On this picture:
D ) Crust ( 5 - 50 km )
C ) Mantle ( 50 - 2900 km )
B ) Outer core ( 2900 - 5100 km )
A ) Inner core ( 5100 - 6370 km )
Magma is a molten rock under the Earth`s surface. Magma is starting from 80 - 160 km below the surface. This is the mantle that is made of liquid materials.
Answer:
The material that forms volcanoes originate at C ) Mantle.