Volcanic Explosivity and Eruption Classification

• Two factors affecting the explosivity of volcanic eruptions:
  • Viscosity of magma, where more viscous magma leads to more explosive eruptions.
  • Amount of dissolved gasses, where more gas in magma results in more explosive eruptions.
• Volcanoes are found at:
  • Interplate locations, specifically at divergent and convergent boundaries.
  • Intraplate locations, such as hotspots where the magma chamber is stationary beneath the crust.

Volcanic Explosivity Index (VEI)

• Scale that describes the size of explosive volcanic eruptions based on magnitude and intensity.
• Numerical scale from 0 to 8, is logarithmic.
• Analogous to the Richter and other magnitude scales for earthquakes.
• Measured by ejecta volume, column height, and classification of eruption.

Classification of Eruption (Least to Most Explosive)

• Phreatic eruptions: Contact of ground water with hot rock producing steam.
• Icelandic: Associated with rift zones (divergent boundaries).
• Hawaiian: Lava fountains and flows due to low viscosity magma, high in Iron and Magnesium.
• Strombolian: Intermittent ejection of lava and ash.
• Pelean: Large quantity of volcanic material erupts, falls, and forms a tongue-like growing avalanche.
• Vulcanian: Discrete ejection of mostly solid and gas from more viscous magma.
• Plinian: Sustained eruption of pyroclastic debris producing high eruption columns.

Volcano Types (Biggest to Smallest)

• Shield: Gentle slopes (2-10 degrees), largest type (10 km).
• Composite: Steeper slopes (less than 33 degrees), smaller (1 to 4 km).
• Cinder: Steepest slopes (33 degrees), smallest type (height less than 300 meters).

History of Plate Tectonics

• Continental Drift Theory:
  • Proposed by Alfred Wegener.
  • Evidence included puzzle fit of continents, fossil distribution, and paleoclimate (glacial deposits in now-hot countries).
  • Initially rejected due to lack of mechanism of movement.
• Seafloor Spreading:
  • Proposed by Harry Hess.
  • Explained how the seafloor moves due to the creation of new crust along divergent plate boundaries, moving until it reaches convergent boundaries where crust is destroyed.
  • Transform plate boundaries are neither zones of creation nor destruction, but rather locations where plates slide past each other.

Types of Faults

• Normal Fault: Associated with divergent boundaries; footwall moves up with respect to the hanging wall.
• Reverse Fault: Associated with convergent boundaries; footwall moves down with respect to the hanging wall.
• Strike-Slip Fault: Associated with transform boundaries.
  • Left lateral strike-slip fault: Features are displaced laterally to the left when facing the fault line.
  • Right lateral strike-slip fault: Features are displaced laterally to the right when facing the fault line.

PHIVOLCS Earthquake Information

• Information derived includes location, depth of focus, magnitude, intensity (if any), and expectation of damage.
• Focus: The point where seismic waves are generated by rapid movement of rocks along a fault line.
• Epicenter: The projection of the earthquake’s focus onto the Earth’s surface.
• Magnitude: Amount of energy released in an earthquake, measured using the Richter Magnitude Scale.
• Intensity: Shaking and damage at a specific location, measured using the PHIVOLCS Earthquake Intensity Scale.

Types of Seismic Waves

• Body Waves: Travel in the Earth’s interior.
  • P Waves.
  • S Waves.
• Surface Waves: Travel on the Earth’s surface.
  • Love Waves.
  • Rayleigh Waves.

Mass Wasting

• General term for gravity-induced movement, characterized by the kind of material and the type of movement.

Mass Movements

• Creep:
  • Slowest movement type.
  • Indicated by trees bent at the base of their trunks.
• Fall:
  • Due to cracks in rocks (weathering).
  • Rocks in cliffs fall straight down.
• Avalanche:
  • Due to rock falls.
  • A layer of air is trapped between the rocks and the surface, reducing friction and causing very fast movement (up to 200mph).
• Slide:
  • Rocks slide along their bedding plane, foliation, or fault planes.
  • Also called translational landslide.
• Slump:
  • Rocks move along a curved surface.
  • Also called rotational landslide.
• Flow:
  • Due to oversaturation of water, materials will liquefy and behave like a fluid.
  • Water decreases friction and increases the weight of material, making it more likely to flow.