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Volcanoes and Plate Tectonics. Section 1- Pages 88-91. 1- Where are volcanoes found?. Most volcanoes occur at plate boundaries. Either divergent boundaries like the mid-ocean ridge, Or… Convergent boundaries where subduction occurs.

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volcanoes and plate tectonics

Volcanoes and Plate Tectonics

Section 1- Pages 88-91

1 where are volcanoes found
1- Where are volcanoes found?
  • Most volcanoes occur at plate boundaries.
  • Either divergent boundaries like the mid-ocean ridge,


  • Convergent boundaries where subduction occurs
2 how do volcanoes form at divergent plate boundaries
2- How do volcanoes form at divergent plate boundaries?

As the plates move away from each other, lava pours out the cracks creating volcanoes.

3 how do volcanoes form at convergent boundaries
3- How do volcanoes form at convergent boundaries?
  • When two plates collide, a subduction zone is created.
  • As the older more dense plate sinks below the less dense plate, the material melts as it heats up.
  • As it heats up, it rises because it becomes less dense.
  • The magma finds its way through cracks in the crust and creates volcanoes.
4 how do hot spot volcanoes form
4- How do hot spot volcanoes form?

Plumes of magma rise from deep in the mantle and melts through the crust creating volcanoes in the middle of plates.


Lo`ihi Seamount is an active volcano built on the seafloor south of Kilauea about 30 km from shore. The seamount rises to 969 m below sea level and generates frequent earthquake swarms, the most intense of which occurred in 1996.

volcanic activity
Volcanic Activity

Section 2- Pages 93-102

1 explain how a volcano erupts
1- Explain how a volcano erupts.

Molten material rises forcing its way through the crust.

As pressure increases eventually the magma reaches the surface causing the eruption of lava and gases.

2 describe the characteristics of magma
2- Describe the characteristics of magma.
  • Magma is hot molten rock and dissolved gasses.
  • Magma could either be thick and flow slowly or thin and flow quickly.
  • Depends on the amount of gasses, temperature, water and silica in the magma.
3 compare contrast magma with high silica content and magma with low silica content
3- Compare/Contrast magma with HIGH silica content and magma with LOW silica content.

Magma with HIGH silica content makes the magma thicker and clumpy,


Magma with LOW silica content is thin and runny.

4 describe a quiet eruption and explain the lava
4- Describe a QUIET eruption, and explain the lava.
  • A quiet eruption has lava that is thin and runny and flows out easily.
  • It can create very long lava flows.
  • Can create Pahoehoe or aa.
  • http://www.youtube.com/watch?v=488BkTUsMa4
5 describe an explosive eruption and explain the lava
5- Describe an EXPLOSIVE eruption, and explain the lava.
  • An explosive eruption is when the very thick and sticky magma causes the pipe to clog up and the volcano to explode due to the huge amount of pressure.
  • Ash- fine grain size rock, cinders- smaller than a baseball, and bombs- larger than a baseball are thrown from the eruption along with the release of gases. (pyroclastic flow)
  • http://www.youtube.com/watch?v=EupnfA-PDaw explosive eruptions
  • http://www.youtube.com/watch?v=Cvjwt9nnwXYpyroclastic flow
6 how do geologists monitor volcanoes
6- How do geologists monitor volcanoes?
  • They use similar devices that are used to monitor faults because small earthquakes occur before an eruption.
  • Geologists also monitor ground water temperatures. An increase in temperature indicates magma moving into the magma chamber.
7 what are some hazards of volcanic eruptions
7- What are some hazards of volcanic eruptions?
  • During a quiet eruption, lava can set fires and bury everything in its path.
  • During an explosive eruption, hot and poisonous gas clouds can be emitted. Ash and cinders can also cover an enormous area.
  • Eruptions can also cause landslides which can cause a lot of damage over a very large area.
  • http://www.youtube.com/watch?v=4aYQixhdWY4
  • (Top 10 Most Active Volcanoes)