Write your own
error: Content is protected !!
PHYSICS: FORM FOUR: Topic 7 - GEOPHYSICS
Both of them, volcano and earthquake are caused by the movement of molten rock and heat deep inside the earth. These movements are referred to as subterranean movements. Most earthquakes and volcanic activity happen near tectonic boundaries.
The Origin of Volcanoes
Explain the origin of volcanoes
Volcanoes are places where molten rock called magma leaks out through a hole or a crack in the earth’s crust.Magma originates from the mantle,where high temperature and pressure cause the rock to melt.When a large pool of magma if formed,it rises through the denser rock layer towards the earth’s surface.
Magma that has reached the earth’s surface is called lava. Most volcanoes form along constructive and destructive boundaries between tectonic plates.However a few form plate boundaries.
Effects of Volcanoes
Describe effects of volcanoes
Effects of volcanoes include:
- Landscape: Most of the earth’s surface is covered with volcanic rocks.Volcanoes are also responsible for the formation of many mountains and islands.
- Vegetation and wildlife: Volcanic eruption sometimes set the surrounding vegetation into fire.Wild animals are also killed by being buried into the lava or being burnt by the forest fires.
- Environment: Volcanic eruptions emit harmful gases into the environment. Such gases include sulphur dioxide. Some of the gases contribute to global warming and climate change.
- Human life and property: Volcanic eruptions sometimes kill people and destroy property.
- Soil: Volcanoes help in soil formation by bringing important minerals from from deep underground onto the earth’s surface.
- Minerals: Volcanoes also bring valuable minerals to the earth’s surface.The minerals are important economic resources.
The Origin of Earthquake
Explain the origin of earthquake
An earthquake is a sudden motion or shaking of the earth caused by a sudden relese of energy that has accumulated within or along the edges of the earth’s tectonic plates.
Earthquakes happen when rocks in the earth’s crust move suddenly, shaking the earth.Earthquake also occur as a result of movement of magma at constructive boundaries under volcanoes and where continental plates collide and push mountain ranges.
The Principle of Measurement
Describe the principle of measurement of earthquake
The nature of an earthquake is usually described by measuring two properties, namely the magnitude and intensity.
The magnitude of an earthquake is a measure of the energy it releases. It is usually measured on the Richter scale.
The Richter scale magnitudes are based on a logarithmic scale(base 10).The intensity of an earthquake is a measure of its strength based on the changes it causes to the landscape.The intensity is usually measured on the Modified Mercalli scale.The scale is calibrated 1 to 12.
Note:An earthquake can have only one magnitude. However its intensity reduces as the seismic waves spread out from the hypocentre,just the same way the loudness of a sound changes as you move away from the source.
The Seismograph:Is an instrument used to record ground movements caused by earthquakes. It measures ground oscillations by recording the relative motion between a pendulum and the ground. It is also possible to use the ratio between the deflection and the of the pendulum and the acceleration of the of the ground to record an earthquake.
Precaution against Earthquake Hazards
Identify precaution against earthquake hazards
The Vertical Structure of the Atmosphere
Describe the vertical structure of the atmosphere
The atmosphere is a layer of gases containing numerous small suspended solid and liquid particles surrounding the earth.It has no outer boundary,it just fades into space.The dense part of the atmosphere lies within 30km above the earth’s surface.
The atmosphere is divided into regions based on its thermal characterestics (temperature changes),chemical composition, movement and density. It is divided into five regions, which are:
The Composition of the Atmosphere
Describe the composition of the atmosphere
The Importance of Various Layers of the Atmosphere
Explain the importance of various layers of the atmosphere
The importance of the atmosphere include the following:
- The troposphere controls the climate and ultimately determines the quality of life on the earth.
- The troposphere is important for life on earth. The layer contains gases which include oxygen which is used for respiration by animals and carbon dioxide which is used by plants in photosynthesis. The nitrogen found in this laye also provides an inactive environment for many chemical processes to take place. The gases also support many important chemical processes such as combustion,weathering and oxidation.
- The stratosphere prevents harmful ultraviolet radiation from reaching the earth.
- The mesosphere,thermosphere and exosphere also prevent harmful radiation such as cosmic rays from reaching the earth’s surface.
- Communication is also made possible by some layers of the atmosphere, specifically the ionosphere.
The Greenhouse Effect
Explain the greenhouse effect
Global warming is the increase of the average temperatures near or on the surface of the earth as a result of what is known as the greenhouse effect. The effect is caused by greenhouse effect. These gases are produced from natural and industrial processes.
The greenhouse effect is the process in which the emission of radiation by the atmosphere warms the earth’s surface.
When heat from the sun reaches the earth’s surface in form of sunlight,some of it is absorbed by the earth.The rest is radiated back to the atmosphere at a longer wavelength than the incoming sunlight.Some of these longer wavelengths are absorbed by greenhouse gases in the atmosphere before they are lost to space.The absorption of this long-wave radiant energy warms the atmosphere.
The greenhouse gases act like a mirror, reflecting back to the earth some of the heat energy which would otherwise be lost to space.
Sources of Greenhouse Effect
Identify sources of greenhouse
Sources of greenhouse effect include:
- Clearing and burning of vegetation
- Burning of fossil fuel
- Dinitrogen oxide
The Occurence of Global Warming
Explain the occurrence of global warming
Global warming is primarily a problem of too much carbon dioxide (CO2) in the atmosphere—which acts as a blanket, trapping heat and warming the planet. As we burn fossil fuels like coal, oil and natural gas for energy or cut down and burn forests to create pastures and plantations, carbon accumulates and overloads our atmosphere. Certain waste management and agricultural practices aggravate the problem by releasing other potent global warming gases, such as methane and nitrous oxide.
The Consequences of Global Warming
State the consequences of global warming
Effects of Global Warming
- Increase in the temperature of the oceans.
- Rise in sea levels.
- Change in world’s climatic pattern.
- Acidification of the oceans.
- Extreme weather events.
- Higher or lower agricultural yields.
- Melting of Arctic ice and snowcaps. This cause landslides, flash floods and glacial lake overflow.
- Extinction of some animal and plant species.
- Increase in the range of disease vectors, that is,organisms that transmit diseases.