Volcanoes and Tectonic Plates

Volcanoes and Tectonic Plates

What are Volcanoes?

• A landform that occurs when magma from the Earth's interior rises to the surface, resulting in eruptions of molten rock, ash, and gas
• Can be found on land and under the ocean

Types of Volcanoes

• Shield Volcanoes: gently sloping, rounded volcanoes with a broad base and gentle slopes
  • Formed by the eruption of fluid lava flows
  • Examples: Hawaiian Islands, Iceland
• Stratovolcanoes: tall, conical volcanoes with steep slopes
  • Formed by a combination of lava flows, ash, and other pyroclastic material
  • Examples: Mount St. Helens, Mount Fuji
• Cinder Cones: small, steep-sided volcanoes formed from accumulated ash and cinder
  • Examples: Paricutin volcano in Mexico

What are Tectonic Plates?

• Large, rigid slabs of the Earth's lithosphere (outer layer) that fit together like a jigsaw puzzle
• In constant motion, sliding over the more fluid asthenosphere (upper mantle) below

Plate Boundaries

• Divergent Boundaries: where plates move apart, new crust is formed
  • Example: Mid-Atlantic Ridge
• Convergent Boundaries: where plates collide, crust is destroyed or thickened
  • Example: Andean mountain building
• Transform Boundaries: where plates slide past each other horizontally
  • Example: San Andreas Fault

Volcanoes and Plate Tectonics

• Most volcanoes are located at plate boundaries, where the Earth's crust is being stretched or compressed
• The movement of tectonic plates is the driving force behind volcanic activity
• Volcanic arcs form when an oceanic plate is being subducted beneath a continental plate
  • Example: Andes mountain range

Hotspots

• Areas of volcanic activity that are not located at plate boundaries
• Thought to be caused by mantle plumes, upwellings of hot rock that rise from the Earth's core-mantle boundary
• Example: Hawaiian Islands