Geography: Earth's Spheres and Natural Hazards

• Geography Term 1 2025 Flashcards

Earth's Spheres

• Lithosphere refers to the land, including the core, mantle, and crust.
• Hydrosphere refers to water.
• Atmosphere refers to air.
• Biosphere refers to the living environment.

Hazards and Disasters

• Natural hazards are extreme events that can harm humans, animals, or the environment.
• A disaster occurs when a hazard causes significant damage or loss of life.

Types of Natural Hazards

• Tropical storms form over warm ocean waters (26°C+).
• Droughts are prolonged periods of low rainfall caused by changes in atmospheric circulation.
• Tornadoes form when warm, moist air meets cold, dry air, creating rotating air columns.
• Landslides are triggered by rain, earthquakes, or human activity.
• Avalanches are unstable snow/ice slides caused by weight, warming, or vibrations.
• Sinkholes are ground collapses due to water erosion of rock like limestone.
• Earthquakes are sudden movements of tectonic plates along faults.
• Volcanic eruptions occur when magma rises due to subduction, rifting, or hotspots.
• Tsunamis are large waves triggered by underwater earthquakes or landslides.

Technological and Human-Caused Hazards

• Nuclear power plant failures and acid rain are technological disasters.
• War, pollution, and terrorism are human-caused hazards.

Disaster Conditions

• Disaster = Natural Hazard + Vulnerable Community

Hazard Characteristics

• Duration: Longer events tend to be more severe.
• Magnitude: Stronger hazards typically cause more damage.
• Predictability: Some hazards (e.g., hurricanes) are easier to predict than others (e.g., earthquakes).
• Frequency: Repeated hazards can increase overall damage.
• Speed of Onset: Sudden hazards (e.g., earthquakes) can be more destructive.
• Areal Extent: Larger affected areas result in a greater impact.
• Number of Hazards: Multiple hazards in one region can worsen effects.

Earth's Structure

• Crust: The thin, outer solid layer of Earth.
• Continental Crust: Mostly composed of granite.
• Oceanic Crust: Primarily made of basalt.
• Asthenosphere: A semi-fluid layer beneath the lithosphere.
• Upper Mantle: Composed of solid silicate rocks.
• Mantle: A thick, semi-solid layer made of magnesium and iron.
• Outer Core: Consists of liquid iron and nickel.
• Inner Core: Composed of solid iron and nickel due to extreme pressure.

Tectonic Plates and Boundaries

• Tectonic Plates: Large sections of Earth's crust.
• Plate Boundaries: Effects vary based on whether they are divergent, convergent, or transform.
• Divergent Boundaries: Plates move apart, leading to new crust formation (mid-ocean ridges), earthquakes, and volcanic activity.
• Convergent Boundaries: Plates collide, causing earthquakes (especially in subduction zones), mountain formation (e.g., Himalayas), and volcanic activity.
• Transform Boundaries: Plates slide past each other, resulting in fault lines (e.g., San Andreas Fault) and earthquakes.
• Oceanic Plates: Dense plates that make up the ocean floor, typically 50-100km thick.
• Continental Plates: Less dense plates that make up the continents, up to 200km thick.

Continental Drift

• Continental Drift: Proposed by Alfred Wegener in 1912, suggesting continents were once a supercontinent (Pangaea) and have since drifted apart.
• Evidence of Continental Drift: Includes the fit of continents, fossil and rock distribution, and climatic patterns.

Earthquake Terminology and Measurement

• Focus: The point in the Earth's crust where plates break during an earthquake.
• Epicentre: The surface point directly above the focus.
• Distance and Damage: Damage is more severe closer to the epicentre.
• Focus Depth: A shallower focus results in stronger surface shockwaves.
• Richter Scale: Measures earthquake magnitude based on the energy released.
• Mercalli Scale: Measures earthquake damage intensity using a I-XII scale.
• Richter Scale Use: More widely used than the Mercalli Scale because it provides a precise measurement of energy released.

Earthquake Impact Factors

• Urban vs. Rural: Urban areas tend to experience more damage.
• Night vs. Day: Earthquakes are more severe at night due to reduced preparedness.
• Rich vs. Poor: Poorer countries often suffer more severe consequences from earthquakes.