Lynne,
I'd start by reviewing the opening chapters of some of the cave diving texts. Don't they have introductory sections that discuss what underwater caves are and why we cave dive?
I'd barrow the basic ground work rather than re-inventing the wheel and then go on to talk about my own experiences or whatever my audience seemed interested in.
Good luck. It sounds like fun.
I'd start by reviewing the opening chapters of some of the cave diving texts. Don't they have introductory sections that discuss what underwater caves are and why we cave dive?
I'd barrow the basic ground work rather than re-inventing the wheel and then go on to talk about my own experiences or whatever my audience seemed interested in.
Good luck. It sounds like fun.