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Earthquakes and volcanoes, earthquakes&volcanoes do not happen…
Earthquakes and volcanoes
Topic 17
Earthquakes
cause
rocks under stress and pressure suddenly break and move
2 main parts:
Focus/Origin
where the earthquake takes place
Epicentre
the point directly above the focus
shockwaves
the energy is released as
waves
they are spread in concentric circles around the epicentre
can travel long distances
can cause shaking and damages
damage depends on:
strenght
depth of focus
distance from epicentre
population&buildings
how to measure:
Richter scale
amount of energy produced my an earthquake with a scale of 0-12
Volcanoes
opening in the Earth's surface
magma (molten rock), solid rocks, gas escape
magma on surface=lava
2 types of volcanoes:
Strato-volcanoes
magma builds up in the magma chambers
explosive eruption
steep sides
thick&acid (viscous) lava
bombs, ash →death&destruction
e.g. Etna (Italy)
Shield volcanoes
formed where there is less pressure but here is a weakness in the Earth's crust where magma can leak from
less explosive
gentle slopes
flat
runny lava
e.g. Mauna Loa (Hawaii)
activity types
Dormant
not erupted recently, may erupt (Mount Fuji - Japan)
Extinct
will not erupt again (La Gomera - Canary Islands)
Active
regular eruptions (Etna)
frequency of eruption
Topic 18
Earth's structure
crust→outer layer (collection of tectonic plates)
mantle → layer of magma
outer core
inner core (hottest point)
plate movement
plates move due to convection currents
they can:
move apart →
Divergent boundary
magma rises and creates new crust
results→ earthquakes&shield volcanoes
move towards each other→
Convergent boundary
one plate goes under the other (subduction)
old crust destroyed
results→ earthquakes&strato-volcanoes
move side by side→
Conservative boundary
no crust created or destroyed
results→earthquakes (no major effect)
speed of movement
about 40mm per year (very slow)
Topic 19
volcanoes&earthquakes → near plate boundaries
but can also happen further
2 main reasons why
plates move at a slow rate
over millions of years→they move far
result→ volcanoes move away from boundaries (becoming dormant or extinct)
weakness in the crust
the crust can have cracks even far from boundaries and can cause earthquakes
Hawaii
2 of the world's most active volcanoes (Kilauea-Mauna Loa)
1250km from the nearest plate boundary
magma rises from a hot spot in the mantle → formation of volcanoes
Earthquakes
positive impacts
underground minerals may be brought up to surface
negative impacts
destruction + death + tsunamis
Volcanoes
positive impacts
tourism
minerals
used for geothermal power
negative impacts
destruction + death + pollution + aircraft problems
Topic 20
volcanic hazards
people at risk
500 million. increasing→urbanisation
high risk areas
Pacific 'Ring of Fire'
hazards → ash,lava
secondary→floods, mudflows, lahars
opportunities
volcanic soils are fertile
volcanic heat provides energy for hot springs&thermal areas
volcanic activity produces mineral wealth
volcano tourism
Topic 21
reducing the impacts of earthquakes
best advanced warning→9sec
construction of buildings that can withstand strong ground movements
low structure with reinforced concrete
built on solid rock
deep foundations
reducing the impacts of volcanoes
most give out warning signs before major eruption
steam+gas
small lava flows
minor earthquakes
changes in chemical composition of air&water around volcano
predicting eruptions
checking the ground from above (satellites)
checking the air from above (aeroplanes use remote sensors)
checking below sea level (plate boundaries are explored by mini submarines)
checking on the volcano (scientists monitor ash etc)
earthquakes&volcanoes do not happen everywhere, mainly at plate boundaries