This ‘conveyor belt’ animation is a simplified version of the formation of hot spot volcanoes/ chains of islands. Internet Links – US Geological Survey Hawaiian volcanoes http://hvo.wr.usgs.gov/ While all care is taken to ensure web links contain useful information, Boardworks does not take responsibility for the content or accuracy of external web sites.
What is a volcano? A volcano is an opening or vent in the earth’s surface through which molten material erupts and solidifies as lava. Volcanic venthttp://www.youtube.com/watch?v=NBPwwt0HuVo&feature=fvst
Label this cross section of a volcano Volcanic Crater bombs, ash, lava, gases Parasitic cone Main vent •Volcanic bombs, ash, lava, gases •Magma chamber •Parasitic cone Magma •Crater chamber •Main vent
Do all volcanoes erupt? 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. http://www.bbc.co.uk/learningzone/clips/volcanic-scotland/9116.html 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!
Why do they happen?Can you remember what is happening to the plates at aCONSTRUCTIVE 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 veryspectacular or explosive. As the crust moves apart for themagma it is easily able to escape and just trickles out the top.The lava here tends to be runny and flows some distance fromthe crater before it solidifies. So, these volcanoes tend to beshallow sided, or SHIELD volcanoes.
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 thickand so does not flow far from the crater. These volcanoes build up layers with eacheruption. These are called COMPOSITE volcanoes.
Example of a composite volcano- Mt.Merapi – Indonesia
Where in the world are volcanoes found? Around which plate do we find most volcanoes?
Where do Earthquakes and volcanoes form?The ‘ring offire’ is anarea aroundthe PacificOcean, proneto A map to show theearthquakes Ring of fire spread of Earthquakesand and volcanoes aroundvolcanoes the earth
Hawaii 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?
Hot spot volcanoes In the animation above, why are the volcanoes to the left of the ‘hot spot’ extinct?
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 fromthe 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 millionsof 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.