Is this a phobia, or whatever, what is this called?

I get this weird feeling inside of my when I am by a really tall tree, and super tall building. But I don't mean on top of them, I mean on the ground beside them. And I kind of get scared and walk away cause I have a fear it will collapse on me. I do not like big boulders or cliffs either. Is this a phobia? Is there a name for it?