I recorded the Otter Hole tidal sump a few years ago. https://youtu.be/kP1jU8YMI_E

My understanding is that chalk is porous whereas carboniferous limestone is only permeable.  The difference being that water falling on chalk can soak through it as though it were a sponge whereas water can only penetrate limestone along joints and bedding planes. It is this restricted route for...

I've had some success with just licking the lens of my TG-2 just to grab the shot. Probably not as good as using a dry clean cloth but having one of those to hand in a cave is not easy.

Ibbeth Peril Cave 36434174_10155424748735685_5083583133324935168_o (1) by Simon Parker, on Flickr

It might be a good idea to rig the top of the fist pitch with maillons rather than carabinas. Tighten them with a spanner. They're harder to remove and less desirable as well. At this rate someone could get stranded underground or worse.

This is the second such incident I've heard of recently. The other being at Bar Pot a couple of weeks ago when a carabiner was removed from the top of the first pitch. I think this warrants police involvement.

Gypsum Caverns, Ease Gill Caverns

Hillier's Cave, Mendip

Lancaster Hole. High level route