volcanoes and earthquakes Flashcards
structure of the earth
crust
mantel
outer-core
inner-core
crust
outer layer, can be thick or thin depending if its on land or ocean
oceanic crust (heavy basaltic rocks)
continental crust (granite rocks, lighter and stronger)
mantel
just below the curst, its a bit like a semi-solid layer.
hot currents moving it causing plates to shift
outer-core
beneath the mantle, its a liquid layer made of melted iron and nickel. this creates the magnetic field around the earth
inner-core
at the very center, there’s a solid ball of iron and nickel. this solid part also adds to the earth’s structure and its magnetic effects.
plate techtonics
earths outer layer
like a puzzel piece: lithospheric plates
these plates float of gooey layer: as asthenosphere
below there’s a slower river of hot melted rock: magma moving steadily
seven major tectonic plates
made up of different types of crust
plate boundries
where plates rub, crash, move away from eachother
types of volcanoes
-active- still erupting frequently
-dormant- not currently errupting but could
-extinct- highly unlikely to errupt
-shield volcanoes- low, gently-sloping sides, formed from thin runny lava and have fairly frequent gently eruptions
- strato volcanoes- alternating layers of ash and lava, eruptions can be violent with ash clouds and lava flows and flows down very fast at high degrees.
effusive eruputions
flows li,e snow, smooth syrap. lava is runny and thin
explosive eruptions
explodes like a burst of fireworks, lava is think and gooey and explodes violently. rocks, ash, debris is thrown into the air =. pyroclastic flows mixing with hot steam ash, rock and dust. these move down the volcano very fast up to 400c
zones of activity
where plates are in almost constant motion. are the plate boundires or margins. these margins are classified in 4 types of groups.
constructive margins
when 2 plates move away from each other
magma rises from the mantel filling the gap, creating new oceanic crust. called sea-floor spreading
mid- atlantic ridge
destructive margins
where continental crust and oceanic crust moves to each other and subduction occurs. (bc oceanic is heavier)
friction causes the crust to melt and some newly formed magma may be forced to surface, forming volcanoes.
can trigger earthquakes, forms trenches
conservative margins
where two plates slide past each other
no new activity, earthquakes can occur
pressure will build until released causing earth to jerk violently
converge
—-> <—- (destructive, subduction)
volcanoes, earthquakes, trenches
diverge
<—- —-> (constructive) (subduction)
volcanoes, earthquakes
conserve
<—- (conservative)
—->. no transformation (if stuck = earthquake)
collision
—-> <—- (2 continental plates)
earthquakes
seismic activities
movement of the earth in an earthquake
measured in a seismograph (seisometer)
measures how much the earth shakes and plots this on a graph
how is the magnitude of an earthquake measured?
strength (magnitude) of an earthquake is measured using the richter scale
an increase 1 = x10 = shaking x10 more = more severe
why live next to a volcano eventhough it is dangerous
fertile land- the ash forms an excellent soil for growing crops and providing food
farming near volcanoes has been going on a long time and now the small settlements have changed into important regional centuries
many volcanoes have become tourist attractions and local businesses have sprung up around them providing much needed employment
many volcanoes are in poor countries so the people don’t have the money to move.
case study- volcano in Montserrat
before 1995, most 11,000 people relied on tourism and farming on the fertile land
Montserrat sits on the destructive (subduction) between Caribbean and atlantic plate
July 1995 increased activity caused evacuation
many evacuated to other Caribbean island or UK
april 1996 south of island was empty
lava was made from andesite and was so thick it didn’t flow
june 1997, erupted, 5 million cubic meters of lava
pyroclastic flows
killed 19 farmers, who were getting food for evacuated people
destroys settlements
the north changed from green to urban settlement bc they needed to support the evacuated people: housing
people are left making a living out of tourism to see the still smoking soufierre hill volcano
seismic monitoring
detect movement of tectonic plates
deformation monitoring
detect movement of ground on and around volcano
environmental monitoring
assessing the gas and ash released and the effects on the environment
volcano logical monitoring
observe the gravity lava dome and the chemistry of the lava
