Volcanoes and Plate Tectonics

Volcanoes Volcanoes and and

Plate TectonicsPlate TectonicsSection 1- Pages 88-91Section 1- Pages 88-91

1- Where are volcanoes found?1- Where are volcanoes found? Most volcanoes occur at plate Most volcanoes occur at plate

boundaries. boundaries. Either divergent boundaries like the Either divergent boundaries like the

mid-ocean ridge, mid-ocean ridge, Or…Or…

Convergent boundaries where Convergent boundaries where subduction occurssubduction occurs

2- How do volcanoes form at 2- How do volcanoes form at divergent plate boundaries?divergent plate boundaries?

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

3- How do volcanoes form at convergent 3- How do volcanoes form at convergent boundaries? 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 Plumes of magma rise from deep in the mantle and melts through the the mantle and melts through the crust creating volcanoes in the crust creating volcanoes in the middle of plates. middle of plates.

Lo`ihi Seamount is Lo`ihi Seamount is an active volcano an active volcano built on the seafloor built on the seafloor south of Kilauea south of Kilauea about 30 km from about 30 km from shore. The seamount shore. The seamount rises to 969 m below rises to 969 m below sea level and sea level and generates frequent generates frequent earthquake swarms, earthquake swarms, the most intense of the most intense of which occurred in which occurred in 1996.1996.

Volcanic Activity Volcanic Activity

Section 2- Pages 93-102Section 2- Pages 93-102

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

Molten material rises forcing its way Molten material rises forcing its way through the crust. through the crust.

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

2- Describe the characteristics of magma.

Magma is hot molten rock and Magma is hot molten rock and dissolved gasses. dissolved gasses.

Magma could either be thick and flow Magma could either be thick and flow slowly or thin and flow quickly. slowly or thin and flow quickly.

Depends on the amount of gasses, Depends on the amount of gasses, temperature, water and silica in the temperature, water and silica in the magma.magma.

3- Compare/Contrast magma with HIGH silica content and magma with

LOW silica content.Magma with Magma with HIGHHIGH silica content silica content

makes the magma thicker and makes the magma thicker and clumpy, clumpy,

But… But… Magma with Magma with LOWLOW silica content is silica content is

thin and runny.thin and runny.

4- Describe a QUIET eruption, and 4- Describe a QUIET eruption, and explain the lava.explain the lava.

A quiet eruption has lava that is thin A quiet eruption has lava that is thin and runny and flows out easily. and runny and flows out easily.

It can create very long lava flows.It can create very long lava flows. Can create Pahoehoe or aa.Can create Pahoehoe or aa. http://www.youtube.com/watch?v=488BkTUsMa4

5- Describe an EXPLOSIVE 5- Describe an EXPLOSIVE eruption, and explain the lava.eruption, and explain the lava.

An explosive eruption is when the very An explosive eruption is when the very thick and sticky magma causes the pipe to thick and sticky magma causes the pipe to clog up and the volcano to explode due to clog up and the volcano to explode due to the huge amount of pressure.the huge amount of pressure.

AshAsh- fine grain size rock, - fine grain size rock, cinderscinders- smaller - smaller than a baseball, and than a baseball, and bombsbombs- larger than a - larger than a baseball are thrown from the eruption along baseball are thrown from the eruption along with the release of gases. (pyroclastic flow)with the release of gases. (pyroclastic flow)

http://www.youtube.com/watch?v=EupnfA-PDaw explosive eruptions explosive eruptions http://www.youtube.com/watch?v=Cvjwt9nnwXY pyroclastic flow pyroclastic flow

6- How do geologists monitor 6- How do geologists monitor volcanoes?volcanoes?

They use similar devices that are used They use similar devices that are used to monitor faults because small to monitor faults because small earthquakes occur before an eruption.earthquakes occur before an eruption.

Geologists also monitor ground water Geologists also monitor ground water temperatures. An increase in temperatures. An increase in temperature indicates magma moving temperature indicates magma moving into the magma chamber.into the magma chamber.

7- What are some hazards of volcanic 7- What are some hazards of volcanic eruptions?eruptions?

During a quiet eruption, lava can set fires and During a quiet eruption, lava can set fires and bury everything in its path.bury everything in its path.

During an explosive eruption, hot and During an explosive eruption, hot and poisonous gas clouds can be emitted. Ash and poisonous gas clouds can be emitted. Ash and cinders can also cover an enormous area.cinders can also cover an enormous area.

Eruptions can also cause landslides which can Eruptions can also cause landslides which can cause a lot of damage over a very large area.cause a lot of damage over a very large area.

http://www.youtube.com/watch?v=4aYQixhdWY4 (Top 10 Most Active Volcanoes)(Top 10 Most Active Volcanoes)