2.3) Lithology

What is lithology?

The physical and chemical composition of rocks

What are the three types of rocks?

igneous, metamorphic, sedimentary

How are igneous rocks formed?

formed from solidified lava or magma, in interlocking crystals

What are examples of an igneous rock?

granite and basalt

What is the rate of erosion in igneous rocks?

less than 0.1 cm per year

What amount of joints, faults and fractures can be found in igneous rocks?

* few joints and weaknesses
* composed of interlocking crystals, forming hard, resistant rock= so less recession

What are the bonds like in igneous rocks?

crystalline structure- interlocking mineral crystals

What are examples of igneous rock are anomalies?

- Newly formed volcanic islands can exhibit very rapid erosion rates of 40m per year

How are metamorphic rocks formed?

formed by recrystallisation under extreme heat and pressure

What are examples of metamorphic rocks?

marble and slate

What is the rate of erosion in metamorphic rocks?

0.1-0.3cm per year

What amount of joints, faults and fractures can be found in metamorphic rocks?

* heavily folded and faulted
* crystals in metamorphic rocks are often orientated in the same direction (foliation) making them weaker than the interlocking crystals of igneous rocks.

What are the bonds like in metamorphic rocks?

- crystalline structure\= foliation means crystals are orientated in one direction which produces weaknesses

How are sedimentary rocks formed?

formed by the compaction and cementation of deposited material

What are examples of sedimentary rocks?

sandstone and limestone

What is the rate of erosion in sedimentary rocks?

0.5-0.10cm per year

What amount of joints, faults and fractures can be found in sedimentary rocks?

* Often heavily jointed as a result of compaction and pressure release.
* Weak bedding planes
* Fractures
* Geologically young

What are the bonds like in sedimentary rocks?

- clastic, unconsolidated materials e.g clay\= so eroded faster

What is an example of a coastline with high rates of recession?

The boulder clay of Holderness coast in Yorkshire retreats at 2-10 m per year

What is the steepness and stability of a landward dip?

steep and stable

What is the steepness and stability of a horizontal dip?

near vertical, stability depends on number of notches due to weaker rock bands

What is the steepness and stability of a seaward dip high angle?

sloping, low angle, unstable, rock falls

What is the steepness and stability of a seaward dip low angle?

profile may exceed 90 degrees, very vulnerable to rock falls

What are the features of permeable rocks?

* they're porous e.g chalk
* they have numerous joints e.g limestone

Why are permeable rocks less resistant to weathering?

* water percolates and comes into contact with a large surface area that can be chemically weathered: e.g limestone weathered by carbonation converting calcium carbonate to soluble calcium bicarbonate

What examples are there of impermeable rock?

Clays, mudstones, and most igneous and metamorphic rocks are impermeable\= don't allow water to flow through them

How can layers of permeable and impermeable rock create an unstable cliff profile?

* Water flows through the permeable (sands) but can't flow through the impermeable (clay), so flows along the interface.
* Groundwater flow through rock layers can weaken rock by removing the cement that binds them together. Weak, unconsolidated layers slump.

How does high pore pressure lead to slumping and sliding?

* Pore water pressure in the saturated layer pushes rock particles apart.
* Reduces friction between grains in unconsolidated material
* Lubricates lines of weakness, e.g. joints and bedding planes.
* Saturation promotes mass movement through lubrication and by adding weight.

How does vegetation stabilise the coast?

* stabilises unconsolidated sediment and protects it from erosion
* plant roots bind sediment together, making it harder to erode
* plant stems and leaves covering the ground surface protect sediment from wave erosion
* prevent sediment from wind erosion at low tide.
* vegetation increases the rate of sediment accumulation: when the vegetation dies it adds its organic matter to the soil.

What does plant succession provide?

* natural coastal protection
* stabilises the coast
* provides environments
* salt marshes= flooding defence

How do pioneer plants change the conditions of the soil?

* add humus (when they decay)
* retain moisture meaning the soil becomes less alkaline
* trap and hold together the sand and mud with their roots= reduces erosion and creates stability

What does the building stage act as during plant succession?

* a physical barrier between land and sea
* new plants can establish and take over
* slows down water so reduces erosion
* grasses e.g Marram grass out competes pioneer plants and grow quickly into tall plants

What does the climax stage act as during plant succession?

* when there is a balance between all the natural factors and vegetation= the final type of vegetation establishes itself
* taller and more complex plant species

What is an example of a pioneer plant?

algae and lichen

What are examples of plants present in the building stage?

Marram grass

What is flocculation?

The mixing of fresh water and sea water in the estuary causes clay particles to stick together and sink.

What are halophytic plants?

specially adapted to saline conditions to colonise mud

What is a halosere?

A salt marsh ecosystem- plant succession in salty water

What are xerophytic plants?

specially adapted to dry conditions to colonise bare sand

What is a psammosere?

A sand dune ecosystem- plant succession on sand

Where do sand dunes form?

Where there is:

* a plentiful supply of sand (low energy coast)
* large areas for sand to dry out
* onshore winds to blow sand on land
* an obstacle to trap the sand e.g driftwood
* wet sand isn't picked up by the wind

How are sand dunes formed?

1. Sand dunes are found in low energy coasts where there are onshore winds and a plentiful supply of sand. They are formed when sand is moved up the beach by the wind.
2. Obstacles e.g driftwood cause wind speeds to decrease so sand is deposited.
3. This then builds up over time forming hummocks.
4. The sand is then colonised by drought tolerant plants such as sea couch- this stabilises the sand and encourages more sand to accumulate there. Over time these pioneer plants die and add humus to the soil and enable better water retention, allowing larger plants such as marram grass to grow here. This further stabilises the dune.
5. Over time the oldest dunes migrate inland as newer embryo dunes are formed.
6. These mature dunes can reach heights of up to 10m.

How are salt marshes formed?

1. Salt marshes form when mudflats are raised to the level of the average high tide.
2. The accumulation of mud is most common in estuaries where the river brings fine-grained sediment to low energy water.
3. Submerged plants in salt marshes like Eelgrass provide a protective layer so the sediment below is not directly exposed to the water and eroded.
4. Over time, the pioneer plants change the conditions and trap more sediment which builds the salt marsh up to a higher level which can then be stabilised by building and climx plants such as salt marsh grass and rush which stabilise these areas further.

4) Over time, the pioneer plants change the conditions and trap more sediment which builds the salt marsh up to a higher level which can then be stabilised by building and climx plants such as salt marsh grass and rush which stabilise these areas further.