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• Volcanoes and the Earth’s interior are related to lesson objectives like identifying different types of volcanoes, discussing the characteristics and parts of volcanoes. Describing different types of volcanic eruption.
• Another objective is to list the advantages and disadvantages of volcanic eruptions to society and the environment.

Volcano Definition and Origin

• Volcano comes from the Italian word "Vulcano," meaning "Burning mountain."
• It also comes from the Latin word "Vulcan," referring to the Roman God of Fire.
• Volcanoes are vents, hills, or mountains that erupt:
  • Releases molten rocks
  • Eeleases rock fragments
  • Gaseous materials onto Earth's surface

Parts of a Volcano

• Main Vent: Allows magma to pass from the magma chamber to Earth's surface.
• Magma Chamber: A large reservoir storing molten rock (magma) prior to eruption.
• Crater: A bowl-shaped depression produced by volcanic activity and explosion.
• Fissures: Narrow cracks in the crust.
• Caldera: Large depressions caused by the collapse of a volcano's summit.
• Lava Flow: The stream of molten rock flowing out of the crater.
• Secondary Vent: Serves as an alternative smaller outlet for magma to reach Earth's surface.
• Fumaroles are secondary vents that emit only gases.
• Secondary Cone: Formed when lava and ashes escape from smaller vents, also known as parasitic cones.
• Ash Cloud: Formed when thick volcanic ashes are discharged into the atmosphere during an eruption.
• Ash: A mixture of rocks, minerals, and glass particles expelled during a volcanic eruption.

Where Volcanoes Form

• Volcanoes form at:
  • Convergent Plate Boundaries
  • Divergent Plate Boundaries
  • Hot Spots.

Convergent (Colliding) Plate Boundaries

• Plates move towards each other and collide at convergent boundaries.
• Subduction occurs when a thinner, denser oceanic plate sinks beneath a thicker continental plate.
• Subduction results in deep ocean trenches.
• A series of magmatic eruptions along the trench can form a chain of volcanoes.

Divergent (Spreading) Plate Boundaries

• Two plates move away from each other.
• Molten rock from the mantle erupts along the opening, forming new crust.
• This can form a ridge, which is a long, narrow chain of folds in the oceanic crust.
• Ridges are produced by diverging forces of convection currents in the asthenosphere and are separated by a valley (rift).

Hotspots

• A hot spot is an area on Earth over a mantle plume.
• Volcanoes form in areas under the rocky outer layer of Earth, called the crust.
• Magma is hotter than surrounding magma.
• The magma plume causes melting and thinning of the rocky crust, leading to widespread volcanic activity.

Types of Volcanoes

• Cinder Cone
• Composite
• Shield

Cinder Cone Volcanoes

• Formed from pyroclastic fragments and volcanic ashes that solidify around the main vent.
• They form a cone that can be either circular or oval.
• Smith Volcano (Mount Babuyan) is an example of a cinder cone volcano.

Composite Volcanoes (Stratovolcanoes)

• Typically symmetrical, steep cones that may rise as high as 2,400 meters (about 8,000 feet) from the ground.
• They have acidic and sticky lava that solidifies without traveling far.
• Usually dormant for many years, making them sometimes considered extinct.
• Mount Fuji is an example.

Shield Volcanoes

• Formed from non-acidic basaltic lava flows of high viscosity.
• They produce broad sloping sides and shield-like structures.
• Not very explosive and are among the largest volcanoes globally.
• The majority of well-known volcanoes in Hawaii are shield volcanoes, like Kilauea Volcano.

Types of Volcano by Eruptive History

• Active
• Extinct
• Dormant

Active Volcanoes

• Erupted during historical times within the last 600 years.
• Shows eruption at least once in the past 10,000 years.
• Examples include Mount Mayon, Mt. Biliran (Anas), and Mt. Hibok-Hibok.

Extinct Volcanoes

• Have not had an eruption in the past 10,000 years.
• Are not expected to erupt anymore.
• Intensively weathered and eroded.
• Example is Mount Guinsiliban, Camiguin Island.

Dormant Volcanoes

• Active but not erupting.
• Expected to soon erupt any time.
• Example: Mahagnao Volcano, Burauen Leyte

Types of Volcanic Eruption

• Phreatic
• Vulcanian
• Strombolian
• Plinian
• Phreatomagmatic

Phreatic Eruption

• An explosion driven by steam produced when groundwater is heated due to an underlying heat source.
• Involves only water, steam, and ash, lacking the ejection of fresh magmatic materials.

Vulcanian Eruption

• Occurs when pressure is enough to blow off the overlying layer of solidified lava.
• The entrapped gases exist in magma.
• Characterized as short, explosive, and violent.

Strombolian Eruption

• Involves a burst of glowing lava due to the bursting of gas bubbles at the vents of the volcano.
• Creates eruptive products such as scoria (hardened chunks of bubbly lava) and lava bombs.

Plinian Eruption

• Most violent among all types.
• Releases huge amounts of gases and ashes at great speeds.
• Often destructive to land and property.

Phreatomagmatic Eruption

• Involves the eruption of magma that reacts to external water.
• The interaction results in an explosion that releases steam and pyroclastic fragments.

Volcanic Eruption Consequences

• Pyroclastic Flow
• Lava Flow
• Ashfall or Tephra Fall
• Lahar
• Volcanic gases
• Debris avalance or volcanic landslide
• Tsunamis
• Secondary explosion
• Formation of Caldedras and Lakes
• Climate change

Pyroclastic Flow

• A fast movement of a turbulent mass of fragmental volcanic materials such as ash and rocks.
• Mixed with hot gases down the slope.

Lava Flow

• It is the flow of incandescent, molten rock materials from a volcano.

Ash Fall or Tephra Fall

• It is Showers of fine-to-coarse-grained volcanic materials and other airborne products of volcanic eruption.

Lahar

• Is the rapid-flowing thick mixture of volcanic material and water.
• These can bury areas with volcanic debris several meters thick.

Volcanic Gasses

• High-temperature mixture of:
  • Water vapor
  • Hydrogen sulfide
  • Sulfur dioxide
  • Carbon monoxide
  • Hydrogen chloride
  • Hydrogen fluoride

Debris Avalanche or Volcanic Landslide

• Massive collapse of a huge portion of a volcano.
• Triggered by an earthquake or a volcanic eruption.

Tsunamis

• Waves are brought about by a sudden displacement of water during volcanic eruptions.

Secondary Explosion

• Non-eruptive event generated when groundwater contacts still-hot pyroclastic flow deposits.
• Occurs at the slope of a volcano and converts deposits into steam.

Formation of Calderas and Lakes

• Volcanic activity changes the landscape.

Climate Change

• During the eruption of Mount Pinatubo in 1991, the country experienced ashfall.
• Surroundongs became dark even at daytime.
• Ashfall reached nearby countries.