Tectonic Hazards

Question 1

What types of plates are involved in a conservative boundary? 
How thick are they?
What are they made of?
An example
Other properties?

Answer 1

Oceanic and Continental
Oceanic : 5-10km, Continental : 40-60km
Oceanic : Basalt, Continental : Granite
San Andreas Fault

Shallow focus depth so seismic waves have to travel less to get to the surface, so they do not lose as much energy along the way
strong earthquakes due to friction building up pressure
Also known as transform boundary

Question 2

What types of plates are involved in a constructive boundary?
An example
Earthquakes/Volcanoes?

Answer 2

2 Oceanic plates
Mid-Atlantic Ridge
The movement of the plates over the mantle can cause earthquakes / shield volcanoes form when the magma from the mantle rises up.

Question 3

What types of plates are involved in a collision boundary?
An example
What forms here?

Answer 3

2 Continental plates
Himalayas
Fold mountains / Earthquakes can occur

Question 4

What types of plates are involved in a destructive boundary?
An example
Earthquakes/Volcanoes?

Answer 4

An oceanic and continental plate (oceanic is subducted beneath continental)
USA: Juan De Fuca
Composite cone volcanoes / earthquakes

Question 5

Internal structure of the Earth

Answer 5

Inner core - solid due to the extreme pressure it experiences, made of iron and nickel, hottest part of the earth (around 6000C) due to primordial heat left over from the Earth’s formation and radiogenic heat produced from radioactive decay.

Outer core - Semi-molten and mostly consists of liquid iron and nickel. Temperatures range between 4500-6000C

Mantle - The upper part is solid, but below it the rock is semi-molten - forming the asthenosphere which acts as a conveyor belt for tectonic plates.

Lithosphere - the crust and upper mantle - the solid layer from which tectonic plates are formed

Crust - Oceanic, a thin, dense layer which lines the ocean floors, or continental, an older, thicker layer, which makes up the Earth’s landmasses. It is less dense than oceanic crust.

Question 6

Processes which cause tectonic plates to move

Answer 6

• Mantle convection
• Slab pull
• Subduction
• Seafloor spreading

Question 7

How does mantle convection work?

Answer 7

Radioactive elements in the core of the Earth decay which produce a lot of thermal energy. This causes the lower mantle to heat up and rise, as the magma rises it cools down and becomes more dense and begins to sink back down to the core. These are convection currents which move in a circular motion in the asthenosphere - causing the plates to move.

Question 8

3 main types of seismic seismic wave

Answer 8

Primary and Secondary waves are called body waves because they travel through the Earth’s body.
Love waves are surface waves, because they travel along the Earth’s surface.

Question 9

Features of Primary waves

Answer 9

Travel through solids, liquids and gases.
Compression wave
Vibrates in the direction of travel
Travels at 6km/s

Question 10

Features of secondary waves

Answer 10

Travel through solids
Vibrate at right angles to the direction of travel
Travel at 3km/s

Question 11

Features of love waves

Answer 11

They are the slowest to arrive, but they cause the most damage.
Rolling motion producing vertical ground movement.
They are larger and focus all of their energy on the Earth’s surface.

Question 12

What is a hazard? Natural Hazards?

Answer 12

A hazard is a potential threat to human life and property.
Natural hazards can either be hydro-meteorological (caused by climatic processes) or geophysical (caused by land processes).

Question 13

What are intraplate and interplate earthquakes?

Answer 13

An intraplate earthquake occurs in the interior of a tectonic plate, the causes are not fully understood but it is assumed that plates have pre-existing weaknesses which become reactivated, forming seismic waves. For example, an intraplate earthquake may occur if solid crust, which has weakened over time, cracks under pressure.

Interplate earthquakes occur at plate boundaries between two or more tectonic plates.

Question 14

On what types of plate boundary do the most powerful earthquakes occur?

Answer 14

Destructive or conservative boundaries

Question 15

What is slab pull?

Answer 15

Slab pull occurs where older, denser tectonic plates sink into the mantle at subduction zones. As these older sections of plates sink, newer and less dense sections of plate are pulled along behind. Sinking in one place leads to plates moving apart in other places.

Question 16

What is seafloor spreading?

Answer 16

Mid-ocean ridges are formed when hot magma is forced up from the asthenosphere and hardens - forming new oceanic crust. This new crust pushes the tectonic plates apart in a process called seafloor spreading.

Question 17

What scale is used to measure volcanic eruptions?

Answer 17

Volcanic Explosivity Index (VEI), it uses a scale from 0 to 8 and is logarithmic, an increase of 1 on the scale indicates a 10 times more powerful eruption. It is based on the height of ejected material and the duration of the eruption and it measures the relative explosiveness of a volcanic eruption.

Question 18

Which scale is used to measure an earthquake’s magnitude?

Answer 18

• Moment Magnitude scale

It measures the total energy released by an earthquake at the moment it occurs, using the size of the seismic waves, amount of rock movement, area of the fault surface broken by the earthquake and the resistance of the affected rocks.
More accurate at measuring larger earthquakes.
The scale is logarithmic, each number is 10 times the magnitude of the number before.
The scale generally goes from 1-10 as the largest earthquake recorded was a magnitude 9.5.

Question 19

Which scale is used to measure an earthquake’s intensity?

Answer 19

• Modified Mercalli Intensity Scale

It takes observations from people who experienced the earthquake and rates them on a scale from 1 (hardly noticed) to 12 (catastrophic).

Question 20

Primary effects of earthquakes

Answer 20

• ground shaking, which causes buildings and infrastructure to collapse - killing or injuring those nearby
• crustal fracturing, when energy released during an earthquake causes the Earth’s crust to crack

Question 21

Secondary effects of earthquakes

Answer 21

• liquefaction
• landslides and avalanches
• tsunamis

Question 22

Primary hazards of volcanoes

Answer 22

• Lava flows
• Pyroclastic flows
• Tephra and ash falls
• Gas eruptions

Question 23

Secondary hazards of volcanoes

Answer 23

• Lahars

- Jökulhlaup

Question 24

What is soil liquefaction?

Answer 24

It affects poorly compacted sand and silt and it is when water moisture within the soil separates from the soil particles and rises to the surface. This can cause the soil to behave like a liquid, which can cause building subsidence or landslides.

Question 25

What are landslides?

Answer 25

The shaking caused by the earthquake can weaken or damage cliff faces, hills and snow material. Unconsolidated material or loose rocks can collapse. Landslides can travel several miles and accumulate material on the way. Risk varies with topography, rainfall, soil and land use.

Question 26

How are tsunamis formed?

Answer 26

Tsunamis are formed when a sub-marine earthquake causes uplift to occur along a fault line causing the displacement of water, which then causes a water column to rise, the water column then collapses due to gravity, sending waves in all directions.

Question 27

Where do most earthquakes geographically occur?

Answer 27

About 70% of all earthquakes are found in the Pacific Ring of Fire

Question 28

Process of an earthquake

Answer 28

As two plates move past each other friction causes pressure to build up over time, which is eventually released as an earthquake. A pulse of energy radiates out in all directions from the focus.

Question 29

Intra-plate volcanoes

Answer 29

Some volcanic eruptions are intra-plate and occur at locations called mid-plate hotspots such as Hawaii and the Galapagos Islands.

At these locations:

1. Isolated plumes of convecting heat, called mantle plumes, rise towards the surface, generating basaltic volcanoes that tend to erupt continuously.
2. A mantle plume is stationary, but the tectonic plate above moves slowly over it.
3. Over thousands of years, this produces a chain of volcanic islands, with extinct ones most distant from the plume’s location.

Question 30

How fast do tectonic plates move?

Answer 30

They move at a speed of 2-5cm per year.

Question 31

What is lava flow?

Answer 31

Lava flow are streams of molten rock that flow from a volcanic event,
the viscosity and speed of which depends on the type of volcano
eruption

Question 32

What is a pyroclastic flow?

Answer 32

A pyroclastic flow is a dense, fast-moving flow of solidified lava pieces, volcanic ash, and hot gases. Temperatures of up to 600C.

Question 33

What can ash fall/tephra cause?

Answer 33

Can blanket large areas in ash, killing vegetation, collapsing buildings and contaminating water sources.

Question 34

What is a gas eruption?

Answer 34

The eruption of carbon dioxide and sulphur dioxide, which can poison people and animals in extreme cases.

Question 35

What are lahars?

Answer 35

Volcanic mudflows, which occur when rainfall mobilises volcanic ash. They travel at high speed down river systems and cause major destruction.

Question 36

What are J​ökulhlaups?

Answer 36

Devastating floods caused when volcanoes erupt beneath glaciers and ice caps, creating huge volumes of meltwater. They are common in Iceland.

Question 37

What can tsunamis be generated by?

Answer 37

landslides, volcanic eruptions, sub-marine earthquakes

Question 38

What is the hazard risk equation?

Answer 38

Risk = (Hazard x Vulnerability) / Capacity to cope

Hazard = Magnitude
Vulnerability = Poverty, lack of mitigation, lack of awareness of potential hazards
Capacity to cope = emergency evacuation / rescue systems, fast response

Question 39

What does Degg’s disaster model show?

Answer 39

It shows the intersection between a hazardous natural event, such as an earthquake, hurricane or landslide and a vulnerable population which experiences human and/or economic loss, to create a disaster.

Question 40

What is the PAR model?

Answer 40

The pressure and release model is used to work out the vulnerability of a country.

According to the PAR model, vulnerability is a process that starts with root causes. These are political and economic systems that control who has power in a society and who has access to resources (such as money).

Through a series of processes called dynamic pressures (lack of education, disaster management systems, enforced building codes), these root causes can lead to unsafe conditions (low GDP per capita led to buildings being constructed cheaply, poor access to water/sanitation).

Question 41

Which case study would it be most beneficial to use the PAR model?

Answer 41

Haiti

Root causes:

• 80% of population lived below the poverty line, country was heavily in debt to US, German and French banks so it had to use much of its little available money for debt repayments, rather than improving the country’s infrastructure.
• extensive corruption within Haiti’s government
• $1200 GDP per capita

Dynamic pressures:

• Lack of education, training and investment.
• Rapid population change and urbanisation, resulting in vulnerable, slum-like housing.
• Lack of disaster management systems

Unsafe conditions:

• Before the earthquake, only 39% of Haitians had access to safe water and 24% to sanitation.
• The soft soil, on which many of Haiti’s buildings were constructed, amplified the seismic waves - increasing ground shaking and damage.
• Poor infrastructure so limited access to people in need and made reaching them more expensive.

Question 42

The Hazard Management Cycle

Answer 42

• Response
  Immediate help in the form of rescue to save lives and aid to keep people alive, emergency shelter, food and water.
• Recovery
  ​Rebuilding infrastructure and services, rehabilitating injured (physically and mentally) people and their lives
• Mitigation
  Acting to reduce the scale of the next disaster: land-use zoning, hazard-resistant buildings and infrastructure.
• Preparation
  Community education and resilience building including how to act before, during and after a disaster, prediction, warning and evacuation technology and systems

Repeat

Question 43

Park’s model

Answer 43

Page 39

Graph
normality -> disruption -> recovery -> improvement/return to normality

Question 44

Evidence for seafloor spreading

Answer 44

Palaeomagnetism - Every 400 000 years, the Earth’s magnetic fields change direction - causing the magnetic north and south poles to swap. When lava cools and becomes rock, minerals inside the rock line up with the Earth’s magnetic direction at the time. Scientists studying mid-ocean ridges found the same pattern of magnetic direction on either side of the ridges, something that could only happen if new rock was being formed at the same time on both sides.

Question 45

How are tsunamis predicted?

Answer 45

Early warning systems - These systems use seismic sensors to detect undersea earthquakes. Not all undersea earthquakes cause tsunami so DART system (Deep-ocean Assessment and Reporting of Tsunami) needs to be used aswell.

The DART system uses seabed sensors and surface buoys to monitor changes in sea level and pressure. When tsunami waves are detected, the system sends the information via a satellite to tsunami warning stations, which estimate the size and direction of the tsunami and inform the areas at risk.