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VIOLENT VOLCANOES…
A volcano is an opening or vent in the earth’s surface through which molten material erupts and solidifies as lava.
Volcanic vent
What is a volcano?
http://www.youtube.com/watch?v=NBPwwt0HuVo&feature=fvst
•Volcanic bombs, ash, lava, gases
•Magma chamber
•Parasitic cone
•Crater
•Main vent
Label this cross section of a volcano
CraterVolcanic bombs, ash, lava, gases
Main vent
Parasitic cone
Magma chamber
What comes out of a volcano?
Active volcano – liable to erupt e.g. Mt Etna & Mt. Merapi in Indonesia.
Dormant (sleeping) volcano – a volcano which has not erupted for many years. For example, Mt Pinatubo erupted in 1991 after 500 years of dormancy.
Extinct volcano – a volcano which has not erupted for many thousands or millions of years e.g. Edinburgh.
However, it is often very difficult to tell whether a volcano will erupt again…El Chichon, Mexico erupted in 1982 after being dormant for approximately 1200 years!
Do all volcanoes erupt?
http://www.bbc.co.uk/learningzone/clips/volcanic-scotland/9116.html
Can you remember what is happening to the plates at a CONSTRUCTIVE plate boundary?
The two plates are moving apart…
What comes up through the gap created in the crust?
A volcano….
Volcanoes at constructive plate boundaries don’t tend to be very spectacular or explosive. As the crust moves apart for the magma it is easily able to escape and just trickles out the top. The lava here tends to be runny and flows some distance from the crater before it solidifies. So, these volcanoes tend to be
shallow sided, or SHIELD volcanoes.
Why do they happen?
Volcanoes also form at DESTRUCTIVE plate boundaries.Where one plate is forced down under the other (called subduction).
What happens to the crust that is forced down into the mantle?
It melts…
What does this create?
Excess magma…
What do you think happens to this extra magma?
Pressure builds and eventually there is a violent, explosive, volcanic eruption!
Volcanoes at destructive plate boundaries tend to be very explosive! The lava is thick and so does not flow far from the crater. These volcanoes build up layers with each
eruption. These are called COMPOSITE volcanoes.
Example of a shield volcano- Mauna Kea, Hawaii
Example of a composite volcano- Mt. Merapi – Indonesia
Around which plate do we find most volcanoes?
Where in the world are volcanoes found?
Ring of fireA map to show the
spread of Earthquakes and volcanoes around
the earth
The ‘ring of fire’ is an area around the Pacific Ocean, prone to earthquakes and volcanoes
Where do Earthquakes and volcanoes form?
The Ring of Fire
The Hawaiian islands are a chain of volcanoes in the Pacific Ocean.
Look at their location on the map below.
Why is this an unusual place for them to be located?
Hawaii
In the animation above, why are the volcanoes to the left of the ‘hot spot’ extinct?
Hot spot volcanoes
HOT SPOT volcanoes are found in the middle of a plate.Here the crust is weaker than usual. There is a plume of hot magma rising from the mantle and it is able to push through the crust at this point.The plate moves across this ‘hotspot’ forming a chain of volcanoes over millions of years e.g. Hawaii.
Your tasks:
• You have one side of A3 paper on which to produce a ‘fact sheet’ about volcanoes. You need to include:
1. Completed ‘pop-up’ volcano.2. An explanation as to how volcanoes form. Try
to include information about both constructive and destructive plate boundaries and what the different volcanoes are known as (shield and composite).
3. An explanation as to what is meant by active, dormant and extinct volcanoes.
4. An explanation of ‘hot-spot’ volcanoes.
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