Types of Plate Margin Flashcards
what types of margin do earthquakes and volcanoes occur at
constructive and destructive
where does a constructive plate margin occur
where two plates are moving apart (diverging)
how does a volcano form?
plates move apart, pressure is released at the margin, release of pressure causes mantle to melt, producing magma, magma is less dense than plate above, so it rises and can erupt to form a volcano
how does an earthquake occur?
plates don’t move in a uniform way - some parts move faster than others, causes pressure to build up, pressure becomes too much and plate cracks, makes a fault line, causes an earthquake. Further earthquakes can occur along the fault line once created.
what landforms occur at constructive plate margins
mid-ocean ridges and rift valleys
example of an ocean ridge
mid-atlantic ridge
what can form along mid-ocean ridges
underwater volcanoes, can build up to be above sea level e.g. iceland
how are rift valleys formed?
- plates diverge beneath land, rising magma causes continental crust to bulge and fracture forming fault lines
- crust between parallel fault lines drops when plates move apart to form a rift valley
- as process continues, valley widens until it becomes a large basin that fills with sediment from the rift walls
where does a destructive plate margin occur
two plates moving towards each other (converging)
what occurs at a destructive oceanic-continental plate margin?
- deep sea trench
- fold mountains
- volcanoes
- earthquake
how is an ocean trench formed?
- continental and oceanic crust converge, more dense oceanic crust is forced under less dense continental crust
- seafloor and lithosphere bend and form a steep v-shaped depression
- leading edge of a less-dense tectonic plate meets the leading edge off a dense plate
- denser plate moves downwards into the subduction zone
what is an ocean trench?
are steep depressions in the deepest parts on the ocean where an old oceanic crust is pushed beneath either another oceanic plate or a continental plate
what is a mid-ocean ridge
an elevated region with a central valley on an ocean floor at a boundary between two diverging plates where crust forms from outpouring magma
what are the two processes concerning the formation of mid-ocean ridges
ridge-push and slab-pull
explain ridge-push (mid ocean ridges)
occurs when the growing bulk of the ridge pushes the rest of the tectonic plate away from the ridge, often towards the subduction zone
explain slab-pull (mid ocean ridges)
comes into effect in the subduction zone - is where the weights of the tectonic plate being subducted below the overlying plate dragging the rest of the plate along with it.
what is a rift valley
a linear-shaped lowland between highlands or mountain ranges created by the action of a geologic fault
what are fold mountains?
mountains formed from the folding of sedimentary rocks (sediment taken from rivers)
how are fold mountains formed?
- two plates pushed together, at compressing boundary
- takes millions of years
- compression zone, tectonic activity forces crustal compression at the edge of crust formation
- rocks are often less stable and so more susceptible to folding
- two plates force rock upwards into a series of folds
how do volcanoes occur at destructive plate margins
- oceanic crust is heated by friction and contact with upper mantle, this melts it into magma
- magma is less dense than continental crust above and so rises to the surface - creates volcanoes
how does an earthquake occur at a destructive plate margin
- when one plate moves under another, it can get stuck
- this causes pressure to build up
- pressure becomes too much and so plates jerk past each other - causes earhtquake
what occurs at a destructive oceanic-oceanic plate boundary
- ocean trench
- earthquakes
- volcanic eruptions
- island arcs
processes occurring at oceanic-oceanic destructive plate margin
same processes occur as at continental-oceanic, two plates moving towards each other, the denser of the two will be subducted
forms ocean trench and triggers an earthquake and volcanic eruptions
what creates an island arc
volcanic eruptions that take place under water
