Coasts - Dunes

Question 1

Movement of sand

Answer 1

Suspension (1%) - sand carried in wind
Traction / Creep (4%) grains rolls and push each other along the ground
Saltation = 95% grains bounce along the wind. The wind picks the grains up but then drops them due to either gravity becoming the stronger force or the wind loses energy.

Question 2

Requirements for dune formation

Answer 2

Sand dunes require the following to form-
A large flat beach
A large supply of sand
A large tidal range so sand has time to dry
Onshore wind to move sand to the back of the beach.
An obstacle such as driftwood for the dune to form against.

Question 3

Foredunes

Answer 3

Vegetation on the foredune has to grow in sand that is very low in nutrients and dries out quickly (poor water retention).

It has to cope with exposure to sun, salt and wind-blown sand.

Spinifex and marram grass are often the first species to colonise the foredune, beginning the process of stabilisation because their roots bind the sand.

Question 4

Yellow Dunes

Answer 4

Dominant plant species is marram grass which is salt tolerant and thrives in sand.

Sand is being blown away and replenished.

These dunes are taller and have some protection from the shore wind allowing the leeward side to support more vegetation such as small shrubs.

Question 5

Grey dunes

Answer 5

Further inland, these are taller, older dunes.
The grey name comes from their colour which contains more soil nutrients and can therefore retain more water and support a more diverse range of vegetation such as banksias and eucalypts.

Question 6

Swales and blowouts

Answer 6

Each line of dunes is separated by a trough called a swale. Swales are formed by the ongoing removal of sediment from the leeward base on one line of dunes and up the windward side of the next dune line.

Sometimes swales are eroded so much that they reach down as far as the water table, resulting in the formation of salty ponds.

Occasionally, a dune may develop a huge depression called a blowout, where strong winds remove sand from an area that has lost its protective vegetation cover