Unit 3: Natural and Man-made Disasters Study Notes

Introduction to Disasters, Hazards, and Vulnerability

• Conceptual Definition: In contemporary academia, disasters are viewed as the consequence of inappropriately managed risk. These risks result from a specific combination of hazards and vulnerability.
• The Disaster Equation: A disaster occurs only when a hazard impacts vulnerable people. For instance, hazards striking uninhabited regions (low vulnerability areas) do not become disasters.
• Natural Disasters: These may cause loss of life or property damage and typically result in economic damage. Their severity is determined by:     * The affected population's resilience (ability to recover).     * The quality of available infrastructure.
• Man-made Disasters: These are the result of human actions, including environmental degradation, pollution, and accidents. The distinguishing factor between natural and man-made disasters is the element of human intent or negligence.
• Causal Synergy: Disasters often result from a combination of hazards, existing vulnerability, and the inability to reduce potential negative consequences.

Geophysical Disasters

• Definition: Destructive events originating within or caused by the internal processes of the Earth. These include earthquakes, volcanic activity, landslides, and tsunamis.
• Earthquakes: Vibrations caused by the rupturing of rocks under stress.     * Fault Plane: The underground surface along which rock breaks and moves.     * Focus: The specific point within the Earth where the earthquake originates.     * Epicenter: The point on the Earth's surface directly above the focus.     * Measurement (Richter Scale): Determined by the amplitude of seismic waves and the seismograph's distance from the event. For every unit increase in magnitude, there is roughly a $23$-fold increase in the energy released.     * Modified Mercalli (MM) Intensity Scale: Rates effects observed by people, ranging from $I$ (imperceptible) to $XII$ (total destruction).     * Local Effects: Shaking and ground rupture are primary effects. Severity depends on magnitude, distance, focus depth, topography, and local geological conditions.     * Secondary Hazards: Earthquakes can trigger tsunamis (if offshore), landslides, and fires (due to damaged gas or power lines).     * Historical Example: The "Great Chilean Earthquake" (or "1960 Valdivia Earthquake") occurred on May 22, 1960. It had a documented magnitude of $9.5$, the largest ever instrumentally recorded.
• Volcanic Eruption: A rupture in the crust allowing hot lava, volcanic ash, and gases to escape from a magma chamber.     * Mechanism: Earth's crust is composed of rigid tectonic plates floating on a hotter, softer mantle. Eruptions typically occur where plates diverge or converge.     * Eruption Types: Explosive (sudden ejection of rock/ash) and Effusive (gentle outpouring of lava).     * Chemical Injections: Large eruptions inject water vapor, $CO_2$, $SO_2$, $HCl$, and $HF$ into the stratosphere ($16-32\,km$ high).     * Climatic Impact: $SO_2$ converts to sulfuric acid ($H_2SO_4$), forming sulfate aerosols that serve as nuclei for cirrus clouds and modify the radiation balance. Volcanic winters (cooling of the lower atmosphere) can cause catastrophic famines.     * Historical Example: The Tambora Strato Volcano eruption (April 10, 1815) on Sanggar Peninsula. It erupted over $50\,km^3$ of magma, created a $6\,km$ wide caldera, and killed over $100,000$ people.
• Landslides: The downward movement of rock, debris, or earth driven by gravity.     * Types: Earth slides, rock falls, and debris flows.     * Speed: Varies from millimeters per year (slow/gradual) to extremely rapid (abrupt collapse).     * Natural Causes: Increase in groundwater pressure, loss of vegetative structure (post-wildfire), erosion of the slope toe, snow/glacier melting, and seismic/volcanic activity.     * Human Aggravation: Deforestation, faulty cultivation, ill-conceived construction, machinery vibrations, and logging.
• Tsunamis: Giant waves caused by undersea earthquakes or volcanic eruptions.     * Shoaling Effect: In the open ocean, waves are often less than $1\,m$ high and travel as fast as jet planes. As they reach shallow water ($< 100\,m$ depth), wave height grows, potentially reaching $30\,m$ above sea level.     * Historical Example: The 2004 Indian Ocean earthquake (December 26). Magnitude $9.1-9.3$ and Mercalli intensity $IX$. Caused by the Indian Plate subducting under the Burma Plate. Resulted in $230,000-280,000$ deaths across $14$ countries.

Hydrological Disasters

• Avalanches (Snowslides): Large masses of snow sliding down mountainsides.     * Surface Avalanche: A layer of snow (e.g., dry loosely packed) slides over a different layer (e.g., dense wet snow).     * Full-Depth Avalanche: The entire snow cover slides from the ground surface.     * Probabilistic Factors: Weather (most important), snowpack height, and terrain angle.
• Floods: Water inundating normally dry land.     * Causes: Excessive rain, dam/levee rupture, rapid ice melt, or beaver dams. Coastal flooding is caused by storms or tsunamis.     * Secondary Impacts: Erosion of foundations, contamination of water with pesticides/sewage/fuel, and mold blooms.     * Health Hazards: Outbreaks of waterborne diseases including typhoid, hepatitis $A$, and cholera.

Climatological Disasters

• Extreme Temperature:     * Heat Waves: Prolonged excessively hot/humid weather. Human risk increases in urban areas due to the "Urban Heat Island Effect," where asphalt and concrete store heat and release it at night.     * Cold Waves: Prolonged periods of cold or sudden invasions of cold air. Associated with frost, hypothermia, and infrastructure damage.
• Droughts: Below-average precipitation resulting in water shortages. Can be declared after as few as $15$ days.     * Meteorological Drought: Specific to regional precipitation patterns.     * Agricultural Drought: Focuses on crop water needs during growth stages (e.g., failed germination).     * Hydrological Drought: Low water volumes in rivers and reservoirs; worsened by human drawdown.     * Socio-economic Drought: Occurs when water demand exceeds supply (e.g., excessive irrigation or reduced hydroelectric output).     * Biological Resistance: Cactaceae (cacti) use reduced leaf area and waxy cuticles to survive.
• Wildfires: Fires in combustible vegetation (brush, forest, grass, etc.).     * Causes: Lightning, volcanic ignition, or human activity.     * Impacts: Destroys property; smoke contains $CO_2$, water vapor, $CO$ (carbon monoxide), formaldehyde, acrolein, polyaromatic hydrocarbons, and benzene. $CO$ and fine particulate matter are primary health threats.
• Cyclones: Large air masses rotating around a center of low pressure (Counterclockwise in Northern Hemisphere; Clockwise in Southern Hemisphere).     * Requirement for Tropical Cyclogenesis:         1. Sufficiently warm sea surface temperatures.         2. Atmospheric instability.         3. High humidity in lower to middle troposphere.         4. Coriolis force sufficient to develop a low-pressure center.         5. Pre-existing low-level focus/disturbance.         6. Low vertical wind shear.     * Storm Surges: Rising sea levels caused by low pressure and winds