Tectonic Hazards

Question 1

What is the structure of the Earth?

Answer 1

Crust, mantle, outer core and inner core.

Question 2

What is the continental crust?

Answer 2

It is 20 - 200km thick and is made up of granite. It is less dense than oceanic crust and is up to 3.8 billion years old.

Question 3

What is the oceanic crust?

Answer 3

It is 5 - 10km in thickness and is mainly made of basalt making it very dense. It is less than 200 million years old.

Question 4

What makes up the lithosphere?

Answer 4

The crust and upper (rigid) part of the mantle. It is around 100km thick and is solid and brittle.

Question 5

What is the lithosphere divided into?

Answer 5

It is divided into sections called tectonic plates. The oceanic lithosphere is topped by oceanic crust and the continental lithosphere is topped by continental crust.

Question 6

What is the asthenosphere?

Answer 6

It is the section of the Earth’s mantle beneath the lithosphere and is 100 - 400km deep.

Question 7

What are the properties of the asthenosphere?

Answer 7

It is solid but ductile and temperatures reach 1300°C.

Question 8

What is the mantle?

Answer 8

The area beneath the Earth’s crust which is made of solid material but can flow slowly. The lower mantle is hotter and denser.

Question 9

What is the outer core?

Answer 9

It is made up of liquid iron and nickel.

Question 10

What is the inner core?

Answer 10

A solid mass of iron and nickel and reaches temperatures of 5500°C.

Question 11

What is plate tectonics theory?

Answer 11

That the Earth’s lithosphere (outer shell) is divided into 7 large tectonic plates that form today’s continents. However, the Earth once had a supercontinent called Pangea that broke up due to continental drift.

Question 12

What is evidence for plate tectonic theory?

Answer 12

• Same types of fossiled plants are found in both South America and Africa
• Continents match up like a jigsaw puzzle.

Question 13

Why do convection currents cause tectonic plates to move?

Answer 13

The outer core heats up the magma in the mantle. As the semi - molten rock is heated, it becomes less dense and rises upwards. Once it cools, it becomes more dense and sinks to the bottom. The plates which lie on top are pushed and pulled by these convection currents.

Question 14

How does ridge push cause plate movement?

Answer 14

Newly formed plates at oceanic ridges (constructive plate margins) are warmer and less dense so they rise. As it cools, it becomes denser and gravity cause the plate and others to slide away from the ridge.

Question 15

Why does slab pull cause plates to move?

Answer 15

This is the most likely explanation for plate movement. At destructive plate margins, the oceanic plate subducts into the mantle (as it is denser and under the influence of gravity). This pulls the rest of the plate with it.

Question 16

Where do tectonic hazards tend to take place?

Answer 16

• Earthquakes and volcanoes tend to occur on plate margins such as the Pacific Ring of Fire
• Volcanoes can also occur at hotspots (where the crust is thin)

Question 17

Why do earthquakes and volcanoes occur along plate margins?

Answer 17

Plate movements cause vibration that triggers earthquakes. Volcanoes occur at plate margins because magma feeds volcanoes and this magma can reach the surface or certain plate margins.

Question 18

What is a constructive or divergent plate boundary and what does it cause?

Answer 18

When plates move away from each other which creates huge fractures in the land causing rift valleys and ocean ridges to form.

Question 19

What type of volcano is formed at constructive plate boundaries?

Answer 19

As the plates separate, magma rises in between the gap and lava then pours onto the surface creating volcanoes. This lava is runny and free flowing forming shield volcanoes.

Question 20

What else occurs at constructive plate boundaries?

Answer 20

Earthquakes can occur as plates shake and vibrate as they move apart. When new land is formed on the ocean floor it is known as sea floor spreading. Furthermore, when lava cools it forms rock that can build up and form islands such as Iceland.

Question 21

Name some examples of constructive plate boundaries.

Answer 21

The Atlantic Ocean, Mid-Atlantic Ridge and the Eurasian and North American plates.

Question 22

Where can divergent boundaries occur?

Answer 22

On continental and oceanic crust.

Question 23

What is a destructive or convergent plate boundary?

Answer 23

When tectonic plates move towards each other.

Question 25

What happens at an oceanic-continental destructive plate margin?

Answer 25

The denser oceanic plate subducts beneath the continental crust. This leaves a deep ocean trench.

Question 26

How do earthquakes and volcanoes occur at an oceanic-continental plate boundary?

Answer 26

Due to friction of the two plates, pressure builds up resulting in strong earthquakes.

The oceanic crust is melted as it is pulled deeper into the mantle creating magma. Magma rises through the lithosphere and pushes though the crust causing volcanic eruptions.

Question 27

What happens at oceanic-oceanic crust destructive plate margins?

Answer 27

When two oceanic plates converge, the older plate subducts because as oceanic plates age they become colder and denser. This can result in the creation of islands such as the Caribbean and oceanic trenches.

Question 28

What occurs when two continental plates converge?

Answer 28

The crust is crumpled upwards by the pressure building between the two plates creating fold mountains.

Question 29

Give an example of two continental plates converging.

Answer 29

The Indian and the Eurasian Plate which formed the Himalayas.