Natural Hazards and Disasters

A sudden accident or a natural catastrophe that causes great damage or loss of life and property is called a disaster. It can be natural like earth quakes, tsunami, floods etc and artificial disasters like terrorist attack etc. Structural measures are any physical construction to reduce or avoid possible impacts of hazards by the application of engineering techniques or technology. Building community shelters at various hazard prone areas is one such example.

A sudden accident or a natural catastrophe that causes great damage or loss of life and property is called a disaster. It can be natural like earth quakes, tsunami, floods etc and artificial disasters like terrorist attack etc. The impact of disaster depends on the precautions we take to save our lives and our environment. Disaster preparedness refers to measures taken to prepare for and reduce the effects of disasters. Disaster preparedness builds capacity at all levels like at individual, social, national and global levels. The approach to disaster preparedness has shifted from need-based to right and community based approach.

A tsunami is a series of large ocean waves caused by underwater earthquakes, volcanic eruptions, or landslides.

The Richter magnitude scale was developed in 1935 by Charles F. Richter of the California Institute of Technology as a mathematical device to compare the size of earthquakes. The magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded by seismographs.

Following activities of humans can trigger an earthquake:

The processes for building new land and coastal plains are called constructive forces. Three of the main constructive forces are crustal deformation, volcanic eruptions, and deposition of sediment.

Crustal deformation occurs when the shape of land (or crust) is changed or deformed. One of the main causes is movement of the Earth's plates. When the plates collide or push toward each other, pressure builds. This can cause two things to happen. The rock can either fold or fault.

Both A and B

Coastal plains are formed when ocean levels fall on continental shelves that are at sea level, or when rivers carry sediment to areas of the ocean. These plains can take hundreds of years to form, and a few are found hundreds of miles inland.

1. Earthquake may sometimes create new coastal plains, by the emergence of a portion of ocean floor.

2. Submergence of coastal land may result in the formation of bays and gulfs which are favorable sites for the development of ports harbors.

3.Earthquakes result in the formation of hot springs and geyser beneficial for medicinal purposes

• Vertical displacement of overlying water causes a stark difference between the elevation of the ocean floor due to which water from higher elevation quickly move towards lower elevation seafloor. 
• This generates very high waves which travel towards the coastal regions and are known as tsunami or harbour waves. Hence option C is correct.
• Note- Horizontal displacement does not cause displacement of a very significant amount of water hence cannot generate tsunamis.

July 9, 1958

On 9 July 1958, a 7.8Mw strike-slip earthquake in southeast Alaska caused 90 million tonnes of rock and ice to drop into the deep water at the head of Lituya Bay. The block fell almost vertically and hit the water with sufficient force to create a wave that surged up the opposite side of the head of the bay to a height of 524 m, and was still many tens of metres high further down the bay, when it carried eyewitnesses Howard Ulrich and his son Howard Jr. over the trees in their fishing boat. They were washed back into the bay and both survived

• The primary effect of the earthquake- shaking of earth's surface.
• Secondary effects- effects caused by primary effect i.e. effects caused by the shaking of the earth's surface viz tsunami, landslides, and fires.
• Hence all options are correct.

The primary destructive effect of Earthquakes include the damage to man-made structures, such as roads, bridges, dams, and buildings from the ground motion depends on the type of construction:

1. concrete and masonry structures are brittle and thus more susceptible to damage and collapse

2. damage to wood and steel structures is far less because of its flexibility.

Rainfall over an extended period and an extended area can cause major rivers to overflow their banks. The water can cover enormous areas. Downstream areas may be affected, even when they didn’t receive much rain themselves. High amounts of water flowing in streams often leads to flooding, and flooding is one of the more common types of natural disasters. A flood results when a stream runs out of its confines and submerges surrounding areas.

• An Earthquake at the bottom of ocean can cause large scale displacement of water leading into very high harbour waves called Tsunami. Tsunamis can in turn cause large scale flooding of the coastal areas. 
• Also Earthquakes the shaking of the mountaneous regions caused by earthquakes can cause landslides. Hence earthquakes can cause tsunami,flooding and landslides. 
• Lightening is an atmospheric phenomenon, hence is unrelated to earthquake.

During winter season land areas become cold and adjoining ocean surface becomes comparatively hot. So low-pressure centers develop in the ocean and the winds started blowing from surrounding high pressure to low pressure areas. As it comes to the low-pressure center, it gets warm and rises up. For this mechanism, devastating cyclones originated in the Bay of Bengal during October to early November.