Hazards 3 Volcanic Hazards

Nature and Distribution:

• Ocean Ridges:
  • Plates are moving apart and magma is moving to the surface
  • Gentle sloped sides because the basaltic lava has a low viscosity 
  • Eruptions are frequent but a relatively effusive
  • e.g. Eyjafjallajökull, Iceland, on the Mid-Atlantic Ridge
• Subduction Zones:
  • e.g. the Ring Of Fire in the Pacific Ocean

Primary Impacts:

• tephra: solid material of varying in grain size ranging from volcanic bombs to ash, all ejected into the atmosphere
• Nuées ardentes: very hot, gas charged, high-velocity flows made up of a mixture of gas and tephra. These usually hug the ground and flow down the sides of a volcano
• Lava flows: 
• Volcanic gases: these include carbon dioxide, carbon monoxide, hydrogen sulphide, sulphur dioxide and chlorine

Secondary Effects:

• Lahars: melted snow and ice as a result of the volcanic ash forms mud flows that can move down the course of the river valley at high speeds
• Flooding: when an eruption melts glaciers and ice caps, serious flooding can occur
• Volcanic landslides:
• Tsunamis: sea wave generated by violent volcanic eruptions
• Acid rain: volcanoes emit gases including sulphur, when this mixes with atmospheric moisture, acid rain can form
• Climatic Change: the ejection of huge amounts of volcanic debris into the atmosphere can reduce global temperatures and is believed to have been an agent in past climatic…