L7: Volcanic Hazards

• Volcano

  ● Is a vent on the Earth’s surface that opens downward to a pool of molten rock, debris and gases.

  ● Craters, depressions, hills or mountains formed by removal or pre-existing material or by accumulation of ejected materials.
• Subduction

  ● Is a geological process that happens at convergent plate boundaries, where one tectonic plate moves under another and sinks into the Earth’s mantle.

  ● The thickness of the magma caused by its silica content makes it difficult for gases to be released easily.

  ● A magma chamber forms inside the steep cone and this collects the gases.

  ● The occurrence of earthquake, lahar flow, debris avalanche, or tsunami is also possible.
• ● The subduction zone is the place where 2 plates converge and the volcano is formed

  ○ 1 plate containing the lithosphere descends below the adjacent plate.

  ○ The plate sinks as deep as 80-160 kilometers.

  ○ The crust releases the trapped fluids

  ○ The fluids melt the overlying minerals and produce magma.

  ○ Magma - is a hot silica rich material that comes from the interior of the Earth

  ■ The magma migrates towards the surface and erupts
• Process of Subduction

  1. Two Plates Collide
  2. Subduction Begins
  3. Melting of the Subducted Plate
  4. Magma Formation
  5. Magma Rises
  6. Volcano Forms
• [1] Two Plates Collide

  • An oceanic plate and a continental plate (or another oceanic plate) move towards each other.
• [2] Subduction Begins

  • The denser oceanic plate is forced beneath the lighter continental plate into the mantle.
• [3] Melting of the Subducted Plate

  • As the oceanic plate sinks, it heats up due to the high temperature and pressure inside the Earth.
  • The water trapped in the subducting plate lowers the melting point of the surrounding mantle, causing it to partially meet.
• [4] Magma Formation

  • The melting produces magma (molten rock), which is less dense than the surrounding solid rock.
• [5] Magma Rises

  • The magma slowly rises through cracks in the Earth’s crust because it’s lighter than the rock around it.
• [6] Volcano Forms

  • When the magma reaches the surface, it erupts, releasing lava, ash and gases
  • Overtime, repeated eruptions build up a volcanic mountain.
• Active Volcano

  ● Is currently erupting or showing signs of volcanic eruption.

  ● Erupted within historic times, accounts of these eruptions were documented by man erupted within the last 10,000 years based on the analysis of material from young volcanic deposits.
• Potentially Active Volcano (Dormant)

  ● Is one of which has erupted and then entered a long period of inactivity.

  ● Morphologically young-looking but with no historical or analytical records of eruption.
• Inactive Volcano (Extinct)

  ● Is one that has not shown any sign of activity for a long period.

  ● No recorded eruptions, physical form has been intensively weathered and eroded, bearing deep and long gullies.
• Volcanic Eruption Hazards

  • Lava Flow
  • Pyroclastic Flow
  • Tephra Falls
  • Ballistic Projectiles
  • Volcanic Gas
  • Lahar
• Lava Flow

  ● Is a mass of magma that flows down the slope of the volcano at a rate of 3 kms/day.

  ● Are rivers incandescent of molten rock or lava moving downslope or away from an eruption vent.
• Pyroclastic Flow

  ● Refers to hot dry masses of fragmented volcanic materials that move along the slope and in contact with ground surface or at a speed greater than 60 kms/hr.

  ● This flows from a collapsed eruption column or lava dome.

  ○ Pyroclastic Surges - Are turbulent low-concentration density currents of gases, rock debris and in some cases, water, that move above the ground surface at high velocities.
• Tephra Falls

  ● Showers of fine to coarse-grained volcanic materials and other airborne products of volcanic eruption.

  ● Less than 2mm in diameter (ash), 2-64mm (lapilli), or greater than 64mm (blocks and bombs).

  ● The ash can reach distant places since it is carried by the wind.

  ○ It causes pollution, health problems, poor visibility and disruption of electricity and communication lines
• Ballistic Projectiles

  ● Rocks that are released into the air by an erupting volcano.

  ● These land within 2 kms of the vent but can travel as far as 5 kms or further if the eruption is very explosive.
• Volcanic Gas

  ● One of the basic components of magma or lava.

  ● These are gases in the form of water vapor, hydrogen sulfide, sulfur dioxide, carbon monoxide, carbon dioxide, hydrogen chloride and hydrogen fluoride released from active and inactive volcanoes.

  ○ Hydrogen chloride and hydrogen fluoride are released by volcanic activity and dissolved in water droplets in steam clouds that creates acid rain that can harm plants, marine life and infrastructures.
• Lahar

  ● A flowing mixture of volcanic debris and water.

  ● Classified as:

  ○ Primary / Hot Lahar - associated directly with volcanic eruption.

  ○ Secondary / Cold Lahar - caused by heavy rainfall
• Volcanic Eruption Preparedness

  ● A volcanic eruption has warning signs that can be detected and can help people prepare for the disaster.
• Precursors of an Impending Eruption

  [1] Increase in the frequency of volcanic quakes with rumbling sounds

  • Occurence of volcanic tremors.

  [2] Increased steaming activity

  • Change in color of steam emission from white to gray due to entrained ash.

  [3] Crater glow due to presence of magma at or near the crater

  [4] Ground swells, ground tilt and ground fissuring due to magma intrusion

  [5] Localized landslides, rockfalls, and landslides from the summit area not attributable to heavy rains
• Precursors of an Impending Eruption

  [6] Noticeable increase in the extent of drying up vegetation around the volcano’s upper slopes

  [7] Increase in the temperature of hot springs, wells, and crater lake near the volcano

  [8] Noticeable variation in the chemical content of springs and crater lakes within the vicinity of the volcano

  [9] Drying up of springs / wells around the volcano

  [10] Development of new thermal areas / and or reactivation of old ones

  • Appearance of solfataras
  • Solfataras - A volcanic area or vent that yields only hot vapors and sulfurous gases
• Evacuation Plan During Eruptions

  ● Mandatory evacuation in the 6-km radius permanent zone.

  ● Forced evacuation on the high-risk zone.

  ● Pre-emptive evacuation in the eastern seaboard.

  ● Voluntary evacuation for indirect victims

  Reducing the Impact of Eruption

  ● To mitigate the impact, PHIVOLCS formulated guidelines on what should be done before and during a volcanic eruption.
• Before a volcanic eruption:

  1. Learn about your community’s warning system.
  2. Make an evacuation plan.
  3. Create an emergency communication plan.
  4. Prepare a disaster supply kit.
  5. Contact your local emergency management office of the red cross chapter for more information on volcanoes.
• During a volcanic eruption:

  1. Listen to a battery-operated radio or television for the latest emergency information.
  2. Follow the evacuation order issued by authorities.
  3. Avoid areas downwind and river valleys downstream of the volcano.
  4. If caught indoors:
  5. Close all windows, doors and dampers
  6. Put all machinery inside a garage or barn
  7. Bring animals and livestock into closed shelters
  8. If trapped outdoors, seeks shelter indoors
  9. Protect yourself by wearing long sleeved shorts and a pair of pants
  10. Use goggles or dust mask or hold a damp cloth over your face
  11. If caught in a rock fall, roll into a ball to protect your head
  12. If caught near a stream, be aware of mudflow.
  13. Protect yourself during ashfall.
  14. Remember to stay out of the area defined by the government officials as a restricted zone.
  15. If possible, stay away from areas of volcanic ash fall.