Plate Tectonics, Earthquakes, & Volcanology

• Tectonics

  Earth's internal processes
• Lecture outline

  1. Theories on Plate Tectonics

  2. Philippine Tectonics

  3. Volcanology

  4. Earthquakes
• Theory of Continental Drift

  The continents were not stationary, but they moved to new positions across vast intervals of geologic time
• Proposed by

  Alfred Wegener
• Pangea


  Late Paleozoic to early Mesozoic era supercontinent mostly located at the Southern Hemisphere, surrounded by superocean (Panthalassa), Laurasia and Gondwana
• Evidence for Continental Drift


  • Jigsaw fit of coastlines
  • Geologic fit of ancient rock outcrops
  • Tectonic fit of Caledonian fold mountain belt
  • Fossil evidence
  • Glacial fit
• Seafloor Spreading Hypothesis

  The sea floor moves like a conveyor belt away from the crest of the mid-oceanic ridge, to disappear finally by plunging beneath a continent or island arc
• Proposed by

  Harry Hess in 1962
• The lithosphere beneath oceans increases in both age and thickness with distance from the crest of the mid-oceanic ridge
• Plate Tectonics Theory

  Regards the lithosphere as broken into plates that are in motion
• Plate


  Large, mobile slab of rock that is part of Earth's surface
• Driving Mechanism

  Mantle Convection
• Plate Tectonic Boundaries

  • Convergent Boundaries
  • Divergent Boundaries
  • Transform Boundaries
• Convergent Boundary

  Two plates moving toward each other
• Divergent Boundary

  Two plates move away from the axis of a mid-ocean ridge, new oceanic crust forms
• Transform Boundary


  Two plates slide past each other on a vertical fault surface
• Philippine Plate

  The Pacific plate subducts beneath the Philippine plate to the east while the Eurasian Plate subducts beneath the west/northwestern region of the Philippine plate
• Philippine Tectonics

  • Philippine Mobile Belt
  • Palawan Microcontinental Block
  • Philippine Fault
• Volcano


  Opening of Earth's crust where hot lava, volcanic ash, and gases escape from the mantle
• Types of Volcanoes

  • Stratovolcano
  • Shield Volcano
  • Cinder Cone Volcano
  • Lava Domes
  • Caldera
• Stratovolcano

  • Volcano constructed of alternating layers of pyroclastics and rock solidified from lava flows, has steep slopes, mostly andesitic
• Shield Volcano

  • Broad, gently sloping (2-10°) volcanoes constructed of solidified lava flow, basaltic in composition
• Cinder Cone Volcano

  • Composed of pyroclastic fragments ejected from a central vent
• Lava Domes


  • Steep-sided, dome- or spine-shaped masses of volcanic rock formed from viscous lava that solidifies in or immediately above a volcanic vent
• Caldera


  • Volcanic depression much larger than the original crater, having a diameter of at least 1 kilometer, extremely violent eruptions
• Volcanoes

  • Mt. Pinatubo
  • Taal Volcano
• Volcano Characteristics


  • Slope
  • Height
  • Composition
  • Lithology
• Hotspot

  Region deep within the Earth's mantle which heat rises through convection, facilitating the melting of rock—magma, often pushes through cracks in the crust to form hotspots, does not occur at the boundaries of Earth tectonic plates, occurs at hot centers called mantle plumes, hotspot volcanoes do not erupt forever
• Volcanic Hazards

  • Lava Flow
  • Pyroclast
  • Lahar
  • Gases
• Lava Flow

  Molten rock which flows out of a volcano/vent, Aa - rough or rubbly surface, Pahoehoe - smooth, billowy, or ropy surface
• Pyroclast

  Broken fragments produced in explosive eruptions, Pyroclastic current, Pyroclastic fall
• Lahar

  Mixture of volcanic ash and water which run downhill as mudflow
• Gases

  Volcanic gases such as water vapor, carbon dioxide, sulfur dioxide, hydrogen sulfide, fluorine gas, hydrogen fluoride, and other gases
• Earthquake

  A trembling or shaking of the ground caused by the sudden release of energy stored in the rocks beneath Earth's surface
• Elastic Rebound Theory


  Involves the sudden release of progressively stored strain in rocks, causing movement along a fault, deep-seated internal forces (tectonic forces) act on a mass of rock over many decades
• Anatomy of an Earthquake

  • Focus
  • Fault
  • Epicenter
• Magnitude


  Measure of an earthquake's effect on people and buildings, expressed as Roman numerals ranging from I to XII on the modified Mercalli scale, different locations report different intensities for the same earthquake
• Intensity

  Measure of the energy released during the earthquake, Moment magnitude scale, Richter scale, uniform measurement across affected locations
• Earthquake

  • M7.0 Luzon Earthquake (July 27, 2022), Magnitude: 7.0, Intensity: VII (Vigan), Epicenter: Tayum, Abra, Abra River Fault, 2,300+ aftershocks, 11 fatalities, 410 injured
• Seismic Waves

  • Body Waves
  • Surface Waves