Q.  What causes volcanos to form?

A.  Volcanos are created by the friction between adjacent domains (small areas of the Earth's crust) when these domains move relative to each other.

Q.  You are saying volcanic rock doesn't come up from molten rock layers deep in the Earth?

A.   That's right. Molten rock isn't found until you go some 700 km down. Even if molten rock existed at shallow depth, standard heat-flow physics wouldn't explain how it could move upward in shafts made through solid rock.

Q.  Why do multiple volcanos tend to lie along a given line?

A.  This line is the border between two adjacent domains which are shifting relative to each other.

Q.   What causes shift of domains?

A.  Ultimately, expansion processes at the Earth's core (See Is the Earth expanding?).

Q.  Where is there more on this?

A.  At Making Mountains Out Of Movements [NU008].