Sand dunes/Mudflats/Mudflows/Lahars

Question 1

List 3 conditions needed for sand dunes to form?

Answer 1

1. Large tidal range= exposed sand can be dried out and moved by the wind
2. Shallow beach gradient= good conditions for sediment transport
3. Vegetation growth for further growth of dune = an obstacle to trap sand

Question 2

Define the process of vegetation succession:

Answer 2

• At each stage of the succession, the plant community alters the soil and microclimate-> growth of another group of species
• Eventually, the climax community is reached where the vegetation is in a state of equilibrium with the environment-> no further influx of species
• If human interferences take place, e.g. allowing cattle on the land, climax will not be reached but a plagioclimax is created

Question 3

Describe the features at Embryo+ Fore dunes

Answer 3

• sand accumulation, which persists above the high tide line, is colonised by the first perennial plants in plant succession
• growth of sandwort

Question 4

Describe features at yellow dunes

Answer 4

• upward growth of the embryo dunes allows this surface to be raised- out of reach except for highest storm waves
• growth of marram grass- tall robust traps sand by reducing the wind speed at the surface, binding sand together

Question 5

Describe features at Grey dunes

Answer 5

• vegetation had developed so creates a more or less complete cover
• PH= high, drought
• Nutrients= short supply
• growth of creeping willow

Question 6

What are Dune slacks ?

Answer 6

• a number of wet, large depressions in the dunes due to wind eroding the sand

Question 7

Describe features at a heath/woodland

Answer 7

• form behind yellow/grey dunes
• supply of sand is cut off- smaller dune features
• growth of birch

Question 8

How do mudflats form?

Answer 8

1. Saltwater flows into the estruary, bringing sediment which meets the river, also carrying sediment
2. Rising tides create a buffer to the river flow, slowing the velocity-> deposition
3. The two flows meet, causing the fine particles to suspend( flocculation)
4. At low tide, the inter-tidal area of mud is left exposed with only water left in the permenant channels
5. The mudflat is formed, but susceptible to changes in sea level, wave actions or a change in discharge

Question 9

Where do mudflats form?
(3 examples)

Answer 9

• sheltered shorelines (not exposed to powerful waves)
• on the landward side of a spit
• on low lying areas which are all submerged at high tide

Question 10

How are mudflows/lahars formed?

Answer 10

Mudflows occur when a mixture of water and sediment (typically clay, silt and sand) moves down a slope. This can happen due to heavy rainfall, snowmelt or changes in the water table