Saturday, January 21, 2012

CORAL REEF

Coral reefs are marine ridges or mounds, which have formed as a result of the deposition of calcium carbonate by living organisms, predominantly corals, but also a rich diversity of other organisms such as coralline algae and shellfish. Coral reefs provide a unique habitat characterised by high diversity and density of life. They occur globally in two distinct marine environments; deep, cold water (3-14°C) coral reefs, and shallow, warm water (21-30°C) coral reefs in tropical latitudes

Major coral reef sites are seen as red dots on this world map. Most of the reefs, with a few exceptions are found in tropical and semitropical waters, between 30° north and 30° south latitudes. 

The condition of the growth of coral polyps.
1. High temperature- temperature above 20 degree Celsius.This is usually found in warm waters where the warm ocean current areas.
2. Clear shallow sea water- for the coral reef to survive well in seawater that is shallow and free from sediment. Coral need sunlight to grow , deep or muddy water is unsuitable.
3. Plentiful supply of oxygen and plankton- Coral need oxygen and plankton to grow. The part of the coast is washed by waves , currents and tides which maintain a fresh and plentiful supply of oxygen and plankton for the coral.

COAST: Formation of Spits and Tombolos

A Spit is a long, narrow ridge of deposited materials that extends from the mainland into the sea. An example in Brunei is Muara Spit and Kuala Tutong Spit. When the spit is connected the island to the mainland to form a feature is called the Tombolos.



The long shore drift transports materials along the coast. If there is a sudden change in the direction of the coast, the longshore drift continues to transport the materials in the original direction to the deep sea. As the longshore drift enters the deep water, the materials are deposited. Over time, these materials accumulate above the water to form a spit. The spit continues to grow with the continuous deposition of materials. The spit join a nearby island to the mainland to form a tombolo.




Dungeness Spit, Washington. Olympic Mountains in background




Spit at Mission Bay, San Diego



COAST: Longshore Drift

Movement of material along a beach. When a wave breaks at an angle to the beach, pebbles are carried up the beach in the direction of the wave (swash). The wave returns to the sea at right angles to the beach (backwash) because that is the steepest gradient, carrying some pebbles with it. In this way, material moves in a zigzag fashion along a beach. Longshore drift is responsible for the erosion of beaches and the formation of spits (ridges of sand or shingle projecting into the water). Attempts are often made to halt longshore drift by erecting barriers, or groynes, at right angles to the shore.


Waves sometimes hit the beach at an angle. The incoming waves (swash) carry sand and shingle up onto the shore and the outgoing wave takes some material away with it. Gradually material is carried down the shoreline in the same direction as the longshore current.

Longshore drift carries sand and shingle up coastlines. Deposited material gradually builds up over time at headlands forming a new stretch of land called a spit. A spit that extends across a bay is known as a bar. 



COAST: Wave Cut Platform

A wave-cut platform, or shore platform is the narrow flat area often found at the base of a sea cliff or along the shoreline of a lake, bay, or sea that was created by the action of waves. Wave-cut platforms are often most obvious at low tide when they become visible as huge areas of flat rock. Sometimes the landward side of the platform is covered by sand, forming the beach, and then the platform can only be identified at low tides or when storms move the sand.

FORMATION
It forms after destructive waves hit against the cliff face, causing undercutting between the high and low water marks, mainly as a result of corrasion and hydraulic power, creating a wave-cut notch. This notch then enlarges into a cave. The waves undermine this portion until the roof of the cave cannot hold due to the pressure and freeze-thaw weathering acting on it, and collapses, resulting in the cliff retreating landward. The base of the cave forms the wave-cut platform as attrition causes the collapsed material to be broken down into smaller pieces, while some cliff material may be washed into the sea. This may be deposited at the end of the platform, forming an off-shore terrace.

Because of the continual wave action, a wave-cut platform represents an extremely hostile environment and only the toughest of organisms can utilize such a niche.

VIDEO: Coastal Landforms


Cliff Slumping 
video


Bays and Head Lands

video


Constructive waves

video


North Landing, Flamborough, The Holderness Coast

video




COAST: Depositional Landforms

Coastal Deposition is when the sea drops or deposits material. This can include sand, sediment and shingle.

Beaches
The beach is the area between the lowest spring tide level and the point reached by the storm waves in the highest tides. Every beach is different but they are usually made up of material deposited on a wave-cut platform.



Spit
Longshore drift moves material along a coastline. Where there is an obstruction or the power of the waves is reduced the material is deposited. Where rivers or estuaries meet the sea deposition often occurs. The sediment which is deposited usually builds up over the years to form a long ridge of material (usually sand or shingle). Such a ridge is called a spit. Spurn Head on the Holderness Coast is an example of this feature.




MARSHES

Salt Marshes
A salt marsh is a coastal marsh that forms on mud flats. They usually form in very sheltered inlets and estuaries, or behind spits (places where fine sediment accumulates). Salt marshes form as vegetation builds up on these mud flats.



Sand Dunes
Sand dunes are created by strong winds and not by coastal erosion or deposition. As sand is blown up a beach is forms small hills. These are often rooted together by long-rooted grasses such as marram grass. Marram grass is usually planted to reduce the erosion of the otherwise unstable sand dunes.


 



COAST: Cliff Collapse

Cliff Recession 
Rates of coastal erosion are determined by a range of factors. These include the fetch of a wave, type of beach, the supply of beach material by longshore drift, slope of the cliff, vegetation cover, local hydrology, the rate at which cliff debris are removed from the foot of the cliffs and the material that cliffs are made of. These are each examined below: .
  • fetch of the wave - the longer the fetch of the wave the greater the erosive energy of the wave
  • type of beach - beaches dissipate wave energy. The higher the beach the lower the energy in the wave as it meets the foot of the cliff (if it does at all!)
  • the supply of beach material by longshore drift - if there is a consistent supply of new beach material by longshore drift this will help preserve the beach. If this has been stopped, by building groynes for example, this can increase the rate of cliff recession as there is no beach material to absorb the energy of the waves.
  • vegetation cover - cliffs with vegetation cover tend to be less resistant to recession as roots help bind and reinforce the cliff material.
  • local hydrology - if there is a large amount of surface run off and infiltration this can increase the rate of cliff recession.
  • the rate at which debris are removed from the foot of cliffs - if material that has formed at the foot of cliffs is rapidly transported away then the cliffs will be quickly exposed to erosion.
  • cliff material - the material that cliffs are made of has a significant impact on cliff recession. Soft boulder clay cliffs recede much quicker than cliffs formed from sedimentary rock such as chalk. These types of cliff recede in quite different ways.
Soft Cliff Material
Cliffs formed from boulder clay, material deposited by glacial periods, are susceptible to high rates of coastal erosion. The Holderness Coast is an example of a coastline formed from boulder clay and is the fastest eroding coastline in Europe. The soft boulder clay is quickly eroded through hydraulic action and abrasion. However this is not the only way it is being eroded. Sub-aerial processes, such as rainfall, also cause erosion. This often happens where layers of boulder clay, left behind by melting glaciers, become saturated and cause the cliff to slump. The debris on the beach is then eroded by the sea leaving the cliff exposed once more.

COAST: Wave action

The size of a wave depends on its fetch. The fetch is the distance a wave travels. The greater the fetch, the larger the wave. Wind also has a significant effect on the size of waves. The stronger the wind the larger the wave. As a wave approaches a beach it slows. This is the result of friction between the water and the beach. This causes a wave to break.




There are two main types of wave. These are constructive and destructive waves. :

Constructive waves build beaches. Each wave is low. As the wave breaks it carries material up the beach in its swash. The beach material will then be deposited as the backwash soaks into the sand or slowly drains away. These waves are most common in summer.



video
Constructive Waves

Destructive waves destroy beaches. The waves are usually very high and very frequent. The back wash has less time to soak into the sand. As waves continue to hit the beach there is more running water to transport the material out to sea. these waves are most common in winter.



THE EARTH'S RING OF FIRE


Circling the Pacific Basin, on the bottom of the sea bed, lie a dramatic series of volcanic arcs and oceanic trenches. The zone - the 'Ring of Fire' - notorious for frequent earthquakes and volcanic eruptions, coincides with the edges of one of the world's main tectonic plates. More than half of the world's active volcanoes above sea level are part of the ring.

VOLCANO

What is a volcano?
A volcano is a conical hill or mountain formed by material from the mantle being forced through an opening or vent in the Earth's crust.

What are the main features of a volcano?




What are active, dormant and extinct volcanoes?
Volcanoes are found in three states - extinct, dormant and active. 
  • An extinct volcano will never erupt again. 
  • A dormant volcano has not erupted in 2000 years. 
  • An active volcano has erupted recently and is likely to erupt again 
What are the different types of volcano?
There are a number of different types of volcanoes. The way they are formed depends on a number of factors e.g. the fluidity of the lava (how runny it is) and the temperature of the lava. 


GLACIATION: Glacial erosion

Glacial Erosion
There are three main types of glacial erosion - plucking, abrasion and freeze thaw.




  • Plucking is when melt water from a glacier freezes around lumps of cracked and broken rock. When the ice moves downhill, rock is plucked from the back wall. 
  • Abrasion is when rock frozen to the base and the back of the glacier scrapes the bed rock. 
  • Freeze-thaw is when melt water or rain gets into cracks in the bed rock, usually the back wall. At night the water freezes, expands and causes the crack to get larger. Eventually the rock will break away.

LIMESTONE

What is Limestone?
Limestone is an organic, sedimentary rock. This means it was formed from the remains of tiny shells and micro-skeletons deposited on the sea bed. They were compressed to form solid rock. Limestone is made up of calcium carbonate and reacts with diluted hydrochloric acid. Limestone is formed in layers - called bedding planes. These bedding planes contain vertical cracks called joints. Joints and bedding planes make the rock permeable.

Stalagmites and stalactites



Erosion of Limestone
Weathering is the breakdown of rock by physical, chemical or biological processes. Limestone areas are weathered when rainwater, which contains a weak carbonic acid, reacts with limestone. When it rains limestone is dissolved. Rainwater erodes the joints and bedding planes. In doing this Karst scenery is created.

Limestone (Karst) Features - overview




Limestone (Karst) Features - above ground
Karst scenery includes:
  • Swallow hole - An exposed limestone joint down which a surface river 'disappears'.
  • Clints and grykes - Rainwater flowing over an impermeable surface will, on reaching (permeable) limestone, be able to dissolve the joints into grooves called grykes, leaving blocks or clumps of limestone in between called clints
  • Limestone pavements - Exposed clints and grykes. The video below shows a limestone pavement at Malham, Yorkshire Dales.
video



Limestone (Karst) Features - below ground
  • Stalactite - Water dripping from the roofs of caves leave behind microscopic particles of calcium carbonate. These build up as icicle shaped stalactites.
  • Stalagmite - Drips splashing onto the floor of caves leave behind microscopic particles of calcium carbonate. These build up on the floor of caves.

Limestone and recreation
Limestone areas are popular due to the range of leisure activities that people can participate in. These include walking, pot holing, climbing and abseiling


WEATHERING

Weathering is the process of weakening and breaking up rocks. It is the physical and chemical breakdown of rocks and minerals at or near earth's surface.


What are the different types of weathering?
There are four main types of weathering. These are freeze-thaw, onion skin (exfoliation), chemical and biological weathering.

Freeze-Thaw
Most rocks are very hard. However, a very small amount of water can cause them to break. When water seeps into cracks and freezes it then expands. This powerful force can increase the size of cracks. Over time the repeated freeze-thaw action of water can break rocks apart. Eventually, pieces of rock break off creating scree.

The image below shows the impact of freeze thaw on a rock in Iceland



Exfoliation or Onion Skin Weathering 
This type of erosion is common in warm areas. As the sun shines on rocks during the day it causes them to expand. During the night the rock contracts due to the colder temperature. Over time this continued process causes small pieces of surface rock to flake off.

The image below shows a close up of onion skin weathering.



Chemical Weathering
Chemical weathering causes an alteration to the chemical composition of rock due to a reaction. Water that is slightly acidic can dissolve rock. An example of this would be slightly acidic rain changing the chemical composition of limestone to form a limestone pavement. This occurs on the surface and along the joints and bedding planes of limestone. You can also see evidence of this on buildings made from limestone.

The image below shows limestone that has been chemically weathered.



Biological Weathering 
Biological weathering is the effect of living things. For example as the roots of a tree extend into the ground they can prise rocks apart. Ivy growing up a building can cause bricks to loosen. It also occurs on a much smaller scale through lichen and moss. 



Friday, January 20, 2012

RIVER: Flooding and management issues


The likelihood of a river bursting its banks and flooding is determined by factors in the surrounding landscape, such as steepness of the river valley, the amount of vegetation and the prevailing rock-type. The short-term impact of floods can be catastrophic, but they can have positive long-term effects as well.
Causes of flooding

A flood occurs when a river bursts its banks and the water spills onto the floodplain. Flooding tends to be caused by heavy rain: the faster the rainwater reaches the river channel, the more likely it is to flood. The nature of the landscape around a river will influence how quickly rainwater reaches the channel.


The following factors may encourage flooding:
  • A steep-sided channel - a river channel surrounded by steep slopes causes fast surface run-off.
  • A lack of vegetation or woodland - trees and plants intercept precipitation (ie they catch or drink water). If there is little vegetation in the drainage basin then surface run-off will be high.
  • A drainage basin, consisting of mainly impermeable rock - this will mean that water cannot percolate through the rock layer, and so will run faster over the surface.
  • A drainage basin in an urban area - these consist largely of impermeable concrete, which encourages overland flow. Drains and sewers take water quickly and directly to the river channel. Houses with sloping roofs further increase the amount of run-off.
Flood management techniques include river engineering, afforestation and planning controls to restrict urban development on floodplains.

RIVER LANDFORMS

Upper-course river features include steep-sided V-shaped valleys, interlocking spurs, rapids, waterfalls and gorges. Middle-course river features include wider, shallower valleys, meanders, and oxbow lakes. Lower-course river features include wide flat-bottomed valleys, floodplains and deltas.

Upper course features



RIVER PROCESSES

River processes shape the land in different ways as the river moves from its source to its mouth.

Erosion
Erosion involves the wearing away of rock and soil found along the river bed and banks. Erosion also involves the breaking down of the rock particles being carried downstream by the river.

The four main forms of river erosion
  • Hydraulic action - the force of the river against the banks can cause air to be trapped in cracks and crevices. The pressure weakens the banks and gradually wears it away.
  • Abrasion - rocks carried along by the river wear down the river bed and banks.
  • Attrition - rocks being carried by the river smash together and break into smaller, smoother and rounder particles.
  • Solution - soluble particles are dissolved into the river.


RIVER PROFILES

A river changes shape as it flows from its source (where a river starts) to its mouth (where a river flows into a sea or lake). The shape of both the long profile (a slice through the river from source to mouth) and the cross profile (a slice across the river) changes.

Long profiles
Long profile of a river



The source of a river is often - but not always - in an upland area. Near the source, a river flows over steep slopes with an uneven surface. It often flows over a series of waterfalls and rapids. Highland areas are usually composed of hard igneous rocks, which are ideal for forming such features.

As a river flows down steep slopes the water performs vertical erosion. This form of erosion cuts down towards the river bed and carves out steep-sided V-shaped valleys. As the river flows towards the mouth, the slopes become less steep. Eventually the river will flow over flat land as it approaches the sea. The discharge (amount of water flowing) will increase as the river approaches the sea.

Cross profiles
Cross profiles of a river


Near the source of a river there is more vertical erosion as the river flows downhill, using its energy to overcome friction (A). As a result the channels are narrow and shallow and may contain large boulders and angular fragments eroded and weathered from the steep valley sides. The sediment in the river creates turbulence and friction.

As the river approaches the mouth, velocity and energy increase due to increased discharge. The river performs more lateral erosion making the channel wider, and smoother (B) and (C). As a result there is less turbulence and friction, making the flow of water more efficient.

RIVER

The hydrological cycle
The hydrological cycle is also known as the water cycle. Seas and oceans contain 97 per cent of the world's water, and ice holds 2 per cent. That leaves just 1 per cent of the world's water as fresh water on land or in the air. This water is recycled again and again through the process of evaporation, condensation and water transfers such as surface run-off.

The key stages in the hydrological cycle


Terminology for the study of rivers
  • Drainage basin - the area of land drained by a river.
  • Catchment area - the area within the drainage basin.
  • Watershed - the edge of highland surrounding a drainage basin. It marks the boundary between two drainage basins.
  • Source - The beginning or start of a river.
  • Confluence - the point at which two rivers or streams join.
  • Tributary - a stream or smaller river which joins a larger stream or river.
  • Mouth - the point where the river comes to the end, usually when entering a sea.
Key features of a river




GEOLOGICAL TIME: Classification of rocks


Rocks found on the Earth's surface actually come from inside the Earth - so they tell us a lot about the Earth's interior. They are classified (organised) into three main groups: igneous rocks, sedimentary rocks and metamorphic rocks.

Rock types

 

Type of rockExample
Igneous rock
Lichen on granite
Granite
Sedimentary rock
Navajo Sandstone formations in Utah
Sandstone
Metamorphic rock
Slate in the Lake District
Slate




Igneous rock
Igneous rocks are formed by magma from the molten interior of the Earth. When magma erupts it cools to form volcanic landforms. If magma cools inside the Earth it forms intrusive rock, which may later be exposed by erosion and weathering. Examples of igneous rocks include basalt and granite.

Example of igneous rocks
Type of rockExample
Basalt
Basalt colums in the Giant's Causeway
Basalt
Granite
A granite outcrop on Bodmin Moor
Granite



Metamorphic rock
Metamorphic rocks have been subjected to tremendous heat and/or pressure, causing them to change into another type of rock. They are usually resistant to weathering and erosion and are therefore very hard-wearing. Examples of metamorphic rocks include marble, which originates from limestone,slate, which originates from clay, and schists formed from sandstone or shale (sedimentary rocks).

Slate Quarry, Cullipool


Sedimentary rock
Sedimentary rocks are formed from sediments that have settled at the bottom of a lake, sea or ocean, and have been compressed over millions of years. The sediment comes from eroded rocks carried there by rivers or ice, and from the skeletons of sea creatures. Examples of sedimentary rocks include sandstone, limestone, chalk and clay.

Limestone pavement on top of Malham Cove





GEOLOGICAL TIME

The geological timescale and the processes that happen occur over a very long period of time, often millions of years. Each geological period describes a particular, major event that is thought to have happened at that time.
Geological time

The Earth is thought to be 4,600 million years old. Life is believed to have become dominant on earth 542 million years ago.

Chart showing the major geological periods




The geological periods relate to events which have happened in the Earth's history. For example, during the carboniferous period there were tropical weather conditions in the UK and coal and limestone were formed.

The most recent period in geological time is called the quaternary, when the Ice Age occurred. Rocks are formed at different times, and are a result of the environment present during that time. For example, chalk is formed in the cretaceous period, as this is when warm tropical seas were present around the shores of the UK.







Courtesy: BBC