Tag: earthquake and volcanoes

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.

  Flood forecasting has been recognized as one of the most important, reliable and cost-effective non-structural measures for flood management.

Central Water Commission started flood-forecasting services in 1958 with the setting up of its first forecasting station on Yamuna at Delhi Railway Bridge.  Presently, a network of 175 Flood Forecasting Stations including 28 inflow forecast, in 9 major river basins and 71 sub basins of the country exists. It covers 15 States besides NCT Delhi and UT of Dadra & Nagar Haveli. Central Water Commission on an average issues 6000 flood forecasts with an accuracy of more than 95% every year.  

Underwater earthquakes push water upward to create the initial movement, then gravity pulls the water downward, creating the horizontal force that forms the tsunami. The waves travel through the ocean in a similar fashion to ripples created by throwing a stone into a body of water.

Earthquakes occur often on the earth's crust that forms the sea floor; however, not all result in a tsunami. For a tsunami to form, the magnitude of the earthquake must measure a minimum of 7.0 on the Richter scale. Below this magnitude, the earthquake does not displace enough water to create the big wave. The movement must also lift or lower the sea bed. Sideways movement does not create the initial wave to start the process. The epicenter of the earthquake must be near the surface of the sea floor to cause the correct movement.

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.