Volcanism Quick Review

Definitions

  • Volcano: opening on Earth’s surface releasing lava, ash, and gases
  • Volcanism: all phenomena linked to eruption of molten rock through the crust/lithosphere

Parts of a Volcano

  • Vent – central opening where magma exits
  • Magma chamber – subterranean reservoir
  • Fumaroles – gas/vapor vents
  • Lava dome – mound of slow, viscous lava
  • Pyroclastic flow – hot, fast mix of ash, gas, rock
  • Lahar – mud/debris flow on volcanic slope

Philippine Context

  • \approx 300 total volcanoes; 24 active
  • Most active: Mayon; 3rd: Mt. Kanlaon (eruption 08/04/2025, 56 min)

Classification by Shape

  • Shield – gentle slopes, low-viscosity basalt; non-explosive (Mauna Loa)
  • Stratovolcano (Composite) – steep cone, viscous lava; explosive (Mayon)
  • Cinder Cone – small, common; scoria, dark lava (Mt. Omuro)
  • Caldera – large depression from collapse (Yellowstone)
  • Lava Dome – steep mound of very viscous magma (Soufrière Hills)

Classification by Eruption Style

  • Phreatic – steam-driven; water + ash only
  • Phreatomagmatic – magma–water; tall column with ring cloud
  • Vulcanian – short, explosive; cauliflower ash clouds
  • Strombolian – moderate lava fountains
  • Pelean – dome growth & collapse → nuee ardente
  • Plinian – extremely explosive; umbrella ash columns
  • Icelandic – basaltic fissure flows; lava plateaus
  • Hawaiian – non-explosive “fire fountains”; fluid basalt rivers

Classification by Activity

  • Active – recent or ongoing eruptions
  • Dormant (Potentially Active) – no eruption in <10\,000 yr but expected (≈1350 globally)
  • Extinct – no future activity anticipated

Zones of Volcanism

  • Convergent: oceanic–oceanic → island arcs; oceanic–continental → volcanic arcs (Pacific Ring of Fire)
  • Divergent (Ocean Ridge): decompression melting forms new ocean floor
  • Hotspots: mantle plumes within plates (Hawaii chain)

Volcanic Hazards

  • Gases: H2O, CO2, SO2, H2S → asphyxiation, respiratory/skin issues
  • Pyroclastic materials: ash, lapilli, blocks, bombs
  • Lava flows: Pahoehoe (smooth), A’a (rough), Pillow (submarine)
  • Lahar: >60\% volcanic debris; dense, deadly
  • Ashfall: <2 mm glassy particles; health & infrastructure damage

Benefits of Volcanism

  • Fertile soils for agriculture
  • Geothermal energy (clean, renewable)
  • Mineral & sulfur resources
  • Hot springs & tourism
  • Atmospheric cooling via SO2 \rightarrow H2SO_4 aerosols
  • New landforms & water release through mantle degassing