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Physical Geography A-level > Plate margins > Flashcards

Plate margins Flashcards

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1
Q

Divergent plate margin is between…

A

oceanic crusts.

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2
Q

Divergent plate margin- the convection currents…

A

diverge the plates apart.

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3
Q

Divergent plate margin has basaltic…

A

magma. It contains less silica than granitic magma, less air is trapped, therefore denser.

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4
Q

A ridge is formed at…

A

divergent plate margin and filled with lava.

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5
Q

Pahoehoe is…

A

a form of a basaltic lava flow, with a smooth or rippled surface.

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6
Q

Pahoehoe type of lava is common in…

A

Hawaiian volcanoes.

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7
Q

A transform fault margin is…

A

conservative plate margin.

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8
Q

At transform fault margin the plates have…

A

similar densities.

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9
Q

A transform fault margin causes…

A

strike-slip(almost vertical fractures) and earthquakes.

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10
Q

At transform fault margin a lot of energy is…

A

stored by the tension.

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11
Q

At transform fault margin the earthquakes are…

A

shallow, so more seismic waves reach the surface and they have more energy. This results in stronger earthquakes.

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12
Q

At Collision plate margin the plates have…

A

similar densities.

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13
Q

Plates At Collision plate margin are mostly…

A

continental.

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14
Q

Because the atmosphere is less dense than mantel At Collision plate margin…

A

the crust moves upwards(isostatic uplift) and mountains are formed.

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15
Q

At Collision plate margin, sometimes, the asthenosphere…

A

moves with crust upwards, cools, solidifies and produces layers=folds.

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16
Q

Strata is…

A

a horizontal layer of material made of several parallel layers on each other.

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17
Q

Strata is formed by…

A

the folds At Collision plate margin.

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18
Q

At convergent plate margin the oceanic plate…

A

melts as it is subducted.

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19
Q

At convergent plate margin, the plates have…

A

different densities. Heavier is subducted.

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20
Q

At convergent plate margin oceanic trench is…

A

formed.

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21
Q

Benioff zone is…

A

the area where the oceanic plate is scratched against the continental plate. This is the focus of an earthquake.

22
Q

The subduction zone is where…

A

the oceanic plate is subducted under the continental crust.

23
Q

At convergent plate margin isostatic change causes…

A

eustatic change, which is a change in the ocean basin. Tsunamis are triggered.

24
Q

The magma chamber is located…

A

under the earth surface.

25
Q

The magma chamber is…

A

a large pool of molten rock. There is a very high temperature and pressure=melting the rock above and causing fractures in the rock.

26
Q

Volcanic island areas have a margin between…

A

two oceanic crusts.

27
Q

At Volcanic island areas both plates are…

A

weak and have similar densities.

28
Q

At Volcanic island areas, an accretionary wedge is…

A

formed.

29
Q

At Volcanic island areas, there is subduction of…

A

the plate below the accretionary wedge.

30
Q

Volcanic island areas the trapped…

A

magma pops up as the pressure builds up by the subduction of one plate.

31
Q

Tephra is…

A

rock and other particles ejected by volcanoes. It must be larger than 2mm, otherwise, it is ash.

32
Q

Types of volcanoes:

A
  • dome volcanoes

- strato / composite volcanoes

33
Q

Dome volcanoes are created by…

A

small masses of rhyolitic magma, which are very viscous as they are high in silica.

34
Q

The dome grows by…

A

an expansion of the lava within, and the mountain forms from material spilling off the sides of the growing dome.

35
Q

A lot of gas is…

A

trapped in the rhyolitic magma, so the lava dome can violently explode, releasing a huge amount of material(ash, tephra)

36
Q

Types of magma:

A
  • basaltic

- rhyolitic

37
Q

A pyroclastic flow is…

A

a fast-moving current of hot gas and tephra.

38
Q

Rhyolitic magma is high in…

A

silica, so very viscous and contains high levels of gas. The temperature is around 650-800 degrees.

39
Q

Basaltic magma has quite low…

A

silica content, so it has low viscosity and traps much less gas. Temperature is around 1000-1200 degrees.

40
Q

An example of a composite volcano is…

A

Mount St. Helens.

41
Q

A composite volcano has…

A

conduit system that channels magma from deep within the Earth to the surface. They can have clusters of vents, with lava breaking through walls on the sides of the mountain.

42
Q

A composite volcano can grow…

A

a thousand meter tall.

43
Q

Composite volcanoes erupt with…

A

great violence.

44
Q

In a composite volcanoes pressure builds as…

A

gases, under immense heat and pressure, are dissolved in the liquid rock. When the magma reaches the conduits the pressure is released and the gases explode.

45
Q

Dome volcanoes can be found…

A

in the crater of Mount St Helen.

46
Q

Cinder cones are created by single…

A

vent.

47
Q

Cinder cone volcano is built as…

A

gas-charged lava is blown violently into the air, it breaks into small fragments that solidify and fall around the vent to form an oval cone.

48
Q

Basaltic magma is present in…

A

cinder cone volcanoes.

49
Q

At the subduction zone, deep sea…

A

ocean trenches are found.

50
Q

Ocean trenches are…

A

long, narrow depressions in the ocean floor, with depths up to 11 km.

51
Q

Tranches are found adjacent…

A

to land areas associated with islands arcs.

52
Q

The trench is usually…

A

asymmetric, with the steep side towards the land mass.

Physical Geography A-level (33 decks)

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