The location of vents associated with an eruption
is very complex. Vents locations are controlled by
the detailed structure of the earth they are found
in. If cracks are present, rising magma will
exploit these natural weakness zones and rise to
the surface. During an eruption, sometimes one
vent shuts down and another one opens up. This has
to do with the balance of pressure and gravity
forces as well as the rate of supply of the magma
from below. Magma that resides deep within the
crust will also deform the surface of the
earth-bowing it upwards like a balloon inflated
with air. This can cause new cracks to form and
these new cracks can become pathways that magma
follows to the surface. So your question is a good
one for which there is no "simple" answer. Like
people, each volcano is an individual and is
unique in certain respects.
I hope this answers
your question. There are many places on the WEB
and in other books where you can read about
volcanic vents and lava flows.
Click Here to return to the search form.