3Q-SCIENCE_9-WEEK_1_pptx

Introduction to Volcanoes

  • Volcanoes: Openings in Earth’s crust allowing molten rock, rock fragments, and gases to erupt.

Learning Objectives

  • Understand how volcanoes form.

  • Describe various types of volcanoes.

  • Identify parts of a volcano.

  • Recognize volcanoes present in the Philippines.

  • Classify Philippine volcanoes.

The Ring of Fire

  • Location: Major area in the basin of the Pacific Ocean where a large number of earthquakes and volcanic eruptions occur.

  • Relation to Volcanoes: Many active volcanoes are found in subduction zones within the Ring of Fire, essential for volcano formation.

Volcano Formation

  • Most volcanoes are found along plate boundaries, especially:

    1. Subduction Zones: One plate sinks beneath another.

    2. Hot Spots: Volcanic regions thought to be fed by underlying mantle that is anomalously hot.

    3. Divergent Boundaries: Where tectonic plates are pulling apart.

Anatomy of a Volcano

  • Key parts include:

    • Magma Chamber: Storage area for molten rock.

    • Main Vent: The main passage through which magma travels to the surface.

    • Side Vent: Secondary passage for magma.

    • Crater: Circular depression at volcano's summit.

    • Lava: Molten rock that has reached the Earth's surface.

    • Volcanic Bombs: Ejected fragments during eruptions.

    • Dust & Ash: Byproducts released during an eruption.

Types of Volcanoes

  • Three Basic Volcano Shapes:*

    1. Cinder Cone Volcano: Smallest, simplest type formed from pyroclastic fragments. Example: Smith Volcano (Mount Babuyan).

    2. Composite Volcano (Stratovolcano): Can be quiet or violent, steep sides, consists of alternating layers of lava and ash. Example: Mount St. Helens.

    3. Shield Volcano: Broad and gently sloping, formed from quiet eruptions of basaltic lava. Example: Kilauea, Mauna Loa.

Classification of Volcanoes by Eruptive History

  • Active Volcanoes: Have erupted within the last 600 years (e.g., Mt. Mayon, Mt. Taal).

  • Dormant Volcanoes: Active but not currently erupting, expected to erupt again (e.g., Mahagnao Volcano, Mount Makiling).

  • Extinct Volcanoes: Have not erupted in over 10,000 years and are not expected to erupt (e.g., Mount Guinsiliban).

Volcanoes in the Philippines

  • Active and Potentially Active Volcanoes: Numerous volcanoes are active, including those in the Ring of Fire, such as:

    • Mt. Taal, Mt. Mayon.

  • Potentially Active Volcanoes and Inactive Volcanoes are also found across the country.

Factors Affecting Eruption Explosiveness

  • Water Vapor: Higher water content increases explosion power.

  • Trapped Gases:

    • Easy escape (low pressure) = quiet eruptions.

    • Difficult escape (high pressure) = explosive eruptions.

  • Magma Type:

    • Basaltic (thin) = quiet eruptions.

    • Granitic/Andestic (thick) = violent eruptions.

  • Note: Pyroclastic flows can be extremely dangerous, comprising fast-moving mixtures of water, gas, and ash.

Conclusion

  • Understanding the formation, structure, types, and active status of volcanoes is crucial for risk assessments and preparation in volcanic regions, particularly in the Philippines.