Overview
This lecture covers the three types of convergent plate boundaries, the geological formations they create, and the process of subduction and recycling of Earth's crust.
Introduction to Plate Boundaries
- Plate boundaries are where two tectonic plates meet.
- Without earthquakes, plates are flat; collisions cause elevation and geological features.
- Compression is the driving stress at convergent boundaries.
Types of Convergent Boundaries
Continental-Continental Convergence
- Occurs when two continental crusts collide.
- Both crusts are light and float, causing both to elevate and form peaks.
- Results in mountains, mountain ranges, and hills.
- Examples: Mount Everest, Himalayan mountain ranges, Sierra Madre mountain range, Chocolate Hills.
- No subduction occurs due to similar low densities.
Oceanic-Oceanic Convergence
- Involves collision of two oceanic crusts (one older/heavier, one younger/lighter).
- Older, denser crust subducts under younger crust.
- Forms volcanoes, islands, and trenches.
- Examples: Augustine Volcano (Alaska), 100 Islands (Philippines), Mariana Trench.
Continental-Oceanic Convergence
- Collision between oceanic (denser) and continental (lighter) crusts.
- Oceanic crust subducts under continental crust.
- Creates volcanoes and trenches, but not islands.
- Subduction happens due to higher density of oceanic crust.
Subduction and Recycling of Crust
- Subducted crust sinks to the mantle, melts to magma.
- Magma is expelled by volcanoes as lava, which cools to rocks.
- Rocks become part of the crust again, repeating the cycle.
- Earth naturally recycles its landforms through these processes.
Recap Questions & Answers
- Identified plate types, stresses, and geological formations for each convergence type.
- Oceanic-oceanic: forms volcanoes, islands, and trenches.
- Continental-oceanic: forms volcanoes and trenches.
- Continental-continental: forms mountains, ranges, and hills; no subduction.
Key Terms & Definitions
- Convergent Boundary — where two tectonic plates move toward each other.
- Compression — the stress that causes plates to collide.
- Subduction — process where one tectonic plate sinks below another.
- Mantle — layer beneath Earth's crust where melting occurs.
- Magma — molten rock beneath Earth's surface.
- Lava — magma that reaches Earth's surface.
- Trench — a deep depression formed at subduction zones.
Action Items / Next Steps
- No homework assigned; review the video lesson if needed.
- Enjoy the long weekend; next class on Tuesday.