Constructive plate boundaries

Question 1

1.

Answer 1

Convectional drag causes Eurasian and NA plates to diverge, resulting in molten magma cooling and spreading sideways, pulling the 2 plates in opposite directions

Question 2

2.

Answer 2

Pressure on underlying asthenosphere decreases, creating 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.

Answer 3

Basaltic magma is low density so rises up, exploiting cracks and fissures in rocks. Results in prominent ridges on ocean floor

Question 4

4.

Answer 4

Ridges characterised by a rift valley and transform faults and are associated with vulcanicity either underwater or on land in cases such as Iceland. Some magma may erupt onto surface as underwater volcano and form land.