5.5

• Lahars


  Wet cement-like mixture of volcanic material and water that flows down the slopes of a volcano
• Lahar in Javanese(an Indonesian dialect)


  Lava or lava flow
• Lahars can form during eruptive episodes or during periods of dormancy
• How lahars are generated


  1. Intense rainfall during an eruption

  2. Occurrence favors stratovolcanoes, tall and steep volcanoes, and those with weak or easily erodible volcano rock layer

  
• Types of lahar processes and deposits

  • Dilute Streamflow (20 to >~60% vol, 40-80% wt.)
  • Hyperconcentrated Streamflow (<20% vol., <40% wt.)
  • Debris Flow (>~60% vol., >80% wt.)
• Lahars


  • Move as fluid masses with the general consistency of wet concrete
  • Can cause serious economic and environmental damage to large floodplain areas, and to those affected by the severed lifelines
  • Can destroy through direct impact of the debris, logs, and the flow itself
• Hazard maps play an important role in identifying the location, magnitude and countermeasures to be undertaken during volcanic crises

  
• Taming lahars


  1. Assess and designate at-risk areas

  2. Investigate past history of lahars to form the bases of predicting the size and frequency of future lahars
• Lahar


  Lava or lava flow
• Lahar


  • Wet cement-like mixture of volcanic material and water flowing down the slopes of a volcano
• Lahars can travel at high speeds
• Lahars can have a significant impact on the surrounding environment
• Effective dissemination of lahar hazard information

  • Educating the local residents, local authorities, and local and national civil defense organizations
  • Coordination between the lahar experts and emergency management agencies
  • Good monitoring and warning system should be in place to alert people early enough for them to evacuate to safe places
• Role of water in lahar formation


  Water acts as a lubricant, allowing volcanic materials to flow more easily downhill

  
• Lahars typically move quickly and pose significant danger to nearby communities