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Flashcards in Tectonics Deck (38):

What is a constructive/divergent plate boundary

When two plates move away from each other , and new crust is formed.


What volcanoes are usually created at constructive plate boundaries

Rift volcanoes form where plates diverge from one another at the site of a thermally botany mid ocean ridge. These are generally less explosive and often occur on the ocean floor, for example the mid ocean ridge. Here there is balsamic magma


What is a destructive plate boundary and what is formed as a result

When two plates move towards each other forming collisions. Subduction zone is created as the more dense oceanic crust is pushed under by the greater buoyancy of the continental lithosphere. Form very powerful volcanoes and fold mountains


What is a conservative plate boundary

When two plates slide past each other. The friction of them sliding past can cause earthquakes


How do plate boundaries move

Heat which is derived from the Earths core due to radioactive decay causes the mantle to move and form convection currents.


What is sea floor spreading and where does it occur

Occurs at constructive plate boundaries- continuous input of magma forming a mid ocean ridge, for example the mid ocean Atlantic ridge. As molten rock is forced up at the ridge where it forms new crust on ocean floor. Slowly as more molten rock behind it is pushed up, the new crust is pushed away on either side.


How is an earthquake caused

-Plates slide past each other
-Movements proceeded by gradual build up of tectonic strain which stored elastic energy
-when pressure exceeds the strength of the fault the rock fractures
-sudden release of energy


What device is used to measure earthquakes

Seisometer- measures the amount of ground shaking during an earthquake


What is soil liquification

The process by which water saturated material can temporarily lose normal strength and behave like a liquid - due to strong shaking


What happens during a tsunami

Tsunamis can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. Tectonic earthquakes are a particular kind of earthquake that are associated with the earth's crustal deformation; when these earthquakes occur beneath the sea, the water above the deformed area is displaced from its equilibrium position. Waves are formed as the displaced water mass, which acts under the influence of gravity, attempts to regain its equilibrium.


What affects the size of a tsunami

Duration of event
Wave amplitude
Physical geography of coast
Timing of event
Degree of coastal development


Give the primary impacts of volcanoes

Pyroclastic flows - hot gasses and ash move extremely fast
Tephra- volcanoes eject material such as rock fragments
Lava flows- pose big threat- move slow
Volcanic gasses - explosive eruptions - co2-carbon monoxide etc - most deaths from this - colourless and odourless


What's the difference between natural hazard and natural disaster

Hazard - natural event that has potential to threaten life and property
Disaster - when a natural event causes significant impact to vulnerable population - e.g.- when more than 10 people killed


What is a tectonic hazard profile

A technique used to try and understand the physical characteristics of different hazards - e.g frequency ,duration,speed of onset


Explain why some groups of people have greater capacity to cope with disasters than others

Developed - have financial recourses ,reinforced housing
Developing - lack recourses for healthcare etc
Children - less acquired knowledge
Migrants - lack language skills and education on dangers


Describe what happened in Christchurch earthquake 2010

7.1 mag
Epicentre 40km from Christchurch
Lasted 40 secs
1 person died
Sewers damaged
Electrical grid disrupted
Railway lines buckled
Soul liquification caused flooding
Cost repairs at 2 billion


Describe what happened on the Japan tsunami 2011

9.0 mag
100km easy of Sendai
40metres high
A segment of North American plate 200km long shifted up
15,894 people died
Ruptured gas pipes
Explosions at Fukushima nuclear plant led to contamination and possibility of a meltdown as the cooling system failed
100,000 troops deployed B
Specialist teams sent


Describe Indian Ocean tsunami 2004

Subduction caused by indo-Australian plate under Eurasian plate
9.1 mag caused 20metre uplift in sea bed
14 countries affected - 250,000 killed
Sumatra - 130,000 alone were killed and 30,000 still missing
Diseases such as cholera spread quickly especially in refugee camps
Bodies buried in mass graves to prevent spread of disease
Early warning systems did not exist


Describe the Iceland volcanic eruption 2010

Volcanic ash ejected several kilometres into the atmosphere
Uk airways closed
100,000 flights cancelled
10 million people stranded
1.7 billion in losses for airlines
Airports lost 250 million
Cost 5 billion to European economy


Describe the Montserrat volcanic eruption 1995-97

Was devastated by pyroclastic flows
Small scale population was evacuated to the north of the island and to neighbouring islands
19 people killed
Destroyed large of areas


Give strategies to manage tectonic hazards

*Store emergency equipment such as tents, clean water, food supplies, first aid and search-and-rescue gear
*Train specialist workers for a hazardous event
*Raise public awareness by having earthquake drills, for example.
*Set up warning system and, if possible, evacuation plans.


Give some long term responses to tectonic hazards

*Construct safer buildings such as earthquake-resistant structures using flexible steel frames, shock absorbers, cross-bracings and counterweights
*Improve prediction and monitoring systems for volcanic activity and the secondary hazards of earthquakes
*Carry out land use zoning- use the areas that are most at risk for recreation, open spaces or low-rise buildings


What causes the movement of tectonic plates

The movement of tectonic plates is driven by thermal convection currents in the upper mantle using heat derived from the radioactive decay of minerals deep within the Earth and residual heat from the Earth's formation. This heat causes plumes of hot magma to rise. If the crust is thinner on the mid-ocean floor, the hotter and less dense magma breaks through to form new crust as it is cooled by the water.


Explain other secondary hazards caused by earthquakes

- spread of disease due to a lack of sanitation
- Tsunamis caused by a displacement of water
- Landslides due to the dislodging of ground material


Explain the tectonic hazards that may result from volcanic activity (6)

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

Tephra are tiny particles of rock and natural glass blasted into the air by a volcanic eruption; they can then be transported by wind thousands of miles; electrostatic charging created by the upward movement of ash can help trigger thunderstorms, which in turn can
trigger lahars

Lahars are caused by rain mixing with either ash on the steep side of a volcano creating a great mudflow (e.g. Java), or ash mixing with rain

Pyroclastic flows are caused by a very explosive eruption when the eruption column itself collapses and can’t continue to rise


Assess whether development and governance are the most important factors in understanding the scale of tectonic disasters. (12)

- Governance means the ability of an organisation / group of people to plan or manage hazard events effectively – e.g. national government might finance emergency care, mandate education strategies

- Scale of tectonic disasters could be measured by the
impact on theeconomy, human life, the environment,

- Development and governance help understand disaster impact – e.g. the level of inequality reflects the level of development for some communities

- If disasters occur in developed countries, there will be less social impact. However, the economic impact might be much higher because of damage to critical infrastructure

- There are other reasons that determine disasters, e.g. physical geography factors, can determine whether some countries are affected more than others; (e.g. direction of ash fall, tsunami wave propagation)

- However, it is clear, whatever the magnitude of a tectonic event, the core factors for the scale of the disaster will lie with the levels of development of a location

- Unequal development means disasters can have significant impact on local communities some of which might not be able to access short-term aid, particularly if vulnerable groups cause emergency resources to
become stretched.



What is used to measure the scale of an earthquake

Richter scale - measurement of the height of the waves
produced by an earthquake.
Mercalli scale- Measures the experienced impacts of an
earthquake. It is a relative scale because
people experience different amounts of
shaking in different places. Based off a
series of key responses such as peoples
awakening and damage to structures.

Moment - A modern measure used by
magnitude seismologists to describe the earthquake
Scale in terms of energy released. It is
based off the seismic moment of an
earthquake calculated from the amount
of slip on the fault.


What is used to measure the scale of a volcanic eruption

Volcanic Explosivity index - A relative measure of the
explosiveness of a volcanic eruption, which is calculated from the volume of products, height of eruption cloud and qualitative observations.


What is the importance of NGO's in dealing with a disaster

NGO's are especially important in disasters where local government is struggling to respond or doesn't have the recourses to do so

For example they can provide funds and send aid


What is meant by a plate boundary

Where two plates meet and interact with each other


What is Paleomagnetism and how does it help in the study of plate tectonics

Paleomagnetism is the study of the earth's past magnetic field.
Paleomagnetism can also be used to match up land masses that are now separated from each other, but which must once have been joined. For example, the orientation of magnetic minerals along the eastern coast of South America very closely matches that of similar minerals on the western coast of Africa.

This adds to the idea that they were once joined together as a single mass


What is a Benioff zone

an inclined zone in which many deep earthquakes occur, situated beneath a destructive plate boundary where oceanic crust is being subducted.


Describe the three types of seismic wave



What is a primary wave

These waves can travel through fluids and solids and are longitudinal. This also means that they transfer energy parallel to the direction of the wave, so if a wave is travelling north to south, the energy will be transferred in this direction.


What are secondary waves

S-waves cannot travel through air or water, only through solids, but they have a larger amplitude (this is the height of a wave, measured from the highest point to the middle line) so are more destructive in the case of an earthquake. They are transverse waves, meaning they transfer energy perpendicular


What are Surface waves

The final type of seismic wave occurs along the boundary between two different substances (e.g. rock and air). They can be either longitudinal or transverse.

These waves travel slower than both S and P waves, but have a higher amplitude and so can be the most destructive of all the seismic waves.


What is a mitigation strategy

A risk mitigation strategy, by definition, is taking steps to reduce the risk (the severity of the impact and/or probability of the occurrence).


What are hydrometerological hazards

Natural processes or phenomena of atmospheric, hydrological or oceanographic nature that may cause the loss of life or injury, property damage, social and economic disruption or environmental degradation.

Hydrometeorological hazards include: floods, debris and mud flows; tropical cyclones, rain and wind storms, sand or dust storms, thunder and hailstorms, blizzards, and other severe storms