Introduction
Natural hazards and disasters are extreme natural events that cause destruction to life, property, and the environment. While natural hazards refer to potential threats posed by natural phenomena, disasters occur when these hazards lead to loss of life and property.
Difference Between Natural Hazards and Natural Disasters
- Natural Hazard: A potential natural event that poses a risk to humans and the environment (e.g., an active fault line).
- Natural Disaster: The actual occurrence of a hazardous event causing destruction (e.g., an earthquake that causes buildings to collapse).
Classification of Natural Hazards and Disasters
Natural disasters are broadly classified into:
- Geophysical Disasters – Earthquakes, volcanic eruptions, tsunamis, landslides.
- Hydro-Meteorological Disasters – Cyclones, floods, droughts, cloudbursts.
- Biological Disasters – Epidemics, pandemics, locust attacks.
- Man-Made Disasters (Triggered by Natural Factors) – Environmental pollution, forest fires.
Geophysical Disasters
Earthquakes
Definition:
An earthquake is a sudden shaking of the Earth’s surface caused by the release of energy from within the Earth’s crust due to tectonic movements.
Mechanism:
- The Earth’s crust is divided into tectonic plates that move due to convection currents in the mantle.
- When stress builds up along fault lines, energy is released as seismic waves, causing the ground to shake.
Types of Earthquake Waves:
- Primary (P) Waves: Fastest, travel through solids and liquids.
- Secondary (S) Waves: Slower, travel only through solids.
- Surface Waves: Cause most destruction.
Measurement of Earthquakes:
- Richter Scale: Measures magnitude (energy released).
- Mercalli Scale: Measures intensity (damage caused).
Examples:
- 2001 Bhuj Earthquake (Gujarat) – Magnitude 7.7
- 2015 Nepal Earthquake – Magnitude 7.8
Volcanic Eruptions
Definition:
A volcanic eruption is the release of magma, gases, and ash from beneath the Earth’s crust.
Mechanism:
- Magma from the mantle rises due to high pressure.
- When it reaches the surface, it erupts as lava, ash, and gases.
- Types: Effusive (slow lava flow) and Explosive (violent eruptions with ash clouds).
Examples:
- Barren Island (Andaman & Nicobar) – India’s only active volcano.
- Mount Vesuvius (Italy) – 79 CE eruption destroyed Pompeii.
Tsunamis
Definition:
A tsunami is a series of large ocean waves caused by underwater earthquakes, volcanic eruptions, or landslides.
Mechanism:
- Underwater tectonic activity displaces a large volume of water.
- Waves travel at high speed in deep waters but slow down and increase in height near the shore.
- Causes massive coastal flooding and destruction.
Examples:
- 2004 Indian Ocean Tsunami – Caused by a 9.1 magnitude earthquake near Sumatra.
- 2011 Japan Tsunami – Triggered by a 9.0 magnitude earthquake.
Landslides
Definition:
A landslide is the sudden movement of rock, soil, and debris down a slope due to gravity.
Causes:
- Natural: Heavy rainfall, earthquakes, volcanic activity.
- Human-Induced: Deforestation, mining, road construction.
Examples:
- Malin Landslide (Maharashtra, 2014).
- Himalayan landslides due to deforestation and heavy rainfall.
Hydro-Meteorological Disasters
Cyclones
Definition:
Cyclones are intense low-pressure systems with strong winds and heavy rainfall, forming over warm ocean waters.
Mechanism:
- Warm ocean water evaporates and rises.
- The Coriolis force causes rotation, forming a spiral system.
- The eye of the cyclone is calm, while the eyewall has the most severe winds.
Types:
- Tropical Cyclones: Form in warm seas (e.g., Indian Ocean, Atlantic).
- Temperate Cyclones: Form in mid-latitude regions.
Examples:
- Cyclone Amphan (2020) – Bay of Bengal.
- Cyclone Tauktae (2021) – Arabian Sea.
Floods
Definition:
A flood is an overflow of water submerging land due to excessive rainfall, river overflow, dam failure, or storm surges.
Causes:
- Heavy monsoon rainfall.
- Snowmelt from glaciers.
- Deforestation and urbanization.
Examples:
- 2013 Uttarakhand Flash Floods – Caused by heavy rainfall and glacial lake outburst.
- 2005 Mumbai Floods – Caused by high rainfall and poor drainage.
Droughts
Definition:
Drought is an extended period of deficient rainfall leading to water scarcity.
Types:
- Meteorological Drought: Below-average rainfall.
- Agricultural Drought: Soil moisture deficit affects crops.
- Hydrological Drought: Low water levels in reservoirs.
Causes:
- Low rainfall.
- Overuse of groundwater.
- Climate change effects.
Examples:
- Marathwada Drought (Maharashtra, 2016).
- 1987 and 2002 India-wide droughts.
Cloudbursts
Definition:
A cloudburst is a sudden, intense rainfall over a small area, often leading to flash floods.
Causes:
- Orographic lifting in hilly regions.
- Warm air mass carrying moisture suddenly cools.
Examples:
- Leh Cloudburst (2010).
- Kedarnath Disaster (2013).
Biological Disasters
Epidemics and Pandemics
Definition:
Epidemics and pandemics refer to widespread outbreaks of diseases affecting large populations.
Examples:
- COVID-19 Pandemic (2020).
- 1918 Spanish Flu Pandemic.
Man-Made Disasters Triggered by Natural Factors
Environmental Pollution
Causes:
- Industrial waste, deforestation, chemical spills.
Examples:
- Bhopal Gas Tragedy (1984).
- Ganga River Pollution.
Forest Fires
Causes:
- Lightning, extreme heat, human negligence.
Examples:
- Australian Bushfires (2019-2020).
- Uttarakhand Forest Fires.
Disaster Management Strategies
Mitigation Measures:
- Earthquake-Resistant Buildings: Use of shock absorbers.
- Early Warning Systems: Tsunami and cyclone alerts.
- Afforestation: Prevents landslides and floods.
- Water Conservation: Reduces drought impact.
Institutional Mechanisms in India:
- National Disaster Management Authority (NDMA).
- Indian Meteorological Department (IMD).
- Geological Survey of India (GSI).
Multiple-Choice Questions (MCQs)
1. Consider the following statements regarding Natural Hazards and Disasters:
- A natural hazard refers to a potential threat posed by natural phenomena.
- A natural disaster occurs when a hazard leads to significant loss of life and property.
- Earthquakes and cyclones are examples of natural hazards, but not natural disasters.
Which of the above statements is/are correct?
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2, and 3
Answer: (a) 1 and 2 only
Explanation: A natural hazard is a potential event, while a natural disaster is the actual occurrence with destruction. Earthquakes and cyclones can be both hazards (potential risk) and disasters (when they cause destruction).
2. Which of the following are correctly classified as Geophysical Disasters?
- Tsunamis
- Cloudbursts
- Landslides
- Volcanic Eruptions
Select the correct answer using the codes given below:
(a) 1, 2, and 3 only
(b) 2 and 4 only
(c) 1, 3, and 4 only
(d) 1, 2, 3, and 4
Answer: (c) 1, 3, and 4 only
Explanation: Geophysical disasters are caused by geological processes such as earthquakes, volcanoes, tsunamis, and landslides. Cloudbursts, however, are classified as hydro-meteorological disasters.
3. Consider the following statements regarding Earthquakes:
- P-waves travel faster than S-waves and can move through both solids and liquids.
- The Richter Scale measures the damage caused by an earthquake.
- Surface waves cause the maximum destruction during an earthquake.
Which of the above statements is/are correct?
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2, and 3
Answer: (c) 1 and 3 only
Explanation: P-waves are the fastest and travel through both solids and liquids. Surface waves cause the most destruction. The Richter Scale measures the magnitude (energy released), while the Mercalli Scale measures damage.
4. With reference to Tsunamis, consider the following statements:
- They are caused by underwater earthquakes, volcanic eruptions, or landslides.
- Tsunami waves travel faster in deep waters and slow down near the coast, increasing in height.
- The 2004 Indian Ocean Tsunami was triggered by a volcanic eruption near Indonesia.
Which of the above statements is/are correct?
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2, and 3
Answer: (a) 1 and 2 only
Explanation: The 2004 Indian Ocean Tsunami was caused by a 9.1 magnitude earthquake near Sumatra, not a volcanic eruption. The first two statements are correct.
5. Consider the following causes of Landslides:
- Heavy rainfall and earthquakes
- Volcanic activity
- Deforestation and road construction
Which of the above are natural causes of landslides?
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2, and 3
Answer: (a) 1 and 2 only
Explanation: Landslides can be caused by both natural and human-induced factors. Heavy rainfall, earthquakes, and volcanic activity are natural causes, while deforestation and road construction are human-induced.
6. Which of the following statements regarding Cyclones are correct?
- Tropical cyclones form over warm ocean waters, while temperate cyclones form in mid-latitude regions.
- The eye of a cyclone is the most violent part of the system.
- The Coriolis force plays a role in the formation of cyclones.
Select the correct answer using the codes given below:
(a) 1 and 2 only
(b) 1 and 3 only
(c) 2 and 3 only
(d) 1, 2, and 3
Answer: (b) 1 and 3 only
Explanation: The eye of a cyclone is calm, while the eyewall surrounding it has the most severe winds. The Coriolis force influences the rotation of cyclones.
7. Consider the following pairs of disasters and their causes:
| Disaster | Cause |
| 1. Uttarakhand Floods (2013) | Cloudburst and glacial lake outburst |
| 2. Kedarnath Disaster (2013) | Tsunami |
| 3. Marathwada Drought (2016) | Rainfall deficit and overuse of groundwater |
| 4. Bhopal Gas Tragedy (1984) | Industrial gas leak |
Which of the pairs are correctly matched?
(a) 1, 3, and 4 only
(b) 2 and 3 only
(c) 1, 2, and 4 only
(d) 1, 2, 3, and 4
Answer: (a) 1, 3, and 4 only
Explanation: The Kedarnath Disaster (2013) was caused by a cloudburst and flash floods, not a tsunami. The other pairs are correctly matched.
8. Consider the following statements regarding Droughts:
- Meteorological drought occurs when rainfall is significantly below normal levels.
- Agricultural drought is caused by a deficiency in soil moisture affecting crops.
- Hydrological drought refers to low water levels in reservoirs and rivers.
Which of the above statements is/are correct?
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2, and 3
Answer: (d) 1, 2, and 3
Explanation: All statements correctly define the different types of droughts.
9. Which of the following are institutional mechanisms for disaster management in India?
- National Disaster Management Authority (NDMA)
- Indian Meteorological Department (IMD)
- Geological Survey of India (GSI)
Select the correct answer using the codes given below:
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2, and 3
Answer: (d) 1, 2, and 3
Explanation: NDMA is responsible for disaster management, IMD provides weather forecasts, and GSI monitors geological hazards like earthquakes and landslides.
10. Consider the following statements about Forest Fires:
- They can be triggered by both natural causes (lightning, extreme heat) and human negligence.
- The 2019-2020 Australian Bushfires were one of the most destructive in history.
- Forest fires only occur in tropical and subtropical regions.
Which of the above statements is/are correct?
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2, and 3
Answer: (a) 1 and 2 only
Explanation: Forest fires can occur in various climatic regions, including temperate forests (e.g., California wildfires). Statement 3 is incorrect.
