DRRR VOLCANO HAZARD

• Volcano


  • A vent, hill or mountain from which molten or hot rocks with gaseous material have been ejected
  • Craters, depressions, hills or mountains formed by removal of pre-existing material or by accumulation of ejected materials
• The Philippines sits on a unique tectonic setting ideal to volcanism and earthquake activity

  
• The Philippines is situated at the boundaries of two tectonic plates - the Philippine Sea Plate and the Eurasian plate - both of which subduct or dive beneath the archipelago along the deep trenches along its east and west seaboard
• The Philippines is a disaster risk epicenter in the Pacific Ring of Fire
• Active Volcanoes


  • Erupted within historical times (within the last 600 years), accounts of these eruptions were documented by man
  • Erupted within the last 10,000 years based on the analyses of material from young volcanic deposits

  
• Potentially Active Volcanoes


  Morphologically young-looking but with no historical or analytical records of eruption

  
• Inactive Volcanoes


  No recorded eruptions, physical form has been intensively weathered and eroded, bearing deep and long gullies

  
• The Philippines has 37 Holocene volcanoes and 39 Pleistocene volcanoes

  
• Lava flow


  • Rivers of incandescent molten rock or lava moving downslope or away from an eruption vent
  • Low silica magma lava flows have low viscosities and tend to flow at high speeds (kilometers per hour)
  • High silica magma lava flows have high viscosities and tend to move slowly (kilometers per day)
  • Steep slopes encourage faster and longer flows than gentle slopes or terrain
• Tephra fall or ashfall and ballistic projectiles


  • Fragmented volcanic particles propelled through the atmosphere in an eruption plume or column that eventually fall or settle downwind, forming blankets
  • Ashfall can also be rained out from ash clouds of PDCs
  • Large particle tephra called volcanic bombs that are too heavy to transport in eruption columns are ejected straight out as ballistic projectiles
  • Tephra or ashfall can accumulate and cause infrastructural damage, roof collapse, water contamination and burial
  • Ashfall is a health hazard and danger to aircraft and industrial machinery

  
• Pyroclastic Density Currents (PDCs)


  • Mixtures of fragmented volcanic particles, hot gases and ash that rush down volcanic slopes or outward from a source vent at high speeds
  • Range from pyroclastic flows (denser, ground-hugging) to pyroclastic surges (more dilute, mobile)
  • Can be generated by gravitational collapse of eruption columns, explosion of lava domes, or spalling/collapse of lava flows
  • A special class called base surges are mobile, water-vapor-rich pyroclastic surges generated by explosive phreatomagmatic eruptions
  • PDCs are the most lethal volcanic hazard, causing incineration, asphyxiation, abrasion, dynamic pressure impact and burial

  
• Lateral blasts


  • Laterally-directed thrusts of hot gas and ash generated from exploding domes or sudden mass failure of volcanic flanks
  • Travel at subsonic speeds, flattening everything in their paths, with impacts similar to PDCs

  
• Volcanic gas


  • Dissolved components of magma released to the atmosphere in large quantities during eruptions
  • Principal gases are water vapor, hydrogen sulfide, sulfur dioxide, carbon dioxide, carbon monoxide, hydrogen chloride and hydrogen fluoride
  • Can form aerosols that cool the atmosphere and deplete ozone
  • Some toxic gases like hydrogen fluoride can endanger livestock
  • Non-toxic gases like carbon dioxide can cause asphyxiation
• Lahar


  • Slurries of volcanic sediment, debris and water that cascade down a volcano's slopes through rivers and channels
  • Mainly generated by torrential rainfall on unconsolidated deposits from past eruptions
  • Can also be triggered by sudden draining of crater lakes, dam failures, or PDCs entering water bodies

  
• Debris avalanche (sector collapse)


  • Mass failure of a volcano's flanks due to magma intrusion, strong earthquakes, or fault movements beneath the edifice
  • Forms a horseshoe-shaped scar or amphitheater from which the collapsed mass detaches to form a field of hummocks downslope
  • Rare but extremely hazardous, endangering areas far beyond usual volcanic hazard extents

  
• Volcanic tsunami


  • Occur in caldera lakes when water is displaced by deformation of the lake floor caused by rising magma, PDCs or landslides entering the lake
  • Or in seas when water is displaced by PDCs or debris avalanches from volcanoes
  • Unlike earthquake-generated tsunamis which are long-period waves from fault displacement or seafloor deformation
• Ground subsidence and fissuring


  • Ascending magma can cause the volcano edifice to swell, breaking the ground into fissures along weaknesses
  • After magma eruption, its removal can cause the ground to sink and subside, further fissuring
  • Accompanied by earthquakes, causing infrastructural and building damage, land degradation, and waterway re-routing

  
• Secondary explosions, PDCs and ashfall


  • Generated when still-hot volcanic deposits like PDCs or lava flows come into contact with water by erosion, rising groundwater or rainfall
  • Can remobilize volcanic material to generate small-scale PDCs and minor ashfall

  
• In times of disaster and calamity, the prepared are the heroes
• What are Holocene Volcanoes


  active during the Holocene period, which spans the last 10,000 years
• What are Pleistocene volcanoes


  olcanoes that were active during the Pleistocene epoch, which spanned 2.5 million years.
• What is Phreatomagnetic Eruptions


  interaction between magma and water
• Where does the ozone reside

  between the stratosphere and mesosphere