Restless Earth - Theory

Question 1

Describe the continental crust.

Answer 1

The continental crust is up to 70km thick and is composed of granite.

Question 2

Describe the oceanic crust.

Answer 2

The oceanic crust is between 6 and 8km thick and is composed of basalt.

Question 3

Describe the asthenosphere.

Answer 3

The asthenosphere is partially molten and is between 900 and 1600 degrees centigrade. It is composed primarily of peridotite.

Question 4

Describe the mantle.

Answer 4

The mantle is solid and composed of peridotite. It is between 1600 and 4000 degrees centigrade.

Question 5

Describe the outer core.

Answer 5

The outer core is liquid and composed of iron and nickel. It is between 4000 and 5000 degrees centigrade.

Question 6

Why is the outer core liquid but the inner core solid?

Answer 6

The inner core is so deep and under huge pressure which keeps it solid. The outer core is liquid because it is under less pressure.

Question 7

In what order are the Earth’s layers found in?

Answer 7

1) The crust
2) The asthenosphere
3) The mantle
4) The outer core
5) The inner core

Question 8

Describe how the tectonic plates are moved.

Answer 8

As heat rises from the core, it creates convection currents in the outer core and mantle. When they near the asthenosphere they plateau and begin to lose heat and begin to drop back down. This creates a series of rotating cells as magma is cooled and warmed up in a cycle. These currents are strong enough to move the tectonic plates resting on the asthenosphere.

Question 9

What is the engine of plate tectonics?

Answer 9

Radioactive decay

Question 10

How many types of plate boundary are there?

Answer 10

4

Question 11

Describe a destructive plate boundary.

Answer 11

A destructive plate boundary is where the continental and oceanic crust collide. The oceanic crust is subducted as it is denser than the continental crust.

Question 12

What risks are present at destructive plate boundaries?

Answer 12

• Very destructive earthquakes

* Very explosive composite volcanoes

Question 13

What is a constructive boundary?

Answer 13

A constructive boundary is where rising convection currents move two plates apart and form new land.

Question 14

What risks are present at constructive plate boundaries?

Answer 14

• Small earthquakes

* Not very explosive shield volcanoes

Question 15

What is a conservative plate boundary?

Answer 15

A conservative plate boundary is where two plates slide past eachother.

Question 16

What risk is present at conservative plate boundaries?

Answer 16

Destructive earthquakes.

Question 17

What is a collision plate boundary?

Answer 17

A collision plate boundary is where two continental plates collide.

Question 18

What are the risks present at a collision plate boundary?

Answer 18

• Destructive earthquakes
• Landslides
• Rare volcanoes

Question 19

What are the characteristics of shield volcanoes?

Answer 19

• Gentle, sloping sides
• Wide base
• Basaltic lava
• Frequent but not violent eruptions

Question 20

How are shield volcanoes formed?

Answer 20

Magma is released into the sea at constructive boundaries and is diluted. This makes it thin and runny so it flows a long way before solidifying.

Question 21

What are the characteristics of a composite volcano?

Answer 21

• Steep sides
• Narrow base
• Andesitic lava
• Infrequent but violent eruptions

Question 22

How are composite volcanoes formed?

Answer 22

They are formed by eruptions of viscous, sticky lava and ash at destructive boundaries. The lava and ash doesn’t travel far.

Question 23

What are the two types of crust?

Answer 23

Continental and Oceanic

Question 24

What are the three warning signs of a volcanic eruption?

Answer 24

• Hundreds of small earthquakes as magma rushed through cracks in crust
• Temperatures around the volcano rise
• Gases begin to be released

Question 25

How can we monitor earthquakes before a volcanic eruption?

Answer 25

By using seismometers

Question 26

How can we monitor temperature rises before a volcanic eruption?

Answer 26

Thermal imaging and satellite cameras.

Question 27

How can we monitor gases being released before an eruption?

Answer 27

By using gas samples and chemical sensors.

Question 28

What should be in place in case of an eruption?

Answer 28

A detailed plan which everyone who could be affected needs to be aware of.

Question 29

What should be included when planning for an eruption?

Answer 29

• An exclusion zone
• Evacuation routes
• Emergency supplies of basic provisions
• Emergency funds to be set aside
• An effective communication system

Question 30

What are the three warning signs of an earthquake?

Answer 30

• Smaller plate movement
• Vibrations in the Earth’s crust
• Radon gas escapes through cracks in the crust

Question 31

How can we monitor the smaller plate movement before an earthquake?

Answer 31

By using laser beams.

Question 32

How can we monitor vibrations in the Earth’s crust before an eruption?

Answer 32

By using seismometers.

Question 33

How can we monitor Radon gas levels before an earthquake?

Answer 33

By using gas samples.

Question 34

How can we plan for an earthquake?

Answer 34

• Training those who could be affected via TV or radio
• Putting together emergency kits including first aid, blankets and tinned food.
• Earthquake-proofing buildings.
• Earthquake-proofing roads and bridges.

Question 35

Give one example of how a building can be earthquake-proofed. Where is it used?

Answer 35

Dampers can be added to roofs and act like pendulums to reduce swaying action. This is commonly used in Japan.