8.2. Sand Dunes, Salt Marshes and Mangroves

Question 1

Sand dunes

Answer 1

ridges of sand that form at the back of a beach and also on spits and barrier islands

Question 2

Importance of Sand Dunes

Answer 2

• most important depositional landforms
• a distinctive coastal ecosystem where many rare plants and animals are found
• help protect land behind them from coastal erosion and from coastal flooding
• sand dunes are easily damaged so people often try to protect them as conservation areas

Question 3

Requirements for formation of sand dunes

Answer 3

• a wide sandy beach that dries out at low tide
• a strong, prevailing, onshore wind to carry the sand up the beach
• some sort of obstacle at the top of the beach to cause the wind to deposit the sand

Question 4

Sand dune stages

Answer 4

1) Embryo Dunes
harsh environment for plants
2) Fore Dunes
hardy plants survive
3) Yellow Dunes
many hardy plants like marram grass
4) Grey Dunes
soil becomes richer and moister so a range of shrubs grow
5) Dune Slack
surface lowered until it reaches water table
6) Mature Dunes
trees grow

Question 5

3 ways in which sand grains move

Answer 5

1) Saltation
- Sand grains bounce or jump slightly above the surface
when blown by the wind.
- With each bounce, the grains usually reach heights of less than 5 cm above the surface, and move horizontally 5-10 cm.
- Saltation accounts for about 95% of a sand grain’s movement.
2) Creep
Heavy sand grains “creep” by rolling along the surface.
3) Suspension
- Very light sand grains, or heavier grains when wind velocities are high, move by “suspension” when it is blown high into the air

Question 6

What determines the way in which sand grains move?

Answer 6

The size, density & shape of the sand particles determine whether they move by suspension, saltation or creep.

Question 7

Salt marshes

Answer 7

• coastal wetlands that are flooded and drained by salt water brought in by the tides
• they are marshy because the soil may be composed of deep mud and peat

Question 8

where are salt marshes located?

Answer 8

• In river estuaries, or behind spits, where large amounts of silt are deposited by the ebbing tides and inflowing rivers.
• Salt marshes start life as a zone of inter-tidal mudflats which later become vegetated.
• Salt marshes are essentially vegetated mudflats

Question 9

Mangroves

Answer 9

• Coastal features found on tidal mudflats in tropical and subtropical areas
• Have stilt roots that anchor the plant in the soft mud, slowing waves movement and encouraging the deposition of more mud
• They need a gently sloping, muddy coastline and a warm climate
• They are halophytic and are well adapted to living in salt water

Question 10

Importance of Mangroves

Answer 10

• Mangroves help protect the coastline from flooding
• Mangroves also protect the coast from erosion as they encourage the deposition of mud, extending the coastal area into the sea