Overview
This lecture covers the three types of plate boundaries—convergent, divergent, and transform—and explains the geological processes and landforms formed at each type.
Types of Plate Boundaries
- The three types of plate boundaries are convergent, divergent, and transform fault boundaries.
- Plate tectonics theory states that the Earth's lithosphere (crust and upper mantle) moves slowly and constantly.
Convergent Plate Boundaries
- Convergence can occur between oceanic and continental plates, two oceanic plates, or two continental plates.
- When oceanic and continental plates converge, the denser oceanic plate subducts beneath the continental plate.
- Subduction creates trenches, mountains, earthquakes, and volcanoes.
- When two oceanic plates converge, the older, denser plate subducts, forming deep earthquakes, tsunamis, trenches, volcanic island arcs, and destroys oceanic lithosphere.
- Converging continental plates do not subduct due to similar densities, leading to the formation of mountain ranges and shallow earthquakes, but not volcanoes or tsunamis.
- Subduction does not occur between continental plates.
Divergent Plate Boundaries
- Divergent boundaries occur where plates move away from each other, usually above rising convection currents.
- This movement forms rift valleys on land and oceanic ridges underwater.
- New crust is created as mantle material rises and cools at the divergence zone.
Transform Fault Boundaries
- Transform boundaries feature plates sliding horizontally past each other, creating faults and strong earthquakes.
- These earthquakes can cause property damage and loss of life.
Earthquake Safety and Response
- During earthquakes, initial response is "duck, cover, and hold": kneel down on one knee, cover your head, and be ready to evacuate.
- Protecting the head is critical to prevent fatal injuries.
- Evacuation centers are designated places for disaster victims to receive government aid.
Key Terms & Definitions
- Convergent Boundary — Plate boundary where plates move toward each other.
- Divergent Boundary — Plate boundary where plates move apart.
- Transform Fault — Plate boundary where plates slide past each other horizontally.
- Subduction — Process where one plate moves under another into the mantle.
- Rift Valley — A lowland region formed at a divergent boundary on land.
- Oceanic Ridge — Underwater mountain range formed at a divergent boundary.
- Fault — A crack in the Earth's crust caused by plate movements.
- Evacuation Center — Place where disaster victims are sheltered and aided.
Action Items / Next Steps
- Complete activities on pages 5-7, 10, 12, and 16 of your module.
- Review earthquake safety procedures: duck, cover, and hold.
- Reflect on how plate boundary concepts relate to real-life events.