Download Video on Plate Dynamics

Geography 10
Plate Dynamics Video
Earth Revealed
Ms. Ripley
Lava
Mountains and valleys
Plates – ridges slabs of rocks – moving and huge (sometimes the side of a
continent). Boundary between plates – coincide of narrow zones of earthquakes and
volcanoes,
San Andreas Fault – N.American plate grinds against P. plate. This interaction is
the steady uplift of the mountain ranges.
Geological development of the landscapes that we live.
Interesting and earth scientist want to figure this out.
Boundaries of the plates
Most plates contain both oceanic and continental crust. In few places – Iceland –
mid Atlantic ridge – broad zone across Iceland. Rifts – small shallow earthquakes.
Guessers and hot springs evidence the plates are hot. Fissures – crust is being
pulled apart. It solidifies adding new edges to the plates. This type of boundary –
divergent boundary. Plates separate from one another.
African continent – divergent boundary – N – new crust formed – S.Arabia have
split apart and the red sea making up the emptiness. Could become as wide as the
Atlantic today.
Oceanic crust 70% of earth’s crust. Mid Ocean ridges. Crustal Growth – sea floor
spreading. Earth’s volume has been the same. Plates can grow as long as some are
growing smaller. Dramatic topography. Deep marine trench. One plate slips
beneath the other (subduction) and some just crumple together.
3 types of convergent plate boundaries
Ocean-ocean – Marianna trench and island – volcanic chain above convergent zone,
lava erupted is basaltic
Oceanic – under continental plate – Andes (S.America). Pacific plate is going
under. Volcanic chain – granitic composition
Continent – Continent (collision zone). There used to be an ocean plate subverging
– ocean plate disappeared. Zone Himalayas/Alps. Conversions will stop along that
zone.
Oceanic rock always sinks under continental rock. B/c it’s heavier. Subduction –
slow moving currents of hot mantle rock. As the plate sinks, earthquakes occur in
it.
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Geography 10
Plate Dynamics Video
Earth Revealed
Ms. Ripley
700km beneath the surface. These allow seismologists – diving into the mantle –
creating friction and heat. Molten rock rises to form arc shape chain of volcanoes.
Island arc system.
Continental crust is thicker, internal structure that has evolved over years.
Plate tectonic theory – forces – finding the mechanism – challenging problem – way
into the earth’s interior.
Lithosphere 100km thick – plates float into the ethnisphere which is soft and
molten. Several different theories all agree unequal distribution of heat within the
mantel. Convection in the mantle for plate movement accepted theory.
Rock inside the earth flows like a fluid (application of heat to a pot of water) –
heat inside the earth – portions of the mantel to
Fundamental force of convection – gravity cool matter more dense – under gravity
it will sink
Silly Putty analogy for rocks. Effects of rate for straining the rock. Silly putty –
fast rate – fracture (near the surface of the earth 0- if we deform them quickly),
if we apply a stress to it – material will flow not fracture- where rocks are hotter,
long term rates – folds etc. Extreme rates – let gravity be the only stress
operating on it. With time it will still flow but at a much slower rate.
Rocks will bend and flow. Allow the convection process to take place within the
earth.
Reason earth’s mantle is convecting – still primary heat – by radioactive decay, this
heat within the interior wants to flow out – it is convecting.
Convection process – fundamental – role of convection in plate motion. Hot rock
concects them. Plates slide away from drag and gravity from the convection
current. Third possibly – plates are being pulled down into the earth by gravity.
Plate Push at ridge – hot rising material falling off the ridge
The Video keeps going but it’s very boring! And theories etc…
Mantle – is like tar – convecting very slowly
Core – like water – convecting very rapidly
Convection is occurring within the planet – it changes the shape of the earth –
satellite – earth is not a smooth sphere. What is left over without the mountains is
very bumpy. Cold currents depressions. We can map the convection patterns.
Beneath the middle of the plates where a special type of convection takes place.
These are known as mantle plooms. Occur in atmosphere – thunderclouds –
accelerated manner. Form of hot spots – regions of volcanic activity – circular in
space.
Topography of ocean floor – we don’t know about all of them but some of them
seem to be hot spots. Extra lava – bubbles out through the plate and it builds an
Island – like Hawaii. Keeps making new volcanoes. Chain of volcanoes – Hawaii.
Showing motions of Hawaiian hot spot.
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Geography 10
Plate Dynamics Video
Earth Revealed
Ms. Ripley
Hawaii will drift off the hot spot as the plate drifts.
Geothermal hot spots – Yellowstone Park.
Not all hot spots are under the ocean floor.
Plate tectonics
Model of how the earth works
Mountain building, sea floor spreading
Questions: Why do plates move? Not answered yet -but soon!
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