Extrusive activity

Question 1

Starter sentence

Answer 1

The outpouring of material from the Earth’s crust produces a variety of landforms, the most significant of which are volcanoes and lava plateaux.

Question 2

What is their global distribution dependent on?

Answer 2

Their global distribution is largely determined by the pattern of tectonic plates.

Question 3

What is their landscape impact dependent on?

Answer 3

Their impact on the landscape depends on a number of factors, including the magnitude and scale of the event causing them and the types of material being extruded.

Question 4

What is the nature of the type of extrusive landform based around?

Answer 4

The nature of the type of extrusive landform is based around how gaseous/ viscous the lava is when it reaches the earth’s surface.

Question 5

Basaltic?

Answer 5

Lava produced by the upward movement of material from the mantle is basaltic and tends to be located along mid­ocean ridges over hot spots and alongside rift valleys.

Question 6

Andesitic?

Answer 6

Lava that results from the process of subduction is described as andesitic and occurs at island arcs or at destructive plate boundaries where oceanic crust is being destroyed.

Question 7

Introducing composite and shield

Answer 7

Magma rising leads to volcanoes but the exact landscape of the volcanoes depends on the lava type and in particular its viscosity, which in turn is related to the processes that lead to the magma reaching the surface.
In this case magma rising from within the mantle and partial melting due to subduction - figure showing shield vs composite volcanoes.