Wednesday, 17 November 2010
Tuesday, 21 September 2010
Plate Tectonics, Earthquakes and Volcanoes!
This can be a particularly fascinating topic for pupils, nonetheless, it can be difficult to understand and grasp certain concepts. Therefore I will try and break it down into sizeable chunks, as well as making it enjoyable and interesting.
To understand earthquakes and volcanoes, it is vital to look at the Earth's plates. So what exactly are the Earth's plates and what do they do?
*The movement of the Earth's plates causes earthquakes and volcanoes.
*The map above shows the world's main tectonic plates. The point at which two plates meet is called a plate boundary.
*Most of the world's earthquakes and volcano zones are found on or near to plate boundaries.
The Earth's plates move in different directions, and there are three main types of plate boundary. These are listed below:
1) At a constructive plate boundary two plates move apart from each other.
2) At a destructive plate boundary two plates move towards each other.
3) At a conservative plate boundary two plates slide past eachother.
An easier way to remember this is that constructive plate boundaries create new land; destructive plate boundaries destroy land; and conservative plate boundaries neither create nor destroy land.
Plate Tectonics in more detail-
Constructive plate boundaries: At a constructive plate boundary (also known as a divergent plate boundary) two plates move apart from each other. As the plates move apart, magma rises through the gap in the Earth's crust and cools down to form new crust. An example is the Mid-Atlantic Ridge, where a chain of underwater volcanoes have formed along the plate boundary.
Destructive plate boundaries: At a destructive plate boundary (also known as a convergent plate boundary) two plates move towards each other. When an oceanic plate moves towards a continental plate, the denser oceanic plate sinks below the continental plate. As the oceanic plate sinks, it melts and forms magma. Magma sometimes rises through the cracks in the continental crust to form a volcano. In addition, at a destructive plate boundary, the movement of the plates may push the continental crust upward to form fold mountains. This process is called folding.
Conservative plate boundaries: At a conservative plate boundary (also known as a transform plate boundary) the plates move horizontally past each other, without creating or destroying the earth's crust. A famous example is the San Andreas Fault, USA.
Below is a diagram to show all three plate boundaries:
Earthquakes-
Instead of me blabbering on, here is a great video by the National Geographic on earthquake destruction:
We have established that the movement of the Earth's plates can cause earthquakes. So why is this? Plates do not move smoothly. Sometimes a plate gets stuck. Pressure builds up and when this pressure is released an earthquake can occur.
The point below the Earth's surface where the pressure is released is called the focus. The point on the Earth's surface directly above the focus is called the epicentre. When pressure is released from the focus, shock waves are produced. These waves are called seismic waves. The seismic waves are strongest at the epicentre of an earthquake. This is where the most damage is caused during an earthquake. The seismic waves spread out from the focus like ripples on a pond. As they travel outwards they lose energy.
Earthquakes can have a devastating effect on people and the environment. The immediate or primary effects of an earthquake include the collapse of buildings, roads and railways. People may be killed or injured and property is damaged. The long-term or secondary effects of an earthquake include gas explosions and fires. Communications can fail, as telephone lines and computer links are cut. Water can become contaminated as sewage and clean water pipes fracture. A lack of clean water can lead to the spread of disease. Below is a video of the Seattle earthquake of 2001. Have a look at the effects of the earthquake. Could it have been more devastating?
Nonetheless, the damage could have been worse if it wasn't for the fact that Seattle is in a MEDC. Natural disasters such as earthquakes tend to have as greater impact upon LEDCs than MEDCs. Buildings in LEDCs are not always strong enough to withstand the damage caused by earthquakes. LEDCs do not have sufficient healthcare facilities to deal with emergency situations. Access and communications in LEDCs tend to be poor. It is difficult to warn people about possible dangers on bring them emergency supplies. LEDCs also have limited money and resources to rebuild areas that are damaged.
Measuring earthquakes-
The strength of an earthquake is recorded using a machine called a seismometer. This picks up vibrations and tremors recording the strength of an earthquake. This strength, or scientifically known as magnitude, is measured using the Richter Scale.
To understand earthquakes and volcanoes, it is vital to look at the Earth's plates. So what exactly are the Earth's plates and what do they do?
*The movement of the Earth's plates causes earthquakes and volcanoes.
*The map above shows the world's main tectonic plates. The point at which two plates meet is called a plate boundary.
*Most of the world's earthquakes and volcano zones are found on or near to plate boundaries.
The Earth's plates move in different directions, and there are three main types of plate boundary. These are listed below:
1) At a constructive plate boundary two plates move apart from each other.
2) At a destructive plate boundary two plates move towards each other.
3) At a conservative plate boundary two plates slide past eachother.
An easier way to remember this is that constructive plate boundaries create new land; destructive plate boundaries destroy land; and conservative plate boundaries neither create nor destroy land.
Plate Tectonics in more detail-
Constructive plate boundaries: At a constructive plate boundary (also known as a divergent plate boundary) two plates move apart from each other. As the plates move apart, magma rises through the gap in the Earth's crust and cools down to form new crust. An example is the Mid-Atlantic Ridge, where a chain of underwater volcanoes have formed along the plate boundary.
Destructive plate boundaries: At a destructive plate boundary (also known as a convergent plate boundary) two plates move towards each other. When an oceanic plate moves towards a continental plate, the denser oceanic plate sinks below the continental plate. As the oceanic plate sinks, it melts and forms magma. Magma sometimes rises through the cracks in the continental crust to form a volcano. In addition, at a destructive plate boundary, the movement of the plates may push the continental crust upward to form fold mountains. This process is called folding.
Conservative plate boundaries: At a conservative plate boundary (also known as a transform plate boundary) the plates move horizontally past each other, without creating or destroying the earth's crust. A famous example is the San Andreas Fault, USA.
Below is a diagram to show all three plate boundaries:
Earthquakes-
Instead of me blabbering on, here is a great video by the National Geographic on earthquake destruction:
We have established that the movement of the Earth's plates can cause earthquakes. So why is this? Plates do not move smoothly. Sometimes a plate gets stuck. Pressure builds up and when this pressure is released an earthquake can occur.
The point below the Earth's surface where the pressure is released is called the focus. The point on the Earth's surface directly above the focus is called the epicentre. When pressure is released from the focus, shock waves are produced. These waves are called seismic waves. The seismic waves are strongest at the epicentre of an earthquake. This is where the most damage is caused during an earthquake. The seismic waves spread out from the focus like ripples on a pond. As they travel outwards they lose energy.
Earthquakes can have a devastating effect on people and the environment. The immediate or primary effects of an earthquake include the collapse of buildings, roads and railways. People may be killed or injured and property is damaged. The long-term or secondary effects of an earthquake include gas explosions and fires. Communications can fail, as telephone lines and computer links are cut. Water can become contaminated as sewage and clean water pipes fracture. A lack of clean water can lead to the spread of disease. Below is a video of the Seattle earthquake of 2001. Have a look at the effects of the earthquake. Could it have been more devastating?
Nonetheless, the damage could have been worse if it wasn't for the fact that Seattle is in a MEDC. Natural disasters such as earthquakes tend to have as greater impact upon LEDCs than MEDCs. Buildings in LEDCs are not always strong enough to withstand the damage caused by earthquakes. LEDCs do not have sufficient healthcare facilities to deal with emergency situations. Access and communications in LEDCs tend to be poor. It is difficult to warn people about possible dangers on bring them emergency supplies. LEDCs also have limited money and resources to rebuild areas that are damaged.
Measuring earthquakes-
The strength of an earthquake is recorded using a machine called a seismometer. This picks up vibrations and tremors recording the strength of an earthquake. This strength, or scientifically known as magnitude, is measured using the Richter Scale.
Saturday, 18 September 2010
Glaciation!
An Introduction-
During the Ice Age, many areas across the world were permanently covered by ice, including the UK. But what actually is glaciation?
A glacier is a body of ice that moves through a valley. Glaciers have shaped many landscapes through the processes of erosion, deposition and transportation. Glaciers are still shaping parts of the world today!
In more depth-
10,000 to 20,000 years ago, glaciers and ice sheets covered 32% of the land surface. Today 10% is covered by ice. 22% of the land is underlain by continuous or discontinuous zones of permanently frozen ground. The glacial age is not over, it has only diminished in its overall extent and intensity.
At maximum glaciation few areas of the earth were unaffected by ice activity and action. The last world-wide glaciation occurred during the Pleistocene epoch which comprised some twenty extreme cold periods interspersed by periods of milder weather, interglacials.
The Ice Age-
*During the last Ice Age, 2 million to 10,000 years ago the climate was much colder than it is today.
*In upland areas, snow remained on the ground all year. As more and more snow was added each year, it slowly compresses to form ice.
*In some areas, enormous ice sheets covered the whole landscape. The whole of northern Britain was covered in ice. Glaciers as a result have shaped many parts of Britain.
*In other places, ice only filled the valleys, forming glaciers. These glaciers moved downhill and shaped the landscape.
*Today, ice and snow still permanently cover countries within the Arctic Circle, such as Greenland, Northern Canada and parts of Russia.
In-depth Ice Age Britain-
No area of tge UK escaped the effects of the ice age: the landscape we see today was created by ice advances over the British land mass. Three main advances have been recognised:
*Anglican Advance (420,000-380,000 years ago, left major deposits in East Anglia)
*Woolstonian Advance (170,000-130,000 years ago, largely affected North Britain)
*Devensian Advance (115,000-18,000 years ago, depositional and meltwater features in Shropshire, Cheshire and Yorkshire)
Glaciation Erosion-
Glaciers form in hollows on the colder, sheltered side of a mountain. These hollows are called corries. Snow and ice gathers in the hollow and over time the corrie gets larger through freeze-thaw weathering. Freeze-thaw weathering also loosens pieces of rocks which then fall onto the glacier. This material is called moraine.
Inside the hollow ice begins to move in a circular motion, called rotational slip. Eventually the ice will move out of the corrie and over the lip of the hollow. The glacier movesa down the mountain-side. At the front of the glacier is the snout. A lake, called a tarn, may form in the corrie. The steep knife-edged ridge between the two corries is called an arete.
As a glacier moves it erodes in the landscape in two ways:
*Abrasion occurs when pieces of rock carried by the ice wear away the landscape. As the glacier moves it transports material with it, which helps the glacier erode and shape the landscape. The material can be frozen within the glacier or found underneath it.
*Plucking occurs when meltwater under a glacier freezes on to the rock surface. As the glacier moves forward it pulls away large fragments of rock from the surface.
Glacial Deposition-
As a glacier moves downhill, temperatures rise and the glacier begins to melt. As the glacier melts, it deposits the material it has been carrying. This deposition usually takes place in lowland areas. Glacial deposition can create distinct landscape features in lowland areas.
Moraine is the rock material carried by the glacier. It is later deposited to form mounds of unsorted rocks and rock particles, which are called moraines. There are several different types of moraine. These are classified according to when and where they were deposited by the glacier.
Types of moraine:
Other facts-
*Drumlins are mounds od boulder clay, deposited by glaciers and shaped by the moving ice. The ice moved over the drumlins to form small egg-shaped hills.
*Erratics are rocks transported many miles by a glacier and later found in an area of a different rock type.
Glacial landforms provide an important resource for the tourist industry. Glaciation helped to create distinctive and interesting landscapes like the Lake District. Tourists and day visitors may visit areas such as the Lake District to go walking, hiking, mountain climbing or absailing. Many glaciated landscapes are protected from large-scale urban or industrial development. Many are National Parks in rural areas where the main land use is for primary industry, such as farming or mining.
During the Ice Age, many areas across the world were permanently covered by ice, including the UK. But what actually is glaciation?
A glacier is a body of ice that moves through a valley. Glaciers have shaped many landscapes through the processes of erosion, deposition and transportation. Glaciers are still shaping parts of the world today!
In more depth-
10,000 to 20,000 years ago, glaciers and ice sheets covered 32% of the land surface. Today 10% is covered by ice. 22% of the land is underlain by continuous or discontinuous zones of permanently frozen ground. The glacial age is not over, it has only diminished in its overall extent and intensity.
At maximum glaciation few areas of the earth were unaffected by ice activity and action. The last world-wide glaciation occurred during the Pleistocene epoch which comprised some twenty extreme cold periods interspersed by periods of milder weather, interglacials.
The Ice Age-
*During the last Ice Age, 2 million to 10,000 years ago the climate was much colder than it is today.
*In upland areas, snow remained on the ground all year. As more and more snow was added each year, it slowly compresses to form ice.
*In some areas, enormous ice sheets covered the whole landscape. The whole of northern Britain was covered in ice. Glaciers as a result have shaped many parts of Britain.
*In other places, ice only filled the valleys, forming glaciers. These glaciers moved downhill and shaped the landscape.
*Today, ice and snow still permanently cover countries within the Arctic Circle, such as Greenland, Northern Canada and parts of Russia.
In-depth Ice Age Britain-
No area of tge UK escaped the effects of the ice age: the landscape we see today was created by ice advances over the British land mass. Three main advances have been recognised:
*Anglican Advance (420,000-380,000 years ago, left major deposits in East Anglia)
*Woolstonian Advance (170,000-130,000 years ago, largely affected North Britain)
*Devensian Advance (115,000-18,000 years ago, depositional and meltwater features in Shropshire, Cheshire and Yorkshire)
Glaciation Erosion-
Glaciers form in hollows on the colder, sheltered side of a mountain. These hollows are called corries. Snow and ice gathers in the hollow and over time the corrie gets larger through freeze-thaw weathering. Freeze-thaw weathering also loosens pieces of rocks which then fall onto the glacier. This material is called moraine.
Inside the hollow ice begins to move in a circular motion, called rotational slip. Eventually the ice will move out of the corrie and over the lip of the hollow. The glacier movesa down the mountain-side. At the front of the glacier is the snout. A lake, called a tarn, may form in the corrie. The steep knife-edged ridge between the two corries is called an arete.
As a glacier moves it erodes in the landscape in two ways:
*Abrasion occurs when pieces of rock carried by the ice wear away the landscape. As the glacier moves it transports material with it, which helps the glacier erode and shape the landscape. The material can be frozen within the glacier or found underneath it.
*Plucking occurs when meltwater under a glacier freezes on to the rock surface. As the glacier moves forward it pulls away large fragments of rock from the surface.
Glacial Deposition-
As a glacier moves downhill, temperatures rise and the glacier begins to melt. As the glacier melts, it deposits the material it has been carrying. This deposition usually takes place in lowland areas. Glacial deposition can create distinct landscape features in lowland areas.
Moraine is the rock material carried by the glacier. It is later deposited to form mounds of unsorted rocks and rock particles, which are called moraines. There are several different types of moraine. These are classified according to when and where they were deposited by the glacier.
Types of moraine:
Other facts-
*Drumlins are mounds od boulder clay, deposited by glaciers and shaped by the moving ice. The ice moved over the drumlins to form small egg-shaped hills.
*Erratics are rocks transported many miles by a glacier and later found in an area of a different rock type.
Glacial landforms provide an important resource for the tourist industry. Glaciation helped to create distinctive and interesting landscapes like the Lake District. Tourists and day visitors may visit areas such as the Lake District to go walking, hiking, mountain climbing or absailing. Many glaciated landscapes are protected from large-scale urban or industrial development. Many are National Parks in rural areas where the main land use is for primary industry, such as farming or mining.
BBC Northern Ireland
There is a great site on the internet that focuses on five key areas of geography, relating it to areas within Northern Ireland. The five key areas are: Coasts; Mountains, Lakes and Rivers; Land Use and Economic Activity; Ecosystems and Settlement. The site covers geographic areas from Key Stage 3 to A Level. The link is provided below:
http://www.bbc.co.uk/northernireland/landscapes/teachers.shtml
http://www.bbc.co.uk/northernireland/landscapes/teachers.shtml
River Landscapes and Processes
Key facts about the river system:
*The point where a river begins is called the source. Where the river reaches the end of its journey is called the mouth.
*The area of land drained by a river and its tributaries is called the drainage basin.
*Tributaries are the small rivers that join the main river channel. The point at which two rivers meet is called a confluence. The greater the number of tributaries, the denser the drainage basin.
*The boundary between two drainage basins is known as the watershed. A watershed is usually a ridge of highland.
Do you think you could draw a river system with the following features and label them? Try to plot these features into your diagram:
Watershed, source of the river, main river channel, tributaries, confluence, mouth of river.
Also, try these websites to further your knowledge on river systems:
GCSE: http://www.bbc.co.uk/schools/gcsebitesize/geography/riverswater/
A Level: http://www.s-cool.co.uk/alevel/geography/river-processes-and-management.html
*The point where a river begins is called the source. Where the river reaches the end of its journey is called the mouth.
*The area of land drained by a river and its tributaries is called the drainage basin.
*Tributaries are the small rivers that join the main river channel. The point at which two rivers meet is called a confluence. The greater the number of tributaries, the denser the drainage basin.
*The boundary between two drainage basins is known as the watershed. A watershed is usually a ridge of highland.
Do you think you could draw a river system with the following features and label them? Try to plot these features into your diagram:
Watershed, source of the river, main river channel, tributaries, confluence, mouth of river.
Also, try these websites to further your knowledge on river systems:
GCSE: http://www.bbc.co.uk/schools/gcsebitesize/geography/riverswater/
A Level: http://www.s-cool.co.uk/alevel/geography/river-processes-and-management.html
Systems in Geography
Geography is often about systems. Examples can include industrial systems, ecological systems and farming systems. Geographical systems can be open or closed.
An open system has inputs and outputs.
A closed system has no inputs or outputs- it is a continuous cycle.
A river is an open system with inputs, processes and outputs. It is also part of a larger system called the hydrological cycle. This is explained in more detail in the post below:
An open system has inputs and outputs.
A closed system has no inputs or outputs- it is a continuous cycle.
A river is an open system with inputs, processes and outputs. It is also part of a larger system called the hydrological cycle. This is explained in more detail in the post below:
Thursday, 29 July 2010
Riparian Environments
The Hydrological Cycle
The Hydrological Cycle is a closed system, where water is continuously cycled between the oceans, the land, and the atmosphere in a series of processes known as the global hydrological cycle.
Water moves through the hydrological cycle via a series of flows or transfers. Water is also stored within the system, for example, in a lake.
Below is a diagram to show the hydrological cycle:
**Student Quiz Round**
Can you match the components to their meanings?
1) _______: water soaking into the soil from the surface.
2) _______: water moving within rocks below the ground.
3) _______: water moving downhill through the soil layers. It will generally move slowly, but flow may concentrate along the lines of roots or soil weaknesses and form natural pipes; the flow in these will be much faster.
4) _______: water deposited on the ground as a liquid or as a solid, for example rain, hail, snow, or even fog.
5) _______: water moving downhill with rivers.
6) _______: water moving across the surface of the ground. This my happen when the rain cannot soak quickly enough into the ground, for example whre there are tarmac surfaces or hard-baked soil, or even during heavy rainfall. Saturated overland flow is more common and occurs when the soil is saturated and infilration cannot take place.
7) _______: the combined processes of evaporaton and transpiration that result in the loss of water from the leaf. Transpiration is the loss of water through tiny holes called stomata in the leaf surface. In practice it is very difficult to calculate the two amounts seperately, so they are often grouped together.
8) _______: plants trap some of the precipitation so it may not immediately pass to the ground. Some may drip to the ground as throughfall; some may flow down the stem as stemflow. Alternatively, the precipitation may evaporate directly off the leaf and never reach the ground.
9) _______: water moving from the surface layers of soil into deeper layers of soil and rock.
10) ______: water changing from its liquid form to a gas (water vapour) and returning to the atmosphere.
**Channel Flow, Evaporation, Evapotranspiration, Groundwater Flow, Infiltration, Interception, Overland/Surface Flow, Percolation, Precipitation, Throughflow**
The drainage basin as part of the hydrological system
A drainage basin is an area of the land's surface from which a river receives its supply of water. The edge of a drainage system can be marked by an imaginary line called the watershed. The watershed is usually marked by areas of higher land.
Drainage Basin System
Unlike the hydrological system, the drainage basin works as an open system requiring inputs from outside in order to function. Below is a diagram of the drainage basin system:
Drainage basins have many different characteristics that influence how quickly or slowly the main river within them responds to a period of intense rainfall. More information is explained in the following section about storm hydrographs.
Storm Hydrographs
The dischatrge of a river at any point can be plotted on a hydrograph. A storm, or flood, hydrograph shows the river's response to a single rainfall event. An annual hydrograph indicates the yearly pattern of flow. Both types of hydrograph are useful tools as they allow us to study drainage basin processes and river channel response.
The main features of a storm hydrograph can be viewed in the figure below:
http://www.s-cool.co.uk/alevel/geography/river-profiles/storm-hydrographs-and-river-discharge.html#reading-the-hydrograph
The Hydrological Cycle is a closed system, where water is continuously cycled between the oceans, the land, and the atmosphere in a series of processes known as the global hydrological cycle.
Water moves through the hydrological cycle via a series of flows or transfers. Water is also stored within the system, for example, in a lake.
Below is a diagram to show the hydrological cycle:
**Student Quiz Round**
Can you match the components to their meanings?
1) _______: water soaking into the soil from the surface.
2) _______: water moving within rocks below the ground.
3) _______: water moving downhill through the soil layers. It will generally move slowly, but flow may concentrate along the lines of roots or soil weaknesses and form natural pipes; the flow in these will be much faster.
4) _______: water deposited on the ground as a liquid or as a solid, for example rain, hail, snow, or even fog.
5) _______: water moving downhill with rivers.
6) _______: water moving across the surface of the ground. This my happen when the rain cannot soak quickly enough into the ground, for example whre there are tarmac surfaces or hard-baked soil, or even during heavy rainfall. Saturated overland flow is more common and occurs when the soil is saturated and infilration cannot take place.
7) _______: the combined processes of evaporaton and transpiration that result in the loss of water from the leaf. Transpiration is the loss of water through tiny holes called stomata in the leaf surface. In practice it is very difficult to calculate the two amounts seperately, so they are often grouped together.
8) _______: plants trap some of the precipitation so it may not immediately pass to the ground. Some may drip to the ground as throughfall; some may flow down the stem as stemflow. Alternatively, the precipitation may evaporate directly off the leaf and never reach the ground.
9) _______: water moving from the surface layers of soil into deeper layers of soil and rock.
10) ______: water changing from its liquid form to a gas (water vapour) and returning to the atmosphere.
**Channel Flow, Evaporation, Evapotranspiration, Groundwater Flow, Infiltration, Interception, Overland/Surface Flow, Percolation, Precipitation, Throughflow**
The drainage basin as part of the hydrological system
A drainage basin is an area of the land's surface from which a river receives its supply of water. The edge of a drainage system can be marked by an imaginary line called the watershed. The watershed is usually marked by areas of higher land.
Drainage Basin System
Unlike the hydrological system, the drainage basin works as an open system requiring inputs from outside in order to function. Below is a diagram of the drainage basin system:
Drainage basins have many different characteristics that influence how quickly or slowly the main river within them responds to a period of intense rainfall. More information is explained in the following section about storm hydrographs.
Storm Hydrographs
The dischatrge of a river at any point can be plotted on a hydrograph. A storm, or flood, hydrograph shows the river's response to a single rainfall event. An annual hydrograph indicates the yearly pattern of flow. Both types of hydrograph are useful tools as they allow us to study drainage basin processes and river channel response.
The main features of a storm hydrograph can be viewed in the figure below:
http://www.s-cool.co.uk/alevel/geography/river-profiles/storm-hydrographs-and-river-discharge.html#reading-the-hydrograph
Coasts: Transport and Deposition
Transport and deposition
Waves approaching at right angles to the coast move material up the beach if the waves are constructive. Constructive waves have a long wavelength but low height. Destructive waves are closer together and higher. As they plunge on the beach they comb down material and flatten the beach gradient.
Waves breaking on a beach at an oblique angle move sand and shingle by the process of longshore drift. The breaking wave (the swash) moves material up the beach at an angle whilst returning water (backwash) moves the material back at right angles to the beach. The net effect is a longshore movement.
Offshore, the build up of water against the coastline creates a current parallel to the shore. Whilst it can only move sand-sized sediments, it is capable of moving tens of thousands of tonnes of sand per year.
Waves approaching at right angles to the coast move material up the beach if the waves are constructive. Constructive waves have a long wavelength but low height. Destructive waves are closer together and higher. As they plunge on the beach they comb down material and flatten the beach gradient.
Waves breaking on a beach at an oblique angle move sand and shingle by the process of longshore drift. The breaking wave (the swash) moves material up the beach at an angle whilst returning water (backwash) moves the material back at right angles to the beach. The net effect is a longshore movement.
Offshore, the build up of water against the coastline creates a current parallel to the shore. Whilst it can only move sand-sized sediments, it is capable of moving tens of thousands of tonnes of sand per year.
Coastal Processes and Landforms
Erosion at the coast
This section will go into greater depth about the processes affecting coastal environments, and what landforms occur because of it. First, I'll look at erosion at the coast.
Erosion can be seen in action on cliff coastlines. It is most rapid on soft rock coastlines. The processes responsible for cliff erosion can be classified into two types:
*Those active at base of cliff (cliff-foot or marine processes, including hydraulic action, corrasion and attrition
*Those active on the cliff face (sub-aerial processes, involving the action of weathering
The patterns of erosion are influenced by a wide range of factors including:
*rock type- its resistance to wave action, its resistance to sub-aerial processes (landslides, gulleying), and its solubility.
*rock structure- the way the rock is divided by joints, bedding planes, and faults. Erosion takes place in joints, cracks and bedding planes.
*beach character- a wide beach may be protective and halt erosion even on weak cliffs. The size of the beach may vary with the seasons. The beach may shrink if erosion and sediment supply is reduced 'updrift' by sea walls or groynes. Offshore dredging may remove beach material from the coast zone.
Hydraulic Action
This is the action of breaking waves on cliffs. A storm may throw hundreds of tonnes of water against a cliff face with every breaker. The shock of the impact can loosen rocks and air trapped in joints and faults can blast the rock with extreme pressure.
Corrasion
This is the process by which pebbles and sand forced against cliffs succeed in wearing away new rock. Corrasion (sometimes referred to as abrasion) produces wave-cut notches under cliffs and, eventually, wave-cut platforms. For corrasion to continue, attrition must be effective.
Attrition
This is the process by which erosion continues to operate by grinding down cliff fall material. After hydraulic action and corrasion have eroded cliffs,the eroded material lies at the base of the cliff, forming a protective armour which is often too large for the sea to move. By grinding smaller particles against these large block, the size is eventually reduced until the sea can move them away.
Solution can also cause coastal erosion as acids in the water dissolve rock particles and minerals.
Wednesday, 28 July 2010
Coastal Environments: An Introduction
Coasts- an introduction.
The coast is that unique, valuable, and often threatened area where the sea meets the land. The coastline is an ever-changing boundary zone between the habitable terrestrial environment and the inhospitable marine environment. Coasts are valued in many ways as they are:
*premium economic sites for industry and marine trade
*rich and diverse habitats and ecosystems
*highly valued sites of tourism and recreation
*a natural form of coastal protection (wide, gently sloping beaches)
*sites of dense residential development
There is considerable competition for land and sea resources by various groups, often resulting in severe conflicts. Coasts form geomorphologically active landscapes, undergoing constant change.
Coastal Systems
It is important to realise that coasts are dynamic and places of constant change. The changes are the result of four independent controlling influences, and they are listed below:
*Global tectonics- can operate over a very long period of time
*Relative land-sea changes- can operate over a very long period of time
*Intervention by humans (short-term of rapid impact)- i.e. sea defences, port development, recreation, industrial or residential development.
*Natural processes of coastal erosion and deposition- accretion.
It is the latter that will be mentioned first in this blog.
Short-term natural processes
This section will focus on the short-term natural processs, and explore how waves, tides, winds and mass movement processes can change the form of coasts. This section will be broken down into a further three sub-sections.
What are the energy and sediment inputs into the coastal system?
Source of coastal sediment- The narrow zone between high and low water (the littoral zone) is a place where energy and sediment concentrate. The energy sources include wind, waves, and tidal currents. The sediments on the coast include sand, shingle and clay. Under natural conditions, there is always a balance between the energy levels and the sediment movements so that erosion taking place in one location is balanced by deposition taking place somewhere else.
Rivers bring sediment from the land to the coast. Usually fine grained silts, clays and sands. This can result in salt-marshes and deltas. Erosion of cliffs by the sea produces large amounts of material for beach building. Usually coarse sand and shingle is produced. The sea is an important source of sediments. Huge volumes of sand and clay were deposited here in the ice age. Tides and waves may bring these shorewards to build offshore bars or add to beaches.
Sources of coastal energy
There are three main energy sources at work in the coastal zone: the wind, waves and currents.
The Wind- The wind can be very effective at moving sand inland to produce sand dunes, particularly on beaches with shallow, offshore gradients and a large supply of sandy sediment. These often produce important ecosystems, such as Oxwich Bay in South Wales, and the Studland dunes of Dorset.
A picture to show dunes that have been formed at Saunton Sands, North Devon.
Waves
The power of waves depends on the wave height. A smallincrease in wave height produces a large increase in wave energy. The wave height depends on the speed of the wind, and the length of time the wind has been blowing over the sea. This depends on the distance- or fetch. In Britain, the maximum fetch is west and south-west over the Atlantic.
Tidal Currents
Incoming (flood) and outgoing (ebb) tidal current can move fine-grained sand and silts. Tidal currents are most powerful where the tide range is high and the coastline is a funnel shape.
Monday, 26 July 2010
An Introduction
Hello!
My name is Christian Capell, and this year I have completed a BSc Degree in Geography and Planning at the University of Birmingham. In September, I will start my PGCE in Secondary Geography at the University of Leicester. In preparation for this, I have created a blogspot to demonstrate development in my subject knowledge. As I have particularly focused on Human Geography in my Degree, I feel it is necessary to focus on Physical Geography. From now until the start of the PGCE, this blog will blossom into a site of useful resources and information relating to Geography. I hope you enjoy visiting my blog!
My name is Christian Capell, and this year I have completed a BSc Degree in Geography and Planning at the University of Birmingham. In September, I will start my PGCE in Secondary Geography at the University of Leicester. In preparation for this, I have created a blogspot to demonstrate development in my subject knowledge. As I have particularly focused on Human Geography in my Degree, I feel it is necessary to focus on Physical Geography. From now until the start of the PGCE, this blog will blossom into a site of useful resources and information relating to Geography. I hope you enjoy visiting my blog!
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