Volcanism and Geology Study Notes

VOLCANISM

  • Learning targets
    • Explain how hot spots form
    • Differentiate the viscosity of lava
    • Analyze how volcanic hazards are related to magma viscosity
  • VOLCANISM defined
    • The process wherein magma escapes from Earth’s interior to form cool and hard rocks.
  • VOLCANO defined
    • A landform with an opening at its tip.

STRUCTURE OF A VOLCANO

  • The volcano is an opening in Earth’s crust through which hot gases and molten rock are erupted or blown out.
  • Key features and terms:
    • CRATER: a bowl-shaped pit or circular depression resulting from the outpour of volcanic materials from the vent.
    • VENT: an opening where volcanic materials escape to the surface.
    • FUMAROLES: openings near an active volcano that emit steam and volcanic gas (cracks, holes, or fissures).
    • MAGMA CHAMBER: pocket where magma collects beneath the surface.
    • ERUPTION COLUMN: clouds of heated ash and tephra released during an eruption.
    • VOLCANIC BOMB: formed when molten rock is thrown out and cools in the air.
    • LAVA FLOW: hot molten rock that pours or cozes onto the surface after an eruption.
    • CONDUIT: a passage through which magma travels to the surface.
  • Reference note (source): Earth How, January 17, 2021, “13 Parts of a Volcano: The Anatomy of Volcanoes.”

TYPES OF VOLCANISM: EXTRUSIVE VS INTRUSIVE

  • EXTRUSIVE VOLCANISM
    • Pertains to magma that has finally reached the surface.
    • When it flows on the surface, it is called extrusive volcanism.
    • Type of rock: igneous rock; LAVA.
  • INTRUSIVE VOLCANISM
    • When magma does not move out from the opening of a volcano.
    • An entrapped lava flow that does not reach the surface.
    • Type of rock: igneous rock.

VISCOSITY & COMPOSITION OF MAGMA

  • VISCOSITY
    • The magma’s ability to flow.
    • The greater the viscosity, the greater its resistance to flow.
    • Flow faster = high temperature; less viscous.
  • COMPOSITION
    • The magma contains silica, which affects the viscosity.
    • The greater the silica content, the more viscous the magma.
    • The less dissolved gases in the magma, the greater its viscosity.
    • The escape of gases in the magma gives the volcano their explosive characteristics.

HOT SPOTS AND MANTLE PLUMES

  • Hot spot concept: magma rises from deep within the mantle, pushing up through the crust to form a chain of volcanoes as tectonic plates move over the plume.
  • Hawaii hot spot:
    • The Pacific Plate motion drags the plume head, causing magma to rise and push through the crust, generating a line of volcanoes (e.g., Mauna Loa, Kilauea, Lō'ihi).
    • Not to scale in the diagram; plume head drives volcanism as the plate moves.
  • Hawaii map (examples of sites): Nihue, Kauai, Honolulu, Oahu, Molokai, Maui, Lanai, Kahoolawe, Kohala Coast, Waikoloa Beach Resort, Kailua-Kona (Big Island), Hilo.
  • Yellowstone hot spot:
    • Visual markers include the Yellowstone caldera and associated geysers; magma beneath the crust drives volcanic activity.
  • Yellowstone and Hawaii serve as examples of mantle plumes generating hotspot volcanism.

OTHER HOT SPOTS & MARKERS

  • Ni'ihau–Kaua'i region and seamounts show the progression of hot-spot–driven volcanism along a plate boundary over geologic time.
  • Hot spots are not fixed in isolation; they interact with lithospheric movement to form volcanic chains.

OCEANIC-ISLAND ARCS & CONTINENTAL ARC TYPES

  • ISLAND ARC-TYPE volcanism
    • Major features: deep-ocean trenches and volcanic arcs; island arc forms above the ocean floor; continental volcanic arc appears on the surface of the lithospheric plate.
    • Occurs when two oceanic plates converge, leading to subduction of one plate beneath the other. Example: Japan and the Philippines.
    • Luzon Island arc is a specific example; Nishinoshima in Japan is another example.
  • CONTINENTAL VOLCANIC ARC (arc-type)
    • Caused by the compression of the crust above the subducting plate in the collision process.
    • Examples: Aleutian Range and Cascade Volcanic Arc.

ANDEAN TYPE MOUNTAIN BUILDING

  • Occurs along continental plate boundaries.
  • Example: Andes Mountains.

OROGENY AND MOUNTAIN BUILDING

  • OROGENY: the process of mountain building.
  • MOUNTAIN: a large surface feature that rises above its surroundings.
  • MOUNTAIN RANGE: a series of connected mountains; a group of mountains that are close to one another.
  • Mountain ranges form through a three-stage process:
    1) Accumulation of sediments.
    2) An orogenic period of rock deformation and crustal uplift.
    3) A period of crustal uplift caused by isostatic rebound and blocking faulting.

FOLDING AND FAULTING (GEOLOGIC STRUCTURES)

  • FOLDING

    • Occurs when a compressive force bends the crust from its sides.
    • Examples: Himalayas, Alps in Europe.
    • Key terms:
    • Anticline: peak of a folded rock layer.
    • Syncline: trough (lowest point) of the fold.
    • Tight Fold: sharp-peaked anticline.
    • Overfold: bending/warping of folding rocks.
    • Recumbent Fold: excessive bending with no vertical region visible.
    • Nappe: an overturned fold with fractured rock layers.

  • FOLDING visuals: bends occur slowly; fold mountains emerge as plates push up during collision.

  • Notable locations cited: Alberta (Anticline), Switzerland (Nappe), Switzerland (Jura Mountains), Switzerland (Syncline in Switzerland context), Europe (Alps).

  • FAULTING

    • Definitions:
    • Dip: slope or inclination of a geological surface.
    • Strike: a horizontal line on the sloping surface.
    • Hanging wall: rock that lies above the fault line.
    • Foot wall: rock that lies below the fault line.
    • Fault plane: the surface where blocks slip past each other.

  • DIPOLE/Types of faults:

    • Dip-slip fault: movement of the hanging wall up or down relative to the footwall, parallel to the dip direction.
    • Normal fault: hanging wall moves downward relative to the footwall.
    • Reversed fault: hanging wall moves upward relative to the footwall.
    • Strike-slip fault: rock on the fault moves horizontally with little or no vertical movement; left-lateral or right-lateral.

VOLCANIC HAZARDS & TYPES OF LAVA FLOWS

  • Lava flow types:
    • Aa: rough, jagged with sharp edges; high viscosity (thicker and stickier); moves slowly and roughly; cooler than pahoehoe.
    • Pahoehoe: smooth surface; lower viscosity (more fluid, runnier); moves fast and smoothly, like thick honey; hotter than Aa (roughly 1,100ext–1,200degextC1{,}100 ext{–}1{,}200^ deg ext{C}).
  • Hazard implications:
    • High eruption rate tends to produce faster, rougher, broken flows (Aa).
    • Low eruption rate tends to produce smoother, ropey flows (Pahoehoe).
  • Gas hazards (thick gas):
    • Water vapor, Carbon dioxide, Nitrogen, Sulfur dioxide, Hydrogen sulfide, Hydrogen halides.
  • Ash hazards:
    • Volcanic ash consists of fine pulverized rock and volcanic glass; can be carried by wind over long distances.

PREPARATION FOR A VOLCANIC ERUPTION

  • STAY INFORMED: pay attention to official warnings, updates, evacuation orders from local authorities.
  • EMERGENCY PLAN: create a family emergency plan with meeting points, communication methods, and a designated emergency kit.
  • EMERGENCY KIT: prepare essential items like food, water, first aid supplies, flashlights, batteries.
  • EVACUATION ROUTES: know evacuation routes and practice evacuation drills with family.

OROGENY: SUMMARY OF MOUNTAIN BUILDING PROCESSES

  • OROGENY is the process by which mountains form; involves mountain-building forces and structural changes in the crust.
  • MOUNTAIN TYPES AND FORMATION PROCESSES:
    • Island arc-type: deep-ocean trenches with volcanic arcs; island arc forms above the ocean floor; continental volcanic arc on the lithospheric plate surface.
    • Andean-type: occurs along continental plate boundaries; associated with major mountain belts like the Andes.

SUMMARY OF KEY CONCEPTS AND IMPLICATIONS

  • Magma viscosity and gas content govern eruption style and hazard potential.
  • Silica-rich magmas are more viscous and tend toward explosive volcanic activity due to gas entrapment and pressure build-up.
  • Hot spots create long-lived volcanic chains as tectonic plates move over mantle plumes (examples: Hawaii, Yellowstone).
  • Island arcs and continental arcs form at convergent plate boundaries via subduction and crustal deformation.
  • Mountain building involves folding and faulting processes that reshape the crust over geological time.
  • Preparing for eruptions requires situational awareness, planning, and practiced response to ensure safety.

NOTES ON CONNECTIONS AND REAL-WORLD RELEVANCE

  • Understanding volcano structures helps in interpreting news and advisories from agencies like PHIVOLCS.
  • Recognizing lava flow types informs hazard assessments and emergency planning for nearby populations.
  • Knowledge of plate tectonics and orogeny explains global distribution of volcanoes and mountain belts.
  • Public safety and infrastructure planning depend on recognizing gas emissions, ash dispersion, and evacuation logistics.

ETHICAL & PRACTICAL IMPLICATIONS

  • Balancing economic development with risk reduction in volcanic regions requires transparent communication and community engagement.
  • Ethical considerations include equitable evacuation access, shelter provision, and infrastructure resilience in hazard-prone areas.
  • Practical implications include land-use planning, early warning systems, and education to improve community response during eruptions.