Wednesday, February 29, 2012

THE UNDERLYING THEORIES AND MODELS OF POPULATION

1. Malthusian Population Theories
  • Malthus argued that "Population grow at a rate that exceeds available food supply"
  • Population can survive only because of positive checks on population growth. That is, in mortality due to famines, epidemics, wars and natural causes, preventive checks e.g. abstinence and contraception.
2. Neo-Malthusian
  • Contemporary follower of the Malthus ideas
  • They focus more on the health and mortality consequences of a changing environment e.g. Each argue that the impact on the environment is a function of population size, level of affluence and technology.

Monday, January 30, 2012

GEOGRAPHIC INFORMATION SYSTEM

The advent of cheap and powerful computers over the last few decades has allowed for the development of innovative software applications for the storage, analysis, and display of geographic data. Many of these applications belong to a group of software known as Geographic Information Systems (GIS). Many definitions have been proposed for what constitutes a GIS. Each of these definitions conforms to the particular task that is being performed. Instead of repeating each of these definitions, I would like to broadly define GIS according to what it does. Thus, the activities normally carried out on a GIS include:
  • The measurement of natural and human made phenomena and processes from a spatial perspective. These measurements emphasize three types of properties commonly associated with these types of systems: elements, attributes, and relationships.
  • The storage of measurements in digital form in a computer database. These measurements are often linked to features on a digital map. The features can be of three types: points, lines, or areas (polygons).
  • The analysis of collected measurements to produce more data and to discover new relationships by numerically manipulating and modeling different pieces of data.
  • The depiction of the measured or analyzed data in some type of display - maps, graphs, lists, or summary statistics.

REMOTE SENSING

Remote sensing can be defined as the collection of data about an object from a distance. Humans and many other types of animals accomplish this task with aid of eyes or by the sense of smell or hearing. Geographers use the technique of remote sensing to monitor or measure phenomena found in the Earth's lithosphere, biosphere, hydrosphere, and atmosphere. Remote sensing of the environment by geographers is usually done with the help of mechanical devices known as remote sensors. These gadgets have a greatly improved ability to receive and record information about an object without any physical contact. Often, these sensors are positioned away from the object of interest by using helicopters, planes, and satellites. Most sensing devices record information about an object by measuring an object's transmission of electromagnetic energy from reflecting and radiating surfaces.

Remote sensing imagery has many applications in mapping land-use and cover, agriculture, soils mapping, forestry, city planning, archaeological investigations, military observation, and geomorphological surveying, among other uses. For example, foresters use aerial photographs for preparing forest cover maps, locating possible access roads, and measuring quantities of trees harvested. Specialized photography using color infrared film has also been used to detect disease and insect damage in forest trees.

Sunday, January 29, 2012

LOCATION, DISTANCE, AND DIRECTION ON MAP

Location on Maps
Most maps allow us to specify the location of points on the Earth's surface using a coordinate system. For a two-dimensional map, this coordinate system can use simple geometric relationships between the perpendicular axes on a grid system to define spatial location. Figure 1 illustrates how the location of a point can be defined on a coordinate system.


Figure 1: A grid coordinate system defines the location of points from the distance traveled along two perpendicular axes from some stated origin. In the example above, the two axes are labeled X and Y. The origin is located in the lower left hand corner. Unit distance traveled along each axis from the origin is shown. In this coordinate system, the value associated with the X-axis is given first, following by the value assigned from the Y-axis. The location represented by the star has the coordinates 7 (X-axis), 4 (Y-axis). 

MAP

A map can be simply defined as a graphic representation of the real world. This representation is always an abstraction of reality. Because of the infinite nature of our Universe it is impossible to capture all of the complexity found in the real world. For example, topographic maps abstract the three-dimensional real world at a reduced scale on a two-dimensional plane of paper.

Maps are used to display both cultural and physical features of the environment. Standard topographic maps show a variety of information including roads, land-use classification, elevation, rivers and other water bodies, political boundaries, and the identification of houses and other types of buildings. Some maps are created with very specific goals in mind.

The art of map construction is called cartography. People who work in this field of knowledge are called cartographers. The construction and use of maps has a long history. Some academics believe that the earliest maps date back to the fifth or sixth century BC. Even in these early maps, the main goal of this tool was to communicate information. 

EARTH - SUN GEOMETRY

Earth Rotation and Revolution
The term Earth rotation refers to the spinning of our planet on its axis. Because of rotation, the Earth's surface moves at the equator at a speed of about 467 m per second or slightly over 1675 km per hour. If you could look down at the Earth's North Pole from space you would notice that the direction of rotation is counter-clockwise (Figure 6h-1). The opposite is true if the Earth is viewed from the South Pole. One rotation takes exactly twenty-four hours and is called a mean solar day. The Earth’s rotation is responsible for the daily cycles of day and night. At any one moment in time, one half of the Earth is in sunlight, while the other half is in darkness. The edge dividing the daylight from night is called the circle of illumination. The Earth’s rotation also creates the apparent movement of the Sun across the horizon.



Figure 6h-1: The movement of the Earth about its axis is known as rotation. The direction of this movement varies with the viewer’s position. From the North Pole the rotation appears to move in a counter-clockwise fashion. Looking down at the South Pole the Earth’s rotation appears clockwise. 

THE SOLAR SOURCE OF THE EARTH'S ENERGY

Almost all of the energy that drives the various systems (climate systems, ecosystems, hydrologic systems, etc.) found on the Earth originates from the Sun. Solar energy is created at the core of the Sun when hydrogen atoms are fused into helium by nuclear fusion. For each second of this nuclear process, 700 million tons of hydrogen are converted into 695 million tons of helium. The remaining 5 million tons are turned into electromagnetic energy that radiates from the Sun's surface out into space.

The radiative surface of the Sun, or photosphere, has an average temperature of about 5800 Kelvins. Most of the electromagnetic radiation emitted from the Sun's surface lies in the visible band centered at 0.5 µm. The total quantity of energy emitted from the Sun's surface is approximately 63,000,000 Watts per square meter (W/m2 or Wm-2).


Figure 6g-1: The Sun observed by SUMER instrument on the SOHO satellite on March 2-4, 1996. (Source: SOHO - SUMER Instrument). 


THE NATURE OF RADIATION

All objects above the temperature of absolute zero (-273.15° Celsius) radiate energy to their surrounding environment. This energy, or radiation, is emitted as electromagnetic waves that travel at the speed of light. Many different types of radiation have been identified. Each of these types is defined by its wavelength. The wavelength of electromagnetic radiation can vary from being infinitely short to infinitely long (Figure 6f-1).


Figure 6f-1: Some of the various types of electromagnetic radiation as defined by wavelength. Visible light has a spectrum that ranges from 0.40 to 0.71 micrometers (µm). 

LAWS OF THERMODYNAMICS

The field of thermodynamics studies the behavior of energy flow in natural systems. From this study, a number of physical laws have been established. The laws of thermodynamics describe some of the fundamental truths of thermodynamics observed in our Universe. Understanding these laws is important to students of Physical Geography because many of the processes studied involve the flow of energy.

First Law of Thermodynamics
The first law of thermodynamics is often called the Law of Conservation of Energy. This law suggests that energy can be transferred from one system to another in many forms. Also, it can not be created or destroyed. Thus, the total amount of energy available in the Universe is constant. Einstein's famous equation (written below) describes the relationship between energy and matter:

E = mc2

In the equation above, energy (E) is equal to matter (m) times the square of a constant (c). Einstein suggested that energy and matter are interchangeable. His equation also suggests that the quantity of energy and matter in the Universe is fixed.

ENERGY AND LIFE

The capture and use of energy in living systems is dominated by two processes: photosynthesis and respiration. Through these two processes living organisms are able to capture and use all of the energy they require for their activities.

Photosynthesis
Plants can capture the electromagnetic energy from the Sun by a chemical process called photosynthesis. This chemical reaction can be described by the following simple equation:

6CO2 + 6H2O + light energy >>> C6H12O6 + 6O2

The product of photosynthesis is the carbohydrate glucose and oxygen which is released into the atmosphere. All of the sugar glucose is produced in the specialized photosynthetic cells of plants and some other organisms. Glucose is produced by chemically combining carbon dioxide and water with sunlight. This chemical reaction is catalyzed by chlorophyll acting in concert with other pigment, lipid, sugars, protein, and nucleic acid molecules. 

ENERGY, TEMPERATURE, AND HEAT

We have learned that energy can take on many forms. One important form of energy, relative to life on Earth, is kinetic energy. Simply defined, kinetic energy is the energy of motion. The amount of kinetic energy that a body possesses is dependent on the speed of its motion and its mass. At the atomic scale, the kinetic energy of atoms and molecules is sometimes referred to as heat energy.

Kinetic energy is also related to the concept of temperature. Temperature is defined as the measure of the average speed of atoms and molecules. The higher the temperature, the faster these particles of matter move. At a temperature of -273.15° Celsius (absolute zero) all atomic motion stops. Heat is often defined as energy in the process of being transferred from one object to another because of difference in temperature between them. Heat is commonly transferred around our planet by the processes of conduction, convection, advection, and radiation.

Some other important definitions related to energy, temperature, and heat are:
  • Heat Capacity - is the amount of heat energy absorbed by a substance associated to its corresponding temperature increase.
  • Specific Heat - is equivalent to the heat capacity of a unit mass of a substance or the heat needed to raise the temperature of one gram (g) of a substance one degree Celsius. Water requires about 4 to 5 times more heat energy to raise its temperature when compared to an equal mass of most types of solid matter. This explains why water bodies heat more slowly than adjacent land surfaces.
  • Sensible Heat - is heat that we can sense. A thermometer can be used to measure this form of heat. Several different scales of measurement exist for measuring sensible heat. The most common are: Celsius scale, Fahrenheit scale, and the Kelvin scale.Latent Heat - is the energy needed to change a substance to a higher state of matter. This same energy is released from the substance when the change of state (or phase) is reversed. The diagram below describes the various exchanges of heat involved with 1 gram of water.


Figure 6c-1: Latent heat exchanges of energy involved with the phase changes of water.

Figures 6c-2 and 6c-3 show the net absorption and release of latent heat energy for the Earth's surface for January and July, respectively. The highest values of flux or flow occur near the subtropical oceans where high temperatures and a plentiful supply of water encourage the evaporation of water. Negative values of latent heat flux indicate a net release of latent energy back into the environment because of the condensation or freezing of water. Values of latent heat flux are generally low over landmasses because of a limited supply of water at the ground surface.


Figure 6c-2: Mean January latent heat flux for the Earth's surface, 1959-1997. (Source of Original Modified Image: Climate Lab Section of the Environmental Change Research Group, Department of Geography, University of Oregon - Global Climate Animations). 


Figure 6c-3: Mean July latent heat flux for the Earth's surface, 1959-1997. (Source of Original Modified Image: Climate Lab Section of the Environmental Change Research Group, Department of Geography, University of Oregon - Global Climate Animations).




CITATION:  Pidwirny, M. (2006). "Energy, Temperature, and Heat". Fundamentals of Physical Geography, 2nd Edition. 29/1/2012.




MEASUREMENT OF ENERGY

In the previous discussion (Characteristics of Energy Matter), we developed the concept of energy. We now must be able to measure and quantify it, using a standard set of units. Worldwide, two systems of units of measurement are commoly used today: the Metric System (Systeme International) and the British System. The units of energy described in these systems are derived from a technical definition of energy used by physicists. This definition suggests that energy can be represented by the following simple equation:

Work = Force x Distance

Similar to the definition given in the previous topic, physicists view energy as the ability to do work. However, they define work as a force applied to some form of matter (object) multiplied by the distance that this object travels. Physicists commonly describe force with a unit of measurement known as a newton (after Sir Isaac Newton). A newton is equal to the force needed to accelerate (move) a mass weighting one kilogram one meter in one second in a vacuum with no friction. The work or energy required to move an object with the force of one newton over a distance of one meter is called a joule.

Some other definitions for the energy measurement units that you may come across in this textbook are as follows:
  • Calorie - equals the amount of heat required to raise 1 gram of pure water from 14.5 to 15.5° Celsius at standard atmospheric pressure. 1 calorie is equal to 4.1855 joules. The abreviation for calorie is cal. A kilocalorie, abbreviated kcal, is equal to a 1000 calories. 1 kilocalorie is equal to 4185 joules.
  • Btu - also called British thermal unit is the amount of energy required to raise the temperature of one pound of water one degree Fahrenheit.
  • Watt (W/m2 or Wm-2) - a metric unit of measurement of the intensity of radiation in watts over a square meter surface. One watt is equal to one joule of work per second. A kilowatt (kW) is the same as 1000 watts.

CITATION: Pidwirny, M. (2006). "Measurement of Energy". Fundamentals of Physical Geography, 2nd Edition. 29/1/2012.

CHARACTERISTIC OF ENERGY MATTER

Energy is defined simply by scientists as the capacity for doing work. Matter is the material (atoms and molecules) that constructs things on the Earth and in the Universe. Albert Einstein suggested early in this century that energy and matter are related to each other at the atomic level. Einstein theorized that it should be possible to convert matter into energy.

 From Einstein's theories, scientists were able to harness the energy of matter beginning in the 1940s through nuclear fission. The most spectacular example of this process is a nuclear explosion from an atomic bomb. A more peaceful example of our use of this fact of nature is the production of electricity from controlled fission reactions in nuclear reactors.Einstein also suggested that it should be possible to transform energy into matter.

Energy and matter are also associated to each other at much larger scales of nature. Later on in this chapter, we will examine how solar radiation provides the energy to create the matter that makes up organisms. Organisms then use some of this matter to power their metabolism.

Saturday, January 28, 2012

DESERT FACTS

A desert is an area of land that is marked by very sparse vegetation due to extreme climatic conditions and extremely low levels of precipitation. There are hot deserts as well as cold deserts. The Antarctic desert which spans across the continent of Antarctica is the most prominent example of a cold desert! Due to extremely low temperatures, vegetation and plant life is very sparse in these regions and the soil is ill suited for farming and cultivation. In hot deserts, the complete lack of moisture coupled with the extremely high temperatures make normal vegetation and cultivation of food items an impossible task. Only about 20% of the Earth's deserts are covered by sand. Based upon topography and region, there are precisely four types of deserts - Mountain-Basin deserts, Plateau Deserts, Regs and Intermontane Basins.

Sunday, January 22, 2012

GEOGRAPHY STANDARDS

Eighteen Standards That the Geographically Informed Person Knows and Understands

The World in Spatial Terms
1. How to use maps and other geographic representations, tools, and technologies to acquire, process, and report information.

2. How to use mental maps to organize information about people, places, and environments.

3. How to analyze the spatial organization of people, places, and environments on Earth's surface.


Places and Regions
4. The physical and human characteristics of places.

5. That people create regions to interpret Earth's complexity.

6. How culture and experience influence people's perception of places and regions.


Physical Systems
7. The physical processes that shape the patterns of Earth's surface.

8. The characteristics and spatial distribution of ecosystems on Earth's surface.


Human Systems
9. The characteristics, distribution, and migration of human populations on Earth's surface.

10. The characteristics, distributions, and complexity of Earth's cultural mosaics.

11. The patterns and networks of economic interdependence on Earth's surface.

12. The process, patterns, and functions of human settlement.

13. How forces of cooperation and conflict among people influence the division and control of Earth's surface.

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.