Hotspots and Volcanoes

Overview

• Most volcanoes occur at plate boundaries, also known as plate margins.
• Exceptions: Volcanoes that occur at hotspots can't be explained by plate movements.
• Examples of hotspots: Hawaiian Islands, Yellowstone.

Location and Formation of Hotspots

• Major hotspots are located away from plate boundaries, such as the Hawaiian Islands, which are 3,200 km from the nearest plate boundary.
• Hotspots are formed due to:
  • Decay of radioactive elements in the Earth's core, which heats the magma in the mantle.
  • Heated magma expands, becomes less dense, and rises to the surface as a mantle plume.

Process of Volcanic Formation at Hotspots

• Crust Weakness: If lines of weakness exist in the crust, magma can break through.
• Underwater Volcanism:
  • Lava cools on contact with ocean water, forming an underwater volcano.
  • Over time, the volcano builds up and can rise above sea level, forming an island.

Island Chain Formation

• The hotspot is stationary while the oceanic plate moves over it due to convection currents in the mantle.
• This movement causes the formation of a chain of separate volcanoes:
  • The volcanic islands furthest from the hotspot are the oldest.
  • The closest islands are the youngest, i.e., most recently formed.
  • The volcano above the hotspot is active, while older ones become extinct as they are no longer supplied with magma.
• Over time, older islands are weathered and eroded, decreasing in size.

Hotspots under Continental Plates

• Magma erupts violently forming a caldera or large crater volcano (e.g., Yellowstone).
• As tectonic plates move, calderas move away from the hotspot, leaving a series of craters.

Summary

• Hotspots explain volcanic activity far from plate boundaries.
• Hotter magma rises in mantle plumes.
• Crust cracks allow magma to escape, forming volcanoes.
• Stationary hotspots lead to new volcano formations as plates move, potentially forming island chains under oceans.

Keywords

• Plate Boundary: Alternative term for a plate margin.
• Magma: Molten rock in the mantle.
• Mantle Plume: An area where mantle magma is hotter than surrounding areas.
• Convection Current: Movement where hot fluid rises and cool fluid sinks.