Types of Plate Boundaries

Overview

Plates interact in three primary ways:

1. Convergent: Plates move towards each other.
2. Divergent: Plates move apart.
3. Transform: Plates slide horizontally past each other.

Convection Currents in the Asthenosphere

• Warm material rises, cool material sinks, creating a circular motion.

Divergent Plate Boundaries

• Definition: Plates move apart, creating new crust.
• Features: Rift valleys and mid-ocean ridges.
• Examples:
  • Great Rift Valley in East Africa
  • Lake Baikal in Russia
  • Mid-Atlantic Ridge (MAR)
• Characteristics:
  • Volcanism and earthquakes occur.
  • No subduction.

Stages of Divergent Boundaries

1. Upwarping: Initial formation due to convection currents.
2. Rift Valley Formation: Leads to series of valleys and ridges.
   • Example: Great Rift Valley.
3. Narrow Sea Formation: Red Sea & Gulf of Aden stage.
4. Ocean Formation: Development of mid-ocean ridge.

Rifting Examples

• The Great Rift Valley:
  • Contains 25% of Earth's unfrozen surface fresh water.
  • Rifting started 35 million years ago.
  • Features deep lakes like Victoria and Tanganyika.
• Lake Baikal, Russia:
  • Widens by 2 cm/year.
  • Deepest and largest lake by volume.
• The Red Sea & Gulf of Aden

Transform Plate Boundaries

• Definition: Tectonic plates move horizontally, no vertical movement.
• Characteristics:
  • No volcanism, but earthquakes occur.
  • No subduction.
• Example: San Andreas Fault.
  • North American and Pacific plates transform motion.

Convergent Boundaries

• Definition: Plates move together.
• Types:
  1. Oceanic-Continental (O-C)
  2. Oceanic-Oceanic (O-O)
  3. Continental-Continental (C-C)

Characteristics and Examples

• Subduction: Denser crust sinks into the asthenosphere.
  • Oceanic crust is more dense than continental crust.
• O-C Boundaries:
  • Formation of mountain ranges and volcanic arcs.
  • Example: Andes Mountains (Nazca plate under South American plate).
• O-O Boundaries:
  • Formation of volcanic island arcs and trenches.
  • Example: Mariana Trench (Pacific plate under Philippine plate).
• C-C Boundaries:
  • Formation of collisional mountain ranges.
  • No volcanism or subduction.
  • Example: Himalayan Mountains (Indian Plate and Eurasian Plate).

Driving Forces of Plate Motions (Honors Only)

• Slab Pull and Ridge Push
• Homework: Explore what drives plate motions.