User blog comment:Mckrongs/Monster Hunter 4 for the Nintendo 3DS/@comment-6050823-20130627024034/@comment-6050823-20130627130907

It is.The Underground Caves is the Underground Volcano.The Underground Caves is the area while the volcano is dormant.The Underground Volcano is this area when the volcano erupts,changing the area.

Some people have suggested,that this may play a major roll in the story.