V & e revision guide

Earthquakes and Volcanoes Revision

A few key words to remember...

Constructive Boundary (Divergent) - where two plates move away from each other resulting in new crust being formed.

Destructive Boundary (Convergent) - where two plates move towards each other - in the case of a plate consisting of continental crust meeting a plate consisting of oceanic crust, the oceanic crust will be subducted and destroyed as it is less dense.

Conservative Boundary - where two plates move alongside each other - although crust is neither created or destroyed here, earthquakes usually occur here.

Collision Boundary - where two plates of continental crust move towards each other creating fold mountains.

Volcano - a vent through which lava, ash etc. is erupted (often, but not always cone-shaped)

Earthquake - a sudden ground movement

Distribution of earthquakes and volcanoes

• All Earthquakes and volcanoes are at plate boundaries.•Many are around the Pacific Ring of Fire.•There is a belt running north to south in the middle of the Atlantic Ocean called Mid Atlantic Ridge•Earthquakes are in a belt across southern Europe and across Asia

Causes of earthquakes and volcanoes

Earthquakes and volcanoesDestructive plate boundaries

Earthquakes Composite volcanoes

Constructive plate boundaries

Earthquakes Shield volcanoes

Conservative plate boundaries

Earthquakes

Why people live near volcanoes and earthquakesVolcanoes• 1)Fertile soil material ejected from the volcano

rapidly breaks down (weathers) into a fertile soil rich in minerals needed for plant growth.

• Productive soil gives HIGH CROP YIELDS this leads to INTENSIVE FARMING in LEDC. E.g. In Merapi (LEDC) the hot wet climate allows 3 crops a year to be grown on the same piece of land (This supports a High population density).

• Mt Etna( MEDC) grapes and fruit yields are 5 times higher than national average

• 2)Tourist attractions e.g. trips to the rim of the crater, see geysers have mud baths or sand baths (Japan, MEDC) hotels accommodation, souvenir shops. Tourism provides jobs and brings money to these areas.

• 3)Valuable raw materials • Minerals e.g. sulphur, borax, pumice, Lava flows

build up new land e.g. Iceland, Hawaii, • 4)Hot springs for bathing heating, • 5)Used to generate geothermal energy. (Iceland)

Earthquakes• Many people have lived

there all their lives and can not afford to move (LEDC)

• Areas e.g California have plenty of jobs especially in the high tech industry

Effects of Kobe earthquake 17 Jan 1995

Primary• 200,000 buildings collapsed• I km stretch of expressway

collapsed• bridges collapsed along

130km of the bullet train route

• Trains derailed on minor lines

• 120 out of 150 quays in the Port of Kobe were destroyed.

Secondary• Electricity, gas and water supplies disrupted• Liquefaction• Fires caused by broken gas pipes lasted days

destroying another 7500 homes many made out of wood.

• Roads were at gridlocked delaying ambulances and fire engines

• 230,000 people made homeless and had to live in temporary shelters

• Short term shortage of blankets, clean water and food.

• 714 aftershocks• Industries including Mitsubishi and Panasonic

were forced to close.• FINAL DEATH Figure was 5500,40,000 injured• 180,000 houses totally destroyed.

Effects of Afghanistan Earthquake 4th Feb 1998

Primary• 27 villages totally destroyed• 4000 people died• 10,000 injured• 15,000 homeless.

secondary• Landslides• Avalanches• Starvation• Homeless people living in

sub zero temperatures without shelter.

• People forced to leave area with herds of goats.

• Communications destroyed

Effects of Mt St Helens volcano, 1980

Primary Every tree within 25km flattened.All wildlife within 25km blast zone destroyed.Road and Railways blocked by ash61 deaths most from poisonous gases.Logging companies destroyed in blast.

SecondaryEstimated 2 million birds, fish and animals killed.Deaths of all fish in local lakes and rivers from acidification.Thick layer of ash covered many western states.Electricity and phone lines disrupted.

LEDC – Mount Pinatubo, 1991

Primary• Volcanic explosion sent ash 30km

into air turning day into night.• Upto 50cm of ash fell on an area

of 50km.• Eruption continued for many days

Secondary• Weight of ash falling caused

200,000 buildings to collapse.• Gas and Electricity cut off for 3

weeks.• Water supply contaminated.• Roads and bridges unusable due

to ash.• Over 1 million animals died and

farming impossible for two years.• Flooding and Lahars killed 70

people.

Reducing the effects of earthquakes.

• If people PLAN and PREPARE then the risks can be REDUCED.• Older buildings can be retrofitted to strengthen them to

reduce the effects of shaking.• Computer controlled roof weights to counter the shock

waves.• Cross bracing to give strength and prevent twisting automatic

sprinkler system and gas shut to prevent fires• Automatic window shutters to prevent falling glass• Rubber shock absorbers

What can LEDCs do?

• Appropriate technology can be used in LEDCs.• Bamboo houses ( Costa Rica) are strong yet

flexible • Hollow concrete bricks used causing less

damage if they fall

Plan prepare act

• Preparation in many schools ( Kobe ) earthquake preparation is taught in schools.

• Drills ( Japan Disaster prevention day)

Reducing the effects of a volcano• Scientists look for increases in seismic activity,

e.g increases in temperature or mineral content of nearby springs.

• Tilt meters to measure the angle of the slope.• Restricting access.• Improve roof design ( e.g sloping roof )• Evacuation.• Build walls/ channels to divert lava from

villages.

Responses to earthquakes

• Earthquake shaking maps can help with planning and responding to earthquakes.

• Seismometers to measure earth movements • Building codes and planning restrictions eg to

avoid areas in danger of liquefaction in Kobe.

Responses to a volcano

• Evacuation.• Divert the lava.• Military bombs to divert lava .• Keep towels and tape, water etc. in

emergency kit.• Exclusion zones.