I understand the process of volcanism and the reason for magma deposition on the surface of the earth.
What is not clear to me, or what seems to be less well explained is why eruptions occur and then stop. What is the operative cause or causes of a flow to start or stop?
As far as my understanding goes there would seem to be two possible obvious explanations:
(1) The magma rises in bubbles, like a lava lamp, through the earth, so the flow begins when the bubble reaches the surface and stops when the bubble is exhausted.
(2) The magma rises as a constant stream, but causes earth to build up around the stream, eventually snuffing it out by mass accumulation. In this explanation, the lava constantly searches for thin spots where it erupts until it blocks itself off, then the pressure forces its way through some new location.
Are either or both of these explanations correct or incorrect? Is there a mechanism I have not considered?
Lava eruption in Iceland the size of Manhatten that began in 2014.