Natural and Man-Made Disaster and their Impact on Environment

Earthquakes, floods and landslides, etc. are natural environmental hazards of disastrous consequences.

In recent years these hazards took toll of thousands of lives and caused massive destruction of property.

These have adversely affected the vital sectors of our development as agriculture, communication, irrigation, power projects and rural and urban settlements.

The time and cost overrun in some cases have been enormous but their indirect impact on our economy has never been calculated. India is among the world’s most disaster prone areas and a large part of the country is exposed to natural hazards, which often turn into disasters causing loss of life and property. The unique geo-climatic conditions have exposed this country to natural catastrophes.

Disasters can be defined as a sudden, accidental event of great magnitude that causes considerable damage to life and property. They are sudden, drastic and normally occur without any alarm or warning. Some disasters may be short lived such as earthquakes and some other may be of long duration, such as floods.

However, irrespective of the duration of a disaster, the damage in the form of deaths, injuries and losses of property is immense. The magnitude of the disasters can be judged by the fact that only during the past two decades, occurrences of floods, earthquakes, landslides, cyclones, etc. have killed several million people.

Most of the disasters have a natural origin, however, some disasters are manmade as well. On this basis, disasters can be broadly classified into two groups:

Natural disasters:

When disasters occur due to natural forces they are called natural disasters, over which man has hardly any control. Some common natural disasters are earthquakes, landslides floods, droughts, cyclones, etc. Tsunamis, volcanic eruptions and wildfires are also included under natural disasters. These disasters cause enormous loss to life and property.

Man-made disasters:

When the disasters are due to carelessness of human or mishandling of dangerous equipment’s they are called man-made disasters. Common examples of these disasters are train accidents, aero plane crashes, collapse of buildings, bridges, mines, tunnels, etc.

Natural Disasters:

Some of the common natural disasters, their impact on environment, and their prevention, control and mitigation are discussed below:

Earthquakes:

An earthquake is the shaking of the earth’s surface caused by rapid movement of the earth’s crust or outer layer. Ever since it came into existence 4.6 billion years ago, the earth has been a dynamic, evolving system. The position of the different continents and oceans that we see today, has changed a number of times in the earth’s history.

The earth is primarily composed of three layers:

1. The outer crust,

2. The middle mantle, and

3. The inner core

The Earth’s outer layer or crust is made up of a number of zig-saw pieces like structures that interlock into one another. These pieces are called tectonic plates. These plates are in continuous motion over the mantle, which is known as tectonic movements. These tectonic processes are also responsible for the mountain building processes.

The plates that are moving past over one another are slowed by friction along their boundaries. Due to this, the rocks are under strain. When the stress on the rocks exceeds certain limits, the rocks rupture and form a fault along which the rocks are displaced during tectonic movements. This sudden rupture of the rocks releases energy in the form of earthquake waves (Fig. 18.1).

Thus earthquake is a form of energy, which is transmitted to the surface of the earth in the form of waves called seismic waves. The study of earthquakes and the waves they create is called seismology (from the Greek seismos, “to shake”). Scientists who study earthquakes are called seismologists. The instrument that records the seismic waves is called seismograph.

The exact spot under the earth surface at which an earthquake originates is called the focus or hypocenter. The point on the earth surface above the focus is called the epicenter. The Richter scale is used to measure the intensity of earthquakes. The intensity is measured on a scale of 0 to 8 and above (Table 18.1).