How’d you get the “gunk” up the hole. Plus, you’d be dealing with felsic material with a lot of gas and water not separated yet from the lava. You’d probably have a non event.
There is undoubtedly a lot of faulting that would provide a route up and out if the lava is mafic and flows easily. Like what you get in Iceland.
Not sure what you mean. Are you referring to molten or semi-molten material going up the open front end of the pipe?