Plates Flashcards
Earths Core?
Inner core - solid ball of iron and nickel, 6000 degrees
Outer core - semi-molten of iron and nickel
Mantle?
Nearest to the core is quite rigid
Asthenosphere (above layer nearest to core) semi-molten
Very top is rigid
1000-3500 degrees
Earths Crust?
Rigid top part of the mantle and the crust is known as the lithosphere.
Continental Crust - thicker (30-70km thick), less dense
Oceanic Crust - thinner (6-10km thick), more dense
Theories about tectonic plates moving?
Convection Currents
Slab Pull
Ridge Push
What are Convection Currents?
Earths mantle is hottest closest to the core, so lower parts of the asthenosphere heat up, become less dense and slowly rise.
As they move towards the top, they cool, become more dense and slowly sink.
Circular movements = convection current.
Drag on base of tectonic plates causing them to move.
What Is Slab Pull?
Destructive plate margin, denser crust forced under less dense crust.
Sinking of plate edge pulls the rest of the plate towards the boundary.
What is Ridge Pull?
Constructive plate, magma rises to surface and forms new crust. Heats surrounding rock, which expand and rise above the surface of surrounding crust, forming a slope.
denser rocks moves downslope, away from plate margin, causes plates to move apart.
Sea-floor spreading?
Tectonic plates diverge, magma ries, cools and forms new crust.
New crust will diverge further and new crust continue to form.
Creates Mid-ocean ridges.
How are Constructive Ocean Ridges formed?
Plates are diverging underwater.
EXAMPLE; Mid-Atlantic Ridge, Eurasian plates and N American plate.
Underwater volcanoes erupt along mid Atlantic ridges, build up to be above sea level. E.G. Iceland
How are Constructive Rift Valleys formed?
where plates diverge beneath land, rising magma causes continental crust to bulge and fracture, forming fault lines.
Plates continue to move apart, crust between two parallel fault lines drop down = Rift Valley.
EXAMPLE; East African Rift System (4000km long)
What are Constructive Plate Margins?
Two plates are moving apart.
Volcanoes - as plates move apart pressure released, mantle melts, magma rises, erupt.
Earthquakes - some parts will move faster than others, pressure builds, plates cracks causing fault lines and causes earthquakes.
What are Destructive Plate Margins?
Occurs when two plates are moving towards each other (converging).
What occurs at Destructive Oceanic-Continental Plate Margins?
- More dense Oceanic crust subjected underneath Continental crust. Forms DEEP SEA TRENCH, e.g. Peru-Chile trench in Pacific
- FOLD MOUNTAINS form where plates meet. Made from sediment that has accumulated on continental crust, folded upwards.
- VOLCANOES, oceanic crust heated by friction, melts into magma, magma less dense and will rise to surface.
- EARTHQUAKES, plates get stuck, pressure builds up, jerk past each other.
What occurs at Destructive Oceanic-Oceanic plate margins?
DEEP SEA TRENCH, EARTHQUAKE and VOLCANOES formed.
Volcanoes can also take place underwater creating ISLAND ARCS, e.g Mariana Islands.
What occurs at Destructive Continental-Continental plate margins?
Two continental plates, neither subjected, so no volcanoes but there will be EARTHQUAKES.
FOLD MOUNTAINS also form.
