Overview
This lecture explains the four types of plate margins involved in tectonic activity, discussing their processes, associated hazards, and typical landforms.
Constructive (Divergent) Plate Margin
- Plates move apart due to convection currents in the mantle.
- Magma rises to fill the gap, forming new oceanic crust.
- Often found at ocean ridges with volcanic activity; shield volcanoes may form here.
- Example: Iceland formed by extensive lava build-up.
Destructive (Convergent) Plate Margin
- Oceanic and continental plates move towards each other; oceanic plate subducts under continental plate.
- Subducting plate melts, leading to magma rising and forming composite volcanoes.
- High pressure and friction cause explosive earthquakes and volcanic eruptions.
- Magma here is more viscous, leading to explosive eruptions.
Collision Zone (Convergent: Continent-Continent)
- Two continental plates collide, neither subducts due to their thickness and buoyancy.
- Results in the formation of fold mountains, such as the Himalayas.
- Generates powerful earthquakes but no volcanic activity.
Conservative Plate Margin
- Plates slide past each other, either in different directions or at different speeds.
- The jagged plate edges lock, building up pressure that is released as earthquakes.
- No volcanic activity occurs at these margins.
- Example: San Francisco (San Andreas Fault).
Summary Table of Hazards
- Constructive & Destructive: Both volcanoes and earthquakes.
- Collision & Conservative: Earthquakes only, no volcanoes.
Key Terms & Definitions
- Plate Margin — The boundary between two tectonic plates.
- Convection Currents — Heat-driven currents in the mantle that move tectonic plates.
- Subduction — The process where one tectonic plate moves under another and melts.
- Shield Volcano — A broad, gentle volcano formed by runny lava at constructive margins.
- Composite Volcano — A tall, steep volcano with explosive eruptions, found at destructive margins.
- Fold Mountain — Mountain formed by the collision of two continental plates.
- Earthquake — Sudden energy release due to moving plates, causing ground shaking.
Action Items / Next Steps
- Memorize the four plate margins, their features, and associated hazards for exams.
- Review examples of landforms created by each plate margin.