A volcanic pipe is a vertical conduit through which magma travels from a magma chamber to the surface during a volcanic eruption. Volcanic pipes are significant in geology for understanding the transport of magma, the formation of volcanic features like diatremes, and the emplacement of kimberlite pipes that may host diamonds.
Reference: Mitchell, R. H. (1986). “Kimberlites: Mineralogy, Geochemistry, and Petrology.” Plenum Press.