Answer:
The geological features that are usually present below an active volcano are as follow-
1) Mantle plume- This is the region containing a huge concentration of magma rising from the mantle-core boundary. This exerts huge pressure towards the surface of the earth thereby lifting the land and subsequently forms a volcano.
2) Magma chamber- These are chambers that are comprised of magma bodies and with the increasing pressure and temperature, they tend to rise up and form volcanoes.
3) D(i)ke- This are vein-like structures within which the magma moves upward with increasing force. They cross-cuts the country rocks.
4) Sills- This is a parallel vein-like structure along which magma flows and they are parallel to the country rocks. They are not that frequently found like d(i)kes.