Tectonics

Question 1

What is a natural hazard?

Answer 1

A naturally occurring process or event that has the potential to affect people.

Question 2

What is a natural disaster?

Answer 2

A major natural hazard that causes significant social, environmental and economic damage.

Question 3

What does vulnerability mean?

Answer 3

The ability to anticipate, cope with, resist and recover from a natural hazard.

Question 4

3 facts about the Nepal earthquake
(magnitude, when, where)

Answer 4

7.8 magnitude
April 2015
80 km northwest of Kathmandu

Question 5

How many people were killed, injured and left homeless after the Nepal earthquake?

Answer 5

8633 killed
21000 injured
3 million homeless

Question 6

What benefit did the time of the N earthquake have?

Answer 6

It was at midday, when most people were act work (in the fields) which reduced the death toll.

Question 7

Why is Nepal vulnerable? (economically)

Answer 7

It’s one of the world’s poorest (in 2016, it was 197th in a world ranking of GDP per capita, out of 229 countries), so the Nepalese were unprepared for the earthquake.

Question 8

True or False
Infrastructure (such as roads, bridges and safe water supplies) was severely damaged or destroyed in the area of the earthquake.

Answer 8

True
Much of the infrastructure was weak and poorly constructed.

Question 9

How many aftershocks did Nepal experience? What effect did they have?

Answer 9

Over 100 which caused further destruction and deaths and made the rescue work very dangerous.

Question 10

What mountain range is in Nepal? What effect did this have?

Answer 10

Himalayas - the earthquake created landslides, which devastated many rural areas and cut them off. This made rescue and aid efforts very difficult.

Question 11

Why did Nepal rely on international aid agencies for help?

Answer 11

The emergency services were not able to cope with the level of destruction.

Question 12

What effect did the Nepal earthquake have on the tourism industry?

Answer 12

It fell significantly after the earthquake - causing the loss of much needed income.

Question 13

How much money did Nepal’s economy lose after the earthquake?

Answer 13

US$5 billion - about 25% of its GDP.

Question 14

How much money was needed for rebuilding work in Nepal?

Answer 14

US$6.6 billion

Question 15

What are the key characteristics of the inner core?

Answer 15

Hottest part - 6000°C
Solid
Mostly consists of iron

Question 16

What are the key characteristics of the outer core?

Answer 16

Semi-molten
Mostly consists of liquid iron and nickel
Temperatures between 4500-6000°C

Question 17

What are the key characteristics of the mantle?

Answer 17

Widest layer making up the Earth
The upper part is solid, but below it the rock is semi-molten Forms the asthenosphere

Question 18

What are the key characteristics of the crust?

Answer 18

Oceanic – a thin, dense layer (6-10 km thick), which lines the ocean floors.
Continental – an older, thicker layer (45-50 km thick), which makes up the Earth’s landmasses. It is less dense.

Question 19

What is the lithosphere?

Answer 19

Made up of the crust and upper mantle – the
solid layer from which tectonic plates are formed.

Question 20

What are tectonic plates?

Answer 20

Large, irregularly shaped slabs of solid rock that vary greatly in size and move slowly.
They move relative to each other over the asthenosphere which caused volcanic eruptions and earthquakes.

Question 21

Explain mantle convection

Answer 21

Heat produced by the decay of radioactive elements in the Earth’s core heats the lower mantle - creating convection currents. These hot, liquid magma currents are thought to move in circles in the asthenosphere – causing the plates to move.

Question 22

Explain slab pull

Answer 22

Newly formed oceanic crust at mid-ocean ridges becomes denser and thicker as it cools. This causes it to sink into the mantle under its own weight – pulling the rest of the plate
further down with it.

Question 23

Explain subduction

Answer 23

As two oceanic plates (or an oceanic plate and a continental
plate) move towards each other, one slides under the other into the mantle – where it melts in an area known as a subduction zone.

Question 24

Explain seafloor spreading

Answer 24

In the middle of many oceans are huge mid-ocean ridges, or underwater mountain ranges. These are formed when hot magma (molten rock) is forced up from the asthenosphere and hardens – forming new oceanic crust. This new crust pushes the tectonic plates apart.

Question 25

What is paleomagnetism?

Answer 25

The study of past changes in the Earth’s magnetic field (determined from rocks, sediment or archaeological
records).

Question 26

What are plate margins?

Answer 26

The areas adjacent to plate boundaries.
Includes areas either side of the boundary that may be
affected by movement, e.g. an earthquake focus that is
quite far underground may be some distance away from
the surface boundary.

Question 27

How are convergent (destructive) margins formed?

Answer 27

When two plate collide.

Question 28

How are divergent (constructive) margins formed?

Answer 28

When two plates move apart.

Question 29

How are conservative (transform) margins formed?

Answer 29

When two plates slide past each other.

Question 30

Why does oceanic plate slide under continental plate when they collide?

Answer 30

It is denser.

Question 31

What do deep ocean trenches mark?

Answer 31

The place where the oceanic plate starts to sink beneath the continental plate.

Question 32

How are fold mountains formed?

Answer 32

As the two plates collide, the continental plate is folded and slowly pushed up.

Question 33

What is the Benioff Zone?

Answer 33

The area where the friction created between the colliding plates causes intermediate and deep earthquakes.

Question 34

How are volcanic eruptions generated on a destructive plate margin?

Answer 34

As magma created by the melting oceanic plate pushes up through faults in the continental crust to reach the surface.

Question 35

What are island arcs?

Answer 35

Volcanoes rise above sea level to form separate island volcanoes, which are usually found in curved lines.

Question 36

What caused the 2004 Indian Ocean tsunami?

Answer 36

An earthquake that occurred when two oceanic plates collided.

Question 37

Which plate is subducted when 2 continental plates meet?

Answer 37

As both plates have about the same density, and are less dense than the asthenosphere beneath them, neither plate is actually subducted.

Question 38

What natural hazards occur when 2 continental plate meet?

Answer 38

There is no volcanic activity, but any earthquakes are likely to have a shallow focus – increasing their severity.

Question 39

What are mid-ocean ridges?

Answer 39

Underwater mountains extend for over 60 000 km across the world’s ocean floors.

Question 40

What type of earthquakes occur at constructive plate margins?

Answer 40

Shallow-focus earthquakes occur, but they pose little risk to humans because the shocks are minor and occur underwater.

Question 41

What are rift valleys?

Answer 41

When plates move apart on continents, the crust stretches and breaks into sets of parallel cracks. The land between these faults then collapses, forming steep-sided valleys.

Question 42

What causes earthquakes at conservative plate margins?

Answer 42

The two plates sometimes stick as they move past each other, causing stress and pressure to build up, which is suddenly released as a strong shallow-focus earthquake.

Question 43

What are seismic waves?

Answer 43

Earthquake’s energy is released as seismic waves that radiate out from the focus.

Question 44

What percentage of earthquakes occur on plate margins?

Answer 44

95%

Question 45

How are seismic waves measured?

Answer 45

Using a seismometer, which detects and measures ground movement.