2.3 - Factors Impacting Coastal Recession And Stability Flashcards
(19 cards)
1
Q
How does lithology impact resistance to erosion
A
- Mineral composition: Some minerals are more reactive than others. This affects the rate of chemical weathering for example: Calcite is reactive and so easily chemically weathered, Quartz is not reactive (inert) so chemical weathering is much slower
- Structure: Rocks with fissures (e.g. faults and joints) or porous rocks, weather and erode rapidly.
- Rock classification: the different rock types erode differently due to their different features
2
Q
Sedimentary rocks
A
- They are formed by the compaction and cementation of deposited material, or sediment.
- Examples of sedimentary rocks include shales, sandstone, and limestone
- Erode and weather more rapidly than other types of rock
- Form in layers
- Have weak bedding planes
- They are clastic which means they are made of smaller sediment particles
- Are heavily jointed
- Often have many bedding planes and fracture
3
Q
Metamorphic rocks
A
- form when sedimentary and igneous rocks are altered through heat and pressure, but do not melt in the process
- Examples of metamorphic rocks include slate and marble
- Have a crystalline structure (interlocking crystals which make a strong structure)
- Are often folded and faulted
- Are more resistant than sedimentary rock and less resistant than igneous rocks
- The crystals have a parallel arrangement (foliation) which means they are weaker than igneous rocks
4
Q
Igneous rocks
A
- form when molten rock from the Earth’s mantle cools and hardens
- form when molten rock from the Earth’s mantle cools and hardens Examples of igneous rocks include granite and basalt
- Erode and weather very slowly
- Can be categorised into two types:
- Intrusive igneous rock - forms within the ground, cools slowly, and has large course crystals
- Extrusive igneous rock - forms on the Earth’s surface, and cools quickly, forming smaller crystals
- Have a crystalline structure (interlocking crystals which make a strong structure)
- Fewer joints and weaknesses than in other rocks
5
Q
A
- More resistant rocks erode more slowly than less resistant rocks
- Differential erosion leads to complex cliff profiles and influences rates of recession
- The differences in geology contribute to landforms generated by processes on the coast
- On a discordant coastline differential erosion leads to headlands and bays
- Where there are layers of alternating rock types (strata) this creates a cliff profile where the more resistant rock layers jut out due to the faster erosion of less resistant rock
- Permeability can also affect on the rate of erosion: where permeable rock overlies impermeable rock, the permeable rock is vulnerable to mass movement because the additional weight and lubrication the water creates leads to instability
6
Q
How does vegetation help to stabilise coasts
A
- The plant roots help to bind the soil/sand together reducing the impact of erosion
- Wind speeds are reduced by vegetation which decreases erosion and increases deposition
- Dead plant material adds organic matter (hummus) to the sand and eventually leads to the formation of soil
- Plant stems and leaves covering the ground surface protect sediment from wave erosion and erosion form tidal or longshore currents when exposed at high tide.
- vegetation increases the rate of sediment accumulation: plant stems and leaves interrupt the flow of wind and water, reducing their velocity and encouraging deposition.
7
Q
Why is the coast a difficult environment for plants
A
- They are exposed to high wind speeds at low tide.
- Lack of shade produces a high daily temperature range.
- They are submerged in salty water for half the day.
- The evaporated sea spray makes the sediment saline.
- Salt is highly porous and permeable, so rain water drains quickly- so plants have little fresh water.
- Submerged sediment has its pores saturated with salt water so theres no oxygen for plant roots to respire with.
- Sand lacks nutrients.
8
Q
What is a pioneer species and what is its role
A
- Pioneer species in the coastal environment are the first plants to grow in the harsh coastal environment, paving the way for other plants that are less able to survive the conditions
- Pioneer species help to stabilise the sediment, add organic matter, increase shade, trap more sediment
9
Q
What are halophytes and xerophytes
A
Halophytes: can tolerate salt water, either around their roots, being submerged in salt water (at high tide) or salt spray from the sea
Xerophytes: can tolerate very dry conditions, such as those found on coastal sand dunes where the sandy soil retains very little water due to drainage
10
Q
What does psammosere mean
A
the sequence of plant succession that has been initiated on sand
11
Q
How is marram grass adapted to sand dunes
A
- has waxy leaves to limit water loss through transpiration and resist wind-blown sand abrasion
- has roots that can grow to 3m to reach down the water table
- the stem can grow 1m a year to avoid burial by deposited sand, allows the dune to grow, rapidly forming a yellow dune.
12
Q
Process of sand dune succession
A
- Embryo dunes form when seaweed driftwood or litter provides a barrier or shelter to trap sand.
- As the embryo grows, it is colonised by xerophytic pioneer plants, like sea couch grass, lyme grass, saltwort and sea rocket.
- the embryo dunes alter the conditions to something other plants can tolerate, allowing other plants to colonise and forms a fore dune
- Pioneer plants stabilise the sand allowing marram grass to colonise.
- As the marram grass and sedge grass dies, it adds hummus to the sand, creating soil. A grey dune develops, with plants such as gorse.
- grey dunes and dune slacks are fixed dunes
- The dune is now above high tide level, so rain washes salt from the soil, making it less saline.
- The soil now has improved nutrients and moisture retention, allowing non-xerophytic plants to colonise the dunes until a climax plant community is reached, in equilibrium with the climate and soil conditions.
13
Q
Embryo dunes
A
- Wind-blown dried sand is trapped by debris and deposition begins
- Pioneer species such as lyme grass and sea couch grass begin to colonise, these are halophytic plants which can tolerate high salt levels
- There is little soil content and high pH levels (alkaline)
- Embryo dunes are very fragile and reach a maximum height of 1 metre
14
Q
Fore dunes
A
- The embryo dunes bring some protection against the prevailing wind
- This allows other species of plant to grow such as marram grass
- Marram grass begins to stabilise the dune with its root system which can grow to 3m to reach the water table
- These plants add organic matter to the dunes making the dunes more hospitable for plants that later grow
- A microclimate forms in the dune slack
- Maximum height is 5 metres
15
Q
Yellow dunes
A
- These are initially yellow but darken as organic material adds humus to the soil
- Marram grass still dominates the vegetation, but more delicate flowering plants and insects are found in the dune slacks
- 20% of the dune is exposed, down from 80%
- Height does not exceed 8 metres
16
Q
Grey dunes
A
- Grey dunes are more stable, with less than 10% of exposed sand and have a good range of biodiversity
- Soil acidity and water content increase as more humus is added
- Shrubs and bushes such as gorse begin to appear
- Height is between 8 - 10 metre
17
Q
What does halosere mean
A
a succession in salty water
18
Q
Why do salt marshes form in estuarine areas
A
- A steady supply of sediment from the river
- Shelter from strong waves
- In the estuarine environment fresh water and seawater mix
- This causes flocculation where clay particles stick together causing sediment to build up
19
Q
What does algae do to the deposited sediment in a salt marsh
A
- Binds the sediment together
- Increases organic matter
- Traps more sediment
- The sediment builds up and is covered by the tide for less and less time allowing other plants such as cord grass to colonise
