Samacheer Class 8 Social Science - Hazards

Hazards may lead to significant impacts on communities and environments. When asked what hazards may lead to, the answer is that they affect the community most severely, causing widespread damage and disruption. Landslide is an example of a geologic hazard, originating from natural geological processes. On the basis of origin, hazards can be grouped into eight categories, reflecting the diverse sources and types of hazards that threaten human societies. Terrorism is recognized as an example of a human-induced hazard, as it results from deliberate human actions. Oxides of nitrogen are classified as primary pollutants which affect human beings directly, being emitted directly into the atmosphere from various sources. The Chernobyl nuclear accident, which took place on 26th April 1986, remains one of the most significant human-induced hazards in history, demonstrating the catastrophic consequences that can result from technological failures and poor safety management in nuclear facilities.

The matching between different types of hazards and their characteristics is as follows: Primary pollutant corresponds to oxides of sulphur, which are directly emitted into the atmosphere. Hazardous waste corresponds to outdated drugs, which represent dangerous materials requiring proper disposal. Earthquake corresponds to tsunami, as earthquakes occurring underwater or near coastal areas can generate tsunamis. Meteorological drought corresponds to reduction in rainfall, as prolonged periods of below-normal precipitation lead to drought conditions. Human-induced hazard corresponds to terrorism, which is a hazard created by deliberate human actions and intentions. These matchings illustrate the diverse nature of hazards affecting human societies, ranging from natural phenomena like earthquakes and droughts to human-created threats like pollution and terrorism, and the importance of understanding their origins and characteristics for effective disaster management and prevention.

‘Hazards are defined as a thing, person, event or factor that poses a threat to people, structures or economic assets and which may cause a disaster.’2. What are the major types of hazards?
Natural hazards
Human-made hazards
Socio-natural hazards
3. Write a brief note on hazardous wastes.
The wastes that may or tend to cause adverse health effects on the ecosystem and human beings are called hazardous wastes.
4. List out the major flood-prone areas of our country.
Punjab, West Bengal, Odisha are the region which is also prone to flood often.
5. Mention the types of drought.
Drought could be classified into three types. They are:
Meteorological drought
Hydrological drought
Agricultural drought
6. Why should not we construct houses in foothill areas?
Because of the presence of steep slopes and heavy rainfall we should not construct houses at the foothills areas.

Pollution of Air:
Air is a mixture of several gases.
The main gases are nitrogen (78.09%) for forming products such as fertilizers for plants and for making the air inert, oxygen (20.95%) for breathing and carbon dioxide (0.03%) for photosynthesis.
Some other gases like argon, neon, helium, krypton, hydrogen, zenon and methane are also present.
Air pollution is the contamination of indoor or outdoor air by a range of gases. Air pollution can be categorized into primary and secondary pollutants.
A primary pollutant is an air pollutant emitted directly from a source.
A secondary pollutant is not directly emitted.
Primary pollutants are as follows:
Oxides of Sulphur
Oxides of Nitrogen
Oxides of Carbon
Particulate Matter and
Other primary pollutants
Secondary pollutants are as follows:
Ground Level Ozone
Smog2. Define earthquake and list out its effects.
Earthquakes:
Earthquake is a violent tremor in the earth’s crust, sending out a series of shock waves in all directions from its place of origin.
Earthquake-prone regions of the country have been identified on the basis of scientific inputs relating to seismicity, earthquakes that occurred in the past, and the tectonic setup of the region.
Based on these inputs, the Bureau of Indian Standards has grouped the country into four seismic zones: Zone II, Zone III, Zone IV, and Zone V (No area of India is classified as Zone I).
Seismic Zones
Level of Risk
Zone V
Very High
Zone IV
High
Zone III
Moderate
Zone II
Low
3. Give a detailed explanation of the causes of landslides.
1. Landslide is a rapid downward movement of rock, soil, and vegetation down the slope under the influence of gravity.
2. The causes of landslides are wide-ranging, They have two aspects in common.
3. Force of gravity and
4. Failure of Soil
5. Landslides are considered of two types. They are:
Naturally occurring disaster.
Human-induced changes in the environment.
6. Natural causes of landslides are:
Climatic changes
Seismic activities
Weathering
Soil erosion
Forest fires
Gravity and
Volcanic eruption
7. Human causes of landslides include deforestation mining, construction of roads, and railways over the mountain.
4. Elaborately discuss the effects of water pollution.
It may cause a harmful effect on any living thing that drinks or uses or lives in it.
It may be defined as alternation in the physical, chemical, and biological characteristics of water, which may cause harmful effects in human and aquatic life.
The major causes of water pollution in India are:
Urbanisation
Industrial effluents
Sewages etc.
Agricultural runoff and improper agricultural practices
Seawater intrusion
Solid wastes

Socio-natural hazards:
These are caused by the combined effect of natural forces and misdeeds of human. Some of the examples are:
The frequency and intensity of floods and droughts may increase due to indiscriminate felling of trees, particularly in the catchment areas of the rivers.
Landslides are caused by natural forces and their frequency, and impact may be aggravated as a result of construction of roads, houses etc., in mountainous areas, excavating tunnels and by mining and quarrying.
Storm surge hazards may be worsened by the destruction of mangroves.
Smog is a serious problem in most big urban areas. The emissions from vehicles and industries, combustion of wood and coal together combined with fog leads to smog.
2. Explain the Hazards based on their origin.
Hazards can be grouped into eight categories
1. Atmospheric hazard:
Tropical storms, Thunderstorms, Lightning, Tornadoes, Avalanches, Heat waves, Fog and Forest fire.
2. Geologic/Seismic hazard:
Earthquakes, Tsunami, Landslide and Land subsidence.
3. Hydrologic hazard:
Floods, Droughts, Coastal erosion and Storm surges.
4. Volcanic hazard:
Eruptions and Lava flows.5. Environmental hazard:
Pollution of soil/ air/water, Desertification, Global warming and Deforestation.
6. Biological hazard:
Chickenpox, Smallpox, AIDS [HIV] and Killer bees.
7. Technological hazard:
Hazardous material incidents, Fires, Infrastructure failures [Bridges, Tunnels, Dams, Nuclear and Radiological accidents].
8. Human-induced hazard:
Terrorism, Bomb blast, War, Transportation accidents and Civil disorder.