Tectonic Hazards Flashcards

Structure of the Earth

• Earth's layers:

  • Inner core: Solid, dense iron and nickel, approximately 1400km diameter, $5000-6000°C$.

  • Outer core: Semi-molten metal, approximately 2100km thick, $4000-6000°C$.

  • Mantle: Semi-molten, less dense than outer core, approximately 2900km thick; includes asthenosphere and lower mantle.

  • Lithosphere: Varies in thickness, composed of crust and rigid upper mantle; includes oceanic and continental crust.

• Crust types:

  • Oceanic: Thinner ($5-10$ km), heavier, denser, mainly basalt.

  • Continental: Thicker ($25-100$ km), older, less dense, mainly granite.

Plate Tectonics and Boundaries

• Earth's crust is divided into approximately 15 large and several smaller tectonic plates.

• Plate boundary: Where plates meet. Most volcanoes and earthquakes occur near these boundaries.

• Types of plate boundaries:

  • Divergent: Plates move apart; e.g., Mid-Atlantic Ridge. Volcanic eruptions and earthquakes occur.

  • Convergent: Plates move together; denser oceanic plate subducts under continental plate. Volcanic eruptions and earthquakes occur.

  • Collision Zone: Two continental plates collide, forming fold mountains (e.g., Himalayas).

  • Conservative: Plates slide past each other; e.g., San Andreas Fault. Earthquakes occur.

Plate Movement

• Convection currents: Heat from Earth's core creates currents in the mantle, moving tectonic plates.

• Slab pull theory: Weight of denser oceanic plates subducting drags the rest of the plate.

• Mantle plumes: Upwellings of superheated rock, leading to divergent boundaries or hot spots.

Volcanoes

• Formation: Magma erupts as lava through a vent.

• Volcanic Explosivity Index (VEI): Measures eruption magnitude (open-ended scale).

• Types:

  • Composite (Strato-volcanoes): Steep-sided, viscous lava, explosive eruptions, alternating ash and lava layers, convergent boundaries.

  • Shield volcanoes: Gently sloping sides, runny lava, less explosive, divergent boundaries or hot spots.

• Activity status: Active, dormant, or extinct.

Earthquakes

• Cause: Sudden, violent shaking due to pressure from tectonic plate movement.

• Epicenter: Point on Earth's surface above the focus.

• Focus: Point where earthquake starts below the surface.

• Measurement: Moment Magnitude Scale; seismometers used.

Volcanic Eruption Features

• Lava: Magma erupted onto the surface; can be thin/runny or thick/slow-moving.

• Ash: Pulverized solid lava, less than 2mm in diameter, travels long distances.

• Pyroclastic flow: Fast-moving, hot poisonous gases mixed with ash, up to 700km/h.

• Lahars: Mudflows of ash mixed with melted snow/ice.

• Volcanic bombs: Ejected molten rock fragments ($60mm-5m$).

• Earthquakes: Tremors due to magma rising.

Primary and Secondary Hazards

• Primary hazards: Direct result of the event (e.g., ground shaking, pyroclastic flow).

• Secondary hazards: Result from primary effects (e.g., tsunamis, fires).

Tsunamis

• Cause: Underwater earthquakes, landslides, or volcanic eruptions displacing water.

• Wave formation: Seafloor movement displaces water, creating waves that increase in height as they approach land (5-10 meters).

Impacts of Earthquakes and Volcanic Eruptions

• Loss of life and injury.

• Building collapse/destruction.

• Transport network damage.

• Loss of jobs and businesses.

• Loss of crops.

• Power and water supply damage.

• Environmental damage.

• Airport closures.