Coastal Environments Content

Question 1

What is a Fetch?

Answer 1

Fetch is the distance over water that the wind blows in a single direction.

Question 2

Formation of Waves

Answer 2

Waves form as a result of friction between wind and the sea surface.

Question 3

How does Wave Refraction Influence Coastal Landforms?

Answer 3

Wave refraction distributes wave energy along the stretch of a coast. —> Along a complex transverse coast of alternating headlands and bays, wave refraction will concentrate wave energy and therefore erosional activity on the headlands while wave energy will be dispersed in the bays. —> Hence, deposition tends to occur in the bays.

Question 4

What are the 3 types of Breaking Waves?

Answer 4

1) Spilling Waves2) Plunging Waves3) Surging Waves

Question 5

Explain the Wave Refraction Process

Answer 5

As wave fronts approach the shore, their speed will be reduced as the waves feel the bottom ground. —> Since wave fronts approach the shore obliquely (indirectly), they bend and swing around in an attempt to break parallel to the shore. —> The change in speed and distortion of wave fronts is called wave refraction. —> (If refraction is completed, wave fronts will break parallel to the shore.)

Question 6

What are the Characteristics of Spilling Waves?

Answer 6

• Steep waves- Gentle beach gradients- Gradual peaking of the wave until the crest becomes unstable —> results in a *gentle spilling forward* of the crest.

Question 7

What are the Characterisitcs of Plunging Waves?

Answer 7

• Intermediate wave steepness- Occur on steeper beaches than spilling breakers- Distinguished by the *shoreward face of the wave becoming vertical, curling over & plunging forward and downward* as an intact mass of water.

Question 8

What are the Characterisitics of Surging Waves?

Answer 8

• Low wave steepness- Occur on steep beaches- The front face and crest of the wave *remain relatively smooth* —> the wave slides up the beach *without breaking*. —> A large proporrtion of the wave energy is *reflected at the beach shore*.

Question 9

What are the Characterisitcs of a Constructive Wave?

Answer 9

• Occur when wave frequency is low —> particularly when waves advance a gently shelving sea floor- Strong swash & weak backwash- Strong swash carries material up the beach while the weak backwash doesn’t take the material away.- Waves are low & further apart

Question 10

What are the Charactertistics of Destructive Waves?

Answer 10

• Are the result of locally generated strong winds —> which creates waves of high frequency- Weak swash & strong backwash- Backwash is much stronger than swash —> rocks, pebbles & sand are carried back to the sea (material is eroded from the beach). - Waves are steep & close together

Question 11

Define Wave Height (amplitude), Wavelength & Wave Frequency.

Answer 11

WH (A) = The distance between the trough & the crest.WL = The distance between 2 successive crests or troughs.WF = Number of waves per minute.

Question 12

What are the 4 Coastal Erosion Processes?

Answer 12

1. Hydraulic Action2. Abrasion (corrasion)3. Attrition4. Solution (corrosion)

Question 13

Explain the process of Hydraulic Action.

Answer 13

From the sheer power of the waves as they smash against the cliff —> any air trapped in cracks, joints & bedding planes will be momentarily placed under great pressure. —> As the wave retreats —> pressure will be released with explosive force.

Question 14

Explain the process of Abrasion (corrasion).

Answer 14

The process whereby a breaking wave can hurl pebbles & shingle agaisnt a coast —> thereby abrading it. —> Overtime, the rock becomes smooth.

Question 15

Explain the process of Attrition.

Answer 15

The rocks that the sea carries knocks agaisnt each other —> the eroded material itself is worn down. —> They break apart to become smaller & more rounded.

Question 16

Explain the process of Solution (corrosion).

Answer 16

It is a form of chemical erosion which affects calcareous (lime-rich) rock. —> Waves speed up this process.

Question 17

What are the 5 Sub-aerial or Cliff-face Weathering Processes?

Answer 17

1. Salt weathering2. Freeze-thaw weathering3. Biological weathering4. Solution weathering5. Slaking(Mass movements are also important in coastal areas - especially slumping & rock falls.)

Question 18

Explain the process of Freeze-thaw Weathering.

Answer 18

Water enters the cracks in a porous or permeable rock —> When temperatures drop —> the water freezes & expands —> causing the crack to widen & degrades its joints. —> The ice melts & water makes its way deeper into the cracks. —> The process repeates itself until the rock splits entirely.

Question 19

Explain the process of Biological Weathering.

Answer 19

Plant roots such as of molluscus, sponges & urchins can get into small cracks in rocks. —> As the roots grow & burrow down —> the cracks widen, weakening the structure of the rock. —> This causes small pieces of rock to break away.(very important on low-energy coasts)

Question 20

Explain the process of Solution Weathering.

Answer 20

(The chemical weathering of calcium by acidic water.)Limestone is made of calcium carbonate. —> When dissolved in seawater from rockpools (due to the presence of organisms secreting organic acids) —> it makes a weak acid called carbonic acid. —> The carbonic acid passes through joints & bedding planes —> reacts with the rock to form calcium bicarbonate. —> The calcium bicarbonate is soluble & is carried away in solution, —> gradually weathering the limestone.

Question 21

Explain the process of Salt Weathering.

Answer 21

Salt weathering happens when salt spray from the sea enters a crack in a rock —> the sodium & magnesium compounds expand in joints & cracks —> thereby weakening rock structures.

Question 22

Explain the process of Slaking.

Answer 22

(Materials disintegrating when exposed to water, which can be caused by hydration cycles.)Slaking is the process of alternate wetting & drying of rocks. —> Rocks, (especially those containing clay) swell when wet, with subsequent contraction on drying. —> When water enters the pores of a rock —> the rock dilates —> creating tensile stresses —> generating tension cracks. —> The consequent development of microcracks & their propogation further increases porosity —> making the rocks more vulnerable to weathering & erosion.

Question 23

What are the 2 Modes of Sediment Transport?

Answer 23

1. Bedload2. Suspended load

Question 24

Explain the Bedload process.

Answer 24

Bedload: the material carried by a river by being bounced or rolled along its bed. Grains are moved/ transported with continous contact (traction or dragging) —> or by discontinuous contact (saltation) with the seafloor. Traction= The stones are rolled along the river bottom by the water as they are too large to transport in the water.Saltation= Small rocks or pebbles which are too big to be carried within the water are transported and bounce along the bottom of the river bed.

Question 25

Explain the Suspended load process.

Answer 25

Suspended load refers sediment transport which is maintained in suspension by turbulence in the flowing water for considerable periods of time without contact with the stream bed.Suspension occurs when mpderate currents are transporting silts or strong currents are transporting sands.

Question 26

Define a littoral cell system.

Answer 26

A littoral cell system a linked system of sources, transfers and sinks of sediment along a section of coastline.It is a simplified model that examines coastal processes and patterns in a given area.

Question 27

Longshore Drift

Answer 27

The zigzag movement of sediment along a shore caused by waves going up the beach at an oblique angle (swash) and returning at right angles (backwash). This results in the gradual movement of beach materials along the coast.

Question 28

Explain the coastal erosion process of cliffs.

Answer 28

1. Wave refraction concentrates erosion on the sides of headlands. Weaknesses such as joints or cracks in the rocks are exploited, forming caves. 2. Caves enlarge and are eroded further back into the headland until eventually the caves from each side meet and an arch is formed. 3. Continued erosion, weathering & mass movements enlarge the arch and cause the roof of the arch to collapse, forming a high standing stack.

Question 29

What is a wave-cut platform?

Answer 29

Refers to a platform formed by the destructive waves at the base of the cliff.

Question 30

What are the 2 types of coastlines? [TBC]

Answer 30

1. Swash- aligned coastline — orientated parallel to the crests of the prevailing waves, they are closed systems in terms of longshore drift transport and the net littoral drift rates are zero. 2. Drift- aligned coastline

Question 31

Spit, Bar, Tombolo [TBC]

Question 32

What are coral reefs?

Answer 32

Coral reefs are calcium carbonate structures that are an underwater ecosystem characterized by reef-building corals.

Question 33

How do corals function? (hint: symbiotic r/s)

Answer 33

There is a symbiotic relationship between the polyps and the algae (also known as zooxanthellae)

• The algae get shelter and food from the polyp, while the polyp also gets food via photosynthesis.

Question 34

What are the 7 factors that control the distribution of coral reefs?

Answer 34

1. Temperature — optimal conditions for growth are between 23-25°C
2. Depth of Water — less than 25m → generally found on the margins of continents & islands
3. Salinity level of water — corals are intolerant of water with salinity levels below 32psu
4. Light — shallow water as they need light for zooxanthellae which supplies 98% of food requirements to corals.
5. Sediment — clogs up feeding structures & cleansing systems, & sediment-rich water blocks light for photosynthesis
6. Wave action — corals generally prefer strong wave action → ensures oxygenated water & a stronger cleansing action → helps remove trapped sediment & supplies microscopic plankton to coral → However, extreme conditions (eg South Asian tsunami) waves may be too destructive
7. Exposure to air — die if exposed for too long → corals mostly found under low tide mark

Question 35

What are the 3 types of coral reefs?

Answer 35

Fringing reefs

• Corals develop along the continental margins or along the islands.
• The seaward slope is steep and vertical while the landward slope is gentle. The upper surface is uneven and corrugated.

Barrier reefs

• Occur at great distances from shore than fringing reefs
• Commonly separated by a wide, deep lagoon
• More broad, old and continuous and fringing reefs

Atolls

• Rise from submerged volcanic foundations
• A ring of narrow growing corals of horseshoe shape and crowned with palm trees is called atoll. It is generally found around an island or in elliptical form on a submarine platform. There is a lagoon in the middle of coral ring.