Download Plate Boundaries

Plate Boundaries
The places where the tectonic plates meet each other are known as plate boundaries; they
are very important as this is where the majority of our planets earthquakes and volcanoes
take place.
Divergent pate boundary – a constructive
margin
The Mid Atlantic Ridge
The Mid Atlantic Ridge is the boundary between the North American and the Eurasian
plates. They are two oceanic plates that are being pushed apart by the convection currents
in the mantle. This creates a gap which releases pressure upon the magma of the mantle;
this in turn allows the magma to become more liquid and rise to the surface.
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The magma that rises to the surface cools and hardens to become new land. For a long time
scientists didn't understand what was happening along the Mid Atlantic Ridge because most
of the ridge is at the bottom of the Atlantic ocean. If you look in an atlas you will see many
small islands such as the Azores and Tristan da Cunha running through the Atlantic; these
have all been created by volcanoes along the Mid Atlantic Ridge. These processes can also be
seen at the surface in Iceland which has many volcanoes.
Samples of rock from the sea bed have been dated. These show that the rock in the centre
of the Atlantic taken from near the Mid Atlantic ridge is far younger than that found at the
edges of the ocean. It is this process, known as sea floor spreading, which is making the
Atlantic Ocean bigger and slowly pushing the continents of North America / South America
and Europe / Africa further apart.
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Volcanoes at the constructive margin
The lava coming out of volcanoes at the constructive margin is runny. This means that it
moves quickly away from the crater and makes volcanoes that are quite flat – these are
known as shield volcanoes. This sort of volcano can also erupt a great deal of ash; in 2010
many aeroplanes across Europe were grounded because of the eruption of a volcano in
Iceland. If ash gets into aeroplane engines it can make them stall. Ash in large quantities also
quickly becomes heavy and can damage property. A quick internet search for volcanic
eruptions in Iceland will give you a good idea of what these eruptions are like.
The volcanoes themselves are rarely dangerous as the eruptions are not violent and Iceland
is not densely populated. The biggest risks come from ash getting into aeroplane engines
and the potential that huge ice-sheets could be melted.
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Earthquakes at the constructive margin
The Mid Atlantic Ridge is not a smooth, neat gap between two plates. As the plates move
they shake, judder and break apart in joined places; magma moving through the volcanoes
can also create earth tremors. Earthquakes at a constructive boundary however are usually
not large and will cause limited damage.
Constructive Margin – Summary.

The plates are moving apart.

A good example is the Mid Atlantic Ridge and Iceland.

New land is created at the Mid Atlantic Ridge.

There are shield volcanoes, not explosive, runny lava and ash.

There are small earthquakes.

The volcanos and earthquakes rarely cause danger to people.

Property will be damaged if it is the way of the lava or ash falls on it.
Spelling!
It is important hta your spelling is accurate on your exam paper – you will get extra marks.
So remember….
Volcano – a single volcano has no “e” adtthe end.
Volcanoes – Two or more volcanoes means you must put a “e” before the S
Erupt/eruption – Only one “r” not two
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Multiple Choice Questions
1. It is important that scientists study plate boundaries because...
a) there are not many of them left
b) it is where most of our earthquakes and volcanoes happen
c) they are the only places that earthquakes and volcanoes don't happen
d) all volcanoes happen there?
2. The North American and Eurasian plates are...
a) moving together
b) one is continental and one is oceanic
c) both oceanic and moving apart
d) both continental and moving together?
3. Much of the Mid Atlantic Ridge is...
a) easy to study as it is found on land next to the Atlantic ocean
b) hard to study because scientists are not sure where it is
c) found in Iceland
d) hard to study as it is under the Atlantic ocean?
4. Magma rises to the surface at the divergent plate boundary because...
a) it explodes through volcanoes
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b) the moving plates release pressure, therefore the magma becomes more
liquid
c) earthquakes shake it to the surface
d) the plates melt in the mantle and create magma which has to escape?
5. The Azores have been created by...
a) volcanic eruptions under the sea
b) earthquakes under the sea
c) earthquakes which broke off pieces of Africa
d) volcanoes that broke of pieces of Africa?
6. Sea floor spreading is...
a) the sea floor getting thicker as lava hardens
b) the Atlantic Ocean getting smaller as it is destroyed by volcanoes
c) New land being created at the Mid Atlantic Ridge making the Atlantic
Ocean bigger
d) Islands created by volcanic eruptions?
7. The sea bed in the centre of the Atlantic ocean is...
a) older than that found at the edges
b) the same age as that found at the edges
c) thicker than that found at the edges
d) younger than that found at the edges?
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8. Shield volcanoes are...
a) found at all types of plate boundary
b) shallow with runny lava
c) shallow with thick lava
d) violent and explosive?
9. Only one of the following sentences is true; which is it...
a) many people have been killed by eruptions at the constructive margin
b) eruptions at the constructive margin are not at all dangerous
c) eruptions at the constructive margin rarely cause deaths but can damage
property
d) ash from a volcano is not heavy so it will not cause damage?
10. Earthquakes at the divergent plate boundary...
a) are generally smaller and less destructive
b) are very large and dangerous
c) have been responsible for many deaths
d) are very rare?
Answers
1 = b, 2 = c, 3 = d, 4 = b, 5 = a, 6 = c, 7 = d, 8 = b, 9 = c, 10 = a.
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