Natural disasters by Malcolm Sant, 3.01Presentation Transcript
Geography Project: Natural Disasters, and their effect on the World Made by: Malcolm Sant 3.1
Earthquakes are shaking movements of the Earth’s surface, resulting from strong pressure inside the earth, creating seismic waves.
At the Earth's surface, earthquakes manifest themselves by shaking and sometimes displacement of the ground. When a large earthquake epicenter is located offshore, the seabed may be displaced sufficiently to cause a tsunami. Earthquakes can also trigger landslides, and occasionally volcanic activity.
Earthquakes are caused mostly by rupture of geological faults, but also by other events such as volcanic activity, landslides, mine blasts, and nuclear tests.
An earthquake's point of initial rupture is called its focus or hypocenter. The epicenter is the point at ground level directly above the hypocenter.
Earthquakes occur all around the World, mainly in large countries, which show us that the crust is not stable.
Scismologists use the Richter Scale to calculate Earthquakes power, which runs from 0 to infinity but we stop at 9 since the most powerful earthquake recorded was 8.9.
We have no control over these Earthquakes, because they come from nature which kill a lot of people and leave the place where it happened in a terrible way with houses and buildings destroyed.
A volcano is formed when a crack or a fault is so deep that it reaches down into the mantle and lava comes out. Since faults can also form in the seabed, volcanoes can form beneath the sea.
There are 3 main types of volcanoes:
Active: When it erupts frequently
Dormant: Which erupts every now and then
Extinct: Which never erupts at all
The word volcano is derived from the name of Vulcano, a volcanic island in the Aeolian Islands of Italy whose name in turn originates from Vulcan, the name of a God of fire in Roman mythology.
Some important parts of a volcano include:
Crates: The hole at the top of the volcano
Main Vent: The central passage from where lava comes out
Dyke: Is a side passage that reaches the surface vertically
Sill: Is a side passage that reaches the surface horizontally
Magma: Is lava when it is still beneath the crust
Lava can come out from the main vent or from the side passage. It then cools and solidifies into igneous rocks.
When a volcano erupts there are often seismic tremors, shockwaves of sound, a rain of ash, and flying molten rock. Their secondary effects are many, but underwater volcanoes are often the cause of tsunamis.
Tropical Cyclones are formed over the ocean in the area around the equator, between the Tropic of Cancer and the Tropic of Capricorn.
In order for a cyclone to form, the ocean waters need to be warm, at least 26°C. Above the warm ocean, water evaporates and form clouds. If there is low air pressure where the clouds are formed, it pulls them in and they begin to rotate. It is the Earth’s rotation and spinning on its axis that causes the cyclone’s clouds to rotate. Clouds will continue to form and begin spinning more.
This is the stage when it can develop into a mature cyclone, or lose its momentum. Even if it has developed into a mature cyclone, it can still grow in size and increase its wind speed.
In order for it to be categorized as a cyclone, its average sustained wind speed needs to exceed 63 kilometers per hour. To be classified as severe, the average sustained wind speed needs to exceed 118 kilometers per hour.
Once they arrive over land, their strength weakens and they begin to fade out. This is due to the lack of moisture and heat compared to the ocean over which it was formed.
Tropical Cyclones are dangerous because they produce destructive winds, heavy rainfall with flooding and damaging storm surges that can cause inundation of low-lying coastal areas. The power of a cyclone is measured using 5 categories, 1 making the least damage while category 5 with the most significant damage, with houses flattered and cars overturned.
The average life of a cyclone is 1 week.
Floods are not always caused by heavy rainfall.
Flooding can be caused by a range of situations that include:
Seawater flooding – coastal areas may be flooded when a cyclone or severe storm causes a surge of sea water.
Tidal flooding – floods that are caused by high tides that coincide with higher than normal river levels.
Run-off from rivers and dams – flooding can be caused when river systems all need to carry more water at the one time following a snow-melt or when dams start to overflow.
Urban drainage – flash flooding is a serious problem in some cities when the drainage systems fail. People can be caught in storm water drains, trapped in their cars or even swept off the roads by water.
Floods can bring welcome relief for people, livestock and areas suffering from drought conditions. Flooding can also be a natural way for wetland areas, swamps and native waterways to survive. Underground aquifers and soils with high salt levels also benefit from flood waters.
There are 3 common types of floods:
Slow-Onset floods: These floods may take days to build-up and they can last for one or more weeks and can even last for months on some occasions. The damage caused by floods in these areas can lead to major losses of livestock, cutting-off rural towns and damaging crops as well as major roads and railways.
Rapid-Onset floods: Rapid-onset flooding can occur more quickly than slow-onset floods. These floods can be potentially much more damaging and can pose a greater risk to loss of life and property. This is because there is generally much less time to take preventative action, and a faster, more dangerous flow of water.
Flash floods: Flash flooding results from relatively short, intense bursts of rainfall, often from thunderstorms. People are often swept away after entering floodwaters on foot or in vehicles.
Tornadoes, popularly known as twisters, are one of nature’s phenomena that occur due to various reasons. These tornadoes are one of the most destructive of storms. Many of these tornadoes take place mainly in the United States of America although they can occur anywhere across the globe. Frightful and terrifying, the tornadoes are fierce columns of air that rotate at a high speed. This is what causes destruction to whatever comes in the way of a tornado.
A tornado always rotates either clockwise or counterclockwise. A large amount of dust is thus raised due to these cyclonic winds. A tornado can occur anytime of the year. However, many of them occur in the month of May. There is no specific size of a tornado, and can occur in any size. The wind speed of a tornado is recorded between 40 mph to 110 mph. These rotating tornadoes can travel many kilometers that cause severe destruction to mankind.
One cannot say a tornado is of a particular colour. Their colours depend upon the environment where it occurs. When the surrounding areas are dry, a tornado may appear partly invisible. The colour of the tornado also depends upon the time of the day. It may appear dark to the observer if the sun is behind the tornado.
These funnel shaped twisters can move in any direction, however on an average, it is said they move from southwest to the northwest direction. People who have witnessed this strong force have also reported loud sounds that occur with the tornado.
These twisters mainly occur when the warm air from the ground level rushes upwards and meets the cool dry air. This causes the warm air to cool down which further causes the moisture to condense and this results in a thundercloud that grows in height. The winds at different levels cause the twister to get its distinctive funnel shape. Tornadoes are known to cause massive destruction wherever they occur. They have the force to uproot trees, damage houses to the extent of ripping off the rooftops, overturn vehicles causing loss of property and life as well.