Not sure what you mean. Are you referring to molten or semi-molten material going up the open front end of the pipe?
When a volcano “explodes” it’s a rhyollte magma. Very high viscosity with lots of water and gas under great pressure. When it gets to the upper levels of the volcano where the pressure holding the gas and water lessens, you have a big explosion. This stuff is plastic in the magma chamber and on its way up, it causes lots of faults. It’s not liquid or even like honey so it won’t go up a drill hole. I suppose a basalt lava might if the diameter of the hole was large enough but I don’t know.
If you go to a smelter, you will immediately see the difficulty they have keeping the tuyeres and tap holes open. The slag will solidify if there is any lessening of hear so lances are used to keep it flowing. The drill hole will have rapidly decreasing heat as you go up and I can’t think of any way to avoid that if you’re going any distance. You can’t artificially retain the heat and pressure of the magma chamber.