Gr 7 Volcanoes

• What makes a volcanoes active?

  Volcanoes that are erupting or that are expected to erupt in the near future
• Active volcanoes are volcanoes that are known to have erupted
• Most of these volcanoes occur in areas close to plate margins
• When Earth's crust moves, it disturbs the mantle and the crust, which results in a volcano or earthquake
• What causes Volcanoes ?

  1. Tectonic plates move apart

  2. Magma pushes through vents and fissures in the Earth's surface

  3. Volcanic eruption occurs
• Volcanoes caused by tectonic plates moving together

  1. One tectonic plate slides under another

  2. Melting plate works its way through Earth's crust

  3. Erupts as a volcano
• What is a Vent?

  Hole through which magma flows
• Explain what a Fissure is.

  Crack through which magma flows
• what is Magma?

  Thick flowing substance in the Earth's mantle
• Lava

  Magma that has erupted
• Batholiths

  Huge pools of magma that cool and solidify underground, later exposed on the Earth's surface as domes
• What volcanoes can erupt

  • Bombs
  • Ash
  • Cinders
  • Lava
• Eruptions can be violent, explosive and quick, or they can be gentler and happen over a period of many months
• Lava flows can cover land, farms, roads and settlements for hundreds of kilometres
• If lava flows into the sea, it cools quickly to form new land
• Shield volcanoes have gentle slopes and are built up by fluid basaltic lava flows that spread out over long distances.
• Volcanoes are classified based on their shape or type of activity as shield volcanoes, composite (stratovolcano) volcanoes, cinder cone volcanoes, lava domes, and calderas.
• A volcanic eruption is the release of magma, ash, rock fragments, hot gases, and other materials from a volcano.
• Stratovolcanoes (also called composite volcanoes) build up steep-sided mountains with alternating layers of ash, pumice and hardened lava. They often have craters at their summits.
• The most common type of stratovolcano is found along subduction zones where tectonic plates collide.
• Composite volcanoes are steep-sided mountains with alternating layers of ash, pumice, rock fragments, and hardened lava. They often have craters at the summit where steam and gases escape from underground magma chambers. Eg Mnt
• Explosive eruptions occur when gas bubbles in molten rock expand rapidly due to pressure changes, causing the rock to shatter and explode violently.
• Cinder cones are small, simple volcanoes formed when viscous lava explodes violently during an eruption, sending molten material high into the air.
• Cinder cones are small volcanoes made mostly of loose rocks ejected during an explosive eruption. Less dangerous. Eg parachutin
• Positives of volcanoes


  • Tourist attractions
  • Lava contains valuable minerals
  • Volcanic ash is very fertile
  • Underground water in volcanic areas can be hot & used to generate electricity
• Negatives of volcanoes


  • Dust can block sunlight & increase rainfall
  • Ash & volcanic lava bombs are dangerous
  • Ash can cover tons
  • Lava can destroy crops & infrastructure
  • People's health suffers from breathing in gases
  • Lava can destroy vegetation
  • Mudflows can kill living things
• Volcanoes can have both positive and negative impacts
• Tourist attractions

  Volcanoes can be popular destinations for tourists due to their unique and awe-inspiring landscapes. Some volcanoes even allow for guided tours, where visitors can hike to the summit and observe the volcanic activity up close.
• Lava contains valuable minerals

  When volcanoes erupt, they can bring valuable minerals to the surface, such as gold, silver, and copper. These minerals can then be extracted and used for various purposes, including jewelry-making and electronics production.
• Underground water in volcanic areas can be hot & used to generate electricity

  In some volcanic areas, underground water can become heated by the magma beneath the surface. This hot water can then be used to generate electricity through a process called geothermal power. This is a clean and renewable source of energy that can help reduce our reliance on fossil fuels.
• Volcanic ash is very fertile

  Volcanic ash is rich in nutrients, such as potassium, phosphorus, and calcium, which are essential for plant growth. This makes volcanic soil extremely fertile, which can lead to increased crop yields and healthier plants.
• How many active volcanoes are there in the world?

  There are about 1 500 active volcanoes in the world