Natural disasters are suddenly events caused by environmental factors that injure people and damage property. Most natural disasters are caused by weather. Volcanic eruptions, earthquake and storms are some examples that create a havoc for mankind and cause heavy damage to life and property.
VOLCANOES
A volcano is a crack in the Earth's surface through which very hot liquid Rock is called lava comes out along with ash and gases. It is usually in the form of a conical mountain.
There is a vertical tunnel within the mountain through that the volcanic rock comes out.
When the lava is underground, it is called magma. When the volcano erupts it can cause destruction but when the lava cools down it hardens into igneous rocks.
Types of Volcanoes
According to the natural eruptions, volcanoes can be classified into three types:
Active volcanoes
The volcanoes that can erupts any time or have erupted in recent past are called actives volcanoes. Many active volcanoes are found around the Pacific ocean. Some well known active volcanoes are- Mount Vesuvius, Mount Etna, Mount Erebus and Mount Fuji.
The Barren Island in the Andaman Islands is an active volcano that erupted first in 1787.
Dormant Volcanoes
The volcanoes that have not erupted in recent years but may erupt in the future are called dormant volcanoes. Some examples of dormant Volcanoes are- Mount Kilimanjaro in Tanzania and Narcondam in Andaman Islands.
Extinct volcanoes
The volcanoes that have stopped erupting and there are no chances of their eruption are called extinct volcanoes. Some examples of extinct volcanoes are- the Emperor Seamount Chain in the Pacific Ocean.
EARTHQUAKES
An earthquake is the sudden shaking of the earth's surface which is made of plates which may be big or small. These plates are called tectonic plates. There is smooth movement is sudden and severe because of shock waves giving rise to earthquakes. The plates where the earthquake begins is called the epicenter. Earthquakes cause a lot of devastation house and building collapse in the area close to the epicenter.
Nepal was shattered in 2005 due to the earthquake which took so many lives and caused massive destruction.
Measuring Earthquakes
Scientists measure earthquake with an instrument called seismograph using a scale known as Richter scale. The weaker earthquake are close to 1 and the severe omes are closed to 9 on the Richter scale.
TIDAL WAVES AND TSUNAMI
Earthquake or volcanic eruption can take place under sea also and is called tsunami (pronounce as su-nami). During tsunami the waves move at a great speed causing a massive destruction at the seashore. The rise and fall of sea waves is called a tidal waves.
During tsunami the tidal waves may travel at a speed of 800 km/hrs.
While Japan could have the longest recorded history of tsunamis, the sheer destruction caused by the 2004 Indian ocean earthquake and tsunami event mark it as the most devastating of
its kind in modern world, killing around 230,000 people.The Sumatran region is also accustomed to tsunamis, with earthquakes of varying magnitudes regularly occurring off the coast of the island.
Relationship between earthquakes, tsunamis.
An 8.9-magnitude earthquake stricken northeastern Japan on Fri afternoon, the largest temblor ever recorded by the Japanese Meteorological Agency.
The earthquake triggered a moving ridge that swamped many kilometers round the epicentre.
The following could be a temporary introduction of the link between earthquakes and tsunamis.
A moving ridge could be a series of harmful waves, sometimes tens of meters high, caused by the displacement of a large volume of water, usually an ocean.
With mammoth energy and quick movement, the waves are catastrophic to the affected coastal areas.
Tsunamis ar sometimes triggered by earthquakes, volcanic eruptions and underwater explosions, landslides and other mass movements.
Underseas earthquakes have generated nearly all the major tsunamis in history.
Tsunamis may be generated once the ocean floor short deforms and vertically displaces the superimposed water.
Tectonic earthquakes ar a specific reasonably seism related to the earth's crustal deformation.
When these earthquakes occur at a lower place the ocean, the water above the deformed area is displaced from its equilibrium position.
However, submarine earthquakes don't essentially result in tsunamis.
Statistics from the China Earthquake Administration show that of the past fifteen,000 undersea tectonic earthquakes, only about 100 generated tsunamis.
Some consultants hold that solely earthquakes of on top of half-dozen.5 magnitude and with a focal depth of less than 25 km underground can cause tsunamis.
Sometimes even strong earthquakes, such as the 8.5-magnitude qukae that occurred near Sumatra in 2005, do not trigger tsunamis because the quake intensity can be largely compromised by the great focal depth, experts say.
In addition to the earthquake magnitude, global climate change may also have a bearing on the occurrence of tsunamis.
According to consultants from the China earth science Administration, the 2004 moving ridge that stricken geographical region was partly connected to the rising water level caused by international global climate change.
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