geography - restless earth

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structure of the earth - key idea 1


inner core - solid - iron and nickle - 5500 degrees - (1260km)

 outer core - liquid - iron and nickle - 4500 degrees - (2220km)

 mantle - solid/liquid - magma - 3000 degrees - (2900km) convection currents happen here

crustsolid - granite (continental - 200 years new) / basalt (oceanic - 3.8 bill yrs old) (5-65km)

wegener suggested all continents were together at some point - continental drift. - this theory was regected untill scientists found outy about convection currents and techtonic plates


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Tectonic plates- key idea 1


TECHTONIC PLATES - The earth's crust is broken up into pieces called plates. These plates can move due to convection currents in the mantle - where 2 plates meet is called a plate boundary.

CONVECTION CURRENTS - In the mantle, the magma is liquid and solid so convection currents move round the more/less dense magma which mnoves the plates.( constructive - eq/volcanoes detructive - eq/volcanoes conservative - eq collision - eq/fold mount

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fold mountains, types of volcanoes and trenches.

oceanic trench -  destructive boundary when a more dense continental plate subducts a less dense oceanic plate leaving a deep ocean trench (e.g. mariana trench)

composite volcano - destructive boundary steep sided volcano which consists of layers of ash and magma, sometimes the magma solidifies in vents which means a huge explosion is needed to get rid of it (e.g. soufiere hills)

shield volcano - constructive boundary wide based, gently sloping volcanoes which are calmer and have runnier lava. the gap filled by the constructive boundary is filled with magma. (e.g. erta ale in ethiopia)

hotspot - constructive/destructive boundary 1. due to hot mantle plumes that rise. 2. lithospheric extension that permits passive rising of melt from shallow depth. (e.g. kilauea and loa - shield volcanoes is hawaii)

fold mountains - collision/destructive boundary when 2 plates push and are of equal density they bunch up to form fold mountains collision boundary, this is due to fold in the sea sediments . Or, a continental plate subducts an oceanic plate so molten material rises to form mountains at destructive boundaries. (e.g. himalayas, rockies, alps andes)


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CASE STUDY - fold mountains (Andes)

The Andes are the longest fold mountain range in the world - stretching the whole east coast of south america.

FARMING - terracing is used on steep slopes (cutting out the slope to create flat areas). this means thinner soils dont slide down the hill and water is retained better. Most crops are grown in lower valleys where the land is flat. - cash crops are produced (soybeans, cotton, rice).

MINING - Andean countries rank in top 10 for tin and half of Peru's exports are from mining. gold ores are loosened by daily dynamite blasts. Rock then sprayed with cyanide and then gold is extracted. gold mines bring new jobs however result in lack of services, increased crime, noise from dynamite, water pollution from cyanide.

HYDRO ELECTRIC POWER (HEP) - Steep slopes encourage the flow of water whivh generates electricity easily. also melting snow in winter adds to the water supply but variation of weather throughout the year is a disadvantage.

TOURISM - Many natural attractions (peaks, volcanoes, glaciers and lakes)

PROBLEMS IN ANDES - El nino (frequent change in climate) - flooding, landslides,  farmers.

                                    - tourism damages landforms (walking and litter)

                                    -people farming coca plant started to chew the plant                                                                    (main ingredient in cocain), taking it away will cause riots

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CASE STUDY - Monserat earthquake (soufriere hills)

Date of eruption : June 25th 1997 (2 smaller eruptions July 1995) - dormant before 1995 (asleep)

Location of eruption : Monserat - small island in caribbean sea. - the captial (plymouth) destroyed

CAUSES - lay on destructive boundary north american plate subducted caribbean plate - magma rises = eruption.

PRIMARY EFFECTS - 19 deaths - capital city abandonned - unemployment rose - 20 villages, schools, airport,                 hospitals, farmland destroyed due to pyroclastic flow. 

SECONDARY EFFECTS - fires started as gas pipes were set alight - smoke and ash poisened water - towns made          unhabitable - tourism droped and businesses destroyed (disrupted economy) - population                                                decline (2/3rds of population left since 1995) - volcanic ash improved soil - tourism is now                                                  increasing to see volcano (increasing economy)  

IMMEDIATE RESPONSES - People evacuated to sfer areas - shelters built - temporary infastructure built (roads) -           UK provided £17million of emergency aid - local services provided search and rescue.

LONG-TERM RESPONSES - Exclusion zone set up - volcanic observatory built - UK gave £41million to help rebuild aiports and housing.


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