I have been attempting to find literature on the ambient and transient charge distribution in underground cavities. Lightning safety web sites state that caves can be dangerous during lightning storms but there is no quantitative information.

The literature also states that the size of the cave is a factor but nothing quantitative. I understand the arguments about the difference in shallow vs deep caves but I would expect that quantitative measurements would reveal the characteristics of charge distribution and when and where there are peaks?

Anyone aware of quantitative studies on this phenomena?