User blog comment:Kogath/Monster Hunter: World Discussion/@comment-6050823-20180106170809/@comment-27465049-20180107130428

Maybe the new area is now half-volcano, half-tundra. I know that wouldn't make sense because you can only fight a specific monster in half of the area but it seemed like a good idea.

Maybe it's also something like the giant selenite crystals formed in the Cave of Crystals in Mexico where an underground magma chamber takes part in it's formation.