Plate Tectonics & Geohazards

Plate Tectonic Theories

• The Earth's layers consist of the crust, mantle, and core.
• The crust is the outermost layer, composed of magma rocks and covering both land and water.
• The mantle is the second layer, divided into the upper (solid) and lower (molten) parts.
• The core is the innermost and hottest layer, also divided into a molten outer core and a solid inner core.
• The lithosphere is made up of the upper mantle and the crust.
• The lithosphere is broken into tectonic plates, including 7 major and 8 minor plates.
• The Pacific plate is the largest plate.
• Continental drift occurs as plates move away from each other.
• Plate boundary movements include convergent (towards each other), divergent (away from each other), and transform (sliding past each other).
• Plate tectonic theory explains plate movement and how it causes geohazards.
• Convection currents, driven by heat from the core, cause plate movement.

Geohazards

• Geohazards are dangerous natural events.
• Earthquakes are caused by sudden movements along faults, releasing energy through waves.
• Tectonic earthquakes are caused by movement in tectonic plates and faults, while volcanic earthquakes are due to magma movement.
• The focus is the location inside the Earth where movement begins, while the epicenter is the surface location above the focus.
• Intensity measures the earthquake's effects on people and residences.
• Magnitude measures the strength of the earthquake and energy released.
• Seismic waves transmit energy in various directions and motions.

Earthquake Safety Measures

• Before: Prepare a go-bag, know evacuation routes, and plan with family.
• During: Evacuate, avoid weak structures, stay low, and use "duck, cover, and hold".
• After: Stay in evacuation centers until cleared, and avoid unstable areas.

Volcanic Eruptions

• Many volcanoes are located in the Pacific Plate/Ring of Fire due to convection currents.
• Volcanoes erupt when pressure and gas build up in the magma chamber.
• Composite volcanoes have a crater, vent, secondary cone, and secondary vent.
• Volcanoes eject ash, steam, gases, lava, and volcanic bombs.
• Composite volcanoes are cone-shaped and found on destructive plate margins; shield volcanoes are on constructive margins or hotspots and have gentle slopes.
• Constructive plate margins form volcanoes as magma fills the gap between separating plates.
• Destructive plate margins form volcanoes as the denser oceanic plate melts under the continental plate, releasing gas and pressure.
• Volcano signs may include changes in crater size or temperature, shaking, and increased sulfur dioxide.
• Magma is melted rock from the mantle/crust, and lava is magma that reaches the surface.

Volcano Safety Measures

• Before: Prepare a go-bag, know evacuation routes, and plan with family.
• During: Go to high ground and away from the ocean, and follow authorities.
• After: Stay on high ground until official updates and be prepared for follow-up hazards.

Tsunamis

• Tsunamis are caused by underwater earthquakes or plate movements.
• Tsunamis form when earthquakes displace water, creating a large wave.
• Warning signs include earthquakes lasting over 20 seconds, rapid water level changes, and a loud roar from the ocean.

Tsunami Safety Measures

• Before: Prepare a go-bag, know evacuation routes, and plan with family.
• During: Evacuate, avoid weak structures, stay low, and use "duck, cover, and hold".
• After: Stay in evacuation centers until cleared and avoid unstable areas.

The Moving of the Earth

• Heat and density affect water behavior.
• Cold water is denser and sinks faster.
• Wind results from temperature changes in air molecules.
• Warm air rises, creating low pressure, while cool air sinks, creating high pressure.
• High pressure moves to low pressure, causing wind.
• Earth's rotation includes both rotation on its axis and revolution around the sun (365 days).
• The Coriolis Effect results from different wind speeds at different points on Earth, causing circular motion.
• The Northern Hemisphere rotates in one circular motion, while the Southern Hemisphere rotates in the opposite direction.

Ocean Currents

• Surface currents make up 10% of the ocean and are driven by wind and tides.
• Deep ocean currents make up 90% of the ocean and are influenced by differences in density, temperature, and salinity.
• Gyres are large loops in the water that move due to surface currents.
• Northern Hemisphere gyres move clockwise, while Southern Hemisphere gyres move counterclockwise.
• Thermohaline Circulation involves cold, deep currents sinking and warm, surface currents rising.
• The Global Conveyor Belt is a long, winding loop created by thermohaline circulation and wind-driven surface currents.
• The Global Conveyor Belt transports nutrients and can take water droplets 1000 years to travel its length.