GCSE Geography Notes

GCSE Geography Notes The Restless Earth Tectonic Plates y

The Earths crust (which is thin  20 km) is continental (thicker and less dense) and oceanic (thinner and more dense).

y

The plates move because of convection currents in the mantle.

y

Plates y

meet at plate boundaries:

Destructive

plate margin

o

Two plates are moving towards each other, eg. N azca and S. A merican plate boundary. boundary.

o

The oceanic crust subducts under the continental crust into the mantle. It melts in the mantle due to friction and heat.

Composite-cone volcanoes (Popacatypetal or Cotopaxi) are formed as the continental continental crust

o

is pushed up, and andesitic, viscous magma rises to the surface. Deep ocean trenches also occur where the oceanic plate goes down. y

Constructive plate margin Constructive margins are where two plates are moving away from each other, eg. Mid-

o

Atlantic ridge. Basaltic,

o

runny magma from the mantle rises and forms shield volcanoes. If high enough,

these can become volcanic islands, eg. Iceland. Ridges

o y

are built built up from the sea b ed, as so much magma is poured.

Conservative plate margin Where

o

the plates are sliding past each other. They are moving in a similar direction but

different angles and speeds, eg. San Andreas Fault. o

The Pacific plate is faster than the N. American plate.

o

Pressure

builds along the fault, and a plate jerks past the other, causing a shallow focus

earthquake. Fold y

Mountains  Formation

At a destructive plate boundary that has two continental crusts (Collisional plate margin) the crust goes vertically to make bilateral fold mountains , eg. Himalayas (Mt. Everest, K2).

y

Fold

mountains are formed when rivers carry sediment, and it accumulates on the sea bed in huge

depressions called geosynclines. Over millions of years, the sediments are compressed into sedimentary sedimentary rocks. The sedimentary rocks were forced upwards into a series of folds by the movement of the tectonic plates. Anticlines, synclines and overfolds may occur. y

Unilateral

fold mountains also occur as the sediment is crumpled into unilateral fold mountains (eg.

Andes) in deep sea trenches. The compression in the trenches squeezes the sedimentary slab or rock

nappa  formation. onto the continent   nappa Fold y

Mountains  Land usage in the Alps (Case Study)

Location:

Central Europe; Formation: 30 million years ago by the collision between the African and

European plates; Population opulation : 12 million people. y

Farming

 The steep upland areas are used to farm goats, which provide milk, cheese and meat. On

the adrêt slope, it is warmer and vineyards are grown. In summer, you grow fruit, and the cows are taken to the top of the mountain, mountain, where milk is sent to the bottom by cable car (Transhumance ). The bottom of the fold mountain is fertile (rivers) and there is protection against the wind.

y

HEP

 The fast flowing water turns turbines in HEP stations. There are steep slopes, high precipitation

and summer melting. The cheap HE P can be used to power sawmills, fertilizer manufacture, etc. y

Mining  Salt, iron ore, gold, silver and copper were mined in the Alps, but the mining has de clines drastically due to cheaper foreign sources.

y

Tourism  (See Chamonix) Good com munication (near (near Geneva and Zurich airports, motorways). Good snowfall and crisp clear days. Beautiful scenery, 100 million tourists visit the Alps. There is a large amount of summer and winter sports available.

y

People adapt to the conditions : Goats are farmed on steep slopes because theyre well adapted at living there. Trees and man-made defences are used to protect against avalanches and rock slides. Animals are grazed in most high areas, as the soil isnt good there. Roads have been built throughout the Alps as there are limited communications. Tunnels have been cut through the mountains.

Volcanoes y

Different types of Volcano o

Composite cone volcanoes (Mt. St. Helens) are formed at destructive margins. Theyre made up of  ash and lava thats erupted, cooled, and hardened into layers. The andesitic lava is viscous and flows slowly. The volcano has steep-side and is usually destructive.

o

Shield volcanoes (Mauna basaltic

y

Destructive

Loa,

Hawaii) are formed at hotspots or constructive margins. The

lava is runny and flows quickly. quickly. The sides are gentle, and it is made up of layers o f lava.

plate margins: The oceanic plate is subducted under the continental crust, and is melted

and destroyed in the mantle. A pool of magma f orms, and rises through cracks in the crust (vents). y

Constructive plate margins : The magma rises up from the mantle into the gap created by the plates moving apart.

y

Hotspots :

y

Scientists predict volcanic eruptions by observing certain signs. Tilt-meters can be used for seeing if 

Some volcanoes also form over parts of the mantle that are really hot.

magma underground is being built-up. Seismographs can measure earthquakes. Gases are also emitted, by using robots to monitor them.

Volcanoes  Montserrat (LE DC) (Case Study) y

Cause: The Caribbean plate collided with the two American plates on each side. They sub ducted under the Caribbean plate. The lava was erupted from the volcano on the Caribbean plate in June 1997 (small eruptions started in July 1995).

y

Short-Term Effects: 5,000 people moved to the north. 23 died. Ash destroyed over 20 villages and two thirds of homes on the island were destroyed. Trees also by pyroclastic flows, and three quarters of  the infrastructure was gone.