Tectonic plates Flashcards
Crust
A thin layer of solid rocks around the outside of the earth.
Continental crust
is crust made up of land is mainly composed of Granite.
Oceanic crust
is crust made up of oceans it is composed of Basalt.
Earth’s crust
is broken up into large slabs of rock called tectonic plates
Mantle
- A layer of semi-molten (melted rock)
- The thickest layer.
- Heat currents called convection currents rise and fall in the mantle.
Outer core
- A layer of molten (melted) rock.
- Average temperatures of 3000 degrees C.
- Composed of iron / nickel.
Inner core
- The centre of the earth
- Temperature of about 2700 degrees C
- Described as a solid ball of iron and nickel
- It is in a solid state due to pressure from the other layers.
The 7 major plates
- The Pacific
- The Eurasian.
- The African
- The American
- The Indo Australian
- The Nazca Plate
- The Antarctic plate.
What is a tectonic plate
- Tectonic plates are sections of very thin crust.
- They float like rafts on the semi-molten material that makes up the earth’s mantle.
- These plates move on top of the mantle by a series of heat (convection) currents.
- The movement is very small at less than 1 cm per year, but it can result in volcanic
eruptions and earthquakes. - Earthquakes and volcanoes are found near plate boundaries. They can happen on the seabed as well as on land.
Destructive/convergent plate margin
Happens when oceanic and continental plates come together
The oceanic plate is heavier (denser) and is subducted (forced down)
Continental plate is forced up (fold mountain)
When the oceanic plate reaches the mantle, it melts to form magma.
The heated magma is less dense so moves up and erupts to form a volcano.
Plates can be locked together where pressure builds and when the tension is released an earthquake most likely occurs.
Constructive/divergent plate margin
- Convection currents at a constructive margin are pulling plates
apart. - The sea floor spreads, and magma wells up to fill the gap.
- The magma erupts forming a volcano.
- New crust is created by the rising magma, this creates mid –
ocean ridges – chains of submarine mountains and volcanoes E.G the Mid-Atlantic Ridge. - New crust is continually being made a constructive boundary and over a long period of
time it can rise forming volcanic islands e.g., Iceland. - Minor earthquakes occur as the plates pull apart.
Conservative/transform margin
- Convection currents cause two plates slide past one
another. - Plates can become locked together, pressure builds up as
the plates are trying to move and earthquakes occur
when the tension is released. E.G. Turkey-Syria
Earthquake 2023. - No crust is created or destroyed, and no volcanic
eruptions take place.
Collision (convergent/destructive):
- Continental plates converge (move towards each other).
- Since two plates of land are of a similar density neither is
subducted. - Instead, plates are buckled and pushed up to form Fold
Mountains (e.g., Himalayas). - There is no subduction and so no volcanoes.
- However, violent earthquakes can occur. As plates push together pressure builds
and earthquakes occur when the tension is released. E.G. Nepal Earthquake 2015.
Volcanic hotspot
- Hotspot volcanoes can be found both along and away from plate boundaries.
- Hotspots are unusually hot magma plumes that rise in the mantle erupt through the
crust. - This creates seamounts which are volcanic mountains beneath the sea.
- Seamounts can rise above the ocean surface to create islands.
- The Hawaiian Island chain formed as the Pacific crustal plate moved over a stationary
source of magma or hotspot. - There are many volcanoes on the Hawaiian islands, however, only a few are active.
- When volcanoes move off the hotspot they lose their source of magma and become
extinct.
Types of volcanoes
- Active – if they have erupted recently
- Dormant – resting – have not erupted recently
- Extinct – will not erupt again
Shield volcanoes
- Shield volcanoes have very runny lava (non-viscous); because of this they do not have
an ‘explosive’ eruption. - Lava spreads quickly across the landscape.
- With each eruption a new layer of rock is built on the previous one.
- Gradually a wide dome of rock is built up.
- It is called a shield volcano because it looks like a curved shield lying on the ground (or
an upside down dinner plate). - The slopes of a shield volcano are very gentle.
- The Hawaiian islands are a chain of shield volcanoes
Composite/strato volcanoes
- Composite volcanoes are the most common type of volcano.
- When you think of a volcano you are probably picturing the classic cone shape of the
composite volcano. - They are formed by hardened layers of lava and ash from successive eruptions.
- The lava is viscous (therefore thicker than with shield volcanos) and it cools and hardens
before spreading very far, therefore the volcanoes are steep sided. - The eruptions tend to be very violent, capable of producing deadly pyroclastic flows.
- Mount Vesuvius in Italy is an example of a Composite Volcano.
Managing volcanoes
Predictions -
* Lasers to detect the physical swelling of the volcano
* Chemical sensors to measure the increases in sulphur levels
* Seismometers to detect the large number of earthquakes that occur due to the magma
rising up
* Satellite images to record the warming of the ground surface as the magma edges
towards the ‘breaking through point’.
Some of the methods scientists and local authorities use to plan are:
- Have an evacuation plan, e.g,. supplies of food and water, medical facilities, face mask to
prevent inhaling ask and temporary homes (tents). - Be ready to establish exclusion zones if needed. For example, in Montserrat in 1997 an
exclusion zone covering 2/3 of the island was established to protect lives. - Government agencies such as the police organise the evacuations. These need to be
practiced and publicized (in the eruption of Eyjafjallajökull in 2010 800 people who were
at risk of flooding were evacuated). - Have plans to manage lava flows if they threaten valuable areas e.g., in Sicily Mount Etna
regularly produces lava flows, the authorities may use powerful jets of water to attempt
to divert the flow away from valuable areas.
Eyjafjallajökull date of eruption
April 2010
Location of Eyjafjallajökull
The mountain lays within the country’s East Volcanic Zone.
Its name is originates from an Icelandic phrase meaning “the island’s mountain glacier,” and the
volcano itself lies beneath Eyjafjallajökull (Eyjafjalla Glacier).
Its highest point rises to 5,466 feet (1,666 metres) above sea level.
Causes of the eruption of Eyjafjallajökull
Iceland has formed at a divergent plate boundary due to the North American and Eurasian
plates moving apart. In addition, Iceland also lies over a hotspot or mantle plume – an upsurge of
abnormally hot rock in the Earth ́s mantle.
As the plates moved apart, excessive eruptions of lava constructed volcanoes and filled rift
valleys.
This has created the Mid Atlantic Ridge, a ridge of mountains and volcanoes that are mostly
below sea level.
However, there are also volcanic islands along the ridge, with Iceland being the largest because of
the additional volcanism caused by the hotspot under the country.
The plates are moving apart at a rate of 1cm to 5 cm per year.
This has created a chain of volcanoes along the SE Rift zone of Iceland, which runs from NE to
SW across Iceland, even passing underneath some of the countries ice caps.
Effects of Eyjafjallajökull
800 people had to be evacuated due to glacial outburst floods.
Travel was severely disrupted as many flights were cancelled between 14 and 21 April 2010
The eruption produced 0.3 cubic kilometres of ash, which resulted in the disruption of 95,000
flights across Europe and economic losses of 5 billion euros.
Businesses lost trade.
Air operators lost millions of pounds each day.
Perishable foods were wasted as they could not be transported.
People were not able to get to work because they were stranded.
The timing of the disruption was during the Easter holidays when levels of tourism are high.
Management of Eyjafjallajökull
Gas sampling - Changes in gas composition indicate the activity levels of magma underground
GPS technology - used to monitor any significant changes on the volcano so that the risk of activity e.g. pyroclastic flow can be assessed.
Seismic monitoring - any minor earthquake activity is detected using seismographs and is recorded. Rising blobs of magma can cause earthquake activity and so this may be a sign of an eruption.
Why people live near eyjafjallajökull despite the risk?
Because the ash from previous eruptions create fertile farmland.
The volcano is being checked daily so the volcano risk can be assessed and scientists will know before hand whether it’s going to erupt or not due to the data of monitoring.
The amount of money to the local community increases as tourism enters to see the eruption from a distance.
Geothermal energy from the eruption can harnessed to provide cheaper energy for locals (85% of houses in iceland is heated by natural geothermal heat from hot springs)
Minerals are contained in the lava which can be mined to make money.
