Natural phenomena encompass both desirable and undesirable occurrences resulting from natural forces. Disasters, which are undesirable occurrences such as earthquakes, cyclones, tsunamis, and droughts, are largely beyond human control. These events can cause or threaten serious disruptions to human lives, prompting the need for protective measures. It is now a global concern that the current climatic changes have been accelerated due to human activities.

Earthquake

A sudden shaking or trembling of the earth which lasts for a very short time is called an earthquake.

• Earthquakes are caused by disturbances inside the uppermost layer of the earth, called the crust.
• The outermost layer of the earth is fragmented into plates, which are in continual motion. When they collide or brush past each other, disturbances occur causing tremors.
• Earthquakes are mainly caused by the movement of plates along their boundaries, known as seismic fault zones.
• The power of an earthquake is measured on the Richter scale, which is logarithmic.

Protection against Earthquakes

• Buildings in seismic zones should be designed to withstand major tremors.
• During an earthquake, take shelter under a table indoors, or find a clear spot away from buildings and trees if outdoors.
• The point below the earth's surface where the earthquake originates is called the hypocenter, and the point on the surface directly above it is the epicenter.

In India, earthquake-prone areas include Kashmir, Western and Central Himalayas, North-East, Rann of Kutch, Rajasthan, Indo-Gangetic plains, and some parts of South India.

Landslides

When large masses of bedrock undergo rapid sliding, it is termed as a landslide. Landslides can be caused by earthquakes, sudden rock failures, or over-steepening of slopes due to excavation or river erosion.

Lightning

Lightning is caused by the accumulation of charges in clouds, resulting in streaks of bright light and sound during thunderstorms.

• During a thunderstorm, air currents move upward while water droplets move downward, causing charge separation.

Safety Measures for Lightning

• Avoid open places during lightning. If outdoors, stay away from poles and metal objects.
• If in a car, stay inside with windows and doors closed. Do not use electrical appliances or phones indoors and avoid contact with running water.

Lightning Conductor

A lightning conductor is a device used to protect buildings from lightning strikes. It consists of a metallic rod taller than the building, which provides a path for electric charge to safely reach the ground.

Floods

A flood is an overflow of water that submerges land. It can occur due to heavy rainfall, collapse of dams, storm surges, or unplanned development on floodplains.

Safety Measures for Floods

• Implement practical watershed management such as preventing deforestation and carrying out reforestation.
• Construct high walls and strong embankments along riverbanks.
• Use floodplains only for recreational or agricultural purposes.

Tsunami

Tsunami is a series of ocean waves generated by large movements or disturbances on the ocean’s floor, such as volcanic eruptions, landslides, and earthquakes. The word "tsunami" is derived from a Japanese word meaning “harbour waves”.

• Tsunamis travel at speeds of 600-800 km per hour depending on water depth.
• Tsunamis are less frequent in the Indian Ocean compared to the Pacific Ocean due to lower seismic activity.
• The devastating Indian Ocean tsunami was caused by a 9.0 magnitude earthquake near the Western boundary of Sumatra.

Drought

Drought is a period of below-average precipitation in a given region, resulting in prolonged shortages of water supply, whether surface water or groundwater.

• A drought can last from a few weeks to several years.

Causes of Drought

• Scarcity of rainfall and inadequate monsoons.
• Lack of irrigation facilities and rainwater harvesting systems.
• Deforestation and reduced soil water retention.

Safety Measures for Drought

• Practice rainwater conservation and storage.
• Educate people on the importance of water conservation.
• Implement improved rainwater harvesting methods.
• Discourage deforestation and promote watershed management.
• Build dams and adopt efficient irrigation techniques.

Wind

Wind is the movement of air caused by differences in atmospheric pressure, which result from the unequal heating of the Earth’s surface by the sun.

• Warm air near the equator rises, creating low-pressure areas, while cooler air from the poles moves towards the equator, forming wind currents.

Cyclones

A cyclone is a violently rotating windstorm with wind speeds of 120-200 km/h, characterized by a central area of very low atmospheric pressure known as the eye of the cyclone.

• Cyclones can cause floods due to water pushed by strong winds.
• They are known as hurricanes in America and typhoons in Asia.
• Tornadoes, a type of cyclone, are rotating columns of high-speed winds.

Most Affected States in India:

Andhra Pradesh, Gujarat, Kerala, Maharashtra, Odisha, and Tamil Nadu. The Eastern coast is more vulnerable to cyclones than the Western coast.

Safety Measures for Cyclones

• Install a cyclone forecast system and heed warnings issued by meteorological departments.
• Advanced technologies now allow for a cyclone alert 48 hours in advance and a cyclone warning 24 hours in advance.

Man-made Disaster

Man-made disasters are the result of human errors or negligence during technological and industrial use. These disasters occur suddenly and result in significant loss of life and property. They can be categorized into two types:

• Direct: These include accidents such as train accidents, terrorism, plane crashes, and industrial disasters like the Bhopal gas tragedy.
• Indirect: These are natural disasters exacerbated by human interference, such as floods caused by dam breakdowns or landslides caused by mining.

Global Warming

Global warming refers to the increasing overall temperature of the Earth's atmosphere due to the growing presence of greenhouse gases emitted by human activities such as burning fossil fuels and deforestation.

• Global warming leads to the melting of glaciers and ice caps, causing flooding in low-lying areas worldwide and adversely affecting climate.

Greenhouse Effect

The greenhouse effect is a process where thermal radiation from the Earth's surface is absorbed by greenhouse gases like carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and chlorofluorocarbons (CFCs). These gases allow sunlight to pass through but trap outgoing infrared radiation, leading to an increase in average surface temperature, or global warming.

Ozone Layer Depletion

The ozone layer is a protective shield in the Earth's stratosphere (17-26 km above the surface) that absorbs about 99% of harmful non-ionizing UV rays from the sun. Depletion of the ozone layer is primarily caused by the increased use of chemicals like chlorofluorocarbons (CFCs), carbon tetrachloride, and halons.