okay guys so this question is for user 8782723 on and I know I couldn't answer the question but it's not letting me answer any questions and all those questions that I asked or wrong plus I tried to answer your question and it just gave a whole bunch of dots so so I'm just going to tell you the answer here so it's the pressure of the gases in the magma plus the new batch of magma ready to fill to the top that causes it to push out ​