Natural Disasters

 Some of the natural Disasters that have a huge impact on the mankind are:

Earthquakes

An earthquake is a sudden tremor or movement of the earth’s crust, which usually originates at or below the surface. The outer layer of the earth is solid and is divided into many sections known as plates. These plates, float over the molten magma that flows beneath the earth’s crust. Many of the earthquakes occur on the edges of these plates along fault lines where the plates collide or try to slide past each other.

Apart from natural causes like the movement of the Earth’s tectonic plates and volcanic eruptions, there are other man-made causes of earthquakes.

These include vibrations caused by big rocks falling down hills because of erosion, hollow parts of mines falling down due to dissolution of minerals by water and, in the present times, due to nuclear explosions.

The point of origin of the earthquake within the crust or mantle is called the seismic focus. Since the focus is often deep below the surface, the location of the earthquake is often referred to as the point on the surface of the earth, vertically above the seismic focus. This point is called the epicentre.

Scientists, who study earthquakes or seismology, measure earthquakes with a device called the seismometer; a device which also records is known as a seismograph. They use an instrument to measure the magnitude of the earthquake, called a ‘Richter Scale’.

Such under-sea earthquakes, give rise to giant waves called the tsunami, which cause great deal of destruction along the coasts.

Floods

Flooding damages crops and contaminates sources of fresh water thus leading to shortage of food and drinking water.

Apart from damaging life and property, floods can also lead to epidemics.

Any flood is preceded by a threat period known as the Probability Period, which allows the authorities to issue warnings and plan evacuation.

Floods occur when land gets submerged under water due to various causes like excessive rain, overflowing rivers, increase in water in reservoirs, cyclones, tsunami, sea tides and melting of glaciers. Floods caused by cloud bursts, bursting of dams, or tsunamis are called flash floods. Any flood is preceded by a threat period known as the Probability Period. This allows the authorities to issue warnings and plan evacuation.

Artificial reservoirs should be built with sluice gates and sand bags should be used to block the flow of water. Low grounds or viaducts can be created to carry water in a certain direction or underground. Trees should be planted in the catchment areas to stop soil erosion.

Volcanic eruptions

Volcanoes can cause widespread destruction and consequent disaster in several ways. One hazard is the volcanic eruption itself, with the force of the explosion and falling rocks able to cause harm. Lava may also be released during the eruption of a volcano; As it leaves the volcano, it can destroy buildings, plants and animals due to its extreme heat. In addition, volcanic ash may form a cloud (generally after cooling) and settles thickly in nearby locations. When mixed with water, this forms a concrete-like material. In sufficient quantities, ash may cause roofs to collapse under its weight. Even small quantities will harm humans if inhaled — it has the consistency of ground glass and therefore causes laceration to the throat and lungs. Volcanic ash can also cause abrasion damage to moving machinery such as engines. The main killer of humans in the immediate surroundings of a volcanic eruption is pyroclastic flows, consisting of a cloud of hot ash which builds up in the air above the volcano and rushes down the slopes when the eruption no longer supports the lifting of the gases. It is believed that Pompeii was destroyed by a pyroclastic flow. A lahar is a volcanic mudflow or landslide. The 1953 Tangiwia was caused by a lahar, as was the 1985 Armero tragedy in which the town of Armero was buried and an estimated 23,000 people were killed.[citation needed]

Volcanoes rated at 8 (the highest level) on the Volcanic Explosivity Index are known as supervolcanoes. According to the Toba catastrophe theory, 75,000 to 80,000 years ago, a supervolcanic eruption at what is now Lake Toba in Sumatra reduced the human population to 10,000 or even 1,000 breeding pairs, creating a bottleneck in human evolution,[54] and killed three- quarters of all plant life in the northern hemisphere. However, there is considerable debate regarding the veracity of this theory. The main danger from a supervolcano is the immense cloud of ash, which has a disastrous global effect on climate and temperature for many years.