Volcanic Hazards

• The magnitude of volcanic eruptions has been measured using a logarithmic scale from 0 to 8, called the Volcano Explosivity Index (VEI).
• Even for those volcanoes known to be dormant, relying on average cycles of activity can only alert volcanologists of the necessity for heightened observation.
• Mount Merapi is located in Indonesia within South East Asia. It is in an island archipelago, on the island of Java, just north of the Java trench.
• The Mount Merapi eruption occured for October 25th 2010 - November 30th 2010 and had a VEI 4
• The Mount Merapi eruption was caused by the fact it is located on a volcanic island arc, subducting oceanic plate sediment causes magma plutons. It is within the most volcanically active place on Earth,.
• Impacts of Mount Merapi eruption

  • 353 died
  • Over 500 injured
  • 350,000 evacuated
  • Volcanic bombs and heat clouds up to 800C
  • Ash improved soil quality
• Responses to Mount Merapi eruption

  • 210 evacuation centres set up
  • 20km exclusion zone set up
  • 6 weeks displacement
  • 2682 people from volcano slopes relocated
• For volcanoes, it can be incredibly difficult to measure frequency and regularity of eruptions, volcanic periodicity can seem a random concept
• As long as active and dormant volcanoes are monitored, using equipment such as seismometers and seismographs, warnings of imminent eruptions can be issued to governments and civil authorities.
• Seismic activity is measured using seismometers and recorded using a seismograph, microquakes indicate the rise of magma and the fracturing of the overlying plate
• Ground deformation is measured using tiltometers, bulging of the ground is caused by rising magma
• There are other signs of eruptions such as, emissons of gases, land slides, small eruptions and rock falls
• Eruptions of lava in fissure eruptions, such as blocky (aa) or smooth and ropy (pahoehoe) can create extensive lava plateaus which fill hollows in the landscape and create basalt plains - these greatly contrivute to climate change
• Shield volcano eruptions are gentle enough to become tourist attractions e.g. Hawaii and Iceland
• Stratovolcanoes form from alternating eruptions of ash, tephra and lava which build up in layers. This produces weaknesses which magma exploits to cover the original volcano in numerous secondary (parasitic) cones
• Calderas result when violent eruptions blow off the volcano's summit, this empties the magma chamber and causes the volcano sides to collapse inwards creating a large crater
• Along constructive plate margins, shield volcanoes form. Along destructive plate margins, strato volcanoes form. On hot spots a volcanic island chain is found which contains shield volcanoes.
• Primary Effects of Volcanoes

  • Tephra = ash ejected into the atmosphere
  • Volcanic Bombs = large particles thrown out of a volcano
  • Pyroclastic Flow = Very hot (over 800 C) mixture of gas and tephra which travels at speeds up to 700km/hr
  • Lava Flows = lava, rarely causes injury to people due to low velocity
  • Volcanic Gases = e.g. Carbon dioxide, sulphur dioxide. In 1986, Carbon Dioxide emissions from Nyos killed 1700 people
• Secondary Effects of Volcanoes

  • Lahars = Unconsolidated ash which combines with water to form a mud flow; Colombia in 1985, mudflow killed a quarter of the 28,700 population
  • Flooding = Explosions can melt glaciers
  • Landslides = Can range in size, the high velocity allows them to cross valleys
  • Tsunami = Sea waves generated from volcanic eruptions. Krakatoa in 1883 caused a tsunami killing 36,000
  • Acid Rain = Volcanoes emit sulfur which combines with moisture to form acid rain
• Mitigating Volcanic Impacts

  • Risk assessments are carried out to provide a series of alerts
  • Once viscous lava flows, digging trenches may be able to divert it from the built environment
  • In 1973, people in Iceland poured seawater on a lava flow to solidify it before it cut off fishing ports
  • In Hawaii, barriers are built to protect from lava flows and lahars
• Adapting to Volcanoes

  • Moving away from them
  • In Congo, farmers returned from evacuating and had to change the crops they cultivated, and in some cases this increased income