Ummm........Those are truely awe-inspiring........You can find alot of lavatubes that run horizontally around Mt Shasta, California......I've been in
a number of them.....some go on for miles.....I remember this one tube that was probably a good sixty feet in diameter that just went on and on...it
would break through the surface occaisionally and the mini-mountains of bat guano were amazing....testament to the hundreds/thousands of years that
the bats called the tubes home............