Very good explanation of caves. As I mentioned down below
I have done a little caving myself mostly in Idaho, solution
type and in the great lava rift, your lava tubes. true most
of these are horizontal and may slope a little. Arizona is
where I worked with some real expert cavers and Colorado
where I tend to look around here and there.
If I can be of assistance let me know.
BTW the entrance is what is peculiare (sp) lookes setup
like a mine entrance or maybe a temple entrance in the mid-
east.
Take Care
D2