Lesson 5 - Oceanic-Continental Convergence

Question 1

What occurs when an oceanic and continental plate meet?

Answer 1

Denser oceanic plate forces under lighter continental plate (Subduction)

Question 2

What happens as the plate sinks into the mantle?

Answer 2

Acts to pull the rest of the plate behind it (Slab Pull)

Question 3

What does the downwarping of a subducted oceanic plate form? (+ example)

Answer 3

Ocean trench
Peru-Chile trench
Nazca plate subducted underneath S.American plate

Question 4

What builds up as the oceanic plate descends?

Answer 4

Friction with overlying continental crust

Question 5

Why does this occur?

Answer 5

Plates unable to move past each other smoothly
Occasionally lock together
Pressure builds up

Question 6

What takes place when this pressure is released?

Answer 6

Earthquakes

Question 7

What does compression + folding of the continental crust create?

Answer 7

Fold mountain chains
On leading edge of continental land masses
E.g Andes, South America

Question 8

What is created alongside friction when the slab of ocean floor descends?

Answer 8

Extreme heat (Also due to asthenosphere temperatures)

Question 9

What does this cause?

Answer 9

Partial melting of the crust

Question 10

What is the name of the area in which the crust is destroyed?

Answer 10

The Benioff zone

Question 11

At which depths does the plate;
start to melt
Get completely destroyed

Answer 11

Beyond 100km
By 700km

Question 12

What does the melting of ocean floor basalts create?

Answer 12

Basaltic lava

Question 13

How does this lava behave + why is this the case?

Answer 13

Rises through fissures in the rock
Lower density than the mantle

Question 14

How does it do this?

Answer 14

Burning/Stoping it’s way through overlying rock

Question 15

What happens when this lava reaches the surface?

Answer 15

Form volcanoes + erupt

Question 16

What is this process known as?

Answer 16

Vulcanicity

Question 17

What occurs when these volcanoes erupt?

Answer 17

Creates young fold mountain ranges (e.g. Andes)

Question 18

Describe the characteristics of the magma produced by these volcanoes

Answer 18

Silica rich
Viscous
Sticky

Question 19

How do these qualities affect the type of eruption which takes place?

Answer 19

Sticky magma blocks off its own vents
Sometimes leads to violent/explosive eruptions
Viscous magma prevents gas bubbles from expanding
Contributes to violent nature

Question 20

What % of all active volcanoes are found above subduction zones?

Answer 20

Around 80%