15

• Volcanic eruption is one of the most dangerous natural events because of the different hazards that it may bring namely: lahars, lava flows, ash falls, pyroclastic flows, debris avalanche, and emission of volcanic gases
• These hazards may inflict devastating effects to people, physical structures and to the environment
• While volcanoes may give off several warning signs they are about to blow, some are taken more seriously by volcanologists who alert and advise government officials regarding when evacuations need to take place
• Warning signs of an impending volcanic eruption

  • Increase in the frequency of volcanic quakes with rumbling sounds
  • Increased steaming activity
  • Crater glow due to presence of magma at or near the crater
  • Ground swells (or inflation)
  • Localized landslides
  • Noticeable increase in drying up of vegetation
  • Increase in temperature of hot springs
  • Noticeable variation in the chemical content of springs
  • Drying up of springs/wells around the volcano
  • Development of new thermal areas and/or reactivation of old ones
• Volcanic quakes


  • Serve as an early warning sign of an impending eruption, as well as a marker for the location of moving magma and sudden rise of gases
• Increased steaming activity


  Change in color of steam from white to gray due to entrained ash
• Crater glow


  Observed when the magma reaches the surface, and thus referred as lava
• Ground swells (or inflation)

  Caused by moving magma, gases and other volcanic fluids that tend to cause the surface of the Earth to bulge upward (inflate) or spread apart which can eventually lead to ground fissuring or cracking
• Localized landslides


  Caused by the movement of rocks and soil influenced by the force of gravity, strength of the material, and steepness of a volcano, as magma rises together with volcanic gases, rocks are altered and weakened
• Noticeable increase in drying up of vegetation

  As the magma rises, the temperature of the volcano also increases, and the heat brought by the rising magma if high enough, can dry up the vegetation
• Increase in temperature of hot springs


  As the magma rises, the temperature of the volcano also increases, and the heat brought by the rising magma influences and causes the temperature of the springs, wells, or lake to increase
• Noticeable variation in the chemical content of springs

  Groundwater deep within the surface of the volcano interacts with magma, volcanic gases, host rocks, and even with other water coming from springs, lakes, wells, and the presence of certain compounds signals the presence of magma such as magmatic carbon dioxide, or high helium isotopes
• Drying up of springs/wells around the volcano

  As rising magma generates quakes and tremors which may cause ground deformation (cracks or fissures) on the surface, this may cause the water from springs or well to receded and seep through these cracks, and the higher the temperature, the higher the chances to dry up the springs
• Development of new thermal areas and/or reactivation of old ones

  Signals the active movement of magma within the volcano as it interacts with groundwater or rocks
• Parameters used to monitor volcanoes

  • Ground deformation
  • Seismic activity
  • Gases
  • Sensory observations (by people living near volcano)
• Ground deformation


  Any surface changes on a volcano (subsidence/sinking, tilting, bulging); often use of satellite imaging which results to less exposure on the ground or safer for volcanologists, but interpretation needs field verification sometimes
• Seismic activity


  When magma rises up, it breaks rock along the way, thus generating earthquakes, which are monitored by using a seismometer that determines which patterns of seismic waves precede an eruption
• Gases


  Monitor types and rate of emission of different gases; Concentrations of gases are sometimes high enough to create acid rain that kills vegetation around the volcano; Collection of samples from vents directly with the use of remote sensing instruments that identify and quantify the present gases
• Sensory observations (by people living near volcano)

  • Visual - intensified presence of steam; drying up of vegetation, wells/spring/lake; crater glow at the mouth of the volcano
  • Auditory - Rumbling sounds are heard
  • Olfactory - observed foul smell (usually rotten egg caused by sulfur) caused by presence of volcanic gases
  • Tactile - ground movement/earthquake is felt
• Volcanic eruption is one of the dangerous events that may happen because it results to different hazards such as: Ballistic Projectiles, Ash Fall, Pyroclastic Flows, Lava Flows, Volcanic Gases, Debris Avalanche or Volcanic Landslide and even Tsunami
• Ballistic projectile


  Rock fragments that are ejected from volcano's mouth that are comparable to cannonballs, reaching up to 5 kilometers or 3 miles, and endanger life and property through the force of impact, loss of agricultural lands, producing suspensions of fine-grained particles, and carrying of noxious gases, acids, salts, and heat
• Ash fall or Tephra fall


  Minute volcanic particles such as pulverized rock, minerals and silicon which has fine to coarse grain, formed during explosive volcanic eruption when dissolved gases in magma escape violently into the atmosphere, and can endanger life and property, kill organisms, cause respiratory tract problems, ruin machines and damage roofing and power/communication lines
• Pyroclastic Flows


  Highly-density mix of hot lava blocks, pumice, ash and volcanic gases that move at very high speed down volcanic slopes, typically following valleys, consisting of a lower basal flow of coarse fragments and a turbulent cloud of ash above, and can destroy anything on its path by direct impact, burn sites with hot rocks debris, and burn forest, farmlands, crops and buildings
• Lava flows


  Streams of molten rocks that are poured or oozed from an erupting vent, characterized as quite effusion of lava, and may instigate other types of hazards such as pyroclastic flow, and damage properties, agricultural lands, and even human lives by burying, burning everything in their path
• Volcanic gases


  Magma contains dissolved gases which provides the driving force that causes most volcanic eruptions, and are all potentially hazardous to all living things as well as to agriculture and property, such as carbon dioxide, sulfur dioxide, and hydrogen sulfide
• Debris Avalanche or Volcanic landslide

  Massive collapse of a volcano, usually triggered by an earthquake or volcanic eruption, resulting in massive destruction
• Tsunami


  Sea waves or wave trains that are generated by sudden displacement of water, which could be generated during undersea eruptions or debris avalanches, and can cause huge waves that result in destruction
• Seismic hazard is the hazard related with probable earthquakes in a particular area, and the possible hazards caused by an earthquake is normally shown in a seismic hazard map that shows how likely can a disaster affect the lives of people living in that area and how can they prepare better for the approaching disaster
• The volcano authority in the Philippines is the Philippine Institute of Volcanology and Seismology (Phivolcs), and the alert level system used by Phivolcs runs from Alert Level 0 (lowest) to Alert Level 5 (highest)
• Volcanic alert levels


  • Alert Level 0 - No Alert: Quiet, no eruption in the foreseeable future
  • Alert Level 1 - Abnormal: Low level unrest, no eruption imminent
  • Alert Level 2 - Increasing Unrest: Moderate unrest, unrest probably of magmatic origin, could eventually lead to eruption
  • Alert Level 3 - Increasing Tendency Towards Eruption: Relatively high unrest, magma is close to the crater
  • Alert Level 4 - Hazardous Eruption Imminent: Intense unrest, hazardous eruption is possible within days
  • Alert Level 5 - Hazardous Eruption: Hazardous eruption ongoing
• Active volcano


  A volcano that has had at least one eruption during the past 10,000 years, and may be erupting or dormant
• Erupting volcano


  An active volcano that is having an eruption
• Dormant volcano


  An active volcano that is not erupting, but supposed to erupt again
• Extinct volcano


  A volcano that has not had an eruption for at least 10,000 years and is not expected to erupt again in a comparable time scale of the future
• This volcanic hazard map basically shows the ballistic projectile or the rocks that an erupting volcano may throw into the air, and the areas in pink, specifically the towns of Balete, San Roque and Talisay, are the places that will mostly be affected by this hazard
• This hazard map indicates the susceptibility of those colored areas to ground unfolding, fast outward moving and raging, dilute clouds of gas and ash that are discharged from an erupting volcano, and those areas must be warned from heavy ash fall and pyroclastic materials that are harmful to the health of people especially those with respiratory problems
• Susceptibility


  Describes the complexity to occur geological disaster in a certain district and reflects physics geological phenomena
• Hazard


  A function of scale and probability of disaster occurrence, reflects activity degree and damage capability of disaster
• Mitigation


  Sustained action that reduces or eliminates long-term risk to people and property from natural hazards and their effects, describing the ongoing effort at the federal, state, local and individual levels to lessen the impact of disasters