Unit 2 - Tectonics Flashcards
What are the names for the 4 layers in the Earth?
- Crust
- Mantle
- Outer core
- Inner core
State the following for the inner core:
- temperature
- thickness/radius
- What it mainly consists of
- around 5,200° C
- radius around 3,485km
- a hot dense ball of (mostly) iron
State the following for the outer core:
- temperature
- thickness
- What it mainly consists of
- 4,500° - 5,500° C
- thickness of about 2,200km
- mostly liquid iron and nickel
State the following for the mantle:
- temperature
- thickness
- What it mainly consists of
- 500-900°C
- thickness of about 2,886km
- it is a silicate rocky shell
State the following for the crust:
- temperature
- thickness
- What it mainly consists of
- 200-400° C
- average thickness of 0-60km
- solid rock
Explain how a convergent plate boundary forms fold mountains.
- Plates move together and collide
- Very violent volcanoes (e.g. Mt St Helens, USA) and Mt. Etna (Sicily) and earthquakes occur.
- Subduction zones form due to downward movement of the dense oceanic crust into the mantle, beneath the less dense continental crust.
- Fold mountains (e.g. the Alps and the Himalayas) can form when both plates are pushed upwards by the force of the collision.
What type of plate boundary is Mt Laki (Iceland) on?
Divergent plate boundary (accept constructive)
Explain how a divergent plate boundary forms ocean ridges e.g. the Mid-Atlantic Ridge.
- Plates move apart.
- Less violent volcanoes and earthquakes occur.
- New sea floor is created at the mid-ocean ridges (e.g. the Mid-Atlantic Ridge) as magma rises up through the ridge and solidifies.
Give a location affected by a conservative boundary.
Many locations accepted, examples are:
- San Andreas Fault
- Alphine Fault (N, Zealand)
- North Anatolian Fault (Turkey)
Explain how earthquakes can occur with a conservative plate boundary.
- Plates slide past each other.
- No crust is destroyed or created, therefore no volcanoes are formed.
- Plates can ‘stick’; this increases pressure which can be released as violent earthquakes.
What is the difference between a collision and convergent plate boundary?
Challenge: Give a location affected by a collision boundary if you can.
A collision boundary has nearly of the same characteristics as a convergent boundary but instead of an oceanic and continental plate being involved, it’s a continental and continental plate e.g. Indo-Australian Plate and Eurasian Plate.
Challenge: A mountain range affected by a collision boundary is the Himalayas.
GIve one general characteristics about a volcano.
- A volcano is formed by eruptions of lava and
ash, with the lava later harding to become new
rock
OR
- Volcanoes usually are cone-shaped and are
mountains or hills that have become active.
OR
- Volcanic eruptions can happen at convergent
and divergent boundaries but not conservative
boundaries
OR
- Some volcanoes happen underwater - like the
Mid-Atlantic Ridge
Explain how a volcano is formed.
- Magma rises through cracks or weaknesses in
the Earth’s crust.
2.Pressure builds up inside the Earth.
3.When this pressure is released, eg as a result of
plate movement, magma explodes to the
surface causing a volcanic eruption.
4.The lava from the eruption cools to form new
crust.
5.Over time, after several eruptions, the rock
builds up and a volcano forms.
Give 4 features located inside a volcano.
• The magma chamber is a collection of magma
inside the Earth, below the volcano.
• The main vent is the main outlet for the magma
to escape.
• Secondary vents are smaller outlets where the
magma escapes.
•The crater is created after an eruption blows off
the top of the volcano
Briefly outline how an eruption occurs,
An eruption occurs when pressure in the magma chamber forces magma up the main vent, towards the crater at the top of the volcano. Some magma will also be forced out of the secondary vent at the side of a volcano.
Name a type of volcano found at convergent plate boundaries.
Composite
What is a pycroclastic flow?
A mixture of hot steam and debris (the more dense material)
Extra info:
Pyroclastic flows roll down the sides of a volcano at very high speeds and with temperatures of over 400°C.
What type of flow causes the largest deaths?
Pyroclastic flows as once people are caught up in one, with all the ash and debris, they have a very little chance of survival
Name 4 methods of predicting and preventing volcanic eruptions.
- Using GPS technology to check the bulging of the volcano as magma approaches the surface
- Gas sampling - as changes in the gas composition indicate the activity levels in the magma underground
- Geothermal monitoring from space, to record changes in heat as magma approaches to the surface
- Seismic monitoring, ‘to listen’ to the rising blobs of magma as they force their way upwards and cause small earthquakes
Extra info:
• Looking out the historical records of past eruptions, to tell you if there is a pattern and when the next eruption could occur
Name 4 methods of protection against volcanic eruptions.
- Spraying the lava with water so it will harden and become rock, so it will stop flowing
- Putting concrete or rock barriers in the path of the lava, diverting the flow away from villages
- setting off explosives to divert the lava flow
- Digging ditches to divert the flow away from areas at risk
State some possible causes for the Monsterrat (Chances Peak) volcanic eruption in 1997.
- N. American (oceanic) plate is subducted below the continental plate (Caribbean), creating a trench (convergent plate boundary)
- Oceanic crust melts due to the mantle’s high temperature
- Build of pressure movement causes earthquakes
- Molten rock is forced up through fissures in the continental crust, and explodes violently in volcanic eruptions
(Note: for cause 1, the specific plates must be named.)
States the effects of the eruption [at Chances Peak (1997)]
- 5 million cubic metres of ash and rock deposited
- Trants village covered in 4 square kilometres of ash
- 19 killed
- 100-150 homes destroyed
- Bramble airport destroyed, disrupting air traffic
- people’s feet and car tyres burnt by ash
State the responses made after the eruption.
- The Montserrat Volcano Observatory was set up to monitor seismic activity
- Face masks were issued to children to prevent silicosis.
- 7000 people were evacuated from the island and the immediate danger zones to parts of the UK and other countries
- The airport began to be rebuilt
What type of country is Monsterrat?
LIC (Low income country)
What type of country was Mt St Helens in?
US - HIC (High income country)
State the possible causes of the 1980 eruption at Mt St Helens.
- Divergent plate boundary
2. on the Pacific Ring of fire
State the effects of the eruption.
- 57 dead
- lateral (sideways) eruption
- up to 1m of ash settled in the surroundings
- millions of trees were destroyed
State the responses of the eruption.
•monitoring - bulge - tilt meter with lasers
◦fissures going up
•exclusion zone set up
•evacuation saved 2500 lives (approx.)
Explain the meaning of each of these terms:
- the focus
- the epicentre
- seismic waves
focus: the point under the ground where the plates shift and earthquake tremors start
epicentre: the point directly above ground and above the focus
seismic waves: the tremors given off the plate movement. They are like ripples in a pond, giving off energy outwards
Name some characteristics of a primary seismic wave.
- The primary waves are the first one given off. -
- They are the faster ones
- They can be crucial as a warning sign to the
monitoring groups of where the secondary
waves will hit first
- causing warning systems to start and
people getting to higher ground. - They are usually within 5 or 6 seconds between
each wave and they travel very fast.
Name some characteristics of a secondary seismic wave.
- The secondary waves are the second and the most destructive.
- They travel at half of the speed of the primary waves and because of their slow speed
- they travel over cities or towns more slowly,
leading to tremors that may make buildings
collapse and groundwater to surface.
Name 2 methods of recording/measuring seismic activity.
Recording:
- on a on a seismometer using the Richter scale
◦often referred as 1-10 but is actually unlimited
Measuring aftermath:
- Mecalli scale
◦a subjective scale that measures the impact
of the earthquake
◦from one to twelve (in roman numerals)
Name 4 ways of predicting earthquakes
•noting strange animal behaviour as this is often
reported before earthquakes
•monitoring electrical discharges, because there is
some evidence that these rise before an
earthquake
•recording minor tremors, because some major
earthquakes are preceded by small foreshocks
•seismic gap theory - USGS (United States
Geological Survey)
Name 4 ways of protection against earthquakes.
•Providing education to local residents - so they
can learn how to prepare and react
•Designing buildings that can withstand
earthquakes - e.g. flexible steel frames and
shutters for windows that might shatter
•Planning regulations
•Nov. 2008 - L.A. had the largest earthquake drill
in history - cost $2 billion
•Transamerica Pyramid in Sans Francisco -
withstood major earthquakes (swayed 30cm)
Name the magnitude on the Richter scale of the Bam earthquake (2003).
6.6
Name some possible causes of the earthquake.
State the effects of the earthquake.
- 300,000 dead
- 20,000+ injured
- 75,000+ homeless
- 85% of buildings destroyed/severely damaged
State the responses to the earthquake
-Short term
◦1,600 aid workers from 44 countries helped
-Long term
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