Volcanoes

Volcanoes - vents in Earth’s Crust

Crust - the outermost layer of the Earth

1500 active volcanoes worldwide

PHIVOLCS (Philippine Institute of Volcanology and Seismology) - a government agency that studies and monitors volcanic activities and earthquakes

23 active, 26 potentially active, and 300 named and unnamed inactive volcanoes in the Philippines

Pacific Ring of Fire - an active region in the basin of the Pacific Ocean

Trenches - areas where plates collide, marked by long, deep depression

Formation of Volcanoes Theory

  • Plate Tectonic Theory - Earth's outer shell (lithosphere) is divided into several plates that glide over the Earth's rocky inner layer above the softcore (mantle).
  • Convection - method of heat transfer by which cold, dense material sinks, whereas hot, less dense material rises.
  • Subduction - two plates of different densities collide, and the denser (oceanic) plate moves beneath the less dense (continental) plate. It happens at plate boundaries called subduction zones.
  • Mid-ocean ridges - When two plates move away from each other, a gap is formed between them. The magma from the mantle then rises and forces its way through the gap, forming a volcano.

Hot Spot - an area in the mantle where rocks melt because of the intense heat.

Six Major Parts of Volcano

  1. Flanks - sides of a Volcano
  2. Summit - apex or the highest point, contains the crater
  3. Crater - mouth of a volcano
  4. Conduit - pipe or channel that conveys the magma
  5. Branch Pipes - originated from conduit
  6. Magma Chamber / Magma Reservoir - a large underground pool of molten rocks

Caldera - a volcanic feature that resembles a cooking pot

Classification of Volcanoes Based on Behavior

  • Active Volcanoes - erupted within the last 600 years
  • Potentially Active Volcanoes - morphologically young-looking volcanoes with no historical record of eruption
  • Inactive Volcanoes - volcanoes with no record of eruption

Classification of Volcanoes Based on Eruptive Patterns and Characteristic Forms

  1. Shield Volcano - has a broad summit area that resembles a warrior’s shield

    -made of fluid lava flows

  2. Cinder Cone or Scoria Cone - a steep, conical hill of volcanic debris deposited around a volcanic vent

    -the smallest type of volcano

  3. Composite Volcano or Stratovolcano - a tall, conical volcano built by several strata or layers of eruptive materials, such as hardened lava, tephra, and volcanic ash.

Nature of Volcanic Eruptions

Lava Flow - a mass of lava or molten rocks flowing downslope from the vent

Types of a Lava flow - 1. Andesitic lava flow - has a high viscosity

2. Rhyolitic lava flow - has a high viscosity

3. Basaltic lava flow - flows in thin, broad sheets because of its low viscosity

Two Types of Basaltic Lava Flow

1. aa flows - have surfaced of rough, jagged blocks with dangerously sharp edges

2. pahoehoe flows - exhibit smooth surfaces, on which one can walk

Lava tubes - hardened basaltic flows that commonly contain cave-like tunnels

Pyroclastic materials - pulverized rocks, volcanic blocks, basaltic bombs, lava, ash, glass fragments, and gases that volcanoes eject from the vent. Materials that volcanoes eject from the vent.

Pyroclastic flow - a flow of hot, dry mass of gases and fragments

Pyroclastic surge - a high-velocity current of rocks, gases, or water.

Tephra flows - consist of volcanic rocks and crystals

Lahar - a type of mudflow that consists of water, volcanic ash, pyroclastic materials, and debris

Theories on Volcanic Eruptions

  1. Buoyancy - the ability to float in the fluid
  2. Solubility - the amount of gases that magma can hold
  3. Brimming - the magma rises because of the additional push exerted by the injected magma

Strength of Volcanic Eruptions

  • Viscosity - the higher the temperature, the less viscous
  • Silica Content - the higher the silica content, the higher the viscous
  • Amount of dissolved gases - dissolved gases cannot increase in pressure

Effects of Volcanic Eruption

  • hazardous to organisms and damaging to the environment
  • can cause substantial changes in Earth’s climate
  • volcanic particles that are ejected into the atmosphere block the sunlight
  • can increase the global temperature
  • can produce acid rain
  • volcanic materials can be good sources
  • volcanic ashes are utilized as soil fertilizer
  • after a volcanic eruption, people may use the fertile soil around or near the volcano for farming

Harnessing Geothermal Energy

Harnessing - to make and control the use of energy

Steps to generate electricity in a geothermal powerplant

  • Hot water is pumped from deep underground through a well under high pressure
  • When hot water reaches the surface, the pressure is dropped, which causes the water to turn into steam
  • The steam spins a turbine, which is connected to a generator that produces electricity
  • The steam cools off in a cooling tower and condenses back to the water
  • The cooled water is pumped back into the Earth to begin the process again

Signs of Impending Volcanic Eruption

  1. Seismic Activity
  2. Release of the high amount of volcanic gases
  3. Deformation of the ground surface in the vicinity of a volcano

Fumarole - small holes

Emergency Preparedness

What to do before a Vulcanic Eruption

  1. Learn about emergency plans and warning systems in your community.
  2. Plan your evacuation routes.
  3. Devise an emergency communication plan.
  4. Prepare an emergency supply, flashlight and extra batteries, first aid kit and manual, food and water, medicines, sturdy shoes, dust masks, and goggles.

Staying safe during a volcanic eruption

  1. Follow the evacuation order given by authorities.
  2. Keep yourself updated on the latest information.
  3. Close all the windows and doors if caught indoors.
  4. If you are caught outdoors, seek shelter or wear a safety outfit and gear such as a long-sleeved shirt and long pants, dust mask, and goggles, to avoid irritation of the skin, respiratory tracts, and eyes.
  5. Avoid going to streams, rivers, or downslope areas as mudflow may occur.

How to stay safe after a volcanic eruption

  1. Clear out ashfall from roofs as houses or buildings may collapse.
  2. Avoid contact with volcanic ash and other volcanic debris.
  3. Stay indoors until the local officials in your community advise that it is safe to go outside.