a sub-set occuring in salt (as opposed to fresh) water is known as halosere

Question 23

What are the key processes leading to salt marsh development?

Answer 23

• Solar energy
  -Tidal energy
  -Sheltered Low Energy Coastline

Question 24

How does solar energy lead to salt marsh development?

Answer 24

-Vital in the formation of saltmarshes as without it the plants would not be able to photosynthesise, grow and colonise the landscape

Question 25

How does tidal energy lead to salt marsh formation?

Answer 25

-Tidal energy as the tide falls it allows the mixing of fresh fluvial water with saltwater which causes small particles of clay to flocculate and be deposited

Question 26

How sheltered low energy coastlines impact salt marsh formation?

Answer 26

-Rates of deposition need to be higher than rates of erosion
-the absence of high energy is significant as this leads to the formation of constructive waves> promotes accretion

Question 27

What is vegetation succession?

Answer 27

Process where over time an environment develops from a pioneer species that adapted to the conditions all the way to a climax community

Question 28

Bars/Barrier Beaches definition/ formation

Answer 28

Forms acoss an esturay or between two headlands across a bay

-formed in the same way as a spit through longshore drift and deposition
-barns that form as spits extent across a bay to join two headlands are also known as barrier beaches

Question 29

Tombolos definition/ formation

Answer 29

A beach that formed between an island and the mainland

> deposition occurs where waves loose their energy and the tombolo begins to build up this can be due to island sheltering the area of sea causing low energy

> may be covered at high tide e.g Sapton Sands, Devon where a lagoon has formed too

Question 30

Offshore bars/Barrier island definition and formation

Answer 30

-An offshore bar forms further out to sea
-Is where we have an area of sea bed that is shallower than normal
-waves approaching a gently sloping coast deposit material due to friction with the sea bed reducing velocity and energy
-builds up then causes waves to break out at sea instead of depositing

-they can also be formed from destructive waves eroding the coastline and depositing it offshore