Chapter 2 - Tectonic Hazards

Question 1

What’s a tectonic hazard

Answer 1

Such as earthquakes or tsunamis which involve the movement of tectonic plates in the earths crust

Question 2

Tell me the order of the earths internal surface starting from the surface

Answer 2

Crust, asthenosphere, mantle, outer core, inner core

The Earths internal structure is divided into layers

Question 3

Tell me about the core

Answer 3

It’s extremely hot and under a lot of pressure

The inner core is solid

The outer core is liquid

Question 4

Tell me about the mantle

Answer 4

It surrounds the core and is made of solid material that can flow very slowly, the upper portion of the mantle is weak
- the ASTHENOSPHERE - which can deform like plastic

Question 5

Tell me about the crust

Answer 5

It’s very thin compared to the thickness of the mantle and core

Question 6

Tell me the 2 types of crust

Answer 6

Continental crust and oceanic crust

Question 7

Compare the 2 types of crust

Answer 7

They differ in chemical composition, thickness and density
Oceanic crust is thinner but denser than continental

Oceanic is younger and can be recycled at destructive plate margins whereas continental is not destroyed

Question 8

What’s the lithosphere

Answer 8

The crust and upper mantle are chemically different but together form a rigid shell as the surface of the earth

It’s broken into several major fragments which move very slowly over the upper mantle

Question 9

How can the movement of plates be tracked

Answer 9

They can be tracked from space using GPS

Question 10

What’s a plate Margin

Answer 10

Where 2 plates meet

Question 11

What are the 3 types of plate margin and what do they mean

Answer 11

They describe the different ways the plates are moving

There constructive, destructive and conservative plate margins

Question 12

How do the tectonic plates lead to earthquakes

Answer 12

The interaction between the different tectonic plates and the mantle beneath leads to triggering of earthquakes and volcanic activity

Question 13

What’s convection

Answer 13

A THEORy of how plates move

The cores temperature is around 6000 C - this caused magma to rise to the mantle and sink towards the core when it cools

The currents flow beneath the lithosphere - building up lateral pressure and carrying the plates with them

However only limited evidence has been found so far of convection currents

Question 14

What’s ridge push and slab pull

Answer 14

Another theory for the movement of plates

At constructive margins- ocean ridges form high about the ocean floor and below the mantle melts - the molten magma rises as the plates pull apart and cool down to form new plague material

As the lithosphere cools, it becomes denser and starts to slide down away from the ridge which causes plages to move away from eachother - this is ridge push

At destructive margins the denser plate sinks back into the Mantle Under the influence of gravity which pulls the rest of the plate along behind it - this is slab pull

Question 15

Where are earthquakes found

Answer 15

Found at all three types of plate margins

Found in land and sea

Question 16

Where are volcanoes found

Answer 16

Only at constructive and destructive plate margins

Found in both land and sea

Question 17

What are hot spots

Answer 17

Some earthquakes and volcanos occur in the middle of plates and these are known as hoy spots

It’s where the crust is through to be particularly thin

Question 18

How do plates move at constructive margins

Answer 18

The margins occur when tectonic plates move apart from each other - most move a few cm a year

Question 19

Tell me the way the plates move and why earthquakes are found on constructive plate margins

Answer 19

The upper part of the mantle melts and hot magma rises

As the tectonic plates are moved away from each other by slab pull, ridge push or a combination. The molten magma rises in between and cools down to form solid rock - this forms part of an oceanic plate, the new solid plate sometimes fractures as it is moved- causing earthquakes, usually small and not violent

Question 20

How are volcanos formed on constructive plate margins

Answer 20

Volcanoes form as much of the magma never reaches the surface but it’s buoyant enough to push up the crust as the margins to form ridge and rift features

In a few places the magma erupts on to the surface producing a lava that is funny and spreads out before solidifying - over many eruptions a volcano that has typically a wide base and gentle slopes known as a shield volcano is formed

Question 21

What forms when constructive plate margins move on land

Answer 21

A Rift Valley, where the land drops as the plates move apart

The strain put on the land as the tectonic plates move away from each other is splitting countries such as Iceland in two and causes cracks of faults to form on either side. So for example 100s of small earthquakes occur on Iceland on a weekly basis

Question 22

How do plates move at destructive margins

Answer 22

Occur when tectonic plates move towards each other and collide. The effect this has depends on what kinds of plates are colliding

If 2 continental plates collide, they are both buoyant and so cannot sink into the mantle. As a result, compression forces the plates to collide and form and mountains

If an oceanic plate and continental plate move towards each other, the denser oceanic plate is subducted and sinks under the continental plate and into the earths mantle where it’s recycled, earthquakes, fold mountains and volcanoes occur

Question 23

Why are earthquakes found at destructive plate margins

Answer 23

The pressure and strain of an oceanic and continental plate moving towards each other can cause the earths crust to crumple and form fold mountains, as the plates converge, pressure builds up and the rocks eventually fracture causing an earthquake

Question 24

Why are volcanoes found at destructive plate margins

Answer 24

As the oceanic plate sinks deeper into the mantle, it causes part of the mantle to mantle. Hot magma rises up through the overlying mantle and lithosphere, and some can eventually erupt out at the surface producing a linear belt of volcanoes. The magma becomes increasingly viscous as it rises to the surface. Producing composite volcanoes which are steep sided and have violent eruptions

Question 25

When does a deep ocean trench form

Answer 25

At a destructive plate margin, The oceanic plate as the denser of the 2 plates is subducted or pulled down into the mantle beneath the lighter and thicker continental plate under gravity. At the surface this creates a deep ocean trench

Question 26

Tell me about Japan’s earthquakes/ volcanoes

Answer 26

It’s prone to earthquakes and volcanic eruptions, it’s has 118 active volcanoes

There are so many Becuase Japan lies on the margin of four plates

Many parts of Japan also experience earthquakes due to pressure built up in the plates as they move at this destructive plate margin

Question 27

How do plates move at conservative margins

Answer 27

Occur when tectonic plates move parallel to each other, the 2 plates can move side by side- either in the same direction but at different speeds or simply in the opposite direction to one another

Question 28

Why are earthquakes found at conservative plate margins

Answer 28

One theory is that pressure builds up at the margin of the tectonic plates as they are pulled along behind a plate being subducted elsewhere

As the plates move past eachother, friction causes them to become stuck

Pressure builds up and up until the rock fractures in an earthquake

Question 29

Why are volcanoes not formed at conservative plate margins

Answer 29

As magma can’t rise to fill a gap as there is no gap created between the tectonic plates and therefore no new land is formed or destroyed Becuase there is no tectonic plate subducted into the mantle

Question 30

What was the largest earthquake ever

Answer 30

It was recorded in chile and was 9.5 on Richter scale in 1960

Question 31

What’s geothermal energy

Answer 31

In volcanically active areas, it’s a major source of electrical power - steam is heated by hot magma in permeable magma, then boreholes are drilled into the Rock to harness the super heated steam to turn turbines at power stations - it’s renewable

So people live in hazardous areas as they produce geothermal energy

Question 32

Why do people live in hazardous areas for farming

Answer 32

Lava and ash eruptions can kill livestock and destroy crops and vegetation, after thousands of years weathering of this lava releases minerals and leaves extremely fertile soil rich in nutrients, land can be farmed to provide food and income

Question 33

Why do people live in hazardous areas for mining

Answer 33

Not just dormant and extinct volcanoes that are mines but active ones too

It’s very dangerous:
Miners can afford little protective clothing
In last 40 years, 74 miners have died from fumes in volcanoes

Sulphur is produced and sold sometimes 100kg are carried up and down the rocky and slippery mountain paths

Miners can earn an average of $6 a day more than a coffee plantation so miners continue to live and work in dangerous areas

Question 34

Why do people live in hazardous areas for tourism

Answer 34

Tourists visit volcanoes for the views, hot springs and adventure

More than 100 million people visit volcanic sites every year

The revenue they generate benefits that locals and the countries they are in

Question 35

Why do people live in hazardous areas for family, friends and feelings

Answer 35

People don’t want to leave because friends and family are there

Often cheaper and easier to step - especially when risks may not be Perceived as dangerous enough

Or residents are in denial a disaster may occur

Question 36

How do seismologists try to predict earthquakes

Answer 36

Use radon detection devices to measure radon gas in the soil and groundwater, which escapes from cracks in the earths surface

Sensitive seismometers are used to measure tremors or foreshocks before the main earthquake

Question 37

How else can earthquakes be monitored and predicted

Answer 37

The locations and times are mapped to spot patterns and predict when the next earthquake will occur

Smartphones have GPS receivers and accelerators built in and can detect movements in the ground, which are analysed to potentially warn others further away

Animals are believed to act strangely when an earthquake is impending

Question 38

How can planning for an earthquake help

Answer 38

Helps the authorities, emergency services and individuals to act quickly and calmly so there is less chaos and fewer injuries and deaths

Question 39

How can you plan for an earthquake

Answer 39

Furniture and objects can be fastened down so they are secure from toppling over

Residents can learn how to turn off the main gas, electricity and water supplies to Their properties

Prepare emergency aid supplies,
- eg the American Red Cross provided safety checklists to help people prepare

Question 40

How can you protect buildings from earthquakes

Answer 40

Designing buildings and strengthening roads and bridges to withstand earthquakes provides protection - called mitigation eg having automatic shutters that come down over Windows

However, very expensive so usually not possible to adapt existing buildings and though it may save live in an earthquake, after is may still need to be repaired and even rebuilt

Question 41

How can monitoring and prediction reduce the risk of volcanic eruptions

Answer 41

Using satellites and tilt meters to Monitor ground deformation (changes in of the volcanos surface)

Seismometers measure small earthquakes and tremors

Thermal heat sensors detect changes in the temperature of the volcanos surface

Gas trapping bottles and satellites measure radon and sulphur gases released

Scientists measure the temperature of water in steams and rivers to see if it has increased

Question 42

How can you protect buildings from volcanic eruptions

Answer 42

Very difficult to design a building from lava flows, Lahars, or weight of Debris and ash falling on roofs

Therefore, people need to evacuate their home to a safe location under the instruction of the authorities

Question 43

How can planning reduce the risk of volcanic eruptions

Answer 43

An evacuation plan is one of the most effective methods of protections

Authorities and emergency services need to prepare emergency shelter, food supplies and form evacuation strategies

Exclusion zones can be designated where no one is allowed to enter where people are considered vulnerable and in danger

Residents can be educated on preventing loss of life, if residents not evacuated, they are taught to seek shelter or go indoors to avoid the dangers of falling ash and rock