Volcanoes: Types and Characteristics

Classification of Volcanoes

• Volcanoes are categorized by shape and size, influenced by the volume/type of material ejected, eruption sequence, and environment.
• Common types of volcanoes:
  • Shield volcanoes
  • Strato volcanoes
  • Cinder cones
  • Craters
  • Calderas

Shield Volcanoes

• Characterized by a broad and low profile, created by fluid lava flows.
• Lava typically consists of basalt and maintains a gentle slope, not exceeding 7 degrees.
• Hawaiian Islands are primarily formed of shield volcanoes, rising about 5 kilometers from the seafloor.

Strato Volcanoes

• Recognized as the most prevalent volcanic form with steep conical shapes.
• Composed of alternating layers of lava and pyroclastics, reflecting a complex eruptive history.
• Eruptions are explosive due to the viscosity of the lava, which does not spread far before solidifying.

Cinder Cone Volcanoes

• Formed by a conical accumulation of cinder-sized pyroclastics.
• The profile depends on the angle of repose, which determines the stability of debris.

Craters and Calderas

• Craters are created by the collapse of material during eruptions or through erosion during dormancy.
• Calderas are larger, basin-shaped depressions formed when a magma chamber drains and causes the overlying structure to collapse.

Intrusive Igneous Rocks

• Form from magma that solidifies beneath the Earth's surface, resulting in various landforms.
• Types of intrusive rocks include:
  • Batholiths: Large dome-shaped intrusions extending over hundreds of square kilometers.
  • Sills: Near-horizontal intrusions between rock layers, creating sheets parallel to surrounding rocks.
  • Dikes: Vertical sheets that form when magma rises through cracks and cools.

Eruption Styles and Lava Types

• Eruption styles and lava composition differ based on plate boundaries.
• Basaltic lava primarily emerges from oceanic divergence zones and mid-ocean volcanic sites.
• Andesite and basalt are common where ocean plates collide.
• Consolidated ash flows occur at zones where oceanic and continental plates converge.

Historical Eruptions

• The 1883 eruption of Krakatoa resulted in a massive tsunami, devastating the coasts of Java and Sumatra, and causing over 36,000 fatalities.