User talk:Mossbrendan

Geography
The Earth and associated landforms. Earth movements and rock structures Internal structure of the earth: Alfred Wegener and the continental drift theory: A meteorologist by profession, Wegener, a German, carefully studied the fit of continents and assembled other evidence to make the strongest case he could for continental drift: -that is, in support of it. He showed that the continents could fit together to form a giant supercontinent which he called the Pangea. Wegener showed that fossils of the Paleozoic age (a geological period) found on several different continents, were quite similar-e.g. the plant fossil Glossopteris found in rocks in South America, Africa, India and Australia. Although these localities are now widely separated from one another, they fit closely together in Wegener’s reconstruction of Pangea, in India, Africa, South America, Australia and Antarctica. All five localities contain rocks of the same type and their edges are overlaid by thick continental sedimentary rocks containing coal beds and glossopteris fossils. The full scope of Wegener’s theory cannot be exhausted at this level. What was the force behind the splitting and drifting apart of continents? To deal with this issue, a more scientific theory was developed- i.e. the Plate Tectonic Theory. What is a plate? It is a large, mobile slab of rock that is part of the earth’s surface. The surface of a plate may be made up entirely of sea floor for example the NAZCA plate. Or it may be made up of both continental and oceanic rock for example the North American plate. Some of the smaller plates are entirely continental, but all the large plates contain some sea floor. Plate tectonics theory has added some new terms based on rock behavior, to the zones of the earth’s interior. The plates are part of a rigid outer shell of the earth called the lithosphere. The lithosphere is 70 to 125kms thick, so it includes the rocks of the earth’s crust and uppermost mantle. Below the rigid lithosphere is the asthenosphere, a zone maybe 100kms thick that behaves like plastic because of increased temperature and pressure. The plastic asthenosphere acts like a lubricating layer under the lithosphere, allowing the plates to move. The asthenosphere, made up of the upper mantle rock, is the seismic low-velocity zone. Below the asthenosphere is the more rigid lower mantle. See diagram below. Major plates of the world Oceanic trenches: If the plate is made up mostly of sea floor (as the Nazca and Pacific plates) the plate can be subducted down into the mantle forming on a deep sea/oceanic trench and its associated feature. If the leading edge of the plate is made up of continental rock (as in the South American plate) that plate will not subduct. The internal structure of the Earth The earth is one of the nine planets in orbit in the solar system. We are mainly concerned with the processes operating on the surface of the earth. However, to understand some of these processes we need to understand the nature of the processes operating inside the earth. As such we begin by making an evaluation on the internal structure of the earth. Diagrammatic presentation of the internal structure of the earth. As shown in the diagram, 3 main divisions of the earth’s internal structure can be identified. Their characteristics are as follows. Crust This is also known as the lithosphere that forms the surface of the earth. The crust is made up of 2 types: 1.      Continental crust

This is also known as SIAL. (This is the short form for silica and magnesium). This forms the continental landmasses of the world. 2.      Oceanic crust

This is also known as SIMMAC. This is the short form for silica and magnesium. The oceanic crust is generally denser than the continental crust and it forms the floors of seas and oceans. Mantle This is the region below the earth’s crust. It is also known as the mesosphere. It is made up of molten rock which is semi viscous in nature. Core This is the central part of the earth. The core is further subdivided into two regions the Inner core and the Outer core. The Inner core is made up of highly radio-active elements and is in solid form. The outer core is also made up of radioactive materials and is in a semi-liquid state. The Core of the earth is the region where the earth gains its energy. In other words, most of the processes that occur on the earth’s surface are a result of the energy released and transferred from the inner core. Energy transfers within the earth It has been highlighted that the core is made up of radio-active elements. This means that this element generates a lot of heat energy which is transferred throughout the month through conventional currents. Process of convectional currents When matter is heated, it expands and becomes less dense. Thus, it rises and as it rises, the dense material above is forced to site and the convective cycle is in operation. These convectional cycles are responsible for the transfer of heat energy from the center of the earth to all the other regions. The origin of present day continents and oceans. Having looked at the present-day distribution of continents and oceans on a world map, the question that arises is: what made these continents to be what they are? A lot of geographers have tried to come up with theories to explain the origin and development of the present-day oceans and continents. One outstanding theory was put forward by a German physiologist, Alfred Wegener. His ideas are widely referred to as the Continental theory. The continental drift theory: A meteorologist by profession, Wegner, a German, carefully studied the features of continents and assembled other evidence to make the strongest case he could for continental drift. He showed that the continents could fit together to form a giant super continent which he called Pangaea. Wegener showed that fossils of the Paleozoic age (a geological period) found on several different continents were quite similar-e.g. the plant fossil Glossopteris found in rocks in South America. Africa, India and Australia. Although these localities are now widely separated from one another, they fit closely together in Wegener’s reconstruction of Pangaea, in India, Africa, South America, Australia and Antarctica. All five localities contain rocks of the same type and edges are overlain by thick continental sedimentary rocks containing coal beds and glossopteris fossils. Wegener however, failed to come up with a logical explanation on the force behind the drifting of continents. During his time people did not take his findings very seriously. In the late 1950s, scientists made a further enquiry onto Wegener’s ideas and with the help of new equipment, improved the continental drift theory and came up with the theory of plate tectonics. Plate tectonics theory It is believed that the earth’s crust is suspended over a semi liquid material called the mantle. As such, the continents are floating continuously, also the convective currents we referred to earlier led to the crust breaking into many pieces referred to as continental or oceanic plates. Plate boundaries and associated landforms. Plate boundaries are zones where two plates meet. It is important that we assess the different characteristics of plates: The lithosphere is made up of two distinct plates, there is the continental plate which consists of aluminum and silica, (SIAL). This plate is less dense as compared to the oceanic plates made up of silica and magnesium as the elements. When the plates meet at plate boundaries, the following may occur:

1.         Plates may move apart from each other to form a constructive plate margin. This is a zone where the earth’s crust is being created as plates move apart due to divergence of convective currents which were explained earlier. This leads to the formation of a ridge due to the accumulation of magma which flows into the surface to fill in the space left by the diverging plates.

2.        Plates may move towards each other. When this happens two scenarios may occur:

a)    If two plates of different characteristics meet i.e. the oceanic plate meeting with a continental plate, the oceanic plate is forced to sink below the continental plate, creating a zone of subduction. This is a zone where the sinking plate is subducted or destroyed due to contact with molten magma and excessive heat created by friction. There is a creation of a deep-sea trench on a chain of volcanoes referred to as the island area. The continental crust will be forced to crumble up and forming a chain of fold mountains.

b)    If two plates of similar characteristics meet, a collision zone is created. This is because the plates are of the same characteristics, and as such, they crumble up to form areas of folded structure. This occurs when two continent plates collide as they are similar in nature. The impact of their collision will force them fold upwards.

When two plates neither converge nor diverge, but slide past each other, a conservation or transform plate boundary is created. This is because no land is created or destroyed Landforms associated with plate boundaries. Plates boundaries are active zones of Landform building. The following are some common landforms associated with plate boundaries. Constructive plate margins The most common feature found in the region is the mid oceanic trench. This is formed due to the releases of magma onto the surface, forming a ridge like feature. Also, this area is characterized by volcanic mountains formed due to the violent releases of molten magma. At times, these mountains are so large that the peaks or tops rise above the water, forming islands. A typical example is Iceland, which rises from the famous mid Atlantic ridge.

Destruction plate margin This area is notable for many features. The most common is the deep-sea trench formed through the subduction or bending downwards of the oceanic plate beneath the continental crust. The depression forms a deep trench as shown below.

Typical examples include the Bolivia trench, the Chile trench and the Japanese trench, among others. As the oceanic plates subduct or bend, large cracking or fissures develop. Magma from the mantle will rush in to fill this cracking. However, due to excessive pressure, volcanic eruptions will occur. This will form underwater volcanos or submerged mountain ranges: when these volcanic eruptions reach the surface, then a chain of volcanic peaks is created, leading to the formation of island arcs. Typical examples include Japan and News Zealand. Due to the impact of the collision between plates, the continental plate cannot bend down wards, but is forced to fold upwards up fold. This leads to the formation of a line of Fold Mountains that runs parallel to the sea shore. At times, the Fold Mountains are characterized by a lot of volcanic activity. This is due to magma and the melting of the subducted oceanic plate. Collision zones: As stated earlier, these are zones of the earth where two continental plates meet. Thus, this leads to the formation of Fold Mountains since these plates are of the same characteristics, such that at the point of impact, they will all crumble upwards (up folding). A typical example is the Alpinic and the Malign fold mountains which were formed in this way. Conservative zones: In this zone, the crust is neither created nor destroyed. Thus, no landforms are found on this zone. This area is characterized by transformation faults caused due to excessive functional force. Hazards associated with plate tectonics: A hazard is a state of instability caused either by natural or manmade causes. Some hazards can be detected and prevented while some cannot. Plate tectonics are associated with hazards that occur in response to the movement or drifting of the crust as well as their impact as they slide or hit against each other. The most common hazards are volcanic eruptions and earthquakes. Earthquakes An earthquake can be defined as the violent shaking or vibration of the earth’s crust. Earthquakes can also be described in terms of its magnitude and intensity. -         Magnitude refers to the energy released by an earthquake, and intensity refers to amount of impact that the earthquake causes. -         Usually earthquakes occur at plate margins or boundaries such as destructive and conservative plate margins -         Shock waves are those sudden jolts of movement. Two terms usually used in the study of earthquakes are focus and epicenter. -         Focus refers to the point where the shock waves begin and epicenter refers to the point on the earth’s surface above the focus where the shock waves are strongest. -         The force of the shock waves is measured by a seismometer and the readings are interpreted by a richer scale, where a higher reading shows a strong earthquake.

(Adopted from Mc Geary. Plummer). NB: The focus of an earthquake is the point where the rock first breaks a fault; Seismic waves radiate from the focus. The epicenter is the point on the earth’s surface directly above the focus. Effects of earthquakes These are: economic, social, and physical in nature 1.      Loss of life.

2.      Destruction of property.

3.     Destruction of vital communication lines.

4.     Landslides or mud flows.

Benefits of volcanic activities

a)        When volcanic rocks are weathered, they produce fertile soils which are good for crop production.

b)       Some volcanic rocks have within them precious minerals, which when exploited can lead to the development of the country.

c)        Some volcanic landforms can be so scenic to the extent that they become tourist features. Geysers and hot springs are thought to have healing properties. They are also tourist features and this may lead to the economic and infrastructure development of the areas where they are found.

Volcanoes Volcanic eruptions are very violent eruptions of magma into the surface of the earth. These eruptions often bring untold suffering to society. Volcanic eruptions like, earthquakes, have got social, economic and physical effects. These include the following: When Earthquakes erupt violently, they force the earth’s crust to shake violently. In response to the violent eruption, Ø Homes are buried.

Ø Destruction of crop land occurs.

Ø Blocking of roads and rivers.

Ø Destruction of communication networks.

Ø Loss of life.

Ø Causes tidal waves and air pollution (Tsunamis).

However, to a lesser extent volcanic eruption have got positive benefits on society. Some of these benefits include. Ø Creation of new land; when volcanoes erupt in the oceans new islands are formed e.g. Iceland.

Ø When volcanic rocks are weathered they produce fertile soils that are good for crop production.

Ø Some volcanic rocks contain precious minerals, which can be exploited and benefit countries economically.

Ø Volcanic physical appearing may be tourist attractions which bring in a lot of foreign currency e.g. mount Tenga, and hot springs found in the Zambezi valley.

Ø Areas of active vulcanicity can be used to generate geo-trend energy as is done in New Zealand.

Measures to minimize the impact of earthquakes and volcanos Despite their destructive nature, man in his interaction with the environment is continuously seeking ways to reduce the negative impact of hazards caused by tectonic activities. These measures have saved a lot of life and expenditure. However, tectonic disasters cannot be totally eradicated. Some of the measures to reduce impact of earthquake and volcanic eruptions are discussed below. Ø Introduction of early warning systems e.g. electronic sonars and seismographs that predict when and where earthquakes will strike.

Ø Early Evacuation of affected communities before disaster strikes

Ø Permanent relocation of communities from disaster prone areas.

Ø Use of new technology in construction of buildings e.g. use of bamboo in Korea and buildings that move when the earth shakes.

Ø Establishment of international rescue agencies that assist affected committing with food and medical supplies.

Ø Introduction of wireless communication that can be used even during periods of disaster as compared to fixed communication networks e.g. cell phones and the G.P.R.S.

Mossbrendan (talk) 17:39, 14 August 2018 (UTC)