Constructive (O - O)

Question 1

1 (movement)

Answer 1

• Convectional drag causes Eurasian and NA plates to diverge

Question 2

2 (pressure)

Answer 2

• Pressure on underlying asthenosphere decreases
• creates a low pressure zone
• Lowers melting point so that upper mantle rock partially melts to form basaltic magma
• Known as decompression melting due to reduction in pressure

Question 3

3 (magma)

Answer 3

• results in molten low-density magma rising
• exploits cracks and fissures in rocks
• magma cools and spreads sideways
• Results in prominent ridges on ocean floor

Question 4

4 (ridges)

Answer 4

• Ridges characterised by a rift valley and transform faults
• associated with vulcanicity either underwater or on land
• e.g. as Iceland

Question 5

5 (new land)

Answer 5

• as plates spread, new land forms by rising lava filling the gaps
• known as sea floor spreading