geog book 4 chap 1 Flashcards
what does the plate tectonic theory explain
earth has a 3 layered structure
earth’s lithosphere is broken up into huge pieces called tectonic plates
tectonic plates are constantly moving
plate movements result in formation of land forms and phenomena
what is the thickness and temperature of the core, mantle and crust
core - 4400-6000°C, 3300km
mantle - 1000-3700°C, 2900km
crust - 6-70km
what are the 2 crusts that make up tectonic plates
continental - makes up land masses, less dense than
oceanic - makes up seafloor
how do convection currents lead to tectonic plate movements
convection currents are the movememt of heat within the mantle
material in the mantle is heated by the core
the mantle becomes less dense, expand and rises
the mantle spreads out beneath the plates
the mantle drag the plates apart as it spreads beneath the plates
the hot mantle cools and starts to sink pulling the plates along
slab pull force occurs when a denser plate is dragged under a less dense plate
the process is subduction
as the plate subducts, it pulls the rest of the plate down into the mantle
this drives the downward moving portion of the convection currents
the sinking mantle will get heated up again by the core and the cycle repeats itself
what is the evidence of seafloor spreading?
where 2 plates move away from each other at divergent plate boundaries causing seafloor spreading
magma from deep within the earth rises through the mid-ocean ridge
forming a new oceanic crust
why does the evidence of seafloor spreading support the plate tectonic theory - age of rocks
the age of rocks at the seabed shows a pattern
the rocks nearer to the crust of the mid ocean ridge are the youngest
rocks further away from the mid ocean ridge are progressively older
this shows how the oceanic crust is created at divergent boundaries
and then moves laterally on both sides of mid ocean ridge as seafloor spreading continues
why does the evidence of seafloor spreading support the plate tectonic theory - little sediment accumulation
sediment accumulation is found at oceanic trenches
as the older oceanic crust is being destroyed at oceanic trenches
oceanic crusts are usually younger than continental crusts
proving that new crust is continually formed at divergent plate boundaries at the mid ocean ridge
as plates moves the older crust is destroyed further away at oceanic trenches
what is normal polarity
when the magnetic north points roughly towards the geographic north and the magnetic south points roughly towards the geographical south
what is reverse polarity
when magnetic north points roughly towards geographic south and vice versa
what is magnetic striping
has a zebra-like pattern
strips of normal polarity rocks alternating alongside strips of reversed polarity rocks on the seafloor
and are symmetrical on both sides of the mid ocean ridge
why does magnetic striping occur, and how is it evidence of earth’s polarity at that time
basaltic rocks from the oceanic crust are volcanic rocks formed from iron-rich lava, which contains magnetic materials
iron rich lava erupts, cools and solidifies
magnetic materials point towards earth’s magnetic north
showing evidence of earth’s polarity at that time
why does the evidence of magnetic striping support the plate tectonic theory
zebra- like pattern is symmetrical on either side of the mid ocean ridge, which is not a random or isolated occurence
this is evidence that plates move supporting plate tectonic theory because
oceanic plates move away from each other
iron rich lava erupts from the of the mid ocean ridge
lava cools and solidifies as plates move apart
when earth’s polarity reverses and rocks record these reversals
over time, as more lava moves away from the ridge due to plate divergence
causing the symmetric zebra like pattern to form
what are divergent plate boundaries?
2 tectonic plates move away from each other
what happens at oceanic-oceanic divergent plate boundaries
- 2 oceanic plates move apart
- decrease in overlying pressure causes parts of the mantle to melt forming magma
- magma rises through weak areas in the crust to the earth’s surface
the magma fill gaps causes by spreading plates
how are mid ocean ridges formed by divergent plate boundaries?
lava cools and solidifies forming basaltic rocks which make up a new oceanic crust
extensive underwater mountain chain, the mid ocean ridge, forms
how are submarine volcanoes formed by divergent plate boundaries?
the centre of the mid ocean ridge is a deep rift valley with steep sides
magma rises through the weak areas to the earth’s surface, forming submarine volcanoes
after multiple eruptions, volcanoes break the surface of oceans forming volcanic islands
hence earthquakes occur due to the stress and tension released when plates move
what happens at continental-continental divergent plate boundaries & how do rift valleys, volcanoes and earthquakes occur there
- 2 continental plates move apart
- rocks eventually fracture forming parallel faults
- rocks between these faults collapse to form a deep rift valley with steep sides
- as plates move apart, there is a decrease in overlying pressure causing parts of the underlying mantle to melt
forming magma
magma rises through the weak areas in the crust to the earth’s surface, forming volcanoes
earthquakes occur as stress and tension are released when plates move
give an example of tectonic phenomena that is formed at oceanic-oceanic divergent plate boundaries
oceanic north american moving away from the oceanic eurasion plate forming
mid atlantic ridge (MOR) and surtsey island (RV)
give an example of tectonic phenomena that is formed at continental-continental divergent plate boundaries
Nubian plate moving away from somalian plate forming
east african rift valley
mount kenya, mount kilimanjaro (volcanoes)
