Overview
This lecture covers divergent plate boundaries, focusing on their processes, locations, and key examples such as mid-ocean ridges, Iceland, and the East African Rift.
Introduction to Divergent Plate Boundaries
- Divergent boundaries occur where two tectonic plates move apart.
- Most commonly found between two oceanic plates at mid-ocean ridges.
- Can also occur between two continental plates, though less common.
Process of Divergent Boundaries
- Plates moving apart allows hot mantle (asthenosphere) material to rise.
- Reduced pressure on the rising mantle causes it to melt, forming magma.
- Magma reaches the surface, cools as lava, and creates new igneous (oceanic) crust.
- Continual creation of new oceanic lithosphere pushes older crust outward.
Major Examples of Divergent Boundaries
- Mid-Atlantic Ridge: A mid-ocean ridge and underwater mountain chain in the Atlantic Ocean.
- New crust forms at the ridge, is hottest and rises, then cools, becoming denser and forming lower topography.
- Iceland: Sits on the Mid-Atlantic Ridge; visible volcanoes due to activity at the divergent plate boundary.
- Iceland's landmass is built by accumulated volcanic eruptions at the ridge.
Continental Divergent Boundaries
- Occur when two continental plates split apart, creating continental rift zones.
- East African Rift: Africa and the Arabian Peninsula are splitting, forming the Red Sea and volcanic features like Mount Kilimanjaro.
- Processes are similar to oceanic divergence: plates split, mantle rises, volcanoes form.
Key Terms & Definitions
- Divergent Boundary — region where two tectonic plates move apart.
- Mid-Ocean Ridge — underwater mountain chain at a divergent boundary between oceanic plates.
- Seafloor Spreading — process of new oceanic crust forming at divergent boundaries.
- Lithosphere — Earth's rigid outer shell, divided into tectonic plates.
- Asthenosphere — partially molten mantle layer beneath the lithosphere.
- Continental Rift Zone — area where continental plates split apart, forming new crust and volcanoes.
Action Items / Next Steps
- Review diagrams of mid-ocean ridges and continental rift zones.
- Prepare for the next lecture on what happens when plates converge.