Volcanoes

• Volcanoes are openings where lava, tephra, and steam erupt onto the Earth's surface
• A crater is a depression above the vent from which volcanic material is ejected, while a caldera is a large depression formed when a volcano erupts and collapses
• Explosive volcanoes build enough pressure to blow their tops, while non-explosive volcanoes allow lava to run down their sides
• Types of volcanic eruptions:

  • Phreatic or hydrothermal: steam-driven eruption as hot rocks contact water, short-lived with ash columns
  • Phreatomagmatic: eruptions driven by magma interacting with bodies of water
  • Strombolian and Hawaiian: least violent explosive eruptions, with fire fountains and lava flows
  • Vulcanian: tall eruption columns with pyroclastic flow and ashfall
  • Plinian: excessively explosive eruption of gas and pyroclastics
• Terminologies:

  • Lava: magma ejected from a volcano
  • Magma: molten rock inside the Earth
  • Ash: fine-grained lava fragments
  • Silica: compound of silicon (SiO2)
  • Pyroclastic: tiny rock materials forming ash and dust
• Types of volcanoes according to activity:

  • Active: erupted within 600 years or 10,000 years ago
  • Inactive: not erupted for the last 10,000 years
  • Potentially active (dormant): not erupting now but could in the future
  • Extinct: not erupted since recorded history and will never erupt again
• The Philippines has around 300 volcanoes, with 24 active and 25 extinct
• Volcanoes are openings or vents where lava, tephra (small rocks), and steam erupt onto the Earth’s surface
• A crater is a bowl or funnel-shaped depression that usually lies above the vent from which volcanic material is ejected
• A caldera is a large depression formed when a volcano erupts and collapses
• Types of volcanoes according to eruption styles:

  • Explosive: build enough pressure to blow the top, sending pyroclastic material into the air
  • Non-explosive: build only enough pressure to allow lava to run down its sides
• Phreatic or hydrothermal eruptions are steam-driven as hot rocks contact water, characterized by ash columns, and may lead to a larger eruption; example: Taal Volcano
• Phreatomagmatic eruptions are driven by the direct interaction between magma and external bodies of water like the sea
• Strombolian and Hawaiian eruptions are the least violent types of explosive eruptions:

  • Hawaiian eruptions have fire fountains and lava flowStrombolian eruptions have explosions causing a shower of lava fragments
• Vulcanian eruptions are characterized by tall eruption columns reaching up to 20 km high with pyroclastic flow and ashfall tephra
• Plinian eruptions are excessively explosive with gas and pyroclastics, having 20 to 35 km tall columns that may collapse to form pyroclastic density
• Terminologies:

  • Lava: magma ejected out of a volcano
  • Magma: molten rock inside the Earth
  • Ash: fragment of rocks; fine-grained lava
  • Silica: compound of silicon (SiO2)
  • Pyroclastic: pieces of rock forming ash and dust
• Types of volcanoes according to activity:

  • Active: erupted within 600 years or 10,000 years ago based on material analysis
  • Inactive: not erupted for the last 10,000 years, undergoing weathering and erosion
  • Potentially active (dormant): not erupting now but could in the future
  • Extinct: not erupted since recorded history and will never erupt again
• The Philippines has around 300 volcanoes, with 24 active and 25 extinct
• Composite Volcano


  Over multiple eruptions, the accumulation of both explosive activity and lava flows form the steep, sweeping sides of this volcano. As it ages, multiple channels to the surface can splinter off of the central vent, influencing its shape.
• Cinder Volcano


  Forms when explosive activity throws magma into the air, which cools into cinders and settles around the volcano’s opening. These emerge in just a few years during one active period; afterward, they are usually extinct, but they may occur on the side of a larger volcano.
• Lava Dome Volcano


  Forms when thick, extremely viscous lava erupts, hardening in a dome shape. These emerge in one active period; afterward, they are usually extinct, but they may occur on the side of a larger volcano.
• Shield Volcano


  Over multiple eruptions, long, fluid lava flows form broad layers, which accumulate into some of the world’s largest volcanoes.
• Secondary vent


  Smaller openings in a volcano from which magma erupts
• Magma

  Molten rock beneath Earth’s surface capable of intrusion and extrusion
• Conduit

  The channel or pipe that carries magma from a reservoir or chamber to the vent where it is erupted
• Throat

  The entrance of a volcano. The part of the conduit that ejects lava and volcanic ash
• Sill


  A flat intrusion of igneous rock that forms between preexisting layers of rock
• Main vent

  The channel through which magma travels to reach the Earth’s surface
• Magma chamber


  The area beneath the volcano where magma is stored
• VISCOSITY

  • Property of material’s resistance to flow
  • Liquid’s thickness and stickiness
• Basaltic Magma

  • formed in upper mantle, low silica and gas content, low viscosity.
• Andesitic Magma

  • formed when oceanic crust subducted into mantle, medium silica and gas content, intermediate viscosity.
• Rhyolitic Magma

  • formed when molten rock mixes with silica and water rich continental crust, high viscosity with large volume of trapped gases.