Class 11 Geography: Natural Hazards and Disasters
A. Multiple Choice Questions (MCQs) - 1 Mark Each (Total: 15 Marks)
Which of the following best defines a 'Natural Hazard'?
a) An event that causes widespread loss of life and property.
b) A potential threat to humans and their environment.
c) A planned human activity causing environmental damage.
d) The recovery phase after an extreme event.
Answer: b) A potential threat to humans and their environment.
Hint: A hazard is the potential, while a disaster is the actualized event.
Rationale: A natural hazard is a natural phenomenon that has the potential to cause harm, but a disaster only occurs when that potential is realized and causes significant damage.
The instrument used to measure the intensity or magnitude of an earthquake is the:
a) Barometer
b) Anemometer
c) Seismograph
d) Hydrometer
Answer: c) Seismograph
Hint: This device records seismic waves.
Rationale: A seismograph is an instrument that detects and records ground motion caused by seismic waves from earthquakes.
Which type of seismic wave causes the most damage to structures during an earthquake?
a) P-waves (Primary waves)
b) S-waves (Secondary waves)
c) Surface waves (L-waves/Rayleigh waves)
d) Body waves
Answer: c) Surface waves (L-waves/Rayleigh waves)
Hint: These waves travel along the Earth's surface and cause significant shaking.
Rationale: While P-waves and S-waves travel through the Earth's interior, surface waves travel along the surface, causing the most destructive ground motion and structural damage.
A sudden rise in sea level caused by a tropical cyclone, pushing water onto coastal areas, is known as a:
a) Tsunami
b) Tidal wave
c) Storm Surge
d) Seiche
Answer: c) Storm Surge
Hint: This is a major destructive element of cyclones.
Rationale: A storm surge is an abnormal rise of water generated by the storm, over and above the predicted astronomical tides, primarily caused by strong winds and low atmospheric pressure.
Which of the following factors is most likely to trigger a landslide on a steep slope?
a) Prolonged drought
b) Heavy rainfall
c) High air pressure
d) Mild winds
Answer: b) Heavy rainfall
Hint: Water often acts as a lubricant and adds weight.
Rationale: Heavy rainfall saturates the soil, reduces its cohesion, adds weight to the slope, and increases pore-water pressure, all of which increase the likelihood of a landslide.
The highest flood-prone states in India are primarily located in the:
a) Peninsular Plateau region
b) Himalayan mountainous region
c) Northern Plains (Ganga-Brahmaputra basin)
d) Western Coastal Plains
Answer: c) Northern Plains (Ganga-Brahmaputra basin)
Hint: These regions have vast river systems and low gradients.
Rationale: The Northern Plains, particularly the Ganga and Brahmaputra basins, are highly susceptible to floods due to heavy monsoon rainfall, large river discharge, and low-lying, flat terrain.
Which type of drought is characterized by a shortage of water impacting agricultural production, leading to crop failure?
a) Meteorological drought
b) Hydrological drought
c) Agricultural drought
d) Socio-economic drought
Answer: c) Agricultural drought
Hint: This type directly affects crops.
Rationale: Agricultural drought occurs when there isn't enough moisture in the soil to support crop production, leading to reduced yields or crop failure. Meteorological drought is a rainfall deficit, and hydrological drought is low streamflow/groundwater.
The Ring of Fire, a zone of frequent earthquakes and volcanic eruptions, is primarily located around the:
a) Atlantic Ocean
b) Indian Ocean
c) Pacific Ocean
d) Arctic Ocean
Answer: c) Pacific Ocean
Hint: This is a major tectonic plate boundary.
Rationale: The Pacific Ring of Fire is a major area in the basin of the Pacific Ocean where a large number of earthquakes and volcanic eruptions occur. It is associated with a series of oceanic trenches, volcanic arcs, and volcanic belts and plate movements.
Which of the following is an example of a mitigation strategy for earthquakes?
a) Providing immediate medical aid after an earthquake.
b) Setting up temporary shelters for displaced people.
c) Constructing earthquake-resistant buildings.
d) Distributing food and water during the recovery phase.
Answer: c) Constructing earthquake-resistant buildings.
Hint: Mitigation aims to reduce the impact before an event.
Rationale: Mitigation measures aim to reduce the loss of life and property by lessening the impact of disasters. Earthquake-resistant construction is a proactive step taken before an earthquake occurs. The other options are part of response or recovery.
A tsunami is most commonly caused by:
a) Strong winds over the ocean surface.
b) The gravitational pull of the Moon.
c) Underwater earthquakes.
d) Heavy rainfall at sea.
Answer: c) Underwater earthquakes.
Hint: It's a seismic sea wave.
Rationale: Tsunamis are giant ocean waves caused by large-scale disturbances that displace a large volume of water, most commonly from submarine earthquakes (especially those with vertical displacement), but also from volcanic eruptions, landslides, or meteor impacts.
Which zone of India is considered to be highly vulnerable to earthquakes?
a) Peninsular Plateau
b) Coastal Plains
c) Himalayan and North-Eastern region
d) Thar Desert
Answer: c) Himalayan and North-Eastern region
Hint: This region lies on an active plate boundary.
Rationale: The Himalayan region and the North-Eastern states lie in seismic zones IV and V, making them highly vulnerable to powerful earthquakes due to the active collision of the Indian and Eurasian plates.
The term 'Disaster Risk Reduction' primarily focuses on:
a) Responding to disasters after they occur.
b) Minimizing vulnerabilities and exposure to hazards.
c) Providing immediate relief to victims.
d) Documenting past disaster events.
Answer: b) Minimizing vulnerabilities and exposure to hazards.
Hint: DRR is a proactive approach.
Rationale: Disaster Risk Reduction (DRR) is about preventing new and reducing existing disaster risk, and managing residual risk, all of which contribute to strengthening resilience and therefore to the achievement of sustainable development. It's a proactive, holistic approach.
What is the main cause of tropical cyclones?
a) Intense heating of landmasses.
b) Warm ocean waters and low atmospheric pressure.
c) Collision of warm and cold air masses.
d) Volcanic eruptions at sea.
Answer: b) Warm ocean waters and low atmospheric pressure.
Hint: They draw energy from warm, moist air over oceans.
Rationale: Tropical cyclones form over warm tropical oceans (sea surface temperature > 27°C) where low atmospheric pressure allows moist air to rise, condense, and release latent heat, fueling the storm.
Which of the following is NOT typically a natural cause of landslides?
a) Earthquakes
b) Heavy rainfall
c) Deforestation
d) Volcanic eruptions
Answer: c) Deforestation
Hint: This is a human activity that exacerbates landslides.
Rationale: Deforestation is a human-induced factor that contributes to landslides by removing vegetation that stabilizes slopes. Earthquakes, heavy rainfall, and volcanic eruptions are natural triggers.
What is the significance of an 'Early Warning System' in disaster management?
a) It helps in post-disaster rehabilitation.
b) It ensures immediate financial aid to victims.
c) It allows for timely evacuation and preparedness, reducing loss of life.
d) It focuses on long-term reconstruction efforts.
Answer: c) It allows for timely evacuation and preparedness, reducing loss of life.
Hint: It's about getting information out before the event.
Rationale: Early Warning Systems provide timely and effective information about impending hazards, enabling individuals and communities to prepare and take action, thereby reducing the risk of loss and harm.
B. Short Answer Questions (2-3 Marks Each) - (Total: 20-30 Marks)
Differentiate between a 'Natural Hazard' and a 'Natural Disaster'.
Answer: A Natural Hazard is a potential threat or a natural phenomenon that has the potential to cause harm to human life and property (e.g., an earthquake fault line, a cyclone developing over the ocean). A Natural Disaster is the actualization of that hazard, an extreme event that causes widespread loss of life, property, and environmental damage, overwhelming the coping capacity of the affected community (e.g., the 2004 Indian Ocean Tsunami, the 2013 Uttarakhand floods).
What is 'Storm Surge'? Why is it considered the most destructive aspect of a tropical cyclone?
Answer: Storm Surge is an abnormal rise of water generated by a storm, over and above the predicted astronomical tides. It is caused primarily by the strong winds of a cyclone pushing water towards the shore and, to a lesser extent, by the low atmospheric pressure in the eye of the storm. It is considered the most destructive aspect because it causes massive coastal inundation, leading to widespread drowning, destruction of coastal infrastructure, salinization of agricultural lands, and makes rescue operations extremely difficult.
Name the three types of seismic waves generated during an earthquake and state which type travels fastest.
Answer: The three types of seismic waves are:
P-waves (Primary or compressional waves): Travel fastest and arrive first.
S-waves (Secondary or shear waves): Travel slower than P-waves and arrive second.
Surface waves (L-waves or Rayleigh/Love waves): Travel along the Earth's surface and are the slowest but cause the most destruction.
List any three human-induced factors that can exacerbate natural disasters like floods or landslides.
Answer: Three human-induced factors:
Deforestation: Removal of trees reduces soil stability (leading to landslides) and reduces water absorption by soil (increasing surface runoff and flood risk).
Unplanned Urbanization/Construction: Construction on vulnerable slopes (for landslides), encroachment on floodplains (increasing flood impact), or construction without proper drainage.
Mining and Quarrying: Can destabilize slopes and alter drainage patterns, increasing landslide and flood risks.
Improper Agricultural Practices: Ploughing up and down slopes (leading to soil erosion), overgrazing.
What are the four types of drought based on its progression?
Answer: The four types of drought are:
Meteorological Drought: Deficiency of rainfall from normal over a long period.
Agricultural Drought: Insufficient soil moisture to support crops, leading to crop failure, even if rainfall is near normal.
Hydrological Drought: Reduced levels of water in rivers, lakes, reservoirs, and groundwater due to prolonged meteorological drought and increased demand.
Ecological Drought: When natural ecosystems face water stress, leading to a decline in their productivity and environmental damage.
Explain the concept of 'Vulnerability' in the context of natural disasters.
Answer: Vulnerability refers to the characteristics and circumstances of a community, system, or asset that make it susceptible to the damaging effects of a hazard. It is a set of conditions that determine the degree to which a population, area, or asset is exposed to, susceptible to, and unable to cope with the adverse impacts of hazards. Factors contributing to vulnerability include poverty, poor housing, lack of infrastructure, limited access to resources, and weak governance.
How do volcanoes typically impact the surrounding environment and atmosphere?
Answer: Volcanoes impact the environment through:
Lava Flows: Destroy everything in their path (buildings, vegetation) but are relatively slow.
Ash Falls: Can cover vast areas, burying crops, collapsing roofs, and causing respiratory problems.
Gases: Release harmful gases like sulfur dioxide (SO 2 ), carbon dioxide (CO 2 ), which can cause acid rain and affect air quality.
Pyroclastic Flows: Fast-moving currents of hot gas and volcanic debris, extremely destructive and lethal.
Lahars (Mudflows): Volcanic ash mixing with water, forming destructive mudflows.
What is the main objective of 'Disaster Mitigation'? Give two examples.
Answer: The main objective of Disaster Mitigation is to reduce the long-term risk to human life and property from natural hazards. It involves proactive measures taken before a disaster occurs to lessen its potential impact.
Examples: Constructing earthquake-resistant buildings, building flood embankments along rivers, implementing land-use zoning to avoid construction in high-risk areas, developing early warning systems.
Why are the Himalayan region and North-Eastern states of India particularly prone to landslides?
Answer: The Himalayan region and North-Eastern states are prone to landslides due to:
Geologically Young and Unstable Terrain: The Himalayas are young, tectonically active mountains with highly fractured and unstable rock formations.
Steep Slopes: The steep gradients increase the susceptibility to gravitational forces.
High Rainfall: Heavy monsoon rainfall saturates the soil, adds weight to slopes, and reduces cohesion.
Seismic Activity: Frequent earthquakes can trigger landslides.
Human Activities: Road construction, deforestation, and unsustainable agricultural practices destabilize slopes.
Explain the difference between 'Flash Floods' and 'Riverine Floods'.
Answer:
Flash Floods: Occur rapidly (within minutes or hours) due to intense rainfall over a short period, typically in small catchments, urban areas, or mountainous regions. They are characterized by a sudden rise in water level and high velocity, causing immediate danger.
Riverine Floods: Occur over a longer period (days or weeks) when prolonged or heavy rainfall causes rivers to exceed their bank capacity and overflow into adjacent floodplains. They are characterized by a gradual rise in water levels but can affect large areas.
C. Long Answer Questions (5-6 Marks Each) - (Total: 10-12 Marks)
Discuss the major causes and devastating consequences of Earthquakes. What measures can be taken to mitigate their impact in vulnerable regions?
Answer:
Earthquakes are sudden tremors or shaking of the Earth's crust caused by the rapid release of energy from within the Earth.
Major Causes of Earthquakes:
The primary cause of most significant earthquakes is Plate Tectonics.
Plate Boundaries: The Earth's lithosphere is divided into several large and small tectonic plates that are constantly moving. Earthquakes occur most frequently along the boundaries where these plates interact:
Convergent Boundaries: Plates collide or subduct (one slides beneath another). The immense pressure and friction cause rocks to deform and eventually rupture, releasing energy. (e.g., Himalayan region where Indian plate collides with Eurasian plate).
Divergent Boundaries: Plates pull apart from each other, creating rifts and allowing magma to rise. (e.g., Mid-Oceanic Ridges).
Transform Boundaries: Plates slide horizontally past each other. (e.g., San Andreas Fault).
Volcanic Activity: Earthquakes can be caused by the movement of magma beneath volcanoes, leading to tremors.
Faulting: Movement along existing geological faults within plates can also trigger earthquakes.
Human-Induced Causes: While usually minor, activities like large dam construction (reservoir-induced seismicity), deep well injection of fluids (e.g., fracking waste), and underground nuclear explosions can also cause tremors.
Devastating Consequences of Earthquakes:
Earthquakes can have widespread and destructive impacts, both immediate and long-term:
Ground Shaking and Collapse of Structures: This is the most direct and devastating impact, leading to the collapse of buildings, bridges, and infrastructure, causing widespread fatalities and injuries.
Liquefaction: In areas with loose, water-saturated soils, ground shaking can cause the soil to lose its strength and behave like a liquid, leading to buildings sinking or toppling.
Landslides and Avalanches: Earthquakes often destabilize slopes, triggering massive landslides, rockfalls, and avalanches, especially in mountainous regions, burying settlements and blocking roads.
Fires: Damaged gas lines, electrical wiring, and overturned stoves can ignite widespread fires, which are often difficult to control due to damaged water lines and blocked roads.
Tsunamis: Underwater earthquakes with significant vertical displacement of the seafloor can generate powerful seismic sea waves (tsunamis) that travel across oceans and cause immense destruction upon reaching coastlines.
Dam Failure and Floods: Earthquakes can damage dams and levees, leading to catastrophic floods in downstream areas.
Loss of Life and Livelihood: Direct fatalities, injuries, displacement of populations, psychological trauma, and long-term economic disruption due to damaged infrastructure and disrupted services.
Measures to Mitigate their Impact in Vulnerable Regions:
Mitigation efforts aim to reduce the vulnerability of structures and populations:
Earthquake-Resistant Construction: Implementing strict building codes and standards for earthquake-resistant design and construction, retrofitting older buildings.
Land-Use Zoning and Hazard Mapping: Identifying seismic hazard zones and regulating land use, discouraging construction in highly vulnerable areas (e.g., active fault lines, liquefaction-prone zones).
Early Warning Systems (Limited): While predicting earthquakes is not yet possible, early warning systems can provide seconds to minutes of warning (e.g., for major cities) after initial seismic waves are detected, allowing for immediate safety actions.
Public Awareness and Education: Educating the public on earthquake preparedness (e.g., "Drop, Cover, and Hold On"), emergency kits, and evacuation routes.
Infrastructure Hardening: Securing non-structural elements (e.g., shelves, water heaters) and protecting critical infrastructure like power lines, gas pipelines, and communication networks.
Emergency Preparedness and Response: Developing robust emergency plans, training search and rescue teams, establishing communication networks, and ensuring stockpiles of relief supplies.
Research and Monitoring: Continuous research into earthquake prediction, monitoring seismic activity, and updating hazard assessments.
Describe the various types of floods, their causes, and the socio-economic impacts they have. Outline effective flood management strategies.
Answer:
Floods are one of the most common and devastating natural disasters, occurring when an overflow of water submerges land that is usually dry.
Various Types of Floods:
Riverine (Fluvial) Floods:
Causes: Occur when prolonged or heavy rainfall (often over a large catchment area) causes rivers to swell beyond their carrying capacity and overflow their banks into adjacent floodplains. Can also be exacerbated by dam/levee failures or snowmelt.
Characteristics: Develop relatively slowly (days to weeks), allowing for some warning. Affect large, low-lying areas along river courses.
Flash Floods:
Causes: Occur rapidly (within minutes to hours) due to intense, short-duration rainfall over a small area, often in mountainous or urban areas, or due to dam/levee failures.
Characteristics: Characterized by a sudden, violent rush of water, high velocity, and destructive power. Provide little to no warning.
Coastal Floods:
Causes: Occur in coastal areas due to storm surges associated with tropical cyclones, high tides, or tsunamis.
Characteristics: Involve inundation of coastal land by seawater.
Urban Floods:
Causes: Specific to urban areas, caused by a combination of heavy rainfall exceeding the capacity of drainage systems, rapid urbanization (increasing impervious surfaces), encroachment on natural drainage channels, and solid waste accumulation blocking drains.
Characteristics: Lead to waterlogging in streets, basements, and homes, disrupting daily life and causing significant damage.
Socio-Economic Impacts of Floods:
Floods have profound and widespread socio-economic consequences:
Loss of Life and Injury: Drowning is a direct cause, and injuries result from debris, collapses, and exposure.
Property Damage: Destruction of homes, commercial buildings, infrastructure (roads, bridges, power lines), leading to massive economic losses and displacement of populations.
Agricultural Loss: Submergence of agricultural land, destruction of standing crops, loss of livestock, and damage to irrigation systems, leading to food shortages and economic hardship for farmers.
Health Risks: Contamination of drinking water sources, spread of waterborne diseases (cholera, typhoid, malaria), and increased vector-borne diseases due to stagnant water.
Disruption of Services: Interruption of transportation, communication, electricity, and water supply, hindering rescue and relief efforts.
Livelihood Disruption: Loss of jobs, businesses, and income for affected communities, leading to long-term economic recovery challenges.
Psychological Trauma: Survivors often suffer from stress, anxiety, and other mental health issues.
Effective Flood Management Strategies:
Flood management involves a combination of structural and non-structural measures, encompassing all phases of the disaster management cycle:
A. Mitigation and Preparedness (Before the Flood):
Structural Measures:
Embankments/Levees: Building earthen or concrete walls along river banks to prevent overflow.
Dams and Reservoirs: Regulating river flow, storing excess water during heavy rainfall.
Channel Improvement: Deepening, widening, or straightening river channels to increase their carrying capacity.
Drainage Improvement: Upgrading and maintaining urban drainage systems, constructing storm sewers.
Non-Structural Measures:
Floodplain Zoning: Restricting construction and development in flood-prone areas to minimize exposure.
Land Use Planning: Promoting appropriate land uses in floodplains (e.g., parks, agriculture) rather than residential or commercial development.
Early Warning Systems: Establishing effective forecasting and warning systems to provide timely alerts for evacuation.
Community Preparedness: Educating communities on flood risks, evacuation plans, and emergency kits.
Afforestation: Planting trees in catchment areas to enhance soil absorption and reduce runoff.
Flood Proofing: Modifying buildings to be more resistant to flood damage.
B. Response (During the Flood):
Evacuation: Timely and organized evacuation of people from vulnerable areas.
Search and Rescue: Deploying trained teams to rescue trapped individuals.
Provision of Relief: Supplying food, water, temporary shelter, and medical aid to affected populations.
C. Recovery (After the Flood):
Rehabilitation: Restoring damaged infrastructure, housing, and essential services.
Reconstruction: Building back stronger and more resilient infrastructure.
Livelihood Restoration: Supporting affected communities to rebuild their economic activities.
Effective flood management requires a holistic approach, integrating these strategies to build resilient communities and minimize the impacts of this recurrent natural disaster.
