Coasts: Why are they different and dynamic? Flashcards
1
Q
What is a coast?
A
Area where land meets the sea, affected by the waves and tides
2
Q
What are the different zones on a shore?
A
- Offshore
- Nearshore
- Foreshore
- Backshore
- Beach face
- Berm
- Dunes
3
Q
What are the factors leading to the differences and dynamism of coastal environments?
A
- Waves
- Currents
- Tides
- Geology
- Human activity
- Types of ecosystems
4
Q
What are the parts of a wave?
A
- Crest
- Trough
5
Q
What is wave length?
A
Distance from crest to crest or trough to trough
6
Q
What is wave height?
A
Vertical distance between crest and trough
7
Q
What is wave frequency?
A
The number of crests or troughs that pass a fixed point
8
Q
What are the factors affecting waves?
A
- Wind velocity
- Wing duration
- Fetch- wind distance
9
Q
What determines wave energy?
A
- Wave steepness
- Wave period (time taken to travel through one wave length)
Higher energy= steep+short
10
Q
What shape do waves have in shallow water?
A
Elliptical shape
11
Q
What shape do waves have in deep water?
A
Circular shape
12
Q
What is the wave length in shallow water?
A
Short
13
Q
Wave is the wave height in shallow water?
A
High
14
Q
What is the wave length in deep water?
A
Long
15
Q
What is the wave height in deep water?
A
Low
16
Q
What is swash?
A
When waves break on the beach, water rushes up, carrying sediments up the shore. Loses energy due to gravity and friction
17
Q
What is backwash?
A
When waves return to the sea, due to the pull of gravity it carries sediments back towards the sea. Loses energy due to friction
18
Q
What are the types of waves?
A
- Constructive waves
- Destructive waves
19
Q
What are constructive wave characteristics?
A
- Calm weather
- Gentle slope, sheltered coast
- Long wave length and low wave height
- Low wave frequency (6-8)
- Swash>backwash
- Deposition is dominant process
- Low energy environment
- Spilling breakers
- Produce gentle slope with fine sediments
20
Q
What are destructive wave characteristics?
A
- Windy, stormy weather
- Steep slope and exposed coast
- Short wave length and high wave height
- High wave frequency (12-14)
- Backwash>swash
- Erosion is dominant process
- High energy environment
- Plunging/surging breakers
- Produce steep slope with coarse sediments
21
Q
What is wave refraction?
A
- Process in which waves change direction (bend) when they approach an uneven coast
- Due to friction with the seabed causing a change in wave speed
- Waves converge on headlands and diverge at bays
- At headlands, increased wave height and greater erosive energy
- At bays, decreased wave height and lower erosive energy
- Uneven impact on shoreline
22
Q
What are the different forms of erosion?
A
HAAS
1. Hydraulic action
2. Abrasion (corrasion)
3. Attrition
4. Solution (corrosion)
23
Q
What is hydraulic action?
A
- Waves strike against rock surface
- Trap air in joints
- Air in compressed, exerts pressure on the joints
- Rocks shatter
24
Q
What is abrasion (corrasion)?
A
- Waves break and sediments carried are hurled against the rock surfafces and coast
- Knock and scrape against coast and rock surfaces
- Repeated hurling action and scraping weaken the surfaces
- Surface breaks down
- Cliff is undercut (mostly by abrasion)
25
What is attrition?
- Waves carry rock particles
- Hit against each other
- Repeated contact break down and smoothen the surfaces of these rock particles
26
What is solution (corrosion)?
- Seawater reacts chemically with water soluble minerals in the coast and rock surfaces
- Dissolve them
- Rock surfaces weaken and disintegrate
- Eg. Limestone dissolved by carbonic acid in seawater
27
What are longshore currents?
- Waves approach coastline at an oblique angle
- Due to direction of prevailing wind
- Create longshore currents which are currents that flow parallel to the coast
28
What is beach drift?
- As waves break, swash carries sediments up the beach at the same angle as the wave approached
- Then brought perpendicularly down the shore through backwash due to gravity
- Zig-zag movement of sediments known as beach drift
29
What is longshore drift?
- A result of both longshore currents and beach drift
- Transport sediments along a coast for some distance
30
Difference between a sheltered and exposed coast in terms of sediments
Sheltered coast: Constructive waves--> Strong swash carry more sediments up the beach--> finer materials further inland, coarser deposited nearer the sea
Exposed coast: Destructive waves--> Strong backwash carries more sediments down the beach--> finer materials nearer the sea, coarser further inland
31
How does sediment size affect deposition?
Coarser ones are deposited first as when wave energy decreases, waves are unable to carrt the load anymore
32
What are the 3 types of erosional landforms?
1. Cliffs and wave-cut platforms
2. Headlands and Bays
3. Caves, arches, stacks and stumps
33
What are the 2 types of depositional landforms?
1. Beaches
2. Spits and Tombolos
34
Describe the formation of cliffs and wave-cut platforms
1. Hydraulic action and abrasion erode **cracks** on the rock surfaces, gradually enlargening the cracks to form a **notch**
2. The **notch** is further eroded and deepened to produce a **cave**
3. As the process continues, the **roof of the cave collapses** due to a **lack of support**
4. Over time, a **overhanging cliff** forms which will also **collapse** due to **lack of support**
5. The **materials deposited** at the foot of the cliff may be **carried by waves** and **thrown against the base** of the cliff to cause **more erosion**
6. The cliff **retreats inland** and a **gently sloping** wave-cut platform **appears at the base** where the cliff used to be and is submerged at high tide.
35
Describe the formation of headlands and bays
1. Coastlines with **alternate bands** of **more resistant** and **less resistant** rock **layers** arranged at **right angles** to the coast have **different rates of erosion**
2. Destructive waves **erode the less resistant rock** more **quickly** than the more resistant rocks to form **bays** (wide, indented coasts)
3. While the harder rocks are more **resistant** and are left **protruding into the sea** forming **headlands**
36
Describe the formation of sea stumps (and thus caves, arches and stacks)
1. **Within headlands**, some rocks may be **less resistant to erosion** and thus are **eroded more quickly** by hydraulic action and abrasion
2. Waves **enlarge lines of weakness** at the base of the headland to form a **notch**
3. The continous action of **erosion** at the base and **undercutting** forms a **cave** when the headland is **hollowed**
4. **Wave refraction** causes two caves at the opposite sides of the headland to be **aligned** and forms an **arch** (a wave eroded passage)
5. Over time, the **roof of the arch becomes unstable** due to further **erosion, gravity and weathering**, causing its **collapse** to form a **stack** (a pillar of rock in the sea left behind when an arch collapses)
6. Continued **wave erosion and weathering** of the stack will **break the rock down** to form a **stump**- smaller rock
37
Define a beach
Zone of sediment deposition, formed by loose sand, gravel, broken shells and corals
38
Why do the composition and size of beach materials vary?
1. Composition depends on the source of materials (eg. eroded cliffs, wave sediments)
2. Size depends on wave energy and source of materials
39
Why does the shape of a beach vary?
Depends on coastal processes
1. Constructive waves
2. Destructive waves
40
Why does the slope of the beach vary?
Depends on grain size
1. Finer grains- gentle gradient
2. Coarse grains- steeper gradient
41
Why do beaches form in bays?
- Due to **wave refraction**, waves approach the shallow sea in front of the **headland first** before they reach the adjacent bays
- As **wave energy** tends to **concentrate at the headland**, **erosion** occurs there
- Along the **bays**, waves are **diverged**, thus energy is spread out and **weakened**
- **Deposition** occurs along the bays and over time, forming a sandy beach
42
Describe the formation of spits and tombolos
1. **Spits** are **long, narrow ridges of sediments** with **one end attached to the land**
2. Formed by **longshore drift**
3. When there is an **abrupt bend** in the coastline, longshore drift **continues to transport sediments** in the **same direction** rather than following the coastline. This **transports the sediments out to sea**
4. As the **strength of the drift weakens** away from the coast, **sediments accumulate** and **rise above the water surface** forming a **spit**
5. When the spit **connects an offshore island to the mainland**, a **tombolo** is formed
