Hi I think it was Ancient Aliens, or a History channel Documenty that first used the pictures of the so called Cave entrances below to support claims of secret Underground UFO bases in Antarctica. I don't know if it has already been discussed and debunked on here apologies if it has. But they are not caves at all. But Lakes, both images are abit of an optical Illusion. It's just ice around lakes. In the second image the Ice is thinning towards the water giving the impression its snow reseading into a cave. There are many Lakes by the coast with a very similar look that shows they are just Lakes.