Coasts Flashcards
How is the coastline protected?
- coastal sand dunes
- coastal salt marshes, found in many river estuaries
- coastal mangrove swamps, which are found on tropical coastlines
How does hydraulic action influence a beaches lithology.
Heavily joined fissured sedimentary rocks are vulnerable. In very hard igneous rocks basalt granite hydraulic action on cooling cracks my be the only erosive process of operating.
What two categories can coats be divided into?
- Swash-aligned
* Drift-aligned
What is a swash-aligned beach?
Wave crests approach parallel to the coast so there’s limited long shore movement of sediment.
What is a drift-aligned beach?
Wave crests break at an angle to the coast so there is consistent long shore drift and elongated depositions features.
What 2 ways can deposition occur in?
- Gravity settling
* Flocculation
What is gravity settling?
- Energy of transporting waves becomes too low to move sediment.
- Large sediment will be deposited first followed by smaller sediment
- Pebbles -> sand -> silt
Define flocculation?
- Depositional process very important for very small particles e.g. Clay, which are so small they remain suspended in water.
- Clay particles lump together because of electrical or chemical attraction and become large enough to sink.
What are spits?
- Definition: sand or shingle beach ridge extending beyond a turn in the coastline usually greater than 30 degrees.
- At the turn, the long shore drift current spreads out and loses energy leading to deposition.
- The length of the spit is determined by the existence of secondary currents causing erosion (flow of a river or a wave action which limits its length).
Define Holocene
The geological epoch that began about 12,000 years ago at the end of the last Pleistocene ice age.
What is a rocky coastline?
It is a cliff varying in height
What is a coastal plain?
Land which gradually slopes towards the sea across an area of deposited sediment. They also have sand dunes and mud flats. These are sometimes referred to as alluvial coasts
What are primary coasts?
These are coasts dominated by land based processes as deposition at the coast from rivers or new coastal land formed from lava flows
What are secondary coasts?
These are coasts dominated by marine erosion or deposition processes.
What are emergent coasts?
These are coasts where they are rising due to sea level or tectonic uplift.
What are submergent coasts?
These are coasts flooded by the sea, either due to rising sea levels and/or subsiding land.
Explain the different types of wave energy
Low energy: limited fetch and low wind speeds resulting in smaller waves.
High energy: prevailing winds with long wave fetches resulting in powerful waves.
Define the term cliff profile?
The height and angle of a cliff face as well as its features, such as the wave-cut notches or changes in slope angle
What is the Littoral zone?
The wider coastal zone including adjacent land areas and shallow parts of the sea just offshore
What is unconsolidated sediment?
Material such as sand, gravel, clay and slit that has not been compacted and cemented to become sedimentary rock (it has not undergone the process of lithification) and so is loose and easily eroded.
When does most wave erosion occur?
Most waves occur when waves have a larger fetch and speed
Waves approach the coast at 90 degrees
The tide is high, propelling higher up the cliff face.
When old debris has been removed so the cliff face has no protection
What is a fault?
Faults represent major weaknesses within rock layer. Either side of a fault line, rocks are often heavily fractured and broken and these weaknesses are exploited by marine erosion.
Where do joints occur?
Joints occur in most rocks, often in regular patterns, dividing rock strata up into `blocks with a regular shape.
What are fissures?
Fissures are much smaller cracks in rocks, often only a few centimetres or millimetres long.
State two dominant cliff profile characteristics.
- The resistance erosion of the rock
2. The dip of rock strata in relation to the coastline.
What is pore water pressure?
The pressure water experiences at a particular point below the water table due to the weight of water above it.
How does abrasion influence a beaches lithology.
Loose sediment such as shingles and pebbles are formed . softer rocks are more vulnerable than hard igneous rock.
How does attrition influence a beaches lithology.
Softer rocks are very rapidly reduced in size by attrition.
How does solution influence a beaches lithology.
Mainly affects limestone which is vulnerable to solution by weak acids.
When does most wave erosion occur?
Most waves occur when waves have a larger fetch and speed
Waves approach the coast at 90 degrees
The tide is high, propelling higher up the cliff face.
Definition of a permeable rock.
Allow water to flow through them, and include many sandstones and limestones.
Definition of an impermeable rock.
Do not allow groundwater flow and include clays, mudstones and most igneous and metamorphic rocks.
How are tides formed?
The gravitational pull of the Moon acts on the water on the Earth’s surface. The gravitational pull of the Sun and the Earth’s rotation make a minor contribution to the tides. The pull of gravity causes a bulge of water which rotates around locations in the oceans called amphidromic points.
What is a dip?
Simply meaning the angle of rock strata in relation to the horizontal. Dip is a tectonic feature.
What is weathering?
the chemical, biological and mechanical breakdown of rocks into smaller fragments and new minerals in situ
What is surface runoff?
water, usually during heavy rain, flowing down the cliff face and causing erosion of it.
How does vegetation stabilise sediment?
- root of plants bind sediment particles together making them harder to erode
- when submerged, plants growing in sediment provide a protective layer so the surface of the sediment is not directly exposed to moving water and therefore erosion
- plants protect sediment from wind erosion by reducing wind speed at the surface due to friction with the vegetation
What are halophytes?
Halophytes can tolerate salt water, either around their roots, being submerged in salt water (at high tide) or salt spray from the sea
What are xerophytes?
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
What are the environmental conditions like at the sea?
Extreme:
- salt water
- strong winds
- strong tide and wave
What is a sand dune ecosystem called?
Psammosere
What is a salt marsh ecosystem called?
Halosere
Define coastal accretion?
The deposition of sediment at the coast and the seaward growth of the coastline, creating new land. It often involves sediment deposition being stabalised by vegetation
Define dynamic equilibrium?
The balanced state of a system when inputs and outputs balance over time
What is pore water pressure?
The pressure watre experiences at a particular point below the water table due to the weight of the water above it
What is beach morphology?
The shape of a beach, including its width and slope (the beach profile) and features such as berms, ridges and runnels
What is a blow hole?
Forms when a coastal cave turns upwards and breaks through the flat cliff top
What are currents?
Flows of seawater in a particulr direction driven by winds or differences in water density, salinity or temperature.
Define mass movement?
The downslope movement of rock and soil, it is an umbrella term for a wide range of specific movements including landslide, rockfall and rotational slide
Define isostatic change?
A local rise or fall in land level
Define eustatic change?
Involves a rise or fall in water level caused by a change in the volume of water. This a global change
What is post-glacial isostatic adjustment?
Refers to the uplift experienced by land following the removal of the weight of sheets
What is a ria?
A drowned river valley in an unglaciated area caused by sea level rise flooding the valley
What is a barrier island?
Offshore sediment bars, usually sand dune covered but unlike spits not attached to the coast
What is dredging?
Scooping or sucking sediment up from the seabed or a river bed, usually for the construction sand or gravel, or to deepen a channel for navigation
What is dissipation?
The term used to describe how the energy of a wave is decreased by friction with beach material during the wave swash up the beach
What is a storm surge?
A short-term change in sea level caused by a low pressure system
What is a megaproject?
A very expensive (over $1 billion), technically difficult and usually long-term engineering project
What is a return period (or recurrence interval)
Refers to the frequency of a flood of a particular magnitude. A 1:100 flood event will occur, on average every 100 years
What are environmental refugees?
Communities forced to abandon their homes due to natural processes
What is sustainable coastal management?
Managing the wider coastal zone in terms of people and their livelihoods
What does SMP stand for?
Shoreline Management Plan
What does ICZM stand for?
Integrated Coastal Zone Management
Name 5 types of hard engineering defence?
Rip-rap Rock breakwater Sea wall Revetments Groynes
Describe 3 features of a marine erosion dominated cliff profile
Steep face
Undercut
Limited cliff face debris
Describe 3 features of a sub-aerial process dominated cliff profile
Curved slope profile
Vegetation
Accumulated debris
Describe the features of marram grass
Waxy leaves
Up to 3 m long roots
Grow 1 m per year
Last in 60 degree heat
What factors affect wave size?
Wind Strength
Wind duration
Water depth
Wave fetch
Name 4 reasons for change in sea levels
Thermal expansion of the ocean
Snow melt on mountains
The melting of major ice sheets
Tectonic activity lifting or lowering coast lines
Name 4 facts about the Maldives
Population of 340000
The highest land is 2.3 m above sea level
By 2100, it’s projected that 77% of the land will be submerged
87% of drinking water is provided through rain as the ground water is unsuitable
