Overview
This lecture explains the three main types of plate boundaries—divergent, convergent, and transform—detailing their movements, features formed, and notable examples.
Plate Boundaries: Definition and Basics
- Plate boundaries are the lines where pieces of Earth's lithosphere (outer shell) meet and interact.
- Plate movements are driven by convection currents in Earth's mantle.
- Interactions at boundaries lead to earthquakes, volcanic activity, and mountain formation.
Divergent Boundaries
- Divergent boundaries form when two plates move apart, creating tension and new crust as magma rises and solidifies.
- Also called constructive boundaries due to the creation of new oceanic crust.
- Features include mid-ocean ridges (e.g., Mid-Atlantic Ridge) and rift valleys.
- Earthquakes and volcanic activity are common at these boundaries.
Convergent Boundaries
- Convergent boundaries form when two plates move toward and collide with each other.
- Oceanic-Continental Convergent: The oceanic plate subducts beneath the continental plate, forming volcanic arcs.
- Oceanic-Oceanic Convergent: One oceanic plate subducts under another, creating island arcs and oceanic trenches.
- Continental-Continental Convergent: Two continental plates collide, causing crust compression and forming mountain ranges (e.g., Himalayas).
- Subduction is the process where one plate sinks below another into the mantle.
Transform Boundaries
- Transform boundaries form when plates slide horizontally past each other.
- Also called strike-slip or transform faults.
- Features include fault valleys and undersea canyons (e.g., San Andreas Fault).
- Earthquakes are frequent at these boundaries.
Key Terms & Definitions
- Plate Boundary — Region where two tectonic plates meet and interact.
- Lithosphere — Rigid outer layer of Earth, divided into tectonic plates.
- Divergent Boundary — Plates move apart, creating new crust.
- Convergent Boundary — Plates move toward each other and collide.
- Transform Boundary — Plates slide past each other horizontally.
- Subduction — Process where one plate moves beneath another.
- Mid-Ocean Ridge — Undersea mountain range at a divergent boundary.
- Rift Valley — Depression formed at divergent boundaries on continents.
- Trench — Deep linear feature in ocean floor at subduction zones.
- Compression — Squeezing and thickening of crust at convergent boundaries.
Action Items / Next Steps
- Review the types and examples of plate boundaries.
- Practice identifying boundary types on world maps.
- Prepare for questions on how each boundary forms specific landforms.