VOLCANOES

• Active Volcanoes:

  • Those that have a record of eruption within the last 600 years or those that erupted 10,000 years ago based on analysis of their materials
  • In the Philippines, 24 volcanoes are active
• Inactive Volcanoes:

  • Those that have not erupted for the last 10,000 years and their physical form is being changed by agents of weathering and erosion through the formation of deep and long gullies
• 6 Most active volcanoes in the Philippines:

  • Mayon
  • Mt. Pinatubo
  • Taal
  • Kanlaon
  • Mt. Bulosan
  • Mt. Hibok hibok
• Divergent plates:

  • Plates that move away from each other
• Convergent plates:

  • Plates that collide
• Volcano:

  • A natural opening in the Earth's surface where molten rocks, smoke, gases, ashes are ejected
• Parts of the volcano:

  • Summit
  • Slope
  • Base
• Crater:

  • A funnel-shaped depression at the top of a volcano
  • Taal volcano has 47 craters
• Caldera:

  • Formed when a part of the wall of a volcano collapses following an explosive reaction
• Magma:

  • Hot fluid or semi-fluid material below the earth's crust, usually made with molten rocks
• Primary factors affecting the volcanoes' eruptive styles:

  • Magma's temperature
  • Its chemical composition
  • The amount of dissolved gases it contains
• Viscosity:

  • The property of the material's resistance to flow
  • The more viscous and thicker the material is, the greater is its resistance to flow
  • Syrup is more viscous than water
• How the temperature of magma affects viscosity:

  • The viscosity of magma decreases with temperature
  • The higher the temperature, the lower its viscosity
  • As lava flows, it cools and begins to harden, its ability to flow decreases and eventually stops
• How compositions of magma affect its viscosity:

  • Magmas with high silica content are more viscous than those with low silica content
  • The magma that contains less silica is relatively fluid and travels far before solidifying
• The amount of gases contained in the magma affects its viscosity:

  • Other factors being equal, gas (mainly water vapor) dissolved in magma tends to increase its ability to flow
  • In near-surface environments, the loss of gases makes magma more viscous, forming a dome or a columnar
• Terminologies:

  • Viscosity: the ability of a substance to resist flow, a measure of its consistency
  • Tephra: pieces of all fragments of rock ejected into the air by an erupting volcano
  • Pyroclastic flow: a dense, fast-moving flow of solidified lava pieces, volcanic ash, and hot gases, extremely dangerous to any living thing in its path
• Volcanic Hazards:

  • Lahar: a violent type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris, and water
  • Ashfalls: can bury nearby land and buildings with several feet of ash and choke animals (dust-size)
  • Lava flows: may destroy property and reshape the landscape but are normally advanced too slowly to endanger human lives
  • Nuèe ardentes: avalanches are dense clouds of ash and superheated gas that may flow down volcanic slopes at 60 miles per hour cooking every living thing in their way
• • Tsunamis: may result if the flanks of island volcanoes collapse into the sea during major eruptions
• Classification of Volcanoes (based on PHIVOLCS):

  • Eruptive styles
  • Active
  • Inactive
• Landforms:

  • Shield: formed by the accumulation of lava that oozes out from the volcano, resembles a warrior's shield, e.g., Mauna Loa in Hawaii
  • Composite or stratovolcanoes: large, nearly perfect sloped structure formed from alternate solidification of both lava and pyroclastic deposits, e.g., Mayon Volcano
  • Cinder: built from ejected lava fragments, have steep slope, wide crater, and are most abundant of the three major volcano types, e.g., Paricutin in Mexico
• • Plinian: excessively explosive type of eruption of gas and pyroclastics, e.g., Mt Pinatubo in Zambales
  • Vulcanian: characterized by tall eruption columns that reach up to 20 km high with pyroclastic flow and ashfall tephra, e.g., Paricutin volcano in Mexico
• Lava Eruptive Types:

  • Phreatic or hydrothermal: a steam-driven eruption as the hot rocks come in contact with water, short-lived, characterized by ash columns but may be an onset of a larger eruption, e.g., Taal volcano in Batangas
  • Phreatomagmatic: a violent eruption due to the contact between water and magma, large column of very fine ash and high-speed and sideway emission of pyroclastics called base surges are observed
  • Strombolian: a periodic weak to violent eruption characterized by fountain lava, e.g., Irazu Volcano in Costa Rica
• Active Volcanoes:

  • Have a record of eruption within the last 600 years or erupted 10,000 years ago based on material analysis
  • In the Philippines, 24 volcanoes are active
• Inactive Volcanoes:

  • Have not erupted for the last 10,000 years
  • Their physical form is being changed by agents of weathering and erosion through the formation of deep and long gullies
• 6 Most active volcanoes in the Philippines:

  • Mayon
  • Mt. Pinatubo
  • Taal
  • Kanlaon
  • Mt. Bulosan
  • Mt. Hibok-hibok
• Divergent plates:

  • Move away from each other
• Convergent plates:

  • Collide
• Volcano:

  • Natural opening in the Earth's surface where molten rocks, smoke, gases, ashes are ejected
• Parts of a volcano:

  • Summit
  • Slope
  • Base
• Crater:

  • Funnel-shaped depression at the top of a volcano
  • Taal volcano has 47 craters
• Caldera:

  • Formed when a part of the wall of a volcano collapses following an explosive reaction
• Magma:

  • Hot fluid or semi-fluid material below the earth's crust, usually made of molten rocks
• Primary factors affecting volcanoes' eruptive styles:

  • Magma's temperature
  • Magma's chemical composition
  • The amount of dissolved gases it contains
• Viscosity:

  • The property of the material's resistance to flow
  • The more viscous and thicker the material is, the greater its resistance to flow
  • Syrup is more viscous than water
• How the temperature of magma affects viscosity:

  • The viscosity of magma decreases with temperature
  • The higher the temperature, the lower its viscosity
  • As lava cools and hardens, its ability to flow decreases
• How compositions of magma affect viscosity:

  • Magmas with high silica content are more viscous than those with low silica content
  • Magma with less silica is relatively fluid and travels far before solidifying
• The amount of gases in magma affects viscosity:

  • Gas dissolved in magma tends to increase its ability to flow
  • Loss of gases in near-surface environments makes magma more viscous, forming a dome or a columnar structure
• Terminologies:

  • Viscosity: the ability of a substance to resist flow
  • Tephra: pieces of all fragments of rock ejected into the air by an erupting volcano
  • Pyroclastic flow: a dense, fast-moving flow of solidified lava pieces, volcanic ash, and hot gases
• Volcanic Hazards:

  • Lahar: a violent mudflow composed of pyroclastic material, rocky debris, and water
  • Ashfalls: can bury land and buildings with ash
  • Lava flows: may destroy property and reshape the landscape
  • Nuée ardentes: dense clouds of ash and superheated gas that flow down volcanic slopes
  • Tsunamis: may result from the collapse of island volcano flanks into the sea during major eruptions
• Classification of Volcanoes (based on PHIVOLCS):

  • Eruptive styles
  • Active
  • Inactive
  • Extinct
  • Landforms
  • Shield volcanoes: formed by the accumulation of lava that oozes out from the volcano
  • Composite or stratovolcanoes: large, nearly perfect sloped structures formed from alternate solidification of lava and pyroclastic deposits
  • Cinder cones: built from ejected lava fragments